Surface Severe Plastic Deformation for Improved Mechanical/Corrosion Properties and Further Applications in the Bio-Medical and Hydrogen Sectors

Various techniques enabling surface severe plastic deformation (SSPD) have been developed or optimised over the past years. This manuscript presents a broad overview of recent developments in the field of SSPD and its application that take advantages of having a deformed gradient surface with both (i) higher strength and (ii) an improved "reactivity". First, the principle and technological advantages/disadvantages of several SSPD technologies, involving either guided or non-directional mechanical impacts, are recalled. Then, after a short recall on the nature of the structure the modified surface formed under SSPD, the effects of the processing parameters and temperature of deformation on the surface roughness and subsurface microstructure modifications are illustrated with a particular emphasis on the surface mechanical attrition treatment (SMAT) and ultrasonic shot peening (USP) techniques deriving from the traditional pre-strain shot peening. The effect of these surface and sub-surface modifications on the mechanical properties, and in particular the fatigue response, are recalled with a special emphasis on the surface integrity and potential over shot peening. Then, the manuscript concentrates on the effect of the surface enhanced diffusion of chemical species induced by the presence of structural defects to modify the corrosion behaviour and enhance the potential assisted SSPD + thermo-chemically "duplex" treatments. In these cases, in addition to induce grain refinement and dislocations, the importance of controlling some potential surface contamination is stressed. Finally, the manuscript terminates by illustrating some new research studies on potential applications for the challenges in the hydrogen sector for its solid-state storage and the protection of mechanical infrastructures as well as for bio-medical applications with biocompatible Ti-based alloys and biodegradable Mg-based ones.