Mechanical properties of laser-deposited composite boride coating using nanoindentation
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INTRODUCTION
SURFACE modification of the engineering components is becoming more and more important for many advanced technological applications. A host of thin films and coatings with various material properties such as wear resistance, erosion resistance, and corrosion resistance is available for several applications. Hence, it is essential to characterize the surface and other properties such as hardness (H ) and Young’s modulus (E ) of such coatings. It is often true that microindentation / nanoindentation are one of the essential tools to assess the mechanical properties of modified surface. Nanoindentation is one such technique, which determines mechanical properties such as hardness, H, and elastic modulus, E, of thin films and coatings by continuous measurement of force and displacement as an indentation is made.[1–6] It offers several advantages over other hardness measurement tools. The greatest advantage of this technique stems from its ability to probe a surface and map its properties on a spatially resolved basis with a resolution of better than 1 mm.[4] Such small size of indentation allows exact measurement of mechanical properties of fine microstructural features such as ultrafine grains, precipitates, and phases. This also enables estimation of mechanical properties of “composite” materials. Another advantage offered by the nanoindentation technique is its ability to measure the surface properties independent of the nature of the substrate.[3] Because the indentation depth is very small (nanometers), plastic deformation of substrate is avoided and only surface properties are measured. In the present work, the mechanical properties (elastic modulus and hardness) of a composite boride coating have been estimated using the nanoindentaion technique. TiB2 ARVIND AGARWAL, Graduate Research Assistant, and NARENDRA B. DAHOTRE, Professor of Materials Science and Engineering are with the Department of Materials Science and Engineering, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388. Manuscript submitted May 17, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
coating is synthesized on AISI 1010 steel using laser surface engineering (LSE). Coating produced by laser is metallurgically bonded to the substrate. Also, coating is composite in nature, with TiB2 particles of various sizes and shapes embedded in the Fe matrix.[7,8,9] A high energy laser beam resulted in formation of some metastable phases with ultrafine microstructure.[7,8,9] The elastic modulus of such composite boride coating has been evaluated for various laser traverse speeds and correlated to the reaction(s) occurring within the coating region. II. EXPERIMENTAL PROCEDURE A. Materials and Coating Process In the present study, TiB2 has been deposited on AISI 1010 steel substrate using laser. TiB2 is a low density, hard refractory material with an excellent oxidation resistance property up to 1673 K.[10] Wear and abrasion resistance of TiB2 is very high, which makes it an excellent coating material for
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