Quantitative evaluation method for micro-region comprehensive mechanical properties of electron beam welded joint

Abstract

The application provides a kind of quantitative evaluation method of micro zone comprehensive mechanical properties of electron beam welding joint, and belongs to the technical field of material mechanical property evaluation.The application obtains load-displacement curve by nanoindentation test, adopts data processing method combining numerical integration and high-order derivative calculation, extracts three types of performance parameters including strength, plasticity and strain hardening, and establishes quantitative mapping relationship between the performance parameters and micro zone structure.The application solves the quantitative evaluation problem of mechanical properties of gradient structure in fusion zone, heat affected zone and base material zone of welding joint, and the problems of high cost, low efficiency and single parameter existing in existing evaluation technology.

Description

Technical Field

[0001] This invention belongs to the field of material mechanical property evaluation technology, and in particular relates to a quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints. Background Technology

[0002] Ti2AlNb-based alloys, as novel high-temperature titanium alloys, possess characteristics such as low density, high-temperature strength, and excellent oxidation resistance, making them ideal structural materials for advanced equipment such as aero-engines and hypersonic vehicles. Electron beam welding, due to its advantages of high energy density, narrow weld seam, and small heat-affected zone, has become the preferred process for joining Ti2AlNb components. However, the rapid heating and cooling during electron beam welding causes the weld joint to form multiple characteristic microregions, including the fusion zone, heat-affected zone, and base metal zone. Each microregion undergoes different thermal cycling processes, resulting in significant differences in the content, morphology, and distribution of multiphase microstructures such as O phase, α2 phase, and B2 phase, thus causing a spatial gradient distribution of mechanical properties such as strength and plasticity. This non-uniformity of microregion properties is the fundamental reason why the weld joint becomes a weak point in the component, severely restricting the application of Ti2AlNb alloys in high-end equipment.

[0003] The mechanical properties of Ti2AlNb alloys are highly dependent on their multiphase microstructure. Studies have shown that the content and morphology of the O phase directly affect the room temperature plasticity of the alloy, the precipitation strengthening effect of the α2 phase determines the high-temperature strength, while the volume fraction of the B2 phase affects the toughness and fracture behavior of the material. During electron beam welding, the fusion zone undergoes complete melting and rapid solidification, often forming coarse columnar crystals and non-equilibrium phase structures, leading to a decrease in plasticity. The peak temperature and cooling rate of the heat-affected zone differ, resulting in gradient changes in phase composition and grain size. If precise control of process parameters such as welding heat input, preheating temperature, and post-weld heat treatment can be achieved to precisely regulate the microstructure of each microzone, refining and uniformly distributing the O phase, ensuring appropriate precipitation of the α2 phase, and optimizing grain size, the micro-region performance matching can be effectively improved, enhancing the overall mechanical properties of the joint. However, such precise regulation requires establishing a quantitative correlation between "process parameters - micro-region microstructure - mechanical properties," which necessitates low-cost, high-throughput micro-region performance evaluation technology.

[0004] The evaluation of the mechanical properties of Ti2AlNb electron beam welded joints presents significant challenges. The weld width is typically only a few millimeters, and the heat-affected zone is even narrower, necessitating mechanical property testing at the micrometer or even submicrometer scale. This renders traditional macroscopic mechanical property evaluation methods (such as tensile testing) inadequate. While existing precision testing techniques such as nanoindentation can achieve micro-area characterization, they only provide hardness and elastic modulus parameters, failing to evaluate plasticity and work hardening capacity, and hindering the establishment of a quantitative correlation between "process-microstructure-property," thus restricting the precise control of the welding process. Therefore, developing a low-cost, high-efficiency quantitative evaluation technology for micro-area properties of Ti2AlNb welded joints is an urgent need for achieving precise joint quality control and microstructure optimization. For this reason, developing low-cost quantitative evaluation technologies for micro-area properties and precise microstructure control methods for welded and packaged components with similar structural characteristics, such as Ti2AlNb electron beam welded joints, is not only necessary for solving practical engineering problems but also has significant scientific value and strategic importance. The establishment of this technical system can provide an effective means for performance prediction and reliability assessment of high-temperature titanium alloy welded joints, supporting the independent development of major equipment such as aero-engines; at the same time, the relevant methodology can be extended to other difficult-to-weld material systems, promoting the development of advanced joining technologies and enhancing the core competitiveness in the high-end manufacturing field. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides a quantitative evaluation method for the comprehensive mechanical properties of micro-regions in electron beam welded joints. This method solves the problem of quantitatively evaluating the mechanical properties of the gradient structure in the fusion zone, heat-affected zone, and base material zone of welded joints, as well as addressing the issues of high cost, low efficiency, and limited parameters in existing evaluation technologies.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints, comprising the following steps:

[0007] S1. Cut the Ti2AlNb electron beam welded joint and obtain the test sample through sample preparation;

[0008] S2. By performing nano-indentation tests on the test samples, the load-displacement curves are recorded in real time.

[0009] S3. Extract strength performance parameters;

[0010] S4. Read the load-displacement curve and extract the plastic performance parameters that characterize the plastic deformation bearing capacity of the material;

[0011] S5. Based on plasticity parameters, strain hardening parameters are extracted by establishing discrete data pairs of total pressure work and indentation depth.

[0012] S6. By performing outlier detection on the test data of each micro-region and conducting statistical analysis on the test data, a sample after testing is obtained.

[0013] S7. Chemically etch the tested samples and observe the microstructure morphology of each micro-region. Based on the observation results, characterize the microstructure by statistically analyzing the content of each phase, morphological parameters, and grain size.

[0014] S8. Based on the characterization results, strength performance parameters, plasticity and hardening capacity, establish a regression model for the comprehensive mechanical properties of the joint, and use the regression model to establish a quantitative correlation between microstructure and properties, thereby completing the quantitative evaluation of the comprehensive mechanical properties of the micro-region of the electron beam welded joint.

