Grain size and growth of Ni-Rich Ni-Al alloy films

Abstract

Ni-rich Ni-Al films have been prepared by co-evaporation (0-55 at.% Al) on substrates held at temperatures between 360 and 790 K. For pure Ni films the grain size decreases with decreasing substrate temperature (Ts) between 800 and 570 K, but between 570 and 480 K the average grain size changes very little, depending on a change in growth mechanism. Below 480 K the grain size decreases again but the temperature dependence is now weak. By alloying Ni with Al the grain size decreases at all temperatures, at low temperatures due to solution of Al in Ni(FCC) and at high temperatures due to the formation of α′-Ni3Al. For Al contents between 30 and 50 at.% the formation of β′-NiAl controls the growth and causes a phase separation into large outgrowths with β′-NiAl structure surrounded by small grains with Ni f.c.c. or α′-Ni3Al structure. At low substrate temperatures (Ts < 0.3 Tm, Tm = melting temperature) we suggest the films crystallize by a collective process involving very short migration paths for the deposited atoms. At high substrate temperatures (Ts > 0.3 Tm) we suggest the microstructure and morphology of the films are controlled by thermally activated processes. © 1983.