A method for analyzing the endurance performance of a GH4706 alloy

Abstract

The application discloses a kind of precision endurance performance analysis and residual life prediction method of GH4706 alloy, belong to high-temperature alloy performance detection technical field.The core process of the method is "high-temperature endurance test→multi-dimensional micro characterization→Larson-Miller model establishment→residual life prediction" closed loop system, and key parameters include "600 ℃ / 5000h aging pretreatment, 600-700 ℃ / 650-750MPa test condition, C=24.53 Larson-Miller model constant".The application effectively solves the pain points of traditional analysis only relying on macro data, low prediction accuracy and long test cycle, can synchronously obtain alloy endurance fracture time, microstructure evolution and crack propagation law, the deviation between predicted life and actual value is less than or equal to 5%, adapts to existing detection equipment, and provides scientific basis for gas turbine component design and safety evaluation.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy performance testing technology, and particularly relates to a method for analyzing the creep performance of GH4706 alloy. Background Technology

[0002] GH4706 alloy, as a γ' / γ'' phase precipitation-strengthened high-temperature alloy, is a core material for hot-end components of heavy-duty gas turbines, and its creep performance directly determines the safety and reliability of the equipment during service. Traditional creep performance analysis has significant drawbacks: data is obtained solely through long-term high-temperature creep tests, which take tens of thousands of hours and are extremely costly; there is a lack of correlation analysis between "macroscopic properties, microstructure, and crack behavior," making it impossible to explain the performance degradation mechanism; life prediction relies on a single isothermal extrapolation method, ignoring the coupling effect of temperature and stress, resulting in low accuracy; and a standardized multi-dimensional characterization process has not been established, leading to poor repeatability of results. Existing technologies are insufficient to meet the needs of efficient and accurate performance evaluation of high-temperature alloy components, thus hindering the development and safe operation of related equipment. Summary of the Invention

[0003] Addressing the core pain points of traditional GH4706 alloy creep rupture performance analysis—namely, long analysis cycles, low accuracy, and unclear mechanisms—this invention aims to provide a creep rupture performance analysis method for GH4706 alloy. It proposes a full-chain analysis method: "high-temperature creep testing → microstructure characterization → crack behavior analysis → Larson-Miller modeling → life prediction." Through standardized aging pretreatment and gradient temperature stress testing, combined with multi-dimensional characterization using metallography and scanning electron microscopy (SEM), the evolution of the γ' / γ'' phase, fracture morphology, and crack propagation patterns are captured. A life prediction model based on the Larson-Miller parameter method is established, enabling accurate acquisition of the alloy's creep rupture performance and remaining life in a short time. This method requires no additional specialized equipment, shortens the analysis cycle by 80% compared to traditional methods, and offers high prediction accuracy, providing a systematic solution for the performance management of high-temperature alloy components.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention provides a method for analyzing the creep rupture properties of GH4706 alloy, comprising the following closed-loop process:

[0006] (1) Sample preparation and pretreatment: Standard samples were cut from the alloy workpiece and pretreated by aging at 600℃ / 5000h. Metallographic samples were treated by chemical etching (0.5gCuCl2+10mLHCl+10mLLC2H5OH) and electrolytic etching (150mLH3PO4+10mLH2SO4+15gCrO3) in two steps.

[0007] (2) High temperature creep test: Set up a gradient temperature stress condition of 600~700℃ / 650~750MPa, and conduct the test according to GB / T2039-2012 standard, and record the creep fracture time;

[0008] (3) Multidimensional microscopic characterization: The fracture morphology and γ' / γ'' phase evolution were observed by SEM, the crack propagation path was analyzed by optical microscopy, and the average phase size was measured;

[0009] (4) Model establishment and life prediction: The Larson-Miller model (C=24.53) was fitted based on experimental data, and the remaining life under different service temperature stresses was extrapolated;

[0010] (5) Output a standardized report containing performance data, mechanism analysis and usage recommendations.

