Method for improving mechanical property of titanium alloy through low-temperature high-speed pre-impact

Abstract

The invention relates to a method for improving the mechanical property of titanium alloy through low-temperature high-speed pre-impact, and belongs to the technical field of titanium alloy development. According to the method, a titanium alloy sample is subjected to small-deformation high-speed pre-impact with specific parameters in a low-temperature environment, so that a high-density sheet-shaped FCC titanium phase and an L-C lock are deliberately introduced into a microstructure of the titanium alloy sample, the special defect structures serve as prefabricated strengthening phases, dislocation can be effectively pinned in the follow-up dynamic loading process, crack propagation is hindered, and the performance of the titanium alloy sample is improved. Therefore, the final mechanical property of the material is synergistically improved. The method is simple and controllable in treatment, the obtained product is excellent in performance, and industrial application is facilitated.

Description

Technical Field

[0001] This invention relates to a method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact, belonging to the field of titanium alloy development technology. Background Technology

[0002] Existing technologies for improving the mechanical properties of titanium alloys mainly include heat treatment control such as solution treatment and aging, plastic working strengthening such as rolling and forging, alloying and composite strengthening by adding alloying elements or introducing reinforcing phases, and additive manufacturing process optimization such as selective laser melting and electron beam melting. These methods improve mechanical properties by adjusting the microstructure or composition of titanium alloys. A search revealed few reports on improving the mechanical properties of titanium alloys through low-temperature, high-speed pre-impact testing. Summary of the Invention

[0003] This invention provides a method for improving the dynamic performance of titanium alloys by inducing the formation of a strengthening phase and LC lock through low-temperature pre-impact.

[0004] The core invention lies in: using a low-temperature environment (especially a deep low-temperature environment, such as -20℃ to -196℃) to subject titanium alloy samples to a small deformation pre-impact with specific parameters (such as causing the titanium alloy to undergo plastic deformation of 0.5% to 8%), thereby deliberately introducing high-density lamellar FCC titanium phase and LC lock into its microstructure. These special defect structures, as "pre-strengthening phases", can effectively pin dislocations and hinder crack propagation during subsequent dynamic loading, thereby synergistically improving the final dynamic strength and fracture strain of the material.

[0005] This invention discloses a method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact. The method utilizes a low-temperature environment to subject titanium alloy samples to small deformation pre-impact with specific parameters, thereby introducing lamellar FCC titanium phase and LC lock into its microstructure. The temperature of the low-temperature environment is -20℃ to -196℃, and the deformation of the small deformation pre-impact is 0.5% to 8%.

[0006] Preferably, an impact force is applied to the low-temperature treated titanium alloy at a strain rate of 100-2000 s. -1 .

[0007] Preferably, the present invention provides a method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact, wherein an impact force is applied to the titanium alloy at a temperature of -70℃ to -196℃, with a strain rate of 100-2000 s⁻¹. -1 This causes the titanium alloy to undergo plastic deformation of 1% to 5%.

[0008] Preferably, the present invention provides a method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact, wherein a strain rate of 700-1200 s⁻¹ is applied to the titanium alloy at a temperature of -80℃ to -196℃. -1 (Further preferred: 900~1100s) -1 A further preferred value is 950~1050s. -1 The impact force causes the titanium alloy to undergo plastic deformation of 1.5% to 3.5%.

[0009] In industrial applications, the impact force is provided by the gas used.

[0010] The titanium alloy is selected from one of TA15, TC4, and TA0.

[0011] The titanium alloy described in this invention is selected from at least one of the following: cast, rolled, printed, and annealed states.

[0012] In actual operation, the sample preparation can be carried out by cutting the sample of the required shape from the titanium alloy plate or bar using wire electrical discharge machining (WEDM).

[0013] Preferably, the specimen is cylindrical, with a height (H) to diameter (D) ratio of 1:2 to 2:1. More preferably, it is 1:1. Standardized specimen dimensions are a prerequisite for obtaining comparable and repeatable mechanical experimental data. High-precision wire cutting can avoid the excessively large heat-affected zone and stress concentration introduced by traditional machining.

[0014] In this invention, the equipment used for cryogenic pre-impact treatment can be a high-speed forming device equipped with an insulated chamber. In practical applications, the high-speed forming device includes a split Hopkinson pressure bar (SHPB) device. Of course, other devices can also be used in this invention.

