以4种典型镍基高温合金(GH4169、GH4169D、GH4738、GH350)为研究对象，在600~780 ℃和260~510 MPa范围内对其进行应力松弛实验，并利用FESEM和TEM对应力松弛后的样品进行组织观察分析，系统研究了典型镍基高温合金服役条件下应力松弛的微观机制。结果表明，在应力松弛实验过程中应力在开始阶段快速下降后趋于稳定；合金的松弛稳定性随着温度的升高而降低。应力松弛实验中试样的形貌不发生明显改变，而TEM分析表明应力松弛的主要微观机制是位错的运动和析出相对位错运动的阻碍。合金中析出相的种类、尺寸、形态和分布影响了析出相对位错运动阻碍作用的大小，从而决定了合金的应力松弛性能。

Since nickel-based superalloys are more and more used as fasteners, it is necessary to investigate the stress relaxation behavior and mechanism of nickel-based superalloy. In present work, the stress relaxation mechanism for four typical nickel-based superalloys (GH4169, GH4169D, GH4738, GH350) for fasteners under service condition was investigated. The stress relaxation tests were carried out according to GB/T 10120-2013 in the temperature range of 600~780 ℃ and initial stress range of 260~510 MPa, and the stress relaxation curves were recorded. The microstructure was studied by FESEM and TEM. The results show that the stress decreases fast in the initial stage of stress relaxation test and then trends to be steady. The stress relaxation stability decreases with increasing temperature. There is no apparent change in the microstructure after stress relaxation test. TEM observation shows that the major mechanism of stress relaxation is the movement of dislocations, and the stress relaxation properties of different alloys depend on the inhibition of dislocation movement. The species, size, shape and distribution of phases determine the ability to hinder dislocation movement and the stress relaxation property of different alloys. GH4169 alloy gets the stress relaxation property mainly by γ' phase, γ'' phase and δ phase hindering the movement of dislocations. In GH4169D alloy, both γ' phase and η phase participate in the stress relaxation process. γ' phase in GH4738 alloy can effectively impede the movement of dislocations and provide good stress relaxation property. The combined effect of γ' phase and η phase guarantees the stress relaxation stability of GH350 alloy.