Interaction of HfB2 with Nickel and Ni–20% Cr Alloy (Nichrome)

Abstract

Interaction in the Ni–HfB2 and NiCr–HfB2 systems is studied. No new reaction products are found to form in the system with pure nickel in solid-phase interaction up to the contact melting point. Solidphase interaction in the NiCr–HfB2 system resulting from the interdiffusion of boron from hafnium diboride and chromium from nichrome leads to a Cr2B layer in the contact area. Contact melting begins at 1370 ± 10°C in the Ni–HfB2 system and at 1450 ± 10°C in the NiCr–HfB2 system. The starting metals and Hf3Ni20B6 and Ni3Hf phases, including the Cr2Ni3B6 phase in the NiCr–HfB2 system, are basic products of the liquid-phase interaction in the hypoeutectic region of the phase diagrams of both systems. In the hypereutectic region of the phase diagrams, the metal component disappears and unreacted HfB2 appears additionally in the NiCr–HfB2 system. Both systems are eutectic and have eutectic melting points of 1370 ± 10°C for Ni–HfB2 and 1450 ± 10°C for NiCr–HfB2 at 20 ± 2% HfB2 in their quasibinary phase diagrams. Therefore, nickel and nichrome can be used to activate sintering since they act as a vanishing liquid phase. On the other hand, hightemperature oxidation-resistant hafnium diboride products can successfully perform in contact with nickel and nichrome products in the temperature range up to 1200°C.