Effect of cubic carbide composition and sintering parameters on the formation of wear resistant surfaces on cemented carbides

The influence of both processing parameters and cubic carbide composition (TiC, TaC, NbC) on the formation of wear resistant graded surface layers on cemented carbides has been investigated. Cemented carbides containing cubic carbides between 5 wt.% and 33 wt.% were sintered in nitrogen atmospheres of 5 bar. The nitridation process was carried out at liquid phase sintering temperatures (1450 degrees C) and at solid state conditions (1200 degrees C). The formation of the wear resistant surface layers depends on the TiC/ (Ta,Nb)C ratio. Nitridation at 1450 degrees C leads to the formation of graded layers in cemented carbides with TiC contents above 3 wt.%. Surface graded layers formed on cemented carbides nitrided at 1200 degrees C with TiC contents higher than 7 wt.%. The morphology of the graded layers depends on the sintering temperature. Samples nitrided at liquid phase temperatures show higher roughness than samples nitrided at solid state conditions. The mechanisms that govern the formation of wear resistant graded layers are discussed in terms of thermodynamic coupling between Ti, Ta, and Nb with nitrogen. (c) 2011 Elsevier Ltd. All rights reserved.