Effect of Ti and TiH2 doping on mechanical and adhesive properties of Fe-Co-Ni binder to diamond in cutting tools

Abstract

This study is aimed at designing novel Fe-Co-Ni binders doped with titanium or titanium hydride for diamond cutting tools in order to improve their mechanical properties and adhesion to diamond monocrystals. Both dopants were added into initial Fe-Co-Ni mixtures by means of mechanical alloying in a planetary ball mill. This allowed to dissolve Ti in an iron-based matrix or redistribute nanosized TiH2 particles uniformly in the mixture. Titanium and titanium hydride provide opposite effects on the mechanical properties of the Fe-Co-Ni binder. Addition of titanium resulted in the embrittlement of the alloy due to the formation of titanium carbide layers on the grain boundaries. Doping with TiH2 at a concentration of 0.5–4 wt% strengthens the binder up to 2900 MPa, which is 45% higher than that of the initial material. Adhesion of binder to diamond is significantly enhanced even at low concentrations of titanium as demonstrated by the fact that the binder covered the large fraction of the diamond surface in fractured specimens. Analysis of interface between the diamonds and matrix revealed the presence of a 50 nm TiC intermediate layer.