Abstract:The oxidation behavior of Ti-22Al-(27-x)Nb-xZr (x=0, 1, 6, at%) was evaluated over a temperature range of 650~800 oC in air. The phase composition and the morphology of the formed scales were investigated by X-ray diffraction and scanning electron microscopy. The results show that the alloys containing Zr exhibit better oxidation resistance than Ti-22Al-27Nb alloy. The main oxidation product is TiO2 for all the alloys oxidized at 650 oC for 100 h. A mixture of TiO2, Al2O3 and AlNbO4 is formed for Ti-22Al-27Nb and Ti-22Al-26Nb-1Zr oxidized at 800 oC for 100 h; however, ZrO2 is also traced in Ti-22Al-21Nb-6Zr. The improved oxidation resistance for Ti-22Al-26Nb-1Zr can be ascribed to the refinement of oxides. While in Ti-22Al-21Nb-6Zr alloy, although formation of Al2O3 is obvious at 800 oC, ZrO2 in the scale can provide sites for rapid oxygen transport, leading to the high mass gain

Abstract:Based on the assumption of spherical grains in polycrystalline materials and the theory of metallography, a mathematical model was developed to calculate the quantitative relationship between apparent and true values of the lamellar spacing cutting through the grain randomly. The results indicate that the grain sizes of most polycrystalline materials are much larger than their lamellar spacings, the ratio of an average apparent value to a true one can be characterized by the corrected coefficient k. The ratio of the apparent lamellar spacing to the grain size reduces from 0.05 to 0.0001, and k increases from 1.5391 to 1.5707, which gradually tends to be π/2. When the ratio of the apparent lamellar spacing to the grain size is smaller than 0.001, value k can be considered as a constant of π/2. The amount of work will be decreased adopting the present model to get the true value of lamellar spacing compared with the conventional methods

Abstract:This paper focused on the fatigue crack growth behavior of TC4-DT titanium alloy with different lamellar microstructures. Heat treatments were performed in order to prepare different microstructures with α lamella width and colony size. The results show that on the premise to guarantee adequate mechanical properties, the microstructures formed through air cooling from the β-phase field present better ability to resist fatigue crack propagation. This is attributed to the existing of bigger plastic deformation field in crack tip. It is also found that wide α lamellae and coarse α colony are beneficial to improve fracture toughness and resistance to fatigue crack propagation

Abstract:The microstructure, the mechanical properties and the oxidation behavior of a novel Ti-46.5Al-3Ta-2Cr-0.2W (at%) alloy after hot extrusion were investigated. The results show that the alloy is mainly composed of γ and α2 phases, which has fine near lamellar microstructure with colony sizes of 50~70 μm after hot extrusion. The different microstructures after hot extrusion were obtained by different cooling rates, and a great amount of massive phase were found at grain boundaries by oil quenching. Tensile test results exhibit that the yield strength (YS) and ultimate tensile strength (UTS) of the alloy after hot extrusion decrease from 807 and 846 MPa at room temperature to 620 and 760 MPa at 800 °C, respectively, and the elongation (EI) of the alloy increases from 2.16% at room temperature to 3% at 800 °C which means that the alloy still keeps higher strength at elevated temperature. The observation of fracture surfaces shows that the crack length of the present alloy is smaller, and the additive of Ta increases the ductility of Ti-46.5Al-3Ta-2Cr-0.2W alloy at room temperature. The oxidation behavior of the novel TiAl based alloy in the experimental range was discussed. It is found that the addition of Ta can reduce the oxygen solubility into the TiAl alloy and suppress TiO2 growth at elevated temperature due to the low diffusivity

Abstract:Total strain controlled low cycle fatigue tests have been performed at 760 and 870 oC on a nickel base single crystal supperalloy and its fatigue behavior and microstructural character have been studied. The dislocation characteristics and the fracture surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. Results show that the fatigue life for specimens increases with the decreased strain amplitude. The homogeneous secondary γ′ particles distribution in the matrix is beneficial for enhancement of fatigue resistance. The formation of persistent slip bands (PSBs) enhances the fatigue crack initiation at micropores and the propagation along the PSBs. At 870 oC and higher strain amplitude, the locally higher stress concentration resulted from dislocation tangling, and progressive coarsening promotes a relatively soon initiation of fatigue microcracks

