Abstract:Micro-arc oxidation is a new surface treatment method, but the structure of the micro-arc oxidation coating is limited to the electrolyte composition. In this paper the micro-arc oxidation coating on Ti6Al4V alloy was modified by addition of micro- Al₂O₃ particles to a sodium phosphate solution. The coating structure and phase was characterized by scanning electron microscopy and X-ray diffraction, and the oxidation resistance and thermal shock properties of the coating were investigated. Results showed that a coating denser than the original coating was produced. This new coating was composed of Al₂TiO₅ and TiO₂. The oxidation resistance and thermal shock property of the coating improved with addition of Al₂O₃ particles to the electrolyte relative to the sample prepared without the particles in the electrolyte. Moving Al₂O₃ particles were adsorbed on the coating surface and penetrated through it. As a result, the phase structure and properties of the original coating were modified.

Abstract:In this paper, the microstructure and mechanical properties of a high strength titanium alloy (Ti–6Al–6Mo–4V) were firstly investigated. The relationship between microstructures and properties of the alloys were investigated after solution treatment at α/β and β regions and then aging at five different temperatures ranging from 460℃ to 620℃ for 6h. The results illustrate the alloys after α/β region solution treatment and aging show a more attractive combination of strength and elongation than β solution treatment and aging. After solution treatment at 850℃ (α/β region) and aging at 460℃, the alloy obtains the highest strength (1572MPa) with elongation (2.63%). When aging at 620℃, the alloy obtains the highest elongation (11.46%) but lower strength (1201MPa). After solution treatment at 825℃ plus aging at 540℃, this alloy reaches a great combination of strength (1328MPa) and elongation (7.58%).Meanwhile, due to the large β grains after β region solution treatment and fine secondary α forms during aging, it does not obtain an attractive strength after β region solution treatment plus aging.

Abstract:Electron beam cold hearth melting (EBCHM) is a promising technique for achieving premium titanium alloys for critical rotating parts of the aero-engine and to recycle the titanium scraps. This article studied the heat transfer, the fluid flow and solidification in the cold hearth during EBCHM process of Ti-6Al-4V alloy. The results show that the melt is constrained to a very shallow depth which is 15mm in our experiment and the melt velocity is about a few centimeters per second. The melt temperature increases with the increase of melting power and decreases with the increase of melting rate. The melt depth increases with the increase of melting power, while the effect of melting rate on the shape of melt pool isn’t obvious. The trajectories of inclusions with different densities and sizes were simulated. The density has great influence on the trajectories of particles. The evaporation model was established to study the influence of melting parameters on the ingot composition. The results indicate that melting temperature, melting rate and composition of row materials have great influence on the ingot composition. Round ingots were produced using the commercial EBCHM furnace in the factory. The morphology of the shell was investigated and the ingot composition was tested. The calculating results are in good agreement with experiment.

Abstract:Macrostructural characterisation was performed for Ti-6Al-4V components produced by wire and arc additive manufacturing (WAAM) to investigate the effects of different deposition direction and interlayer dwell time on grain morphology of prior-β. By extending the interlayer dwell time between each deposited layer, the full equiaxed β grain were obtained. The results indicated that the equiaxed β grains at the bottom were caused by recrystallization. The sizes of the equiaxed β grains at the bottom were both affected by the thermal cycle and the degree of recrystallization.

Abstract:Due to the defects of high aluminum residue and high oxygen residue, high titanium ferro alloy prepared by thermite reaction outside the furnace cannot be directly used in liquid steel refining process. In this paper, thermodynamics of the high titanium ferro with high aluminum used in liquid steel refining process was researched, and then effects of the amount and the aluminum content in high titanium ferro onthe liquid steel refining process were also studied. The results indicate that: using Ti and Al as composite deoxidizers, the deoxidizing product at 1873K is Ti2O3 when the aTi/aAl in liquid steel is above 8; but in fact, only when the aTi/aAl value in liquid steel is above 10, Ti2O3 precipitates as deoxidizing product. Using high titanium ferro with high aluminum content as deoxidizer, the content of aluminum and titanium in liquid steel can meet the requirements of composition for the related steel. With the increasing amount of high titanium ferro, inclusions in cast steel after refining transformed from silicate into Ti-Al-Mn composite inclusions；and at the same time, obvious or part of radial acicular ferrite forms around those inclusions, which refines the microstructure of steel. The aTi/aAl value in the actual system is 17.78(>8), which is consistent with the theoretical results. It is vital to control the values of aTi/aAl in the liquid steel when the oxygen content in liquid steel is high.

Abstract:Macrosegregation is a typical defect occurred during the vacuum arc remelting (VAR) of titanium alloy ingot. In the subsequent heat treatment serious segregation of special elements would lead to the so called beta-fleck, which will significantly reduce the property of product. Reducing the incidence of macrosegregtion requires a thorough understanding of the formation mechanism of such defect. In this paper a continuum model for alloy solidification has been used to simulate the temperature evolution, solute distribution and liquid flow. The segregation patterns obtained in simulations are consistent with the observations in experiments. The development of segregation in the conditions with different thermal and solute buoyancy forces were analyzed. It was shown that the inhibition of flow can minimize the macrosegregation to the greatest extent. It was also found that the solute partition coefficient determines the segregation pattern and severity in the same fluid flow conditions.

Abstract:In Wire Arc Additive Manufacturing (WAAM), residual stress is easily generated during solidification and subsequent cooling, which affects the formation and use of the components. In this paper, finite element simulations are carried out to investitgate the influence of roller reductions on the temperature, stress, strain and residual stress distribution in components during the hybrid forming of Ti-6Al-4V alloy by WAAM and interlayer rolling. The results show that interlayer rolling reduce the residual macroscopic stress significantly in the deposited metal, and at the same time reduce the overall stress on the substrate. Increasing reduction can reduce significantly the macroscopic residual stresses and distorsion of the components. The microstructure of the material can be changed dramatically by the plastic deformation after rolling, which lead to a new route for the optimization of the microstructure during additive manufcturing.

