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

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 1.0x10(7) 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%.