Abstract:Several 93W-4.6Ni-1.9Fe-0.5Co alloys have been prepared by liquid phase sintering in vacuum atmosphere using powders with different contents of carbon and oxygen. The microstructures and mechanical properties of sintered samples have been investigated. Results show that the carbon in the starting powders has a stronger deoxidization ability in the high temperature vacuum sintering process due to the carbon-oxygen reaction, which decreases the contents of carbon and oxygen in the sintered samples and prevents the formation of carbide and oxide inclusions, resulting in a strong interfacial boundary between tungsten and bonding phase. The mechanical properties are improved significantly when the oxygen content is controlled to be lower than 500 mg/g

Abstract:After grain refinement through hot-forging and δ-phase precipitation and recrystallization heat-treatment processes, the high temperature tensile experiments were carried out to investigate the effect of heat treatment and deformation process on the superplasticity of Inconel 718 alloy. Two tensile processes were used as follows: the maximum m value superplastic deformation method and the strain-reduced superplasticity deformation process based maximum m value method. The results indicate the fine and homogeneous grain structure of Inconel alloy is obtained by hot forging, δ phase precipitation and recrystallization heat treatment processes, and the δ phase can play a role in controlling grain size during recrystallization annealing and hot deformation. Upon stretching by the above two processes at 950 oC, the percentage elongations of Inconel 718 alloy are improved from 340% and 566%, respectively. The results show that the higher value of percentage elongation can be obtained by the strain-induced superplastic deformation process based maximum m value method

Abstract:We have synthesized two types of Cu2O samples with size about 700 nm by a facile reduction route. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and surface photovoltage spectroscopy (SPS). It is noteworthy that one sample prepared using polyethylene glycol (PEG) as template is oxidized in air, but the other one prepared using glucose as template is stable in air. The testing results demonstrate that the difference of nanosized Cu2O morphology greatly affects its stability. In addition, we analyzed the effect of surface oxidation on the SPV signal of the two samples

Abstract:Our previous studies showed that at a considerably high plating speed up to 1 mm/h, the nickel electrodeposits with smooth surface, few deposition defects and some improved properties could be prepared under the conditions of an additive-free bath at a reduced pressure of 5 kPa and a temperature gradient of 35 °C /65 °C. This paper aims at further analyzing the effect of bath pressure and temperature gradient on the surface morphology, the microstructure and the properties of electrodeposited nickel coatings in a subatmospheric environment. Our findings indicate that the surface quality, the microstructure and the properties of the deposited nickel coatings are, to some extent, affected by the applied bath pressure and the temperature gradient; favorable nickel electrodeposits can be only achieved when the electrolyte in the vicinity of cathode surface is in a boiling state. The temperature gradient influences the texture characteristic of nickel deposits, but the bath pressure has few effects on the preferred orientation. Grain-fining, microhardness, and corrosion resistance of nickel deposits are improved with increasing of the temperature-gradient and/or the reducing of bath pressure. These variations are closely relevant with the boiling-driven mass transfer effect and the vacuum-degassing effect during the electrodeposition in a reduced pressure bath.

Abstract:Porous tantalum materials were prepared by a vacuum sintering technique using fine tantalum powder (< 0.45 μm) as the starting raw material. Effects of sintering time (10, 20, 30, 40 and 50 min) at 1250 oC on the microstructures and the porous characteristics of the porous tantalum were investigated. The results show that the porous tantalum materials have the porosity of about 50% with pore size distribution of 0.08 cm3/g

Abstract:The ultra-fine grained (UFG) Ti-55511 near β titanium alloy with grain size 0.1~0.5 μm was prepared by hot rolling. The effects of heat treatment on the microstructure and mechanical properties were investigated using SEM and TEM. The results indicate that both strength and hardness increase firstly and then reduce with increasing of heat treatment temperature from 350 ℃ to 650 ℃. The peak strength (1486 MPa) appears at 450 ℃. The strength dramatically reaches to 1536 MPa and then is stablized with increasing of the holding time when heat treated at 450 ℃. While the elongation increases firstly and then decreases. The microstructure analysis shows that the dynamic recovery occurs and the grain sizes remain at smaller than 1 μm during annealing. The recovery stimulates the grain refinement effect by eliminating the hardening process and stimulating the grain boundary/phase boundary to be stable. The phase transformation of α→α2 and β→ω→α enhances the second phase particle dispersion effect during annealing. However, the ductility of the alloy could significant decrease when the second phase particles grow up to a certain size. The mechanical properties evolution during annealing are mainly related to the effect of strengthening mechanisms.

