Electrodeposition of dilute Ni-W alloy with enhanced thermal stability: Accessing nanotwinned to nanocrystalline microstructures

Hasegawa, Madoka; Guillonneau, Gaylord; Maeder, Xavier; Mohanty, Gaurav; Wehrs, Juri; Michler, Johann; Philippe, Laetitia

Materials Today Communications 12 (2017)

We report on the effects of W content on the microstructure, mechanical properties and thermal stability of dilute NiW electrodeposits − up to 5 at% W. The microstructure of NiW is significantly affected by W content. Pure Ni films were nanocrystalline (nc), whereas NiW films with 0.5 at% W showed a bimodal microstructure consisting of nanotwinned (nt) fiber-like micrometer-grains and nc-grains. Further microstructural change was observed at 4 at% W and more; the growth of nt-grains was largely suppressed and nc-grains were uniformly distributed in the film. This microstructural transition with W content can be explained by two distinct and competing effects of W: the reduction of stacking fault energy and the grain growth restriction. Nc-NiW shows an enhanced hardness compared with those of nc-Ni and nt-NiW, due to the grain refinement effect of W. Moreover, it shows a grain-boundary stability significantly superior to nc-Ni, suggesting potential improvement in the time-dependent deformation properties. Because a dilute Ni-W alloy can be electrodeposited with a relatively low stress, which is essential for thick-film applications, such an alloy will be a promising alternative of nc-Ni for applications to micromechanical components where thick films with better thermal stability and creep resistance are required.