Assessment of mechanical property gradients after impact-based surface treatment: application to pure α-iron

Mechanical surface treatments are known for their ability to improve material resistance to abrasive wear and local fatigue crack microstructure of the home-made crack propagation. These treatments are based on repeated contact loadings which create large plastic strains in the near-surface that can induce a local grain refinement. In this case, a significant increase in the near-surface local mechanical properties is thus usually observed. In this paper, nano-mechanical tests are used to quantify the mechanical property gradient in the near-surface of a purity-controlled α-iron after an impact-based treatment. A methodology based on the combination of two different techniques is proposed: nano-indentation and in-situ micro-pillar compression. The resulting in-depth mechanical properties gradient is compared to the average grain size measured by EBSD. A positive relationship with the well-known Hall-Petch effect is observed.