[0015] Further, S1 includes the following steps:

[0016] S101, Cut the Ti2AlNb electron beam welding joint;

[0017] S102. Based on the cutting results, metallographic preparation is performed on the cross-section of the sample perpendicular to the weld direction, and then sandpaper is used to polish it in sequence.

[0018] S103. After grinding, the sample is polished and finely polished.

[0019] S104. After fine polishing, use ultrasonic cleaning, and then dry to obtain a test sample with a smooth, scratch-free surface that fully exposes the fusion zone, heat-affected zone, and base material zone.

[0020] Furthermore, S2 includes the following steps:

[0021] S201. Using a Berkovich diamond indenter, fix the test sample on the indenter sample stage in a constant temperature laboratory and place it in the test chamber for 60 min - 90 min.

[0022] S202. After the indenter contacts the sample surface, hold it for 200s-400s until the thermal drift rate is ≤0.05nm / s before starting the test.

[0023] S203. Using a trapezoidal loading function, linearly load to the target load of 5-10mN in 5s, hold the load for 2s, and then linearly unload to 0mN in 5s.

[0024] S204. Perform multiple indentation tests in each micro-area, with an indentation spacing ≥ 20 times the indentation depth, and record the load-displacement curve in real time.

[0025] Furthermore, S3 specifically involves using the hardness H calculated using a nanoindenter as a strength performance parameter.

[0026] Furthermore, the expression for the plasticity is as follows:

[0027] ;

[0028] ;

[0029] ;

[0030] in, Indicates plasticity, Indicates the total work pushed in. Indicates elastic work. i This indicates the data point sequence number during the loading phase. j This indicates the data point number during the unloading phase. Indicates the load on the loaded segment. Indicates the loading phase i The push depth corresponding to +1 data point Indicates the loading phase i The push depth corresponding to each data point Indicates the unloading phase. j The push depth corresponding to +1 data point Indicates the unloading phase. j The indentation depth corresponding to each data point.

[0031] Furthermore, step S5 includes the following steps:

[0032] S501. Based on plasticity performance parameters, establish discrete data pairs between total pressure work S and indentation depth h;

[0033] S502. Based on discrete data pairs, a fifth-order polynomial is used to fit the relationship between the total pressure work S and the indentation depth h.

[0034] S503. Based on the fitting results, calculate the first derivative of the total pressure work S with respect to the pressure depth h;

[0035] S504. Based on the first derivative, calculate the second derivative of the total pressure work S with respect to the pressure depth h, and use the second derivative as the strain hardening parameter S to complete the extraction of the hardening capacity parameter.

[0036] Furthermore, the expression for the strain hardening parameter is as follows:

[0037] ;

[0038] in, This represents the strain hardening parameter. , , and All represent polynomial fitting coefficients.

[0039] Furthermore, the expression for the regression model of the joint's comprehensive mechanical properties is as follows:

[0040] H = α0+ α1f_O + α2f_α2+ α3f_B2 + α4 / d;

[0041] S p = β0+ β1f_O + β2f_α2 + β3f_B2 + β4 / d;

[0042] = γ0+ γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d;

[0043] In the above, H represents strength performance. Indicates plasticity, Let f_O, f_α2, and f_B2 represent the volume fractions of the O, α2, and B2 phases, respectively. Let α0 represent the intrinsic hardness, and let α1, α2, α3, and α4 represent the contribution rates of the O, α2, B2, and grain size to the hardness, respectively. Let β0 represent the intrinsic indentation work, and let β1, β2, β3, and β4 represent the contribution rates of the O, α2, B2, and grain size to the total indentation work, respectively. Let γ0 represent the intrinsic strain hardening parameter, and let γ1, γ2, γ3, and γ4 represent the contribution rates of the O, α2, B2, and grain size to the strain hardening parameter, respectively. Let d represent the average grain size.

[0044] Furthermore, the quantitative evaluation method also includes a process-performance mapping relationship establishment step: repeating S1 to S8 for joints under different welding heat inputs and heat treatment processes to establish a welding parameter-microzone structure-mechanical property database. The welding parameter-microzone structure-mechanical property database is used to fit the influence law of process parameters on performance parameters.

[0045] The beneficial effects of this invention are:

[0046] This invention discloses a quantitative evaluation method for the comprehensive mechanical properties of micro-regions in Ti2AlNb alloy electron beam welded joints. Addressing the gradient distribution of mechanical properties caused by differences in microstructure among the fusion zone, heat-affected zone, and base metal region of the welded joint, and the problems of high cost, low efficiency, and single parameter limitations in existing evaluation techniques, this invention obtains load-displacement curves through nano-indentation testing. It employs a data processing method combining numerical integration and higher-order derivative calculations to simultaneously extract three types of performance parameters: strength properties, plastic work (i.e., plasticity), and strain hardening parameters. This enables quantitative characterization of the strength, plasticity, and strain hardening capacity of each micro-region of the welded joint. Specifically, this invention proposes for the first time using the second derivative of the total indentation work with respect to indentation depth, d²S / dh², as a quantitative evaluation index of strain hardening capacity. Furthermore, it establishes a multiple linear regression model—a regression model for the comprehensive mechanical properties of the joint—to achieve a quantitative correlation between micro-region microstructure (content of O phase, α2 phase, B2 phase, and grain size) and mechanical properties, providing a basis for welding process optimization and performance prediction. This invention offers advantages such as short testing cycle, low testing cost, diverse results, and high spatial resolution. It can be extended to the micro-area performance evaluation and microstructure optimization of welded or packaged components made of titanium alloys, nickel-based superalloys, and composite materials. It can be used for quality assessment, process optimization, and microstructure control of welded joints in high-temperature alloys such as Ti2AlNb, and can be further expanded into the field of quality evaluation of welded and packaged components. Attached Figure Description

[0047] Figure 1 This is a flowchart of the method of the present invention.

[0048] Figure 2 Scanning electron microscope (SEM) images of the microstructure of different regions of the electron beam welded joint of Ti2AlNb-based alloy.

[0049] Figure 3 This is a schematic diagram showing the nano-indentation curves and indentation work parameters of different regions of the electron beam welded joint of Ti2AlNb-based alloy.

