INVESTIGATION ON COARSENING BEHAVIORS OF SERRATED GRAIN BOUNDARIES IN K480 NICKEL BASE SUPERALLOY DURING LONG TERM AGING AT 900 ℃
Received date: 2012-07-17
Revised date: 2012-09-27
Online published: 2013-01-11
Serrated grain boundaries in conventional cast nickel base superalloys can enhance high temperature mechanical properties of the alloy due to a large number of precipitates arranged in grain boundaries, which effectively inhibited the movement of dislocations. During service at elevated temperatures, the ripening, coalescence or degeneration process may occur in these precipitates, resulting in the coarsening of grain boundaries with time. This paper aims to investigate the coarsening kinetics and microstructure evolution of serrated grain boundaries in a conventional nickel base superalloy during long term aging. After solution and aging heat treatment, a long term aging treatment at 900 ℃ for 3000 h was carried out on a cast K480 nickel base superalloy. The microstructure of grain boundaries (GBs) was observed using OM and SEM respectively, and phase composition was measured using EDS. The results showed that the GBs of K480 alloy were the irregular serrated GBs composed of carbide GBs andγ’ GBs respectively, both of which coarsened with aging time. During the course of aging, the MC carbides in the carbide GB were decomposed with the formation of new phases of M6C carbide andη phase; the discontinuous large-sizedγ’ particles in the γ’ GB were coalesced with each other along the GB direction with aging time andγ’ bands formed after aging treatment.The coarsening ratio of the carbide GB was higher than that ofγ’ GB at the beginning of aging treatment and the difference in these two values became larger with increase in aging time. A Johnson-Mehl-Avrami-Kolmogorov (JMAK) type of function was employed to quantify the evolution of coarsening behaviors of the two kinds of GBs with aging time. The good agreement between calculated results and experimental data indicated that the coarsening behaviors of carbide GB andγ’ GB in the serrated GB were evolved as a JMAK type of function of aging time in K480 nickel base superalloy long term aged at 900 ℃.
ZENG Qiang , YAN Ping , SHAO Chong , ZHAO Jingchen , HAN Fengkui , ZHANG Longfei . INVESTIGATION ON COARSENING BEHAVIORS OF SERRATED GRAIN BOUNDARIES IN K480 NICKEL BASE SUPERALLOY DURING LONG TERM AGING AT 900 ℃[J]. Acta Metall Sin, 2013 , 49(1) : 63 -70 . DOI: 10.3724/SP.J.1037.2012.00428
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