定向凝固DZ444镍基高温合金初生MC碳化物的分解行为  

THE DECOMPOSITION BEHAVIOR OF PRIMARY MC CARBIDE IN NICKEL BASE DIRECTIONALLY SOLIDIFIED SUPERALLOY DZ444

作　　者：肖旋[1] 曾超[1,2] 侯介山[2] 秦学智[2] 郭建亭[2] 周兰章[2] 

机构地区：[1]沈阳理工大学材料科学与工程学院,沈阳110159 [2]中国科学院金属研究所,沈阳110016

出　　处：《金属学报》2014年第9期1031-1038,共8页Acta Metallurgica Sinica

基　　金：国家自然科学基金资助项目51001101~~

摘　　要：研究了定向凝固镍基高温合金DZ444在800,850和900℃下最长达104h长期时效过程中初生MC碳化物的热稳定性、MC分解机制及其分解对组织演化的影响.结果表明:DZ444合金初生MC碳化物的热稳定性较低.在长期时效过程中,MC分解不断加剧;同时,MC分解区域内产物不断发生变化,在MC分解初期产生了典型的SM结构(sandwich microstructure),在MC分解中期出现了h相,在MC分解末期析出一定量的h-M6C和h-M23C6.MC分解过程可以大体地描述为:MC+g→SM-M23C6+SM-M6C+SM-g'→SM-M23C6+SM-M6C+SM-g'+h→SM-M23C6+SM-M6C+SM-g'+h+h-M6C+h-M23C6,其中二次碳化物的类型主要为M23C6,且随着时效温度的升高和时效时间的延长,二次M6C含量略有增加.MC的分解能够促进晶内M23C6沉淀、s相析出和晶界粗化.Hot-corrosion directionally solidified Nickel base superalloy DZ444 is generally used as the candidate material for blade of gas turbine, which required excellent alloy microstructural stability. As one of the consti- tutional phase of the alloy, primary MC carbides are often thermally unstable, and its degradation reactions can happen when the alloys are in services or thermally exposed in high temperature circumstances. There existed several different kinds of MC decompostion reactions in some traditional Ni-based superalloys. To figure out the thermal stability of primary MC carbide in the DZ444 alloy and better understand its degradation mechanism, some related discussions to the thermal stability and degeneration process of primary MC carbide and its effects on the micro- structure were made. In this work, microstructures of DZ444 alloy after long-term exposure up to 1 ×10^4 h at 800, 850 and 900 ℃ have been observed by OM, SEM and TEM. The results show that the thermal stability of MC was low. As long-term exposure proceeds, MC decompostion became more and more serious. Firstly, a typical sand- wich microstructure （SM） gradually formed and thickened in the MC/γ, interface; secondly, 17 phase precipitated in the SM/MC interface; lastly,η-M_6C and η-M_23C_6 locally precipitated inside the 77 phase. Finally, SM structure, 7/ phase,η-M_6C and η-M_23C_6 successively formed in MC degeneration areas at three stages of its decomposition pro- cess. Basically, MC decompostion process could be described with such raction formula as follows： MC＋γ→SM- M_23C_6＋ SM-M_6C ＋ SM-γ＇→SM-M_23C_6＋ SM-M_6C ＋ SM- γ ＇＋η→ SM-M_23C_6＋ SM-M_6C ＋ SM- γ＇＋ η＋η-M_6C ＋ η-M_23C_6. Gener- ally, the type of secondary carbide from MC degeneration was M_23C_6, and, with the increase of long-term exposure temperature and time, the amount of secondary M6C carbide slightly increased. Besides, MC degeneration might re- sult in the precipitation of transgranular M23C6 carbide and cr phase in the

关 键 词：定向凝固高温合金 初生MC碳化物 分解机制 显微组织 

分 类 号：TG141[一般工业技术—材料科学与工程]