Abstract:With the large-scale development of marine equipment and the improvement of its performance, it is necessary to research and develop ultra-large sized titanium alloy ingots with high uniform composition. Based on the simulation results by MeltFlow, the 1st 12 tons ingot of Ti80 alloy is melted in Chinese and then was verified by two times. The chemical testing results show that the composition difference of the upper, middle and bottom of the ingot is less than 1000ppm, and the composition difference of the 17 positions of the riser is less than 3000ppm. Both of them are equivalent to that of the 5 tons ingot. Further, the macrosegregation at the riser was investigated and it is found that Al, Nb, Mo are enriched in the edge of the ingot and poor in the center of the ingot, whereas Zr has the opposite phenomenon. EDS was used to study the microsegregation between the grain boundary and interior. The results show that Nb and Mo are enriched within grain and poor at grain boundary. On the contrary, Al and Zr are enriched in grain boundary and poor within grain. The macro and micro segregation are consistent for Nb, Mo and Zr and opposite for Al. This is largely because the distribution of Nb, Mo and Zr is more largely depended on the solute redistribution at the solidification interface. By contrast, due to the highSsaturated vapor pressure at high temperature, Al is volatilized severe during the long time and high vacuum melting process and the solute redistribution at the solidification interface.

Abstract:As oxidizable metals, titanium alloys are very active on melting point. It is easier for large-size titanium castings to react with the casting materials which will affect the surface quality of the castings during casting . In this experiment, large-scale titanium alloy castings were casted by Yttrium oxide mould in vacuum consumable shell furnace, and the surface layer of samples with different thickness was tested and analyzed by SEM, XRD and EDS. The results show that there is a certain thickness of oxygen diffusion layer on the surface of the samples. And there is a certain thickness of tissue transition zone on the surface. Finally, the experiment was carried out by acid. Finally, the acid pickling method was used to remove the reaction layer and the transition zone of the sample surface, which effectively improved the surface quality of the castings.

Abstract:Lamellar Ti–55511 near-beta Ti alloy was conducted on 750°C hot rolling and subsequent 600°C annealing to investigate the microstructure evolution and mechanical properties. The Burgers orientation relationship between α and β phase is broken down owing to dynamic recrystallization (DRX) of lamellar α phase during hot deformation, forming fine and equiaxed α plates, which leads to the increasing tensile strength and elongation. During annealing, secondary α grains are precipitated from β matrix, resulting in higher strength but lower elongation. Meanwhile, further spheroidization and growth of α phase via static recrystallization (SRX) happen during annealing. The recrystallization of β phase only happens in subsequent annealing rather than hot rolling. At the beginning of the deformation, two twin variants can be found in lamellar α phase. With an increase in deformation, three twin variants are formed in α phase. The nano-scaled twins and stacking fault was formed resulting from twins decomposing during annealing.

Abstract:Micro TiB and nano La₂O₃ particles hybrid reinforced difficult-to-deformation Ti-6Al-4V TMCs were processed by severe plastic deformation of equal-channel angular pressing (ECAP). The effect of ECAP temperature on microstructure, formation mechanism of ultrafine grains and mechanical properties was studies by SEM, TEM and room temperature tensile in detail. The results show that ultrafine-grained (UFG) structure has formed in ECAPed matrix, and ECAP temperature have significant impact on the formation mechanism. Plenty of dislocation pile-ups and tangling contribute to cell structures of hundreds of nanometers in matrix at lower ECAP temperature, while dynamic recrystallization occurs at higher ECAP temperature, which promotes the formation of a large number of new ultrafine grains (100~500 nm). The ultimate tensile strength of ECAPed TMCs at 800℃ is up to 1128.01MPa, which is 18% higher than unECAPed ones. In addition, micro-nano reinforcements induce continuous dynamic recrystallization in the interface microdomain, resulting in further refined grains. However, the average aspect ratio of ECAPed TiB whiskers decreases with the increase of ECAP temperature, which makes TiB tend to debond with matrix and be disabled to play a load-bearing role. It results in the inapparent effect of ECAP temperature on ultimate tensile strength. And the voids in matrix formed by debonding induce stress concentration, cause crack easily and reduce ductility of TMCs.

Abstract:Microstructure characterization and evolution analysis of Ti6242 alloy with equiaxed microstructure was studied by optical and scanning electronic microscopes, combining with image processing software. The origin alloy was processed under different heat treatments. Four parameters, including volume fraction Vα, size Dα, distribution density ρα and degree of aggregation Eα, were used to accurately describe the characteristics and evolution process of the equiaxed primary α phase. It was found that Vα, Dα, ρα and Eα all decrease with the solution temperature T increasing, and the relationships of Vα vs. T and ρα vs. T satisfy the linear and parabolic law, respectively. The declining rate of Vα increases with the T arising and decreases with time prolonging. With the Vα dropping, the content of element Al in β phase increases, while the content of Sn, Zr, and Mo decreases; the difference of the content of the four alloying element in β and α phase becomes smaller. At 850℃ and 800℃，the [Mo]eq of β phase is in the [Mo]eq range of α+β and metastable β alloy type respectively. After being quenched in water, the β phase occurs martensitic transformation at 850℃ and retains metastable β phase at 800℃。

Abstract:The impact resistance performance of Marine titanium alloy valves was analyzed in this paper, according to the equipment grade, installation location and the parameters specified in GJB 1060.1-91 "requirements for mechanical environment of ship environmental conditions".Taking angle globe valve as an example, the modal and impact resistance performance was analyzed with response spectrum analysis method, and the modal frequency and three-way stress of titanium alloy valve was obtained. The impact resistance performance was verified by test method. After that, different types of common materials were analyzed with the same angle globe valve, and the impact resistance was obtained. The results show that the response spectrum analysis method could provide an effective reference for the impact performance of the valve. In addition, the stress distribution is greatly affected by the structure, little by the material, and the maximum stress value is greatly affected by the material, while the model is impacted. Finally, the impact resistance of valves with the same construction was from high to low for TA31, TA2, QAl10-5-5 and 06Cr19Ni10.In this paper, the impact resistance of valve was analyzed and studied by means of simulation analysis and test method, which provided a reference for the engineering design of this kind of valve.

Abstract:Ti/Al metal layered composites were prepared by ultrasonic consolidation test. The microstructure of the material was observed by optical microscope The laminar composites containing different volume fraction were prepared by hot pressing reaction. The phase composition of the reaction products was determined by EDS. Through SEM measurement of Al3Ti thickness between layers, to establish the relationship between the Al3Ti concentration and reaction time. The study shows that the intermetallic compound Al3Ti is the only product in the process of in situ reaction of Ti/Al layered composites when the Al is not completely reacted. At the initial stage of in situ reaction, the accumulation of the reaction products is slow. As the reaction time goes on, the reaction products increase and the growth rate of the reaction products increases gradually.The relationship between the reaction product and the reaction time is a power exponential function.

