Enhanced wear resistance of LDED 316L stainless steel fabricated by in-situ ultrasonic rolling

Stainless steel parts with complex shape can be fabricated using additive manufacturing, which do not rely on molds and dies. However, coarse dendrites induced by repeated heating of additive manufacturing result in weak properties, which limits its application. In this study, an in-situ ultrasonic rolling (UR) device was developed to assist the laser directed energy deposition (LDED) process. The microstructural characteristics, as well as the microhardness and wear behavior, were studied for the 316L stainless steel manufactured by in-situ ultrasonic rolling assisted LDED. It is found that austenite, ferrite, and small Si oxides are the main constituents of both the LDED and LDED-UR alloy samples. Under the severe plastic deformation of ultrasonic rolling, the long-branched ferrites by LDED are transformed into the rod-like phases by LDED-UR. Meanwhile, the ferrite is more uniformly distributed in the LDED-UR alloy sample compared with that in LDED alloy sample. Columnar grains with the size of 97.85 µm appear in the LDED alloy sample, which is larger than the fully equiaxed grains (22.35 µm) of the LDED-UR alloy. The hardness of the LDED-UR alloy sample is about 266.13±13.62 HV0.2, which is larger than that of the LDED alloy sample (212.93±12.85 HV0.2). Meanwhile, the wear resistance is also greatly enhanced by applying the assisted in-situ ultrasonic rolling. The achieved high wear resistance can be ascribed to the uniformly distributed hard matter (ferrites) and the impedance of dislocations by high fraction of grain boundaries. Abrasive wear and adhesive wear are identified as the primary wear mechanisms of the studied alloy. Gaining an in-depth understanding of the relationship between wear mechanisms and microstructures offers an effective approach in manufacturing high wear resistant alloys suitable for use in harsh working environments.