Preparation method of titanium alloy bar for evaluating hard alpha defect influence
By using porous titanium nitride sponge in the preparation of titanium alloy rods, combined with specific process parameters, the problems of complex preparation and large error in the existing technology are solved, and a simple and efficient hard α defect assessment is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-14
- Publication Date
- 2026-03-31
AI Technical Summary
Existing technologies for preparing hard α-defect titanium alloy bars involve complex processes that are difficult to simulate the actual melting process, resulting in large experimental errors and failing to meet airworthiness certification requirements.
Using porous titanium nitride sponge as a defect implant, titanium alloy rods containing hard α defects were prepared by pressing electrode blocks, welding consumable electrodes and vacuum consumable arc melting processes, combined with specific melting parameters and water cooling conditions.
The preparation process was simplified, the consistency with actual production was improved, experimental errors were reduced, and the impact of hard α defects on the properties of titanium alloys could be effectively evaluated.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of non-ferrous metal processing technology and relates to a method for preparing titanium alloy bars for evaluating the influence of hard α defects. Background Technology
[0002] Titanium alloys, due to their superior properties such as low density, high specific strength, good corrosion resistance, low thermal conductivity, and wide operating temperature range, are widely used in components of aero engines, including compressors, fan discs, blades, and casings. The amount of titanium alloy used in engines has become one of the important indicators for evaluating the advancement of engines. With the continuous improvement of the thrust-to-weight ratio requirements of aero engines, the loads on related components (compressors, fan discs, blades, and casings) are becoming increasingly complex, and the operating conditions are becoming increasingly demanding. The metallurgical quality of titanium alloys directly affects the reliability and service safety of aircraft. Therefore, eliminating metallurgical defects in titanium alloys, especially TiN-type hard α inclusions, has become a key research direction for high-end titanium materials both domestically and internationally. Among them, hard α inclusions are a type of metallurgical defect that poses a significant threat to titanium alloys. Hard α defects mainly occur during the titanium alloy smelting process when elements such as N and O are mixed in, forming high-melting-point compounds such as TiN (2950℃) with Ti. Because these compounds have a melting point far exceeding that of titanium alloys, they are difficult to fully dissolve in the molten pool of titanium alloys. These compounds have high melting points, high hardness, and are brittle. During service, titanium alloy materials containing hard α defects exhibit incompatibility between the hard α defects and the matrix structure in response to loaded loads, especially alternating fatigue loads. Hard α defects often become crack initiations for premature fatigue failure, seriously threatening the service safety of engines.
[0003] Current processes for preparing TiN-containing hard α-inclusion titanium alloy rods typically involve inserting a dense TiN bulk material into machined cavities in a normal titanium alloy rod, then retaining it within the rod using hot isostatic pressing, welding, or smelting. However, this method is complex and differs significantly from the normal titanium alloy ingot production process (vacuum arc melting), making it difficult to accurately simulate the formation mechanism and distribution characteristics of TiN inclusions in titanium alloy ingots. Furthermore, machining the cavities may introduce crack initiation sites in subsequent experiments, and the placement of the dense TiN bulk material within the cavities may entrain other gases. Therefore, in subsequent fatigue crack propagation experiments, the hard α-inclusion titanium alloy discs obtained through this method introduce various uncertainties due to the pre-machined cavities and entrained gases, failing to effectively simulate the formation process and actual characteristics of hard α defects in actual production, leading to significant experimental errors.
[0004] In view of this, the present invention is hereby proposed. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing titanium alloy bars for evaluating the influence of hard α defects, so as to solve the problems of complex preparation process of hard α defect bars, poor consistency with actual melting process, large subsequent experimental error, and difficulty in meeting the relevant requirements of airworthiness certification.
[0006] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a method for preparing titanium alloy rods for evaluating the influence of hard α defects. The method involves adding porous sponge titanium nitride to titanium alloy raw materials, wherein the sponge titanium nitride is distributed in the geometric center region of the raw materials within the electrode pressing mold cavity. The titanium alloy rod containing hard α defects is formed through the process of "pressing electrode block → welding consumable electrode → vacuum consumable arc melting → forging".
[0007] Specifically, see Figure 1 The specific steps of the preparation method are as follows: Step 1: Prepare titanium nitride sponge; Step 2: Crush the titanium nitride sponge to a particle size range of 8mm~30mm, and select loose and porous titanium nitride sponge with N content ≥8% as the defect implant; Step 3: Proportion the titanium alloy raw materials according to the national standard, mix the various raw materials evenly, and put them into the mold cavity of the hydraulic press to press and obtain electrode blocks containing titanium nitride sponge and normal electrode blocks; the defective implants are distributed in the geometric center area of the raw materials in the electrode pressing mold cavity, and the distance between the defective implants and the outer surface of the electrode block is ≥30mm. Step 4: Use a vacuum plasma welding box to weld the electrode block containing titanium nitride sponge and the normal electrode block together to form a consumable electrode. Step 5: First, place the self-consuming electrode in the crucible, then put it into the vacuum self-consuming electric arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, after arc ignition, perform one melting, two melting and three melting in sequence to obtain a titanium alloy ingot containing hard α defects. After cooling, peel off the skin and saw off the riser. Step 6: Forge the titanium alloy ingot into titanium alloy bars of the target specifications, peel off the outer layer, perform water immersion testing, and evaluate the impact of hard α defects on the performance of the titanium alloy.
