Copper coatings for minimization of retention and permeation of implanted tritium in aluminum alloy 6061

Abstract

Copper coatings deposited on Al-6061 substrates by radio frequency magnetron sputtering, to prevent the retention and permeation of energetically implanted tritium in Al-6061, were evaluated by a variety of characterization techniques. The coatings, weighing in the 0.03 to 0.088 kg/m² range, were smooth and had a fine grain structure. They contained the intermetallic phases Cu₉Al₄ and CuAl₂ as well as copper. The fractions of Al and Cu in any coating increased and decreased, respectively, with increasing depth below the surface. Furthermore, the fractions of Al and Cu on the coating surface decreased and increased, respectively, with increasing coating weight. There was no texture or preferred orientation in the Cu phase of the coatings. A significant amount of oxygen was also detected at the original substrate surface. Residual stress measurements revealed that, in both Cu and CuAl₂, the stresses in the coating plane were compressive, while the stress normal to the coating plane was zero in Cu but tensile in CuAl₂. The shear-stress components were, however, negligible in both the Cu and CuAl₂ phases. In the coating plane, the residual stress in Cu was always much smaller than that in the CuAl₂ phase. Bond-strength measurements using tensile-pull testing provided a lower limit of the bond strength of about 2 MPa.