Phase relation and microstructure in multi-phase intermetallic alloys based on Ni_3Al-Ni_3Nb-Ni_3V pseudo-ternary alloy system

摘要

The phase relation and microstructure of alloys based on the Ni_3Al-Ni_3Nb-Ni_3V pseudo-ternary alloy system at 1273 and 1373 K were investigated by optical microscopy, X-ray diffraction, and scanning electron microscopy (attached with a wavelength dispersive spectroscope). There was no other intermediate phase besides LI_ 2 (M3A1), D0_a (Ni_3Nb) and D0_(22) (Ni_3V). The phase fields of Ll_2 (Ni)3Al), D0_0 (Ni_3Nb) and D0_(22) (Ni)3V) have been shown to primarily depend upon the free electron concentration {ela} of the constituent atoms. Among the three constituent intermetallic phases, one kind of three-phase relation (i.e. Ll_2-D0_a-D0_(22)) and three kinds of two-phase relations (i.e. Ll_2-D0_a, D0_a-D0_(22) and Ll_2-D0_(22)) were found to exist at 1273 K. The prepared alloys exhibited widely different microstructures, depending on alloy composition and temperature. In the low Nb concentration region, dual multi-phase microstructures composed of Ll_2 + D0_a + Al(-- > D0_(22)) were formed by a eutectic reaction.