The ultrafine cemented carbides were prepared with ultrafine WC powders synthesized with two different methods. Meanwhile, the causes of non-correspondence of Fisher particle size of ultrafine WC powder to WC grain size of ultrafine cemented carbide were analyzed from the two respects of the aggregates and sintering necks of WC powders. The results show that existence of aggregates and sintering necks can result in the deviation between Fisher particle size and primary particle size of WC powder. In ad- dition,the WC grains grow on the primary particles and therefore the deviation develops between actual WC grain size of cemented carbide and that predicted by Fisher particle size of WC powder.

Based on introduction for working principle of pressure-sintering furnace, factors are summarized causing deformation of low-pressure sintered cemented carbide products, with systematic analysis combined with actual production cases. The results show that the main factor is furnace leakage, resulting in gas entry into the furnace. O2 in the gas influences the carbon balance of the products,and then causes their de- formation.

The common problems of EDM equipment in cemented carbides are discussed and the factors in- fluencing processing quality and efficiency of the equipment are presented,and the constructive advices are proposed for future improvement and development of the equipment.

Macroscopic residual stress distribution in polycrystalline diamond compacts was calculated with finite element method. The results show that both radial residual stress and axial residual stress are tensile stress in the polycrystalline diamond layer along cylindrical edge of the compact,and therefore the edge of the compact is easily broken off in the form of large pieces during operation. Decreasing the thickness of polyerystalline diamond layer can effectively reduce its tensile stress at the edge.

Preparation methods, domestic and oversea development and problems are reviewed of the cemented carbides with nonuniform microstructure. The preparation processes of this type o{ cemented carbides have many influencing factors with complicated steps,and the microstructure of their products is difficult to be precisely controlled. Therefore, development trends in this field are proposed.

The cathode was synthesized with TiO2, CaO and C as raw materials,and then TiC powders were prepared by electrolysis in CaCl2-NaCl mixed molten salt. The resultant cathode and its electrolytic product were characterized by SEM, EDX and XRD. The results show that under 1 300℃ sintering temperature and 2 h sintering duration,CaTiO3-C compound with favorable electrical conductivity and strength can be obtained to meet the requirement of molten salt electrolysis for cathode. With the resultant compound as cathode,TiC powders with irregular spheroidal distribution and uniform particle sizes can be obtained by molten salt electrolysis.

The causes are analyzed for high solid content of crude TICl4 produced by molten salt chlorination. It is pointed out the high solid content of crude TICl4 is caused mainly by raw materials,chlorination temperature and molten salt composition in the molten salt chlorination section, the temperature of dust collection chamber and chamber connection pattern in the dust collection section, scrubbing temperature and circulating pump tank allocation in the scrubbing section as well as the stirring rate and settlement time in the settlement section. The related countermeasures are discussed.

Sr and Ba separation is a technical difficult problem in the production of high compounds. The principle,characteristics and application of main methods for Sr and Ba viewed,and the study orientation for Sr and Ba separation is also discussed.

Precursor solution was prepared through ultrasonic vibrating and setting,and then ulltra-fine RE-doped MoO3 powder was prepared by hydrothermal synthesis through the modification of the solution pH value, synthesis temperature and filling rate. Finally, nanometer-sized RE-doped Mo powder was produced after two-stage hydrogen reduction. MoO3 powder was characterized by XRD and SEM. The results show that nanometer-sized RE-doped Mo powder synthesized under the conditions of pH=0.5,180℃ synthesis temperature and 90% filling rate has fine and uniform particle size and good dispersibility.

The Ti-Nb-Cr-C doped molybdenum alloy was prepared by powder metallurgy, and its microstructure, particle size and composition were analyzed. Thermodynamics was discussed of oxide generation during ball milling and carbide formation during sintering. The results show that the second phase particles are mainly distributed on the grain boundary, and also distributed inside the grain when Nb content is eno- ugh. The second phase mainly contains Nb,Ti and C,possibly being composite carbides of Nb and Ti based on the thermodynamics analysis. The second phase particles can refine the grains of molybdenum alloy, and the effect of grain refinement is strongest with Nb content of 3 %. Cr exists in molybdenum alloy mainly in the form of solid solution.