Microstructural Evolution During Friction Surfacing of Austenitic Stainless Steel AISI 304 on Low Carbon Steel
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INTRODUCTION
FRICTION surfacing is a promising new technology for depositing metallurgically bonded coatings on engineering components to combat wear and corrosion. Being a solid-state process, friction surfacing eliminates the problems such as porosity, hot cracking, segregation, and dilution which are commonly associated with conventional fusion-based techniques. In this process, a rotating cylindrical consumable rod is fed against a substrate with axial force acting simultaneously on the rod. The frictional heat is generated between the substrate and the consumable rod. Once the rubbing end of the consumable rod is sufficiently plasticized, the substrate is traversed horizontally with respect to the vertical consumable rod. Material flow at the area of contact occurs due to the combined effect of axial load, rod rotational speed, and substrate traverse speed. As the substrate moves at a specific rate, the plasticized metal deposits over it. The vertical force consolidates the plasticized metal and results in the formation of a continuous and metallurgically bonded layer. A schematic representation of friction surfacing process is shown in Figure 1. Realizing the potential of friction surfacing, attempts were made by many researchers to coat a variety of metallic materials on different metallic substrates by means of friction surfacing.[1–5] They found that ferrous materials in general are readily coatable.[1–3,5] NonH. KHALID RAFI, formerly with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India, is now Post Doctoral Associate with Department of Industrial Engineering, J.B. Speed School of Engineering, University of Louisville, Louisville, KY 40292. Contact e-mail: khalidrafi@ gmail.com N. KISHORE BABU, Scientist, is with the Joining Technology Group, Singapore Institute of Manufacturing Technology (SIMTech), 71 Nanyang Drive, Singapore 638075, Singapore. G. PHANIKUMAR, Associate Professor, and K. PRASAD RAO, Professor, are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras. Manuscript submitted February 20, 2012. Article published online September 5, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
ferrous materials pose some problems due to their high thermal conductivity and high temperature instability.[2,4] Among ferrous materials, stainless steels were found to be more attractive coating materials owing to their application potential as candidate materials for corrosion protection. Traditionally, stainless steel claddings were made by means of the Laser/TIG welding process. To minimize dilution and to retain material chemistry, buffer layers or highly alloyed stainless steels (like AISI 308 and AISI 309) are always used.[6] However, it suffers from problems associated with solidification. In addition, the process is time consuming and not cost effective. Therefore, a solid-state process which does not involve melting can address these issues and friction surfacing is an ideal solid-state process whi
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