Crystal structure of δ-NiMo phase in a ternary NiMoAl alloy

The high-temperature phase, δ-NiMo, in a ternary NiMoAl alloy system has been investigated systematically by means of scanning electron microscopy, analytical transmission electron microscopy and X-ray energy-dispersive spectrum analysis. It is found that, unlike in the binary alloy [1,2], the δ-NiMo phase in this alloy has a C-centered orthorhombic crystal structure with lattice parameters a = 0.455 nm, b = 1.663 nm and c = 0.873 nm. Its space group has been determined to be Cmem (No. 63) by the reflection condition analysis of selected-area diffraction patterns and zone-axis symmetry analysis of convergent-beam electron diffraction patterns.