A constitutive model based on internal variable method for the microstructure simulation of four-layer structure formed by the superplastic forming/diffusion bonding process

Abstract

This study set out to realize the prediction of microstructure evolution and mechanical properties of the titanium alloy four-layer structure formed by the superplastic forming/diffusion bonding (SPF/DB) process. The flow behavior and the microstructure evolution of TC31 alloy were studied by the high-temperature experiments. A physically-based constitutive model was established and applied in the superplastic forming process of the four-layer structure. The TC31 titanium alloy four-layer structure was fabricated to verify the accuracy of the constitutive model. The results showed that the main reason for the increase in material stress and the decrease in elongation was the growth of grains. The TC31 four-layer structure was soundly fabricated by SPF/DB process, and the maximum damage value of the structure was located at the sidewall area with a value of 0.16. The compression strength of the structure was 19.0MPa, and the compression failure mode of the four-layer structure was the cracking of the bonding area. The experimental results were similar to the simulation results, which demonstrated that the finite element simulation with the internal variable model could accurately predict the shape, the thickness distribution and the damage distribution of the four-layer structure during the SPF process.