A method of correlating relaxation and creep performance

Abstract

The application provides a relaxation and creep performance correlation method, and belongs to the field of new materials and is used for developing new materials by testing related activities. First, a high-temperature relaxation test is carried out to obtain corresponding data of temperature-stress-creep relaxation rate. Second, a high-temperature creep test is carried out to obtain minimum creep rate data. Finally, the third step is data processing, and a correlation model is constructed. The application aims at the shortcomings of long data obtaining time and large sample consumption of existing creep performance data, and proposes to use the characteristics of short stress relaxation test, i.e., more creep information and less sample consumption, to quickly obtain a large amount of stress relaxation performance data, and then combine the correlation method shown in the application to quickly and massively obtain the creep performance, so that the service performance can be evaluated.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for correlating stress relaxation and creep performance, which belongs to the field of new materials and is used for testing related activities for the development of new materials. The method uses the characteristics of short stress relaxation test time, multiple creep information and less sample loss to quickly and massively transform creep performance. The method can break the limitations of traditional methods in terms of long time consumption and large material consumption for obtaining creep performance, and can achieve fast acquisition of creep performance and evaluation of service performance. BACKGROUND

[0002] Creep is an important factor for performance degradation and even failure of all materials during high-temperature service. As one of the key performance indicators of creep performance, the minimum creep rate is usually used to evaluate the service life of components with boundary conditions.

[0003] Generally, the minimum creep rate of the service material is obtained by creep test. However, since the creep test is a constant temperature and constant stress test method, it leads to large amount of test materials on one hand: the characteristics of obtaining only a single minimum creep rate data from a single test determine that a large number of creep tests are needed to support more accurate performance evaluation and analysis, which consumes a large amount of test materials; on the other hand, it leads to a very long total test time: in order to obtain effective minimum creep rate data, a single creep test needs to be performed for a long time, and necessary single low stress creep test can reach thousands of hours or even tens of thousands of hours of data. Although people have invented relatively more methods to alleviate the consumption of manpower and material resources, but until now, the related methods still have the disadvantages of long time and large amount of materials. These disadvantages restrict people's quick understanding of material creep performance, and further reduce the speed of new material research and application. Therefore, there is an urgent need for a fast and accurate performance prediction and evaluation method.

[0004] Based on this, the present application provides a method for correlating stress relaxation and creep performance, which obtains stress relaxation data in a short time and converts the minimum creep rate by combining a specific model, so as to quickly evaluate the creep performance of the material. SUMMARY

[0005] The present application solves the problems of long time and large amount of samples in obtaining existing creep performance data, and proposes a method for quickly obtaining a large amount of stress relaxation performance data by using short-time stress relaxation test, and quickly and massively obtaining creep performance by constructing a creep performance conversion model.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A method for correlating stress relaxation and creep performance, comprising the following steps:

[0008] First step: Conduct high temperature relaxation test to obtain the corresponding data of temperature-stress-creep relaxation rate

[0009] a: Cut and prepare the sample for high temperature relaxation test from the parts or materials;

[0010] b: Conduct high temperature relaxation test at a specified temperature: heat the sample to a specified temperature and keep the temperature constant, the specified temperature is within 400°C-1200°C, and the temperature holding time is within 0.5h-10h. After the holding time, load the sample at a strain rate of 1.0x10 -6 / s-1.0x10 -2 / s to a specified strain, the specified strain is within 0.1%-10.0%. After reaching the specified strain, keep the specified strain constant for 3h-200h;

[0011] c: Record the corresponding relationship between stress σ and time t during the process of b in the first step, which should ensure that the stress relaxation curve is clearly drawn;

[0012] d: According to the methods of b in the first step and c in the first step, conduct high temperature relaxation test at other specified temperatures, the specified temperature range is 400°C-1200°C, and obtain the stress relaxation curves at other specified temperatures T SRT ;

[0013] e: According to the stress relaxation curves obtained in c in the first step and d in the first step, i.e. the corresponding relationship between stress σ and time t, calculate the stress change rate and stress relationship data using formula (1);

[0014]

[0015] f: According to the stress change rate and stress relationship calculated in e in the first step, calculate the high temperature relaxation creep rate at different test temperatures and test stresses using formula (2) to obtain the corresponding data among temperature-stress-creep relaxation rate, i.e. In formula (2), E is the elastic modulus at the specified temperature;

[0016]

[0017] Second step: Conduct high temperature creep test to obtain the minimum creep rate data

[0018] a: Cut and prepare the sample for creep test from the parts or materials;

[0019] b: Conduct a high-temperature creep test: Heat the sample to the specified temperature and hold it at that temperature for 0.5h to 10h; after the holding time is reached, apply the specified stress steadily at a stress rate of 5MPa to 20MPa / s; after the specified stress is reached, keep the specified stress constant until the second stage of creep is reached or later, then end the test.

