Volume 17 Preprint 21


Corrosion resistance studies of SS316L surface generated by Magnetic Field Assisted Abrasive Finishing

T. C. Kanish, P. Kuppan, S. Narayanan, S.Karthikeyan

Keywords: Corrosion resistance; Magnetic field assisted abrasive finishing; SS316L; Potentiodynamic polarization.

Abstract:
In this paper, an attempt has been made to investigate the corrosion resistance of SS316L surface generated by Magnetic Field Assisted Abrasive Finishing (MFAAF) process. The characterization on the finished surface of SS316L was studied by electro chemical studies like potentiodynamic polarization and impedance studies. These studies indicated that the MFAAF process could enhance the corrosion resistance of the surface in sea water medium. The polarization studies had shown that MFAAF process could be adopted to improve the corrosion resistance of the machined SS316L surfaces. To examine the microscopic changes in the surface texture resulting from corrosion, the Scanning Electron Microscopy images have been carried out to gain insight of corroded surfaces.

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ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 Corrosion resistance studies of SS316L surface generated by Magnetic Field Assisted Abrasive Finishing T. C. Kanish*1, P. Kuppan2, S. Narayanan3, S.Karthikeyan4 1,2,3School of Mechanical and Building Sciences, VIT University, Vellore 632014, India 4Centre for Nanobiotechnolgy, VIT University, Vellore-632014, India *Corresponding Author: tckanish@vit.ac.in Abstract In this paper, an attempt has been made to investigate the corrosion resistance of SS316L surface generated by Magnetic Field Assisted Abrasive Finishing (MFAAF) process. The characterization on the finished surface of SS316L was studied by electro chemical studies like potentiodynamic polarization and impedance studies. These studies indicated that the MFAAF process could enhance the corrosion resistance of the surface in sea water medium. The polarization studies had shown that MFAAF process could be adopted to improve the corrosion resistance of the machined SS316L surfaces. To examine the microscopic changes in the surface texture resulting from corrosion, the Scanning Electron Microscopy images have been carried out to gain insight of corroded surfaces. Keywords: Corrosion resistance; Magnetic field assisted abrasive finishing; SS316L; Potentiodynamic polarization. Introduction Surface finish is an important quality characteristic of machined components in terms of corrosion resistance, aesthetics, tribological considerations and fatigue life improvement as well as precision fit of critical mating surfaces. To obtain high level finishing of surfaces, from the last two decades many newer methods are identified by the researchers. Magnetic Field Assisted Abrasive Finishing (MFAAF) is one of the fine finishing methods to achieve smoother surfaces. Salient feature of MFAAF process is the use of controllable magnetic field in the finishing zone to produce mirror like nano level finishing without making any micro cracks and simple in operation [1]. Many researchers [2-5] conducted the experimental investigations to identify the significant process parameters to improve the surface obtained by the MFAAF process. Researchers made attempts to optimize the process parameters to improve the surface finish in MFAAF process. The obtained finished surfaces were studied using surface roughness profiles, Atomic Force Micrographs, 1 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 Scanning Electron micrographs [6-8]. It was reported that to reduce the gradual degradation of material by electro chemical attack the surface corrosion resistance of the parts are need much care. This corrosion resistance could be increased by careful finishing technique to reduce surface scratching. From the literature, it is identified that limited work has been carried out on the corrosion studies for the surface generated by the MFAAF process. Hence, this paper investigates the study of corrosion resistance of MFAAF machined surfaces of SS316L material using electrochemical techniques. The obtained results were reported and discussed on the electrochemical behaviour and corrosion resistance of SS316L surface produced by MFAAF process in a 3% NaCl solution. Potentiodynamic studies like