[0015] In this invention, the deep cryogenic pre-impact treatment process involves placing the sample in a high-rate impact chamber and cooling it to a low-temperature environment of -20℃ to -196℃. Liquid nitrogen can be used as the cooling medium to achieve cooling and maintain temperature stability.

[0016] In this invention, when the titanium alloy is a printed titanium alloy or a printed titanium alloy after annealing, an impact force is applied to the titanium alloy at -120℃ to -196℃, causing the titanium alloy to undergo plastic deformation of 1.5% to 3.5%. Preferably, a strain rate of 800-1200 s⁻¹ is applied to the titanium alloy at -140℃ to -196℃. -1 (Preferred 950~1050s) -1 The impact force causes the titanium alloy to undergo plastic deformation of 2% to 3%.

[0017] As a preferred option, the printing parameters for the printed titanium alloy are: laser power 400~700W, scanning speed 300~400mm / s, scanning spacing 0.2~0.4mm, powder layer thickness 0.3~0.5mm, and powder feeding rate 10~15g / min.

[0018] As a further preferred option, the printing parameters for the printed titanium alloy are: laser power 600 W, scanning speed 360 mm / s, scanning spacing 0.3 mm, powder layer thickness 0.4 mm, and powder feeding rate 12 g / min.

[0019] This invention yields a product with extremely excellent performance for printed titanium alloys through the synergistic effect of appropriate printing parameters and cryogenic shock treatment parameters.

[0020] Function and Principle: Low-temperature environments significantly suppress the thermally activated slip and dynamic recovery processes of dislocations. Under impact loads, dislocation multiplication and movement are hindered, leading to extremely high stress concentration within the material to coordinate deformation. This high-stress state forces the metastable HCP structure α-Ti to undergo stress-induced phase transformation, generating lamellar FCC structure titanium. Furthermore, it promotes the initiation of deformation modes such as {10-12}〈-1011〉 twinning, resulting in strong interactions between twins and dislocations, and between phase boundaries and dislocations, forming a large number of large-size FCC titanium particles. During deformation, LC-locking reinforcement occurs. LC-locking is a type of immobile dislocation lock formed by the reaction of two partially dislocations on different slip surfaces. It effectively hinders the movement of other dislocations and is a powerful strengthening source.

[0021] Dynamic compression performance test:

[0022] The specimens that underwent deep cryogenic pre-impact treatment, along with the specimens used as comparative examples that were not pre-impacted or were pre-impacted at room temperature, were subjected to a final high strain rate compression test at room temperature.

[0023] Test parameters: High-speed forming equipment was used, with a high impact air pressure (0.23 MPa ± 0.02 MPa) to achieve a specific strain rate loading until the specimen fractured.

[0024] Findings: The specimens treated with cryogenic pre-impact therapy showed an increase of ≥15% in dynamic compressive yield strength and ultimate compressive strength compared to the control specimens, while their true strain at fracture increased by ≥5%. The static tensile yield strength and ultimate compressive strength increased by ≥20% compared to the control specimens, while their true strain at fracture increased by ≥33%.

[0025] Beneficial effects

[0026] This technical solution is based on the following principles of materials science:

[0027] Low-temperature plastic deformation principle: Low temperature significantly increases the rheological stress of materials and changes their main plastic deformation mechanism (such as promoting twinning and inhibiting dynamic recovery).

[0028] Stress-induced phase transition: When the mechanical driving force (stress) exceeds the phase transition energy barrier, even under thermodynamic conditions unsuitable for phase transition (such as low temperature), the crystal structure can be forced to change.

[0029] Dislocation Locking Reinforcement Mechanism: As a surface defect, LC lock is a powerful obstacle to dislocation motion, and its reinforcement effect conforms to the classical dislocation reinforcement theory.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] Synergistic effect: The simultaneous introduction of second-phase strengthening (FCC-Ti) and defect strengthening (LC lock) achieves a simultaneous improvement in strength and plasticity.

[0032] Significant results: substantial performance improvement (strength >15%, strain >5%), with particularly outstanding benefits under dynamic loads. Static tensile yield strength and ultimate compressive strength are increased by ≥20% compared to the control specimen, while true strain at fracture is increased by ≥33%.

[0033] The process is simple and efficient: only a low-temperature pre-impact step is added before testing with existing high-speed forming equipment, without the need for complex heat treatment or chemical treatment, and it is easy to integrate and implement.

