Nickel Aluminide Superalloys Created by SHS of Nano-Particle Reactants
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Nickel Aluminide Superalloys Created by SHS of Nano-Particle Reactants Emily M. Hunt, John J. Granier, Keith B. Plantier and Michelle L. Pantoya Department of Mechanical Engineering, Texas Tech University, Lubbock, TX 79409 ABSTRACT Advancements in nanotechnology for material processing have spurred the development of superalloys that provide improved protection against corrosion and wear. Nano-scale reactant particles offer unique thermal properties and increased homogeneity that may improve the microstructural features and macroscopic properties of the final product. In this study up to 10-wt % nano-scale molybdenum tri-oxide (MoO3) particles were added to micron scale nickel (Ni) and aluminum (Al). The goal was to produce a superalloy by generating excessively high heating rates and adding an oxidizer that would produce small quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. Experiments were performed on pellets pressed to 60% theoretical maximum density. Ignition and flame propagation were examined using a CO2 laser and imaging diagnostics that include a copper-vapor laser coupled with a high-speed camera. Product microstructure was examined using scanning electron microscopy. Abrasion testing was performed to evaluate the wear resistance properties of the superalloy. Results show that adding MoO3 increases the flame temperature and produces greater ignition sensitivity. Also, small quantities of MoO3 produce a more homogeneous microstructure and increase the overall wear resistance of the product. INTRODUCTION Nickel aluminide superalloys are being considered to support the new challenging environmental demands and requirements of industrial gas turbines [1]. In particular, recent strategies for reducing operation and maintenance (O&M) costs associated with gas turbines for stationary power generation have been directed towards advanced coating technologies [2]. Both wear and corrosion resistant superalloys are ideal for cold and hot-section components. Wear-resistant coatings are applied to surfaces that experience a second- or third- body interaction that may lead to material transfer or loss from either surface during service. To protect against wear, hard coatings are usually applied on the contact surfaces. When this superalloy also has good corrosion resistant properties, the material may be ideal for turbine hot section components as well. Nickel aluminide is a good candidate material because the alloy offers superior hardness inherent from Ni and the oxidation and hot corrosion resistance associated with Al [1]. Nano-particles have unique thermal properties, such as a reduced melting temperature, and exhibit distinctive ignition and combustion behaviors when compared to traditional micron scale thermites. Granier and Pantoya [3] first showed that nano-Al based thermites are extremely sensitive to thermal ignition compared with traditional micron-composite thermites. In fact, they showed that ignition delay times were reduced by three orders of magnitude (from 1
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