Quantitative evaluation method for micro-area comprehensive mechanical properties of electron beam welding joint

Abstract

The invention provides a quantitative evaluation method for micro-area comprehensive mechanical properties of an electron beam welding joint, and belongs to the technical field of material mechanical property evaluation.A load-displacement curve is obtained through a nanoindentation test, and a data processing method combining numerical integration and high-order derivative calculation is adopted, so that the comprehensive mechanical properties of the electron beam welding joint are evaluated. Meanwhile, three performance parameters of strength, plasticity and strain hardening are extracted, and a quantitative mapping relation between the three performance parameters and the microcell structure is established. The method solves the problem of mechanical property quantitative evaluation of gradient structures of a fusion zone, a heat affected zone and a base metal zone of a welding joint, and the problems of high cost, low efficiency, single parameter and the like in the existing evaluation technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material mechanical property evaluation, and particularly relates to a quantitative evaluation method for micro-region comprehensive mechanical properties of an electron beam welded joint. BACKGROUND

[0002] Ti2AlNb-based alloy, as a new type of high-temperature titanium alloy, has the characteristics of low density, high high-temperature strength and excellent oxidation resistance, and is an ideal structural material for advanced equipment such as aero-engines and hypersonic aircraft. Electron beam welding, due to its high energy density, narrow weld, and small heat-affected zone, has become the preferred process for connecting Ti2AlNb components. However, the rapid heating and cooling during electron beam welding results in the formation of fusion zone, heat-affected zone and base material zone, and each micro-zone experiences different thermal cycle processes, resulting in significant differences in the content, morphology and distribution of O phase, alpha2 phase and B2 phase, and further causing spatial gradient distribution of mechanical properties such as strength and plasticity. This non-uniformity of micro-zone performance is the root cause of the weakness of the welded joint, which seriously restricts the application of Ti2AlNb alloy in high-end equipment.

[0003] The mechanical properties of Ti2AlNb alloy are highly dependent on its multi-phase structure. Studies have shown that the content and morphology of O phase directly affect the room temperature plasticity of the alloy, the precipitation strengthening effect of alpha2 phase determines the high temperature strength, and the volume fraction of B2 phase affects the toughness and fracture behavior of the material. In the electron beam welding process, the fusion zone often forms coarse columnar crystals and non-equilibrium phase structures due to complete melting and rapid solidification, resulting in a decrease in plasticity; the peak temperature and cooling rate of the heat-affected zone are different, and the phase composition and grain size show a gradient change. If the welding heat input, preheating temperature, post-weld heat treatment and other process parameters can be precisely controlled to precisely regulate the micro-zone structure, so that the O phase is uniformly distributed, the alpha2 phase is appropriately precipitated, and the grain size is optimized, the micro-zone performance matching can be effectively improved, and the overall mechanical properties of the joint can be improved. However, the prerequisite for such precise regulation is to establish a quantitative correlation between "process parameters-micro-zone structure-mechanical properties", and this requires a low-cost, high-throughput micro-zone performance evaluation technology as support.

[0004] There are great challenges in evaluating the mechanical properties of Ti2AlNb electron beam welded joints. The weld width is usually only a few millimeters, and the heat-affected zone is even narrower. Therefore, the mechanical properties need to be tested at the micron or sub-micron scale, making it difficult for traditional macroscopic mechanical property evaluation methods (such as tensile testing) to meet the requirements. Although existing precision testing techniques such as nanoindentation can achieve micro-area characterization, they can only provide hardness and elastic modulus parameters, and cannot evaluate plasticity and work hardening capacity. Therefore, it is difficult to establish a quantitative correlation between process, microstructure and performance, which restricts the precise control of welding process. Therefore, developing a low-cost and high-efficiency micro-area performance quantitative evaluation technology suitable for Ti2AlNb welded joints is an urgent need to realize the precise control of joint quality and the optimization of microstructure regulation. Therefore, for Ti2AlNb electron beam welded joints and other welding and packaging components with similar structural characteristics, developing a low-cost micro-area performance quantitative evaluation technology and precise microstructure regulation method is not only a need to solve practical engineering problems, but also has important scientific value and strategic significance. The establishment of this technology system can provide an effective means for performance prediction and reliability evaluation of high-temperature titanium alloy welded joints, and support the independent development of major equipment such as aircraft engines; at the same time, the related methodology can be extended to other difficult-to-weld material systems, promoting the development of advanced joining technology and enhancing the core competitiveness in high-end manufacturing field. SUMMARY