polarization measurements and impedance studies were made before and after MAAF process for comparative purposes. From the obtained results, it was observed that the MFAAF finished surface is offering better corrosion resistance comparing the surface obtained by grinding process. To study the enhancement of corrosion resistance, SEM micrographs of corroded samples obtained before and after MFAAF were also studied and reported. Experimental Details Workpiece material Austenitic stainless steel grade 316L (SS316L) non-magnetic material was selected for this study. The chemical composition of selected SS316L material is shown the Table1. MFAAF experimental setup An electromagnet assembly was fitted to the spindle of precision vertical milling machine to conduct the MFAAF experiments. The experimental setup consists of electro magnet, mandrel, sleeve, lock-nut, contact brushes and power supply for electromagnet. The photographic view of MFAAF spindle assembly is shown in figure 1. The MFAAF experiment was conducted as per the following process parameters for the present study which are as follows: voltage supplied to the electromagnet at 22 V; machining gap at 1.5mm; rotational speed of electromagnet at 540 rpm; abrasive size at 1200 mesh; and Feed rate at 35 mm/min. The other parameters like finishing time (15min), grain size of iron particle (300 mesh), total amount of magnetic abrasive particle (10g) and mixing ratio (80% Fe, 20% SiC abrasive) were kept constant for the experiment. The MFAAF experiment before and after samples were utilized for the electrochemical studies. Before starting the electrochemical experiments, the surface roughness of the samples before and after MFAAF process were obtain (by Mitutoyo surftest SJ301) to 2 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 understand the surface irregularities. The obtained surface roughness profiles are shown in figure 2. Experimental setup for corrosion studies: An experimental setup was developed to study corrosion behaviour of SS316L material via potentiodynamic polarization and impedance measurements using the electrochemical analyzer, 3% of NaCl solution, platinum electrode for working electrode and a PC with data acquisition system. The developed experimental arrangement was shown in Figure 3. For the electrochemical studies of SS316L surface with 1 cm2 exposed area, Hg/Hg2cl2/3.5%NaCl and 4 cm2 area of platinum surface were used as working electrode, reference and counter electrodes respectively. The corrosion studies were carried out in 3.5% NaCl. During Potentiodynamic polarization studies, 200mV were shifted from open circuit potential with scan rate of 1mV/sec. Results and Discussion Corrosion studies Potentiodynamic polarization measurements This potentiodynamic polarization measurement was carried out on the machined surface obtained by MFAAF process and the results were presented in Fig 4. It is evident from the figure 3 that Ecorr (0.0197mV/sec) value is shifted to positive potential with simultaneous shifting of Icorr [9]. Hence the machined surface is offering better corrosion resistance in sea water medium than the machined surface obtained by grinding. The above observation clearly indicated that MFAAF process increases the homogeneity of surface atoms at their lattice planes with high degree of alignment of atomic structures by MFAAF. This could not be achieved through other conventional finishing processes. Also it was visualised that the corrosion potential values for MFAAF surface was 10 decades in mV/sec higher than the surface finishes resulted from grinding process. Impedance studies The Nyquist diagram for the corrosion resistance of metallic layer produced from MFAAF processes are presented in Figure 5. The real resistance was potted against imaginary resistance and the charge transfer resistance along with double layer capacitance values were calculated from the frequency maximum. These studies indicated that the corrosion resistance process is not following diffusion control as the perfect semi circles have not been encountered. The resistance was noted by best fitting the curve through alteration of electrochemical Randles circuits (Fig 6) as this seems to be peculiar for highly corrosion resistance surfaces [10]. 