[0034] Highly targeted: Designed specifically to improve the performance of titanium alloys under ultra-high strain rates. Attached Figure Description

[0035] Figure 1 Here is a high-resolution transmission electron microscope image of the product obtained in Example 1;

[0036] Figure 2 This is a high-resolution transmission electron microscope image of the product obtained in Comparative Example 1. Detailed Implementation

[0037] Raw materials and equipment used:

[0038] Raw materials:

[0039] The chemical composition (wt%) of TA15 titanium alloy rolled sheet is shown in the table below, with the remainder being Ti and unavoidable impurities.

[0040] equipment:

[0041] Electrical discharge wire cutting machine;

[0042] High-speed forming equipment: incident rod, transmission rod, and absorption rod, made of 18Ni maraging steel;

[0043] Low temperature environment chamber (can be integrated with high-speed forming equipment, temperature control accuracy ±5℃).

[0044]

[0045] Example 1

[0046] This embodiment details the most basic implementation process of the present invention.

[0047] Sample preparation:

[0048] Cylindrical specimens with an aspect ratio of 1 were cut from the aforementioned TA15 titanium alloy sheet using an electrical discharge wire cutting machine. Slow wire cutting and a finishing mode were employed during the machining process to minimize the machining damage layer.

[0049] The cut sample was polished on both ends with metallographic sandpaper of 400#, 800# and 1500# in sequence to ensure that the parallelism error of the two ends was less than 0.02 mm, so as to reduce the waveform oscillation in the high-speed forming equipment experiment.

[0050] Cryogenic pre-impact treatment:

[0051] A number of samples were randomly selected and installed in the low-temperature environment chamber of the high-speed forming equipment system.

[0052] Liquid nitrogen was introduced into the environmental chamber to cool the sample and keep it at -150°C for 5 minutes to ensure uniform temperature throughout the sample.

[0053] The impact pressure was set to 0.14 MPa, the gas valve was triggered, and a single impact loading was applied to the sample at low temperature with a strain rate of 1000 s⁻¹. -1 .

[0054] The impact-recovered sample was measured for height change, and the pre-strain was calculated to be ~2.5% (small deformation).

[0055] Dynamic compression test:

[0056] The sample treated in step 2 (denoted as LT-0.14) was subjected to the final dynamic compression test at room temperature (25°C).

[0057] The impact gas pressure of the high-speed forming equipment was set to 0.23 MPa. The strain rate was calculated to be approximately 1500 s⁻¹ after the experiment. -1 .

[0058] Test results: The dynamic compressive stress-strain curve of the specimen shows that its yield strength (σ) 0.2 The true strain at fracture is 2050 MPa, and the true strain at fracture is ε. f The value is 0.20.

[0059] Microstructure characterization

[0060] Thin slices were cut from the LT-0.15 sample after compression testing, and then mechanically thinned and ion-polished to prepare TEM observation samples.

[0061] Observation was performed using a Talos-F200 transmission electron microscope. Bright-field TEM images revealed numerous nanoscale sheet-like structures (20-50 nm wide, 100-300 nm long) distributed within the α-Ti matrix. Selected-area electron diffraction (SAED) analysis confirmed that these sheet-like structures are face-centered cubic (FCC) titanium. High-resolution transmission electron microscopy (HRTEM) images showed a typical LC-locked structure, formed by dislocation reactions on two slip systems, effectively pinning the surrounding dislocation lines.

[0062] Example 2

[0063] Cryogenic pre-impact treatment:

[0064] A number of samples were randomly selected and installed in the low-temperature environment chamber of the high-speed forming equipment system.

[0065] Liquid nitrogen was introduced into the environmental chamber to cool the sample and keep it at -150°C for 10 minutes to ensure uniform temperature throughout the sample.

[0066] The impact gas pressure was set to 0.14 MPa, the gas valve was triggered, and the sample under low temperature conditions was subjected to a single impact loading at a strain rate of 1100 s⁻¹. -1 .

[0067] The impact-recovered sample was measured for height change, and the pre-strain was calculated to be ~2.5% (small deformation).

[0068] Dynamic compression test:

[0069] The sample treated in step 2 (denoted as LT-0.14) was subjected to the final dynamic compression test at room temperature (25°C).

[0070] The impact gas pressure of the high-speed forming equipment was set to 0.23 MPa. The strain rate was calculated to be approximately 1500 s⁻¹ after the experiment. -1 .

[0071] Test results: The dynamic compressive stress-strain curve of the specimen shows that its yield strength (σ) 0.2 The true strain at fracture is 2000 MPa, and the true strain at fracture is ε. f The value is 0.09.