[0005] In view of the above problems in the prior art, the present application provides a micro-area comprehensive mechanical property quantitative evaluation method for electron beam welded joints, which solves the problem of quantitative evaluation of the mechanical properties of the gradient structure in the fusion zone, heat-affected zone and base material of the welded joint, and the problems of high cost, low efficiency and single parameter of existing evaluation techniques.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a micro-area comprehensive mechanical property quantitative evaluation method for electron beam welded joints, comprising the following steps: S1, cutting a Ti2AlNb electron beam welded joint, and obtaining a test sample through sample preparation; S2, performing nanoindentation test on the test sample to obtain a load-displacement curve in real time; S3, extracting strength performance parameters; S4, reading the load-displacement curve to extract plasticity performance parameters representing the plastic deformation load-bearing capacity of the material; S5, based on the plasticity performance parameters, establishing a discrete data pair of total pressure work and indentation depth, and extracting strain hardening parameters; S6, performing outlier detection on the test data of each micro-area, and performing statistical analysis on the test data to obtain a sample after testing; S7, performing chemical corrosion on the tested sample, observing microstructure morphology of each micro area, and based on the observation results, characterizing the microstructure by counting phase content, morphology parameters and grain size; S8, establishing a joint comprehensive mechanical property regression model based on the characterization results, strength performance parameters, plasticity performance and hardening energy, and using the joint comprehensive mechanical property regression model to establish a quantitative correlation between microstructure and performance, and completing quantitative evaluation of the micro area comprehensive mechanical properties of the electron beam welded joint.

[0007] Further, the S1 comprises the following steps: S101, cutting a Ti2AlNb electron beam welded joint; S102, based on the cutting results, preparing a metallographic section of the sample perpendicular to the weld direction, and sequentially polishing and grinding using sandpaper; S103, after grinding, polishing and fine polishing the sample; S104, after fine polishing, using ultrasonic cleaning, drying after cleaning, obtaining a smooth and scratch-free surface, and fully exposing the fusion zone, heat affected zone and base material zone of the test sample.

[0008] Further, the S2 comprises the following steps: S201, using a Berkovich diamond indenter in a constant temperature laboratory, fixing the test sample on the indenter sample table and placing it in the test chamber for 60-90 min; S202, after the indenter contacts the sample surface, keep for 200-400 s, and start testing after the thermal drift rate is ≤0.05 nm / s; S203, using a trapezoidal loading function, linearly loading to the target load of 5-10 mN for 5 s, holding for 2 s, and then linearly unloading to 0 mN for 5 s; S204, performing multiple indentation tests in each micro area, with an indentation spacing of ≥20 times the indentation depth, and recording the load-displacement curve in real time.

[0009] Further, the S3 is specifically: using the hardness H calculated by the nanoindenter as the strength performance parameter.

[0010] Further, the expression of the plasticity performance is as follows: ; ; ; wherein, represents the plasticity performance, represents the total indentation work, represents the elastic work, idata point number representing the loading stage, j data point number representing the unloading stage, representing the loading segment load, representing the loading stage i +1 data point corresponding to the indentation depth, representing the loading stage i data point corresponding to the indentation depth, representing the unloading stage j +1 data point corresponding to the indentation depth, representing the unloading stage j data point corresponding to the indentation depth.

[0011] Further, the S5 comprises the following steps: S501, based on the plastic property parameters, establishing a discrete data pair of the total pressure work S and the indentation depth h; S502, based on the discrete data pair, fitting the relationship between the total pressure work S and the indentation depth h by using a quintic polynomial; S503, based on the fitting result, calculating the first derivative of the total pressure work S to the pressure depth h; S504, based on the first derivative, calculating the second derivative of the total pressure work S to the pressure depth h, taking the second derivative as the strain hardening parameter S, and completing the extraction of the hardening ability parameter.

[0012] Further, the expression of the strain hardening parameter is as follows: ; wherein, represents the strain hardening parameter, , , and all represent polynomial fitting coefficients.

[0013] Further, the expression of the joint comprehensive mechanical property regression model 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; Among them, H represents the strength performance, represents the plastic performance, denotes a strain hardening parameter, f_O, f_α2, f_B2 respectively denote the volume fraction of O phase, α2 phase and B2 phase, α0 denotes intrinsic hardness, α1, α2, α3, α4 respectively denote the contribution rate of O phase, α2 phase, B2 and grain size to hardness, β0 denotes intrinsic total penetration work, β1, β2, β3, β4 respectively denote the contribution rate of O phase, α2 phase, B2 and grain size to total penetration work, γ0 denotes intrinsic strain hardening parameter, γ1, γ2, γ3, γ4 respectively denote the contribution rate of O phase, α2 phase, B2 and grain size to strain hardening parameter, and d denotes average grain size.

[0014] Further, the quantitative evaluation method further comprises a process-property mapping relationship establishing step: repeating S1 to S8 on the joint under different welding heat input and heat treatment processes, and establishing a welding parameter-microstructure-mechanical property database, which is used for fitting the influence law of process parameters on performance parameters.

[0015] The beneficial effects of the present application are as follows: The application discloses a quantitative evaluation method for micro area comprehensive mechanical properties of Ti2AlNb alloy electron beam welded joints. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The method flowchart of the present application.

[0017] Figure 2The scanning electron microscope (SEM) image of the microstructure of different regions of the electron beam welded joint of the Ti2AlNb-based alloy.

[0018] Figure 3 The schematic diagram of the nanoindentation curve and the indentation work of different regions of the electron beam welded joint of the Ti2AlNb-based alloy.

[0019] Figure 4 The schematic diagram of the nanoindentation total work and the first-order and second-order derivatives of the indentation depth of different regions of the electron beam welded joint of the Ti2AlNb-based alloy.

