Microstructural development and sintering kinetics in ceramic reinforced high speed steel metal matrix composites

Studies were made of sintering kinetics and microstructural development when additions of either TiC or NbC were made to a sintered M3/2 high speed steel. Sintering occurred by a supersolidus liquid phase mechanism with diffusion controlled solution-reprecipitation as the predominant sintering mechanism, except in the case of TiC based composites where a much slower, unidentified, liquid phase sintering reaction occurred. Both ceramic carbide found to raise the temperature sinter to full density but they also increased the width of the 'sintering window' and restricted the formation of the coarse carbide grain boundary films and eutectics normally produced by oversintering in M3/2 high speed steel. These effects were related to changes in the alloy composition and phase equilibria caused by interaction between the steel and carbide additive. In the case of the TiC composite, some TIC particles were retained but their solution into the steel caused the M6C matrix carbides to be replaced by a titanium/vanadium containing MC carbide. Conversion of NbC into a more complex alloyed MC carbide containing both vanadium and molybdenum took place in the NbC based composite.