[0050] Figure 4 This is a schematic diagram showing the variation trend of the total nano-indentation work and its first and second derivatives with respect to indentation depth in different regions of the electron beam welded joint of Ti2AlNb-based alloy.

[0051] Figure 5 These are scanning electron microscope (SEM) images of the microstructure of different regions of the electron beam welded joint of Ti2AlNb-based alloy after heat treatment.

[0052] Figure 6 This is a schematic diagram showing the nano-indentation curves and indentation work parameters of different regions of the electron beam welded joint of Ti2AlNb-based alloy after heat treatment.

[0053] Figure 7This is a schematic diagram showing the variation trend of the total nano-indentation work in different regions of the Ti2AlNb-based alloy electron beam welded joint after heat treatment and its first and second derivatives with respect to the indentation depth. Detailed Implementation

[0054] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0055] Example 1

[0056] This invention obtains load-displacement curves through nanoindentation testing, employs a data processing method combining numerical integration and higher-order derivative calculations, and simultaneously extracts three types of performance parameters: strength, plasticity, and strain hardening. Furthermore, it establishes a quantitative mapping relationship between these parameters and the microstructure. Figure 1 As shown, this invention provides a quantitative evaluation method for the comprehensive mechanical properties of micro-regions in electron beam welded joints, the implementation method of which is as follows:

[0057] S1. Cut the Ti2AlNb electron beam welded joint and prepare the test sample. The method is as follows:

[0058] S101, Cut the Ti2AlNb electron beam welding joint;

[0059] S102. Based on the cutting results, metallographic preparation is performed on the cross-section of the sample perpendicular to the weld direction, and then sandpaper is used to polish it in sequence.

[0060] S103. After grinding, the sample is polished and finely polished.

[0061] S104. After fine polishing, use ultrasonic cleaning, and then dry to obtain a test sample with a smooth, scratch-free surface that fully exposes the fusion zone, heat-affected zone, and base material zone.

[0062] In this embodiment, the materials and welding are as follows: A Ti2AlNb-based alloy is used, with a nominal composition of Ti-22Al-25Nb (at.%) and an actual composition (wt.%) of: Aluminum (Al) 8.7%, Niobium (Nb) 41.6%, Carbon (C) 5.1%, O (O) 2.7%, and the balance being Titanium (Ti). Electron beam welding parameters are: accelerating voltage 50kV, beam current 40mA, and welding speed 300mm / min. The welded joint consists of a fusion zone (FZ, approximately 2.5mm wide), a heat-affected zone (HAZ, approximately 0.5mm wide), and a base metal zone (BM).

[0063] In this embodiment, sample preparation is as follows: Ti2AlNb electron beam welded joints are cut using wire electrical discharge machining (EDM) technology, with sample dimensions of 8-15mm × 5-10mm × 3-8mm; metallographic preparation is performed on the cross-section of the sample perpendicular to the weld direction, which is then polished with 400# to 2000# sandpaper, followed by polishing with diamond polishing paste, and finally fine polishing with 0.05μm silica suspension; after ultrasonic cleaning, the sample is dried to obtain a smooth, scratch-free surface that fully exposes the fusion zone, heat-affected zone, and base material zone.

[0064] Samples were prepared according to S1, resulting in test specimens with dimensions of 10 mm × 7 mm × 5 mm and a surface roughness Ra = 6 nm. Scanning electron microscopy (SEM) results are shown below. Figure 2 As shown, the joint FZ (melting zone) contains a small amount of nano-O phase (3%) and B2 matrix (average grain size 600 μm); HAZ (heat-affected zone) contains a small amount of nano-O phase (6.5%) and B2 matrix (average grain size 250 μm); BM (base material zone) contains 4% α2 phase (average grain size 3 μm) and B2 matrix (average grain size 120 μm).

[0065] S2. By performing nanoindentation tests on the test samples, the load-displacement curves are recorded in real time. The method for achieving this is as follows:

[0066] S201. Using a Berkovich diamond indenter, fix the test sample on the indenter sample stage in a constant temperature laboratory and place it in the test chamber for 60-90 minutes.

[0067] S202. After the indenter contacts the sample surface, hold it for 200s-400s until the thermal drift rate is ≤0.05nm / s before starting the test.

[0068] S203. Using a trapezoidal loading function, linearly load to the target load of 5-10mN in 5s, hold the load for 2s, and then linearly unload to 0mN in 5s.

[0069] S204. Perform multiple indentation tests in each micro-area, with an indentation spacing ≥ 20 times the indentation depth, and record the load-displacement curve in real time.

[0070] In this embodiment, the nano-indentation test was conducted in a constant temperature laboratory (temperature 24±2℃, humidity 50±10%). The sample was fixed on the sample stage of the indenter and placed in the test chamber for 60-90 minutes. After the indenter contacted the sample surface, it was held for 200-400 seconds until the thermal drift rate was ≤0.05nm / s before the test began. A trapezoidal loading function was used to linearly load the sample to the target load of 5-10mN for 5 seconds, hold the load for 2 seconds, and then linearly unload the sample to 0mN for 5 seconds. At least 5 indentation tests were performed in each micro-region, with an indentation spacing ≥20 times the indentation depth. The load-displacement curve was recorded in real time.

[0071] For nanoindentation testing, a Hysitron TI950 nanoindenter with a Berkovich diamond indenter was used. Test conditions were: temperature 24.2±0.3℃, humidity 47%, sample stabilization time 75 min, thermal drift rate 0.03 nm / s, loading program 5 s–2 s–5 s, maximum load 10 mN. Ten tests were performed in each of the FZ (melted zone), HAZ (heat-affected zone), and BM (base material zone).

[0072] The nanoindentation test uses a Berkovich diamond indenter with a target load of 1-10 mN and a loading program of 5s-2s-5s.

[0073] S3. Extract the strength performance parameters, specifically: use the hardness H calculated using a nanoindenter as the strength performance parameter.

