On the creep behaviour of Ni based solid solution alloys from binary to quaternary

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PhD; 2023; Materials engineering

On the creep behavior of Ni based solid solution alloys from binary to quaternary A power-law relationship between the steady state strain rate (𝜀̇) and imposed stress (σ) is well established so that the 𝜀̇∝𝜎^𝑛, at a fixed temperature, where n is termed the stress exponent. Additional microstructural terms influencing creep such as the grain size and stacking fault energy (γ) have been incorporated into the creep equation in a power-law form, such as 𝜀̇∝𝛾^𝑞. In the case of an intragranular dislocation climb controlled creep in a solid solution alloy, the creep rate has been expressed as 𝜀̇∝𝐷𝜎^5𝛾^3, where D is the appropriate diffusion coefficient, n~5 and q~3. However, an evaluation of the earlier creep data suggests that while q~3 is reasonable for pure metals, there is considerable uncertainty in the value of q for solid solution alloys. The current study focuses on characterizing the creep behavior and the value of q for Ni – xCo alloys, with x = 10, 33, and 60, where the addition of Co reduces the stacking fault energy. Following creep in Ni-Co alloys, the creep behaviour of CSSAs NiCoCr and NiCoCrFe was also investigated to probe potential changes in the creep mechanisms with the addition of alloying element. All alloys are single phase solid solutions with a face-centered cubic (f.c.c.) crystal structure. Prior to the creep, all alloys had a grain size d~100 μm.