Effect of binder compositions on microstructure, hardness and magnetic properties of (Ta,Nb)C-Co and (Ta,Nb)C-Ni cemented carbides

Abstract

Fabrication by powder technology routes, as well as microstructure characterization and measurement of hardness and magnetic properties of two types of (Ta,Nb)C sintered carbides having different composition of Ni and Co binders were carried out in the present study. Each carbide binder composition mixer was cold pressed in a uniaxial direction die at 400 MPa followed by vacuum sintering at 1450 degrees C. Nearly full dense (Ta,Nb)C sintered carbides with a relative density between 99.5% and 99.8% were obtained. The highest macrohardness values were observed for composition of (Ta,Nb)C-5 wt%Co and (Ta,Nb)C-5 wt%Ni of 1400 H(V) and 1300 H(V) respectively. The magnetic B-H hysteresis loops were measured at 0.8 T by the VSM method. In the case of (Ta,Nb)C-Co, higher magnetic saturation values of 47 emu/g were obtained for (Ta,Nb)C-30 wt%Co and 13.5 emu/g for (Ta,Nb)C-5 wt%Co. However, the magnetic saturation values for the prepared carbide having a composition of (Ta,Nb)C-Ni displayed smaller magnetic saturation than the corresponding (Ta,Nb)C-Co carbides. On the other hand, the coercivities of the (Ta,Nb)C-Co has higher value than those of (Ta,Nb)C-Ni. As the metal binder phase was increased, the coercivity decreased. The influence of the distribution of Ta, Nb, Co and Ni in the carbide phase and the metal binder phase were investigated by EDAX compositional analysis and its relation with the hardness and the magnetic properties were studied. (C) 2008 Elsevier Ltd. All rights reserved.