Abstract
In this study, two innovative surface severe plastic deformation (SSPD) methods, namely abrasive waterjet peening (AWJP) and ultrasonic nanocrystal surface modification (UNSM), were applied to a 304 stainless steel to improve the mechanical behavior. The surface roughness, microstructure, residual stress, hardness, and tensile mechanical properties of the alloy after the two SSPD treatments were studied systematically. The results show that both the AWJP and UNSM treatments have greatly positive effects on the mechanical-properties improvements by successfully introducing a hardening layer. Especially the UNSM-processed specimen possesses the most outstanding comprehensive mechanical properties (high strength with the comparable ductility). The yield strength with the UNSM treatment is 443 MPa, corresponding to the 109% and 19% improvements, as compared to that of the base (212 MPa) and AWJP-treated specimens (372 MPa). The results can be attributed to a much thicker hardening layer (about 500 μm) and a better surface integrity with lower roughness (Ra: 0.10 μm) formed by the UNSM technique.
Highlights
Metal engineering materials often fail as a result of the overload, corrosion, high speed, fatigue, and wear, causing catastrophic consequences
(2007) [6] investigated the fatigue behaviors of a Ni-based C-2000 superalloy subjected to the surface nanocrystallization and hardening (SNH) process, the results show that the nanostructured surface layer, work-hardened region, and residual compressive stress introduced by SNH could enhance the fatigue strength
Surface Morphology roughness is related closely to related to the strength, material strength, wear resistance, SurfaceSurface roughness is closely the material wear resistance, corrosioncorrosion resistance, Surface roughness is closely related to the material strength, wear resistance, corrosion resistance, and sealing performance of mechanical components
Summary
Metal engineering materials often fail as a result of the overload, corrosion, high speed, fatigue, and wear, causing catastrophic consequences. The fundamental principle of SSPD is to produce the partial plastic deformation near the surface by impact or extrusion, form a certain depth of the deformation layer accompanying with the residual compressive stress and microstructural change, and improve the material properties. Zhang et al (2017a) [16] found that the UNSM-treatment can significantly improve surface finish, decrease subsurface porosity, increase surface hardness, and at the same time change the residual stresses from tensile to compressive. Yasuoka et al (2013) [17] utilized UNSM technique to improve the fatigue strength of SUS304 austenite stainless steel, after UNSM-treatment gradient nanocrystalline plastic deformation layer with increased hardness was created at the specimen surface. The surface morphology, microstructure, residual stress, hardness, and tensile mechanical properties of AWJP/UNSM-treated 304 materials were systematically studied. The aim is to find a valid method to improve the surface quality and mechanical properties and illuminate which factor has the greatest contribution to the improvement of mechanical performance and bedding for the subsequent work
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