Thermal Stabilization of Nanocrystalline Nickel Through Minor Tin Addition

Nanocrystalline (NC) materials, owing to their superior properties, have found applications in electronics, MEMS, coatings, etc. However, they suffer from thermal instability. Inspired by thermodynamic calculations in the literature for improving thermal stability, we have studied the effect of a small amount (0.8 at.%) of Sn on the thermal stability, microstructure, and hardness of NC Ni synthesized through a manufacturing-friendly electrodeposition route. The presence of a small amount of Sn was sufficient to significantly suppress the grain growth on exposure to 573 K for 1 h, where Ni-Sn showed only ~ 30% grain growth versus ~ 2000% in pure Ni. Microstructural characterization revealed that moderate heat treatment (HT) promoted low-energy (111) planes in both Ni and Ni-Sn. However, the presence of Sn promoted higher index (311) and (320) planes on HT at 873 K based on XRD and pole figure analyses. Microhardness measurements also confirmed the thermal stability improvement on Sn alloying, where Ni-Sn needed HT at 873 K before it became as soft as pure Ni post-473 K HT. Ni-Sn also showed anneal hardening associated with GB relaxation post-573 K HT and a gradual drop in hardness post-HT at higher temperatures. Superior performance of this alloy will help in high-temperature MEMS and coating applications.