Study of Macroscopic Defects of Four-Layer Structure of Ti–6Al–4V During Superplastic Forming/Diffusion Bonding

Abstract

Superplastic forming/ diffusion bonding (SPF/DB) is a key technology for preparation of light-weight and integrated multi-layer structures as superplastic deformation and diffusion joints can be achieved in one heat cycle. However, groove defects and inhomogeneous sheets thickness distribution usually appear during SPF/DB, which decreases the mechanical properties of multi-layer structures. In this study, numerical models of four-layer honeycomb and hollow blade structure are established and the effects of forming parameters (thickness ratio, strain rate, DB distance and width) on groove defect and thickness distribution are analyzed. The results show that groove defect for honeycomb structure can be eliminated under proper thickness ratio between face sheet to core sheet. The groove defect decreases with increasing DB distance and decreasing DB width. Insufficient deformation of vertical stiffener is the main problem for hollow blade structure and it can be improved by adjustment of the sheets thickness and the strain rate. Experiments are conducted on the basis of optimized parameters from simulation and agree with results from FEM. This study provides guidance for parameters selection for manufacturing of Ti–6Al–4V multi-layer structure.