[0020] c: Record the relationship between strain ε and test time t during the test shown in step b in step 2. This record should ensure that the creep curve is clearly plotted.

[0021] d: Calculate the creep elongation using the creep curve obtained in step c, and obtain the minimum creep rate at the specified temperature / stress.

[0022] e: Referring to steps b to d in Part 2, conduct high-temperature creep tests at other specified temperatures or under other specified stresses to obtain the other specified temperature T. c And the minimum creep rate under other specified stress σ Among them, the other specified temperature range is 400℃~1200℃, and the other specified stress range is 10MPa~1000MPa;

[0023] f: Through steps a to e, obtain different temperature-stress-minimum creep rate data, i.e.

[0024]

[0025] Step 3: Data processing and building a correlation model

[0026] a: Regarding what was obtained in the first step Using formula Processing is performed. Among them, C... SRT The constant is used to determine the value of T. SRT Down The standard deviation of the data overlap is minimized;

[0027] b: Regarding the results obtained in the second step use Processing is performed. Among them, C... c The constant is used to determine the value of T. c Down The standard deviation of the data overlap is minimized;

[0028] c: Under the same stress conditions, the high-temperature relaxation creep rate and the minimum creep rate follow the relationship shown in formula (3);

[0029]

[0030] In formula (3), k is a coefficient, and SZ is constant.

[0031] d: when C c = C SRT , k = 1 in formula (3). Further when T c = T SRT , formula (3) is further:

[0032]

[0033] where S Z is constant, representing and mutual conversion parameters.

[0034] Through the above steps, the present application obtains the correlation model of the relaxation creep rate of the high temperature relaxation test under the same stress and the minimum creep rate of the high temperature creep test, i.e. formula (3), and the special condition application model, i.e. formula (4). Through the first step of the present application, a large amount of temperature-stress-creep relaxation rate data can be obtained in a short time by using a small amount of samples. Through the second step of the present application, temperature-stress-minimum creep rate data with relatively short test time can be obtained by using a small amount of samples. Through formula (3) or formula (4) shown in the third step of the present application, the large amount of temperature-stress-creep relaxation rate data of the first step can be correlated with the small amount of temperature-stress-minimum creep rate data of the second step, and a large amount of creep relaxation rate can be converted into minimum creep rate, reducing the amount of high temperature creep test and the total time of data acquisition.

[0035] The beneficial effects of the present application are:

[0036] The present application reduces the loss of time and samples in the existing creep property acquisition method, and through the correlation model of the creep relaxation rate and the minimum creep rate, a large amount of creep relaxation rate obtained in a short time can be converted into minimum creep rate for the evaluation of the high temperature material creep property. The method is time-saving, material-saving, and saves a lot of manpower and material resources. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is the stress relaxation curve under different temperatures

[0038] Figure 2 is the stress relaxation rate data under different temperatures and stresses, i.e.

[0039] Figure 3 is the creep curve under the condition of 850℃ / 450MPa

[0040] Figure 4 is the minimum creep rate data under different temperatures and stresses, i.e.

[0041] Figure 5 σ vs t σ vs t σ vs t

[0042] σ vs t Figure 6 σ vs t σ vs t

[0043] σ vs t Figure 7 σ vs t DETAILED DESCRIPTION

[0044] The present application alleviates the problem of long time consumption and large material consumption in traditional creep test. Based on stress relaxation test which can obtain a large amount of creep information in a short time, the present application invents a correlation model of stress relaxation rate and traditional creep performance on the basis of analyzing the change rule of stress relaxation rate and minimum creep rate. The specific embodiments of the present application will be described in detail in combination with stress relaxation data and creep performance of a nickel-based high-temperature alloy.