[0008] Specifically, in step 1, the specific process for preparing titanium sponge nitride is as follows: During the reduction stage, the temperature is controlled within the range of 800℃ to 950℃, compressed air is introduced into the reactor, and the pressure inside the reactor is maintained at 80kPa to 120kPa for 20 to 30 hours. During the distillation stage, the distillation temperature is 850℃ to 1000℃, the vacuum pressure is controlled at ≤5Pa, and the duration is 40 to 80 hours.
[0009] Specifically, in step 3, the number of defective implants in a single electrode block is ≤10, and the spacing between adjacent defective implants is ≥30mm.
[0010] Specifically, in step 4, when assembling and welding the consumable electrodes: Along the length of the consumable electrode, the normal electrode block is located at the end and center region, and the remaining positions are electrode blocks containing titanium nitride sponge. The centers of the normal electrode block and the electrode blocks containing titanium nitride sponge are located on the same straight line. The consumable electrode assembly is completed in a vacuum plasma welding box.
[0011] Furthermore, in a vacuum plasma welding box, when the pre-vacuum degree is ≤2Pa and the leakage rate is ≤1Pa / min, a current of 300A~400A and a voltage of 50V~90V are used for the assembly welding of consumable electrodes.
[0012] Specifically, in step 5, the melting current during a normal melting period is 9kA~13kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts DC arc stabilizing current, and the arc stabilizing current is 5A~10A. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
[0013] Specifically, in step 5, the melting current during the normal melting period of the secondary melting is 16kA~20kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 5A~10A with a period of 5s~10s. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
[0014] Specifically, in step 5, the melting speed during the normal melting period of the three melting processes is 15kg / min~18kg / min, the melting voltage is 34V~36V, the arc stabilization current is AC arc stabilization, and the arc stabilization current is 8A~13A, the arc stabilization period is 5s~10s, and the cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
[0015] On the other hand, the present invention also provides a titanium alloy rod prepared by some or all of the preparation methods described above, wherein the titanium alloy rod has a specification of Φ50mm~Φ400mm and a hard α defect size of 450μm~700μm.
[0016] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: 1) Compared with the existing preparation process of titanium nitride bulk, the loose and porous titanium nitride sponge provided by the present invention, in the process of reduction distillation, by introducing compressed air, under specific reaction temperature, reaction pressure and holding time, simulates the air leakage of reactor pipeline in actual production, thereby obtaining loose and porous titanium nitride sponge particles. Moreover, the preparation process is simple and has a good consistency with the actual production process.
[0017] 2) In the normal preparation process of titanium alloy ingots, titanium nitride sponge of a specific size (particle size range of 8mm~30mm) is pressed into an electrode block and located in the geometric center region of the raw material within the electrode pressing mold cavity. Titanium alloy ingots are obtained by welding consumable electrodes and performing primary, secondary, and tertiary melting according to the conventional ingot production process. During the melting process, the degree of dissolution of titanium nitride sponge particles from the primary melting to the final product melting is controlled by adjusting the melting current, arc stabilization current, and water cooling parameters to obtain a TiN-containing hard α-defect ingot. After forging and surface scraping for inspection, a bar containing hard α-defects is finally obtained, facilitating the evaluation of the impact of hard α-defects on the properties of the titanium alloy.
[0018] In summary, this invention places loose and porous titanium nitride sponge particles directly in the geometric center region of the raw material within the electrode pressing mold cavity during the electrode pressing process. Titanium alloy ingots are then produced by welding consumable electrodes and performing primary, secondary, and tertiary melting according to conventional ingot production procedures. This eliminates processes such as drilling holes in the rods, hot isostatic pressing, and welding to treat pre-set holes, while avoiding uncertain experimental factors. Furthermore, it exhibits small experimental errors, a simple processing flow, and is applicable to the preparation of titanium alloy rods of different grades and with different hardness α defects. Attached Figure Description
[0019] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a flowchart of the preparation method of titanium alloy rods for evaluating the influence of hard α defects according to the present invention; Figure 2 This is a schematic diagram of the structure of the defective implant electrode block pressed according to Embodiment 1 of the present invention; Figure 3 This is a schematic diagram showing the assembly and distribution of all electrode blocks in a consumable electrode system. Figure 4This is a schematic diagram of water immersion testing of a titanium alloy bar containing a hard α defect prepared in Example 1 of the present invention; Figure 5 This is a microstructure diagram of the titanium alloy rod containing hard α defects prepared in Example 1 of the present invention; Figure 6 This is a schematic diagram of water immersion testing of a titanium alloy bar containing hard α defects prepared in Example 2 of the present invention; Figure 7 This is a microstructure diagram of the titanium alloy rod containing hard α defects prepared in Example 2 of the present invention; Figure 8 This is a schematic diagram of water immersion testing of a titanium alloy bar containing hard α defects prepared in Example 3 of the present invention; Figure 9 This is a microstructure diagram of the titanium alloy rod containing hard α defects prepared in Example 3 of the present invention; Figure 10 This is a schematic diagram of water immersion testing of the titanium alloy bar without hard α defects prepared in Comparative Example 1. Figure 11 This is a microstructure diagram of the titanium alloy bar without hard α defects prepared in Comparative Example 1; Figure 12 This is a schematic diagram of water immersion testing of the titanium alloy bar without hard α defects prepared in Comparative Example 2. Figure 13 This is a microstructure diagram of the titanium alloy bar without hard α defects prepared in Comparative Example 2; Figure 14 This is a schematic diagram of water immersion testing of the titanium alloy bar without hard α defects prepared in Comparative Example 3. Figure 15 This is a microstructure diagram of the titanium alloy bar without hard α defects prepared in Comparative Example 3. Detailed Implementation
[0022] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.
