Modeling and Experimental Analysis of Superplastic Forming and Diffusion Bonding

Thesis (Ph.D.)--University of Washington, 2020Superplastic forming and diffusion bonding is a well-established manufacturing process. It has been implemented with a variety of materials. This work specifically deals with titanium which, while being a very useful aerospace material, and is commonly used with both superplastic on diffusion bonding. It deals with the forming and bonding of double sheet structures and four sheet structures. There has been a significant amount of both experimental and theoretical work done on diffusion bonding and superplasticity with titanium. However, there has yet to be a definitive and accurate model for diffusion bonding and the effects of more complex sheet formation. Work progressed toward alleviating this knowledge gap. Several models were created with increasing complexity. Work started with more rigorous initial conditions applied to conventional bonding models. Then models were created that used conventional physics but in a freeform way to see how the voids changed without restriction on void shape. Finally, micrographs of voids were digitized and used as inputs into an energy-based phase field simulation that allowed each of the alloying elements to diffusion independently, grain growth, and for the voids to close due to strain energy. Superplasticity modelling was done using finite element methods in two and three dimensions to examine how the four-sheet forms. Research was also done to determine how one can better destructively and non-destructively test diffusion bonded specimens. The results of all this showed that while superplasticity and diffusion bonding are complex subjects there is a lot of information to gain through experiments and modelling of the process