Microstructural and Passivation Response of Severely Deformed AISI 304 Steel Surface: The Role of Surface Mechanical Att
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JMEPEG https://doi.org/10.1007/s11665-020-05161-6
Microstructural and Passivation Response of Severely Deformed AISI 304 Steel Surface: The Role of Surface Mechanical Attrition Treatment Digvijay Singh
, Dudekula A. Basha, Alok Singh, Rupesh S. Devan, and Santosh S. Hosmani (Submitted April 3, 2020; in revised form August 31, 2020)
The present study investigates the microstructural and passivation behavior of surface mechanical attrition treated (SMAT) AISI 304 stainless steel in a 0.6 M NaCl solution at room temperature. SMAT process, which is more advanced than the classical shot-peening, causes 2-3 times improvement in surface hardness of the steel. Ball size, a vital SMAT parameter, plays a significant role in controlling the microstructure and corrosion behavior of the steel. Larger diameter (6 mm) balls induce thicker deformed layer (450 lm), a higher proportion of deformation-induced martensite ( 50%), a higher density of dislocations and twins, and higher lattice strain. TEM results confirm the presence of {111} twins throughout the deformed layer. SMAT enhances the corrosion properties of the steel. Specimen SMATed with 4-mm-diameter-balls displays the lowest corrosion rate (1.80 3 1024 mmpy). SMAT increases the pitting resistance of the steel surface. XPS is utilized to understand the passivation mechanism of steel comprehensively. SMAT alters the proportion of Cr2O3, Cr(OH)3, Fe2O3, and FeO compounds in the passive layer. SMAT increases the thickness of the passive layer. Keywords
AISI 304, corrosion, passive film, SMAT, surface nanostructuring
1. Introduction In recent years, surface nanostructuring of metallic materials is emerging as a new paradigm in the development of highperformance materials due to its several novel properties than its coarse-grained counterpart (Ref 1, 2]. A nanostructured surface enhances the mechanical and physiochemical responses of various alloys (Ref 3-6]. The severe plastic deformation method is capable of forming a nanostructured layer of several microns thick on the metallic materials. Among the surface nanostructuring processes, surface mechanical attrition treatment (SMAT) is an advanced and novel technique. SMAT is fundamentally different from the classical shot-peening process, and it is useful to enhance mechanical properties. SMAT deforms the metal surface severely at high strain-rate resulting in the formation of a nanostructured gradient layer with a thickness of tens of micrometers (Ref 1, 2]. SMATed surface can improve the properties without altering the material chemistry (Ref 1, 7]. Stainless steel is an up-and coming-class of materials for various industrial applications. Without a surface-treated con-
Digvijay Singh, Dudekula A. Basha, Rupesh S. Devan, and Santosh S. Hosmani, Department of Metallurgy Engineering and Materials Science, Indian Institute of Technology Indore, Indore 453552, India; and Alok Singh, Research Center for Structural Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. Contact e-mail
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