Production of Ni 3 Ti-TiC x intermetallic-ceramic composites employing combustion synthesis reactions
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I. INTRODUCTION
COMBUSTION synthesis (CS) is an alternative technique for producing advanced ceramics, ceramic composites, and intermetallic compounds.[1,2] The CS is dependent upon the ability of a highly exothermic chemical reaction to become self-sustaining after only a short energy pulse is applied to initiate the reaction. In general, exothermic CS reactions tend to become self-sustaining at adiabatic temperatures (Tad) above 1527 °C (1800 K).[3] This article examines the CS of a range of porous Ni3TiTiCx composites. The wide compositional range of TiCx (0.3 x 0.5) creates the possibility of synthesizing NiTi-TiC and Ni3Ti-TiCx composites, i.e., stoichiometric TiC or substoichiometric TiCx. Typically, reactant powders are mixed in a desired stoichiometric ratio, subjected to the CS process, and converted to desired final products. Elemental nickel, titanium, and carbon (graphite) reactant powders were used in the present investigation to produce Ni3Ti-TiCx composites. The CS reaction sequence and amount of energy present within the reaction zone are important to the formation and size of the synthesized TiCx particles. Initially, there is a reaction between nickel and titanium reactant particles at regions of contact resulting in localized formation of Ni-Ti intermetallics. The intermetallics along with additional nickel (1455 °C) and titanium (1670 °C) reactants correspondingly melt in the reaction zone, as provided by the exothermicity and combustion temperature of the reaction, followed by local DOUGLAS E. BURKES, Postdoctoral Fellow, and JOHN J. MOORE, Professor and Head of Department, are with the Metallurgical and Materials Engineering Department, Institute for Space Resources, Colorado School of Mines, Golden, CO 80401. Contact e-mail: [email protected] GUGLIELMO GOTTOLI, formerly Graduate Research Assistant, Metallurgical and Materials Engineering Department, Institute for Space Resources, Colorado School of Mines, is Postdoctoral Fellow, Department of Chemical and Biomolecular Engineering, University of Melbourne, Melbourne, Victoria, 3010 Australia. HU CHUN YI, Director, is with the Advanced Materials and Combustion Laboratory, Guigne International Ltd., St. John’s, NL, Canada A1L 1C1. Manuscript submitted July 21, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
formation and homogenization of an intermetallic Ni-Ti melt. Dissolution of carbon (graphite) within the intermetallic melt occurs as the melt spreads over the surface of the carbon (graphite) reactant particles. A reaction between titanium and carbon subsequently takes place that results in the precipitation of spherical TiCx particles from the intermetallic melt. The capillary force that controls spreading of the intermetallic melt over the surface of carbon particles is more influential for reactions with higher initial porosity.[4] A regrouping of TiCx particles accompanies this reaction followed by an Ostwald ripening process, whereby larger TiCx particles coarsen at the expense of smaller TiCx particles. Solidification of the int
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