[0020] Figure 5 The scanning electron microscope (SEM) image of the microstructure of different regions of the electron beam welded joint of the Ti2AlNb-based alloy after heat treatment.

[0021] Figure 6 The schematic diagram of the nanoindentation curve and the indentation work of different regions of the electron beam welded joint of the Ti2AlNb-based alloy after heat treatment.

[0022] Figure 7 The schematic diagram of the nanoindentation total work and the first-order and second-order derivatives of the indentation depth of different regions of the electron beam welded joint of the Ti2AlNb-based alloy after heat treatment. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0024] Example 1 The present application obtains the load-displacement curve by nanoindentation test, adopts the data processing method combining numerical integration and high-order derivative calculation, extracts three types of performance parameters of strength, plasticity and strain hardening, and establishes the quantitative mapping relationship with the microstructure, as shown in the following formula: Figure 1 The present application provides a quantitative evaluation method for the micro-area comprehensive mechanical properties of an electron beam welded joint, and the implementation method is as follows: S1, cutting the Ti2AlNb electron beam welded joint, and obtaining the test sample through sample preparation, and the implementation method is as follows: S101, cutting the Ti2AlNb electron beam welded joint; S102, based on the cutting result, performing metallographic preparation on the cross section of the sample perpendicular to the weld, and sequentially using sandpaper to polish; S103, polishing and fine polishing the sample after grinding; S104, after fine polishing, ultrasonic cleaning, drying after cleaning, obtaining a test sample with smooth and scratch-free surface, and fully exposing the fusion zone, heat affected zone and base material zone.

[0025] In this embodiment, the material and welding: Ti2AlNb-based alloy is used, with nominal composition Ti-22Al-25Nb (at.%), and actual composition (wt.%): aluminum Al 8.7%, niobium Nb 41.6%, carbon C 5.1%, oxygen O 2.7%, and the balance titanium Ti. The electron beam welding parameters are: accelerating voltage 50 kV, beam current 40 mA, and welding speed 300 mm / min. The welded joint is composed of a fusion zone (FZ, about 2.5 mm wide), a heat affected zone (HAZ, about 0.5 mm wide), and a base material zone (BM).

[0026] In this embodiment, sample preparation: Ti2AlNb electron beam welded joints are cut using wire electrical discharge machining technology, with sample size 8-15 mm x 5-10 mm x 3-8 mm; the cross section of the sample perpendicular to the weld direction is prepared by metallography, and then polished using diamond polishing paste after polishing with 400# to 2000# sandpaper; after ultrasonic cleaning and drying, a test sample with smooth and scratch-free surface is obtained, and the fusion zone, heat affected zone and base material zone are fully exposed.

[0027] Prepare the sample according to S1 to obtain a test sample with size 10 mm x 7 mm x 5 mm and surface roughness Ra = 6 nm. The scanning electron microscope (SEM) results are shown in Figure 2 The results show that the joint FZ (fusion zone) has a small amount of nano O phase (3%) and B2 matrix (average grain size 600 μm); the HAZ (heat affected zone) has a small amount of nano O phase (6.5%) and B2 matrix (average grain size 250 μm); and the BM (base material zone) has 4% of α2 phase (average grain size 3 μm) and B2 matrix (average grain size 120 μm).

[0028] S2, by performing nanoindentation test on the test sample, the load-displacement curve is recorded in real time, and the implementation method is as follows: S201, in a constant temperature laboratory, fix the test sample on the indentation instrument sample table and place it in the test chamber for 60-90 min; S202, keep the indenter in contact with the sample surface for 200 s -400 s, and start testing after the thermal drift rate is ≤0.05 nm / s; S203, using trapezoidal loading function, 5s linear loading to target load 5-10 mN, holding for 2s, then 5s linear unloading to 0 mN; S204, multiple indentation tests were performed in each micro area, the indentation spacing was ≥20 times the indentation depth, and the load-displacement curve was recorded in real time.

[0029] In this embodiment, nanoindentation test: test in constant temperature laboratory (temperature 24±2℃, humidity 50±10%); fix the sample on the indentation instrument sample table and place it in the test cabin for 60-90min; keep the indenter in contact with the sample surface for 200s-400s, and start the test after the thermal drift rate is ≤0.05nm / s; use trapezoidal loading function, 5s linear loading to target load 5-10 mN, holding for 2s, then 5s linear unloading to 0 mN; perform not less than 5 indentation tests in each micro area, the indentation spacing is ≥20 times the indentation depth; record the load-displacement curve in real time.

[0030] In the nanoindentation test, Hysitron TI950 nanoindenter was used, and Berkovich diamond indenter was used. Test conditions: temperature 24.2±0.3℃, humidity 47%, sample stabilization time 75min, thermal drift rate 0.03nm / s, loading program 5s-2s-5s, maximum load 10mN. 10 tests were performed in FZ (fusion zone), HAZ (heat affected zone) and BM (base material zone) respectively.

[0031] That is, the nanoindentation test uses Berkovich diamond indenter, the target load is 1-10mN, and the loading program is 5s-2s-5s.

[0032] S3, extract the strength performance parameter, which is specifically: the hardness H calculated by using the nanoindenter is taken as the strength performance parameter.

