Liquidus projection for the Mo-rich portion of the Mo–Si–B ternary system

The solidification behavior in the Mo-rich portion of the Mo–Si–B ternary system has been examined based on the microstructures of arc-cast alloys. Several solidification characteristics in the Mo-rich portion of the system have been identified using XRD, SEM and TEM. The liquidus projection in the Mo-rich portion includes six primary solidification reactions; five reactions originating from the Mo–Si and Mo–B binary sections (Mo, Mo2B, βMoB, Mo3Si and Mo5Si3) and one from the ternary-based (Mo5SiB2) T2 phase. The liquidus surface in general descends from the high melting temperature Mo–B binary side to the lower melting temperature Mo–Si binary side. The solidification path of alloys with compositions in the T2 phase region is always preceded by the peritectic reaction of βMoB+L⇒T2. In addition, four Class II reactions (four-phase reactions) and one Class I reaction (invariant ternary eutectic reaction) have been identified. The extent of solidification segregation in alloys with compositions in the Mo(ss)+T2 two-phase field is discussed as it pertains to materials processing.