[0023] The inventors of this patent previously used qualified titanium sponge particles, mixed them with air at 800℃~1000℃, and held them at that temperature for 30min~60min to obtain titanium nitride sponge particles. However, during the experiment, it was found that the surface of the loose and porous finished titanium sponge particles melted first during heating and combined with oxygen in the air, forming a dense oxide layer, which to some extent hindered the nitride reaction. Furthermore, the titanium nitride sponge particles prepared using this method not only differed significantly in appearance from those produced during the titanium sponge production process, but also in nitrogen content, failing to effectively simulate the actual situation during the production process of titanium nitride-like hard α defects.
[0024] In response, the inventors of this patent conducted extensive exploratory experimental research: 1) In the reduction distillation stage of titanium sponge production, compressed air was introduced to obtain loose and porous titanium nitride particles with controllable nitrogen content under specific reaction temperature, pressure, and holding time. However, for those skilled in the art, obtaining loose and porous titanium nitride particles with controllable nitrogen content is only the basis for preparing titanium alloy bars with hard α defects according to the normal titanium alloy production process. If the electrode preparation and melting process settings are unreasonable, the loose and porous titanium nitride particles may still dissolve too quickly during melting, failing to be retained in the finished ingots and forged bars, resulting in the inability to form hard α defects and failing to meet the requirements of subsequent high-quality testing.
[0025] To control the dissolution of porous titanium nitride in the VAR molten pool, the solution proposed in this invention is as follows: Select porous titanium nitride with an N content ≥8% and a particle size range of 8mm~30mm. In the electrode preparation stage, place the titanium nitride in the geometric center region of the raw material within the electrode pressing mold cavity, and weld the electrode block containing titanium nitride to a specific part (non-end and non-center position) of the consumable electrode. By adjusting the process parameters and water cooling parameters of the first, second, and third melting processes, the dissolution rate of titanium nitride in the VAR molten pool is controlled, allowing it to remain in the finished ingot, which can be effectively detected by forging and water immersion testing.
[0026] Meanwhile, the inventors of this patent also discovered in exploratory experiments that the degree of dissolution of loose and porous titanium nitride in a VAR molten pool is closely related to the nitrogen content in the titanium sponge particles and the original size of the titanium nitride. The lower the nitrogen content and the smaller the size of the titanium nitride, the greater the probability of it being dissolved in the VAR molten pool. To ensure the successful preparation of titanium alloy rods containing hard α defects, this invention selects loose and porous titanium nitride with an nitrogen content ≥8% and a particle size range of 8mm~30mm as the defect implant.
[0027] 2) During exploratory experiments, the inventors of this patent discovered that, under certain conditions of N content and particle size in titanium sponge, its position in the molten pool, as well as the melting power, water cooling parameters, and N dissolution rate, are significantly related. Specifically, this is reflected in: When titanium nitride sponge particles are located on the surface of the consumable electrode, due to the stirring effect of the arc-stabilizing magnetic field during the melting process, the titanium nitride sponge particles will be fixed to the edge of the molten pool, i.e., the edge of the ingot, due to the influence of gravity and the stirring effect of the arc-stabilizing magnetic field during VAR melting. Even if the solubility of the titanium nitride sponge particles in this position is insufficient during melting, the hard α defects formed are often machined away during subsequent heating, forging losses, and machining peeling processes, and are difficult to retain in the finished bar. Therefore, placing titanium nitride sponge particles of a specific size in the core position of the consumable electrode during the electrode preparation stage avoids machining losses during subsequent processing. Similarly, when titanium nitride sponge particles are located near the surface or bottom of the consumable electrode, there is a risk of loss during machining. When they are located at the center of the consumable electrode, the heat is higher due to the deeper molten pool, which will also accelerate the diffusion rate of N. Therefore, titanium nitride sponge particles should be located near the lower part of the molten pool where the heat is relatively lower. Thus, this invention selects titanium nitride sponge particles located in the geometric center region of the raw material in the electrode pressing mold cavity, and allows the electrode block containing titanium nitride sponge to be welded to a specific part of the consumable electrode (not the end or the center).
