Studies of the Thermal Fatigue of Superalloys to Obtain Data to Calculate the Life of Parts

IF 0.4 Q4 METALLURGY & METALLURGICAL ENGINEERING
S. P. Degtyareva, T. V. Prokhorova, D. A. Safronov
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Abstract

The reported results of studying the thermal fatigue of superalloys by the Coffin method are analyzed after varying the plastic deformation in a cycle εpl by changing the constraint stiffness of free thermal deformation ε0, which induces elastoplastic deformation Δε = εel + εpl in half-cycles equal to 0.6, 1.0, and 1.3%, according to the results of testing a ZhS6F superalloy. It is found that, in tests with Δε = 0.6%, plastic deformation εpl is absent, and elastic deformation εel completely compensates the entire constraint part of ε0. In these tests, fracture cannot be considered as a result of thermal fatigue, since, according to the Coffin law, the existence of εpl is a necessary condition for it. In tests with full constraint ε0 and Δε = ε0 = 1.3% in both half-cycles, plastic deformation occurs, and the measured maximum compression stresses σcomp and tensile stresses σt correspond to the values of the yield strength achieved in the temperature ranges of heating and cooling after removing εel of the preceding half-cycle. In tests with partial constraint of ε0 (when Δε = 1.0%), the situation is ambiguous. In this case, the change in Δε with temperature includes plastic deformation, as TC maps show. However, the measured values of stresses σcomp and σt are substantially lower than yield strength σy. The observed results and the existence of εpl cannot be explained because of the absence of required data. The results of the analysis carried out in this work show that the construction of the dependence of life Nf on εpl provided by the Coffin method using the data obtained in the tests considered above is impossible. Therefore, the reliability of numerous reference data on the dependence of Nf on εpl obtained before in identical tests on the same equipment needs a verification for many superalloys.

Abstract Image

Abstract Image

研究超耐热合金的热疲劳,获取计算零件寿命的数据
摘要-通过改变自由热变形的约束刚度 ε0,在等于 0.6%、1.0% 和 1.3% 的半周期内引起弹塑性变形 Δε = εel + εpl,从而改变周期内的塑性变形 εpl,分析了用 Coffin 方法研究超级合金热疲劳的报告结果。结果发现,在 Δε = 0.6% 的试验中,不存在塑性变形 εpl,弹性变形 εel 完全补偿了 ε0 的全部约束部分。在这些试验中,断裂不能视为热疲劳的结果,因为根据科芬定律,εpl 的存在是热疲劳的必要条件。在完全约束ε0 和两个半周期中的Δε = ε0 = 1.3% 的试验中,发生了塑性变形,测得的最大压缩应力 σcomp 和拉伸应力 σt 与去除前一个半周期的εel 后在加热和冷却温度范围内达到的屈服强度值一致。在部分限制ε0的试验中(当Δε = 1.0%时),情况是模糊的。在这种情况下,正如 TC 图所示,Δε 随温度的变化包括塑性变形。然而,应力 σcomp 和 σt 的测量值大大低于屈服强度 σy。由于缺乏所需的数据,无法解释观察到的结果和 εpl 的存在。这项工作的分析结果表明,利用上述试验获得的数据来构建 Coffin 方法提供的寿命 Nf 对 εpl 的依赖关系是不可能的。因此,以前在相同设备上进行的相同试验中获得的 Nf 与 εpl 关系的大量参考数据的可靠性需要对许多超合金进行验证。
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来源期刊
Russian Metallurgy (Metally)
Russian Metallurgy (Metally) METALLURGY & METALLURGICAL ENGINEERING-
CiteScore
0.70
自引率
25.00%
发文量
140
期刊介绍: Russian Metallurgy (Metally)  publishes results of original experimental and theoretical research in the form of reviews and regular articles devoted to topical problems of metallurgy, physical metallurgy, and treatment of ferrous, nonferrous, rare, and other metals and alloys, intermetallic compounds, and metallic composite materials. The journal focuses on physicochemical properties of metallurgical materials (ores, slags, matters, and melts of metals and alloys); physicochemical processes (thermodynamics and kinetics of pyrometallurgical, hydrometallurgical, electrochemical, and other processes); theoretical metallurgy; metal forming; thermoplastic and thermochemical treatment; computation and experimental determination of phase diagrams and thermokinetic diagrams; mechanisms and kinetics of phase transitions in metallic materials; relations between the chemical composition, phase and structural states of materials and their physicochemical and service properties; interaction between metallic materials and external media; and effects of radiation on these materials.
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