Thermally-triggered grain boundary relaxation in a nanograined Ni-Mo-W alloy

Conventionally, nanograined metals and alloys can be stabilized through segregating foreign elements at grain boundaries (GBs). Yet such an effect may be offset by formation of second phase at elevated temperatures. In this paper, by introducing minor W into a binary Ni-Mo alloy, we found precipitation of intermetallic phases was suppressed, enhancing thermal stability of the nanograined structure. Characterized faceted GBs and a high-fraction of sigma 3 coincidence site lattice (CSL) boundaries illustrate that GB structures are relaxed by formation of copious annealing twins. Adding W reduces stacking fault energy of the solid solution and facilitates the thermally-triggered GB relaxation. Suppressed precipitation of the intermetallic phases may be attributed to depletion of solutes at relaxed GBs.

Automated summary

By introducing a small amount of tungsten, the precipitation of intermetallic phases is suppressed, enhancing the thermal stability of the nanograined structure. The relaxation of grain boundary structures is achieved through the formation of annealing twins, facilitated by the reduction of stacking fault energy in the solid solution caused by tungsten addition.