Fractionation of Ni–Cr–Cu–Al Alloys during Vacuum Evaporation

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Abstract
Several apparent anomalies were found between experimental and theoretical compositions of thin films when deposited from Ni–Cr–Cu–Al alloys. Films were obtained by condensation during successive intervals of evaporation and analyses were performed by emission-spectrographic techniques. Theoretical compositions were calculated by successive approximations using Langmuir’s equation and Raoult’s law. Theoretically, the initial major components should be Al and Cr with the concentration of Cu remaining fairly constant throughout the evaporation. Experimentally, there was more Ni and Cu and less Cr in the initial films than theory predicted. The rate of evaporation of Al was strongly dependent upon the source temperature and initial compositions. These anomalies are explained by the formation of intermetallic compounds in the source. A model for the evaporation mechanism is proposed.

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