Seminar on A novel recovery mechanism in two-phase superalloy single crystals

Prof Kai Chen

School of Materials Science and Engineering, Xi'an Jiaotong University

Ni-based superalloy single crystals are the material of choice for modern turbine blades. They face, however, a long-standing challenge of recrystallization, which degrades the high-temperature mechanical properties and can be triggered by only 1-2% plastic strains. Attempts to avoid recrystallization have not been successful thus far. Examining superalloy single crystals compressed at room temperature to 4.5% plastic strain, here we show populous straight dislocations preferentially residing in the -matrix but locked at the /′ interface. We observe a critical annealing temperature corresponding to the onset of γʹ-dissolution, above which the trapped dislocations are set in motion from the shifting interphase boundaries, allowing for dislocation annihilation and rearrangement into low-energy network configurations, diminishing the stored strain energy and therefore the driving force for recrystallization. Our discovery thus resolves a pressing problem currently plaguing the superalloys, retaining them as single crystals after supersolvus solutionizing treatment even at plastic strains more than twice that of previously reported critical values. The recovery is interphase-boundary-motion controlled, defying traditional wisdom of dislocation climb/cross-slip as the rate-limiting process. This finding has broad implications for high-volume fraction multiphase alloys, including refractory and high-entropy ones for high-temperature applications.