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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.
The effect of MC decomposition mechanism and its decomposition on the microstructure evolution of the primary MC carbide during the long-term aging at 800, 850 and 900 ℃ for up to 104h was investigated. The results show that the primary growth of the DZ444 alloy MC carbides have lower thermal stability. In the long-term aging process, MC decomposition is aggravating; at the same time, the products in the decomposition area of MC continue to change, resulting in the typical sandwich microstructure at the initial stage of MC decomposition, The h phase appears in the middle stage and a certain amount of h-M6C and h- M23C are precipitated at the end of MC decomposition. The decomposition process of MC can be described as 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, where the type of secondary carbide is predominantly M23C6, Aging temperature and aging time, the content of secondary M6C slightly increased.The decomposition of MC could promote the precipitation of intragranular M23C6, the precipitation of s phase and the coarsening of grain boundary.