[0072] Example 3

[0073] Cryogenic pre-impact treatment:

[0074] A number of samples were randomly selected and installed in the low-temperature environment chamber of the high-speed forming equipment system.

[0075] Liquid nitrogen was introduced into the environmental chamber to cool the sample and keep it at -150°C for 5 minutes to ensure uniform temperature throughout the sample.

[0076] The impact gas pressure was set to 0.10 MPa, the gas valve was triggered, and a single impact loading was applied to the sample under low temperature conditions at a strain rate of 800 s⁻¹. -1 .

[0077] The impact-recovered sample was measured for height change, and the pre-strain was calculated to be ~2.5% (small deformation).

[0078] Dynamic compression test:

[0079] The sample treated in step 2 (denoted as LT-0.14) was subjected to the final dynamic compression test at room temperature (25°C).

[0080] The impact gas pressure of the high-speed forming equipment was set to 0.23 MPa. The strain rate was calculated to be approximately 1500 s⁻¹ after the experiment. -1 .

[0081] Test results: The dynamic compressive stress-strain curve of the specimen shows that its yield strength (σ) 0.2 The true strain at fracture is 1950 MPa, and the true strain at fracture is ε. f The value is 0.11.

[0082] Example 4

[0083] Using TA15 titanium alloy powder with a particle size of ≤74 micrometers as raw material, the printing parameters were controlled as follows: laser power 600 W, scanning speed 360 mm / s, scanning spacing 0.3 mm, powder layer thickness 0.4 mm, and powder feeding rate 12 g / min, to obtain the printed blank.

[0084] The printing blank is a cylindrical sample with a diameter / height of 1.

[0085] The two ends of the printed blank were polished sequentially with 400#, 800#, and 1500# metallographic sandpaper to ensure that the parallelism error of the two ends was less than 0.02mm, so as to reduce the waveform oscillation in the high-speed forming equipment experiment.

[0086] Cryogenic pre-impact treatment:

[0087] The printed preform is installed in the low-temperature environment chamber of the high-speed forming equipment system.

[0088] Liquid nitrogen was introduced into the environmental chamber to cool the sample and keep it at -150°C for 5 minutes to ensure uniform temperature throughout the sample.

[0089] The impact pressure was set to 0.14 MPa, the gas valve was triggered, and a single impact loading was applied to the sample at low temperature with a strain rate of 1000 s⁻¹. -1 .

[0090] The impact-recovered sample was measured for height change, and the pre-strain was calculated to be ~2.5% (small deformation).

[0091] Dynamic compression test:

[0092] The sample treated in step 2 was subjected to a final dynamic compression test at room temperature (25°C).

[0093] The impact gas pressure of the high-speed forming equipment was set to 0.23 MPa. The strain rate was calculated to be approximately 1500 s⁻¹ after the experiment. -1 .

[0094] Test results: The dynamic compressive stress-strain curve of the specimen shows that its yield strength (σ) 0.2 The true strain at fracture is 2000 MPa, and the true strain at fracture is ε. f The value is 0.20. This invention is the first to obtain a product with extremely high mechanical properties, in which the overall shape of the 3D printed blank does not change significantly. This provides the necessary conditions for the subsequent preparation of high-strength products with irregular and special structures.

[0095] Example 5

[0096] All other conditions were exactly the same as in Example 4, except that the specimen treated in step 2 was subjected to a final static tensile test at room temperature (25°C).

[0097] Test results: The static tensile stress-strain curve of the specimen shows that its yield strength (σ) 0.2 The true strain at fracture (ε) is 1382 MPa. f The value is 0.20. This invention is the first to obtain a product with extremely high mechanical properties, in which the overall shape of the 3D printed blank does not change significantly. This provides the necessary conditions for the subsequent preparation of high-strength products with irregular and special structures.

[0098] Comparative Example 1

[0099] This comparative example is provided to demonstrate the uniqueness and necessity of the cryogenic pre-impact method of the present invention.

[0100] Sample preparation: Same as in Example 1. However, instead of the -150°C heat treatment for 5 minutes, the sample underwent a room temperature pre-impact treatment directly at room temperature.

[0101] The room temperature pre-impact treatment involved pre-impacting the specimen at room temperature (25°C) using a high-speed forming device. The impact pressure was set to 0.14 MPa, and the pre-strain was measured to be ~2.5% after impact, with a strain rate of 1000 s⁻¹. -1 Similar to Example 1.

[0102] The sample was designated RT-0.14.

[0103] Dynamic compression test:

[0104] The test conditions were the same as in Example 1 (room temperature, 0.23 MPa).

