Microstructural mechanisms governing hot ductility recovery in VDM Alloy 780 superalloy: Competing effects of grain-boundary boron segregation and grain size

The hot ductility recovery of the recently developed VDM Alloy 780 superalloy was systematically investigated under solution-annealing (SA) conditions at 1050–1150 °C using Gleeble thermomechanical simulations to evaluate the effects of grain-boundary (GB) boron segregation and grain size on the alloy's susceptibility to hot cracking. Nanoscale secondary ion-mass spectrometry (NanoSIMS) analysis reveals a higher level of GB segregation of boron after lower-temperature SA, suggesting that the level of boron segregation is primarily governed by equilibrium segregation. Although increasing the final SA temperature from 1050°C to 1150°C results in approximately a twofold increase in grain size, the concurrent reduction in equilibrium boron segregation at higher SA temperatures partially counteracts the detrimental effect of grain coarsening, leading to only minimal degradation of hot ductility recovery. These findings demonstrate that SA temperature influences hot ductility recovery through competing effects of grain size and GB boron segregation, providing guidance for optimizing SA strategies to mitigate hot cracking in VDM Alloy 780.