Abstract:With the development of titanium alloy industry, the cost control of titanium alloys" products has become an important competitiveness. The yield rate of titanium alloy ingots is closely related to the surface quality of ingot. In this paper, the factors affecting the surface quality of ingots are analyzed by numerical simulation to improve the yield rate. We used meltflow VAR software to analyze the temperature field in VAR process, the relationship between the surface quality and the contact length, which represent the distance between the high temperature liquid phase and crucible wall are established. It is concluded that the three factors, melting current, stirring coils current and period have influnces with the surface quality of ingots. the experiment results show that the higher melting current, the greater stirring coils current and the shorter coils current period are beneficial to improve the surface quality and yield rate of ingots.

Abstract:In the paper, the damage of the SiC_f/Ti6242 composite in the thermomechanical fatigue test was monitored by the acoustic emission technique and the high-resolution X-ray tomography. The thermomechanical fatigue test was conducted with a trapezoidal waveform to simulate the actual loading of the bladed ring. The applied stress range is 130–1300 MPa and the temperature range is 100–500 °C. The maximum stress was held for 2 min at 500 °C. The AE events emerged mainly in the loading stage and the dwell stage for the cycle where the AE signals of fiber fracture and matrix cracking were found. The matrix cracks of the unbroken specimen were detected by the high-resolution X-ray tomography. The necking of the tungsten filament in the broken fiber in the cracking region was also found. These results show that the damage mechanism of the specimen is dominated by a mixture of fiber fracture and matrix cracking.

Abstract:To investigate the influences of applied shear stress on the nucleation process and micro-texture formation of α precipitates, β→α transformation in Ti-6Al-4V alloy was simulated by phase field method using Pandat software and JmatPro (TTT-Ti) databases as direct input in the model. The effects of applied positive and negative shear stresses (10, 30 and 50 MPa) along (101)[-111]β or (12-1)[-111]β on the microstructure evolution of Ti-6Al-4V alloy were explored under aging at certain temperature. The results show that. with the increase of shear stress, the elastic interaction between applied stress and α variants gradually plays more significant role in determining the microstructure of the system under certain undercooling, t herefore, the selection of α variants is gradually enhanced. It was found that the shear stress has a stronger effect on the variant selection than that of normal stress, therefore maybe more effective on microtexture formation. With the increase of shear stress, two or one type of variant are selected under positive shear, and one type of variant is favored by the negative shear along (101)[-111]β or (12-1)[-111]β respectively.

Abstract:Titanium alloys with high strength and toughness are the backbone material for manufacturing super-standard aeronautical structures. In present research, High temperature deformation behavior of the Ti-4.5Al-6.5Mo-2Cr-2.6Nb-2Zr-1Sn Ti-alloy has been investigated by thermal simulation compression experiment. The critical condition dynamic model was used to establish the prediction model of dynamic recrystallization volume fraction during hot deformation processing. The results obtained in this study will provide an effective theoretical support for the integrated manufacturing of key structural components with super-large size and complex shape.

Abstract:The shape indicators of sperical Ti-6Al-4V powders prepared by four kinds of method were quantitatively analyzed by image analysis technology, The sphericity, ellipticity, outgrow and roughness were measured . The results show the mean sphericity of powders is all above 90%. Sphericity of powders reduces sequentially from plasma rotating electrode process(PREP),plasma torch atomization(PA), plasma inert gas atomization(PIGA) to electrode inert gas atomization(EIGA), while the corresponding roughness successively increases. Satellite ball adhesion on the powder surface increases in turn from PREP, PA, EIGA to PIGA.For powders prepared by PREP method, the finer the particle size range, the higher the sphericity and the smaller the average roughness.The difference of shape indicator is related to the principle of preparation methods. The shape indicator of metal powder can be scientific quantitative analyzed by image analysis technology.

Abstract:The multipass hot rolling simulation of Ti-6Al-4V alloy was carried out by thermo-mechanical coupling method. The distribution characteristics of temperature and equivalent plastic strain at different passes on the cross section were studied. The simulation results showed that the temperature of surface was lower than that of the center. With increasing the rolling passes, the temperature of surface area decreased, the temperature of central increased first and then decreased. Equivalent plastic strains in both surface and center increased with increasing the rolling passes. The equivalent strain in the center was larger than that in the surface. The experimental results showed that with increasing the rolling passes, the deformation of microstructure in the central region was larger than that in the surface region. The temperature in the central region was higher and dynamic spheroidization ocurred easier.

Abstract:In this paper, the changes of microstructure, strength and plasticity of Ti6Al4V-DT (TC4-DT) alloy are studied by metallographic microscope and tensile tester under different solid solution, cooling rates and aging treatments. The results demonstrate that the main influencing factors of tensile strength and plasticity are solution temperature and cooling methods. Solid solution and aging treatment at 550 ℃ for 8 h in the α+β phase and the single β phase region can obtain the bimodal structure and the lamellar structure, respectively. When the solid solution temperature rises below the phase transition temperature, the amount of primary α phase obviously decreases, meanwhile, the strength and plasticity are better in the two-phase region. As the cooling rate decreases, the lamellar α phase becomes coarsened under the solution treatment above the phase transition temperature, and the tensile strength and yield strength gradually decrease. Moreover, the size of α phase increases as the aging temperature increases at the α+β phase region. Furthermore, the dispersion strengthening of α phase makes the strength of the alloy higher at the lower aging temperature. In general, the strength and plasticity of TC4-DT alloy can be well matched, the tensile strength can reach up to 1017MPa and the elongation is 22% under solid solution treatment at 950 ℃ for 1.5 h, aging treatment at 550 ℃ for 8 h and in the air-cooled state.

Abstract:Large size Ti70 alloy ingot were manufactured by vacuum consumable arc melting(VAR) in this paper. The effect of melting rate on component homogeneity of Fe element was studied. Chemical composition of the ingots were measured by chemical composition analyser and compared with perp results. Micro area composition were detected with EDS. Microstructure of follow-up rolling plate was observed by a metalloscope and mechanical properties of the plate were tested by a tensile tester. The results show that the mush zone during solidification process of the ingot reducing and macrosegregation of Fe element decreasing with cutting down the melting rate to a stable level. Meanwhile, eutectic phase spacing narrowing down and microsegregation of Fe element alleviating with reducing the melting rate. The microstructure and tensile properties of the follow-up rolling plate compliancing with the standard requirements.

