| Phase transformations in the binary Ni(,4)Mo alloy and ternary Ni(,4)Mo alloys containing 0 to 4 weight percent chromium are reported using electrical resistivity and microhardness measurements, optical, scanning, and transmission electron microscopy (TEM). The transformation behavior was studied by resistivity measurements during continuous heating, cooling, or isothermally. The isothermal transformation behavior was also investigated in alloys aged at 600, 700, 800 and 850(DEGREES)C for times to 4500 hours.; The resistivity changes associated with short range order (SRO) and long range order (LRO) in Ni(,4)Mo have been completely characterized. The negative temperature coefficient of resistivity that is observed in the SRO state, and the change in slope of the LRO resistivity-temperature curve are explained on the basis of s-d electron scattering.; The 111 and 110 fcc striations observed in the optical microstructure of ordered Ni(,4)Mo have been studied using TEM and explained on the basis of structural considerations. Domain growth in Ni(,4)Mo can be described by the relationship D('n) = kt, in a manner parallel to metallurgical grain growth. The activation energy for domain growth is obtained as 80 kcal/mole. A better understanding has been gained of the domain coarsening reaction that is observed at the grain boundaries on low temperature aging (700 and 600(DEGREES)C) of Ni(,4)Mo.; The isothermal transformation behavior of ternary Ni(,4)Mo alloys containing chromium in the range 2 to 4 wt pct aged at 850, 800, 700 and 600(DEGREES)C has been studied. A variety of Mo-rich second phases, such as DO(,22), Ni(,3)Mo, Ni(,2)Mo, and eta-carbides is observed.; The Ni(,3)Mo forms by two mechanisms. One mechanism observed at 850, 800 and 700(DEGREES)C involves direct transformation from bands of DO(,22) aligned parallel to 111 fcc planes. A second mechanism occurs at the grain boundaries on aging at 700 and 600(DEGREES)C, and involves initial formation of large domains of Ni(,4)Mo at the grain boundaries, followed by subsequent transformation to Ni(,3)Mo, with the simultaneous presence of stacking faults on (010) Ni(,3)Mo planes.; Composition analyses of the phases has established that chromium predominantly substitutes for the molybdenum in Ni(,4)Mo-Cr alloys. Isothermal sections at 800 and 850(DEGREES)C of the ternary Ni-Mo-Cr phase diagram near the Ni(,4)Mo composition have been proposed. |
