Fatigue behavior of a harmonic structure designed austenitic stainless steel under uniaxial stress loading

Harmonic structured materials present a good balance of high strength and high ductility due to their peculiar network structure topology. Since long-term durability is critical for their practical applications, so the present work investigated the fatigue properties of a harmonic structured austenitic stainless steel at room temperature under uniaxial stress loading. The harmonic structure designed SUS316L steels were prepared by mechanical milling and subsequent hot isostatic pressing. The enhanced tensile strength in the harmonic structured SUS316L steels was attributed to the ultrafine grains (shell region), which also resulted in the improved resistance to fatigue crack initiation during cyclic loading. Compared to the conventional SUS316L bulk, increased fatigue limit can be achieved in the harmonic structured SUS316L steels. However, the fatigue ratio tends to be a constant value in SUS316L steels having homogeneous grain structure or bimodal grain structure. Moreover, the change of grain size was not significant after fatigue, which demonstrated the harmonic structured SUS316L steels showed good cyclic stability. In addition, the fatigue cracks tended to initiate at core/shell surface due to strain localization. The harmonic structure designed stainless steel demonstrates great attraction for commercial applications due to its good combination of high yield strength, large uniform elongation, good fatigue resistance and cyclic stability.