3 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 The charge transfer resistance value for surface produced by MFAAF process 5.5K /cm2 which is higher than (Rt = 2.3K ) the finishing achieved through grinding process. SEM Micrographs SEM micro graphs of corroded surfaces of SS316L in 3.5% NaCl is presented in figure 7. It is seen that the appearance of laminated structures with voids and streak lines indicating that the attack of chloride ion is more than the surface finishing of SS316L prepared by MFAAF process. The appearance of uniform and layered structure along with absence of nonuniformity in the surface confirming that MFAAF process could enhance the corrosion resistance of the said alloy in sea water medium. These results are found to be in good agreement with the results of electrochemical studies reported in this work. Conclusions Based on the above investigations, the following conclusions are drawn: i) The corrosion kinetic parameters indicated that the surface finish of MFAAF Process is superior than the other conventional finishing techniques ii) There is no heterogeneity on the surface of SS316L prepared from MFAAF technique which is further evidence from its enhanced charged transfer resistance iii) SEM images showed the presence of the layered structure along with decreased voids and pits on MFAAF patterned SS316L confirming its high corrosion resistance characteristics. References [1] V.K. Jain, “Advanced Machining processes”. 2002, Allied Publishers, Delhi. [2] „Study on magnetic abrasive finishing process-development of plane finishing apparatus using a stationary type electromagnet‟, T Shinmura, and T Aizawa, Bulletin of the Japan Society of Precision Engineering, 23, 3, pp 236–239, 1989. [3] „Parametric study of magnetic abrasive finishing process‟, Dhirendra K Singh, V.K Jain and V. Raghuram, Journal of material processing technology, 149, 22-29, 2004. [4] „Experimental investigations into forces acting during a magnetic abrasive finishing process‟, Dhirendra K Singh., and V.K Jain, International Journal of Advanced [5] Manufacturing Technology, 30, 652-662, 2006. „Clarification of abrasive finishing mechanism‟, T. Mori, K. Hirota, and Y. Kawashima, Journal of material processing technology, 143-144, pp 682-686, 2003. 4 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 [6] Volume 17, Preprint 21 submitted 11 April 2014 „Study of the surface modification resulting from an internal magnetic abrasive finishing process‟, Hitomi Yamaguchi, Takeo Shinmura, Wear, 225-229, pp 246-255, 1999. [7] „Analysis of surface texture generated by a flexible magnetic abrasive brush‟, Dhirendra K Singh, V.K Jain, V Raghuram and R Komanduri, Wear, 259, pp12541261, 2005. [8] „Magnetic abrasive finishing of hardened AISI 52100 steel‟, R.S. Mulik and P.M Pandey, International Journal of Advanced Manufacturing Technology, 55 (5-8), pp501-15, 2011. [9] „Surface modification with compositionally modulated multilayer coatings‟, G.D. Wilcox, Journal of Corrosion Science and Engineering, pp. 6 -9, 2003. [10] „Oxidation-Reduction Resistance of Advanced Copper Alloys‟, L. U. Ogbuji, D. L. Humphrey and J. Setlock, Journal of Corrosion Science and Engineering, pp. 6-9, 2003. Figures 1. CNC machine spindle 9 1 2. Slip ring 2 3. Electromagnet 3 8 5. SS316L Workpiece 4 5 4. Magnetic Abrasive Flexible Brush (MAFB) 7 6 6. Dynamometer 1. Fixture 2. Wires from power supply Figure 1 Photographic view of MFAAF spindle assembly 3. Contact brush 5 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 b) Before MFAAF process b) After MFAAF process Figure 2 Surface roughness profiles Figure 3 Schematic view of experimental setup for electrochemical corrosion studies 6 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 a) Before MFAAF process submitted 11 April 2014 b) After MFAAF process Figure 4 Potentiodynamic plots for Corrosion behaviour a) Before MFAAF process b) After MFAAF process Figure 5 Nyquist diagram for Corrosion behaviour of SS316L Figure 6 Electrical equivalent circuit 7 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 17, Preprint 21 submitted 11 April 2014 Before MFAAF process b) After MFAAF process Figure 7 SEM images Tables Table 1 Chemical composition of SS316L work material (Wt.%) Alloying Elements Observed weight ratio (%) Cr Ni Mo Mn Si P S C 16.1 10.0 2.0 1.8 0.5 0.03 0.003 0.021 2 4 3 5 1 4 8 © 2014 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.