Abstract:Ti-3Cu alloy exhibits excellent mechanical properties, corrosion resistance and antibacterial properties. Alkali heat treatment is an effective surface treatment method for titanium alloys, which can improve the surface biocompatibility of titanium alloys. The effect of alkali heat treatment on the microstructure, surface roughness, contact angle and antibacterial properties of Ti-3Cu alloy were studied in this research to reveal the possibility of applying alkali heat treatment to biological surface modification of Ti-3Cu alloy. The results have shown that a layer of titanate gel was formed on the surface of titanium alloy after alkali heat treatment, and a large number of nano-sized pores with a size of about 100 nm were distributed homogeneously on the surface of the gel layer, which reduced the roughness of Ti-3Cu alloy but improved the hydrophobicity of the alloy surface. The formation of the titanate gel layer on the alloy surface reduced the antibacterial property of the alloy from 92% before treatment to 77% after alkali heat treatment. The bacterial adhesion test also confirmed that alkali heat treatment reduced the antibacterial property of the alloy. It is believed that the titanate gel layer partly blocked the contact between Ti₂Cu phase and bacteria in the alloy, so the antibacterial effect of the alloy decreased.

Abstract:Based on TiAl turbocharger wheel with the diameter of 100mm after rig endurance test for total 240 hours, this paper evaluated the endurance of turbocharger wheel hub from the microstructure and mechanical properties. The microstructure and mechanical properties of the samples cut from the hub core of turbocharger wheel still retained a considerable level after endurance test. And the microstructure of the sample cut from the hub core of turbocharger wheel without rig test had an excellent stability after stress creep loading for 1000 hours at the actual working condition. So the hub of the turbocharger wheel had an condirable endurance that could meet the application requirement.

Abstract:In this paper, the effects of varied solution time on the microstructures and tensile properties in α+β phase field of Ti-5553 alloy were studied. The volume fraction and feret ratio distribution of primary α (αp) with varied solution time was emphatically analyzed. The microstructures of Ti-5553 alloy were observed by scanning electron microscopy. The orientation evolution of grain boundary primary α and intragranular α phase during solution was characterized by EBSD technique. The tensile properties were tested by the electronic universal testing machine. The results showed that the volume fraction of αp decreases with the extension of solution time, meanwhile, the equiaxation and coarsening of αp would decrease the resistance to dislocation movement, which resulted in the decrease of strength and the increase of plasticity. The grain boundary αp was truncated in the form of "hot trench " during solution process, however the truncated grain boundary αp remained the same orientation.

Abstract:Vacuum electron beam welding was used to realize the full thickness welding of Ti-6321 (nominal component Ti-6Al-3Nb-2Zr-1Mo)titanium alloy with 94mm large thickness.The full thickness of the welded joint can be well formed with the method of bottom locking at the bottom. The welded joint shows approximately parallel weld morphology, and the depth width ratio is about 16.The results show that the weld center is composed of coarse columnar crystal and internally staggered acicular α and α" phase.The transition from coarse grain to fine grain near the fusion zone. The width of unilateral heat affected zone is about 2 mm. The microhardness of the weld zone and the heat affected zone were both lower than that of base metal.The tensile strength of welded joint was equivalent to that of the base metal, and the fracture occured in the weld metal.Both the weld zone and the heat affected zone have better impact toughness.The strength and toughness of the welded joint are excellent.The mechanical properties in the direction of welded joint have good uniformity.

Abstract:In this paper, the alloy of Ti-Al-Sn-Zr-Mo-Cr-V-Fe system was used as the research object. Design different solution heat treatments were to establish foundation of the optimization of the best match between the toughness and hardness of the alloy. The influence of solution time on the globularization of α layer were studied by observing metallographic organization and analysis of lamellae size. It was found that the relationship between the solution time and the α lamellae globularization was that as the increase of the solution time, and the globularization rate increased to the highest,controlled by boundary splitting and termination migration. That provides experimental basis for the design of thermal processing parameters and the matching of strength and toughness in α / β two-phase zone.

Abstract:The effects of slab microstructure type and heat treatment on mircrostructure and properties of Ti6321 alloy were studied by means of mechanical properties test,OM and SEM analysis. The results show that slab microstructure type of Ti6321 alloy has a significant effect on the microstructure and properties of the rolling sheet. By the same rolling process, that is, the first fire: 980℃ start rolling, finish rolling temperature 800℃, ε=70%, and the second fire: 995℃ start rolling, finish rolling temperature 800℃, ε=50%,equiaxed slabs form bimodal slabs, and Westernized slabs form equiaxed slabs. After annealing below (α+β)/β phase transformation point, the longitudinal and transverse yield strength and tensile strength of the plate made of equiaxed slab are higher than those of the corresponding direction of the plate made of Widmanstatten slab, while the elongation and impact energy are opposite. With the increase of annealing temperature, the yield strength and tensile strength of the sheets prepared with different slab structures decrease slightly, while the impact energy increases sharply. When annealed above (α+β)/β transformation point, the tensile properties and impact work of the two alloys decreased significantly. During the annealing process in the α+β two-phase zone, the sensitivity of the initial α phase to temperature is higher than that to the holding time of annealing. With the increase of temperature, the content of primary α phase decreases sharply, while the content of secondary flake α phase increases obviously. The suitable annealing process range of Ti6321 alloy is (940～980)℃/(2～3) h.

Abstract:A new designed space-controlled self-propagating synthesis process was used to prepare porous NiTi shape memory alloys (SMAs) after the pretreatment of Ti powder and Ni powder. Properties including pore structures, phase composition and superelasticity of the alloys are characterized, and the biological safety was evaluated through the experiment mcludmg hemolysls test and cytotoxicity test (MTT). The results show that it is difficult to obtain SMAs with ideal pore structures without pretreating the mixed powders. After pretreating the raw powders properly, SMAs with excellent comprehensive properties can be fabricated. Nearly spherical pores with 34% porosity and diameters between 100 and 500 μm are homogeneously distributed in the alloys. The alloys are composed of single B2 and have good superelasticity. After three cyclic loading and unloading compression tests at 2.5% and 4.0% strains, no residual strain is generated. The corresponding compressive strength is 250MP and 363MPa respectively, and the elastic modulus is 15.4GPa. MTT tests show morphologies of cells in SMAs leaching solution are normal and the cytotoxicity is estimated level 1, indicating SMAs have good biological safety.

