Tribological study of surface treated and coated stainless steel

Abstract

The tribological performance of surface-treated and coated stainless steel is investigated in this study. The novel surface mechanical attrition treatment (SMAT) is explored as a surface treatment method which generates nano-grains on the stainless-steel surface. The microstructure, micro/nanomechanical response, and tribological behaviour of stainless steel are investigated in detail. The role of ball velocity (which influences SMAT parameter) on microstructure and tribological (dry/lubrication conditions) properties is also explored in the current investigation. Further, the effect of SMAT pre-treatment on the tribological behaviour of soft (polymer and composite) and hard (AlCrN/DLC) coating is investigated. The following characterisation tools are used in this work to study the surface-engineered steels: scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle measurement, Vickers microhardness tester, nano-indenter with Berkovich tip, ball-on-disc type tribometer, and 2D surface profilometer. SMAT using 6 mm diameter balls improve the surface hardness of AISI 316L steel maximum by ~89%. The higher velocity balls deform the surface with a higher strain rate, show a highly dense network of mechanical twins, generate a thick deformed layer, and form ~43% deformation-induced martensite (DIM/’ phase). The EBSD results suggest that the DIM/’ phase forms in the severely deformed layer along the grain boundaries, deformation bands, and their intersections. Likewise, the TEM results confirm the nano-grains on the AISI 316L steel surface after the SMAT process. The maximum nano-hardness of ~4.2 GPa is found near the surface of the specimen SMATed with 10 m/s velocity balls. The strain-rate sensitivity (SRS) and activation volume increase with an increasing distance from the SMATed surface. Presence of DIM causes these variations in SMATed AISI 316L steel.