Abstract:The influence of cerium and lanthanum conversion coatings on AZ63 magnesium alloy surface was investigated by Tafel polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The results show that the dual rare-earth conversion film treated in the mixture solution containing cerium nitrate and lanthanum nitrate is denser and more uniform than that in single rare-earth solution. EDX and XPS analysis demonstrates that the coatings are composed of rare earth oxides and hydrated hydroxides. The cerium and lanthanum conversion coatings can improve the corrosion resistance of AZ63 magnesium alloy evidently. The inhibition effect of dual rare-earth film on magnesium alloy increases with the increase of immersion time. With the extension of aging time, the inhibition effect increases first and then decreases. The coating aged for 48 h possesses the best inhibition effect

Abstract:The diffusion bonding between Ti/Ni was carried out by Field Activated Diffusion Bonding process (FADB). The formation of new phase during interfacial diffusion reaction between Ti/Ni and its effect on bonding strength were studied. The microstructure, phase component and element distribution across interfaces were observed and determined by SEM and EDS. The shearing properties of bonded interface were evaluated by a universal testing machine. The results indicate that complete metallurgical bonding between Ti/Ni has been reached, which is composed of intermetallics of Ni3Ti, NiTi2 and NiTi in order. When the diffusion bonding temperature is as high as 750 oC, Ti shows good performance of superplasticity and high diffusivity, which promotes Ni3Ti to transform into Ti-rich layer during diffusion bonding. The formation of Ti-rich layer improves the shearing strength of interface. The shearing strength of the Ti/Ni interface increases with increase of current, and when the current is 930~1200 A, it reaches 90.54 MPa

Abstract:This study combines the mold process with the hot isostatic pressing method, and the complex monolithic bladed disks are formed by near-net-shaping. Based on this, it gives a scientific analysis of the mold deformation, forming precision and structure property. The results show that the near-net-shaped monolithic bladed disks have a relative density of 99.5%. The SEM results indicate that there is fine and homogeneous strip α+β phase in the parts, with no obvious pores and cracks. Besides, the structure is compact, and the "layered" phenomenon appears in the microstructure. The tensile strength of parts in the same furnaces can reach 920 MPa, which is better than that of the same size castings, and as same as that of the forgings. The fracture morphology analysis suggests that the sample has a ductile fracture. The HIP method has a high material utilization, which can reduce the process costs, and the molding cycle is longer. This study provides a reference to the near-net-shaping hot isostatic pressing for the bladed disk parts

Abstract:In order to investigate the strengthening effect of highly dispersed ceramics on metal films, TiB2/Al composite films with different TiB2 contents were prepared by magnetron co-sputtering with Al and TiB2 targets. The

Abstract:The Cr2Nb-20Ti (atomic fraction) prepared by directional solidification with the withdrawal rates of 5, 10, 20, 100 μm/s were investigated to understand the microstructure evolution of the Laves phase Cr2Nb/Ti alloy. OM, XRD, and SEM apparatus were employed to determine the solidified phases and microstructure. The results indicate that the microstructures of directionally solidified Cr2Nb-20Ti alloy are all consisted of C15-Cr2Nb dendrite and interdendritic β-Ti. The formation of metastable β-Ti instead of stable α-Ti is induced by the stabilization of Cr element. With the increase in withdrawal rate and perturbation at the liquid/solid interface, the C15-Cr2Nb dendrites are refined and the dendritic morphology evolves from the petal-like pattern at 5 μm/s to the polygon-like pattern at 100 μm/s; simultaneously, the growth direction of the C15-Cr2Nb dendrite gradually deviates from the heat flow direction and transits to the preferred growth direction. From the XRD experimental result, it shows that the C15-Cr2Nb dendrite exhibits the (220) preferred growth plane due to the fact that the plane (220) has the maximal bare bond energy, leading to the fast growth kinetic and elimination of other growth planes

