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.