Effect of Solution Cooling Rate on the Microstructure and Creep Deformation Mechanism of a Rhenium-Free Second-Generation Single Crystal Superalloy

Various cooling scenarios (water, oil, air and furnace) were employed to study the impacts of the solution cooling rate (SCR) on the microstructure and creep behavior of a novel single-crystal (SX) superalloy. The results showed that the cubic degree and size of the gamma' phases were inversely proportional to the SCR. The creep life first increased and then dropped dramatically with a reduction in the SCR. The creep life of the sample cooled with air cooling (AC) was the highest, up to 144.90 h at 800 degrees C/750 MPa and 160.15 h at 1100 degrees C/137 MPa. During creep at 800 degrees C/750 MPa, the improved creep life of the AC sample was mainly attributed to the fine cubic gamma' phases, which decreased the rate of gamma'-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations. The AC helped the gamma' phases become rich in Al, Ti and Ta while depleted in Co and Cr, which enhanced its stacking fault energy, thus promoting the formation of dislocation locks. Meanwhile, the largest negative lattice misfit caused by AC induced denser gamma/gamma' interface dislocation networks at 1100 degrees C/137 MPa, which efficiently reduced the minimum creep rate. The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample, proving its greatest creep resistance. Interestingly, the size of the secondary gamma' phases first decreased and then increased sharply with decreasing SCR during creep at 1100 degrees C/137 MPa, when fine secondary gamma' phases had a positive role in the blockage of dislocation movement in the matrix. Eventually, the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.