Effect of the Rare-Earth Addition (R = Ce, Sm) on the Phase Equilibria and Microstructure of Ni-Al Alloys

The peculiarities in the phase formation in the Al-rich region of the Ce-Ni-Al and Sm-Ni-Al ternary systems have been investigated by means of optical and scanning electron microscopy, electron probe microanalysis and x-ray powder diffraction (XRD) study. The following ternary phases have been identified: Ce4Ni6Al23 (τ1, mS66-Y4Ni6Al23), CeNiAl4 (τ3, oS24-YNiAl4), Sm3Ni5Al19 (τ2, oS108-Gd3Ni5Al19), Sm4Ni6Al23 (τ1, mS66-Y4Ni6Al23) and SmNiAl4 (τ3, oS24-YNiAl4). Moreover, a temperature of 622 °C ± 1 has been established for the ternary eutectic reaction L ↔ (Al) + NiAl3 + αCe3Al11 using a differential scanning calorimeter (DSC). The general characteristics of the sections are discussed in comparison with those of other R-Ni-Al systems (R = rare earths).