Effect of cobalt replacement by nickel on functionally graded cemented carbonitrides

Abstract

Functionally graded cemented carbonitrides (FGCCs) are applied in cutting tools industry. Indexable inserts made from mentioned alloys have superior cutting performance and tool life thanks the formation of a surface modified layer with enhanced properties as well as crater wear resistance. Cemented carbonitrides are made of hard carbide/nitride/carbonitride particles that have been embedded in a metallic binder. Excellent wetting ability of tungsten carbide with cobalt has made this metal the first choice as binder. However, cobalt has high cost and environmental pollution impacts. Substitution of cobalt with other metals has always been figured out. Some other metals that have been used as binder are iron, nickel and manganese. In addition to lower cost, nickel has higher corrosion resistance than cobalt. In the present work, gradual substitution of cobalt with nickel in WC/2.5TiC 0.7N 0.3/2.5TiC/0.2VC/8Co (numbers indicate wt.%) cemented carbonitride has been studied. This is supposed to make some alterations in mechanical and magnetic properties as well as formation of Cubic Free Layer. As sintered samples with different binder characteristics were prepared by powder metallurgy techniques and use of Hot Isostatic Pressure (HIP) and vacuum furnaces. Magnetic saturation, coercive force, Vickers hardness, and transverse rupture strength tests were carried out together with optical and scanning electron microscopy. Computational thermodynamics was applied to explain changes in magnetic properties of investigated alloys as well as plotting phase diagrams. Complete displacement of cobalt by nickel made an increase in transverse rupture strength (TRS) of final alloy by 37% with less than 6% decrease in Vickers hardness and doubled the thickness of Cubic Free Layer.