[0045] First step: carry out high-temperature relaxation test to obtain temperature-stress-creep relaxation rate corresponding data

[0046] a: cut and prepare a sample for high-temperature relaxation test from a component or test material;

[0047] b: implement high-temperature relaxation test at a specified temperature: heat the sample to 750℃ and keep it for 2h, then load it to 2.0% strain at a strain rate of 4.0×10 -4 / s, and then keep the 2.0% strain constant for 24h.

[0048] c: record the corresponding relationship between stress σ and time t in the process of b in the first step, and draw a stress relaxation curve;

[0049] d: according to the method of b in the first step and c in the first step, implement high-temperature relaxation test at other specified temperatures: heat the sample to 800℃, 850℃, 900℃, 950℃ or 980℃ and keep it for 2h, then load it to 2.0% strain at a strain rate of 4.0×10 -4 / s, and then keep the 2.0% strain constant for 24h, during which the corresponding relationship between stress σ and time t is recorded, and a stress relaxation curve is drawn. The stress relaxation curves at 750℃-980℃ are shown in Figure 1 It can be seen that the stress relaxation curve at 750℃ starts from a relatively high stress, but the stress decreases with the increase of test time, showing a typical stress relaxation characteristic. In addition, it is noted that the stress decreases at the same test time with the increase of test temperature, showing that the stress relaxation curve moves downward continuously.

[0050] e: According to the stress relaxation curve obtained in the first step c and the first step d, i.e. the correspondence between stress σ and time t, the formula The stress change rate is calculated

[0051] f: According to the stress change rate at 750℃, 800℃, 850℃, 900℃, 950℃ and 980℃ calculated in the first step e and the elastic modulus E at each temperature, the formula The creep relaxation rate at each temperature is calculated The relationship diagram is obtained The results are shown in Figure 2 It can be seen that the creep relaxation rate decreases with the decrease of stress, but the temperature has the effect of increasing the creep relaxation rate.

[0052] Second step: carry out high temperature creep test to obtain minimum creep rate data

[0053] a: cut and prepare the sample for creep test from the spare parts or test materials;

[0054] b: implement high temperature creep test: heat the sample to 850℃ and keep for 2h, then apply 450MPa stress at a stress rate of 10MPa / s, then keep the force value constant until the sample breaks and the test is ended;

[0055] c: record the correspondence between strain ε and test time t during the test process shown in the second step b, and the creep curve is shown in Figure 3 . Figure 3 In the figure, the creep curve is divided into three stages, the first stage, the second stage and the third stage, and the creep curve in the present application can be executed to the end of the second stage or above.

[0056] d: calculate the creep elongation rate by using the creep curve obtained in the second step c to obtain the minimum creep rate at the specified temperature / stress

[0057] e: refer to the second step b~second step d, implement high temperature creep test at different stresses under the conditions of 900℃, 950℃ and 980℃ to obtain the minimum creep rate at other specified temperatures T c and other specified stresses σ

[0058] f: through the first step a~first step e, the corresponding data among temperature-stress-minimum creep rate are obtained, i.e. The results are shown in Figure 4 . Figure 4The minimum creep rate varies under different temperatures and stresses, and even the minimum creep rate obtained from repeated tests under the same temperature and stress conditions shows a certain degree of data dispersion.

[0059] Step 3: Data processing and building a correlation model

[0060] a: Regarding what was obtained in the first step, such as Figure 2 shown Using formula Processing is required. When the standard deviation of overlapping data is minimized, C... SRT The value is -49. Construct σ and... Relationship diagram, results as follows Figure 5 As shown. Figure 5 In the data, the creep relaxation rates at different temperatures overlap to form a data band, which can be represented by the master curve for subsequent analysis.

[0061] b: Regarding the results obtained in the second step, such as... Figure 4 shown use Processing is required. When the standard deviation of overlapping data is minimized, C... c The value is -49;

[0062] c: According to the formula Draw diagrams under the same stress and Relationship diagram, where C SRT =C c =-49, the result is as follows Figure 6 As shown, the solid data points exhibit a good linear relationship.

