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

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: τ1∼Ho3(CuxAl1−x)11 (0.12≤x≤0.185, oI28-La3Al11), τ2-Ho(CuxAl1−x)3 (0.215≤x≤0.41, hR36-PuNi3), τ3-Ho(CuxAl1−x)2 (0.43≤x≤0.615, hP9-Fe2P), τ4-Ho(CuxAl1−x)12 (0.36≤x≤0.55, tI26 ThMn12-type), τ5-Ho2(CuxAl1−x)17 (0.42≤x≤0.69, hR57 Th2Zn17-type), τ6-Ho(CuxAl1−x)5 (0.45≤x≤0.815, hP6 CaCu5-type), τ7-Ho6Cu15.4Al7.6 (cF116-Th6Mn23), τ8-Ho(CuxAl1−x)6 (0.805≤x≤0.83, tI14-YbMo2Al4). 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.