Dual-scale clusters enabling exceptional mechanical properties of a CoNiCr-based MP159 superalloy at 650 °C

Abstract

Prior or early-stage precipitation products, e.g., GP zones and chemical short-range ordering, attract tons of interests recently due to their extremely small size and notable hardening effects. In this work in a commercial CoNiCr-based MP159 superalloy, we, for the first time, simultaneously introduced two kinds of these products, i.e., the atomic-scale L11 cluster, and the nano L12 cluster with 2.7 nm in size, by simply removing the standard annealing process and directly conducting the intermediate 650 °C tension. The ultra-dense co-existence of these dual-scale clusters generates over 200 MPa hardening effect at the specific 650 °C when compared to the standardly-annealed MP159 alloy that contains only larger (∼6.0 nm) L12 precipitates. High-angle annular dark field-transmission electron microscopy associated with atom probe tomography evidence that firstly, the atomic-scale cluster is of the L11 type, similar to the one observed in the NiCoV medium entropy alloy. And secondly, the composition of the nano L12 cluster is abnormally close to (Ni,Co)3Ti, whose equilibrium crystalline structure is otherwise D024. This likely leads to a high anti-phase boundary energy hence high shearing resistance for dislocations.