Nickel aluminum superalloys created by the self-propagating high-temperature synthesis of nanoparticlereactants
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Advancements in nanotechnology for material processing via combustion synthesis have spurred the development of superalloys that provide improved protective properties. Nanoscale reactant particles offer unique thermal properties and increased homogeneity that improve the microstructural features and macroscopic properties of the synthesized product. In this study nanoscale molybdenum trioxide (MoO3) particles were added to micron scale nickel (Ni) and aluminum (Al). The goal was to incorporate a nanoscale additive within the reactant matrix that would produce a superalloy by generating excessively high heating rates and creating controlled quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. 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 micro-x-ray diffraction analysis and 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, results in greater ignition sensitivity, produces a more homogeneous microstructure, and increases the overall wear resistance of the product.
I. 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 high-temperature structural 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 Nanoparticles have unique thermal properties, such as a reduced melting temperature3 and exhibit distinctive a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0389 3028
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 10, Oct 2004 Downloaded: 14 Mar 2015
ignition and combustion behaviors when compared to traditional micron-scale thermites. Experimental measurements by Eckert et al.3 show that Al melting temperature as a function of particle size corresponds nicely with the Gibbs–Thompson theory. Granier and Pantoya4 showed that nano-Al-based thermites are extremely sensitive to thermal ignition compared with traditional micron-composite thermites. In
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