[0105] Test results: The dynamic compression properties of the RT-0.14 specimen are: yield strength 1750MPa, true strain at fracture 0.16.

[0106] Microstructure characterization:

[0107] High-resolution transmission electron microscopy (HRTEM) was performed on the RT-0.14 sample. Only a small amount of dispersed nanosheet-like FCC titanium (different in morphology from the LT sample) was observed in its microstructure; the high-density LC-locking structure shown in Example 1 was not found. Although the dislocation density increased, it mainly existed in the form of discrete dislocation lines, lacking effective pinning points.

[0108] Comparative Example 2

[0109] The conditions were the same as in Example 1, except that the sample was cooled and kept at a constant temperature of -10°C. The mechanical properties of the resulting product were far inferior to those of the product obtained in Example 1.

[0110] The specific performance is as follows:

[0111] Dynamic compression test:

[0112] The test conditions were the same as in Example 1 (room temperature, 0.23 MPa).

[0113] Test results: The dynamic compression properties of the specimen are: yield strength 1850MPa, true strain at fracture 0.18.

[0114] Comparative Example 3

[0115] The conditions were the same as in Example 1, except that the impact pressure was set to 0.4 MPa and the strain rate to 3100 s after cryogenic treatment. -1 .

[0116] Dynamic compression test:

[0117] The test conditions were the same as in Example 1 (room temperature, 0.23 MPa).

[0118] Test results: The dynamic compression properties of the specimen are: yield strength 1710 MPa, true strain at fracture 0.13.

[0119] Comparative Example 4

[0120] This comparative example is provided to demonstrate the uniqueness and necessity of the cryogenic pre-impact method of the present invention.

[0121] Sample preparation: Same as in Example 5. However, instead of the -150°C, 5-minute heat treatment, a room temperature pre-impact treatment was performed directly at room temperature.

[0122] The room temperature pre-impact treatment involved pre-impacting the specimen at room temperature (25°C) using a high-speed forming device. The impact pressure was set to 0.14 MPa, and the pre-strain was measured to be ~2.5% after impact, with a strain rate of 1000 s⁻¹. -1 Similar to Example 1.

[0123] Static tensile test:

[0124] The test conditions are the same as in Example 5.

[0125] Test results: The static tensile properties of the specimen are: yield strength 970 MPa, true strain at fracture 0.13.

Claims

1. A method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact, characterized in that: A low-temperature environment is used to subject titanium alloy samples to small deformation pre-impact with specific parameters, thereby introducing lamellar FCC titanium phase and LC lock into its microstructure. The temperature of the low-temperature environment is -20℃ to -196℃, and the deformation of the small deformation pre-impact is 0.5% to 8%.

2. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: A strain rate of 100-2000 s⁻¹ is applied to a titanium alloy at a temperature ranging from -70℃ to -196℃. -1 The impact force causes the titanium alloy to undergo small plastic deformation of 1% to 5%.

3. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: A strain rate of 700-1200 s⁻¹ is applied to the titanium alloy at a temperature ranging from -80℃ to -196℃. -1 The impact force causes the titanium alloy to undergo small plastic deformation of 1.5% to 3.5%.

4. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: The titanium alloy is selected from one of TA15, TC4, and TA0.

5. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 4, characterized in that: The titanium alloy is selected from at least one of the following: cast, rolled, printed, and annealed states.

6. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: Samples of the desired shape are cut from titanium alloy plates or bars using wire electrical discharge machining.

7. The method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: When the titanium alloy is in the printed state or is an annealed printed preform, an impact force is applied to the titanium alloy at -120℃ to -196℃, causing the titanium alloy to undergo a small plastic deformation of 1.5% to 3.5%. Preferably, a strain rate of 800-1200 s⁻¹ is applied to the titanium alloy at -140℃ to -196℃. -1 The impact force causes the titanium alloy to undergo small plastic deformation of 2% to 3%.

8. A method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 7, characterized in that: The printing parameters for the printed titanium alloy are: laser power 400~700W, scanning speed 300~400mm / s, scanning spacing 0.2~0.4mm, powder layer thickness 0.3~0.5mm, and powder feeding rate 10~15g / min.

9. A method for improving the mechanical properties of titanium alloys through low-temperature high-speed pre-impact as described in claim 1, characterized in that: The sample was placed in the heat preservation chamber of the forming equipment and cooled to a low temperature environment of -20℃ to -196℃; liquid nitrogen was used to achieve cooling and maintain temperature stability.

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