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+→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.

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