Study of cemented carbonitrides with nickel as binder: Experimental investigations and computer calculations

Cobalt is the most common binder in cemented carbides industry. However, there are some interests in use of alternatives. The similarity in properties has made nickel the first choice. In the present work, the effect of initial composition on modern hardmetals containing transition metal carbides/carbonitrides that are called “cemented carbonitrides” with nickel as binder was investigated. Change in quantity of additive carbides and tungsten to carbon (C/W) weight ratio through applying metallic tungsten powder in primary powder mixture had some effects on final hardness, transverse rupture strength, and microstructure of studied alloys. Addition of vanadium carbide not more than 0.2 wt.%, increased the final hardness. Application of (Ta,Nb)C solid solution carbide cancelled the grain refinement effect of VC. Formation of eta (η) phase was observed in SEM micrographs as a result of increase in W/C weight ratio. Surface modified layers with thicknesses ranging from 55 to 65 μm called Cubic Free Layer (CFL) was observed in vacuum sintered specimens. DICTRA® module from Thermo-Calc® software package was applied for simulation of CFL formation process in studied alloys. Formation of eta phase and consumption of metallic binder was predicted using calculations of Thermo-Calc® ver. P software. A state of the art technique was developed to prove linear relationship between Labyrinth factor (λ) and binder phase volume fraction (f).