Fabrication and Characterization of Advanced NbC Cutting Tool Cermets

Abstract

NbC-Ni cermets have recently come under attention as a possible green alternative to WC-Co cemented carbide tools due to their mutagenic/carcinogenic behavior. To improve base NbC-Ni cermets multipronged approach was utilized via grain inhibition, strengthening and crack bridging reinforcements. In the present study NbC-12Ni (Vol%) based cermets were prepared via vacuum liquid phase sintering. Two temperature studies were performed at 1400°C and 1450°C.VC, Mo2C, TiC and SiC whiskers were added in various compositions to the base cermet (4VC4Mo2C,10-15- 20TiC,2.5SiCw vol%). XRD and SEM results confirm formation of (Nb, X, Y) C solid solution cubic FCC carbides. Hardness and fracture toughness were improved by reducing residual porosity and improving solute reprecipitation. Significant grain refinement was observed in inhibited cermets. Maximum and minimum grain size 6.84(NbC12Ni) and 2.05(10%TiC) μm were observed. Maximum and minimum Vickers hardness values(1Kgf) recorded were 12.08 and 18.46GPa respectively while 30KgF loads exhibited 10.66 and 14.53GPa. This difference is due to indentation size effect. Maximum flexural strength 939 N/mm2 was recorded in grain inhibited cermets marking a 10.4% improvement to base cermet. Tribotesting (10-40N loads) against diamond pin counter-body via sliding pin on disk method (ASTM-G99) revealed significant wear resistance in cermets which improved with increased normal loads. Fracture toughness improved with increased sintering temperatures. Silicon carbides reinforcement resulted in silicide formation and reduction in mechanical properties.