The isothermal section of the Al-Cr-Si system at 800 °C and the crystal structure of τ2 (Cr3Al9Si)

The system Al-Cr-Si at 800 °C is investigated using XRD and SEM/EDX on equilibrated alloys. Three ternary phases are found: τ1-Cr4Al13Si4 (F-43m, Cr4Al13Si4-type, a = 1.09270(2) nm), τ2-Cr3Al9Si (P63/mmc, Mn3Al9Si-type, a = 0.75346(3) nm, c = 0.78393(4) nm) and τ3-Cr4(Al,Si)11 (P-1, Mn4Al11-type, a = 0.51260(2) nm, b = 0.89802(4) nm, c = 0.50472(3) nm, α = 89.775(4)°, β = 100.711(4)° and γ = 106.605(3)° for Cr27Al63Si10). Extended homogeneity ranges for τ3 and several solid binary phases into the ternary are observed. The tie-lines between these phases are determined and the isothermal section at 800 °C over the entire composition range is presented.