中文摘要：

采用TEM和SEM研究了C276镍基高温合金在700℃长期时效过程中的组织变化，利用万能高温材料试验机研究时效后合金试样700℃高温力学性能，并利用SEM对拉伸断口进行形貌分析．结果表明，700℃长期时效后，C276合金在晶界和晶内析出大量块状μ相和M6C碳化物，且随时效时间的延长，块状析出相长大，晶界处的析出相向晶内呈针状生长．析出相对合金有一定的强化效果，高温长期时效，合金强度不会降低．合金的塑性随时效时间的延长先降低后增加，在时效720h达到峰值后又随着时间延长而降低，但在较长时效时间内合金保持较好的塑性．高温长期时效的C276合金高温拉伸断裂方式为韧性断裂．

英文摘要：

Nickel-based superalloy C276 had become one of the alternative materials in simulation loop of thorium molten salt reactor （TMSR） nuclear power system. The strength and plasticity decay of C276 alloy under high temperature environment for long time will directly threatened the security of simulation loop of TMSR. The microstructure of C276 alloy after long-term aging at 700℃ was studied by TEM and SEM with EDS, and the high temperature mechanical performance of C276 alloy after aging was researched at 700 ℃ with an universal high temperature materials testing machine. At the same time, the morphology of tensile fracture was analyzed by SEM. The results show that massive block μ phase and M6C carbides are precipitated after long-term aging with 700℃ at the grain boundaries and within grains of C276 alloy, and the block precipitated phase grains grow up with aging time, some precipitated grains at boundaries extend forward the interior of based crystal. The alloy is strengthened by the effect of precipitation phase, so the strength is not reduced after long-term aging at 700℃ high temperature. As aging time increases, the plasticity of C276 alloy reduces firstly and then increases to the peak after aging 720 h, and decreases again. However, the plasticity of C276 alloy still maintain well after longer aging time. The high temperature tensile fracture mode of C276 alloy is ductile fracture after long term aging.