Author： Sundararaman M. Kumar Lalit Prasad G. Mukhopadhyay P. Banerjee S.
Publisher： Springer Publishing Company
ISSN： 1543-1940
Source： Metallurgical and Materials Transactions A, Vol.30, Iss.1, 1999-01, pp. : 41-52
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Abstract
The microstructure of Alloy 625, which has undergone prolonged (∼70,000 hours) service at temperatures close to but less than 600 °C, has been characterized by transmission electron microscopy. The precipitation of an intermetallic phase Ni2(Cr, Mo) with Pt2Mo-type structure has been observed in addition to that of the γ″ phase. Six variants of Ni2(Cr, Mo) precipitates have been found to occur in the austenite grains. These particles exhibit a snowflake-like morphology and are uniformly distributed in the matrix. They have been found to dissolve when the alloy is subjected to short heat treatments at 700 °C. The occurrence of the Ni2(Cr, Mo) phase has been discussed by taking the alloy chemistry into consideration. Apart from the intermetallic phases, the precipitation of a M6C-type carbide phase within the matrix and the formation of near continuous films, comprising discrete M6C/M23C6 carbide particles, at the austenite grain boundaries have been noticed in the alloy after prolonged service.
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