Phase relation and microstructure in multi-phase intermetallic alloys based on Ni3Al–Ni3Nb–Ni3V pseudo-ternary alloy system

The phase relation and microstructure of alloys based on the Ni3Al–Ni3Nb–Ni3V 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 L12 (Ni3Al), D0a (Ni3Nb) and D022 (Ni3V). The phase fields of L12 (Ni3Al), D0a (Ni3Nb) and D022 (Ni3V) have been shown to primarily depend upon the free electron concentration (e/a) of the constituent atoms. Among the three constituent intermetallic phases, one kind of three-phase relation (i.e. L12–D0a–D022) and three kinds of two-phase relations (i.e. L12–D0a, D0a–D022 and L12–D022) 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 L12+D0a+A1(→L12+D022) were formed by a eutectic reaction.