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

摘要

The solidification behavior in the Mo-rich portionof the Mo-Si-B ternary system has been examined based on themicrostructures of arc-cast alloys. Several solidificationcharacteristics in the Mo-rich portion of the system have beenidentified using XRD, SEM and TEM. The liquidus projection inthe Mo-rich portion includes six primary solidification reactions;five reactions origination from the Mo-Si and Mo-B binarysections (Mo, Mo_2B, #beta#MoB, Mo_3Si and Mo_5Si_3) andone from the ternary-based (Mo_5SiB_2) T_2 phase. Theliquidus surface in general descends from the high meltingtemperature Mo-B binary side to the lower melting temperatureMo-Si binary side. The solidification path of alloys withcompositions in the T_2 phase region is always preceded by theperitectic reaction of #beta#MoB + L =>T_2. In addition, fourClass II reactions (four-phase reactions) and one Class I reaction(invariant ternary eutectic reaction) have been identified. Theextent of solidification segregation in alloys with compositionsin the Mo(ss) + T_2 two-phase field is discussed as it pertains tomaterials processing.