FAST-DB: A novel solid-state approach for diffusion bonding dissimilar titanium alloy powders for next generation critical components

Titanium alloy components are subjected to challenging conditions in high performance applications, consisting of complex loads and thermal gradients. To improve the performance and efficiency of such components, it is desirable to introduce different microstructures into subcomponent regions which cannot be achieved by the conventional melt-wrought processing route. Instead, a solid-state consolidation route using dissimilar titanium alloy powders is proposed. In this study commercially pure Ti (CP-Ti), Ti-6Al-4V (Ti-6-4), and Ti-5Al-5Mo-5V-3Cr (Ti-5553) have been diffusion bonded using field assisted sintering technology (FAST) for dwell times of 10, 20, and 60 min. The effectiveness of FAST for diffusion bonding (DB) of dissimilar alloy powders has led to the authors terming this hybrid process as "FAST-DB". Excellent bond integrity was produced with no cracking, unbonded regions or voids in the dissimilar bond combinations, at all dwell times. Furthermore, reliable control and prediction of the bond characteristics and degree of elemental diffusion was demonstrated through commercial thermodynamic software. Elemental diffusion was characterised across the bonds and the chemical diffusion bond width increased linearly with dwell time. Peak hardness values occurred directly on the interface for Ti-5553 and CP-Ti bonds, whilst slightly into the Ti-6-4 alloy for the Ti-5553 and Ti-6-4 bonds, which can be attributed to fine scale alpha at the interface. In Ti-6-4 with CP-Ti bonds, a smooth transition was observed. Mechanical testing demonstrated that the FAST-DB interface had excellent structural integrity, with necking and fracture occurring in the lower strength alloy.