Abstract
The strengthening effects produced by various metallic coatings on copper single crystals were studied. There was no relation between the magnitude of the strengthening produced and the mechanical strength of the various coatings. On this basis, a mechanism involving the operation of the coating as a simple barrier to dislocation egress from the crystal was considered inappropriate. Likewise, there was no relation between the relative shear moduli of coating and substrate and the strengthening produced. Thus, the elastic repulsion of dislocations from the coating-substrate interface was also considered to be unimportant as a mechanism. None of the results suggested that the suppression of surface Frank-Read sources or coating-substrate incompatibility made an important contribution to the strengthening effect. Significant film strengthening effects were always accompanied by cracking of the coating either prior to or during deformation. Associated with film cracking was an increase in dislocation density at the substrate surface. This surface damage which resulted from residual stresses in the coating is believed to be the critical factor in producing the film strengthening effects which were observed.
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