Date of Award
Doctor of Philosophy
Materials Science and Engineering
Diffusion bonding is a well known metallurgical joining technique which allows materials to be bonded together to near net shape. Diffusion bonds between dissimilar materials are of unique interest due to the complex interactions at the bond line. Previous experimental work has shown that the bond strength is dependent on the extent of interdiffusion between the two base materials. A systematic investigation of diffusion bonding between Cu and Ni was undertaken to study these effects and to find a means of evaluating the bond quality nondestructively. This system was chosen as it exhibits complete solid solubility which yields the simplest metallurgical system of diffusion bonds between dissimilar materials;A large body of work exists on modelling the kinetics of diffusion bonding between similar materials to predict the time for elimination of voids at the bond line. While most bonding conditions, for similar materials, follow the power law creep model, this is not the case for the Cu-Ni system studied. It has been shown that the diffusive flux of Cu on a Ni surface is orders of magnitude faster than any other flux possible and leads to the filling of the voids at the bond line prior to a prediction made by the power law creep model. This allows the entire face to be in intimate contact but with no apparent strength. Only when sufficient conditions of time and temperature are present for interdiffusion to occur uniformly does the strength of the sample increase. A direct correlation exists between increasing interdiffusion distance and increasing strength of the bond;Ultrasonically, the challenge is to measure the extent and uniformity of the interdiffusion layer. Reflection coefficient measurements have been shown not to be sensitive enough to differentiate the samples. A total energy analysis has been shown to be able to differentiate the quality of the Cu-Ni diffusion bonds produced. This measurement is taking advantage of a resonance effect within the interdiffusion layer and the roughness modified reflection coefficient;Thus, this type of analysis appears to be a versatile NDE technique to monitor bond quality in diffusion bonds between dissimilar materials.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Greg Congdon Ojard
Ojard, Greg Congdon, "Strength, ultrasonic and metallurgical evaluation of diffusion bonds of dissimilar materials " (1991). Retrospective Theses and Dissertations. 9672.