[0074] S4. Read the load-displacement curve and extract the plastic performance parameters that characterize the plastic deformation bearing capacity of the material;

[0075] The expression for plasticity is as follows:

[0076] ;

[0077] ;

[0078] ;

[0079] in, Indicates plasticity, Indicates the total work pushed in. Indicates elastic work. i This indicates the data point sequence number during the loading phase. j This indicates the data point number during the unloading phase. Indicates the load on the loaded segment. Indicates the loading phase i The push depth corresponding to +1 data point Indicates the loading phase i The push depth corresponding to each data point Indicates the unloading phase. j The push depth corresponding to +1 data point Indicates the unloading phase. j The indentation depth corresponding to each data point.

[0080] In this embodiment, load-displacement curve data are read; the total indentation work S and the elastic work S' are calculated using the trapezoidal integral method. e The integration step size Δh < 5 nm; calculate the plastic work (i.e., plastic properties) S. p =SS e This parameter characterizes the material's ability to withstand plastic deformation.

[0081] S5. Based on plasticity parameters, strain hardening parameters are extracted by establishing discrete data pairs between total pressure work and indentation depth. The implementation method is as follows:

[0082] S501. Based on plasticity performance parameters, establish discrete data pairs between total pressure work S and indentation depth h;

[0083] S502. Based on discrete data pairs, a fifth-order polynomial is used to fit the relationship between the total pressure work S and the indentation depth h.

[0084] S503. Based on the fitting results, calculate the first derivative of the total pressure work S with respect to the pressure depth h;

[0085] S504. Based on the first derivative, calculate the second derivative of the total pressure work S with respect to the pressure depth h, and use the second derivative as the strain hardening parameter S to complete the extraction of the hardening capacity parameter.

[0086] In this embodiment, the strain hardening capability parameter is extracted as follows: A discrete data pair of total indentation work S and indentation depth h is established; a fifth-order polynomial is used to fit the relationship between Sh and h, requiring a goodness of fit R² > 0.98; the first derivative of the indentation work with respect to depth, dS / dh, is calculated; the second derivative of the indentation work with respect to depth, d²S / dh², is calculated as the strain hardening parameter. The average value of the second derivative of the loaded segment is taken as the strain hardening parameter at that measuring point.

[0087] ;

[0088] in, This represents the strain hardening parameter. , , and All represent polynomial fitting coefficients.

[0089] The hardening index is calculated by performing a fifth-order polynomial fit on the Sh data: S(h) = a0 + a1h + a2h² + a3h³ + a4h4 + a5h 5 Calculate the first derivative: dS / dh = a1 + 2a2h + 3a3h² + 4a4h³ + 5a5h 4 Calculate the second derivative: d²S / dh² = 2a² + 6a³h + 12a⁴h² + 20a⁵h³; take the value of the second derivative at the maximum load point h = hmax as the strain hardening parameter. ,in, , Represents the polynomial fitting coefficients.

[0090] S6. By performing outlier detection on the test data of each micro-region and conducting statistical analysis on the test data, a sample after testing is obtained.

[0091] In this embodiment, the data statistical analysis is as follows: outlier detection is performed on the test data of each micro-region, the mean and standard deviation are calculated, and data points that deviate from the mean by more than 1.5 times the standard deviation are removed; the mean, standard deviation and coefficient of variation of the retained data are calculated, and the coefficient of variation is required to be <10%. That is, the outlier detection adopts the 1.5 times standard deviation criterion, and data points that deviate from the mean by more than 1.5 times the standard deviation are removed, and the coefficient of variation is required to be less than 10%.

[0092] S7. Chemically etch the tested samples and observe the microstructure morphology of each micro-region. Based on the observation results, characterize the microstructure by statistically analyzing the content of each phase, morphological parameters, and grain size.

[0093] In this embodiment, the microstructure characterization is performed as follows: the sample after testing is chemically etched; the microstructure morphology of each micro-region is observed using a scanning electron microscope; and the content, morphological parameters and grain size of each phase are quantitatively calculated using image analysis software.

[0094] S8. Based on strength performance parameters, plasticity performance and hardening capacity, establish a regression model for the comprehensive mechanical properties of the joint, and use the regression model for the comprehensive mechanical properties of the joint to establish a quantitative correlation between microstructure and properties, and complete the quantitative evaluation of the comprehensive mechanical properties of the micro-region of the electron beam welded joint.

[0095] In this embodiment, the quantitative correlation between tissue and properties is established as follows: a multiple linear regression model is established, where f_O, f_α2, and f_B2 represent the volume fractions of the O phase, α2 phase, and B2 phase, respectively, and d represents the average grain size; the least squares method is used to fit the regression coefficients; the significance of the model is verified, requiring the coefficient of determination R² > 0.85.

[0096] The expression for the regression model of the joint's comprehensive mechanical properties is as follows:

[0097] H = α0+ α1f_O + α2f_α2+ α3f_B2 + α4 / d;

[0098] S p = β0+ β1f_O + β2f_α2 + β3f_B2 + β4 / d;

[0099] = γ0+ γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d;

[0100] H = α0+ α1f_O + α2f_α2+ α3f_B2 + α4 / d;

[0101] S p = β0+ β1f_O + β2f_α2 + β3f_B2 + β4 / d;

[0102] = γ0+ γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d;

[0103] In the above, H represents strength performance. Indicates plasticity, Let f_O, f_α2, and f_B2 represent the volume fractions of the O, α2, and B2 phases, respectively. Let α0 represent the intrinsic hardness, and let α1, α2, α3, and α4 represent the contribution rates of the O, α2, B2, and grain size to the hardness, respectively. Let β0 represent the intrinsic indentation work, and let β1, β2, β3, and β4 represent the contribution rates of the O, α2, B2, and grain size to the total indentation work, respectively. Let γ0 represent the intrinsic strain hardening parameter, and let γ1, γ2, γ3, and γ4 represent the contribution rates of the O, α2, B2, and grain size to the strain hardening parameter, respectively. Let d represent the average grain size.

