Application of compression lubricant as final porosity controller in the sintering of tungsten powders

Sintering behavior of two tungsten powders (1.2 μm and 6 μm) was studied for preparing infiltrable porous skeleton. Both powders were compressed by mechanical press (MP) and cold isostatic press (CIP) with and without stearic acid respectively as compaction lubricant. Results showed that presence of solid lubricant powder in addition of its essential effect on soundness of parts, depending on its size and distribution, could mainly affect sintered microstructure. Stearic acid as compaction lubricant in addition of decreasing friction between particles during the compaction, has acted as spacing particles between primary powder particles. In the cases that lubricant particles are much bigger than tungsten particles a big pore remained after evaporation of lubricant. During the sintering, big pores became bigger due to coarsening mechanism and formed an interconnected network of pores and on the other hand small pores shrank or even disappeared due to densification. By exact controlling of the size of tungsten powder and lubricant powder, infiltrable tungsten skeletons with 80% of theoretical density were produced successfully at low sintering temperatures such as 1500 °C.