Structure and Properties of Ni–Al Alloys in the Liquid State

Resumo

The structure and the properties of liquid Ni–Al alloys have been studied in a wide temperature range. An analysis of the temperature dependences of the physical and chemical properties of these alloys has discovered a hysteresis phenomenon, i.e., discrepancy between heating and cooling polytherms. This discrepancy is called the temperature hysteresis. A physical model of the Ni–Al alloy structure is proposed on the basis of a quasi-chemical model for a nonequilibrium melt structure. The liquid metal is found to be in a nonequilibrium state after melting. It contains Ni_xAl-type microgroups with a strong Ni–Al bond and fcc-like structure and microgroups with weaker Ni–Ni bonds. The sizes and the life times of these clusters decrease after melting (above the liquidus temperature). The Ni_xAl-type clusters disappear as the melt temperature becomes higher than a critical temperature. The melt transforms from a microinhomogeneous state into an equilibrium state.