The application of PIM (powder injection molding) process of cemented carbide parts bas been studied. Two kinds of cemented carbide powders, with the particle size of 3um and 0.4um respectively, were used in the experiments. Two kinds of binders were applied. The rheological properties of feedstocks were studied. The thermogravimetry analysis and thermal debinding cycles were investigated. Possible defects introduced in PIM process steps were described. The influences of holding temperature and holding time during debinding on the carbon content in compacts were studied. The mechanical properties of cemented carbide parts prepared with different partiele sized powders were compared.

Ti'/AI203 Functionally Gradient Material (FGM) was prepared by an explosive compaction/SHS process. Ten sheets of the compounding powder were laminated and pressed to get a green body of FGM. It was then compacted explosively. By burying the explosive compaction body into a stoichiometric AI/TiO2 mixture and igniting the combustion of the stoichiometric AI/TiO2 mixture, the SHS reaction of the explosive compaction body was initiated by the heat released from the combustion of the stoichiometric AI/TiO2 mixture. In this way, Ti/AI203 FGM was synthesized. The adiabatic temperatures of each gradient layer were calculated when the pre-heating temperatures were 298 K and 1173 K, respectively. The microstructure, composition and properties of Ti/AI203 FGM and the reaction mechanism of each gradient layer were studied. It was found that Ti/AI203 FGM prepared by the explosive cornpaction/SHS process had a high density and a high microhardness. Its structure, composition and properties showed apparent gradient distribution. The structure of the standard stoichiometric ratio gradient layer of FGM was a network structure. Its reaction mode could be described as follows: AI powder melted first, then the molten AI penetrated into the TiO2 zone and reacted with TiO2, and big pores were left in the original positions of AI powder. The reaction of gradient layers with the addition of AI203 as diluents was similar to that of the standard stoichiometric ratio gradient layer, so were their structure and composition. However, the reaction of gradient layers with the addition of Ti as diluents was more complex and the composition deviated slightly from the designed one.

The process of thermal debinding of injection molded water atomized 316L stainless steel powder compacts was studied in a vacuum and hydrogen atmosphere using a mercury porosimetry and the thermogravimetric analysis method. The vacuum debinding rate was investigated under the conditions of different binder compositions and temperature-increase rates, especially at the low temperature stage. The process of thermal debinding in the hydrogen atmosphere was compared with that in vacuum. It was found that the binder removal rate was much higher in vacuum than that in the hydrogen atmosphere under the same experimental conditions. The mercury porosimetry was used to measure the pore structure evolution. The results of the mercury porosimetry indicated that the pore structure evolution in injection molded compacts during thermal debinding in vacuum was greatly different from that in hydrogen atmosphere. A fine inter-connected pore structure developed as a result of the evaporation and removal of the low molecular binder components at the early stage of debinding. The reason for the difference in binder removal rate and the inter-connected pore structure in these two debinding environments lies in the difference of the vapor pressure drop, which was the vapor pressure difference between that in the molded compacts and that in the ambient environment. At the different thermal debinding stages and environments, the pore structure evolution and changes in the mean pore size in the thermally debound compacts were also different. From the low debinding temperature stage to the intermediate temperature stage of about 300 8C, the pores in the thermally debound compacts in the hydrogen atmosphere were finer and the pore size distribution was more homogeneous than that in the vacuum. At the final debinding stage, the pore size distribution was almost the same in the hydrogen atmosphere as in the vacuum.

The 1724PH stainless steel compacts sintered at 1 380 ℃for 90 min have the best me2 chanical properties and the good microstructure with homogeneously distributed pore structure and the moderate2sized grains. Whereas the compacts sintered for 60 min and 120 min show an inadequate and an over2sintered microstructure re2 spectively. The compacts sintered at 1380 ℃for 90 min have the density of 7.70g/cm3, the strength of 1275MPa, the elongation of 5%, and hardness of HRC36. With the increase of sintering temperature, the density, strength and hard2 ness increase, while the elongation decreases. The 1724PH stainless steel has good corrosion resistance, showing an activa2 tion2passivation polarization curve. But the passivation potential range is narrow and the spot corrosion potential is low, in2 dicating a low anti2spot corrosive properties.