Fine Precipitation in the Channel Region of Two-Phase Ni3Al and Ni3V Intermetallic Alloys Containing Mo and W

Fine precipitation was observed in the channel region of the Ni-based, two-phase Ni3Al and Ni3V intermetallic alloys containing Mo and W, which are soluble in the A1 phase at high temperatures but less soluble in the two intermetallic phases at low temperatures. The fine precipitates were identified as Mo- or W-rich phases (Mo solid solution with a body-centered-cubic (bcc) structure or Ni4W with a tetragonal structure) accompanied by a rigid orientation relationship and a habit plane with the constituent phases in the channel region. Fine precipitation was induced when added elements were substituted for Ni, thus, stabilizing the two intermetallic phases; however, it was not induced when the two intermetallic phases were destabilized by the addition of elements to substitute for Al and V. Fine precipitation was induced to a greater extent when Nb was concomitantly added to the alloys with Mo or W and when the two intermetallic phases were stabilized. Annealing at temperatures below the eutectoid temperature was necessary to induce fine precipitation in the alloys containing W. Accordingly, age hardening by annealing did not occur in the alloys containing Mo but did occur in the alloys containing W, whose behavior was correlated with the difference in the diffusivity of the Mo and W elements in the two-phase eutectoid microstructures (phases).