Abstract:

Abstract:The electrocrystallization hydrothermal synthesis process was used for fabricating hydroxyapatite biocoatings on metallic substrates at low temperatures with aqueous electrolytes containing Ca and P bearing ions. Scanning electron microscopy (SEM) , X ray diffraction (XRD) and infrared spectroscopy (IR) were used to analyze the morphology, structure and chemical composition of the coatings. Bonding strength and biocompatibility of the coatings were measured. The results show that the coatings prepared by this process are wholly composed of needle like hydroxyapatite, and hvae a good uniformity and high purity. The bonding strength is about 15 MPa. Though the mass of the coating decreases as the coating is immersed in the Ringer's solution for 12 months, no changes in the phase composition and morphology were observed.

Abstract:

Abstract:By means of the empirical electron theory (EET),the valence electron structures and cleavage energy(Gc) of titanium aluminides with hydrogen are calculated. The analysis shows that hydrogen embrittlement in Ti3Al results from brittle phase() transformation, and hydrogen embrittlement in TiAl results from solute hydrogen induced weakening of main bonds in the TiAl crystal cell with hydrogen, which results in a decrease of the cleavage energy, Gc. A practical method of reducing hydrogen embrittlement are proposed.

Abstract:The alloys Ti 35V 15Cr(c) and Ti 25V 15Cr 02Si(Ti40) exhibit good burn resistance,however,the influence of the alloying element,Cr,on alloy burning behavior is not clear.Effect of alloying element,Cr,on titanium alloy burning behavior is studied by means of the direct current simulation burn(DCSB) ignition method.The results indicate that the burn resistance is improved as the Cr content is increased beyond 10%,even more so beyond 15%.However,Ti Cr binary alloys do not reveal burn resistant behavior.The reason is that the burned Ti Cr alloy surface is porous and cracked,and the interface between burned product and the matrix is the same as it is when the Cr content is less than 10%,which is insufficient to retard oxygen diffusion into the matrix.But the interface of Ti (>10)Cr alloys is rich in Cr,and the oxide film is tenacious and able to retard oxygen diffusion into the matrix thereby decreasing the burning velocity.The burned products of Ti Cr alloys are TiO\-2,TiO and TiCrO\-3.

Abstract:The effect of hydrogen on the microstructure and high temperature deformation of a Ti3Al based alloy (Ti 24Al 14Nb 3V 0.5Mo(at%) has been studied. The results show that the hydrides as a result of form hydrogenation decompose at high temperatures, introducing some dislocations. The volumn fraction of the O phase decreases due to the addition of hydrogen. Under high temperature deformation, the hydrogen facilitates the dynamic recrystallization of the O phase and dislocation movement in the B2 phase. The activation energy is also reduced. The mechanisms of hydrogen reduced flow stress and increased m value at high temperature deformation are also analyzed in detail.

Abstract:The influence of alloying elements (Cu, Nb) on the bending strength and fracture toughness of sintered NdFeB permanent magnets is studied. The strengthening mechanism is also studied using microanalysis method. It is shown that the bending strength of the magnets can be greatly improved with proper alloying additions, mainly due to the appearance of new phases and simultaneous constitution changes of original phases in the alloys.

Abstract:The virtues of the silicon nitride ceramic tools reinforced by transition metal nitride particles are compared with those of the carbides. It is found that the nitrides have better compatibility than the carbides when they are introduced into silicon nitride. Furthermore, because nitride particles can dissolve small amounts of carbon and oxygen, the carbonization of the silicon nitride matrix decreases, and hot pressing without an inert atmosphere is possible. In addition, electrical discharge machining and wear resistance are improved by the introduction of nitrides.

Abstract:The effect of free carbon on the hotpressing behavior of boron carbide powders, flexural strength and toughness of hotpressed boroncarbide ceramic materials is studied. The composition, microstructure and fracture behavior of hotpressed ceramic materials were examined and analyzed using Xray diffraction and SEM. The experimental results show that density and properties of sintered materials are depended on additive carbon content in powders. For a certain hotpressing conditions, relative density, flexural strength and fracture toughness of the materials hotpressed from boron carbide powder with 7wt% carbon are 985%, 460 MPa and 765 MPam1/2,respectively. From the analyses of compositions and fracture surface, it is found that crack branching and blunting are the main reasons for flexural strength decrease and fracture toughness increase with the increase of the carbon content.

