Experimental Study of the Phase Equilibria in the R-Al-Si Ternary Systems (R: Rare Earth Element) the Ho-Al-Si Isothermal Section at 500˚C

The effect of holmium addition to the Al-Si system has been experimentally studied, as the isothermal section at 500˚C. The constitution of the alloys has been determined by means of scanning electron microscopy (SEM), electron microprobe analysis (EDXS) and X-ray powder diffraction. The knowledge of the phase relationships in the R-Al-Si ternary systems (R: rare earths element) is essential to deeply understand the technological properties of the Al-Si based alloys, that are useful in different industrial fields. In the system investigated have been identify nineteen ternary fields and twelve two phase fields. Three ternary compounds have been found in this ternary section: τ2-Ho2Al3Si2 (mS14-Y2Al3Si2), τ4-Ho2AlSi2 (oI10-W2CoB2) and τ5-Ho6Al3Si (tI80-Tb6Al3Si). The results obtained can be useful compared with the other known R-Al-Si systems also for predictive purposes.