The Effect of Ternary Addition on Structure and Stability of NbCr₂ Laves Phases

The alloying effect on microstructure and stability of the NbCr₂ Laves phases is investigated using x-ray diffraction (XRD) and transmission electron microscopy (TEM). In as-cast condition, the binary alloy as well as the ternary alloy containing V consisted of the C15 phase while the ternary alloys containing Mo, Ti, and W consisted of both the C14 (or C36) and the C15 phases, accompanied by a number of stacking faults and microtwins in their constituent phases. By a prolonged heat treatment at 1673 K, the retained C14 (or C36) phase is completely transformed to the C15 phase. However, their kinetics is slower in the sequence of the ternary alloys containing Mo > Ti > W. The alloying effect on the stability of the C15 (or the C14) phase and the associated transformation process is discussed on the basis of phase stability and kinetics.