Interplay between γ′ precipitation, residual stress and strain-age cracking in CM247LC produced by powder bed fusion – laser beam

Journal article, 2026

Ni-base superalloys with high γ′ volume fraction, such as CM247LC, manufactured by powder bed fusion–laser beam (PBF–LB) are highly susceptible to strain-age cracking (SAC) due to the combination of process-induced residual stress (RS) and rapid γ′ precipitation during post-processing heat treatment. This work establishes a relationship between γ′ precipitation and RS relief across a matrix of ex-situ isothermal heat treatments (650–1050 °C, 1–8 h) to identify a candidate processing window for SAC mitigation in CM247LC. This is done using a correlative approach combining scanning electron microscopy, atom probe tomography and synchrotron X-ray diffraction. The as-built microstructure exhibits nano-scale spinodal-like clustering of Cr–Co-rich and Al-(Ni, Al, Ti, Ta, Hf)-rich regions, which evolve into well-defined γ′ precipitates above 750 °C, while RS relief is negligible at 650 °C, partial at 700 °C and substantial at ≥ 750 °C. Critically, heat treatment at 700 °C for 1–4 h provides partial RS relief without extensive γ′ precipitation and SAC, whereas prolonged holding or higher temperatures promote SAC. These findings establish a qualitative map of γ′ precipitation–RS relief–SAC, enabling design of post-processing heat treatments to mitigate SAC in PBF–LB processed high γ′ superalloys.