The effect of heat input on the microstructure and properties of nickel aluminum bronze laser clad with a consumable of
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INTRODUCTION
Laser cladding with nickel aluminum bronze offers the promise of order-of-magnitude improvements in the surface-sensitive properties of nickel aluminum bronzes and other alloys. It is also a promising repair and reclamation method for high-value components. Cladding of nickel aluminum bronze castings with nickel aluminum bronze is of particular interest in marine engineering applications. Here, the development of seawater handling, propulsion, and combat system equipment capable of lasting the life of a ship would offer enormous cost benefits. Nickel aluminum bronzes are selected for use in high-performance marine engineering applications for their ease of fabrication by casting, welding, and forging and for their properties.[1,2] Their resistance to corrosion, erosion-corrosion, cavitationerosion, corrosion-fatigue, stress corrosion cracking, and dealloying are particularly important. So are their toughness and strength. These properties impose limitations on the design, use, and life of components made of nickel aluminum bronze. For example, the design guidelines for propellers made of nickel aluminum bronze are basically limited by corrosion fatigue,[2,3,4] the life and inspection intervals of nickel aluminum bronze valves in seawater handling systems are limited by dealloying,[5–8] and the damage of nickel aluminum bronze impellers and propellers by cavitation-erosion does occur. Improvements in these properties, without degradation of others, could give significant cost and performance benefits. It has been known for some time that the properties of aluminum bronzes can be modified by solid-state quenching[9] and by rapid solidification and laser surface melting.[10–16] C.V. HYATT, Defence Scientist, is with Defence Research Establishment Atlantic, Dartmouth, NS, Canada B2Y 3Z7. K.H. MAGEE, formerly Metallurgical Engineer with The Laser Institute, Edmonton, AB, Canada T6E 5J1, is Senior Metallurgical Engineer with CANSPEC Group Inc., Edmonton, AB, Canada T6P 1N8. T. BETANCOURT, formerly Corrosion Scientist with the Nova Scotia Innovation Corp., Dartmouth, NS, Canada B2Y 3Z7, is retired. Manuscript submitted August 29, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
Because the intermetallic compounds in nickel aluminum bronzes are very stable and the a-b phase boundary is near the solidus line, it is very difficult to homogenize these alloys in the solid state.[9,17] Thus, a welding approach is required. There exists information on the development of microstructures in low-heat-input welding of nickel aluminum bronze.[18–29] Except for some weld simulation studies,[29] all this work has dealt with alloys rich enough in aluminum that martensite can be produced following rapid quenching from the melt. For the alloys examined thus far, in the asdeposited material, a martensite with a 9-R structure is common in low-heat-input nickel aluminum bronze welds over a range of compositions. Other phases, identified by various workers as Widmansta¨tten a, bainite, or lath martensite, also form. Weld simul
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