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Title: Metastable solidification of hypereutectic Co 2Si-CoSi composition: Microstructural studies and in-situ observations

Metastable solidification of undercooled Co 60Si 40 melts was investigated by microstructural studies and in-situ high-energy X-ray diffraction. Five solidification paths were identified. Three of them were observed at low undercoolings, which show uncoupled and coupled growth of stable β-Co 2Si and CoSi compounds. The other paths were observed at high undercoolings, which show peritectic and primary crystallization of a metastable Co 5Si 3 compound. The β-Co 2Si and Co 5Si 3 compounds crystallize into a hexagonal crystal structure and experience solid-state decomposition. Microstructure formation depends on solidification path. The coupled and uncoupled growth of the stable compounds produces a regular lamellar eutectic structure and an anomalous eutectic structure, respectively. The crystallization and solid-state decomposition of the metastable Co 5Si 3 compound brings about a fine-grained two-phase mixture, which represents another type of anomalous eutectic structure. Here, the results provide proof of two rare mechanisms of anomalous eutectic formation and shed light onto metastable phase relations in the undercooled region of the Co-Si system.
Authors:
 [1] ; ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Northeastern Univ., Shenyang (China)
  2. Institut fur Materialphysik im Weltraum, Koln (Germany)
  3. (Chih-Pin) [Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
  5. Tufts Univ., Medford, MA (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 142; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Scientific User Facilities Division; National Science Foundation (NSF); National Natural Science Foundation of China (NNSFC)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Co-Si system; Metastable phases; Microstructure formation; Undercooling; X-ray diffraction
OSTI Identifier:
1406109