Ductility Improvement by Microstructural Control on Multiphase Intermetallic Alloys Using Phase

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There have been several examples in which the control in the microstructure consisting of intermetallic phases with different ordered crystal structure which are neighboring in the multi-component alloy systems was successful to provide appreciable tensile ductility at room temperature. However it seems in those cases to be difficult to achieve enough high temperature strength at the same time due to the instability of a fine microstructure at elevated temperatures.The present work is designed to develop multi-phase intermetallic alloys through a phase decomposition at a high enough temperature so that a microstructure produced would be stable at temperatures over 1273 K.The Ni-Al-Mo system was chosen as an alloy system because there seems to be a compositional region in which the B2 phase decomposes into the Ll_2 Ni_3Al and the alpha-Mo terminal solid solution, alpha(Mo), at around 1573 K.Phase diagram evaluation by differential thermal analysis and microstructural observation is followed by fabrication of selected alloys by arc-melting. It is then shown that some alloys, typically aNi-22at%Al-8at%Mo alloy, exhibits an excellent high temperature strength with some room temperature ductility.