[0011] Furthermore, in step (1), the electrolytic etching conditions are an electrolytic voltage of 15V and a time of 8s, and a chemical etching time of 5~8s, to ensure that the structure and phase morphology are clearly presented.

[0012] Furthermore, in step (2), three parallel specimens are set for each group of tests, the average fracture time is taken, and the temperature stress gradient intervals are 50℃ and 30~40MPa, respectively.

[0013] Furthermore, in step (3), the magnification of SEM observation of the fracture surface is 500 to 5000 times, the magnification of phase morphology observation is 10000 to 50000 times, and the magnification of metallographic observation is 200 to 1000 times.

[0014] Furthermore, in step (4), the Larson-Miller model coefficients are A0 = 3.82468 × 10⁻⁶. 8 A1 = -4.04154 × 10 8 A2 = 1.42367 × 10 8 A3 = -1.67168 × 10 8 .

[0015] Furthermore, the remaining service life prediction is extrapolated from high-temperature short-time data, with the formula T1(24.53+lgtᵣ1)=T2(24.53+lgtᵣ2), and the prediction deviation is ≤5%; where: T1 and tᵣ1 are the test temperature and fracture time; T2 is the service temperature; and tᵣ2 is the predicted remaining service life.

[0016] Furthermore, it is applicable to high-temperature components such as GH4706 alloy turbine disk forgings, and can be extended to the creep performance analysis and life prediction of similar γ' / γ'' phase precipitation-strengthened high-temperature alloys.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] The analysis efficiency has been greatly improved: By using the Larson-Miller extrapolation method, long-term service life can be predicted based on short-term high-temperature test data of 600~700℃. The test cycle has been shortened from tens of thousands of hours to hundreds of hours, and the efficiency has been improved by more than 80%.

[0019] Comprehensive characterization dimensions and clear mechanisms: Simultaneous acquisition of macroscopic long-term fracture time, microscopic γ' / γ'' phase size evolution, fracture morphology and crack propagation path, clarifying the coupling relationship between temperature / stress and microstructure properties, and explaining the root cause of performance degradation.

[0020] High prediction accuracy and high reliability: A dedicated Larson-Miller model with C=24.53 is established, and the deviation between the remaining service life prediction value and the actual service data is ≤5%, which is far better than the 15% deviation threshold of traditional methods.

[0021] Standardized processes and high repeatability: Clearly defined process specifications for sample pretreatment, experimental parameters, and characterization methods ensure consistency of results across different laboratories (≥98%), eliminating human error.

[0022] It is compatible with existing equipment and has strong scalability: relying on conventional high-temperature endurance testing machines, optical microscopes, SEM and other equipment, no new special equipment is required, the testing and characterization costs are reduced by 60%, and it can be applied on a large scale. Detailed Implementation

[0023] A method for analyzing the creep rupture properties of GH4706 alloy. To achieve the above-mentioned objective, the method for analyzing the creep rupture properties of GH4706 alloy provided by this invention comprises the following steps:

[0024] 1. Sample standardization preparation and pretreatment:

[0025] (1) Sampling specifications

[0026] Samples were taken from workpieces such as GH4706 alloy turbine disk forgings, with specifications conforming to GB / T2039-2012 standard: tensile specimen diameter 10mm, gauge length 50mm, metallographic / fracture analysis sample size 10mm×10mm×5mm, ensuring that the sampling location avoids defect areas and representatively covers the key service parts of the workpiece.

[0027] (2) Time Preprocessing

[0028] All samples were placed in a heat treatment furnace and aged using a process of “holding at 600℃ for 5000h + cooling in the furnace” to simulate the stable microstructure of the alloy before service and to ensure consistency of the test standards. (3) Sample pretreatment

[0029] Metallographic samples: successively polished with 200# → 800# → 2000# sandpaper, and then diamond polished to a mirror finish; treated with two different etchants: ① chemical etching with 0.5g CuCl2 + 10mL HCl + 10mL C2H5OH solution for 5~8s, used to observe the microstructure and crack path; ② electrolytic etching with a mixed solution of 150mL H3PO4 + 10mL H2SO4 + 15g CrO3, electrolysis voltage 15V, time 8s, used to observe the γ' / γ'' phase morphology.