[0104] In this embodiment, the quantitative evaluation method further includes a process-performance mapping relationship establishment step: repeating S1 to S8 for joints under different welding heat inputs and heat treatment processes to establish a welding parameter-micro-region structure-mechanical property database, and fitting the influence law of process parameters on performance parameters based on the welding parameter-micro-region structure-mechanical property database.

[0105] In this embodiment, the present invention is applicable to the evaluation of the micro-area mechanical properties of welded or packaged components such as titanium alloys, nickel-based superalloys, and aluminum-based composite materials.

[0106] In this embodiment, a multi-parameter extraction method for mechanical properties based on nano-indentation load-displacement curves is used to quantitatively characterize strain hardening capability through numerical integration and higher-order derivative calculations. The process is as follows:

[0107] Obtain nano-indentation load-displacement curve data, including loading and unloading phases; calculate the total indentation work S and elastic work S using the trapezoidal integral method. e Integration step size < 5 nm; Calculate plastic work S p =SS e A fifth-order polynomial fit is performed on the total indentation work S and the indentation depth h, requiring a goodness of fit R² > 0.98; the second derivative of the total indentation work S with respect to the indentation depth h, d²S / dh², is calculated as the strain hardening parameter; the second derivative value at the maximum load is taken as the final strain hardening capacity characterization parameter.

[0108] In this embodiment, the trapezoidal integral algorithm is used to calculate the indentation work and elastic work; the fifth-order polynomial fitting algorithm is used to establish the functional relationship between the indentation work and the depth; the higher-order derivative calculation algorithm is used to extract strain hardening parameters; and the outlier detection algorithm is used to remove data points that deviate from the mean by more than 1.5 times the standard deviation.

[0109] In this embodiment, a multiple linear regression method is used to establish a quantitative correlation model between strength performance parameters, plasticity performance and hardening ability index and the volume fraction of O phase, α2 phase, B2 phase and grain size, requiring the coefficient of determination R²>0.85 and p value<0.05.

[0110] In this embodiment, the relevant curves are as follows: Figure 3 and Figure 4 As shown, the obtained comprehensive mechanical property parameters are as follows:

[0111] Strength parameter - Hardness H:

[0112] FZ (Melting Zone): H = 5.07 ± 0.12 GPa; HAZ (Heat Affected Zone): H = 5.11 ± 0.15 GPa; BM (Base Material Zone): H = 4.86 ± 0.09 GPa. The results show that the hardness of FZ (Melting Zone) and HAZ (Heat Affected Zone) is significantly higher than that of BM. FZ (Melting Zone) represents the fusion zone, HAZ (Heat Affected Zone) represents the heat affected zone, and BM (Base Material Zone) represents the base material zone.

[0113] Plasticity parameter - plastic work S p :

[0114] Calculated by numerical integration: FZ (melting zone): S p =910.27±35.2nJ; HAZ (Heat Affected Zone): S p =884.20±32.8nJ; BM (base material region): S p =938.94±28.6nJ, indicating that BM has the highest plastic work, which means that it has the strongest plastic deformation bearing capacity.

[0115] Strain hardening parameters - strain hardening parameters :

[0116] A fifth-order polynomial fit (R²>0.995) was performed on the Sh data to calculate the work hardening capacity index of each microregion: FZ (melting zone): =31.33±2.1MJ / m²; HAZ (Heat Affected Zone): 29.31±1.8MJ / m²; BM (base material zone): =27.97±1.6MJ / m²;

[0117] FZ has the highest strain hardening capacity.

[0118] Statistical analysis: The coefficients of variation (CV) for each parameter are: hardness 2.4-2.9%, plasticity 3.1-3.9%, and strain hardening parameter 5.2-7.1%, all meeting the requirement of CV < 10%. The linear regression model for the comprehensive mechanical performance parameters of the joint is as follows:

[0119] H = 5.1867+ 0.0242·f_O - 0.0217·f_α2- 0.0025·f_B2 - 0.0000 / d;

[0120] S p = -67.4092 - 6.7342·f_O - 3.9116·f_α2+ 10.6458·f_B2 - 0.0246 / d;

[0121] = -90.9359 - 0.0567·f_O - 1.2333·f_α2+ 1.2900·f_B2 - 0.0045 / d.

[0122] Example 2

[0123] In this embodiment, the performance evaluation of the heat-treated Ti2AlNb electron beam connector micro-region is as follows:

[0124] 1. Microstructure of the heat-treated welded joint: The Ti2AlNb electron beam welded joint in Example 1 was heat-treated at 800℃ for 2 hours and then furnace cooled to room temperature. The microstructure of the heat-treated sample consisted of the FZ (melt zone), HAZ (heat-affected zone), and base metal (BM). Scanning electron microscopy (SEM) results are shown below. Figure 5As shown, the joint FZ consists of 60% nano-O phase and B2 matrix (average grain size 600 μm); the HAZ (heat-affected zone) consists of 60% nano-O phase, 5% α2 phase (average grain size 3 μm) and B2 matrix (average grain size 250 μm); and the base material (BM) consists of 55% nano-O phase, 4% α2 phase (average grain size 3.5 μm) and B2 matrix (average grain size 120 μm).

[0125] 2. Nanoindentation Test: A Hysitron TI950 nanoindenter with a Berkovich diamond indenter was used. Test conditions: temperature 24.2±0.3℃, humidity 47%, sample stabilization time 75 min, thermal drift rate 0.03 nm / s, loading program 5 s-2 s-5 s, maximum load 10 mN. Ten tests were performed in each of the fusion zone (FZ), heat-affected zone (HAZ), and base material zone (BM).

[0126] 3. Data processing results: Correlation curves are as follows Figure 6 and Figure 7 As shown, the obtained comprehensive mechanical property parameters are as follows:

[0127] (1) Strength parameter - hardness H:

[0128] FZ: 5.61±0.13GPa (+10.7%); HAZ: 5.73±0.16GPa (+12.1%); BM: 5.69±0.11GPa (+17.1%), indicating that heat treatment significantly improved the hardness of the three micro-zones and reduced the differences.

