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

Abstract

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.