Characterization of nanocrystalline surface layer induced by shot peening and effect on their fatigue strength.

Abstract

The shot peening process is known to produce a hard layer, known as the white layer" on the surface of coil springs. However, little is known about the fatigue properties of this white-layer.In this study, coil springs with a white-layer were manufactured. The surface of these springs was then examined using micro Vickers hardness, FE-SEM etc. to test fatigue strength of the springs. From the results obtained, a microstructure of the white-layer with grain size of 50-100 nm was observed, with a Vickers hardness rating of 8-10 GPa. Tow category springs were manufactured utilizing a double-peening process. These springs had the same residual stress destruction and surface roughness. Only one difference was observed: one spring had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test realized an increase in the fatigue life of the nanocrystalline surface layer by 9%.

Effect of micro ploughing during fine particle peening process on the microstructure of metallic materials

“…In addition, shot peening attracts interest because it can create various functionable surfaces. For example, a surface with a nanocrystalline microstructure that exhibits extremely high hardness is created by severe plastic deformation during peening treatment (Wu et al, 2002;Tao et al, 2002;Gu et al, 2002;Wang et al, 2003a,b;Zhang et al, 2003;Zhu et al, 2004;Mano et al, 2005;Takagi et al, 2006). Ceramic thin films used for MEMS, dental applications, and so on, can be generated by depositing particles (Akedo and Lebedev, 1999;Yoshihara et al, 2005;Noji et al, 2005).…”