Experiments and Modeling of the Surface Nanocrystallization and Hardening (SNH) Process

Abstract

A surface nanocrystallization and hardening (SNH) process is developed to process bulk metallic components with a nanocrystalline surface and coarse-grained interior. The SNH process entails impacting metallic components repeatedly with high-energy balls under a controlled atmosphere. The efficacy of the SNH process is demonstrated using a nickel-based Hastelloy C-2000® alloy. The hardening layer and grain size refinement are evaluated as a function of the processing time. The result suggests that surface strengthening of C-2000® alloy obtained via the SNH treatment (about 150% increase) is mainly due to work hardening, whereas the contribution of grain refinement to strengthening, if any, is small. Such a conclusion is also consistent with the result obtained from a three-dimensional finite element model developed to simulate the SNH process.