Progress in Powder Metallurgy

Abstract: One append way of liquid state inhibitor was investigated, which putting V, Cr into W-Co composite solutions in the form of ionization. After spray drying and being calcined, W-Co composite oxides could come into being. Then taking fluidization techniques, well-proportioned W-Co composite powder compounded with inhibitor could be produced in the end.

Abstract: A new tungsten heavy alloy with hybrid structure was manufactured for the kinetic energy penetrator. The tungsten heavy alloy is composed of two parts: core region is molybdenum added heavy alloy to promote the self-sharpening; outer part encompassing the core is conventional heavy alloy to sustain severe load in a muzzle during firing. The fracture surfaces of the specimen is observed after ballistic tests. The core region revealed brittle behavior with W/W inter-granular fracture which activates self-sharpening. On the other hand, outer part exhibited conventional ductile fracture mode. From ballistic test, it was found that the penetration performance of the hybrid structure tungsten heavy alloy is higher than that of conventional heavy alloy. This heavy alloy is thought to be very useful for the penetrator in the near future.

Abstract: The effect of Cu on the hydrogen reduction of molybdenum oxide powders was investigated by measuring the humidity change during a non-isothermal process of hydrogen reduction. The presence of Cu induced a shift in the reduction temperature and strongly affected the reduction processes of MoO3→Mo4O11→MoO2, which comprised the contained chemical vapor transport of MoOx(OH)2. This study suggests that the surface of the Cu grains acts as a nucleation site for the reduction of MoOx(OH)2 to MoO2 particles from MoO3 or Mo4O11 phases. Such an activated reduction process results in the deposition of metallic Mo and MoO2 particles on the surface of the Cu grains.

Abstract: An infiltration technique using W-Cu composite powder has been developed to enhance microstructural uniformity of W-Cu pseudo-alloy. W-Cu composite powder, manufactured by reduction from WO3 and CuO powder mixtures, were blended with W powder and then cold isostatically pressed into a cylindrical bar under 150 MPa. The pressed samples were pre-sintered at 1300 oC for 1 hour under hydrogen to make a skeleton structure. This skeleton structure was more homogeneous than that formed by using W and Cu powder mixtures. The skeleton structures were infiltrated with Cu under hydrogen atmosphere. The infiltrated W-Cu pseudo-alloy showed homogeneous microstructure without Cu rich region.

Abstract: In this paper, the microstructure and mechanical properties of yttrium oxide dispersed 90W-7Ni-3Fe alloy were studied. The 90W-7Ni-3Fe nano-crystalline composite powder dispersed with Y2O3 addition was firstly fabricated by MA process, and then the powder was pressed and sintered at 1480°C for 30 min. A fine-grained 90W-7Ni-3Fe alloy with high tensile strength and elongation properties was obtained, in which the tungsten grain size was 8-12μm, the maximum tensile strength was 1050 MPa and the elongation was 30%. The Influence of rare earth oxide Y2O3 on the mechanical properties and microstructure characteristics is discussed in detail herein.

Abstract: Lanthanum oxide was introduced to molybdenum powder by liquid-liquid doping and liquid-solid doping respectively. Mo alloys were prepared by powder metallurgy technology. The size distribution and feature of dopant particles and the fractographs of Mo alloys were investigated by TEM and SEM respectively. The results indicated that liquid-liquid doping method is favorable for refining and dispersing La2O3 particles uniformly in matrix. Fracture toughness of Mo alloys prepared by liquid-liquid doping showed better results than that of liquid-solid doping. Furthermore, the influences of the size distribution of La2O3 on properties of Mo alloys was discussed by dislocation pile-up theory.

Abstract: Driven by the unavailibility of commercial test equipment for tensile and creep testing at temperatures up to 3000°C a measuring system has been developed and constructed at the University of Applied Sciences, Jena. These temperatures are reached with precision by heating samples directly by electric current. Contact-less strain measurements are carried out with image processing software utilizing a CCD camera system. This paper covers results of creep tests which have been conducted on TZM sheet material (thickness 2 mm) in the temperature range between 1200°C and 1600°C. It is the aim of this work to show the influence of heat-treatment conditions on creep performance in the investigated temperature range.

Abstract: Tungsten-molydiside WxMo1-xSi2 was synthesized by self-propagating high temperature synthesis. The SHS product with the initial composition of (0.5Mo+0.5W+2Si) contains 23.9% MoSi2, 40.89% WSi2 with remaining 9.11% Mo, 9.16% Si and 16.94%W. Lattice parameters of the MoSi2 and WSi2 determined by Rietvelt analysis were a=0.3206 nm, c=0.7841 nm and a=0.3212 nm, c=0.7822 nm, respectively.

Abstract: In recent years, the research in porous metal got rapid development in China, especial in Northwest Institute for Non-ferrous Metal Research (NIN). Many porous metals with different raw material and different shapes were developed, which successfully employed in many fields. We believe we will earn more rapid development in the future.