Phase separation tendency in the as solidified Zr₃Al-Nb alloys studied by microstructural observations and thermodynamic analysis

The formation of Zr₃Al involves one eutectic (L→β + Zr₅Al₃; at temperature (T_e) =1623 K) and two peritectoid (β + Zr₅Al₃→Z₂Al; at temperature (T_p1) =1523 K and β + Zr₂Al→Zr₃Al; (T_p2) = 1248 K) reactions. Recent investigations have shown that in Zr-Al-Nb alloys, Al does not act as an effective α stabilizer but remains in the β-Zr phase in a condition of supersaturation. In alloys containing relatively low concentrations of Nb, (e.g., Zr₃Al_-3Nb) the formation of an ordered β phase or of a supersaturated β phase with a Zr₂(Al,Nb) phase could be expected. In the present work microstructural investigations have been carried out on the as solidified Zr₃Al-Nb alloys (Zr₃Al, Zr₃Al-3Nb and Zr₃Al-10Nb alloys). Chemical composition of the different phases encountered in the present study have been determined by using a wavelength dispersive spectroscopy (WDS) attachment of an electron probe microanalysis (EPMA) and an energy dispersive spectroscopy (EDS) an attachment of a transmission electron microscope