Inﬂuence of surface mechanical attrition treatment (SMAT) on the corrosion behaviour of AISI 304 stainless steel T. Balusamy a,b , T.S.N. Sankara Narayanan a,c,⇑ , K. Ravichandran b , Il Song Park c , Min Ho Lee c,⇑ a CSIR-National Metallurgical Laboratory, Madras Centre, CSIR Complex, Taramani, Chennai 600 113, India b Department of Analytical Chemistry, University of Madras, Maraimalai (Guindy) Campus, Chennai 600 025, India c Department of Dental Biomaterials, School of Dentistry, Chonbuk National University, Jeonju 561-756, South Korea article info Article history: Received 28 November 2012 Accepted 30 April 2013 Available online 20 May 2013 Keywords: A. Stainless steel B. Polarization B. Potentiostatic B. EIS C. Passive ﬁlms C. Pitting corrosion abstract The inﬂuence of surface mechanical attrition treatment (SMAT) on the corrosion behaviour of AISI 304 stainless steel in 0.6 M NaCl was studied. SMAT of 304 SS induced plastic deformation, enabled formation of mechanical twins and strain induced  a-martensite phase, increased the surface roughness and imparted compressive residual stress. SMAT caused a deleterious inﬂuence on the corrosion resistance of 304 SS in 0.6 M NaCl. Double log plots of current–time transients at 25 mV (SCE) indicate formation of defective passive ﬁlm on SMATed 304 SS. Increase in surface roughness, strain induced martensite and dislocations nullify the beneﬁcial inﬂuence of surface nanocrystallization. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Nanostructured materials have received considerable attention among materials scientists due to their ability to offer unique physical, chemical, and mechanical properties that can be explored for numerous technological applications [1–3]. Most of the mate- rial related failures such as corrosion, wear, fretting fatigue, and fa- tigue fracture occur on the surface. Hence, optimization of the microstructure and properties of materials by means of various surface modiﬁcation techniques is necessary to enhance their glo- bal behaviour and lifetime without affecting their inherent prop- erty. Surface mechanical attrition treatment (SMAT) is an effective way of inducing localized plastic deformation that results in grain reﬁnement down to nanometer scale without changing the chemical composition of the material [4,5]. It is a very promising method to produce functionally gradient materials, in which the nanocrystalline surface layer provides suitable surface properties while the coarse-grained matrix provides the ductility. The SMAT process has been successfully applied to various material systems including titanium [6,7], aluminum [8,9], iron [10,11], stainless steel (SS) [12,13], carbon steels [14], etc. The corrosion behaviour of nanocrystalline materials and coat- ings is an interesting area of research [13,15–17]. The plastic defor- mation induced by SMAT or other methods such as cold rolling, cold working, extrusion, shot peening, ultrasonic peening, equal channel angular extrusion (ECAE), and equal channel angular pressing (ECAP) has a signiﬁcant inﬂuence on the corrosion resis- tance of a variety of metallic materials [18–27]. It has been re- ported that plastic deformation has a detrimental effect on the corrosion resistance of stainless steels. This is due to the defects in- duced during deformation that lead to the formation of defective interfaces in corrosive medium [28,29]. Plastic deformation has been shown to decrease the corrosion resistance of AZ31 Mg alloy [24]. However, a beneﬁcial effect on the corrosion resistance of high strength cast iron is observed after deformation [30]. This is due to the change in shape of graphite following deformation that results in a surface with relatively smaller number of inclusions per unit area [30]. Hence, evaluation of corrosion behaviour of metallic materials subjected to SMAT will be an interesting area of research. SMAT has been shown to introduce surface defects, prevents the formation of passive ﬁlm, and deteriorate the corrosion resis- tance of AISI 316 SS in 0.1 M NaCl [31]. The formation of nanocrys- talline boundaries by SMAT leads to a reduction in corrosion resistance whereas the formation of twin boundaries enables an improvement in corrosion resistance of AISI 316L SS in 0.05 M H 2 SO 4 + 0.25 M Na 2 SO 4 [32]. SMAT of AISI 409 SS using 8 mm £ AISI 316 SS balls for 900, 1800 and 2700 s and by 5 mm £ balls for 1800 and 2700 s decreased the corrosion resistance following the increase in microstrain and defect density induced during the treatment. In contrast, SMAT using 2 mm £ balls for 900, 1800 0010-938X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.corsci.2013.04.056 ⇑ Corresponding authors. Address: Department of Dental Biomaterials, School of Dentistry, Chonbuk National University, Jeonju 561-756, South Korea. Tel./fax: +82 062704040. E-mail addresses: tsnsn@rediffmail.com (T.S.N. Sankara Narayanan), lmh@jbnu.ac.kr (Min Ho Lee). Corrosion Science 74 (2013) 332–344 Contents lists available at SciVerse ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci