PHASE-FORMATION DURING DISSOLUTION OF NICKEL IN LIQUID ALUMINUM

The intermetallic phases formed between solid nickel and molten alumin ium have been studied under isothermal conditions. For temperatures ra nging from 695 to 800 degrees C, the interfacial microstructure consis ted of two phase layers, Al3Ni2 and Al3Ni. It was found that the phase growth was diffusion controlled. The identified compounds, which coin cide with the Al-rich phases of the Al-Ni phase diagram, have the high est interdiffusion coefficients. The observation of these phases was w ell linked with the thermodynamic behaviour of the melt, in agreement with the associate model applied to liquid alloys. The calorimetric ex periments have indicated a negative curvature for the enthalpies of di ssolution of Ni, which is consistent with the formation of transitory compound layers at the solid-liquid interface. Moreover, it was found that the dissolution time of Ni increased when interfacial compound la yers were formed.