S. P. Degtyareva, T. V. Prokhorova, D. A. Safronov
{"title":"Studies of the Thermal Fatigue of Superalloys to Obtain Data to Calculate the Life of Parts","authors":"S. P. Degtyareva, T. V. Prokhorova, D. A. Safronov","doi":"10.1134/s0036029523700313","DOIUrl":null,"url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">\n<b>Abstract</b>—</h3><p>The reported results of studying the thermal fatigue of superalloys by the Coffin method are analyzed after varying the plastic deformation in a cycle ε<sub>pl</sub> by changing the constraint stiffness of free thermal deformation ε<sub>0</sub>, which induces elastoplastic deformation Δε = ε<sub>el</sub> + ε<sub>pl</sub> 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 ε<sub>pl</sub> is absent, and elastic deformation ε<sub>el</sub> completely compensates the entire constraint part of ε<sub>0</sub>. In these tests, fracture cannot be considered as a result of thermal fatigue, since, according to the Coffin law, the existence of ε<sub>pl</sub> is a necessary condition for it. In tests with full constraint ε<sub>0</sub> and Δε = ε<sub>0</sub> = 1.3% in both half-cycles, plastic deformation occurs, and the measured maximum compression stresses σ<sub>comp</sub> and tensile stresses σ<sub>t</sub> correspond to the values of the yield strength achieved in the temperature ranges of heating and cooling after removing ε<sub>el</sub> of the preceding half-cycle. In tests with partial constraint of ε<sub>0</sub> (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 σ<sub>comp</sub> and σ<sub>t</sub> are substantially lower than yield strength σ<sub>y</sub>. The observed results and the existence of ε<sub>pl</sub> 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 <i>N</i><sub>f</sub> on ε<sub>pl</sub> 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 <i>N</i><sub>f</sub> on ε<sub>pl</sub> obtained before in identical tests on the same equipment needs a verification for many superalloys.</p>","PeriodicalId":769,"journal":{"name":"Russian Metallurgy (Metally)","volume":null,"pages":null},"PeriodicalIF":0.4000,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Russian Metallurgy (Metally)","FirstCategoryId":"5","ListUrlMain":"https://doi.org/10.1134/s0036029523700313","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"METALLURGY & METALLURGICAL ENGINEERING","Score":null,"Total":0}
引用次数: 0
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.
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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