Formation of less-known structurally complex ζb and orthorhombic quasicrystalline approximant εn on solidification of selected Al-Pd-Cr alloys

The evolution of phases was investigated on cooling of Al71Pd24Cr5, Al73Pd20Cr7, and Al73Pd23Cr4 alloys from 1350 °C down to ambient temperature with the rate of 10 °C·min− 1. To perform the investigation, differential thermal analysis, synchrotron X-ray powder diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used. In all the investigated alloys structurally complex phases εn (ε6 + ε28) and ζb, as well as the δ-phase were identified. Based on the results of differential thermal analysis, sequences of phase transformations were determined. The Al71Pd24Cr5 alloy started to solidify at 1031.4 °C through β. Primary dendrites of ζb were observed in Al73Pd20Cr7 and Al73Pd23Cr4 alloys. In the second step of solidification δ and/or ζb were formed. The peritectic reaction, liquid + ζb + δ → εn + ζb + δ, leading to the formation of the quasicrystalline approximant εn (ε6 + ε28) took place in the final step of solidification at approximately 792 °C.