laser cladding of Ni-Al bronze on Al alloy AA333
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I.
INTRODUCTION
SURFACE treatment by energetic beams opens a new category of processing opportunities in composite material formation. Laser cladding is a process in which a molten pool on the surface of a substrate metal is generated by laser illumination with simultaneous injection of a stream powder. The solidified clad track generally has a composition very close to the powder with a fine microstructure resulting from high cooling rates. The method has been used to obtain extended solid solution of Hf in Ni-based super alloy,tl,z3 improved wear resistance in Fe-Cr-Mn-C alloys,f3J and high-temperature oxidation resistance in Ni-Cr-A1-Hf alloys.[4] The application of laser cladding in material processing can be considered in two aspects. First, the effect of a high cooling rate associated with laser cladding may be used to produce extremely fine microstructures with extended solubility of some desired elements. Second, the process has the ability to combine metallurgically two kinds of materials, possessing substantially different properties without limitation by the equilibrium phase diagrams. In either case, a small dilution from the substrate is desirable. Generally, a good clad is characterized by a good fusion bond, minimum dilution, poro.sity, and distortion, and a crack-free clad-substrate interface. The preceding quality requirement for the clad track imposes a prerequisite on the clad and substrate materials. First, the melting points of the two materials should be near each other. Second, brittle-compound formation between clad and substrate should be avoided. Third, the clad material and substrate material should have some Y. LIU, formerly Research Associate, Center for Laser Aided Materials Processing, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, is Research Assistant Professor, Department of Mechanical Engineering, University of Nebraska, Lincoln, NE 68588-0656. J. MAZUMDER is Professor with the Center for Laser Aided Material Processing, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. K. SHIBATA is Senior Scientist with the Nissan Research Center, Nissan Motor Co., Ltd., Yokosuka 237, Japan. Manuscript submitted April 14, 1993. METALLURGICALAND MATERIALSTRANSACTIONS B
ductility to compensate for thermal stresses. The first physical property guarantees the coupling of the clad and substrate with the smallest dilution. The second metallurgical property ensures the interface strength. If these two conditions are satisfied but the third one is not, cracks may be formed across the clad because of thermal stresses. On the other hand, in engineering applications, first priority is usually given to the properties of cladding materials and substrates in order to achieve the maximum advantages. For example, the cladding of Fe, Cu, and Ni alloys on AI alloys is attractive, because AI alloy has low density and low cost compared to Ni and Cu alloys. Heat resistance, oxidation resistance, and
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