In Situ Laser Synthesis of Fe-Based Amorphous Matrix Composite Coating on Structural Steel
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TRODUCTION
AMORPHOUS materials have attracted substantial interest due to their unique properties such as high yield strength, corrosion resistance, and wear resistance.[1–3] These materials lack long-range periodicity and ordering; therefore, there are no defects like grain boundaries and dislocations, distinguishing them from other crystalline counterparts. Processing of conventional amorphous materials requires a high rate of cooling ~105 K/s, which places a limitation on the section thickness to which these materials can be cast. In contrast, bulk metallic glasses (BMGs) can be produced at much lower cooling rates owing to their increased glass-forming ability (GFA). However, BMGs are not used for structural applications as their dimensions are limited due to strong composition dependence of critical cooling rate to obtain a fully amorphous structure. In order to SHRAVANA KATAKAM and HITESH VORA, Graduate Students, SAMEER PAITAL, Post Doctor, and NARENDRA B. DAHOTRE, Professor & Chairman, are with the Laboratory of Laser Materials Processing and Synthesis, Department of Materials Science and Engineering, University of North Texas, Denton, TX 76207. Contact e-mail: [email protected] JUN Y. HWANG, formerly Post Doctor, with the Center for Advanced Research Technology, University of North Texas, is now Research Staff Member, with the Korea Institute of Science and Technology, Jeonbuk 565-902, Republic of Korea. RAJARSHI BANERJEE, Professor, is with the Center for Advanced Research Technology, Department of Materials Science and Engineering, University of North Texas. Manuscript submitted August 26, 2011. Article published online July 19, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
exploit the unique properties of these materials, a coating of these materials on crystalline substrate is most promising. These coatings are best suitable for improving the surface properties like wear and corrosion. Wear and corrosion are two surface phenomena that result in the degradation of material due to the environment. The degradation due to these processes can be mitigated by producing a functional surface that can withstand extreme environments. Many processing routes like high-velocity oxygen fuel spraying,[4] high-velocity air fuel, thermal spraying,[5] magnetron sputtering,[6] and electro spark deposition[7] have been employed to deposit amorphous coatings. There are some limitations associated with each of these techniques such as processing time, adhesion to the substrate, and cost. On the contrary, laser cladding has been used to produce coatings for corrosion and wear resistance,[8–12] which has many advantages such as being economically more attractive, being a rapid processing technique, resulting in good adhesion between the coating and substrate, and reaching substantially higher rates of cooling. Several researchers have reported the enhancement of surface properties during laser processing by changing the thermal conditions to obtain desired microstructures within the coating.[13–16] Many models have bee
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