Industrial parts always need to be lighter without loss of strength. A way to improve the mechanical resistance of material is to carry out a superficial strain hardening by Surface Severe Plastic Deformation (SSPD) treatments. These techniques are known to create gradient materials with gradients of properties (grain size, hardness…). Among these techniques, the Surface Mechanical Attrition Treatment (SMAT) is a derivative from the conventional Shot Peening (SP), where shots are confined in a chamber and deform the sample surface with multidirectional impacts.

The SSPD efficiency is directly related to the deformation of the impacted surface. Thus, SSPD become limited when the material is hard to deform. Furthermore, SSPD over processing can introduce defects (cracks, pollution) in sample surface which can affect fatigue properties. A way to deal with these limits is to introduce the temperature as a treatment parameter. Increasing the temperature during surface treatment enables to lower the elastic resistance of the sample and thus, introduces more superficial plastic deformation .

This study shows that raising the temperature at which the SMAT is carried out enables to increase the depth affected by the treatment. In addition, the deformation mechanisms are modified: Planar slips and formation of martensite at cryogenic SMAT are replaced by dynamic recrystallisation at higher temperature and leads to the formation of a thicker ultrafine grain layer.