Effect of Solution Annealing Temperature on Liquation Cracking Susceptibility of Alloy 617M

Improvement in liquation cracking susceptibility of Alloy 617M, a Ni base superalloy is observed on modification of solution annealing conditions for the first time in the present investigation. Results suggest that the heat affected zone of the alloy in as received condition is more susceptible to liquation cracking than in modified solution annealed condition. A reduction in total crack length up to 62% is observed after modification of solution annealing condition. Discontinuous elemental segregation in grain boundary, reduced precipitation and formation of low-energy serrated boundaries after solution annealing is observed. This decelerate complete wetting of grain boundaries in the heat affected zone during welding/thermal cycling, resulting in improved resistance to liquation cracking in alloy 617M. Marginal decrease in strength is attributed to increased grain size of material, whereas increased ductility in solution annealed condition is attributed to, reduced elemental segregation at grain boundaries and increased number fraction of low energy special boundaries. In this study, influence of secondary precipitates and segregation on liquation cracking in the alloy is brought out and elucidated using scanning electron microscopy and electron back scattered diffraction techniques.