Peritectic solidification mechanism and accompanying microhardness enhancement of rapidly quenched Ni–Zr alloys

Abstract

Hypoperitectic, peritectic, and hyperperitectic Ni–Zr alloys were rapidly solidified by melt spinning technique. The effect of cooling rate on their phase selection and microhardness was investigated. When the cooling rate reaches 1.0 × 107 K/s, the growth of primary Ni7Zr2 and interdendritic eutectic ((Ni) + Ni5Zr) phases during the solidification of peritectic Ni-16.7 at.% Zr alloy melt is inhibited, and complete peritectic Ni5Zr phase forms. The formation ability of complete peritectic Ni5Zr phase of hypoperitectic Ni-16 at.% Zr alloy is considerably higher than that of peritectic Ni-16.7 at.% Zr alloy. With the increase of cooling rate, the competitive growth of the primary Ni7Zr2 phase and the peritectic Ni5Zr phase occurs in the hyperperitectic Ni-20 at.% Zr alloy. The microstructure of primary Ni7Zr2 phase evolves from coarse dendrite to island banding. Furthermore, the microhardness of Ni–Zr peritectic type alloys is enhanced with the rise of cooling rate. In the case of peritectic Ni-16.7 at.% Zr alloy, this increases from 3.98 to 7.01 GPa, realizing an enhancement of 76.8%.