Interaction of titanium diboride with nickel and Ni–20% Cr nickel alloy (nichrome)

Abstract

The interaction in the Ni–Ti–B and Ni–Ti–B–Cr systems along the Ni–TiB₂ and (Ni–20% Cr)–TiB₂ sections was studied. Solid-phase interaction was not found to occur for Ni–TiB₂ up to a temperature of 1200 °C. In the case of (Ni–20% Cr)–TiB₂, a new phase was formed, Cr₂B with a thickness of ~5 μm, at a temperature of 1200 °C. The contact melting in the Ni–TiB₂ system began at a temperature above 1200 °C and in the (Ni–20% Cr)–TiB₂ system above 1180 °C. In the (Ni–20% Cr)–TiB₂ system, the emerged liquid wetted titanium diboride with an angle 50° and when temperature increased to 1450 °C, the liquid spread completely on the TiB₂ surface. In the contact melting process, several areas formed: titanium diboride area, Ni₃B and TiB area, Ni and TiB area, and pure nickel. Therefore, the considered systems are eutectic and their quasibinary phase diagrams have a eutectic at ~9% TiB₂ with a melting point of ~ 1200 °C at the Ni–TiB₂ section and a melting point of ~1180 °C at the (Ni–20% Cr)–TiB₂ section. The alloys in the hypoeutectic part of the phase diagram consist of the Ni, Ni₃B, and TiB phases and additionally of the Cr₂B phase in the (Ni–20% Cr)–TiB₂ system. In the hypereutectic part of the phase diagram, the metal component disappears and unreacted TiB₂ additionally appears in the (Ni–20% Cr)–TiB₂ system. Zero solid-phase interaction and contact melting observed at temperatures of 1200 and 1180 °C, which are significantly lower than the melting points of the interacting components (Ni, Ni–Cr), promote favorable conditions for the use of nickel as a metal component in wear-resistant composites produced from granular titanium diboride, capable of operating under dynamic and shock loads at elevated temperatures (~900 °C) and in corrosive environments.