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Vol.5 No.2 previous AA 68-SP10(69-70-71)-NT 58 -59

Academic Articles
Regular Paper(Invited) Vol.5 No.3 (2013) p.165 - p.174
 

Relationship between Duplex Grain Structure and Grain-boundary Precipitates in Ni2M-stabilized Alloy

 
Toshiaki HORIUCHI1* and Naohiro SATOH1
 
1Hokkaido Institute of Technology, 7-15-4-1, Maeda, Teine-ku, Sapporo, Hokkaido 006-8585, Japan
 
Abstract
An experimental characterization of grain boundaries using field-emission Auger electron spectroscopy has been carried out for Ni2M-stabilized alloy (where M mainly corresponds to Cr) and Alloy 690, which have duplex and non-duplex grain sizes, respectively, in order to determine the relationship between grain-boundary precipitates and the grain structure. Thermodynamic calculations based on the Scheil-Gulliver model with and without back diffusion of the C solute in the solid phase were also performed in order to investigate the solidification process in both alloys. Chromium carbide precipitates, with a predicted composition of M23C6, were observed at grain boundaries in both the Ni2M-stabilized alloy and Alloy 690. The M23C6 precipitates in the Ni2M-stabilized alloy wer considerably coarser than those in the Alloy 690. A small number of coarse titanium carbonitride precipitates were also observed on the fracture surfaces of both alloys at intergranular and intragranular positions. The simulations predicted that the M23C6 precipitates are likely to be formed during the final stages of solidification, and it is thought that this occurs more readily in the Ni2M-stabilized alloy. The results indicate that the duplex grain structure observed in the Ni2M-stabilized alloy is most likely due to the presence of undissolved coarse M23C6 grain-boundary precipitates.
 
Keywords
Ni2M-stabilized alloy, Alloy 690, bimodal grain size distribution, M23C6 carbide, Scheil-Gulliver model, phase stability, thermodynamic calculation, Thermo-Calc, stress corrosion cracking
 
Full Paper: PDF EJAM Vol.5No.3 pp.165-174 "Relationship between Duplex Grain Structure and Grain-boundary Precipitates in Ni2M-stabilized Alloy"
















Article Information
Article history:
Received 30 June 2013
Accepted 2 October 2013