| 研究実績の概要 |
Microstructures of several rare-earth (RE)-containing Mg alloys have been investigated systematically from micron-scale to atomic scale using electron microscopy. The major results focusing on unique long-period stacking/order (LPSO) atructures are summarized as follows.
1) Short-range order (SRO) solute clusters in the LPSO phases with an intrinsic-I (I1) type stacking faults (SFs), which have been uniquely formed in Mg-Co-Y alloys, are investigated. The Co3Y5 SRO cluster model embedded across the I1-type SFs has been successfully constructed to satisfy the observed electron diffraction, STEM images and computed energetic stabilities. The optimized Co3Y5 cluster configurations appear to be significantly deviated from the host Mg atom positions and consequently provide a significant gain for the energetic stability of the I1-type LPSO phases.
2)In a MgHo2.0Cu0.4Zr0.1 alloy, it is found that 18R, 14H and 24R LPSO phases coexist with fully coherent interfaces along step-like composition gradient in a blocky intermetallic compound distributed at grain boundaries. Importantly, the estimated chemical compositions of solute-enriched stacking-fault (SESF) in all LPSO variants are almost identical with the ideal SESF composition of 9M in-plane order, regardless of the type of LPSO phases. The results support the viewpoint that the robust L12-type SRO TM6RE8 clusters play an important role in governing LPSO phase formation.
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