[0033] S4, read the load-displacement curve, and extract the plasticity performance parameter representing the plastic deformation bearing capacity of the material; The expression of plasticity performance is as follows: ; ; ; Among them, represents the plasticity performance, represents the total indentation work, represents the elastic work, i represents the data point number of the loading stage, j represents the data point number of the unloading stage, represents the loading segment load, represents the loading stage data point number,i indentation depth corresponding to the +1th data point, represents the indentation depth corresponding to the 1th data point in the loading stage, i represents the indentation depth corresponding to the +1th data point in the loading stage, represents the indentation depth corresponding to the 1th data point in the unloading stage, j represents the indentation depth corresponding to the +1th data point in the unloading stage, represents the indentation depth corresponding to the 1th data point in the unloading stage. j

[0034] In this embodiment, the load-displacement curve data is read; the trapezoidal integral method is used to calculate the total indentation work S and the elastic work S e , the integral step size Δh < 5 nm; the plastic work (i.e. plastic performance) S p = S-S e , which represents the plastic deformation load-carrying capacity of the material.

[0035] S5, based on the plastic performance parameter, a strain hardening parameter is extracted by establishing a discrete data pair of total pressure work and indentation depth, and the implementation method is as follows: S501, based on the plastic performance parameter, a discrete data pair of total pressure work S and indentation depth h is established; S502, based on the discrete data pair, a quintic polynomial is used to fit the relationship between the total pressure work S and the indentation depth h; S503, based on the fitting result, the first derivative of the total pressure work S with respect to the pressure depth h is calculated; S504, based on the first derivative, the second derivative of the total pressure work S with respect to the pressure depth h is calculated, and the second derivative is taken as the strain hardening parameter S, completing the extraction of the hardening capacity parameter.

[0036] In this embodiment, the strain hardening capacity parameter is extracted: a discrete data pair of total indentation work S and indentation depth h is established: a quintic polynomial is used to fit the S-h relationship, and the goodness of fit R²> 0.98 is required; the first derivative of the indentation work with respect to the depth dS / dh is calculated; the second derivative of the indentation work with respect to the depth d²S / dh² is taken as the strain hardening parameter , and the average value of the second derivative values in the loading segment is taken as the strain hardening parameter of the measurement point: ; wherein, represents the strain hardening parameter, , , and all represent polynomial fitting coefficients.

[0037] The calculation method of the strain hardening index is: a quintic polynomial is fitted for S-h data: S(h) = a0+ a1h +a2h² + a3h³ + a4h​4 + 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 h = hmax as the strain hardening parameter wherein, , denote the polynomial fitting coefficients.

[0038] S6, performing statistical analysis on the test data by performing outlier detection on the test data of each micro zone to obtain a sample after testing; In this embodiment, data statistical analysis: outlier detection is performed on the test data of each micro zone, the average value and the standard deviation are calculated, and the data points deviating from the average value by more than 1.5 times the standard deviation are removed; the average value, the standard deviation and the coefficient of variation of the retained data are calculated, and the coefficient of variation is required to be less than 10%, that is, the 1.5 times standard deviation criterion is adopted for outlier detection, and the data points deviating from the average value by more than 1.5 times the standard deviation are removed, and the coefficient of variation is required to be less than 10%.

[0039] S7, performing chemical etching on the sample after testing, observing the microstructure morphology of each micro zone, and based on the observation results, characterizing the microstructure by statistically analyzing the phase content, morphological parameters and grain size; In this embodiment, microstructure characterization: chemical etching is performed on the sample after testing; the microstructure morphology of each micro zone is observed using a scanning electron microscope; the phase content, morphological parameters and grain size are quantitatively analyzed using image analysis software.

[0040] S8, establishing a joint comprehensive mechanical property regression model based on the strength performance parameters, plasticity and hardening energy, and establishing a microstructure-property quantitative correlation using the joint comprehensive mechanical property regression model to complete the quantitative evaluation of the comprehensive mechanical properties of the electron beam welded joint micro zone.

[0041] In this embodiment, the microstructure-property quantitative correlation is established: a multiple linear regression model is established, wherein f_O, f_α2 and f_B2 represent the volume fractions of 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 model significance is verified, and the determination coefficient R² is required to be greater than 0.85.

[0042] The expression of the joint comprehensive mechanical property regression model 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; 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; H represents the strength performance, represents the plasticity performance, represents the strain hardening parameter, f_O, f_α2, f_B2 represent the volume fractions of O phase, α2 phase and B2 phase respectively, α0 represents the intrinsic hardness, α1, α2, α3, α4 represent the contribution rates of O phase, α2 phase, B2 and grain size to hardness respectively, β0 represents the intrinsic total work of indentation, β1, β2, β3, β4 represent the contribution rates of O phase, α2 phase, B2 and grain size to the total work of indentation respectively, γ0 represents the intrinsic strain hardening parameter, γ1, γ2, γ3, γ4 represent the contribution rates of O phase, α2 phase, B2 and grain size to the strain hardening parameter respectively, and d represents the average grain size.

