Microtwinning mechanism revealed by its orientation dependence and tension-compression asymmetry in γ′ precipitate-strengthened Ni-based superalloys.

Microtwinning is observed as an important mechanism in γ′ precipitate-strengthened Ni-based superalloys during service at intermediate temperatures. Here, the effect of crystal orientation and stress direction on microtwinning was investigated. The result indicates that the formation of microtwins exhibits orientation dependence and tension-compression asymmetry. Based on the analysis of slip and twinning competition behavior under different conditions, it is deemed that the a/2〈110〉 matrix dislocations would dissociate into a/6〈112〉 Shockley partials in the γ matrix and then a Shockley partial sheared γ' phase and formed microtwins. IMPACT STATEMENT: For the first time, this work explains why microtwinning exhibits orientation dependence and tension-compression asymmetry while stacking faults do not, although they both originate from the activity of {111} 〈112〉 slip systems. [ABSTRACT FROM AUTHOR]