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TECHNICAL PAPER

TP 2671

Nucleation Criteria for the Formation of Aluminum Nitride in Aluminum Matrix by Nitridation Sandeep Fale • Ajay Likhite • Jatin Bhatt

Received: 4 December 2012 / Accepted: 7 March 2013 / Published online: 30 March 2013 Ó Indian Institute of Metals 2013

Abstract Synthesis of in situ metal matrix composites using liquid metallurgy technique involves processing the melt to generate ceramic particles and entrap them into the matrix during solidification. The process parameters such as temperature, holding time and buoyancy effect generated in the molten bath are crucial factors governing the size and distribution of ceramic particles into the matrix. Temperature being most important parameter and its role is easy to comprehend for in situ formation of ceramic particles using established nucleation criteria. In the present research paper, thermodynamic study is carried to understand the role of temperature on formation of aluminum nitride by nitridation of aluminum melt using ammonium chloride and calcium oxide. Mechanism of aluminum nitride formation by heterogeneous nucleation and its growth has also been discussed based on the nucleation theory. An attempt is also made to correlate nucleation theory for the formation of AlN in Al matrix at different temperatures. The mechanical behavior under compressive loading is carried out on synthesized composites to understand its capability to withstand static loading. Composite strength is analyzed and attempt is made to correlate nucleation dynamics of AlN particles. Keywords Composite  Nitride  Nucleation and growth  Thermodynamics

S. Fale (&)  A. Likhite  J. Bhatt Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur 440 010, Maharashtra, India e-mail: [email protected]; [email protected]

1 Introduction Aluminum nitride (AlN) in Al matrix composites can be synthesized by using two methods: ex-situ and in situ depending on the introduction of AlN particles into the matrix [1, 2]. In ex-situ process, AlN particles in powder form are added into the molten Al with associated risk of contamination by oxidization or hydration of the pre-synthesized powder [3]. Contamination results in poor wetting of powder particles with molten Al due to unclean interfaces producing poor bond strength between particle and matrix which significantly deteriorates the strength of synthesized metal matrix composites (MMCs). In the in situ process, AlN can be generated inside the Al melt with clean interface between nitride and matrix thus ensuring strong interfacial bonding. Present study discusses formation of AlN by in situ process in Al melt using NH4Cl ? CaO as nitridation precursor at different temperatures. It is practically easy to generate ammonia gas in the melt by adding NH4Cl and CaO powder. The present method of generating ammonia gas is cost effective and does not require handling of ammonia/ nitrogen gas cylinders. Rosenband and Gany [4] used NH4Cl in self propagating high temperature synt