Nano-twinning in a γ′ precipitate strengthened Ni-based superalloy

Abstract

Twinning has been found to be a dominate mechanism in the γ precipitate strengthened Ni-based superalloys during service at intermediate temperatures. Here, high-resolution transmission electron microscopy and atomistic simulations have been combined to show that the twin nucleation process can be facilitated by Co replacing a fraction of Al in the γ precipitates, due to the negative binding energy of Co-Co atoms. The study further reveals that the presence of Co promotes a new twinning pathway featured with nucleation of one complex stacking fault (CSF) on the middle plane in between two separated CSFs. IMPACT STATEMENT We demonstrate that Co in the γ precipitates promotes a new twinning pathway featured with nucleation of one CSF on the middle plane between two separated CSFs.

Stress orientation dependence for the propagation of stacking faults and superlattice stacking faults in nickel-based superalloys

“…Lastly, segregation assisted microtwinning can be seen as a variation of the SESF mechanism in which more leading partials shear the matrix and the precipitates on adjacent planes. Different pathways for the order in which the planes are sheared have been proposed both in fcc and L1 2 structures [47] but the resulting stress orientation dependence is the same; glide on consecutive adjacent planes is considered here. It is not fully clear how microtwins nucleate, but the athermal stopping of the trailing partials may be a necessary condition.…”

“…Studies have shown that the energy difference between a 2-and a 3-layer fault is rather small both in the fcc and the L1 2 phases, i.e. γ ISF ≈ γ ESF ≈ 2γ T m [48,49] and γ SESF ≈ 2γ T p [47,50].…”

Topologically inverse microstructure in single-crystal superalloys: microstructural stability and properties at ultrahigh temperature

“…Ni-based single-crystal superalloys are key materials for hottest sections in aero-engines and gas turbines, and rendering them more resistant to elevating temperatures is extremely challenging [1][2][3][4]. Their excellent performance relies on well-optimized matrix (γ phase) -precipitate (γ ' phase) microstructure [5]. During high-temperature service, this microstructure inevitably degrades, as shown in Figure 1(a).…”