Experimental determination of phase equilibria in the system Fe–Zr (0–100 at.% Zr) by using the “spot” technique, DSC, and XRD

Abstract

The phase equilibria in the binary alloy system Fe–Zr were experimentally determined by using the thermo-optometric technique viz., the spot technique, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and SEM along with EDX. Liquidus temperature of alloys pertaining to the composition 0 to 100 at.% Zr was measured in the temperature range 1273–2273 K by using the spot technique. All the other invariant equilibria have also been re-established. The temperature pertaining to the congruent melting C15–Fe2Zr ↔ L was measured to be 1944 ± 6 K. The temperatures pertaining to the Fe and Zr-rich eutectic transformations L ↔ γ-Fe + C36–Fe2Zr and L ↔ FeZr2 + β-Zr were re-determined to be 1571 ± 2 and 1244 ± 3 K, respectively. The temperatures pertaining to peritectic transformations L + C15–Fe2Zr ↔ C36–Fe2Zr and L + C15–Fe2Zr ↔ FeZr2 were determined to be 1623 ± 3 K and 1250 ± 3 K respectively. The temperature pertaining to the catatectic reaction δ-Fe ↔ γ-Fe + L was re-determined to be 1637 ± 3 K. All these phases were characterized by using XRD. Microstructures of the alloy samples were analyzed by using SEM along with EDX. The experimental liquidus data obtained were found to be in good agreement with the values obtained by interpolating the phase boundaries suggested in a recent thermodynamic assessment. All the liquidus measurements have been carried out in homemade Y2O3 crucibles. The composition of Fe–Zr alloys was measured by both gravimetric and spectrophotometry techniques and the measured uncertainty in the composition was estimated to be maximum ±1 at.% Zr. The experimental data presented in this paper are more reliable and accurate and supersede the values reported in the literature. The liquidus curve in the composition range from 33.3 to 67 at.% Zr has been established experimentally for the first time by using the spot technique.