GH4169 合金圆盘时效过程残余应力的演化规律研究

GH4169 alloy, a precipitation-strengthened nickel-iron base superalloy, has been widely used in aerospace and energy industries due to its excellent high-temperature strength which derived from the coherent phases (γ″ and γ'). To form these precipitates, the manufacturing process of GH4169 usually involves solid solution heat treatment followed by rapid cooling and double ageing heat treatment. Significant residual stresses are induced during rapid cooling and then partially relieved during the subsequent ageing treatment. However, the reduced residual stress after ageing are still large enough to affect the final machining operations, resulting in the component exceeding the dimensional tolerances if they are not well considered. Furthermore, residual stresses in the final components may lead to further distortion beyond estimation during service, which could deteriorate the engine performances. In the present study, the evolution of residual stresses at heating, isothermal ageing, and air-cooling stages of ageing heat treatment in a GH4169 alloy disk was characterized by in situ neutron diffraction. Considering the effect of residual stresses on the precipitation behavior of γ″, two different types of stress-free samples were used as the basis for the stress analysis. The results show that significant residual stresses were induced during water quenching, which were found to be 340.62 MPa tensile in hoop/radial directions and 33.34 MPa compressive in axial direction in the center of the disk. Subsequently, an in situ ageing heat treatment was undertaken at 720℃ for 8 h. During the heating stage, the yield strength of the material decreases with increasing temperature, leading to residual stress relaxation through plastic deformation from 340.62 MPa to 227.67 MPa in hoop/radial direction in the disk center. At the isothermal ageing stage, residual stresses relieved apparently by about 40 MPa during the first 100 min, later on a slower linear relaxation remained for the rest of the ageing heat treatment. The strength of the alloy increased and the creep rate decreased due to the formation of γ″ and γ ' strengthening phases, indicating that most of stress relaxation occurred as a result of creep deformation at the early stage of isothermal ageing. The magnitude of residual stress was almost invariable in the subsequent air-cooling stage.