[0043] In this embodiment, the quantitative evaluation method further comprises a process-performance mapping relationship establishing step: repeating S1 to S8 under different welding heat inputs and heat treatment processes, establishing a welding parameter-microstructure-mechanical property database, and fitting the influence law of process parameters on performance parameters based on the welding parameter-microstructure-mechanical property database.

[0044] In this embodiment, the present application is suitable for micro-mechanical property evaluation of welded or packaged components of titanium alloy, nickel-based high-temperature alloy, aluminum-based composite material and the like.

[0045] In this embodiment, the mechanical property multi-parameter extraction method based on the nanoindentation load-displacement curve realizes quantitative characterization of the strain hardening capacity through numerical integration and high-order derivative calculation, and the process is as follows: Obtain the nanoindentation load-displacement curve data, including the loading stage and the unloading stage; calculate the total work of indentation S and the elastic work S e by using the trapezoidal integral method, the integral step is <5nm; calculate the plastic work S p = S-S e; the total indentation work S and the indentation depth h are fitted by a quintic polynomial with 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 value of the second derivative at the maximum load is taken as the final strain hardening capacity characterization parameter.

[0046] In this embodiment, the trapezoidal integral algorithm is used to calculate the indentation work and the elastic work; the quintic polynomial fitting algorithm is used to establish the functional relationship between the indentation work and the depth; the high-order derivative calculation algorithm is used to extract the strain hardening parameter; and the outlier test algorithm is used to eliminate data points deviating from the mean value by more than 1.5 times the standard deviation.

[0047] In this embodiment, a quantitative correlation model of the strength performance parameters, the plasticity performance and the hardening capacity index and the volume fraction of O phase, alpha2 phase and B2 phase and the grain size is established by using the multiple linear regression method, with a determination coefficient R²>0.85 and a p value <0.05.

[0048] In this embodiment, the correlation curves are shown in Figure 3 and Figure 4 The comprehensive mechanical performance parameters obtained are as follows: Strength parameter-hardness H: FZ (fusion 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, which shows that the hardness of FZ (fusion zone) and HAZ (heat affected zone) is significantly higher than that of BM, FZ (fusion zone) represents the fusion zone, HAZ (heat affected zone) represents the heat affected zone, and BM (base material zone) represents the base material zone.

[0049] Plasticity parameter-plastic work S p : The plastic work S is calculated by numerical integration: FZ (fusion zone): S p = 910.27 ± 35.2 nJ; HAZ (heat affected zone): S p = 884.20 ± 32.8 nJ; BM (base material zone): S p = 938.94 ± 28.6 nJ, which shows that BM has the highest plastic work, indicating that it has the strongest plastic deformation bearing capacity.

[0050] Strain hardening parameter-strain hardening parameter : The S-h data is fitted by a quintic polynomial (R²>0.995), and the work hardening capacity index of each micro zone is calculated: FZ (fusion zone): = 31.33 ± 2.1 MJ / m²; HAZ (heat affected zone): 29.31 ± 1.8 MJ / m²; BM (base material zone): = 27.97 ± 1.6 MJ / m2; FZ has the highest strain hardening ability.

[0051] Statistical analysis: the coefficient of variation CV of each parameter: hardness 2.4-2.9%, plastic work 3.1-3.9%, strain hardening parameter 5.2-7.1%, all meet the requirement of CV < 10%. The linear regression model of the comprehensive mechanical property parameters of the joint is: H = 5.1867 + 0.0242·f_O - 0.0217·f_α2- 0.0025·f_B2 - 0.0000 / d; S p = -67.4092 - 6.7342·f_O - 3.9116·f_α2+ 10.6458·f_B2 - 0.0246 / d; = -90.9359 - 0.0567·f_O - 1.2333·f_α2+ 1.2900·f_B2 - 0.0045 / d.

[0052] Example 2 In this example, the micro-area performance evaluation of the heat-treated Ti2AlNb electron beam joint is as follows: 1. Microstructure of welded joint after heat treatment: the welded Ti2AlNb electron beam welded joint in Example 1 is heat treated at 800℃ for 2h and then furnace cooled to room temperature. The microstructure of the heat treated sample is composed of FZ (fusion zone), HAZ (heat affected zone) and base material zone (BM). The results of scanning electron microscope SEM are shown in Figure 5 , which shows that the FZ of the joint is 60% of nano O phase and B2 matrix (average grain size 600μm); the HAZ (heat affected zone) is 60% of nano O phase, 5% of α2 phase (average grain size 3μm) and B2 matrix (average grain size 250μm); the base material zone (BM) is 55% of nano O phase, 4% of α2 phase (average grain size 3.5μm) and B2 matrix (average grain size 120μm).

[0053] 2. Nanoindentation test: Hysitron TI950 nanoindenter, Berkovich diamond indenter. Test conditions: temperature 24.2±0.3℃, humidity 47%, sample stabilization time 75min, thermal drift rate 0.03nm / s, loading program 5s-2s-5s, maximum load 10mN. 10 tests were performed in the fusion zone (FZ), heat affected zone (HAZ) and base material zone (BM).

