Yttrium effect on the structural-phase state in situ of Mo – 15.3 V – 10.5 Si composite

The effect of yttrium on the structural-phase state of the Mo – 15.3 V – 10.5 Si hypereutectic alloy has been investigated using X-ray phase analysis and scanning electron microscopy with energy-dispersive X-ray analysis. It has been established that the main phases of Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys obtained under nonequilibrium crystallization are the metal solid solution (Mo1 – xVx)ss-matrix, silicide solid solution (Mo1 – xVx)3Si and silicide Y5Si3. In alloys doped with yttrium up to 1.0 at. %, the space between the dendrites of the (Mo1 – xVx)ss metal phase is filled with (Mo1 – xVx)3Si solid solution, and Y5Si3 is located at the boundaries of the metal solid solution. At a concentration of yttrium in alloys above 3.0 at. % the space between (Mo1 – xVx)ss dendrites is filled with Y5Si3 silicide, inside which (Mo1 – xVx)3Si grains are formed. Triple or quaternary compounds containing yttrium were not detected. Elemental composition of alloy phases of the Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys is almost identical and is characterized by non-stoichiometry with respect to silicon. According to well-known literature data, the silicon contents in the (Mo1 – xVx)ss and (Mo1 – xVx)3Si phases are within the acceptable limits of the homogeneity region, and the silicon concentration in Y5Si3 (≈ 35.4 at.%) is beyond the established limits. Doping of the Mo – 15.3 V – 10.5 Si alloy with yttrium increases the dispersion of the structure. Particles of the main structural components become close in size. Wherein the volume ratio of the metallic phase to the silicide with increasing yttrium content in the alloys increases. The density of alloys varies between 8.7 – 9.0 g/cm3.