Tensile Deformation Behaviors and Damage Mechanisms of SRR99 Superalloy Bicrystals with Different Grain Boundary Misorientations

Abstract

To understand the intrinsic tensile influence mechanisms of grain boundary (GB) misorientations, SRR99 bicrystal superalloys with the different misorientation angles () of 4°, 10°, 16°, and 18° are prepared to carry out conventional and in situ tensile tests at room temperature and fracture feature analysis. With the increment of , tensile strength and elongation to fracture show successive decrement. The fracture features exhibit two types (4° and 10°–18°): (I) when equals to 4°, the cracks initiate and propagate along slip bands (SBs)‐matrix interface. (II) As ranges from 10° to 18°, the cracks initiate along the carbide–matrix interface at GBs. Interestingly, the main crack in 10° bicrystal propagates first along the GB then along the SB, but completely along the GB in 16°–18° bicrystals. The former one is absolutely controlled by SBs, and the latter is dominated by carbides and GBs. Finally, a new parameter, defined as the cracking threshold value (), is proposed to explain the tensile deformation behaviors and damage mechanisms. The new findings will beneficially provide research foundation for the further understanding fatigue damage mechanisms at high temperature.