[0028] 3) During the exploration process, the inventors of this patent also discovered that a melting current greater than 14kA and an arc-stabilizing magnetic field strength greater than 15A during the normal melting period of the first melting stage, as well as insufficient cooling intensity during ingot melting, all increase the dissolution rate of titanium nitride sponge particles in the molten pool. Similarly, during the second and third melting stages, excessive melting current and increased arc-stabilizing magnetic field stirring intensity, coupled with weak ingot cooling conditions, significantly increase the dissolution rate of titanium nitride sponge in the molten pool, making it difficult for it to form hard α defects and remain inside the ingot or bar. Likewise, if the melting current from the first melting stage to the finished product melting is too low, the melting rate decreases significantly, the melting time increases markedly, and the nitrogen-containing titanium sponge particles in the consumable electrode undergo a longer arc-light baking effect. Due to the high-temperature, long-term baking effect of the arc, it actually accelerates the dissolution rate during the VAR melting process, making it difficult for them to form hard α defects in the ingot. Therefore, based on the above experiments, and after extensive theoretical research and experimentation, the inventors of this patent finally obtained the following technical solution of the present invention: This invention provides a method for preparing titanium alloy rods for evaluating the impact of hard α defects. Porous, porous titanium nitride sponge is added to the titanium alloy raw material, with the titanium nitride sponge distributed in the geometric center region of the raw material within the electrode pressing mold cavity. The process involves "pressing electrode blocks → welding consumable electrodes → vacuum consumable arc melting → forging" to form a titanium alloy rod containing hard α defects, facilitating the evaluation of the impact of hard α defects. See also... Figure 1 The specific steps are as follows: Step 1: Preparation of titanium nitride sponge, the specific process is as follows: During the reduction stage, the temperature is controlled within the range of 800℃ to 950℃, compressed air is introduced into the reactor, and the pressure inside the reactor is maintained at 80kPa to 120kPa for 20 to 30 hours. During the distillation stage, the distillation temperature is 850℃ to 1000℃, the vacuum pressure is controlled at ≤5Pa, and the duration is 40 to 80 hours.
[0029] Step 2: Crush the titanium nitride sponge to a particle size range of 8mm to 30mm, and select loose porous titanium nitride sponge with an N content of ≥8% as the defect implant.
[0030] Step 3: Proportion the titanium alloy raw materials according to the national standard nominal composition, mix the various raw materials evenly, and put them into the mold cavity of the hydraulic press to press and obtain electrode blocks containing titanium nitride sponge and normal electrode blocks (without titanium nitride sponge); wherein, the defective implants are distributed in the geometric center area of the raw materials in the electrode pressing mold cavity, the number of defective implants in a single electrode block is ≤10, the distance between adjacent defective implants is ≥30mm, and the distance between the defective implants and the outer surface of the electrode block is ≥30mm.
[0031] It should be noted that, taking the preparation process of an electrode block containing titanium nitride sponge as an example, the weight of a single electrode block is set as A kg; after A kg of various raw materials are mixed evenly, 0.5A kg of raw materials are first placed into the hydraulic press mold cavity to ensure that the thickness of the raw materials is uniform in the hydraulic press mold cavity. Then, no more than 10 defect implants (loose and porous titanium nitride sponge) are placed on the surface of the raw materials in the electrode pressing mold cavity to ensure that the distance between adjacent defect implants is ≥30mm and the distance between the defect implants and the outer surface of the electrode block is ≥30mm. Then, the remaining 0.5A kg of raw materials are poured into the hydraulic press mold cavity, and the electrode block containing titanium nitride sponge is obtained after pressing.
[0032] Step 4: Use a vacuum plasma welding oven to weld the above-mentioned electrode block containing titanium nitride sponge and the normal electrode block into a consumable electrode; when welding the consumable electrode: Along the length of the consumable electrode, the normal electrode block is located at the end and center region, and the remaining positions are electrode blocks containing titanium sponge nitride. The centers of the normal electrode block and the electrode blocks containing titanium sponge nitride are located on the same straight line. The consumable electrode assembly is completed in a vacuum plasma welding box.
[0033] Step 5: First, place the consumable electrode in a crucible, then load it into a vacuum consumable arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, perform a first melting, a second melting, and a third melting in sequence after arc ignition to obtain a titanium alloy ingot containing hard α defects. After cooling, peel off the outer layer and saw off the riser. During a normal smelting period, the smelting current is 9kA~13kA, the smelting voltage is 34V~36V, the arc stabilizing magnetic field adopts DC arc stabilizing current, and the arc stabilizing current is 5A~10A. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min. During the normal melting period of the secondary melting process, the melting current is 16kA~20kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 5A~10A with a period of 5s~10s. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min. The melting speed during the normal melting period of the three melting processes is 15kg / min~18kg / min, the melting voltage is 34V~36V, the arc stabilization current is AC stabilization current of 8A~13A, the arc stabilization period is 5s~10s, and the cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
[0034] Step 6: Forge the ingot into a bar with a diameter of 50mm to 400mm and remove the outer layer. Perform water immersion testing using a flat-bottomed hole with a diameter of 0.8mm to evaluate the impact of hard α defects on the properties of the titanium alloy.
