Vacuum diffusion bonding of high-entropy Al_0.85CoCrFeNi alloy to TiAl intermetallic

High-entropy alloy Al_0.85CoCrFeNi was joined to TiAl alloy through vacuum diffusion bonding. The typical interfacial microstructure of Al_0.85CoCrFeNi/TiAl joint was TiAl/ α₂-Ti₃Al + solid solution strengthened γ-TiAl / FeNi, AlNiTi / Al(Co, Ni)₂Ti /Cr(Fe, Co)ss / Al_0.85CoCrFeNi. The formation of Al(Co, Ni)₂Ti phase and Cr(Fe, Co)ss layer was result from the diffusion of Ni and Co atoms from Al_0.85CoCrFeNi into TiAl substrate and the accumulation of Fe and Cr atoms at the Al_0.85CoCrFeNi side. The effects of joining temperature and holding time on the microstructure and mechanical properties of joints were revealed. The joint with the maximum shear strength of ∼70 MPa was obtained at the joining temperature of 850 °C for 1.5 h under pressure of 30 MPa. The fracture path was deflected from solid strengthened γ-TiAl layer where FeNi, AlNiTi existed to Cr(Fe, Co)ss layer.