Titanium alloy workpiece with long fatigue life and preparation method thereof

Abstract

The invention belongs to the technical field of powder metallurgy, and particularly relates to a long-fatigue-life titanium alloy workpiece and a preparation method thereof.The preparation method of the long-fatigue-life titanium alloy workpiece comprises the following steps that mixed powder of hydrogenated and dehydrogenated titanium alloy powder and yttrium powder is subjected to cold isostatic pressing forming, carrying out two-step sintering treatment on the prepared powder pressed blank under vacuum protection to prepare a sintered blank; and under the protective atmosphere, the sintered blank is heated to the two-phase region temperature, one-heating-number multi-direction upsetting and drawing forging is carried out after heat preservation, and the titanium alloy workpiece with the long fatigue life is obtained. According to the preparation method, hydrogenated and dehydrogenated titanium alloy powder and yttrium powder are used as raw materials to prepare the powder metallurgy titanium alloy with the long fatigue life, the process is simple, operability is high, and short-process preparation of the powder metallurgy titanium alloy with the long fatigue life is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy, and particularly relates to a titanium alloy part with high fatigue life and a preparation method thereof. Background Art

[0002] Titanium alloys have the characteristics of light weight, high strength, heat resistance, corrosion resistance, etc., and have become key structural materials in the fields of aerospace, military, ocean engineering, energy and chemical engineering, etc. The production process of traditional melt-forged titanium alloys is complex, and multiple smelting and multi-pass modified forging are required to ensure the stability of tissue properties, resulting in high production costs and low material utilization rates. As a near-net-shape forming process, powder forging can effectively improve material utilization rates and reduce subsequent processing costs. At the same time, it can eliminate pore defects and improve the mechanical properties of parts, which is an effective way to prepare high-performance titanium alloys.

[0003] The fatigue performance under cyclic loading is a key factor for the long-term safe and reliable use of parts. The fatigue performance of titanium alloys is closely related to their microstructural morphology. Among them, the duplex structure exhibits excellent high fatigue life due to the plastic bearing capacity of the equiaxed α phase and the crack propagation resistance of the β transformation structure. At present, traditional powder sintering often adopts a single high-temperature holding strategy, resulting in grain coarsening, requiring subsequent multi-fire forging, or constructing a duplex structure through complex heat treatment. Although tissue control can be achieved, the process flow is long, the energy consumption is high, and the risk of abnormal grain growth increases, leading to rapid propagation of fatigue cracks along grain boundaries and low fatigue life.

[0004] Therefore, how to break through the technical barriers to improving the fatigue performance of titanium alloys and achieve in-situ construction and genetic retention of the duplex structure while streamlining the process is an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a titanium alloy part with high fatigue life and a preparation method thereof. The preparation method in the present invention uses hydrogenated and dehydrogenated titanium alloy powder and yttrium powder as raw materials to prepare a powder metallurgy titanium alloy with high fatigue life. The process is simple, highly operable, and realizes the short-process preparation of a powder metallurgy titanium alloy with high fatigue life.

[0006] The first aspect of the present invention provides a preparation method for a titanium alloy part with high fatigue life. The preparation method includes the following steps: cold isostatic pressing and forming a mixed powder of hydrogenated and dehydrogenated titanium alloy powder and yttrium powder, and subjecting the obtained powder compact to two-step sintering treatment under vacuum protection to obtain a sintered blank; heating the sintered blank to the two-phase region temperature under a protective atmosphere, holding for a period of time, and then performing one-fire multi-directional upsetting and drawing forging to obtain the titanium alloy part with high fatigue life.

[0007] In some embodiments of the present invention, based on the mixed powder, the mass percentage of the yttrium powder is 0.1 wt.% to 0.5 wt.%.

[0008] In some embodiments of the present invention, the particle size D50 of the yttrium powder is 1 μm to 5 μm, and the purity is ≥99.99%.