[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0036] Example 1 (Preparation of TC11 titanium alloy rods containing hard α defects) This embodiment provides a method for preparing titanium alloy bars for evaluating the influence of hard α defects. The specific steps are as follows: Step 1: Preparation of titanium nitride sponge: In the reduction stage, when the temperature is 800℃, compressed air is introduced into the reactor to maintain the pressure inside the reactor at 80kPa for 20h; in the distillation stage, the distillation temperature is 950℃, the vacuum pressure is controlled at ≤5Pa, and the duration is 50h. Step 2: Crush the titanium nitride sponge to a particle size range of 8mm~10mm, and select loose and porous titanium nitride sponge with an N content of 10%~12% as the defect implant. Step 3: According to the national standard nominal composition ratio of TC11 alloy raw materials, the input amount is 2800kg, and the weight of a single electrode block is 50kg. After mixing the various raw materials evenly, first put 25kg of raw materials into the hydraulic press mold cavity, ensuring that the raw materials are of uniform thickness in the hydraulic press mold cavity. Then, place the above 6 defective implants (loose and porous titanium nitride sponge) on the surface of the core area of the raw materials in the electrode pressing mold cavity, ensuring that the distance between adjacent defective implants is 60mm and the distance between the defective implants and the outer surface of the electrode block is 30mm. Then, continue to pour the remaining 25kg of raw materials into the hydraulic press mold cavity, and after pressing, obtain electrode blocks containing titanium nitride sponge. According to this method, 6 electrode blocks containing defective implants and 50 normal electrode blocks are obtained. The distribution diagram of the defective implants in the electrode blocks is shown in the figure. Figure 2 As shown; Step 4: Place the electrode blocks containing the defective implants into the second, third, and fourth sections, and the penultimate, third, and fourth sections of the entire consumable electrode. The first, penultimate, and other sections are normal electrode blocks. See [link to relevant documentation]. Figure 3 As shown, the above 56 electrode blocks were placed in a vacuum plasma welding box and evacuated. When the pre-vacuum degree was ≤2Pa and the leakage rate was ≤1Pa / min, the self-consumable electrode assembly was completed with a current of 300A~400A and a voltage of 50V~90V and cooled for 1 hour before being taken out of the furnace. Step 5: Place the consumable electrode in a crucible, then load it into a vacuum consumable arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, perform a first melting, a second melting, and a third melting in sequence after arc ignition to obtain a titanium alloy ingot. After cooling, peel off the outer layer and saw off the riser. The melting current during a normal melting period is 9kA, the melting voltage is 34V, the arc stabilizing magnetic field adopts DC arc stabilizing current and the arc stabilizing current is 5A, and the cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 1800L / min. During the normal melting period of the secondary melting process, the melting current is 16kA, the melting voltage is 34V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 5A with a period of 5s. The cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 1800L / min. The melting speed during the normal melting period of the three melting processes is 15 kg / min, the melting voltage is 34 V, the arc stabilization current is AC stabilization current of 8 A, the arc stabilization period is 5 s, and the cooling conditions are: inlet water temperature of 30 ℃, outlet water temperature of 33 ℃, and cooling water flow rate of 1800 L / min. Step 6: Forge the titanium alloy ingot into a Φ50mm bar and peel off the outer layer. Perform water immersion testing using a Φ0.8mm diameter flat-bottom hole to evaluate the impact of hard α defects on the properties of the titanium alloy.
[0037] In this embodiment, the titanium nitride sponge obtained in step 1 was subjected to SEM detection, and the N content was in the range of 11% to 12%, with an average N content of 11%.
[0038] The final finished bar stock is subjected to water immersion testing, see [link / reference]. Figure 4 The corresponding abnormal areas were dissected and metallographic samples were prepared. The hard α defects obtained were as follows: Figure 5 As shown. From Figure 5 It can be seen that the hard α defect is significantly different from the matrix. Due to its high hardness, it is difficult to deform. The core of the defect has a hole-like feature, and the defect size is about 500 μm.
