Abstract

Cobalt and VC powders were ball milled with M2 grade high speed steel powders under various ball to powder ratios. The powders milled under higher ball to powder ratio become finer, more irregular and have a broader size distribution, and thus possess a lower compressibility and a better sinterability regarding densification. Increasing the ball to powder ratio lowered the sintering temperature to obtain the density level necessary to isolate all the pores. Lowering the sintering temperature is very critical to maintain fine microstructure since grain and carbide coarsening are accelerated by higher sintering temperature due to more liquid phase formation. The powders obtained by ball milling at 20 to 1 ratio has the lowest compressibility but has the best sinterability, almost compatible to unmilled pure M2 powders. A sintered body over 97% theoretical density with fine microstructures having average grain size of ~10 microns was obtained from the powder by sintering at 1260 °C for 1 hour in vacuum. XRD results indicate that two types of carbides are mainly present in the sintered structure, MC and M_6C type. The MC type carbides are more or less round shaped and mainly located at the grain boundaries whereas the M_6C type are angular shaped and mainly located inside the grains.