Abstract:The effects of composition changes of major elements on glass forming ability and microstructure in Cu50-xZr40+xAl5Nb5 (x=0, 2, 4, 6) alloy system were investigated. And the relationship between microstructure and mechanical properties were studied. The results show that Cu46Zr44Al5Nb5 with good thermal stability and best glass forming ability in the alloy system, whose ΔTx, Trg and γ are up to 51.9 K, 0.60 and 0.401, respectively. The fracture strength of Cu46Zr44Al5Nb5 amorphous alloy is up to 1811 MPa with no obvious macro-plastic deformation. And the fracture surface is comparatively smooth, with the vein-like patterns widely distributed in the same extend direction. The Cu44Zr46Al5Nb5 alloy with an amorphous and crystalline composite structure exhibits good comprehensive mechanical properties including the fracture strength of 1747 MPa and plastic strain of 3.94%. And its vein-like patterns on fracture surface are closer and deeper. The shear bands width is about 40 μm with the axial compressive direction about 45°. The crystalline phase of Cu44Zr46Al5Nb5 alloy is well-distributed, the size of which is smaller than the shear band width, toughening the glass matrix as loading. The microstructure, size and distribution of the crystalline phase determine the mechanical behavior of the composites

Abstract:The energies and electronic structures of Nb alloying Mg2Ni and the corresponding hydrides were investigated by the first-principles plane-wave pseudopotential method based on the density functional theory. The results of the formation enthalpy show that when Nb atom occupies the Mg(6i) lattice sites, the structure of Mg2Ni has the highest structure stability. The further analysis of the hydrides shows that Nb alloying significantly decreases the stability of the hydrides and the dissociated energies of H atoms, indicating that Nb alloying benefits the improvement of the dehydrogenating properties of Mg2Ni hydrides. Analysis of the electronic structures suggests that Ni-H bond is stronger than the Mg-H bond in Mg2NiH4 phase. The Ni-H bond is weakened because the interaction between Nb and H is stronger than the interaction between Mg and H. This may be one of the reasons of decreasing structure stability of the hydrides

Abstract:The microstructures and corrosion behavior of the hypoeutectoid U-Nb alloy laser welded joint were investigated by OM, SEM, XRD and electrochemical analysis. The results indicate that the grain size of the weld zone of the hypoeutectoid pearlite U-Nb alloy is about 50 μm and the weld zone is only composed of α′ martensite with orthogonal crystal structure. After immersion in 3.5%NaCl solution, the corrosion potential of weld metal is ~400 mV lower than the substrate’s, and the corrosion couple forms between weld metal and the rest of the welded. The results of surface morphology and linear polarization show that the corrosion process of the welded joint includes galvanic corrosion and self-corrosion while galvanic corrosion behavior is the dominated. The corrosion current of welded joint is about 3 times higher than that of the substrate and 10 times higher than that of the weld metal. The overall anti-corrosion property of welded joint is depressed. The corrosion is uniform

Abstract:A composite coating was prepared to control drug release and corrosion of magnesium alloys stent materials AZ81, and the corrosion resistance, drug release and biocompatibility were investigated. IR spectrum and DSC results show that paclitaxel can be evenly dispersed in the PLGA. The drug-release curves indicate that the cumulative release rate after 30 d reaches approximately 80%. SEM, the electrochemical impedance spectroscopy, polarization curve and magnesium release results suggest that the PLLA coating improve the corrosion resistance by preventing the corrosive ions from diffusing to the magnesium substrate. The blood and cell test results reveal that the samples have good hemocompatibility and no cytotoxicity

Abstract:The high-temperature oxidation behaviors of GH4700 alloy were studied by means of XRD, SEM and EDS. The results indicate that the oxidation kinetics obey parabolic law in a temperature range of 800 to 900 oC, and the growth of the oxide film is controlled by the diffusion of oxygen in the film; the oxidation scale formed for 100 h consists of three parts, and the addition of Nb can effectively improve the oxidation resistance properties

Abstract:This paper introduces a method to measure critical current of high-temperature superconductor (HTS) tapes continuously using magnetic circuits. This method has two featured advantages. First, it is resistant to noises caused by mechanical vibration in principle, so high speed stable measurements are achieved; second, it can measure HTS tapes with magnetic substrates (e.g. RABiTS). In this paper, the principle of the method is introduced and the apparatus for kilometer-length HTS tapes measurements is constructed. Several Bi2223/Ag and YBCO tapes are measured to verify advantages of the method

