Development of Ni-Al 2 O 3 In-Situ Nanocomposite by Reactive Milling and Spark Plasma Sintering
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INTRODUCTION
NANOCOMPOSITES, in which both the matrix and the reinforcement are nanocrystalline or the nanoreinforcement in microcrystalline matrix, exhibit superior mechanical properties compared to their microcrystalline counterpart with similar volume fraction of reinforcement particles. In-situ formation of the reinforcement particles by powder metallurgy route is reported to overcome the difficulty in dispersion and segregation problems of very fine reinforcement particles normally being faced in casting route. Moreover, the in-situ reinforcement particles are thermodynamically stable and compatible with the matrix.[1] Mechanical alloying is a popular technique to synthesize nanocrystalline, amorphous and intermetallics. In addition, development of nanocomposites by activating the displacement reaction where the metal oxides are reduced by more reactive metal to a pure metal is also one of the applications of the mechanical alloying.[2,3] Nickel was widely used as coating material since it is strong, tough, and resistant to corrosion, erosion, and abrasion. However, during severe environmental and stress conditions, the mechanical properties deteriorate. Hence, one of the methods to improve this is reinforcing Ni with hard particles such as Al2O3,[4–7] CeO2,[8] TiO2,[9–11] ZrO2,[12–14] SiC,[15–17] WC,[18–20] and V. UDHAYABANU, Assistant Professor, is with the Department of Metallurgical Engineering, PSG College of Technology, Coimbatore 641 004, India, and is also with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036, India. K.R. RAVI, Assistant Professor, is with the PSG, Institute of Advanced Studies, Coimbatore 641 004, India, and is also with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras. K. MURUGAN and D. SIVAPRAHASAM, Scientists ‘C’, are with the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500 005, India. B.S. MURTY, Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras. Contact e-mail: [email protected] Manuscript submitted June 22, 2010. Article published online January 27, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
TiC.[21,22] These particles act as barriers to dislocation motion within the metal matrix and increase the strength by Orowan hardening phenomena. Moreover, additional benefit can be realized if the particles pin the grain boundaries, thereby impeding grain growth during heat treatment.[23] All these preceding reinforcing particles were added externally to Ni matrix. In the present work, an attempt has been made to develop in-situ nanoAl2O3 particles reinforced in Ni matrix (Ni-30 vol pct Al2O3), by subjecting the NiO-Al-Ni powder mixture to reactive milling. The phase evolution during milling and subsequent heating was analyzed. The microstructure and mechanical properties were investigated after the spark plasma sintering (SPS) and compared with the monoli
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