Abstract:The low cost preparation of TiAl master alloy is an important direction of current research. In this paper, TiO2 as raw material, KClO3 as heating agent, Al as reducing agent and alloying agent, Ca as deep reducing agent were used for the preparation of TiAl master alloy by metallothermic reduction method. The heat effect per unit mass, the proportion of slag-making agent, the amount and composition of reducing agent on the stability of the reaction process, the composition and yield of alloy were investigated. The results showed that when Ca and Al were used as reducing agents, the adiabatic temperature of the system was 2426 K and 1806 K, respectively. The TiAl master alloy was composed of TiAl, Ti3Al and a small amount of Al2O3 inclusions. The contents of Ti, Al and O in the alloy were 58.36%, 40.19% and 1.41%, respectively.

Abstract:Titanium is an important strategic commercial metal. At present, the titanium industry is based on the high-energy Kroll process. At present, electrochemical methods and metal thermal reduction methods have different degrees of difficulty in preparing elemental titanium.There is a technical bottleneck in the preparation of metallic titanium powder by conventional thermal reduction of TiO₂ with calcium, magnesium, or other metals, such as low efficiency and incomplete deoxidation. Based on the thermodynamic equilibrium characteristics of the step-by-step reduction of TiO₂, a comparative study method was used, and the thermodynamic and kinetic differences between magnesia and calcium heat reduction of TiO₂ were investigated in this paper. Considering the difference in the electronegativity between magnesium and calcium, a new idea was put forward that the primary reduction product is prepared through a primary reduction process of TiO₂ in the form of magnesiothermic self–propagation high–temperature synthesis (SHS), and then the reduced titanium powder is obtained through the primary reduction product for a deep calcium-thermal reduction reaction. The reduction degree and mechanism of TiO₂ during the primary magnesium thermal reaction and deoxidation mechanism of primary reduction products in different deep reduction modes were investigated in this paper. The results showed that it is more conducive to undergo complete deoxygenation such that the primary reduction product is first acid-impregnated followed by deep calciothermic reduction. High purity reduced titanium powder with a final oxygen content of only 0.21% and purity greater than 99.0% was obtained.

Abstract:The microstructure and tensile properties of TC17/TC11 dual alloy fabricated with direct laser melting deposition method using two connecting processes (direct connection and gradient connection) were investigated. The results show that, according to composition changes, the TC17/TC11 dual alloy can be divided into three parts: uniform TC17 zone, transition zone and uniform TC11 zone. The as-deposited microstructure of uniform TC17 and TC11 zones shows cyclic layer-like characteristics. For direct connection process, there exists a extremely narrow transition zone between TC17 and TC11 zones. Sharp changes of both chemical composition, microstrucuture and microhardness are found between uniform TC17 and TC11 zones. For gradient connection process, the transition zone encompasses a wider region in which continuous changes of chemical composition and microhardness is found. The intermediate microstructure which is different from TC17 and TC11 emerges in the gradient transition zone. Room temperature tensile tests show that all as-deposited dual alloy samples regardless of connecting process are fractured in the TC11 zone, with approximate tensile strengths and dispersed elongations.

Abstract:With HDH-Ti powder and carbonyl Fe powder as raw materials and formed by cold isostatic pressing, Ti-xFe alloys (x=1%, 5%, 10% and 15wt%) were prepared by vacuum sintering and hydrogen induced phase transformation sintering (HSPT), respectively. The density, phase, microstructure evolution and microhardness of the alloys in the two sintering processes were compared. The results show that the HSPT alloy contains more pores and the density is significantly lower than that of the vacuum sintered alloy. The content of β phase in the two alloys increases with the increase of Fe content, and TiFe phase appears only in the Ti-15Fe alloy prepared by HSPT. During the preparation of HSPT alloy, H has a significant inhibitory effect on the diffusion of Fe. When Fe content is no less than5%, short rod-like or needle-like secondary α phase is precipitated inside the β phase of the alloy after dehydrogenation, which makes the β phase structure fine. When Fe content reaches 10% or higher, Fe appears significant enrichment. At the same time, H leads to the development of the β phase growing coarsening, and the β phase coarsening is more obvious with the increase of Fe content. The microhardness of HSPT alloy is higher than that of the vacuum sintered alloy, especially that of α phase increases linearly with the increase of Fe content.

Abstract:In this study, effects of solution-treatment and aging temperature on microstructure and mechanical properties of TC6 titanium alloy were investigated. The results show that when specimens were solution-treated at 800~840 _^oC, primary α and metastable β phases formed and they grew up with increasing temperature, which resulted in the slight increases in strength and ductility. The metastable β phase was also retained after solution-treatment at 880 _^oC though its stability was weakened, while at this moment double yield phenomenon was observed, which was attributed to stress-induced α″ orthorhombic martensite in the metastable β phase. When specimens were solution-treated at 920~960 _^oC, the strength increased and the ductility decreased in that primary α phase dissolved and a large amount of fine acicular α″ orthorhombic martensite precipitated from the metastable β phase. The alloy was almost composed of coarse α￠ hexagonal martensite after solution treatment above the β transus, which led to the decrease in strength and the brittle fracture during tensile test. In terms of different aging temperatures for solution-treated specimens (880 _^oC/1.5 h/WQ), the main microstructural changes were the precipitation of secondary α phase from the metastable β phase and its growth. Compared with solution-treated specimens, the specimens aged at 300 _^oC exhibited higher strength and lower ductility, and it can be seen that some secondary α phase and ω phase had precipitated from the β matrix. As the aging temperature increased to 400 _^oC, the maximum strength as well as minimum ductility was obtained. The specimens aged at 500 _^oC maintained the maximum strength, while the ductility was improved due to the sufficient diffusion of alloying elements. When the specimens were aged at 550 _^oC, these possessed the optimum balance of strength and ductility. The primary α phase gradually gathered to grow up and the lamellar secondary α phase apparently dispersed in the β matrix after aging at 600~700 _^oC, which led to the decrease in strength and the increase in ductility.