[0030] Fracture surface sample: ultrasonically cleaned with acetone for 10 minutes to remove surface oxidation products and impurities, while preserving the original fracture morphology.

[0031] 2. High-temperature endurance test:

[0032] (1) Experimental conditions

[0033] A high-temperature creep testing machine was used, with a gradient temperature stress test group to cover the service and extreme conditions of the alloy.

[0034] Temperature gradient: 600℃, 650℃, 700℃ (50℃ interval);

[0035] Stress gradient: 650MPa, 690MPa, 720MPa, 750MPa (intervals of 30~40MPa);

[0036] Three parallel specimens were set up in each group. The fracture time was recorded in real time during the test, and the average value was taken as the sustained fracture time under the condition.

[0037] (2) Test operation specifications

[0038] Sample clamping: Ensure the coaxiality deviation of the sample is ≤0.02mm to avoid additional stress;

[0039] Heating and loading: Heat to the target temperature at a rate of 5℃ / min, hold for 30min, and then load at a constant rate to the set stress, keeping the load constant until the sample breaks.

[0040] Data recording: Simultaneously record fracture time, fracture location, and macroscopic deformation.

[0041] 3. Multidimensional microscopic representation:

[0042] (1) Analysis of fracture morphology

[0043] The macroscopic and microscopic fracture morphology of the fractured sample was observed using a tungsten filament scanning electron microscope (SEM):

[0044] Macroscopic fracture surface: Records characteristics such as the proportion of intergranular fracture region and shear lip size;

[0045] Microscopic fracture: At magnification of 500 to 5000 times, observe the cleavage facets, dimples, river patterns and secondary crack distribution to distinguish between transgranular and intergranular fracture modes.

[0046] (2) Microstructural characterization

[0047] Metallographic observation: Using an Olympus GX71 optical microscope (200~1000x), the grain state, γ' / γ'' phase size and distribution of the alloy under different temperature stress conditions were observed, and the average size of the γ' / γ'' phase was measured (≥50 particles were counted under a 200nm scale).

[0048] SEM observation: A JSM-7800F SEM (10000~50000x) was used to analyze the coarsening and dissolution patterns of the γ' / γ'' phase and record the phase evolution characteristics at the grain boundaries at high temperatures.

[0049] (3) Crack propagation path analysis

[0050] Longitudinal shovel sampling was performed on the notch of the long-term fracture specimen. After corrosion treatment, the crack propagation path was observed using an optical microscope. The crack morphology (wavy / zigzag), propagation direction, and number of secondary cracks were recorded, and the relationship between temperature / stress and crack propagation rate was correlated.

[0051] 4. Larson-Miller Model Establishment and Remaining Life Prediction:

[0052] Model parameter fitting

[0053] Data preprocessing: Organize the duration of fracture (tᵣ) and thermodynamic temperature (T, unit K, T = test temperature + 273.15) under all thermal stress conditions.

[0054] Model constants determination: Linear fitting was performed with lgtᵣ as the ordinate and 1 / T as the abscissa to obtain the Larson-Miller model characteristic constant C=24.53 for GH4706 alloy;

[0055] Model Establishment: Based on the fitting results, a stress-temperature-time correlation model is established.

[0056] PL−M=(T+273.15)×(24.53+lgtr)

[0057] Further, by fitting the model using the polynomial PL−M(σ)−lgσ, the model coefficients A0 = 3.82468 × 10⁻⁶. 8 A1 = -4.04154 × 10 8 A2 = 1.42367 × 10 8 A3 = -1.67168 × 10 8 Improve the accuracy of the model.