[0129] (2) Plasticity parameter - plasticity work S p :

[0130] FZ: 824.02±31.5nJ (-9.5%); HAZ: 813.40±28.9nJ (-8.0%); BM: 807.84±26.2nJ (-14.0%). The plastic work decreased after heat treatment, but FZ (melting zone) was higher than BM (base material zone), indicating that its plastic deformation capacity was relatively improved.

[0131] (3) Strain hardening parameters - strain hardening parameters :

[0132] FZ: 36.47±2.4MN / m² (+16.4%); HAZ: 35.30±2.1MN / m² (+20.4%); BM: 31.87±1.9MN / m² (+13.9%). The strain hardening capacity was improved after heat treatment, with the most significant improvement in FZ (melting zone).

[0133] 4. Regression model for comprehensive mechanical properties of the joint:

[0134] H =5.1300 + 0.0080·f_O + 0.0240·f_α2;

[0135] S p = 757.30 + 1.11·f_O - 2.12·f_α2;

[0136] = -4.69 + 0.69·f_O - 0.23·f_α 2。

[0137] This invention is applicable to the evaluation of micro-area performance of welded or packaged components made of other titanium alloys, nickel-based high-temperature alloys, aluminum-based composite materials, etc.

[0138] The initial source and derivation process of the formulas in this invention will be explained below.

[0139] 1. Source of the original formula

[0140] The formula S used in this invention for calculating plastic work (i.e., plastic properties) p =SS e This is derived from the Oliver-Pharr nanoindentation model in the field of micro-nano mechanics, where the plastic work is S. p That is, plasticity, the total work of indentation is S, and the elastic recovery work is S. e This invention combines the plastic work calculation formula with the nanoindentation test control program, enabling highly efficient measurement of elastic work corresponding to different indentation depths.

[0141] This invention employs a fifth-order polynomial to fit discrete data pairs of the total work S and the indentation depth h during nanoindentation, requiring a goodness-of-fit coefficient R² > 0.98. This is derived from the nanoindentation model, where the general form of the fitting formula is: S(h) = a0 + a1h + a2h² + a3h³ + a4h 4 + a5h 5 The goodness-of-fit coefficient R² = 1 - (SSE / SST), where SSE represents the sum of squares of the differences between the measured values ​​and the fitted values, and SST represents the sum of squares of the differences between the actual values ​​and the mean.

[0142] This invention uses a multiple linear regression model Y i =β0+β1X 1i +,…,+β k X ki +μ i The volume fractions of O phase, α2 phase, and B2 phase and the average grain size of the matrix in the microstructure of Ti2AlNb electron beam welded joints were established, and their correlation with nanoindentation properties, hardness (H), and plasticity (S) was determined. pQuantitative correlation of strain hardening parameter S'', β0 represents the total intrinsic indentation work, X 1i X k These represent the constituent phases in the microstructure, β1, β2, and β3, respectively. k The values ​​represent the contribution rates of each component in the microstructure to the relative mechanical properties, μ. i Indicates error.

[0143] The detailed derivation of the application formula and the innovative definition are as follows:

[0144] 1. This invention employs a trapezoidal differential algorithm to realize the plastic work S for nano-indentation curves at different indentation depths. p The calculation, that is

[0145] .

[0146] 2. Based on the S-polynomial fitting of the indentation work, this invention analyzes the strain hardening parameters of the micro-region material by solving the boundary conditions through second derivative. The expression, that is:

[0147] The numerical expression for the compressive work is S(h) = a0 + a1h + a2h² + a3h³ + a4h 4 + a5h 5 ;

[0148] First derivative =dS / dh = a1+ 2a2h + 3a3h² + 4a4h³ + 5a5h 4 ;

[0149] Second derivative =d²S / dh² = 2a² + 6a³h + 12a⁴h² + 20a⁵h³, and define the pressure depth h to obtain the maximum indentation value hmax. The value is the strain hardening parameter of the material.

[0150] 3. This invention quantifies the microstructural characteristics of micro-regions (volume fraction of constituent phases, matrix grain size) and nano-indentation mechanical property parameters, and inputs them into a regression model of the joint's comprehensive mechanical properties. The parameters of this regression model are then solved to quantitatively evaluate the contribution of each structural parameter to the mechanical properties. The regression model of the joint's comprehensive mechanical properties is as follows:

[0151] H = α0+ α1f_O + α2f_α2+ α3f_B2 + α4 / d;

[0152] S p = β0+ β1f_O + β2f_α2 + β3f_B2 + β4 / d;

[0153] = γ0+ γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d;

[0154] Where H represents hardness, S p This represents plastic work, or plastic properties. The parameters represent strain hardening, where f_O, f_α2, and f_B2 represent the volume fractions (%) of the O, α2, and B2 phases, respectively, and d represents the average grain size (μm). The microstructure characteristics and mechanical properties dataset used in the model are [f_O, f_α2, f_B2, d; H, S]. p , ].

[0155] The dimensions of the formula are verified as follows:

[0156] 1. For the formula for calculating the plastic work of indentation, i.e. the plastic properties, the dimension of the left side of the formula is J, and the dimension of the right side of the formula is the product of the load N and the indentation displacement m, i.e. J=N·m, and the dimensions of both sides are consistent.

[0157] 2. For the formula for calculating the strain hardening parameters of micro-region materials, the left side is... The acceleration that describes the change of the total work done in pressing along the pressing depth is expressed in J / m. 2 The right side represents d²S / dh², with corresponding dimensions of N / m = N·m / m. 2 =Left side, meaning the dimensions of both sides are the same.

[0158] 3. For the regression model of the comprehensive mechanical properties of the joint with nano-indentation mechanical property parameters, the left side of the formula contains hardness H and plastic work S. p and strain hardening parameters The dimensions are GPa, J and J / m, respectively. 2 The right side of the formula represents the volume fractions (%) of the dimensionless parametric O phase, α2 phase, and B2 phase, and the average grain size d (dimensionless in μm). To ensure dimensionality consistency on both sides, α is defined as... 0-3 The unit is GPa, and the unit for α4 is GPa·μm; β 0-3 The unit is J; β4 is in J·μm; γ 0-3 The unit is J / m 2 γ4 is measured in J·μm / m 2 .

