Heat-affected zone cracking in new 718-type superalloy VDM alloy 780: Effect of solution heat treatments and comparison with alloy 718

• Liquation cracking in VDM 780 occurs via supersolidus and MC carbide liquation. • Heat treatment at 1050 °C yields the lowest liquation cracking susceptibility. • Grain coarsening outweighs boron segregation in increasing cracking propensity. • Severe grain coarsening occurs at 1150 °C; 1050 °C promotes strong boron segregation. • VDM 780 exhibits superior liquation cracking resistance over Alloy 718. The weld heat-affected zone liquation cracking susceptibility of new 718-type superalloy VDM Alloy 780 was studied under various pre-weld solution heat treatment (SHT) conditions using the Varestraint test and compared with Alloy 718. Similar to Alloy 718, liquation cracking in VDM Alloy 780 occurs by constitutional liquation of NbC and supersolidus melting. Among the conditions studied, the 1050 °C/0.5 h SHT exhibits the lowest cracking propensity, followed by 1090 °C/2h, 1150 °C/4h, and 1150 °C/4h + 1050 °C/0.5 h. Within this SHT range, grain coarsening and equilibrium segregation of boron at the grain boundaries are identified as major factors deteriorating the cracking resistance in VDM Alloy 780, with grain coarsening being the more dominant factor. When both factors coexist, the cracking susceptibility further increases. The most significant grain coarsening takes place at 1150 °C, while the strongest boron segregation occurs after the 1050 °C SHT. In its optimal SHT condition that resists cracking (1050 °C/0.5 h), VDM Alloy 780 exhibits superior liquation cracking resistance to Alloy 718 despite having a six times coarser grain size, which appears to be due to its substantially higher fraction of coincident site lattice boundaries (25 % higher).