Ordering transformations in the M3Si refractory metal silicides

The metal-rich sides of the equilibrium phase diagrams of refractory metal(M)-Si systems, where M = Zr, Nb or Mo share many features with each other. All the three M-Si systems show the formation of line compounds of the M{sub 3}Si type, by a peritectic reaction at higher temperatures (1,650 to 2,025 C), followed by eutectic transformation at lower temperatures (1,570 to 2,020 C), and resulting in the formation [M(Si) + M{sub 3}Si] eutectic mixtures in the cases below the eutectic temperatures M{sub 5}Si{sub 3} in the case of Mo-Si system. Recent investigations have shown that the Nb{sub 3}Si phase present in the Nb-10 at.% Si alloy undergoes ordering transformations. The study of phase stability of the M{sub 3}Si type compounds is important, since these compounds are being considered as matrix materials for high temperature in situ composites. This paper reports that Zr{sub 3}Si phase also undergo similar transformation. However, this type of ordering transformation was absent in the Mo{sub 3}Si phase in the Mo-25 at.% Si alloys.