[0159] The logical relationships and derivation process of the multiple formulas are as follows:

[0160] The first step is to obtain the compressive work S(h) through numerical fitting: S(h) = a0 + a1h + a2h² + a3h³ + a4h 4 + a5h5 ;

[0161] The second step is to solve for the second derivative of S(h). =( a1+ 2a2h + 3a3h² + 4a4h³ + 5a5h 4 )=2a2+ 6a3h+ 12a4h² + 20a5h³;

[0162] The third step involves obtaining the dataset [f_O, f_α2, f_B2, d; H, S] p Substitute [S''] into the multivariate linear model and solve for the model parameters using the normal equation method.

[0163] The process of algorithmic deduction of technical effects is as follows:

[0164] 1. Parameter Acquisition and Dataset Construction: The volume fractions f_O, f_α2, and f_B2 of the O phase, α2 phase, and B2 phase in the fusion zone (FZ), heat-affected zone (HAZ), and matrix (BM) of the Ti2AlNb welded joint were obtained using microstructural characterization techniques, as well as the B2 grain size d in the matrix. Nanoindentation techniques were used to obtain the nanoindentation load-displacement curves and hardness H of each microregion of the Ti2AlNb welded joint. Based on the numerical integration of the nanoindentation curves, the total indentation work S at different indentation depths was obtained, and the plastic work S was calculated. p and strain hardening parameters Based on this, a dataset [f_O, f_α2, f_B2, d; H, S] is constructed. p , ].

[0165] 2. Data Calculation: Phase proportions and matrix grain sizes of each micro-region in the as-welded Ti2AlNb joint: FZ: f_O=3%, f_α2=0, f_B2=97%, d=600 μm; HAZ: f_O=6.5%, f_α2=0, f_B2=93.5%, d=250 μm; BM: f_O=0, f_α2=4%, f_B2=96%, d=120 μm. Based on the nanoindentation curves of each micro-region in the as-welded Ti2AlNb joint, the hardness H and plasticity work S were obtained. p and strain hardening parameters Fusion zone (FZ): H = 5.07 ± 0.12 GPa, S p =910.27±35.2nJ, fusion zone (FZ)=31.33±2.1MJ / m²; heat-affected zone (HAZ): H=5.11±0.15GPa, S p =884.20±32.8nJ, =29.31±1.8 MJ / m²; matrix (BM)H=4.86±0.09 GPa, S p =938.94±28.6nJ, =27.97±1.6MJ / m².

[0166] 3. Results: The dataset [f_O, f_α2, f_B2, d; H, S] was processed. p , Substituting into the regression model of the joint's comprehensive mechanical properties, we obtain:

[0167] H = 5.1867+ 0.0242·f_O - 0.0217·f_α2- 0.0025·f_B2 - 0.0000 / d;

[0168] S p = -67.4092 - 6.7342·f_O - 3.9116·f_α2+ 10.6458·f_B2 - 0.0246 / d;

[0169] = -90.9359 - 0.0567·f_O - 1.2333·f_α2+ 1.2900·f_B2 - 0.0045 / d.

[0170] Based on the above regression model (i.e., the regression model of the comprehensive mechanical properties of the joint), it was found that the O phase has a higher micro-region hardening effect compared with the α2 phase and B2 phase. Compared with the α2 phase and O phase, the B2 phase has a more significant contribution to the micro-region plastic deformation capacity and strain hardening trend. This is directly related to the characteristics of the hard and brittle O phase and the strong plastic deformation capacity of B2 phase in Ti2AlNb alloy. This proves the reliability of the linear regression model obtained by this method for quantitatively evaluating the contribution of each micro-region of the welded joint to the relative mechanical properties.

[0171] The following is an example of quantization calculation:

[0172] The quantitative evaluation of the contribution of microstructure to mechanical properties of aged Ti2AlNb welded joints is taken as an example.

[0173] 1. Parameter Acquisition and Dataset Construction: The electron beam welded Ti2AlNb joint in its welded state was heat-treated at 800℃ for 2 hours and then furnace-cooled to room temperature. Microstructural characterization techniques were used to obtain the volume fractions f_O, f_α2, and f_B2 of the O phase, α2 phase, and B2 phase in the fusion zone (FZ), heat-affected zone (HAZ), and matrix (BM) of the Ti2AlNb welded joint, as well as the B2 grain size d in the matrix. Nanoindentation techniques were used to obtain the nanoindentation load-displacement curves and hardness H of each microregion of the Ti2AlNb welded joint. Based on the numerical integration of the nanoindentation curves, the indentation work S at different indentation depths was obtained, and the plastic work S was calculated. p and strain hardening parameters Based on this, a dataset [f_O, f_α2, f_B2, d; H, S] is constructed. p , ].

[0174] 2. Data Calculation: Phase Proportion and Matrix Grain Size of Each Microregion in the Aging Ti2AlNb Welded Joint: FZ: f_O=60%, f_α2=0, f_B2=40%, d=600 μm; HAZ: f_O=60%, f_α2=0, f_B2=40%, d=250 μm; BM: f_O=55%, f_α2=4%, f_B2=45%, d=120 μm.

[0175] Based on the nanoindentation curves of each micro-region of the aged Ti2AlNb welded joint, the hardness H and plasticity S were obtained. p and strain hardening parameters For FZ: H = 5.61 ± 0.13 GPa, S p =824.02±31.5 nJ, =36.47±2.4 MJ / m²; HAZ:H=5.73±0.16 GPa, S p =813.40±28.9 nJ, =35.30±2.1 MJ / m²; BM: H=5.69±0.11GPa, S p =807.84±26.2 nJ, =31.87±1.9 MJ / m².

[0176] 3. Results: Substituting the dataset into the regression model of the joint's comprehensive mechanical properties, we obtain:

[0177] H =5.1300 + 0.0080·f_O + 0.0240·f_α2;

[0178] S p= 757.30 + 1.11·f_O - 2.12·f_α2;

[0179] = -4.69 + 0.69·f_O - 0.23·f_α2.