Abstract:Mg2Sn based thermoelectric (TE) materials were prepared by a low-temperature solid-state reaction between MgH2 and Sn. Reaction between tin and magnesium hydride instead of pure magnesium minimizes the oxidation and volatilization of magnesium. The thermoelectric performance was measured over the temperature range 300~750 K. All samples indicate n-type conduction within the whole temperature region, while they show a tendency to be nearly p-type with the temperature increasing. The Seebeck coefficient of Y-doped Mg2Sn has been enhanced, and the power factor has been 40% higher than the value of reference. The 0.2% Y-doped Mg2Sn exhibits a maximum figure of merit ZT of 0.033 at 350 K, which is nearly 3 times of the value of reference.

Abstract:Zirconia coatings as hydrogen were formed on disk-type ZrH2 substrate by a sol-gel method. Properties of oxide coatings were studied with different precursor concentrations. The phase structure and morphology of oxide coatings were analyzed by XRD and SEM, respectively. The anti-permeation effect was tested by a vacuum dehydrogenation experiment. Results show that the thickness of total oxide coatings varied from 5 μm to 14.3 μm, which increased first and then decreased with the precursor concentration increasing. SEM images of oxide coating morphology and cross section demonstrate the continuous coatings couldn’t be generated when the concentration was set below 1.0 mol/L; however, when the concentration was higher than 1.0 mol/L, particle accumulation and cracks occurred on the surface of the coating and the coating was not continuous. The phase structure of the oxide coating is monoclinic ZrO2 and tetragonal ZrOx. Permeation reduction factor values range from 9.86 to 10.43

Abstract:Ag/Cu composite wires were prepared by a solid-liquid casting method and drawing. The influence of annealing temperature on interface and mechanical properties of the Ag/Cu bimetal composite wires was investigated. The Ag/Cu interface was analyzed by scanning electron microscope and optical microscope to investigate the microstructure, elements distribution and bonding level. The effect of annealing temperature on diffusion thickness was also analyzed by EDS and line scan. The results show that the width of the diffusion region along the interface in the both sides increases with higher annealing temperature. Good bonding properties of the interface could be obtained when the optimal annealing temperature is 400 oC ~ 500 oC and the holding time 60 min.

Abstract:Magnesium matrix composite reinforced with SiC nanoparticles (n-SiCp/AZ91D) was fabricated by squeeze casting. The microstructure and mechanical properties of the nanocomposite at as-cast state (F), solid solution state (T4) and artificial aging state (T6) were investigated by optical microscopy, X-ray diffraction, scanning electronic microscopy (SEM) and tensile tests. The results show that the solid solution treatment can dissolve the β-Mg17Al12 eutectic phase in the matrix of n-SiCp/AZ91D composites to produce single supersaturated solid solution α-Mg phase and the ultimate tensile strength and elongation are significantly improved which can be up to 265 MPa and 13.7%, respectively. After aging treatment, the ultimate tensile strength and yield strength of the nanocomposite are further improved, which is 275 MPa and 145 MPa, respectively. SEM results show that the β-Mg17Al12 phase is mainly precipitated in grain and at grain boundary as continuous or non continuous forms. In particular SiC nanoparticles have an important effect on the morphology, size and distribution of the β-Mg17Al12 precipitation phase and they result in the fine and uniformly dispersed secondary precipitate phase to be formed, which gives full play to the secondary precipitation strengthening effect. Finally, the fracture morphology of n-SiCp/AZ91D composites at different heat treatment conditions were observed by SEM and the fracture behavior were analyzed and discussed

Abstract:An experimental set-up was designed for measuring the self-field losses of Bi2223/Ag HTS tapes using a transport current method. In this paper, Zr-based metallic glass composite with tungsten wire of 62~66 vol% in different diameters were fabricated by continuous infiltration casting process. Results show that the fracture strength and plastic strain of the metallic glass composite reach peak values at the diameter of tungsten wire of 80 μm. When the diameter of tungsten wire continues to increase to 150 μm, the fracture strength and plastic strain slump for the metallic glass composite. According to the analysis of fracture surfaces of the composites after tensile test, it is concluded that the ratio of surface to volume for different-diameter tungsten wire reinforced composites has an important effect on the tensile mechanical properties of composites through affecting the stress at interface between tungsten wire and metallic glass matrix, deformation and fracturing of tungsten wire and the formation and propagation of shear band in the metallic glass matrix

