The effect of pressure upon void formation in diffusion couples

Abstract Sandwiches of copper and nickel have been diffused under various hydrostatic pressures. This reduces the number of voids and above a critical pressure there are no voids. Similarly, voids previously formed by an anneal in vacuo are eliminated by applying pressure during a subsequent heat treatment, but the critical pressure is greater than that necessary to prevent them forming. It is concluded that the vacancy supersaturation is about 1 per cent and that the voids nucleate heterogeneously upon nuclei (about 10−5 cm in size) which are included in the weld between the two metals. There is no evidence of an alteration in the diffusion coefficient of copper into nickel with the pressures used.