摘要:
本文针对不同微结构特征镍基单晶高温合金开展了一系列SHTB试验，系统研究了沉淀相体积分数、相粗化程度、加载速率和加载角度等因素对合金动态拉伸性能的影响。结果表明，微结构和加载速率对镍基单晶高温合金动态拉伸性能具有显著影响，且拉伸性能呈现出复杂的各向异性特征。总体而言，合金屈服强度和抗拉强度呈正相关关系，随着沉淀颗粒体积分数或加载速率增大，试件逐渐表现出脆性断裂特征，且其屈服强度和抗拉强度逐渐增大，而断后伸长率则逐渐减小；再者，时效处理所导致的颗粒相粗化对合金强度有着明显的弱化作用，而对断后伸长率起到强化效果；此外，合金强度和断后伸长率随着加载角度增加皆呈现出下降趋势，然而在加载速率较高时，对于体积分数和相粗化程度均较大的合金，其断后伸长率随加载角度增加而增大，并在55°加载角度时取得最大值。相关变化同断口纤维区面积和解理面特征密切相关，材料微结构和加载条件的改变将影响材料内部微裂纹形核和运动特性，进而影响试件变形特征和动态拉伸性能。本研究可为提高镍基单晶高温合金性能和优化热端部件结构设计提供理论指导和数据支撑。
Abstract:
A serious SHTB tests and related SEM characterization were conducted regarding to Ni-based single crystal superalloys with various microstructures, and the influences different factors, including volume fraction of precipitation particles, phase coarsening, loading angle and loading rate, etc., on the dynamic tensile properties of superalloys were investigated systematically, then the relationships between these factors and fracture morphology of alloys were explored in detail. The results indicated that the microstructure features and loading rate have significant effect on the dynamic tensile properties of Ni-based single crystal superalloys, and complex anisotropic characteristics occur in the dynamic tensile properties after phase coarsening. In general, the yielding strength displays a positive relationship with the tensile strength. Along with the volume fraction of precipitation particles or the loading rate increases, the alloy specimen gradually exhibits a brittle fracture characteristic, with an increase in strength and a decrease in elongation. Besides, phase coarsening derived from aging treatment significantly weakens the strength of alloys while enhances their elongation, i.e., the specimens progressively show mixed fracture characteristics after phase coarsening, and both the yielding strength and the tensile strength gradually decrease while the elongation increases along with the degree of phase coarsening. Furthermore, the strength and the elongation of alloys usually decrease along with the increase of loading angle, however, for the alloys with high volume fraction of precipitation particle and high degree of phase coarsening, the elongation gradually increases along with the loading angle in the condition of high loading rate, achieving maximum value at the loading angle of 55°. The corresponding variation characteristics are firmly related to the fibrous zone and the cleavage plane on the fracture surface; meanwhile, the variations in material microstructure and loading conditions will affect the microcrack nucleation and fracture mode within the specimen, leading to various dynamic tensile properties in Ni-based single crystal superalloys. The present research and related results can provide theoretical guidance and data support for improving the mechanical performance of Ni-based single crystal superalloys and optimizing the structure of hot-end components.
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