Effect of heat treatment on the microstructure and properties of solid-state joints of dissimilar Ni-based superalloys

This article discusses the effects of solid-state bonding (SSB) and subsequent heat treatment (HT) on the microstructure, phase composition, and mechanical properties of solid-state joints (SSJ) made of wrought (EK61) and powder (EP741NP) heat-resistant nickel superalloys. SSB was performed in a vacuum under the temperature gradually increasing from 850°C to 1000°C. After SSB, in the EK61 superalloy transformation of the ultrafine-grained structure into a coarse-grained one with an average grain size of 38 ± 7 μm is observed, while the microstructure of the EP741NP superalloy remained of fine-grained microduplex type. After subsequent HT, grain growth is observed up to the size of 300 ± 48 µm in the EK61 superalloy and up to 49 ± 5 µm in the EP741NP superalloy. The width of the diffusion zone after SSB was 18 μm, and after HT it increased significantly, up to 150 μm. The results of mechanical tests showed that the fracture of the obtained EK61//EP741NP joints immediately after SSB occurred in the SSJ zone, and after subsequent HT, the fracture occurred outside the SSJ zone in the less heat-resistant EK61 superalloy. The strength after SSB is 660 MPa, and after following HT it is 770 MPa. It was found that after SSB, the microhardness of the EK61 superalloy decreased from 3.9 GPa to 2.4 GPa, and in the EP741NP superalloy it remained at the level of the initial state. In the SSJ zone, the microhardness, both after SSB and after HT, possesses intermediate values between the microhardness values of the superalloys being joined.

1. the State assignment of the IMSP RAS - 124022900007-9