Microstructural studies on phase evolution sequence in rapidly solidified Zr3Al based binary and ternary alloys

Transformation sequences in the alloys Zr3Al, Zr3Al–3Nb and Zr3Al–10Nb are described and rationalized in terms of some basic tendencies such as phase separation and chemical ordering in the β phase and displacive omega and β→α (h.c.p.) transformations. These alloys were melt-spun and aged at different temperatures to study the evolution of different phases. The rapidly solidified Zr3Al alloy showed the presence of an amorphous phase or of a spinodally decomposed microstructure depending upon the severity of quenching, whereas the microstructure of the Zr3Al–3Nb and the Zr3Al–10Nb alloys exhibited a distribution of cuboidal particles (D88 phase) in the β matrix. Ageing of these alloys showed the formation of several metastable phases prior to the formation of equilibrium phase. The transformation sequence was found to involve a gradual filling of the open structure into a close packed configuration without reconstruction of the lattice.