[0039] Example 2 (Preparation of TC4 titanium alloy rods containing hard α defects) This embodiment provides a method for preparing titanium alloy bars for evaluating the influence of hard α defects. The specific steps are as follows: Step 1: Preparation of titanium nitride sponge: In the reduction stage, when the temperature is 850℃, compressed air is introduced into the reactor to maintain the pressure inside the reactor at 90kPa for 25h; in the distillation stage, when the distillation temperature is 1000℃, the vacuum pressure is controlled to be ≤3Pa for 60h. Step 2: Crush the nitrided sponge titanium to a particle size range of 8mm~12.7mm, and select loose porous nitrided sponge titanium with an N content of 10%~12% as the defect implant; Step 3: According to the national standard nominal composition ratio of TC4 alloy raw materials, the input amount is 5600kg, and the weight of a single electrode block is 100kg. After the various raw materials in the 100kg mixture are evenly mixed, 50kg of raw materials are first put into the hydraulic press mold cavity to ensure that the raw materials are of uniform thickness in the hydraulic press mold cavity. Then, the above-mentioned 8 defective implants (loose and porous titanium nitride sponge) are placed on the surface of the core area of the raw materials in the electrode pressing mold cavity, ensuring that the distance between adjacent defective implants is 50mm and the distance between the defective implants and the outer surface of the electrode block is 40mm. Then, the remaining 50kg of raw materials are poured into the hydraulic press mold cavity. After pressing, electrode blocks containing titanium nitride sponge are obtained. According to this method, 6 electrode blocks containing defective implants and 50 normal electrode blocks are obtained. Step 4: Place the electrode block containing the defective implant into the third, fourth, fifth, and third-to-last, fourth, and fifth sections of the entire consumable electrode assembly. The first, second, last, and second-to-last sections, as well as the other sections, are normal electrode blocks. See [link to relevant documentation]. Figure 3As shown, the above 56 electrode blocks were placed in a vacuum plasma welding box and evacuated. When the pre-vacuum degree was ≤2Pa and the leakage rate was ≤1Pa / min, the self-consumable electrode assembly was completed using a current of 300 A~400A and a voltage of 50V~90V and cooled for 1 hour before being taken out of the furnace. Step 5: Place the consumable electrode in a crucible, then load it into a vacuum consumable arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, perform a first melting, a second melting, and a third melting in sequence after arc ignition to obtain a titanium alloy ingot. After cooling, peel off the outer layer and saw off the riser. The melting current during a normal melting period is 13kA, the melting voltage is 36V, the arc stabilizing magnetic field adopts DC arc stabilizing current, and the arc stabilizing current is 10A. The cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 2800L / min. During the normal melting period of the secondary melting process, the melting current is 20kA, the melting voltage is 36V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 10A with a cycle of 10s. The cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 2800L / min. The melting speed during the normal melting period of the three melting processes is 18 kg / min, the melting voltage is 36 V, the arc stabilization current is AC stabilization current of 13 A, the arc stabilization period is 10 s, and the cooling conditions are: inlet water temperature 30 ℃, outlet water temperature 33 ℃, and cooling water flow rate 2800 L / min. Step 6: Forge the titanium alloy ingot into a Φ400mm bar and peel off the outer layer. Perform water immersion testing using a Φ0.8mm diameter flat-bottom hole to evaluate the impact of hard α defects on the properties of the titanium alloy.
[0040] In this embodiment, the titanium nitride sponge obtained in step 1 was subjected to SEM detection, and the N content was in the range of 13% to 15%, with an average N content of 14%.
[0041] The finished bar obtained in step 7 is subjected to water immersion testing, see [reference needed]. Figure 6 The corresponding abnormal areas were dissected and metallographic samples were prepared. The hard α defects obtained were as follows: Figure 7 As shown. From Figure 7 It is evident that the large hard α defects differ significantly from the matrix structure. Due to their high hardness, they are difficult to deform, and the core of the defects exhibits a pore-like characteristic, with a defect size of approximately 700 μm.