[0054] 3. Data processing results: the correlation curves are as shown in Figure 6 andFigure 7 The obtained comprehensive mechanical performance parameters are as follows: (1) Strength parameter-hardness H: FZ: 5.61±0.13 GPa (+10.7%); HAZ: 5.73±0.16 GPa (+12.1%); BM: 5.69±0.11 GPa (+17.1%), which indicates that the hardness of the three microzones is significantly improved after heat treatment, and the difference is reduced.

[0055] (2) Plasticity parameter-plastic work S p : FZ: 824.02±31.5 nJ (-9.5%); HAZ: 813.40±28.9 nJ (-8.0%); BM: 807.84±26.2 nJ (-14.0%), the plastic work is decreased after heat treatment, but the FZ (melting zone) is higher than the BM (base material zone), which indicates that the plastic deformation capacity is relatively improved.

[0056] (3) Strain hardening parameter-strain hardening parameter : FZ: 36.47±2.4 MN / m² (+16.4%); HAZ: 35.30±2.1 MN / m² (+20.4%); BM: 31.87±1.9 MN / m² (+13.9%), the strain hardening capacity is improved after heat treatment, and the FZ (melting zone) is improved most significantly.

[0057] 4. Joint comprehensive mechanical performance regression model: H = 5.1300 + 0.0080·f_O + 0.0240·f_α2; S p = 757.30 + 1.11·f_O - 2.12·f_α2; = -4.69 + 0.69·f_O - 0.23·f_α 2。

[0058] The application is suitable for microzone performance evaluation of other titanium alloys, nickel-based high-temperature alloys, aluminum-based composite materials and the like welding or packaging components.

[0059] The initial source and derivation process of the formula in the application are described below.

[0060] 1. Original formula source The plastic work (i.e. plastic performance) calculation formula S p =S-S e adopted by the application is derived from the Oliver-Pharr nanoindentation model in the field of micro-nano mechanics, wherein the plastic work is S pThat is, plasticity, the total work of indentation is S, and the work of elastic recovery 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.

[0061] 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.

[0062] 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. p Quantitative 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.

[0063] The detailed derivation of the application formula and the innovative definition are as follows: 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 .

[0064] 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: The numerical expression for the compressive work is S(h) = a0 + a1h + a2h² + a3h³ + a4h 4 + a5h 5 ; First derivative = dS / dh = a1+ 2a2h + 3a3h² + 4a4h³ + 5a5h 4 ; Second derivative = d²S / dh² = 2a2+ 6a3h + 12a4h² + 20a5h³, and define the pressure depth h to take the maximum value hmax when The value is the material strain hardening parameter value.

[0065] 3、The present application quantifies the microstructure characteristics (constituent phase volume fraction, matrix grain size) and nanoindentation mechanical property parameters, and brings them into the joint comprehensive mechanical property regression model to solve the joint comprehensive mechanical property regression model parameters, so as to realize the quantitative evaluation of the contribution of each structure parameter to the mechanical property, wherein the joint comprehensive mechanical property regression model is: 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; Wherein, H represents hardness, S p represents plastic work, i.e. plastic property, represents strain hardening parameter, f_O, f_α2, f_B2 represent volume fraction (%) of O phase, α2 phase and B2 phase respectively, and d represents average grain size (μm). The microstructure characteristics and mechanical property data set used in the model are [f_O, f_α2, f_B2, d; H, S p , ].

[0066] The dimensional verification of the formula is as follows: 1、For the indentation plastic work calculation formula, i.e. plastic property, the dimension on the left side of the formula is J, and the right side of the formula is the product of load N and indentation displacement m, i.e. J=N·m, and the dimensions on both sides are consistent.

[0067] 2、For the micro area material strain hardening parameter calculation formula, the left side is , which describes the acceleration of the change of the total indentation work with the indentation depth, and its dimension is J / m 2 , and the right side is d²S / dh², and the corresponding dimension is N / m=N·m / m 2 = left side, i.e. the dimensions on both sides are consistent.

[0068] 3、For the joint comprehensive mechanical properties regression model of nanoindentation mechanical properties parameters, the formula left side hardness H, plastic work S p and strain hardening parameter The dimensions are GPa, J and J / m 2 ; The right side of the formula is the volume fraction (%) of O phase, α2 phase, B2 phase and the average grain size d (dimension μm), to ensure the dimensions of both sides are consistent, define α 0-3 The unit is GPa, and the unit of α4 is GPa·μm; β 0-3 The unit is J, and the unit of β4 is J·μm; γ 0-3 The unit is J / m 2 , and the unit of γ4 is J·μm / m 2 .

[0069] The logical relationship and derivation process of multiple formulas are as follows: The first step is to obtain the indentation work S(h) = a0+ a1h + a2h² + a3h³ + a4h 4 + a5h 5 by numerical fitting; The second step is to solve the second derivative of S(h) = (a1+ 2a2h + 3a3h² + 4a4h³ + 5a5h 4 ) = 2a2+ 6a3h+ 12a4h² + 20a5h³; The third step is to bring the obtained data set [f_O, f_α2, f_B2, d; H, S p , S’’] into the multiple linear model, and solve the model parameters by normal equation method.