Abstract:This paper deals with the simulation of rotary piercing process of Ti80 alloy seamless tube via a 3D thermal-mechanical coupling model. The model can visualize the complex continuous piercing process from biting to steady piercing and to final drilling. Concurrently, the simulated result helps to understand the central fracturing and physical fields distribution. Combining the stress state of (+, -, +) along the rolling centerline with non-negligible plastic deformation at the centre of the billet, the cavity formation was determined to be caused by plastic cracking under tensile stress. During the piercing process, the strain distribution was U1+W+2U2 along the axial direction and lamellar along the radial direction. The final equivalent strain of the capillary can reach 5-11. The strain rate in the contact area between the blank surface and the discs was 0.71~3.6s_^-1, while that between the surface and the rolls was up to 4.6~26s_^-1, thus contributing to the plastic forming process. The billet temperature in front of the plug was the highest, and the area in contact with the piercing tools decreased slightly. But they were still in the single β phase field. Based on the parameters optimized by the finite element method, the Ti80 alloy seamless tube was successfully pierced through the experimental Diescher mill. The microstructure of the tube was presented as a single Widmanstatten microstructure. Due to the severe deformation, the fine and equiaxed dynamic recrystallization β grains were found from outer surface to the middle layer and to inner surface. The mechanical property test showed that the strength and plasticity of the tube can meet the requirements of the project.

Abstract:Titanium foam was prepared by space holder sintering process under different particle diameter, volume ratio and sintering temperature and time. The pore structure of titanium foam was analyzed by optical metallography and scanning electron microscope. The mechanical properties of titanium foam were evaluated by compression test at room temperature. The results show that the pore of titanium foam is round on the cross-section and is elliptical on the longitudinal section. The difference between the porosity of titanium foam and the volume ratio of space holder increases with the increase of the particle diameter, volume ratio, sintering temperature and time. At the same time, the higher the sintering temperature, the denser the pore wall of titanium foam is. Unlike the traditional foam materials, there is no obvious stress platform in the relationship between the stress and strain of titanium foam. The compressive strength and elastic modulus decrease with the increase of porosity. When the porosity is 67.6%, the compressive strength and elastic modulus reach 14.4MPa and 1.17GPa respectively. The compressive strength increases first and then decreases with the increase of pore diameter, while the elastic modulus remains unchanged. When the pore diameter reaches 1.15-1.53 mm, the compressive strength and elastic modulus reach 48.9 MPa and 1.72 GPa respectively.

Abstract:Nanodiamonds (NDs) reinforced titanium (Ti) matrix composites with network microstructures were prepared by using spark plasma sintering technique. Spherical Ti particles were modified with polyvinyl alcohol and then crosslinked with the NDs. Finally, the NDs were distributed uniformly on the surface of the spherical Ti particles. The effects of ND contents on the microstructures，thermal conductivity and compression performance of the Ti nanocomposites were studied. The results show that TiC particles are in-situ formed due to the reaction between the Ti and NDs but some NDs are still preserved in the nanocompoties, the NDs/TiC hybrid reinforcements have a three-dimensional network distribution in the Ti matrix and the size of network is 100-200 μm. The results of thermal conductivity test show that the thermal conductivity of the nanocomposites decreases with the increase of the content of the reinforcing phases. The compressive tests show that the Ti-1.0wt% NDs composites have excellent mechanical properties where the ductility of the composites remains high enough while the hardness and strength are greatly improved. The fracture surfaces of the composites show that the cracks propagate along the network-structured boundary. The network microstructures with hundreds of microns play the role of reinforcing beams, while the internal matrix of the network still maintains low hardness and high ductility of the pure Ti. Eventually, the contradiction between strength and ductility of the Ti matrix composites is reconciled effectively.

Abstract:Ti-18Mo, Ti-18Mo-0.5Si, Ti-18Mo-1Si and Ti-18Mo-2Si alloys were prepared by high-energy ball mill and SPS. The effects of Si content on the oxidation-resistance behavior of Ti-18Mo-xSi alloys at high temperature oxidation under 700℃ and 800℃ in air were investigated by analyzing the microstructure, phase composition of sintered and oxidized alloys.The results show that the sintered alloys contain Ti(Mo) solid solution and the alloys with Si contain Mo5Si3 phase. After oxidation at 700℃ and 800℃ for 100 h, the main phases of alloys were TiO2, TiO, MoO2 and MoO3, and the oxidized alloys with Si contain SiO2 phase. The oxidation resistance of Ti-18Mo-xSi alloys at 700℃ is better than that at 800℃. Especially, Ti-18Mo-0.5Si alloy with average oxidation rate of 0.09 g·m-2·h-1and 0.10 g·m-2·h-1 at 700℃and 800℃, respectively. The oxidation resistance of Ti-18Mo-0.5Si alloy is superior to other alloys.

Abstract:The properties of titanium alloys can be improved by cold deformation and aging heat. However, there are limited report on the performance transformation of titanium alloys under the combination of cold deformation and aging heat treatment. In this work, the influence of prior cold deformation and the subsequent aging heat treatment on the phase types, α precipitation behaviors and the tensile properties of TB9 titanium alloy were studied using the X-ray diffraction, optical microstructure, scanning electron microscope and uniaxial tensile. The results showed that longitudinal and cross section of the bars formed different type macro texture through produced different microstructure and affected the microhardness. TB9 titanium alloy consisted of α and β phases after aging heat treatment. With the increase of the cold deformation rate, the tensile strength was increased and the ductile was reduced. Due to the defects produced during the cold deformation process, the precipitation free zones were disappeared in cold deformation samples and the mixmum tensile strength reach 1800MPa with an elongation of 4%.

Abstract:This paper reviews the research results of titanium alloys in deep ocean corrosive environment. The present research status of titanium alloys in the deep ocean environments is summarized from corrosive characteristics of the deep oceans and corrosion modes such as the stress cracking corrosion, low-frequency fatigue corrosion, etc. The failures and leakages of the titanium alloys for the applications in the deep ocean environments caused by high hydrostatic pressure from above the seawaters is of important for the applications of the deep sea stations. On the other hand, corresponding electrode reactions of titanium alloy in deep oceans are dramatically affected by the high hydrostatic pressures. The application of integrated materials calculations and simulations in the fields of metallic corrosion and the testing equipments for simulating the specific corrosion condition in the deep oceans are introduced. At the same time, the main problems and future development of corrosion researches of titanium alloy in the deep ocean environments are summarized and analyzed.

Abstract:Titanium alloys have become the hot spot of material selection for future warships because of their high specific strength and excellent seawater corrosion resistance. In order to promote the application and popularization of titanium alloys in marine pipelines, this paper mainly analyses the research work on material selection, welding technology, pipe bending technology, corrosion protection and marine biofouling prevention of titanium alloys.