[0180] Comparison with the as-welded model parameters reveals that the precipitation of the O phase after aging significantly increases the microhardness (H) of the Ti2AlNb alloy joint. The O and α2 phases contribute more significantly to hardness than the B2 phase. Simultaneously, the plastic work of all microregions in the Ti2AlNb alloy decreases after aging, while the strain hardening parameters increase. Model parameter analysis indicates that the O phase is the main constituent phase enhancing the plastic work and strain hardening capacity of the aged Ti2AlNb joint in all microregions. The contribution of the B2 phase is negligible, while the α2 phase exhibits a negative contribution. This verifies the effectiveness of this method for quantitatively evaluating the relative mechanical properties of complex microstructure samples.

Claims

1. A quantitative evaluation method for the comprehensive mechanical properties of micro-regions in electron beam welded joints, characterized in that, Includes the following steps: S1. Cut the Ti2AlNb electron beam welded joint and obtain the test sample through sample preparation; S2. By performing nano-indentation tests on the test samples, the load-displacement curves are recorded in real time. S3. Extract strength performance parameters; S4. Read the load-displacement curve and extract the plastic performance parameters that characterize the plastic deformation bearing capacity of the material; The expression for the plasticity is as follows: ； ； ； in, Indicates plasticity, Indicates the total work done. Indicates elastic work. i This indicates the data point sequence number during the loading phase. j This indicates the data point number during the unloading phase. Indicates the load on the loaded segment. Indicates the loading phase i The push depth corresponding to +1 data point Indicates the loading phase i The push depth corresponding to each data point Indicates the unloading phase j The push depth corresponding to +1 data point Indicates the unloading phase j The indentation depth corresponding to each data point; S5. Based on plasticity parameters, strain hardening parameters are extracted by establishing discrete data pairs of total pressure work and indentation depth. S5 includes the following steps: S501. Based on plasticity performance parameters, establish discrete data pairs between total pressure work S and indentation depth h; S502. Based on discrete data pairs, a fifth-order polynomial is used to fit the relationship between the total pressure work S and the indentation depth h. S503. Based on the fitting results, calculate the first derivative of the total pressure work S with respect to the pressure depth h; S504. Based on the first derivative, calculate the second derivative of the total pressure work S with respect to the pressure depth h, and use the second derivative as the strain hardening parameter S to complete the extraction of the hardening capacity parameter. The expression for the strain hardening parameter is as follows: ； in, This represents the strain hardening parameter. , , and All represent polynomial fitting coefficients; S6. By performing outlier detection on the test data of each micro-region and conducting statistical analysis on the test data, a sample after testing is obtained. S7. Chemically etch the tested samples and observe the microstructure morphology of each micro-region. Based on the observation results, characterize the microstructure by statistically analyzing the content of each phase, morphological parameters, and grain size. S8. Based on the characterization results, strength performance parameters, plasticity and hardening capacity, establish a regression model for the comprehensive mechanical properties of the joint, and use the regression model to establish a quantitative correlation between microstructure and properties, thereby completing the quantitative evaluation of the comprehensive mechanical properties of the micro-region of the electron beam welded joint.

2. The quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints according to claim 1, characterized in that, S1 includes the following steps: S101, Cut the Ti2AlNb electron beam welding joint; S102. Based on the cutting results, metallographic preparation is performed on the cross-section of the sample perpendicular to the weld direction, and then sandpaper is used to polish it in sequence. S103. After grinding, the sample is polished and finely polished. S104. After fine polishing, use ultrasonic cleaning, and then dry to obtain a test sample with a smooth, scratch-free surface that fully exposes the fusion zone, heat-affected zone, and base material zone.

3. The quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints according to claim 1, characterized in that, S2 includes the following steps: S201. Using a Berkovich diamond indenter, fix the test sample on the indenter sample stage in a constant temperature laboratory and place it in the test chamber for 60 min - 90 min. S202. After the indenter contacts the sample surface, hold it for 200s-400s until the thermal drift rate is ≤0.05nm / s before starting the test. S203. Using a trapezoidal loading function, linearly load to the target load of 5-10mN in 5s, hold the load for 2s, and then linearly unload to 0mN in 5s. S204. Perform multiple indentation tests in each micro-area, with an indentation spacing ≥ 20 times the indentation depth, and record the load-displacement curve in real time.

4. The quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints according to claim 1, characterized in that, Specifically, S3 involves using the hardness H calculated using a nanoindenter as a strength performance parameter.

5. The quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints according to claim 1, characterized in that, The expression for the regression model of the joint's comprehensive mechanical properties is as follows: H = α0+ α1f_O + α2f_α2+ α3f_B2 + α4 / d; S p = β0+ β1f_O + β2f_α2 + β3f_B2 + β4 / d; = γ0+ γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d; In this context, H represents strength performance. Indicates plasticity, Let f_O, f_α2, and f_B2 represent the volume fractions of the O, α2, and B2 phases, respectively. Let α0 represent the intrinsic hardness, and let α1, α2, α3, and α4 represent the contribution rates of the O, α2, B2, and grain size to the hardness, respectively. Let β0 represent the intrinsic indentation work, and let β1, β2, β3, and β4 represent the contribution rates of the O, α2, B2, and grain size to the total indentation work, respectively. Let γ0 represent the intrinsic strain hardening parameter, and let γ1, γ2, γ3, and γ4 represent the contribution rates of the O, α2, B2, and grain size to the strain hardening parameter, respectively. Let d represent the average grain size.

6. The quantitative evaluation method for the comprehensive mechanical properties of micro-regions of electron beam welded joints according to claim 1, characterized in that, The quantitative evaluation method also includes a process-performance mapping relationship establishment step: repeating S1 to S8 for joints under different welding heat inputs and heat treatment processes, establishing a welding parameter-microzone structure-mechanical property database, and fitting the influence law of process parameters on performance parameters based on the welding parameter-microzone structure-mechanical property database.

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