Abstract:Commercially pure titanium (TA2) pipes were prepared by drawing processing with different angles. The effect of the angles on the microstructures and mechanical properties of the titanium pipes were investigated. Meanwhile the type of textures was researched by X-ray diffraction. The results show that the annealed samples which are drawn in different angles possess two different grain orientations, (0002) basal plane parallel to the transversal section and c axis of the hexagonal close-packed parallel to axial direction of the pipe. Both crystal orientations influence the mechanical properties of the drawing pipes significantly. There are obvious differences in the type of textures between TA2 pipes by the drawing method only and the rolling method.

Abstract:Dissimilar welding experiments of Hastelloy C-276/316L thin sheet was performed by Nd:YAG continuous laser. The element content changes of the weld under different laser offsets were studied and the effects of laser offset on the corrosion performance of Hastelloy C-276/316L weld in HCL solution were also investigated by means of polarization curves and electrochemical impedance spectroscopy. The results show that Ni, Fe and Mo contents change significantly with adjusting the laser offset, while Cr element content has no obvious change. When the laser offset is between 0.1~0.3 mm, the main element contents in the weld change slightly, the corrosion voltage and the charge transfer resistance are the largest and the corrosion current density is minimal. At this time the corrosion trend and the corrosion rate of the weld is minimum. Therefore, the corrosion resistance of the weld is the best under this parameter. When the laser offset changes from 0 to –0.2 mm, the content of Fe in the weld increases gradually, but the contents of Ni and Mo decrease. It is the main cause of the decrement of corrosion voltage and the charge transfer resistance. Corrosion current density increases and the corrosion trend as well as the corrosion rate of the weld increase gradually. As a result, the corrosion resistance of weld shows a trend of weakening under this parameter

Abstract:The effect of cold processing deformation, annealing temperature and annealing time on the microstructure and mechanical properties of 617B alloy was studied. The results show that with the increase of deformation, grains are elongated along the direction of maximum principal strain to form a deformed strip belt, the tensile strength and yield strength of the alloy at room temperature gradually increase, while the elongation decreases. When the annealing temperature increases from 1080 oC to 1160 oC, the grains of the alloy gradually grow up, the tensile strength and yield strength are reduced, and the ductility is improved. When the annealing temperature of 1160 oC continues to increase, the grain growth velocity increases obviously, while the strength and plasticity changes little; grain growth activation energy (Q) of the alloy with different deformation amounts is much higher than that of pure Ni, and the Q value increases first s and then decreases with the amount of deformation increasing; the grain growth exponent η of the alloy increases first and then decreases with the increase of annealing temperature

Abstract:Based on the research and development of titanium alloys for biomedical applications in China and abroad during the past few years, the metal ions release mechanism from titanium-based alloys, and their pathogenic mechanism and protective coatings and measurements were investigated. A systematic analysis is made of the effect of the corrosion on the metal ions release mechanism from the Ti6Al4V alloy and TiNi shape memory alloy, of the relationship of metal ions with pathogenic mechanism of some diseases, and of the protective coatings and surface modification techniques inhibiting the release of the metal ions. It shows that a large number of surface modification techniques were developed in recent years to improve the biocompatibility and corrosion resistance of titanium alloys and the release of metal ions were inhibited

Abstract:On the basis of brief introduction of electromagnetic flat sheet forming principle, the research progress of this technique at home and abroad is summarized in the following four aspects. In tool coils designing, the flat coil, uniform pressure coil, alongside double coil and the electromagnetic sizing coil are listed; in magnetic force calculation, the analytical method and the finite element method are narrated; in experimental research, the research for forming property of sheet and the study of electromagnetically assisted forming are stated; in the application of numerical simulation technique, the application of numerical simulation method and finite element software are related. At last, some technical challenges that should be overcome for popularizing the electromagnetic flat sheet forming technique are presented