Abstract:The dissolution mechanism of CeO₂ in molten CeF₃–LiF–BaF₂ and the electrochemical behavior of Ce(III) on molybdenum electrode in molten CeF₃–LiF–BaF₂ were investigated. Cyclic voltammetry, chronoamperometry and potentiostatic electrolysis were performed to investigate the reduction mechanism of Ce(III) ions. The products obtained by dissolution reaction and potentiostatic electrolysis were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results show that CeO₂ can dissolve into the fluoride molten salts in the form of CeOF, by reacting with CeF₃. Further, cerium oxyfluorides can be directly reduced to cerium metal with a purity of 99.38–99.81 wt% on molybdenum electrode via a reversible three-electron-transfer process, which is controlled by diffusion.

Abstract:Zinc codoping Gd₃Ga₃Al₂O₁₂:Ce (Ce:GAGG) ceramic precursors have been synthesized by chemical co-precipitation method. Thermal gravimetric and differential thermal analysis of the precursor powders are obtained, and phases including GdAlO₃ and GAGG are generated at 883°C. The chemical molecule of precursors is analyzed by FTIR. The phases and morphology of the precursors for different calcination temperature are studied by XRD and SEM. Precursors absolutely convert to Ce:GAGG powders at 900°C. The particles calcined at 1200°C for Ce:GAGG powders with size of 20~60nm become homogeneous and smooth. The effect of PEG on the morphology of the precursors is investigated. Particle size and size range of Ce:GAGG powders calcined at different temperatures were investigated. The influence of codoping of Ce:GAGG with different Zn_²⁺ content on photoluminescence, radioluminescence, excitation spectra and fluorescent lifetime are analyzed. The emission spectra of Ce:GAGG codoping 0.4% Zn_²⁺ content has the highest intensity. The Zn_²⁺ in Ce:GAGG powders has a positive effect on a fast component with short fluorescence lifetime.

Abstract:Four types of CeO₂-based oxide samples were prepared by co-precipitation, and their physicochemical properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption-desorption (Brunauer-Emmet-Teller method; BET), H₂-temperature-programmed reduction (H₂-TPR), oxygen pulsing technique, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD profiles revealed that only broad diffraction lines characteristic of CeO₂ were observed in the case of CeO₂ and CeO₂-Al₂O₃ (CA), while CeO₂-ZrO₂ (CZ) and CeO₂-ZrO₂-Al₂O₃ (CZA) disclosed Ce_0.75Zr_0.25O₂ phase. The paper revealed that homogeneous solid solutions were formed for all the CeO₂-based oxygen storage materials. XPS studies showed that 4+ and 3+ oxidation states of cerium were coexisted on the surface of CZ, CA and CZA_。 However, almost no 3+ oxidation state was detected for pure CeO₂. The best textural properties, higher oxygen storage capacity (OSC) and excellent thermal stability were obtained for CZA. In addition to compare the differences among the four samples, this article proposed a new insight that Al₃₊ might insert among the inter-space of the fluorite structure or highly dispersed in the solid solution. CZA solid solution might be composed of interstitial solid solution and substitutional solid solution, which was verified by the presence of two oxygen species or two types of oxygen channels for CA and CZA. However, the evidence was not detailed enough to sustain this argument, so that further investigation was necessary.

Abstract:The microstructure and mechanical properties of the ZM81 alloys with varying Sn contents subjected to the extrusion and T6 treatments were investigated by OM, XRD, SEM, TEM, hardness test and uniaxial tensile test at room temperature, respectively. The results show that after the addition of Sn element, an Mg2Sn eutectic phase is formed, which can refine the as-cast microstructure. Sn element has an obvious effect on refining the microstructure of as-extruded alloys by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion, and improves the mechanical properties. T6 treatments, especially double aging, can significantly increase the strengths of the extruded alloys. Among them, the ZM81-4Sn alloy with double aging exhibits an ultimate tensile strength of 416MPa, a 0.2% yield strength of 393MPa and an elongation of 4.1%. The microstructure characterization suggests that the high strengths of the peak-aged alloys are attributed to the combined precipitation strengthening of the fine and dispersed MgZn2 and Mg2Sn precipitates, and the pre-cipitates after double peak aging are finer than those after single peak aging.

Abstract:This study aims to design and fabricate a new kind of radiation shielding composite against both neutron and gamma rays. Based on Monte Carlo simulations, novel (W+B)/6061Al composite sheets with different W mass fractions (40-70%) were first fabricated by ball-milling and SPS followed by hot-rolling, then the microstructure and mechanical properties were investigated. Results show that after rolling process, W and B particles uniformly distributed in the matrix and the interface of W-Al exhibited good metallurgical bonding containing solid solution. The composites were mainly consisted of W and Al phases. EBSD results show that W particles had the effects of promoting dynamic recrystallization (DRX) nucleation, confining the grain growth and reducing the texture of 6061Al matrix. Through tensile tests, the composite with 50 wt.% W shows the highest strength and better plasticity. Together with the simulation results, composite of this composition is believed to meet the demand of practical applications. The strengthening mechanisms of (W+B)/6061Al composites include dislocation strengthening and load transfer effect.

Abstract:The effects of sole Cr, Mn, Zr, Ti addition on the precipitation of secondary phases (especially AlCuYb), matrix recrystallization behaviour and tensile intergranular fracture of an AlZnMgCuYb based alloy has been investigated by using tensile test, together with detailed microstructural characterization XRD, TEM, SEM, and EBSD technique. The results indicate that coarse micro-scaled AlCuYb phase precipitated can not be inevitable in the Yb and Cu containing Al alloy. It is interesting that the least coarsen phases are formed in the AlZnMgCuYb-Mn alloy due to the precipitation of submicro-scaled Al₂₀Cu₂Mn₃ phase resulting in the effective decreasing of coarse AlCuYb phases. The addition of Zr to AlZnMgCuYb alloy can effectively inhibit the recrystallization of ɑ(Al) matrix by the formation of nano-scale coherent Al₃(Yb, Zr) dispersoids. However, the formation of AlCuYb phases consuming Yb will reduce secondary coherent Al₃(Yb, Zr) precipitation and particleSstimulated partial recrystallization nucleation, resulting in a decline in strength of AlZnMgCuYb-Zr alloy. T6-tempered AlZnMgCuYb-Zr and AlZnMgCuYb-Mn alloys still remain an unrecrystallized fiber-like structure, the fraction of low-angle grain boundaries (LAGBs) increased up to 50%, and the average grain size decreased to 2~7 μm. However, more homogeneous recrystallization grains are observed in Cr or Ti containing AlZnMgCuYb alloy, the fraction of high-angle grain boundaries (HAGBs) and the average grain size achieve 80% and 40-96 μm, respectively. The primary 1~3 μm Al₂CuMg particles, not coarse AlCuYb preferentially cracked, and cracking propagated along high-angle recrystallized grain boundaries or original grain boundaries with continuous, coarser grain boundary precipitates and broadening precipitate-freeSzones (PFZs) at its periphery.

