Reasons for Volume Contraction after Long-Term Annealing of Waspaloy

Some materials for turbine applications show volume contraction during service lifetime. Relative shrinkage (Δl/l0) of up to about −4 · 10−4 may occur. In this study Waspaloy samples were exposed up to 10 000 h at 550 °C, 650 °C and 750 °C. High resolution length measurements unveil remarkable contraction during exposure at 550 °C and 650 °C and less contraction at 750 °C. The main contribution to sample contraction is compositional variation due to temperature dependent phase fraction changes. Lattice parameters of matrix and γ′ phase decrease within the first 300 h of temperature exposure. In addition carbide transformation from TiC to Cr23C6 contributes to the observed contraction. The influence of long‐term annealing on sample length and microstructure of Ni‐base alloy Waspaloy is investigated. Sample contraction during annealing is caused by microstructural changes. Changes in the volume fraction of γ′ phase and matrix are accompanied by compositional differences which influence the lattice parameter. Another contribution to length change is given by carbide transformation.