[0063] d: According to Figure 6 The constants k and S were obtained through fitting. Z K=1, S Z =-1957, thus obtaining the formula Using formula The minimum creep rate under different temperature and stress conditions is calculated using the principal curve in step 3a. The results are as follows Figure 7 As shown. Figure 7 The solid line in the middle is due to Figure 5 The principal curve is obtained through the formula Calculated The solid point represents the minimum creep rate obtained from the experiment, and the two values ​​show a good overlap. Using... Figure 7 The minimum creep rate can be obtained under different temperatures and stress conditions. For example, to obtain the minimum creep rate under 850℃ / 600MPa conditions, the minimum creep rate can be directly read as 4×10⁻⁶.-8 s -1 ,like Figure 7 As shown by the dashed line, a large amount of data was provided for creep performance evaluation through a combination of 144 hours of stress relaxation testing and seven creep tests. The time and material costs of this invention are significantly reduced compared to traditional creep performance evaluation methods.

[0064] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for correlating relaxation and creep performance, characterized in that, Includes the following steps: Step 1: Conduct high-temperature relaxation tests to obtain data corresponding to temperature, stress, and creep relaxation rates. a: Take samples from parts or materials and prepare them for high-temperature relaxation tests; b: Conduct a high-temperature relaxation test at a specified temperature: Heat the sample to a specified temperature and maintain the temperature constant. The specified temperature is within the range of 400℃ to 1200℃, and the temperature holding time is within the range of 0.5h to 10h. After reaching the holding time, apply a strain at a certain strain rate to the specified strain, and the specified strain is within the range of 0.1% to 10.0%. After reaching the specified strain, maintain the specified strain constant for 3h to 200h. c: Record the relationship between stress σ and time t during step b. This record should clearly show the stress relaxation curve. d: Following steps b and c, conduct high-temperature relaxation tests at other specified temperatures, with the specified temperature range being 400℃~1200℃, to obtain the other specified temperatures. The stress relaxation curve is shown below. e: Based on the stress relaxation curves obtained in steps c and d, i.e. the relationship between stress σ and time t, the stress change rate is calculated using formula (1). Data related to stress; （1）； f: Based on the stress change rate calculated in step e. The creep relaxation rate under different test temperatures and test stresses is calculated using formula (2) in relation to stress. To obtain the corresponding data between temperature, stress, and creep relaxation rate, i.e. -σ- In formula (2), E is the elastic modulus at a specified temperature. （2）； Step 2: Conduct high-temperature creep tests to obtain minimum creep rate data. a: To cut and prepare specimens for high-temperature creep testing from parts or samples; b: Conduct a high-temperature creep test: Heat the sample to the specified temperature and hold it at that temperature for 0.5h to 10h; after the holding time is reached, apply the specified stress steadily at a certain stress rate; after the specified stress is reached, keep the specified stress constant until the second stage of creep is reached or later, then end the test. c: Record the relationship between strain ε and test time t during the test shown in step b in step 2. This record should ensure that the creep curve is clearly plotted. d: Calculate the creep elongation using the creep curve obtained in step c, and obtain the minimum creep rate at the specified temperature / stress. ; e: Referring to steps b to d in Part 2, conduct high-temperature creep tests at other specified temperatures or under other specified stresses to obtain the other specified temperatures. And the minimum creep rate under other specified stress σ ; f: Through steps a through e, obtain different temperature-stress-minimum creep rate data, i.e. -σ- ; Step 3: Data processing and building a correlation model a: Regarding what was obtained in the first step -σ- Using formula Processing is required; among them, It is a constant, and its value is significant because it makes different values ​​equal. Lower σ- The standard deviation of the data overlap is minimized; b: Regarding the results obtained in the second step -σ- ,use Processing is required; among them, It is a constant, and its value is significant because it makes different values ​​equal. Lower σ- The standard deviation of the data overlap is minimized; c: Under the same stress conditions, the creep relaxation rate and the minimum creep rate follow the relationship shown in formula (3); （3）； In formula (3), k is a coefficient. It is a constant.

2. The method for correlating relaxation and creep performance according to claim 1, characterized in that, In step b of the first step, the strain rate is 1.0 × 10⁻⁶. -6 / s~1.0×10 -2 / s.

3. The method for correlating relaxation and creep performance according to claim 1, characterized in that, In step b of the second step, the stress rate is 5MPa~20MPa / s.

4. The method for correlating relaxation and creep performance according to claim 1, characterized in that, In the second step e, the other specified temperature range is 400℃~1200℃, and the other specified stress range is 10MPa~1000MPa.

5. The method for correlating relaxation and creep performance according to claim 1, characterized in that, In the third step c, when , When k = 1 in formula (3), formula (3) is: （4）； in, A constant, representing and Convert parameters between each other.

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