Multi-materials additive manufacturing of Ti64/Cu/316L by electron beam freeform fabrication

Abstract

Titanium/steel multi-material, given full play to their superiorities, has tremendous value for parts exposed to complexity service environments, yet invariably, its common joining techniques are lack of design freedom. To this end, we employ electron beam freeform fabrication (EBF3) to successfully prepare this multi-material system for the first time, whose interfacial microstructure and property are systematically investigated. Applying Cu as an interlayer, instead of causing extensive cracking and delamination at the interface of Ti64/316L, can effectively suppress the formation of continuous Fe–Ti intermetallic compounds (IMCs), and thus improve the strength of Ti64/Cu/316L interfaces. For the Cu/316L interface, besides the characteristic spherical Cu-rich and Fe-rich solid solutions, a few Fe–Ti IMCs appear within the Fe-rich solid solutions owing to the long-range diffusion of minor Ti atoms. Correspondingly, the dendritic Cu-rich solid solutions can also be found at the Ti64/Cu interface, which is regarded as a critical interface due to the concomitant of complex Cu–Ti IMCs. These Cu–Ti IMCs have less negative effect on the Ti64/Cu interface property relative to Fe–Ti IMCs, and the local strain produced by the deformed α-Ti near the interface and Cu-rich solid solutions can effectively relieve the concentration of residual stress. Consequently, the Ti64/Cu interface exhibits maximum micro-hardness to 490 HV and superior shear strength to 196.5 ± 2.2 MPa, which was attributed to the reinforcement for the tip of keyhole molten pool, as well as the synergy between Cu-rich solid solution and interdendritic Cu–Ti IMCs.

Keywords

• Multi-material
• Electron beam freeform fabrication
• Titanium alloy
• Interfacial microstructure
• Shear strength