Abstract:The effect of rare earth Ce on microstructure and friction and wear properties of HMn64-8-5-1.5 alloy was systematically studied. The results indicate that rare earth Ce plays the role of deoxidation, desulfurization, dehydrogenation and impurity removal during the smelting process, which can purify the alloy matrix and make the grain size remarkably refined. The friction and wear experiments show that the rare earth Ce can significantly improve the friction and wear properties of the material. When 0.2wt% Ce is added, the weight loss of the alloy is less than 25%. The wear mechanism of the alloy is analyzed by combining two kinds of friction and wear models. The major wear behavior of the alloy changes from adhesive wear to abrasive wear by adding 0.2 wt% Ce. The main reason for the change of wear mechanism of the alloy with and without the Ce addition is the effects of removing impurities and refining crystal grains by Ce, which increases the surface strength and ultimate deformation value of the alloy itself.

Abstract:The effect of natural aging time on tensile properties and fracture of the heat-treated AA2024-O Al-alloy was investigated. The stress-strain curves, the yield strength and the tensile strength of the specimens with different natural aging time were obtained by carrying out tensile test at room temperature. The constitutive equation that could predict the stress was established. The effect of natural aging time on the material microstructure was analyzed by observing the fracture. The results of the experiment demonstrated that the specimens were gradually strengthened to a certain point, and then the yield stress and the ultimate tensile strength decreased until the material reached a stable state. There were many dimples distributed on the fracture surface that was observed by SEM, so the fracture surfaces were thought to be a ductile fracture. Despite natural aging during long periods, the specimens of dimples became fewer and the plasticity worsened. A series of phenomenological functions were presented for establishing the constitutive equation of AA2024-O Al-alloy strengthened. The model could predict the stress of the naturally aged material.

Abstract:We investigated the properties of functionally graded WC-based cemented carbide, prepared with a new approach featured by sintering the WC-Co/WC-Fe-Ni double-layer compacts together. For this approach, the reasonable pressing pressure to prepare the alloys should be about 15 MPa, under which the two layers have consistent sintering shrinkages and the unexpected phenomena (e.g. layering and cracking) were not observed. The phase composition and microstructure analysis based on the X-ray diffraction, optical and scanning electron microscopy experiments indicate that the η or graphite phase is not existed in both WC-Co and WC-Fe-Ni layers, and that the interface of these two layers are well combined together. Meanwhile, a significant gradient of Fe, Ni and Co is observed at the interface between the above two layers, and this composition gradient results in a noticeable hardness gradient, which further leads to the WC-Co/WC-Fe-Ni double-layer cemented carbide being of high hardness, wear resistance and toughness.

Abstract:The high-temperature vacuum brazing of Titanium-Zirconium-Molybdenum (TZM) alloys was efficiently realized while using the Ti-8.5Si, Ti-33Cr and Ti-30V-3Mo brazing filler metals, respectively. The thermostability of the brazing joint interface after high temperature thermal cycle was studied by SEM, EDS, wettability test and shearing test, etc. And so as to the thermostability of the brazing process. The results showed that, under the technological parameter of 1520℃/6min, both Ti-8.5Si、Ti-33Cr brazing filler metals had good wettability on the surface of TZM alloy, the wetting angle was 10° and 9°, respectively. The spreading area of Ti-8.5Si brazing filler metal was larger than that of the Ti-33Cr brazing filler metal. Under the technological parameter of 1680℃/8min, the Ti-30V-3Mo brazing filler metal had a 5° wetting angle on the surface of the TZM alloy. The (Ti, Mo) solid solution was formed in the interfaces of the Ti-8.5Si/TZM and the Ti-33Cr/TZM brazing joints. The center of the Ti-8.5Si/TZM brazing seam was composed of (Ti, Mo) solid solution and Ti₅Si₃ phase. The center of the Ti-33Cr/TZM brazing seam was composed of (βTi, Cr) solid solution and the αTi + (αTi+αTiCr₂) eutectic. The brazing seam of the Ti-30V-3Mo/TZM joint was consist of (βTi, V) solid solution and the αTi phase, and the boundary zone was consist of (Ti, Mo) solid solution. There all formed solid solutions in the brazing joints to realize the metallurgical bonding between the brazing filler metals and the TZM alloys when using these three kinds of brazing filler metals. The shearing strength of the brazing joints were 135.8MPa (Ti-8.5Si), 132MPa (Ti-33Cr) and 131MPa (Ti-30V-3Mo), respectively. There were no obvious intergranular infiltration and parent metal dissolution phenomena in the Ti-8.5Si/TZM and Ti-33Cr/TZM brazing joints after the 1200℃/60min thermal cycle treatment, the boundary zone was still combined by the solid solution. In the Ti-30V-3Mo/TZM brazing joint after 1550℃/60min thermal cycle, there was one crystalline grain depth intergranular dissolution phenomenon, no obvious parent metal dissolution was observed, and the interface remaining combined by the solid solution. These three kinds of Titanium based brazing filler metals can realize the high-temperature vacuum brazing of the TZM alloy through metallurgical bonding of the interfacial solid solution. The microstructure of the brazing joint after long time high temperature thermal cycle is stable, and the intergranular infiltration sensitively is low. The research of this subject provides theoretical and experimental guidance for the high temperature application connection of the TZM alloy.

Abstract:Aiming to reduce the friction coefficient of WC-12Co wear-resistant coating, the self-lubricating coating was developed by adding graphene to WC–Co coating deposited via detonation gun spraying. In this study, four powder processes, including wet ball milling, wet mixing, spray granulation, and sintering and crushing, were used to obtaingraphene/WC–Co composite powders. The presence, microstructure and phase composition of graphene in powder and coating were analyzed by means of SEM, EDS and Raman. The mechanical properties of the coating were studied by the microhardness tester and the universal tensile machine. When the spray granulation process is used to prepare the composite powder, a greater amount of graphene covers the surface of the WC–Copowder, and the transparent thin-layered structure of the graphene remains unchanged. The bonding strength and hardness of the resultant coating are approximately 68 MPa and 940 HV0.3, respectively. Graphene modification causes a 25% reduction in the friction coefficient. During the friction process, the graphene constantly forms a lubricating film that serves as an excellent self-lubricating layer.