Huiping Shao

Preparation and properties of biomedical porous titanium alloys by gelcasting

Porous titanium alloys have been prepared by gelcasting in this study. The elastic solid green body was first polymerized and then vacuum sintered to porous titanium alloys with low contamination by controlling sintering conditions. The microstructure and the total porosity of the vacuum sintered porous Ti-Co and Ti-Mo alloys were analyzed by using scanning electron microscopy and x-ray diffraction. Moreover, compression and bending tests were conducted to investigate their mechanical properties. The results show that open and closed three-dimensional pore morphologies and total porosity ranging from 38.34% to 58.32% can be achieved. In contrast to porous Ti by gelcasting, the compression and bending strengths of porous titanium alloys were significantly increased by adding Mo and Co with Youngs modulus ranging between 7-25 GPa, which is close to that of human cortical bone, therefore being suited for potential application in load-bearing implants.

Consolidation and properties of ultrafine binderless cemented carbide by spark plasma sintering

Abstract Owing to the absence of metal binder, binderless cemented carbides have higher wear, corrosion, and oxidation resistance. WC-0.3VC- 0.5Cr3C2 powders with an average particle size of 200 nm and a little amount of active element were consolidated by spark plasma sintering. The sintered microstructure revealed that the average WC grain size was 0.24 μm, which was almost consistent with the initial fine powder. The results of XRD showed that W2C phase was formed. Nearly complete densification of ultrafine binderless cemented carbide was achieved by sintering at 1400°C for 120 s under 50 MPa. The resulting hardness and the fracture toughness were 28.18 GPa and 6.05 MPa·m½, respectively.

Near-net shape processing of spherical high Nb-TiAl alloy powder by gelcasting

Spherical Ti-45Al-8.5Nb-(W,B,Y) alloy powder prepared by an argon plasma process was near-net shape by gelcasting. In the non-aqueous system, methaerylate-2-hydroxy ethyl, toluene, benzoyl peroxide, and N,N-dimethylaniline were used as the monomer, solvent, initiator, and catalyst, respectively. To improve sintering and forming behaviors, many additives were included in the suspension. The concentrated suspension with a solid loading of 70vol% was prepared. The high Nb-TiAl powder was analyzed by electron microscopy and X-ray diffraction. It was found that the green bodies had a smooth surface and homogeneous microstructure, exhibiting a bending strength as high as 50 MPa. After sintering at 1480°C for 2 h in vacuum, uniform complex-shaped high Nb-TiAl parts were successfully produced.

Influence of nano-Al2O3-reinforced oxide-dispersion-strengthened Cu on the mechanical and tribological properties of Cu-based composites

The mechanical and tribological properties of Cu-based powder metallurgy (P/M) friction composites containing 10wt%–50wt% oxide-dispersion-strengthened (ODS) Cu reinforced with nano-Al2O3 were investigated. Additionally, the friction and wear behaviors as well as the wear mechanism of the Cu-based composites were characterized by scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS) elemental mapping. The results indicated that the Cu-based friction composite containing 30wt% ODS Cu exhibited the highest hardness and shear strength. The average and instantaneous friction coefficient curves of this sample, when operated in a high-speed train at a speed of 300 km/h, were similar to those of a commercial disc brake pad produced by Knorr-Bremse AG (Germany). Additionally, the lowest linear wear loss of the obtained samples was (0.008 ± 0.001) mm per time per face, which is much lower than that of the Knorr-Bremse pad ((0.01 ± 0.001) mm). The excellent performance of the developed pad is a consequence of the formation of a dense oxide composite layer and its close combination with the pad body.

Characterization of nanometer tungsten powders

Abstract Three types of tungsten powders were prepared by hydrogen reduction of three precursor powders at low temperature, which were used as samples, and were then characterized by Brunauer-Emmer-Teller (BET) method, scanning electron microscopy (SEM), transmission electronic microscopy (TEM), small angle X-ray scattering (SAXS), and field-emission scanning electron microscopy (FESEM) respectively. The results showed that although BET and SEM could not characterize the particle size of nanometer powders, they were important means of assistance to exclude non-nanometer powders. TEM and FESEM could directly measure the particle size of nanometer powders, but this needs a lot of time, to count the average particle size and particle size distribution. SAXS could not describe the state of agglomeration. By the combination of FESEM and SAXS, the particle size, particle size distribution, and particle shape of nanometer powders could be precisely characterized.