The isothermal section at 500 °C of the Al–Cu–Ho ternary system

Abstract The Ho–Al–Cu isothermal section at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, optical and scanning electron microscopy and electron probe microanalysis. The following ternary phases have been identified or confirmed: τ 1 ∼Ho 3 (Cu x Al 1− x ) 11 (0.12≤ x ≤0.185, oI28–La 3 Al 11 ), τ 2 -Ho(Cu x Al 1− x ) 3 (0.215≤ x ≤0.41, hR36–PuNi 3 ), τ 3 -Ho(Cu x Al 1− x ) 2 (0.43≤ x ≤0.615, hP9–Fe 2 P), τ 4 -Ho(Cu x Al 1− x ) 12 (0.36≤ x ≤0.55, tI26 ThMn 12 -type), τ 5 -Ho 2 (Cu x Al 1− x ) 17 (0.42≤ x ≤0.69, hR57 Th 2 Zn 17 -type), τ 6 -Ho(Cu x Al 1− x ) 5 (0.45≤ x ≤0.815, hP6 CaCu 5 -type), τ 7 -Ho 6 Cu 15.4 Al 7.6 (cF116–Th 6 Mn 23 ), τ 8 -Ho(Cu x Al 1− x ) 6 (0.805≤ x ≤0.83, tI14–YbMo 2 Al 4 ). The phase equilibria resulting from the large number of binary and ternary compounds were determined. The general characteristics of the section have been discussed in comparison with those of other R–Al–Cu systems.