PERITECTOID PHASE TRANSFORMATIONS IN Ni_3Mo ALLOY

摘要

High-energy ball milling was used to produce a partially alloyed elemental nickel and molybdenum of Ni_3Mo composition, cold-compacted and then sintered/solutionized at 1300°C for 100 h and quenched. Three transformation studies were performed. First, the intermetallic γ-Ni_3Mo was formed from the supersaturated solution at temperatures below the peritectoid isotherm. Cellular precipitation was observed in some samples. Second, the reversed peritectoid transformation from γ-Ni_3Mo to α-Ni and δ-NiMo was performed. Regardless of heat-treatment temperature, samples heat-treated for short times exhibited small precipitates of δ-NiMo along and within grain boundaries of α-Ni phase. Third, the transformation from the supersaturated solution to the peritectoid two-phase region was performed. Precipitates of δ-NiMo were observed and additionally, spinodal structure with compositions of 14 and 24 at. % Mo developed in the solid solution matrix for most samples. In all three cases, hardness values increased and peaked in a way similar to that of traditional aging, except that the peak occurred much rapidly in the second and third cases.