Lattice parameters, densities, expansion coefficients and perfection of structure of Cu and of Cu–In α phase

Spectroscopically pure Cu has a lattice parameter a25 = 3.61491 Å (corrected for refraction), and a thermal expansion coefficient α = 14.87 × 10−6°C−1 between 15 and 55°C. The measured density d25 is 8.9314 ± 0.0002 g.cm−3 in agreement with the calculated value dx = 8.9316. In the α solid solution region additions of In increase the lattice parameter of Cu according to ax = 3.6149 + 0.0091x up to x = 10.4 (x = atomic % In, balance Cu). The thermal expansion coefficients between 15 and 65°C of the homogeneous alloys increase from 14.87 (pure Cu) to 17.2 × 10−6°C−1 at the solid solubility limit (10.4 atomic % In, quenched from 650°C). With the increase of In content the experimental densities become increasingly lower than the calculated ones because of void formation. Upon cold rolling the voids close and the differences disappear. The α phase represents a substitutional solid solution without structural defects. Alloys quenched from the liquid state do not show any microporosity; the voids appear after homogenization at 800°C. Micropore formation is explained by differential shrinkage of the various crystalline fractions formed during solidification, giving rise to internal stresses in the solid alloy. Relief of stresses results in vacancies or micropores, which coalesce into voids upon heat treatment.