Effect of interlayer on microstructure and mechanical properties of diffusional-bonded Ni3Al-based superalloy/S31042 steel joint

The combination of Ni3Al-based superalloy and S31042 steel could meet service requirement of different parts in nuclear power units. To broaden the application of Ni3Al-based alloy, vacuum diffusion bonding with S31042 austenitic heat-resistant steel was studied in this work. Different thicknesses (2, 5, 10, 15, 30 mu m) of pure Ni interlayer were adopted to obtain a sound bonded joint. Result shows that the formed AlN phase in bonding process hindered atom diffusion and deteriorated joint properties. When interlayer thickness is 15 mu m, the joint strength reached 96% of Ni3Al-based alloy, meanwhile elongation was 320% of Ni3Al-based alloy and 62% of S31042 alloy. The less AlN phase, uniform precipitation of gamma ' phase and grain boundary intermigration behavior in two substrates contribute to the high strength and elongation of joint. The prevailing mechanism of the dissimilar joint bonded by 15 mu m interlayer is ductile fracture. However, the fracture with low elongation showed the equiaxial pot and intergranular torn edges in other bonded samples due to the typical dual-phase structure in interlayer.

Automated summary

The combination of Ni3Al-based superalloy and S31042 steel for vacuum diffusion bonding with different thicknesses of pure Ni interlayer resulted in joints with high strength and elongation, with the prevailing mechanism of ductile fracture in the 15 µm interlayer bonded joint. Other joints with different thicknesses exhibited equiaxial pot and intergranular torn edges due to the typical dual-phase structure in the interlayer.