The Gd–Ni–Al system: Phases formation and isothermal sections at 500 °C and 800 °C

Phase relations in the Gd–Ni–Al ternary system have been established for two isothermal sections (500 and 800 °C) based on X-ray powder diffraction analysis (XRD), Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) coupled with Energy dispersive Microprobe Analysis (EPMA) on about 31 annealed alloys in the 50–100 at.% Al region. Seven intermetallic phases have been identified in samples annealed at 500 °C and 800 °C: Gd3Ni5Al19 (oS108–Gd3Ni5Al19), Gd4Ni6Al23 (mS66–Y4Ni6Al23), GdNiAl4 (oS24–YNiAl4), GdNiAl3 (oP20–YNiAl3), Gd3Ni7Al14 (hP72–Gd3Ni7Al14), GdNiAl2 (oS16–CuMgAl2) and GdNi2Al3 (hP18–GdNi2Al3). One additional ternary phase GdNi3Al9 (hR78–ErNi3Al9) has been found only in samples annealed at 800 °C. The isothermal sections have been determined and then compared, the crystal structures of the ternary phases have been confirmed and lattice parameters calculated.