[0070] The process of algorithm derivation technique effect is as follows: 1、Parameter acquisition and data set construction: Obtain the volume fraction f_O, f_α2, f_B2 of O phase, α2 phase, B2 phase and the grain size d of the base B2 in the fusion zone (FZ), heat affected zone (HAZ) and base (BM) of Ti2AlNb welded joint by microstructure characterization technology; Obtain the nanoindentation load displacement curve and hardness H of each micro area of Ti2AlNb welded joint by nanoindentation technology; Based on the numerical integration of nanoindentation curve, obtain the total indentation work S under different indentation depths, calculate the plastic work S p and strain hardening parameter , and construct the data set [f_O, f_α2, f_B2, d; H, S p , ] accordingly.

[0071] 2. Data calculation: phase fraction and grain size of each micro-zone of the as-welded Ti2AlNb welded 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. According to the nanoindentation curve of each micro-zone of the as-welded Ti2AlNb welded joint, the hardness H, plastic work S p and strain hardening parameter are obtained for fusion zone (FZ): H=5.07±0.12 GPa, S p =910.27±35.2 nJ, fusion zone (FZ)=31.33±2.1 MJ / m²; heat affected zone (HAZ): H=5.11±0.15 GPa, S p =884.20±32.8 nJ, =29.31±1.8 MJ / m²; base metal (BM) H=4.86±0.09 GPa, S p =938.94±28.6 nJ, =27.97±1.6 MJ / m².

[0072] 3. Results: the data set [f_O, f_α2, f_B2, d; H, S p , ] is brought into the regression model of comprehensive mechanical properties of the joint, and the following is obtained: H = 5.1867+ 0.0242·f_O - 0.0217·f_α2- 0.0025·f_B2 - 0.0000 / d; S p = -67.4092 - 6.7342·f_O - 3.9116·f_α2+ 10.6458·f_B2 - 0.0246 / d; = -90.9359 - 0.0567·f_O - 1.2333·f_α2+ 1.2900·f_B2 - 0.0045 / d.

[0073] According to the above regression model (i.e., the joint comprehensive mechanical property regression model), it is found that the O phase has a higher micro-hardening effect compared with the a2 phase and the B2 phase, and the B2 phase has a more significant contribution to the micro-plastic deformation ability and strain hardening trend compared with the a2 phase and the O phase, which is directly related to the characteristics of the O phase being hard and brittle and the B2 phase having strong plastic deformation ability in the Ti2AlNb alloy, which proves the reliability of the linear regression model obtained by the method for quantitative evaluation of the mechanical property contribution of each micro-zone constituting phase of the welded joint.

[0074] The quantitative calculation implementation is as follows: Taking the quantitative evaluation of the contribution of the micro-zone structure of the aged Ti2AlNb welded joint to the mechanical property as an example.

[0075] 1. Parameter collection and data set construction: After the welded Ti2AlNb electron beam welded joint is heat treated at 800°C for 2h and then furnace-cooled to room temperature, the volume fractions f_O, f_α2, f_B2 of the O phase, the a2 phase and the B2 phase in the fusion zone (FZ), the heat affected zone (HAZ) and the base metal (BM) of the Ti2AlNb welded joint are obtained by microstructure characterization technology, and the B2 grain size d is obtained; the nanoindentation load displacement curve and the hardness H of each micro-zone of the Ti2AlNb welded joint are obtained by nanoindentation technology; the indentation work S at different indentation depths is obtained based on the numerical integration of the nanoindentation curve, and the plastic work S p and the strain hardening parameter are calculated, and the data set [f_O, f_α2, f_B2, d; H, S p , ] is constructed accordingly.

[0076] 2. Data calculation: The proportion of each micro-zone constituting phase and the base metal grain size of the aged Ti2AlNb welded joint are as follows: 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.

[0077] According to the nanoindentation curve of each micro-zone of the aged Ti2AlNb welded joint, the hardness H, the plastic work S p and the strain hardening parameter are obtained as follows: 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 ± 0.11 GPa, S p = 807.84 ± 26.2 nJ, = 31.87 ± 1.9 MJ / m2.

[0078] 3. Results: The dataset was brought into the joint comprehensive mechanical property regression model, and the results were: H = 5.1300 + 0.0080·f_O + 0.0240·f_α2; S p = 757.30 + 1.11·f_O - 2.12·f_α2; = -4.69 + 0.69·f_O - 0.23·f_α2.

[0079] Compared with the model parameters of the as-welded state, the O phase precipitation after aging caused the microhardness H of the Ti2AlNb alloy joint to increase significantly, and the O phase and the α2 phase had more obvious hardness contribution than the B2 phase. At the same time, the plastic work of each micro area of the Ti2AlNb alloy decreased and the strain hardening parameter improved after aging. Model parameter analysis showed that the O phase was the main constituent phase for improving the plastic work and strain hardening capacity of the aged Ti2AlNb joint, the B2 phase had negligible contribution, and the α2 phase showed negative contribution, which verified the effectiveness of the method for quantitative evaluation of various mechanical properties of complex microstructure samples.