[0042] Example 3 (Preparation of TC17 titanium alloy rods with hard α defects) This embodiment provides a method for preparing titanium alloy bars for evaluating the influence of hard α defects. The specific steps are as follows: Step 1: Preparation of titanium nitride sponge: In the reduction stage, when the temperature is 950℃, compressed air is introduced into the reactor to maintain the pressure inside the reactor at 120kPa for 30h; in the distillation stage, when the distillation temperature is 1050℃, the vacuum pressure is controlled to be ≤2Pa for 70h. Step 2: Crush the nitrided sponge titanium to a particle size range of 25.4mm~30mm, and select loose porous nitrided sponge titanium with an N content of 18%~20% as the defect implant; Step 3: According to the national standard nominal composition ratio of TC17 alloy raw materials, the input amount is 3520kg, and the weight of a single electrode block is 80kg. After the 80kg of various raw materials are mixed evenly, 40kg of raw materials are first put into the hydraulic press mold cavity to ensure that the raw materials are of uniform thickness in the hydraulic press mold cavity. Then, the above-mentioned 8 defective implants (loose and porous titanium nitride sponge) are placed on the surface of the core area of the raw materials in the electrode pressing mold cavity, ensuring that the distance between adjacent defective implants is 60mm and the distance between the defective implants and the outer surface of the electrode block is 40mm. Then, the remaining 40kg of raw materials are poured into the hydraulic press mold cavity. After pressing, electrode blocks containing titanium nitride sponge are obtained. According to this method, 4 electrode blocks containing defective implants and 40 normal electrode blocks are obtained. Step 4: Place the electrode block containing the defective implant into the second, third, penultimate, and third sections of the entire consumable electrode assembly. The first, penultimate, and other sections are normal electrode blocks. See [link to relevant documentation]. Figure 3 As shown, the above 44 electrode blocks were placed in a vacuum plasma welding box and evacuated. When the pre-vacuum degree was ≤2Pa and the leakage rate was ≤1Pa / min, the self-consumable electrode assembly was completed using a current of 300A~400A and a voltage of 50V~90V and cooled for 1 hour before being taken out of the furnace. Step 5: Place the aforementioned consumable electrode in a crucible, then load it into a vacuum consumable arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, perform a first melting, a second melting, and a third melting in sequence after arc ignition to obtain a titanium alloy ingot. After cooling, peel off the outer layer and saw off the riser; among which, The melting current during a normal melting period is 11kA, the melting voltage is 35V, the arc stabilizing magnetic field adopts DC arc stabilizing current, and the arc stabilizing current is 8A. The cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 2800L / min. During the normal melting period of the secondary melting process, the melting current is 18kA, the melting voltage is 35V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 8A with a period of 8s. The cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 2400L / min. The melting speed during the normal melting period of the three melting processes is 16.5 kg / min, the melting voltage is 35V, the arc stabilization current is AC stabilization current of 11A, the arc stabilization period is 8s, and the cooling conditions are: inlet water temperature 30℃, outlet water temperature 33℃, and cooling water flow rate 2400L / min. Step 6: Forge the titanium alloy ingot into a Φ200mm bar and peel off the outer layer. Perform water immersion testing using a Φ0.8mm diameter flat-bottom hole to evaluate the impact of hard α defects on the properties of the titanium alloy.
[0043] In this embodiment, the titanium nitride sponge obtained in step 1 was subjected to SEM detection, and the N content was in the range of 18% to 20%, with an average N content of 19%.
[0044] The finished bar obtained in step 7 is subjected to water immersion testing, see [link to relevant documentation]. Figure 8 The corresponding abnormal areas were dissected and metallographic samples were prepared. The hard α defects obtained were as follows: Figure 9 As shown. From Figure 9 It is evident that the large hard α defects differ significantly from the matrix structure. Due to their high hardness, they are difficult to deform, and the core of the defects exhibits a pore-like characteristic, with a defect size of approximately 450 μm.
[0045] Comparative Example 1 This comparative example provides a method for preparing a titanium alloy bar for evaluating the effect of hard α defects, which differs from Example 1 in that: In step 1, when the temperature is 600℃, compressed air is introduced into the reactor, and the pressure inside the reactor is 60kPa, which is maintained for 20 minutes.
[0046] In step 2, the nitrided sponge titanium is crushed to a particle size range of 3mm to 5mm. Since the N content of the nitrided sponge titanium obtained under the reaction conditions in step 1 is less than 3%, loose and porous nitrided sponge titanium with an N content of 2% to 3% is selected as the defect implant.
[0047] The remaining steps are exactly the same as in Example 1. The TC11 titanium alloy bar obtained in Comparative Example 1 is subjected to water immersion testing with a flat bottom hole of Φ0.8mm diameter. The test results are shown in [Figure 1]. Figure 10 ,Depend on Figure 10 It can be seen that no individual display signal corresponding to the flaw detection anomaly was found in the TC11 titanium alloy bar prepared in this comparative example, indicating that no TiN-type hard α defects were generated in the TC11 titanium alloy bar. See [link to relevant documentation]. Figure 11 Tissue observation showed that the bar material had normal tissue.
[0048] Comparative Example 2 This comparative example provides a method for preparing a titanium alloy bar for evaluating the effect of hard α defects, which differs from Example 2 in that: Step 4: Using a vacuum plasma welding box, place all the electrode blocks containing the defective implants at the center of the overall length of the consumable electrode, i.e., at the position with the deepest molten pool, to complete the consumable electrode assembly welding. In step 5, the current during the normal melting period of the first melting is 7kA, the current during the normal melting period of the second melting is 12kA, and the melting rate during the normal melting period of the third melting (i.e., finished product melting) is 12kg / min. The cooling conditions for the first melting, second melting, and finished product melting are: inlet water temperature 25℃, outlet water temperature 40℃, and cooling water flow rate 800L / min.
[0049] The remaining steps are exactly the same as in Example 2. The TC4 titanium alloy bar obtained in Comparative Example 2 is subjected to a 0.8mm diameter flat-bottomed hole water immersion flaw detection test. The flaw detection results are shown in [Figure 2]. Figure 12 As shown, by Figure 12 It can be seen that no individual display signal corresponding to the flaw detection anomaly was found in the TC4 titanium alloy bar prepared in this comparative example, indicating that no TiN-type hard α defects were generated in the TC11 titanium alloy bar. (See [reference]). Figure 13 Tissue observation showed that the bar material had normal tissue.
