DECOMPOSITION REACTIONS AND TOUGHENING IN NiAI-Cu ALLOYS. Allen, W., P., Foley, J., C., Cooper, R., F., & Perepezko, J., H. Technical Report
In the NiAl-Cu 3 Al pseudobinary section of the Ni-Al-Cu ternary system, the structural similarity of the binary phases yields a miscibility gap between NiAl (B2 structure with ao=-0.2880 nm) and Cu 3 Al (bcc structure above 5670 C with ao= 0 .2946 nm). Due to the extensive mutual solubility, alloys can be solution-treated as single-phase NiAI and then aged at temperatures within the miscibility gap to investigate possible decomposition reactions. Several NiAl-Cu alloys (containing up to 30 at% Cu) were solution-treated at 1000° C, water-quenched, and then aged at either 475" C or 525* C. The decomposition of the supersaturated NiAl was characterized using XRD and SEM. A modulated microstructure was observed for an initial aging of 24 hours, and is consistent with the presence of a conditional spinodal between the NiAl and the Cu 3

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