Claims

1. A method for quantitatively evaluating micro-zone comprehensive mechanical properties of an electron beam welded joint, characterized in that, It comprises the following steps: S1, cutting Ti2AlNb electron beam welded joint, and obtaining test sample through sample preparation; S2, obtaining load-displacement curve by real-time recording through nanoindentation test on test sample; S3, extracting strength performance parameters; S4, reading load-displacement curve, and extracting plasticity performance parameters for characterizing plastic deformation load capacity of material; S5, based on plasticity performance parameters, extracting strain hardening parameters by establishing discrete data pairs of total pressure work and indentation depth; S6, through outlier detection on test data of each micro area, obtaining sample after test through statistical analysis on test data; S7, performing chemical corrosion on sample after test, observing microstructure morphology of each micro area, and characterizing microstructure based on observation results through statistics of phase content, morphology parameters and grain size; S8, based on characterization results, strength performance parameters, plasticity performance and hardening energy, establishing joint comprehensive mechanical property regression model, and establishing organization-performance quantitative correlation by using joint comprehensive mechanical property regression model, and completing quantitative evaluation on micro area comprehensive mechanical property of electron beam welded joint.

2. The method according to claim 1, wherein the method is characterized by, The S1 comprises the following steps: S101, cutting Ti2AlNb electron beam welded joint; S102, based on cutting results, performing metallographic preparation on cross section of sample perpendicular to weld joint, and polishing in turn using sandpaper; S103, after polishing, polishing and fine polishing are performed on the sample; S104, after fine polishing, ultrasonic cleaning is used, and after cleaning, drying is performed to obtain test sample with smooth and scratch-free surface, and fusion zone, heat affected zone and base material zone are fully exposed.

3. The method according to claim 1, wherein the method is characterized by, The S2 comprises the following steps: S201, in a constant temperature laboratory, using a Berkovich diamond indenter, fixing the test sample on the indenter sample table and placing it in the test chamber for 60-90 min; S202, after the indenter contacts the sample surface, keep for 200-400 s, and start testing after the thermal drift rate is less than or equal to 0.05 nm / s; S203, using a trapezoidal loading function, linearly loading to a target load of 5-10 mN for 5 s, holding for 2 s, and then linearly unloading to 0 mN for 5 s; S204, performing multiple indentation tests on each micro area, and the indentation spacing is greater than or equal to 20 times the indentation depth, and the load-displacement curve is recorded in real time.

4. The method according to claim 1, wherein the method is characterized by, The S3 is specifically: using the hardness H calculated by the nanoindenter as the strength performance parameter.

5. The method according to claim 1, wherein the method is characterized by, The expression of the plasticity performance is as follows: ； ； ； wherein, represents the plastic property, represents the total work of indentation, represents the elastic work, i represents the data point number of the loading stage, j represents the data point number of the unloading stage, represents the loading segment load, represents the indentation depth corresponding to the data point number of the loading stage, i +1, represents the indentation depth corresponding to the data point number of the loading stage, i +1, represents the indentation depth corresponding to the data point number of the unloading stage, j +1, represents the indentation depth corresponding to the data point number of the unloading stage, j +1.

6. The method according to claim 1, wherein the method is characterized by, The S5 comprises the following steps: S501, based on the plasticity performance parameters, establishing discrete data pairs of total pressure work S and indentation depth h; S502, based on the discrete data pairs, fitting the relationship between total pressure work S and indentation depth h by using a quintic polynomial; S503, based on the fitting results, calculating the first derivative of total pressure work S with respect to pressure depth h; S504, based on the first derivative, calculating the second derivative of total pressure work S with respect to pressure depth h, taking the second derivative as the strain hardening parameter S, and completing the extraction of the hardening capacity parameter.

7. The method according to claim 6, wherein the method is characterized by, The expression of the strain hardening parameter is as follows: ； wherein represents a strain hardening parameter, , , and all represent polynomial fit coefficients.

8. The method according to claim 1, wherein the method is characterized by, The expression of the joint comprehensive mechanical property regression model is as follows: H = a0 + a1f_0 + a2f_a2 + a3f_b2 + a4 / d; S p = β0 + β1f_O + β2f_α2 + β3f_B2 + β4 / d; = γ0 + γ1f_O + γ2f_α2 + γ3f_B2 + γ4 / d; H represents the strength performance, f represents the plastic performance, f_O, f_α2, f_B2 represent the volume fraction of O phase, α2 phase and B2 phase, respectively, α0 represents the intrinsic hardness, α1, α2, α3, α4 represent the contribution rate of O phase, α2 phase, B2 and grain size to hardness, respectively, β0 represents the intrinsic total work of indentation, β1, β2, β3, β4 represent the contribution rate of O phase, α2 phase, B2 and grain size to the total work of indentation, respectively, γ0 represents the intrinsic strain hardening parameter, γ1, γ2, γ3, γ4 represent the contribution rate of O phase, α2 phase, B2 and grain size to the strain hardening parameter, respectively, and d represents the average grain size.

9. The method according to claim 1, wherein the method is characterized by, The quantitative evaluation method further comprises a process-performance mapping relationship establishing step: repeating S1 to S8 under different welding heat inputs and heat treatment processes, establishing a welding parameter-microstructure-mechanical property database, and fitting the influence law of process parameters on performance parameters based on the welding parameter-microstructure-mechanical property database.

Images