Scripta METALLURGICA Vol. 30, pp. 463-468, 1994 Pergamon Press Ltd. et MATERIALIA Printed in the U.S.A. All rights reserved JOINING NiAI USING SIMULTANEOUS COMBUSTION SYNTHESIS AND PRESSURE R.D. Torres and T.R. Strohaecker PPGEMM/UFRGS Porto Alegre, Brazil J.J. Moore and G.R. Edwards Department of Metallurgical and Materials Engineering Colorado School of Mines Golden, Colorado 80401 (Received September 13, 1993) (Revised November 9, 1993) Introduction Nickel aluminide-based intermetallics are attractive in applications requiring high thermal stability, corrosion and oxidation resistance, and high-temperature mechanical properties. However, if components are to be produced using these intermetallics, efficient joining techniques need to be developed. This paper provides an initial investigation of the application of combustion (self propagating, high temperature) synthesis (SHS) as a means of joining NiAI intermetallic materials. Combustion synthesis [1-4] is a technique whereby an exothermic reaction mixture is used to synthesize the required product(s). If the reaction is sufficiently exothermic, it can be self sustaining once initiated at the ignition temperature, Tig. The heat generated by the reaction results in an increase in temperature to a maximum combustion temperature, Tc, which is usually less than the calculated adiabatic temperature, Tad, on account of heat losses from the reaction. Combustion synthesis reactions can be operated in two different modes of ignition, i.e. propagating and simultaneous combustion modes. In each case, the exothermic reactant mix, typically in powder form, is pressed in the required reaction stoichiometry and at a certain green density. In reaction mixtures which are less exothermic, such as the synthesis of an intermetallic compound from its elements, e.g. reaction (1), the simultaneous combustion mode is often used. In this case, the whole pellet is heated to above the ignition temperature of the reaction, whereupon the exothermic reaction is initiated in a near-simultaneous process. Ni + AI = NiAI (1) An enthalpy-temperature plot for the reactants and products for the combustion synthesis of NiAI using reaction (1) is presented in Figure 1, i.e, line Ni + AI (reactants) and line NiAI (product). The Ni-AI phase diagram is presented in Figure 2. The theoretically predicted Tad (NiAI), [5] associated with an ignition temperature, Tig, of 1000K for the combustion synthesis reaction (1) ignited in the simultaneous combustion mode is also schematically presented in Figure 1. The incorporation of a diluent or inert material into the reaction mix will decrease Tad and therefore, Tc, since this material will take heat out of the reaction enthalpy. Therefore, the addition of such diluents to the reactants provides a useful technique of controlling Tc. In this investigation, either AI203 or previously synthesized NiAI were added as diluents to the reactant mixture for reaction (1) in order 463 0956-716X/94 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.