The surface of mechanical components is a critical zone subjected to specific mechanical and chemical solicitations. Component failure generally occurs at the surface, driving the industry to seek solutions to enhance surface properties. Among these, mechanical surface treatments modify surface properties by plastic deformation while preserving core ductility. Ultrasonic shot peening, a severe surface deformation process, introduces gradients of microstructure and properties (hardness, residual stresses) through random shot impacts. However, its effectiveness may be limited when the material is difficult to deform, potentially leading to over-processing and crack formation. A possible solution is to introduce temperature as a processing variable to lower flow stress and facilitate deformation, enabling the formation of microstructures not achievable at room temperature.
This study analyzes the deformation microstructures induced by ultrasonic shot peening at different temperatures on 316L stainless steel. It was demonstrated that deformation temperature controls microstructure and property gradients by modifying activated mechanisms. At cryogenic temperature, deformation is dominated by the TRIP effect with deformation-induced and stressassisted martensite. At room temperature and up to 250°C, the TWIP effect predominates, whereas at 500°C, dislocation glide and dynamic recrystallization form an ultrafine-grained surface layer.
Fatigue testing revealed that high-temperature ultrasonic shot peening, despite inducing higher roughness and lower surface compressive residual stresses, improves the endurance limit by 15% compared to lower temperatures. This is attributed to reduced residual stress relaxation under cyclic loading due to dislocation stabilization, along with a deeper hardness gradient and lower subsurface stress peak.
However, high-temperature ultrasonic shot peening promotes surface contamination via increased material transfer from peening shots and specimen oxidation. This heterogeneous contamination degrades the corrosion resistance of 316L stainless steel.
| Date | 1 Dec 2025 |
|---|
| Original language | French |
|---|
| Awarding Institution | - École de technologie supérieure
|
|---|
| Supervisor | Philippe Bocher (Supervisor), Thierry Grosdidier (Co-supervisor) & Marc Novelli (Co-supervisor) |
|---|
Austernaud, Y. (Author),
Bocher (Supervisor), Grosdidier (Co-supervisor) & Novelli (Co-supervisor),
1 Dec 2025Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering