A method for predicting the impact toughness of additively manufactured high temperature alloys at different temperatures

Abstract

This invention belongs to the field of mechanical property prediction technology for metallic materials, and relates to a method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures. This method obtains the impact energy A of the high-temperature alloy through Charpy impact and tensile tests. k Impact toughness and yield strength σ y By statistically analyzing the area R of the impact plastic zone on the side of the impact fracture surface... p Taking the square root gives r p The quantitative relationships between yield strength, parameters, plastic work per unit volume, and temperature were established. Predictive equations for impact toughness at different temperatures were then obtained. This prediction method establishes a quantitative relationship between the impact toughness of additively manufactured high-temperature alloys and temperature and yield strength. It is applicable to high-temperature alloys and other metallic materials whose impact toughness is dominated by dislocation multiplication and annihilation mechanisms. This provides an important theoretical basis for the quantitative evaluation of the impact toughness of such alloys and the selection of service temperatures to obtain optimal impact fracture resistance.

Description

Technical Field

[0001] This invention belongs to the field of mechanical property prediction technology of metallic materials, and specifically relates to a method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures. Background Technology

[0002] High-temperature alloys, due to their excellent high-temperature strength, good creep resistance, and outstanding corrosion resistance, have become core materials for hot-end components of critical equipment such as aero-engines and gas turbines. Compared with traditional manufacturing processes, additive manufacturing technology has three major advantages: free fabrication, topology optimization, and near-net-shape forming, providing a new approach for manufacturing complex high-temperature alloy components. Therefore, additive-manufactured high-temperature alloys have broad application prospects in the aerospace field. In actual service, aero-engines and spacecraft hot-end components need to operate for extended periods in a wide temperature range (-60℃ to over 700℃) and are frequently subjected to dynamic impact loads such as bird strikes, blade fragment impacts, and rapid start-stop. Therefore, studying the fracture resistance, i.e., impact toughness, of additive-manufactured high-temperature alloys under high-speed impact loads at different temperatures is of great significance for ensuring their safe and reliable service.

[0003] Furthermore, with the deepening of scientific research and application, cutting-edge equipment places more stringent requirements on the prediction and reliability of high-temperature alloy components under complex operating conditions. However, current research focuses more on the influence of microstructure on the impact toughness and fracture mechanism of high-temperature alloys, and systematic research is still lacking on the evolution of impact toughness of additively manufactured high-temperature alloys over a wide temperature range, especially its differences and correlation with static mechanical properties. At the same time, the research and development of high-temperature alloys and component design still heavily rely on time-consuming and costly "trial and error" experiments, which greatly restricts innovation efficiency.

[0004] Therefore, there is an urgent need to develop a method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures. Summary of the Invention

[0005] To address the challenge of lacking an effective quantitative relationship between the impact toughness of additively manufactured high-temperature alloys at different temperatures, this invention aims to provide a method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures. This method combines impact and tensile tests to obtain the impact toughness and yield strength of the high-temperature alloy at different temperatures. It establishes a quantitative relationship between impact toughness and static mechanical properties by segmenting the transformation of the material's internal dislocation-dominant mechanism, and constructs a quantitative prediction model for impact toughness based on plastic work and energy conservation. Using this invention, the impact toughness and yield strength of the material can be obtained through a small number of impact and tensile tests within the service temperature range. Predictive equations for impact toughness at different temperatures can be constructed, and the impact toughness of the material can be predicted simply by inputting the temperature value.

[0006] To achieve the above objectives, this invention proposes a method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures, characterized by comprising the following steps: (1) Take the additive manufacturing high-temperature alloy sample and obtain the impact energy A of the high-temperature alloy at n different temperatures through Charpy impact test and tensile test. k Impact toughness With yield strength Establish yield strength A quantitative formula relating temperature; (2) The area R of the impact plastic zone on the side of the impact fracture surface of the specimen at n different temperatures. p Statistically, taking the square root yields the size r of the plastic region. p ; (3) Through the plastic zone size r p and and The relationship was obtained at different temperatures. The value, establish A quantitative formula relating temperature; (4) The yield strength obtained in steps (1) and (3) Substituting the quantitative relationship between temperature and plasticity into the formula relating plastic zone size, we obtain R. p A quantitative formula relating temperature; (5) Through impact energy A k The plastic work per unit volume is obtained from the impact plastic zone volume. The experimental values ​​were used to establish... A quantitative formula relating temperature; (6) Take the R obtained in steps (4) and (5) p and Substituting the quantitative relationship between temperature and impact toughness into the formula for impact toughness, we obtain the impact toughness at different temperatures. The prediction equation; (7) Use the above prediction equation to predict the impact toughness at the specified temperature.

[0007] In step (1), the high-temperature alloy is a nickel-based, iron-based, or cobalt-based high-temperature alloy; the value of n is greater than or equal to 3; the value of the temperature is -200℃ to 1000℃, and the number of experimental samples at each temperature is greater than or equal to 3.

[0008] The tensile test requires that the strain rate be controlled to be the same. The yield strength The quantitative relationship with temperature satisfies an exponential relationship: ; Where σ y0 σyr and n are the fitting parameters, The reference strain rate is used.

[0009] In step (2), the impact plastic zone includes two parts: plastic zone I, where cracks initiate and propagate, and plastic zone II, which is generated by high-speed impact.

[0010] In step (3), the plastic zone size r p and and The specific relationships are as follows: ; in, and These represent the corresponding loading strain rates. and the stress intensity factor and yield strength of the material at temperature T; This represents the strain rate correction factor; The The quantitative relationship between temperature and temperature follows an exponential relationship: ; Where D and β represent the values ​​at 0 ℃, respectively. Value and decay rate. Where D and β represent the values ​​at 0℃ and the decay rate, respectively. Values ​​and decay rates. It is important to note that impact damage in high-temperature alloys is primarily driven by dislocation multiplication at low temperatures, but becomes primarily driven by dislocation annihilation at high temperatures. Therefore, it is necessary to consider the critical temperature T at which the dominant mechanism transitions. c The parameter values ​​of D and β are determined by segmenting the data before and after.

[0011] In step (4), the area R of the impact plastic zone p The quantitative relationship with temperature is as follows: ; In step (5), the plastic work per unit volume The experimental value is derived from the impact energy A k The volume of the plastic region is obtained by comparing it with the volume of the plastic region; the volume of the plastic region is the area R of the plastic region. p ×Sample thickness B; The The quantitative relationship with temperature follows an exponential relationship, as follows: ; Among them, G0, G r and k are the fitting parameters.

[0012] In step (6), based on the law of conservation of energy, impact toughness It can be obtained through the following formula: ; Where B and W represent the sample thickness and ligament width, respectively.

[0013] Impact toughness at different temperatures The prediction equation is: .

[0014] The theoretical derivation and technical route of this invention are as follows: Theoretical derivation: According to fracture mechanics theory, the size of the plastic zone of a material r p The following formula can usually be used to calculate it: (1) in and These represent the corresponding loading strain rates. The stress intensity factor and the yield strength of the material at temperature T, R p This represents the area of ​​the plastic region. Generally, the stress-strain constitutive relationship at different strain rates and temperatures can be described using the classic Johnson-Cook model: (2) in A It is the initial yield stress. B It is the hardening constant. It is the actual strain rate. n It is the hardening index. and T 0 For reference strain rate and reference temperature, C It is the strain rate constant. m The thermal softening index, T m This is the melting point of the material. The model shows that the effects of strain rate and temperature on material strength are independent, i.e., it adopts... and Expressed as correction factors for strain rate and temperature, formula (2) can be simplified to: (3) Therefore, based on the relationship between the yield strength and temperature of additively manufactured high-temperature alloys at conventional tensile strain rates, the relevant parameters in the temperature correction parameter f(T) can be determined. The yield strength of most additively manufactured high-temperature alloys exhibits an exponential variation with temperature, rather than the power function form of the Johnson-Cook model. Therefore, this invention uses an exponential function to correct for temperature: (4) in These are the fitting parameters.

[0015] Combining formulas (1), (3), and (4), we can obtain: (5) Therefore, to establish a quantitative relationship between temperature and the size of the plastic zone, it is still necessary to reveal... Quantitative correlation with temperature. This is achieved through the relationship between plastic zone size and stress intensity factor. and yield strength The correlation formula is used to obtain parameters at different temperatures. The values ​​are established through linear relationships. The quantitative relationship with temperature. In fact, It exhibits a piecewise linear decreasing trend with temperature changes, which can be described piecewise using the following expression: (6) Where D and β represent the values ​​at 0 ℃, respectively. Value and decay rate. It is important to note that... The piecewise linear decrease in impact toughness during temperature rise is caused by a shift in the dislocation-dominated mechanism of the high-temperature alloy's impact toughness. The critical temperature for this shift is denoted as T. c At low temperatures (T < T) c ) and high temperature (T≥T c Two temperature ranges, The decay rates are significantly different at low temperatures (T < T). c Under these conditions, impact damage is dominated by a dislocation multiplication mechanism, with multiple slip and dislocation sources continuously being excited. This leads to a significant change in the uniformity of plastic deformation and a substantial release of local stress concentration. The decrease is rapid, and the absolute value of β is relatively large. However, at high temperatures (T≥T...), c Under these conditions, the dislocation annihilation mechanism begins to dominate the evolution of impact damage, which slows down the stress concentration release rate, resulting in a smaller absolute value of β.

[0016] Therefore, by simultaneously solving formulas (1), (5) and (6), the area R of the impact plastic zone can be successfully obtained. p The relationship between temperature and temperature is: (7) Substituting the relevant parameter values ​​into formula (7) can achieve quantitative prediction of the area of ​​the impact plastic zone at different temperatures.

[0017] To quantitatively predict impact toughness, a quantitative correlation needs to be established between temperature and the plastic work consumed per unit area. The plastic work consumed per unit volume can be obtained by comparing the impact work to the volume of the plastic region. At low temperatures, dislocation multiplication dominates impact damage. As the temperature increases, the dislocation density and hardening capacity within the plastic region of the material increase, thus the plastic work consumed per unit volume gradually increases. However, when the temperature exceeds the critical temperature Tc... c Dislocation annihilation gradually becomes dominant, and the amount of plastic work consumed per unit volume gradually decreases with increasing temperature. (Plastic work per unit volume) The trend of energy consumption changing with temperature can be well described using an exponential form: (8) Among them, G0, G r and k are the fitting parameters.

[0018] Assuming all impact energy is converted into plastic work within the material, based on the law of conservation of energy, the impact toughness of additively manufactured high-temperature alloys at different temperatures is investigated. It can be obtained through the following formula: (9) Among them, A k B and W represent impact energy, sample thickness, and ligament width, respectively.

[0019] Furthermore, by simultaneously solving equations (7), (8), and (9), we can obtain the specific expression for impact toughness: (10) By substituting the relevant parameters of additive manufacturing high-temperature alloys and the temperature to be predicted into formula (10), the impact toughness at a specified temperature can be predicted.

[0020] The design mechanism and beneficial effects of this invention are as follows: 1. This invention addresses the initial increase followed by a decrease in impact toughness of additively manufactured high-temperature alloys with increasing temperature. It reveals a shift in the dislocation-dominated mechanism before and after the critical impact toughness temperature: in the low-temperature region, increased temperature promotes dislocation multiplication and multiple slip, increasing the size of the ductile region and its hardening capacity, thus increasing impact toughness; in the high-temperature region, dislocation annihilation dominates, and increased temperature leads to a decrease in the hardening capacity of the ductile region, resulting in a decline in impact toughness. Based on this, a method for segmentally determining the values ​​of parameters D and β is designed.

[0021] 2. Based on the quantitative analysis of the plastic zone size and the energy absorbed by plastic deformation per unit volume, and the principle of energy conservation, this invention establishes a quantitative relationship between the impact toughness of additively manufactured high-temperature alloys and temperature and yield strength. This provides an important theoretical basis for the quantitative evaluation of the impact toughness of this type of alloy and the selection of service temperature to obtain optimal impact fracture resistance.

[0022] 3. This invention enables the quantitative prediction of the impact toughness of high-temperature alloys over a wide service temperature range through impact and tensile tests at several typical temperatures within the service temperature range. It is applicable to high-temperature alloys and other metallic materials whose impact toughness is dominated by dislocation multiplication and annihilation mechanisms. Simultaneously, it significantly reduces the experimental time and cost of high-temperature alloy impact testing, while saving energy consumption associated with creating low-temperature and high-temperature experimental environments. It provides a rapid, reliable, and environmentally friendly prediction method, which has significant practical implications for accelerating the innovative research and development of high-temperature alloys. Attached Figure Description

[0023] Figure 1 The tensile fracture morphology of the specimens at different temperatures; Figure 2 The impact fracture morphology of the samples at different temperatures; Figure 3 The actual value and predicted curve of the yield strength of this invention as a function of temperature are shown. Figure 4 Morphology of the side plastic zone of GH4169 high-temperature alloy at different temperatures for additive manufacturing; (a) Schematic diagram of impact plastic zone; (b) -180℃; (c) 25℃; (d) 200℃; (e) 300℃; (f) 450℃; (g) 600℃; (h) 800℃; Figure 5 This is the equivalent stress intensity factor of the present invention. Actual values ​​and predicted curves as a function of temperature; Figure 6 The impact plastic zone dimension R of this invention p Actual values ​​and predicted curves as a function of temperature; Figure 7 The plastic work per unit volume of the present invention Actual values ​​and predicted curves as a function of temperature; Figure 8 For the impact toughness of this invention Actual values ​​and predicted curves as a function of temperature; Detailed Implementation

[0024] The present invention will be described in more detail below with reference to the embodiments. These embodiments are merely descriptions of the best mode of implementation of the present invention and do not limit the scope of the present invention in any way.

[0025] Example 1: This embodiment takes additive manufacturing of high-temperature alloy GH4169 as an example and gives the prediction equation for its impact toughness within the service temperature range (-180℃-600℃).

[0026] (1) The impact energy A at typical temperatures within the service temperature range of the high-temperature alloy was obtained by Charpy impact test (GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method") and tensile test (ASTM E8 / E8M-21 "Metallic Materials Tensile Test Method"). k Impact toughness With yield strength σ y The experimental values ​​are shown in Table 1; multiple samples (3) were tested, and the specific values ​​of the relevant parameters are expressed as the average value ± error of multiple samples.

[0027] Table 1 Impact Energy A at Different Temperatures k Impact toughness With yield strength σ y Experimental values

[0028] Since the yield strength of additively manufactured high-temperature alloy GH4169 exhibits an exponential variation with temperature, rather than the power function form of the Johnson-Cook model, the yield strength is established using the exponential relationship shown in formula (4). Regarding the quantitative relationship with temperature, it's important to note that the tensile fracture mechanism changes significantly at 800℃ (from ductile to brittle), and therefore it is not included in the fitting of the yield strength. Figure 1 The tensile fracture surface characterization results are shown. However, due to the high strain rate of impact testing, this transition to a different fracture mechanism can be avoided, such as... Figure 2 As shown in the impact fracture characterization results, the subsequent fitting of impact performance parameters still considers 800℃. The predicted yield strength curve is as follows. Figure 3 As shown, the expression is as follows: (11) (2) The area R of the impact plastic zone on the side of the impact fracture surface was statistically analyzed using a stereomicroscope. p The square root is used to obtain the dimension r of the lateral impact plastic zone. p Plastic region, such as Figure 4 As shown in Table 2, the dimensions of the plastic zone are statistically analyzed. Table 2 Impact plastic zone dimensions r at different temperatures p Experimental values

[0029] (3) The plastic zone size r according to formula (5)p With stress intensity factor and yield strength The relationship was calculated to obtain parameters at different temperatures. The values ​​are shown in Table 3.

[0030] Table 3 Parameters at different temperatures numerical value

[0031] As temperature increases, the change in impact toughness is altered by a dislocation-dominated mechanism. Therefore, a piecewise linear relationship is established using formula (6). The quantitative relationship with temperature, the prediction curve is as follows: Figure 3 As shown, the expression is as follows: (12) (4) Set the parameters (Formula (12)) and yield strength Substituting (Equation (11)) into Equation (7) respectively, we establish the impact plastic zone size r. p The quantitative relationship with temperature, r p Squaring gives R p R p The prediction curve is as follows Figure 6 As shown, the expression is as follows: (13) (5) The plastic work per unit volume is obtained by combining the impact energy with the volume of the impact plastic zone (plastic zone area × sample thickness). The actual values ​​are shown in Table 4: Table 4 Plastic work per unit volume at different temperatures actual value

[0032] Established through the exponential relationship described in formula (8) The quantitative relationship with temperature, the prediction curve is as follows: Figure 7 As shown, the expression is as follows: (14) (6) Substitute formulas (13), (14), the sample thickness B, and the ligament width W into formula (9) to establish the impact toughness. Prediction equations for different temperatures. The measured values ​​of sample thickness B and ligament width W are shown in Table 5. The errors with the standard values ​​are small, so the standard values ​​are uniformly taken in the equations, that is, sample thickness B = 10 mm and ligament width W = 8 mm.

