STUDIES OF A QUASI-BINARY I~-NiA1 AND ix-Re EUTECTIC

Future improvements to jet engine performance will require materials which are lower in density and can withstand higher temperatures; thus increasing the thrust-to-weight ratio and the engine efficiency. The intermetallic compound IB-NiA1 is a prime candidate for this new high temperature material. This intermetallic offers a low density, a high melting temperatme, and excellent oxidation resistance, but exhibits poor creep resistance. The creep resistance may be improved by composite engineering with refractory metal fibers and of particular interest to the present study are the refractory composites formed by eutectic solidification. There are three known refractory metals which may be solidified as a eutectic with I~-NiAI: W(1), Mo(2,3), and Cr(2-5). Another useful refractory metal addition would be Re. Indeed, a-Re fibers would offer greater high-temperature strength than either Mo or W in the temperature range of 950 to 1250°C(6). This is in part a result of the close packed hexagonal crystal structure of a-Re. The mechanical properties of B-NiAI alloyed with Re via a powder metallurgy technique have been studied by Vedula et al.(7). This study revealed that the addition of Re to 13-NiAI did not produce an extended solid solution or a new phase equilibrium and the consolidated alloys exhibited microstructures of 13-NiAI with a dispersion of a-Re particles. One possible explanation for this result is that Re forms a quasi-binary eutectic isopleth with 13-NiA1. Thus, the purpose of this study was to determine if a composite with a matrix of 13-NiAI and fibers of a-Re could be produced by eutectic solidification and if so, to determine the nature of the quasi-binary phase diagram.