Constitutional and microstructural investigation of the pseudobinary NiAl–W system

Pseudobinary NiAl–W section in the range 0.7–1.8 at% was characterised regarding solidification microstructure and constitution. The existence of eutectic reaction was confirmed and occurs at temperature of 1664 ± 2 °C and the composition of 1.5 at% W. As-cast microstructures indicated that the NiAl–W system is an anomalous eutectic with skewed coupled zone and that the NiAl phase is a preferential phase for eutectic nucleation. Directionally solidified alloy containing 1.5 at% W exhibited entirely eutectic structure characterised by eutectic cells with the average value of 500 μm, interfibre spacing 3.5 μm, fibre diameter 300 nm, and volume fraction of the W phase 1.4%. The solubility of W in the intermetallic phase is <0.04 at% and the solubility of Ni and Al in the W phase is negligible. Crystallographic orientation between the constituent phases was established to be cube on cube. Based on the results obtained by DTA, microstructural and compositional analysis, a new isoplethal section NiAl–W of the ternary Al–Ni–W system has been proposed.

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► Eutectic reaction in psuedobinary NiAl–W system occurs at 1664 ± 12°C and 1.5 at% and W.
► It is anomalous eutectic with skewed coupled zone.
► Preferential phase for eutectic nucleation is NiAl and both phases are non-facted.
► Size of eutectic cell is 500 μm, fibre diameter 300 nm and fibre spacing 3.5 μm.
► Constituent phases show cube on cube orientation relationship.