Materials Transactions Online

Materials Transactions, Vol.51 No.09 (2010) pp.1699-1704
© 2010 The Japan Institute of Metals

Phase Formation and Solidification Routes Near Mo-Mo5SiB2 Eutectic Point in Mo-Si-B System

Seong-Ho Ha1, Kyosuke Yoshimi1, Kouichi Maruyama1, Rong Tu2 and Takashi Goto2

1Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan
2Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

The phase formation behavior during solidification in the Mo-Si-B system was experimentally examined around the triple junction point (T) of the Mo solid solution (Moss), Mo5SiB2 (T2) and Mo2B primary phases in the Mo-Si-B liquidus projection suggested by Yang and Chang through thermodynamic calculations, and the solidification routes of the Mo-Si-B alloys were reconsidered based on the obtained results. Alloys of four different compositions around the T point were produced by arc-melting. The primary phases observed in these alloys were in excellent agreement with the liquidus projection proposed by Yang and Chang. The solidification routes were basically Moss (primary) → Moss + Mo2B → Moss + T2 eutectic → Moss + T2 + Mo3Si (A15), T2 (primary) → Moss + T2 eutectic → Moss + T2 + A15, or Mo2B (primary) → Moss + T2 eutectic → Moss + T2 + A15, depending on the composition. However, a quantitative EPMA analysis indicated the compositions of the Moss-T2 eutectic and Moss + T2 + A15 phases differed from the reported liquidus projection. This is due to the difficulties interpreting the unusual solidification routes in the Mo-Si-B system and their as-cast microstructures.

(Received 2010/4/30; Accepted 2010/7/6; Published 2010/8/19)

Keywords: molybdenum-silicon-boron system, liquidus projection, eutectic, quantitative analysis, calibration

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