High-temperature sliding wear, elastic modulus and transverse rupture strength of Ni bonded NbC and WC cermets

The effects of rapid pulse electric current sintering (PECS), substitution of WC by NbC and Co by Ni, and carbide additives (TiC and Mo2C) on the microstructure, elastic modulus, B3B transverse rupture strength (TRS) and high temperature sliding wear on WC-Co, WC-Ni, NbC-Co and NbC-Ni cermets were studied. Additions of x% Mo2C and y% TiC (where x and y were< 10 wt%), coupled with PECS, significantly refined the NbC-Ni cermet's carbide grain size from similar to 5.0 mu m to < 0.8 mu m, giving mechanical properties comparable to WC-Co and WC-Ni cermets:> 14 GPa hardness and similar to 10 MPa.m(1/2) fracture toughness (K-IC) and ball-on-three-balls (B3B) TRS > 1600 MPa. The sintering techniques had negligible effect on the samples' elastic and shear modulus, and all WC-based samples had higher elastic modulus than all NbC-based samples (by similar to 120 GPa). High temperature sliding wear tests were carried out using a ball-on-disk tribometer, with a 10 N force, at a sliding speed of 1.34 m/s for 0.8 km (10 min) and 2.4 km (30 min), using 100Cr6 (AISI 52100) steel balls at 400 degrees C and 0% humidity. For the 2.4 km sliding distance, all the WC cermets had lower wear volumes than NbC cermets, with LPS WC-0.5Cr(3)C(2)-10Co having the lowest wear volume. Additions of TiC and Mo2C to NbC-12Ni improved the sliding wear resistance, with TiC having the greater effect, reducing the sample wear rate by over 30% from 15.1x10(-6)mm(3)/N.m to 9.4x10(-6)mm(3)/N.m after sliding distance of 2.4 km. Generally, the LPS samples had lower wear volumes than the corresponding SPS samples, due to higher K1c and TRS.