Thermal cycle coordination in diffusion bonding of TA37/TC19 alloys: microstructural and mechanical insights

To meet the stringent demands of next-generation aeroengines, this paper has developed solid diffusion-bonded joints potentially used in centrifugal impellers by joining the high-temperature titanium alloy TA37 to the high-strength alloy TC19. Given the intrinsic divergence in heat-treatment requirements between two alloys—where TA37 relies on high-temperature solution treatment while TC19 demands precise aging to refine α/β lamellae—we systematically compared two diffusion bonding protocols with a basic process of 860 °C, 20 MPa for 60 min. The first strategy utilized as-received wrought base materials without additional processing, representing conventional industrial practice. In contrast, the other implemented a harmonized thermal sequence: TA37 underwent pre-bonding solution treatment (1033 °C/2 h, WQ) to activate nano-silicide formation, while TC19 received post-bonding solution-aging (930 °C/2 h, AQ + 593 °C/8 h, AC) to preserve phase stability. This coordinated approach aimed to reconcile the alloys' conflicting thermal histories and mitigate interfacial degradation. We systematically characterized the joints' interfacial morphology, microstructure evolution, and mechanical behavior using SEM, TEM, EBSD, EPMA, nanoindentation, and in-situ tensile testing. In both cases, a diffusion-affected zone approximately 10 μm thick formed at the interface, within which the TC19 alloy developed a duplex α + β structure. Crucially, the heat-treatment-modified joint achieved a tensile strength of 1076 MPa， significantly higher than the 959 MPa measured for the joint bonded using as-wrought materials. In-situ tensile experiments revealed that deformation proceeds via cooperative yielding of the α and β phases across the bonded region, confirming that the modified thermal cycle promotes uniform load sharing and suppresses localized strain concentrations. Together, these results demonstrate that integrating pre- and post-bonding heat treatments with the diffusion-bonding cycle markedly enhances joint performance. This work thus provides a practical framework for optimizing heat-treatment schedules in the diffusion bonding of dissimilar titanium alloys, laying a foundation for designing high-performance dual-alloy components in advanced aeroengine architectures.