Processing parameter, microstructure and hardness of Ni base intermetallic alloy coating fabricated by laser cladding
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Processing parameter, microstructure and hardness of Ni base intermetallic alloy coating fabricated by laser cladding Takeshi Okuno1, Yasuyuki Kaneno1, Takuto Yamaguchi2, Takayuki Takasugi1, Satoshi Semboshi3, and Hideki Hagino2 1
Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan 2 Technology Research Institute of Osaka Prefecture, 2-7-1 Ayumino, Izumi, Osaka 5941157, Japan 3 Trans-Regional Corporation Center, Institute for Materials Research, Tohoku University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan ABSTRACT Ni base intermetallic alloy coating was fabricated by laser cladding, controlling the laser power and powder feed rate. Atomized powder of the Ni base intermetallic alloy was lasercladded on the substrate of stainless steel 304. The hardness and microstructure of the clad layers were investigated by Vickers hardness test, SEM, XRD and TEM observations. The hardness of the cladding layer was affected by the dilution with the substrate; it increased with decreasing laser power and increasing powder feed rate. By optimizing the dilution with the substrate, the cladding layer with an almost identical hardness level to that of the Ni base intermetallic alloy fabricated by ingot metallurgy was obtained. The TEM observations revealed that a very finesized microstructure composed of Ni3Al and Ni3V was partially formed even in the as-cladded state. After annealing, the two-phase microstructure composed of Ni3Al and Ni3V was developed in the cladding layer, resulting in enhanced hardness in the cladding layers fabricated in the majority of cladding conditions. INTRODUCTION The present authors have recently developed a new type of two-phase intermetallic alloys composed of Ni3Al (L12) and Ni3V (D022) phases [1-4]. The microstructure is composed of Ni3Al and Ni solid solution (A1) phases at high temperature, and the Ni solid solution phase is decomposed into (Ni3Al + Ni3V) by a eutectoid reaction at a low temperature. The so called dual two-phase microstructure is thus comprised of whole intermetallic (ordered) phases with high structural coherency, leading to high microstructural stability at high temperature. The dual twophase intermetallic alloys have been found to exhibit excellent strength and hardness at high temperatures due to their stable microstructure, and thereby are expected to be used for hightemperature structural and wear-resistant applications such as high-temperature dies, molds and tools. For wear-resistant applications, coating processes such as thermal spraying and cladding by welding have been practically used. Recently, laser cladding has become widely used as a surface modification processing because of many advantages over other conventional techniques such as thermal spraying and arc welding [5-7]. Laser cladding has a high potential for coatings with low dilution with substrate, minimal distortion and strong metallurgical bonding with substrate, leading to refurbishment or improvement of corrosion, wear and other surf
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