The Relationship Between Strain-Age Cracking and the Evolution of γ′ in Laser Powder-Bed-Fusion Processed Ni-Based Superalloys

Factors affecting strain-age crackingStrain-age cracking (SAC) have been quantitatively assessed in a range of Ni-base superalloysNi-base superalloys with differing γ′ contents. Differences in the amount of γ′ present in the as-built condition of HA282, STAL 15DE, CM247LC, and IN713LC are highlighted. In the as-built condition, γ′ are absent in HA282, but appear as nano-clusters in IN713LC. On heating, γ′ precipitatesPrecipitates coherently in the γ phase, increasing the yield strength. The kinetics of precipitationPrecipitation are dependent on the heating rate and precipitationPrecipitation terminates at different temperatures in different alloys. The propensity to SAC is assessed via volume changes accompanying precipitationPrecipitation, increase in elastic modulusElastic modulus accompanying γ′ precipitationPrecipitation, and a loss in ductility/grain boundaryGrain boundary cohesive strength with increasing temperature. A marked feature of additively built microstructuresMicrostructure is the dramatically low grain boundaryGrain boundary cohesive strength at ~800 °C, which is related to the segregationSegregation within the terminal liquid film at the grain boundaryGrain boundary. The most important factor contributing to SAC is the lack of ductility and reduced grain boundaryGrain boundary cohesive strength.