Study of diffusion damage in the copper-nickel system

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Virginia Polytechnic Institute and State University

Study of prolonged diffusion in Cu-Au and Cu-Pd systems has revealed that the diffusion generated misorientations tend to mend themselves because of reduced concentration gradients. Previous studies of the Cu-Ni system in which a 8.0 micron nickel plated single crystal copper was diffused up to 5 hours at 900°C, did not reveal such features. It was desirable to obtain more information on the structure oriented diffusion of this system at prolonged diffusion times. For this purpose a 3.0 micron nickel plated copper single crystal was subjected to diffusion anneals at 900°C for times as long as 7 hours. The diffusion and structure data were obtained by the nondestructive X-ray method with supporting measurements using a Scanning Electron Microscope and computer simulations.

It has been found that the diffusion behavior is dynamic and is influenced by structure. At lower times a unified grain boundary-volume diffusion model is able to account for the diffusion behavior whereas at intermediate and higher times a volume diffusion model with anomalously varying range of pseudo diffusion coefficients is required to match the experimental intensity patterns. Scanning Electron Microscope studies made at the end of the six different anneals show extensive flow patterns and porosities indicative of structural modifications.

Rocking curve measurements obtained at chosen compositions over the treatments indicate no tendency of reorientation of the structure; the variance and halfwidth analysis demonstrate this feature. In fact, strong indications of the structure, having undergone a recrystallization are revealed at the end of the last diffusion anneal.