Abstract:Many studies have shown that the phase assemblage of starting powders influences the phase evolution of the 2223 phase; but it is quite difficult to control the phase balance in precursor powders using a singlepowder process. In this study, (Bi,Pb)2212 and CaCuO2 are formed as separate intermediate phases, then mixed and processed together within a silver sheath. The phase transformation kinetics, microstructure and transport properties of the resulting tapes are strongly dependence on the phase content of the precursor powders. Nearly pure 2223 can been produced when sintering for as little as 40 h, using (Bi, Pb)2212 and CaCuO2 presursors, and the fraction of nonsuperconducting phases seem to become minimum at the boundary of the oxide core. The effects of mechanical deformation and heat treatment cycles on silvercore interfaces and critical current densities in 37,61 and 85 filament tapes have been studied for the tapes fabricated using the twopowder process. A smooth Agoxide interface has been obtained through accurate control of the pass reduction ratios. This experiment demonstrates that the existence of large platelike 2212 grains in the presursors can accelerate the diffusion of Ca, Cu during sintering stage and increase the degree of texture of 2223 grains.Tapes with a thickness of 024 mm can be made using flat rolling without any sausaging effect. Jc values of 30104 A/cm2(Ic=53 A) and 17104 A/cm2(Ic=35 A) at 77 K and self field are achieved for rolled short samples and tapes 20 m long, respectively.

Abstract:The kinetics of microstructural transformation has been analyzed using an endquenching and extinguishing method for a Ti50at%Al alloy synthesized by combustion. It is shown that from start of aluminum powder melting, a series of transition reactions takes place one after another as follows: Ti+Al1/3TiAl3+2/3TiTixAl+(1-x)TiTiAl. The liquidsolid reaction at the early stage may heat the sample quickly, which can create a good condition for later solidsolid reactions. Since masstransfer during solidstate diffusion is much slower than that within liquid reactants, the later solidsolid reactions slow and some Ti core is left in the alloy for rapid cooling. The aluminum contents of the boundary layers of the Ti cores are higher than those of central parts of the Ti cores, and the boundary layers transform into annular 2Ti3Al phase during cooling.

Abstract:The effects of powder loading and sintering temperature on the mechanical properties of a metal injection molded (MIM) tungsten heavy alloy are studied. The properties of MIM products are compared with those of traditional pressed/sintered products with the same compositions. The following optimal properties have been attained for the 97W 2Ni 1Fe alloy made by the MIM process with a powder loading of 47vol% and sintered at 1 530 for 2 hrs: b=936 MPa,02=649 MPa,=114%,HRC=31 They are much better than those of pressed/sintered alloy.

Abstract:The effects of sintering temperature,holding time and hot pressure on the density and mechanical properties of a hot pressed(PM)powder metallurgy 30vol%TiC\-p/W composite have been investigated. An optimum process for the preparation of 30vol%TiC\-p/W composite with higher strength and toughness has been devised.The 30vol%TiC\-p/W composite has excellent high temperature strength.This is attributed to a brittle ductile transision of the tungsten matrix combined with the strengthening effect of hard TiC particles in the W matrix.

Abstract:The effect of nickel on the conductivity of reaction*4]bonded SiC is studied. The results show that the resistivity of reaction bonded SiC decreases with increase of nickel content The Ni doped SiC has negative temperature coefficient of resistivity. The resistivity of SiC is almost constant with holding time at 900. The results above show that the resistivity of reaction bonded SiC can be improved through adding nickel. The microstructure of the Ni doped SiC is studied in detail.

Abstract:A liquid penetration method for Nb/20Cu composite fabrication is presented. The microstructure and the properties of the Nb/20Cu composite are also investigated in detail. The results show that the electrical and thermal conductivities, oxidizationresistance and mechanic properties of Nb/20Cu are better than those of pure Nb made by powder metallurgy. It provides an experimental base for improving property of Nb products.

Abstract:The microstructure and properties of a SiC particle reinforced and toughened siliconnitridebase matrix ceramic cuttingtool material have been investigated.The results show that this material has excellent mechanical properties.By adding the SiC particles,strength,toughness and hardness can be greatly improved,as compared with those of the pure siliconnitride ceramic.Microstructural analysis shows that the SiC particles prevents the grain growth of Si\-3N\-4,and also improves the microstructure of Si\-3N\-4base ceramic.The toughening mechanism of SiC in the Si\-3N\-4 matrix is also discussed.

Abstract:Microstructures, tensile strength, elongation and flexibility before and after annealing have been studied for 06 mm diameter MoLa wire made by powder metallurgy and pressure working, as compared with the same size of Mo1 wire. The results show that the recrystalling temperature of MoLa wire is 1 800, which is 600 higher than that of Mo1 wire. After complete recrystallization, MoLa wire has an interlocking grain structure. The tensile strength, plasticity and tonghness of MoLa wire is higher than those of Mo1 wire after high temperature annealing and/or recrystallization annealing.

Abstract:The principle and method of plotting new kUP (tube voltage)T(thickness of specimen)F(focal distance) exposure curves for the use of radiographic examination of Ti with focal distances of 0412 m are described. The test results show that the method of plotting the kUpTF curve is not only simple, economical and practical, but also good for the image quality of the photographic plate and the photographic efficiency. The curve is also ideal for choosing an accurate value of tube voltage for the onsite radiographic examination of Ti pressure vessels.