Phase Transformation And Its Theoritical Models Of Al-Cu Nanogranular Films

Conventional bulk Al-Cu alloy is of typical age-hardening. In general, a precipitation sequence of supper-saturated solution→GP I zone→GP II zone (orθ″phase)→θ′phase→θphase occurs during aging or cooling. Nanocrystalline materials are being extensively studied and applied due to their unique properties different from those of the bulk materials such as optical, electric, magnetic, acoustic, mechanical properties and the phase transformation behavior. Some researches concerning the phase transformation in sub-micro granular Al-Cu films show different characterization of phase transformation from that of the conventional materials. However, no research on Al-Cu films in which grains keep nanometer scale after heat treatment has yet been reported. This paper experimentally and theoretically focuses on the phase transformation of nanogranular Al-Cu films. The main research results are described as follows.In order to obtain nanogranules in Al-Cu films, especially to keep them still in nanometer scale after heat treatment, a proper sputtering technology was explored by trial-error method. The granular size as small as possible in sputtered films at room temperature (RT) should be prepared by controlling the film thickness. This is because that when a film is too thin, a large number of precipitates preferentially nucleate at the surface during sequent heat treatment; when it is too thick, enough small nanogranules cannot be obtained during preparation owing to the requirement of long sputtering time. Through trial more than ten times, the resultant sputtering parameters were chosen as sputtering gas pressure of 0.6Pa, sputtering power of 100W and sputtering time of 60 minutes. A series of Al-Cu films containing 1, 2 and 4wt%Cu with thickness of about 5μm and average granule (grain) size about 20nm were sputtered by alloy targets induction-melted and cast using pure Al and pure Cu of 99.999% in purity.