Improving strength and toughness of Ti–6Al–4V alloy/pure copper diffusion bonded joint with VCrAl1.86Ni1.86 eutectic medium-entropy alloy interlayer

To solve the metallurgical incompatibility of titanium alloy/copper dissimilar metal joining, a suitable interlayer was used to adjust the interface structure, achieving the strength and toughness of joint. The vacuum diffusion bonding between Ti–6Al–4V alloy (TC4) and pure copper (T2) with VCrAl1.86Ni1.86 eutectic medium entropy alloy (EMEA) foil was investigated. Ti3Al, Al(V, Cr)Ti2, Al(V, Cr, Ni)Ti, and AlNi2Ti phases formed in the TC4/EMEA interface. FCC and BCC double-phase solid solution appeared in the EMEA/T2 diffusion zone, resulting in the high-entropy seam between VCrAl1.86Ni1.86 interlayer and T2. The maximum shear strength of joint made at 880 °C for 90 min reached 215 MPa. The growth activation energy of reaction layers (I-III) in the TC4/EMEA interface were 283 kJ/mol, 379 kJ/mol and 431 kJ/mol, respectively. The Ti3Al/Al(V, Cr)Ti2/Al(V, Cr, Ni)Ti/AlNi2Ti interface was coherent. Nevertheless, the AlNi(V, Cr)2/Al(Cu, Ni)2 and AlNi(V, Cr)2/FCC-Cu interface was non-coherent with high strain energy. All joints broke through the EMEA/T2 interface during test. The fracture surface presented some cleavage ravines and auspicious cloud features. This study provided an effective strategy for the joining of titanium alloy and copper in high precision components of aerospace engines.