[0033] Table 5. Measured values ​​of thickness B and ligament width W of specimens at different temperatures.

[0034] Impact toughness The prediction curve is as follows Figure 8 As shown. 。

[0035] The prediction equations for different temperatures are shown below: (15) (7) Predict the impact toughness at a specified temperature: Substitute the specified temperature and use the prediction equation (15) to complete the prediction of the impact toughness at the specified temperature, as shown in Table 6.

[0036] Table 6 Impact toughness predicted based on formula (15)

Claims

1. A method for predicting the impact toughness of additively manufactured high-temperature alloys at different temperatures, characterized in that, Includes the following steps: (1) Take the additive manufacturing high-temperature alloy sample and obtain the impact energy A of the high-temperature alloy at n different temperatures through Charpy impact test and tensile test. k Impact toughness With yield strength Establish yield strength A quantitative formula relating temperature; (2) The area R of the impact plastic zone on the side of the impact fracture surface of the specimen at n different temperatures. p Statistically, taking the square root yields the size r of the plastic region. p ; (3) Through the plastic zone size r p and and The relationship was obtained at different temperatures. The value, establish A quantitative formula relating temperature; (4) The yield strength obtained in steps (1) and (3) Substituting the quantitative relationship between temperature and plasticity into the formula relating plastic zone size, we obtain R. p A quantitative formula relating temperature; (5) Through impact energy A k The plastic work per unit volume is obtained from the impact plastic zone volume. The experimental values ​​were used to establish... A quantitative formula relating temperature; (6) Take the R obtained in steps (4) and (5) p and Substituting the quantitative relationship between temperature and impact toughness into the formula for impact toughness, we obtain the impact toughness at different temperatures. The prediction equation; (7) Use the above prediction equation to predict the impact toughness at the specified temperature.

2. The prediction method according to claim 1, characterized in that, In step (1), the high-temperature alloy is a nickel-based, iron-based, or cobalt-based high-temperature alloy; the value of n is greater than or equal to 3; the value of the temperature is -200℃ to 1000℃, and the number of experimental samples at each temperature is greater than or equal to 3. The tensile test requires that the strain rate be controlled to be the same. The yield strength The quantitative relationship with temperature satisfies an exponential relationship: ； Where σ y0 σ yr and n are the fitting parameters, The reference strain rate is used.

3. The prediction method according to claim 1, characterized in that, In step (2), the impact plastic zone includes two parts: plastic zone I, where cracks initiate and propagate, and plastic zone II, which is generated by high-speed impact.

4. The prediction method according to claim 1, characterized in that, In step (3), the plastic zone size r p and and The specific relationships are as follows: ； in, and These represent the corresponding loading strain rates. and the stress intensity factor and yield strength of the material at temperature T; This represents the strain rate correction factor; The The quantitative relationship between temperature and temperature follows an exponential relationship: ； Where D and β represent the values ​​at 0 ℃, respectively. Value and decay rate.

5. The prediction method according to claim 1, characterized in that: In step (4), the area R of the impact plastic zone p The quantitative relationship with temperature is as follows: 。 6. The prediction method according to claim 1, characterized in that: In step (5), the plastic work per unit volume The experimental value is derived from the impact energy A k The volume of the plastic region is obtained by comparing it with the volume of the plastic region; the volume of the plastic region is the area R of the plastic region. p ×Sample thickness B; The The quantitative relationship with temperature follows an exponential relationship, as follows: ； Among them, G0, G r and k are the fitting parameters.

7. The prediction method according to claim 1, characterized in that: In step (6), based on the law of conservation of energy, impact toughness It can be obtained through the following formula: ； Wherein, B and W represent the sample thickness and ligament width, respectively; Impact toughness at different temperatures The prediction equation is: 。

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