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采用真空冶炼和定向凝固工艺制备一种具有优异抗腐蚀性能的镍基高温合金,并利用光学显微镜、扫描电镜和透射电镜研究合金的微观组织,分析合金在不同温度下的拉伸性能。结果表明,除γ′颗粒和γ基体外,在合金晶界上析出了一些MC碳化物、M3B2硼化物和Ni5Hf相。合金拉伸性能对温度有很强的依赖性,并呈现明显的的反常屈服和中温脆性行为。在650°C以下,合金的屈服强度随着温度的升高而略微降低,但抗拉强度几乎没有变化。当温度在650°C和750°C之间时,合金的屈服、抗拉强度快速升高,但拉伸塑性显著降低,并在700°C时达到最低值。当温度进一步升高时,合金的屈服、抗拉强度逐渐降低,塑性升高。透射电镜观察发现,在低温条件下,位错切割γ′是主要的变形机制;在高温条件下,位错绕过γ′是主要的变形机制;由位错切割γ′转变至位错绕过γ′的温度约为800°C。合金的反常屈服和中温脆性行为主要归因于合金中高的γ′含量。此外,碳化物和共晶组织对合金的中温脆性行为也有影响。
A nickel base superalloy with excellent corrosion resistance was prepared by vacuum smelting and directional solidification process. The microstructure of the alloy was studied by optical microscope, scanning electron microscope and transmission electron microscope. The tensile properties of the alloy at different temperatures were analyzed. The results show that some MC carbides, M3B2 borides and Ni5Hf phases are precipitated on the grain boundaries of the alloys except γ ’particles and γ matrix. Tensile properties of the alloy has a strong dependence on temperature, and showed obvious abnormal yield and brittleness behavior at medium temperature. Below 650 ° C, the yield strength of the alloy slightly decreases with increasing temperature, but the tensile strength shows little change. At temperatures between 650 ° C and 750 ° C, the yield strength and the tensile strength of the alloy increase rapidly, but the tensile ductility is significantly reduced and reaches a minimum at 700 ° C. When the temperature is further increased, the alloy yield, tensile strength gradually decreased, plasticity increased. Transmission electron microscopy revealed that dislocation-cutting γ ’was the main deformation mechanism at low temperature. At high temperature, dislocation around γ’ was the main deformation mechanism. From dislocation cutting γ ’to dislocation bypassing The temperature of γ ’is about 800 ° C. Abnormal alloy yield and brittleness at medium temperature brittle behavior is mainly due to high γ ’alloy content. In addition, carbides and eutectic microstructure also affect the brittleness of the alloy.