Nickel-aluminides/steel clad pipe fabricated by reactive centrifugal casting method from liquid aluminum and solid nicke
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25/3/04
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Nickel-Aluminides/Steel Clad Pipe Fabricated by Reactive Centrifugal Casting Method from Liquid Aluminum and Solid Nickel YOSHIMI WATANABE, SATORU WATANABE, and KIYOTAKA MATSUURA A novel method to produce an aluminide/steel clad pipe has been proposed. The method is based on a combination of the self-propagating high-temperature synthesis (SHS) reaction and centrifugal casting, and is named the reactive centrifugal casting method. Nickel powder was placed on a rotating steel pipe, and aluminum liquid was poured into the steel pipe. The aluminum liquid and nickel powder exothermically reacted and produced a composite layer consisting of nickel aluminides on the inner surface of the steel pipe. The heat generated by the exothermic reaction melted the inner surface of the steel pipe and bonded the composite layer to the steel. It was found that increases in centrifugal force generated by rotating the steel pipe, the pouring temperature of the aluminum, and the preheating temperature of the nickel and steel remarkably promote the reaction between nickel and aluminum. In addition, the amounts of initial aluminum and nickel were found to play an important role in controlling the microstructure of the composite layer. Thus, the aluminide/steel clad pipe can be successfully fabricated by the proposed reactive centrifugal casting method.
I. INTRODUCTION
AN intermetallic compound of nickel monoaluminide, NiAl, offers new opportunities for developing low-density and high-strength structural materials, which might be used at temperatures higher than currently possible with conventional nickel-based superalloys. This is because the NiAl has the attractive combinations of low density (5.86 Mg/m3), high melting point (1911 K), high strength, good corrosion and oxidation resistance, high thermal conductivity, and low cost.[1] Unfortunately, NiAl has very low ductility at temperatures below 600 K, which is a significant disadvantage and impedes the practical use of NiAl as a structural material.[2] An effective way to avoid trouble due to this disadvantage may be joining NiAl to a ductile material or making a composite material consisting of NiAl and a ductile material, which may lead to an application of NiAl as a new corrosion and oxidation-resistant structural material. Recently, Matsuura et al.[3–7] developed a new technique named reactive casting, which involves an exothermic reaction between elemental liquids, and enables one to produce the liquid of a high melting point intermetallic compound without the need for external heating. For example, they produced a NiAl liquid of 2876 K by simply mixing aluminum liquid of 1023 K and nickel liquid of 1773 K. An increment in temperature over 1000 K was achieved by heat generation from an exothermic reaction of Ni Al : NiAl, which is characterized as the self-propagating high-temperature synthesis (SHS) reaction. Moreover, they found that when the two liquids are poured onto a base material such as steel, YOSHIMI WATANABE, Associate Professor, and SATOR
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