[0058] (2) Remaining life prediction

[0059] Using the established Larson-Miller model, the remaining lifetime at low temperature for long periods is extrapolated from the high-temperature short-time test data: T1(24.53+lgtr1)=T2(24.53+lgtr2)

[0060] In the formula: T1 and tᵣ1 are the test temperature and fracture time; T2 is the service temperature (600~650℃); tᵣ2 is the predicted remaining life.

[0061] (3) Result verification

[0062] The rationality of the model is verified by combining the microstructure characterization results: if the γ' / γ'' phase size and fracture mode corresponding to the predicted lifetime are consistent with the actual service law, the prediction is deemed effective.

[0063] 5. Analysis report output:

[0064] The report includes: basic information on GH4706 alloy (composition, workpiece type), sample pretreatment and test parameters, macroscopic creep performance data (fracture time-temperature stress curve), microscopic characterization map (fracture morphology, microstructure evolution, crack path), Larson-Miller model formula and parameters, remaining service life prediction results, performance degradation mechanism analysis and usage recommendations (e.g., service life exceeding 100,000 hours at 600℃ / 625MPa, and service with caution when stress exceeds 650MPa).

[0065] The core of this invention lies in the "deep coupling of macroscopic performance and microscopic mechanisms": it rapidly acquires endurance data through gradient temperature stress testing, utilizes multi-dimensional microscopic characterization to reveal the correlation between γ' / γ'' phase coarsening, crack propagation, and performance degradation, and achieves accurate long-term lifetime extrapolation using the Larson-Miller model, distinguishing it from the limitations of traditional single-data acquisition or theoretical prediction. All parameters are based on the material properties of GH4706 alloy and industrial test verification, exhibiting a high degree of standardization and compatibility with existing conventional testing equipment. It can be directly applied to the performance evaluation of key components of GH4706 alloy and can also be extended to the endurance performance analysis of similar γ' / γ'' phase precipitation-strengthened high-temperature alloys.

[0066] Example

[0067] Sample preparation: Samples were cut from GH4706 alloy turbine disk forgings, pretreated with 600℃ / 5000h aging, and then processed into standard creep test specimens and metallographic samples.

[0068] High-temperature endurance test: The test conditions were set to 650℃ / 690MPa, 700℃ / 690MPa, and 650℃ / 750MPa, and the fracture times were obtained to be 1850h, 210h, and 85h, respectively.

[0069] Microscopic characterization:

[0070] Fracture analysis: at 650℃ / 690MPa, the intergranular fracture region accounts for 30%, and the micro-fracture contains a small number of dimples; at 700℃ / 690MPa, the intergranular fracture accounts for 80%, and the cleavage facets are enlarged;

[0071] Tissue observation: The average size of the γ' / γ'' phase was 30.7 nm at 650 °C, and increased to 41.2 nm at 700 °C, showing significant coarsening;

[0072] Crack path: At 650℃, the crack is wavy (mixed transgranular and intergranular fracture), and at 700℃, it is zigzag (intergranular dominant fracture).

[0073] Model prediction: Substituting into the Larson-Miller model, the extrapolated remaining service life under the service conditions of 650℃ / 600MPa is 102,000h, which deviates from the actual long-term test data (105,000h) by 2.9%.

[0074] Conclusion: This batch of GH4706 alloy can safely serve for over 100,000 hours at 650℃ / 600MPa, but its service life significantly decreases after the stress exceeds 625MPa.

[0075] Comparative Example

[0076] Analysis procedure: A 3000-hour endurance test was conducted only at 650℃ / 690MPa, and the lifetime at 650℃ / 600MPa was predicted using the isothermal extrapolation method.

[0077] Analysis results: The predicted lifetime was 85,000 hours, which deviated from the actual lifetime by 19%, and the microscopic mechanism of lifetime decay was not explained.

[0078] Defects: The influence of temperature on microstructure is not considered, and the coarsening and crack behavior of the γ' / γ'' phase are ignored, resulting in low prediction accuracy and an inability to provide targeted guidance for the safe use of components.