[0050] Comparative Example 3 This comparative example provides a method for preparing a titanium alloy bar for evaluating the effect of hard α defects, which differs from Example 3 in that: In step 5, the melting current during the normal melting period of the first melting stage is 15kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts DC arc stabilizing magnetic field strength, and the arc stabilizing current is 20A; the melting current during the normal melting period of the second melting stage is 28kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 20A, with a period of 15s; the melting speed during the normal melting period of the third melting stage is 30kg / min, the melting voltage is 34V~36V, the arc stabilizing current adopts AC arc stabilizing current, and the arc stabilizing current is 25A, with an arc stabilizing period of 20s.
[0051] The remaining steps are exactly the same as in Example 3.
[0052] The TC17 titanium alloy bar obtained in Comparative Example 3 was subjected to water immersion testing with a Φ0.8mm diameter flat-bottom hole. The test results are shown in [Figure 1]. Figure 14 ,Depend on Figure 14 It can be seen that no individual display signal corresponding to the flaw detection abnormality was found in the TC17 titanium alloy bar, indicating that no TiN-type hard α defects were generated in the TC17 titanium alloy bar. (See [link]). Figure 15 Tissue observation showed that the bar material had normal tissue.
[0053] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.
[0054] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.
Claims
1. A method for preparing titanium alloy bars for evaluating the influence of hard α defects, characterized in that, Porous titanium nitride sponge is added to titanium alloy raw material, and the titanium nitride sponge is distributed in the geometric center region of the raw material in the electrode pressing mold cavity. The titanium alloy rod containing hard α defects is formed by the process of "pressing electrode block → welding consumable electrode → vacuum consumable arc melting → forging".
2. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 1, characterized in that, The specific steps are as follows: Step 1: Prepare titanium nitride sponge; Step 2: Crush the titanium nitride sponge to a particle size range of 8mm~30mm, and select loose and porous titanium nitride sponge with N content ≥8% as the defect implant; Step 3: Proportion the titanium alloy raw materials according to the national standard, mix the various raw materials evenly, and put them into the mold cavity of the hydraulic press to press and obtain electrode blocks containing titanium nitride sponge and normal electrode blocks; the defective implants are distributed in the geometric center area of the raw materials in the electrode pressing mold cavity, and the distance between the defective implants and the outer surface of the electrode block is ≥30mm. Step 4: Use a vacuum plasma welding box to weld the electrode block containing titanium nitride sponge and the normal electrode block together to form a consumable electrode. Step 5: First, place the self-consuming electrode in the crucible, then put it into the vacuum self-consuming electric arc furnace. After the pre-vacuum degree and leakage rate reach the set requirements, after arc ignition, perform one melting, two melting and three melting in sequence to obtain a titanium alloy ingot containing hard α defects. After cooling, peel off the skin and saw off the riser. Step 6: Forge the titanium alloy ingot into titanium alloy bars of the target specifications, peel off the outer layer, perform water immersion testing, and evaluate the impact of hard α defects on the performance of the titanium alloy.
3. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 1, the specific process for preparing titanium sponge nitride is as follows: During the reduction stage, the temperature is controlled within the range of 800℃ to 950℃, compressed air is introduced into the reactor, and the pressure inside the reactor is maintained at 80kPa to 120kPa for 20 to 30 hours.
4. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 3, the number of defective implants in a single electrode block is ≤10, and the spacing between adjacent defective implants is ≥30mm.
5. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 4, during the assembly and welding of consumable electrodes: Along the length of the consumable electrode, the normal electrode block is located at the end and center region, and the remaining positions are electrode blocks containing titanium nitride sponge. The centers of the normal electrode block and the electrode blocks containing titanium nitride sponge are located on the same straight line. The consumable electrode assembly is completed in a vacuum plasma welding box.
6. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 5, characterized in that, In a vacuum plasma welding box, when the pre-vacuum degree is ≤2Pa and the leakage rate is ≤1Pa / min, the consumable electrode assembly is performed using a current of 300A~400A and a voltage of 50V~90V.
7. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 5, the melting current during a normal melting period is 9kA~13kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts DC arc stabilizing current, and the arc stabilizing current is 5A~10A. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
8. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 5, the melting current during the normal melting period of the secondary melting is 16kA~20kA, the melting voltage is 34V~36V, the arc stabilizing magnetic field adopts AC arc stabilizing current, and the arc stabilizing current is 5A~10A with a period of 5s~10s. The cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.
9. The method for preparing titanium alloy bars for evaluating the influence of hard α defects according to claim 2, characterized in that, In step 5, the melting speed during the normal melting period of the three melting processes is 15kg / min~18kg / min, the melting voltage is 34V~36V, the arc stabilization current is AC arc stabilization, and the arc stabilization current is 8A~13A, the arc stabilization period is 5s~10s, and the cooling conditions are: inlet and outlet water temperature difference ≤5℃, cooling water flow rate ≥1200L / min.