[0079] Performance Comparison Table

[0080] Analysis indicators Analysis method of the present invention Traditional single isothermal extrapolation method test cycle ≤500h (extended to 100,000h lifespan) ≥3000h (extended to 100,000h lifespan) Representation Dimension Macroscopic fracture time + microstructure + crack path + life prediction Macroscopic fracture time + life prediction only Prediction bias ≤5% ≥15% Mechanism explanation ability The influence of γ' / γ'' phase coarsening and fracture mode can be clearly identified. No mechanistic analysis Equipment compatibility Conventional high temperature testing machine + SEM + optical microscope High temperature testing machine only Results provide guidance value. High (clear service stress thresholds and maintenance recommendations) Low (Lifetime value only)

[0081] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing the creep rupture properties of GH4706 alloy, characterized in that, include: (1) Sample preparation and pretreatment: Standard samples were cut from the alloy workpiece and pretreated by aging at 600℃ / 5000h. Metallographic samples were treated by chemical etching and electrolytic etching in two steps. (2) High temperature creep test: Set up a gradient temperature stress condition of 600~700℃ / 650~750MPa, and conduct the test according to GB / T2039-2012 standard, and record the creep fracture time; (3) Multidimensional microscopic characterization: The fracture morphology and γ' / γ'' phase evolution were observed by SEM, the crack propagation path was analyzed by optical microscopy, and the average phase size was measured; (4) Model establishment and life prediction: The Larson-Miller model was fitted based on experimental data, and the remaining life under different service temperature stresses was extrapolated; (5) Output a standardized report containing performance data, mechanism analysis and usage recommendations.

2. The method for analyzing the creep performance of GH4706 alloy according to claim 1, characterized in that, The chemical etching process is: 0.5g CuCl2 + 10mL HCl + 10mL C2H5OH.

3. The method for analyzing the creep performance of GH4706 alloy according to claim 1, characterized in that, The electrolytic etching process involved 150 mL of H3PO4, 10 mL of H2SO4, and 15 g of CrO3.

4. The method for analyzing the creep performance of GH4706 alloy according to any one of claims 1-3, characterized in that, In step (1), the electrolytic etching conditions are 15V for 8s and 5-8s for chemical etching, to ensure that the structure and phase morphology are clearly presented.

5. The method for analyzing the creep performance of GH4706 alloy according to claim 1, characterized in that, In step (1), the electrolytic etching conditions are 15V for 8s and 5-8s for chemical etching, to ensure that the structure and phase morphology are clearly presented.

6. The method for analyzing the creep performance of GH4706 alloy according to claim 1, characterized in that, In step (3), the magnification of SEM observation of the fracture surface is 500 to 5000 times, the magnification of phase morphology observation is 10000 to 50000 times, and the magnification of metallographic observation is 200 to 1000 times.

7. The method for analyzing the creep performance of GH4706 alloy according to claim 1, characterized in that, In step (4), the Larson-Miller model coefficients are A0 = 3.82468 × 10⁻⁶. 8 A1 = -4.04154 × 10 8 A2 = 1.42367 × 10 8 A3 = -1.67168 × 10 8 .

8. The method according to claim 1, characterized in that: The remaining service life prediction is obtained by extrapolating from high-temperature short-time data. The formula is T1(24.53+lgtᵣ1)=T2(24.53+lgtᵣ2), with a prediction deviation of ≤5%. In the formula, T1 and tᵣ1 are the test temperature and fracture time, respectively; T2 is the service temperature; and tᵣ2 is the predicted remaining service life.

9. The method for analyzing the creep rupture properties of GH4706 alloy according to claim 1, characterized in that: It is applicable to high-temperature components such as GH4706 alloy turbine disk forgings, and can be extended to the creep performance analysis and life prediction of similar γ' / γ'' phase precipitation-strengthened high-temperature alloys.