[0009] In some embodiments of the present invention, the particle size D50 of the hydrogenated dehydrogenated titanium alloy powder is 15 μm to 25 μm, and the oxygen content is ≤2200 ppm.

[0010] In some embodiments of the present invention, the pressure holding pressure for cold isostatic pressing is 150 MPa to 300 MPa, and the pressure holding time is 5 min to 30 min.

[0011] In some embodiments of the present invention, the process of the two-step sintering treatment includes: the first sintering, heating the powder compact from room temperature to 1050 °C to 1200 °C at a rate of 5 °C / min to 10 °C / min, and holding for 0.5 h to 1 h; the second sintering, then cooling to 980 °C to 1030 °C at a rate of 1 °C / min to 5 °C / min, and holding for 3 h to 7 h.

[0012] In some embodiments of the present invention, after the holding of the second sintering is completed, the green body is cooled to 800 °C at a rate of 1 °C / min to 5 °C / min, held for 1 h to 4 h, and then furnace-cooled.

[0013] In some embodiments of the present invention, the vacuum degree of the two-step sintering treatment is 10 -4 Pa to 10 -2 Pa.

[0014] In some embodiments of the present invention, the two-phase region temperature is 930 °C to 980 °C, the holding time is 40 min to 90 min, and the heating rate to the two-phase region temperature is 10 °C / min to 15 °C / min.

[0015] In some embodiments of the present invention, the multi-directional upsetting and drawing forging in one heat treatment includes completing three alternating upsetting and drawing deformations within a single heating cycle.

[0016] In some embodiments of the present invention, after the multi-directional upsetting and drawing forging in one heat treatment, the forging is air-cooled to room temperature at a rate of 20 °C / min to 30 °C / min.

[0017] In some embodiments of the present invention, the completion of three alternating upsetting and drawing deformations within the single heating cycle includes: for the first upsetting, applying pressure along the axial direction of the green body to reduce the height of the green body, and then drawing the upset green body along the radial direction. Repeat the above process, and perform the second and third upsetting and drawing along the axial and radial directions in sequence. The total cumulative deformation amount is 30% to 50%, and the time interval between each deformation does not exceed 5 s.

[0018] In some embodiments of the present invention, the hydrogenated dehydrogenated titanium alloy powder and the yttrium powder are ball-milled and mixed to form the mixed powder, wherein the ball-to-material ratio is 3:1 to 9:1, the diameter of the grinding balls is 3 mm to 6 mm, the mixing speed is 70 rpm to 200 rpm, it rotates forward for 30 min and stops for 5 min and then rotates backward for 30 min, and the mixing time is 8 h to 15 h.

[0019] The second aspect of the present invention also provides a high-fatigue-life titanium alloy component prepared by using the preparation method of the high-fatigue-life titanium alloy component described in the first aspect. The structure of the titanium alloy component includes a duplex structure composed of 30% to 50% primary α phase and β transformation structure. Among them, the primary α phase is evenly distributed in an equiaxed shape, the grain size is 10 μm to 20 μm, and there are a large number of type tensile twins inside, the twin lamellar thickness is 200 nm to 500 nm and shows the characteristics of parallel arrangement and cross distribution; the β transformation structure is composed of α lamellae with a lamellar spacing of 0.5 μm to 0.8 μm and the residual β phase, and there are nanoscale type compressive twins inside the α lamellae.

[0020] In the present invention, by adding the rare earth element yttrium to the hydrogenated dehydrogenated titanium alloy powder and combining two-step sintering, the synergistic control of sintering densification and grain refinement of the powder blank is realized, and a fine and uniform duplex structure is formed; and through single-pass multi-directional alternating free forging in the two-phase region, the characteristics of the sintered duplex structure are retained by using tissue heredity. Compared with traditional multi-pass forging, the energy consumption is reduced by more than 40%.

[0021] The titanium alloy component in the present invention has a duplex structure with enhanced fatigue performance, specifically a twin-reinforced duplex structure composed of 30% to 50% equiaxed α phase and β transformation structure, and its fatigue limit strength is increased by more than 20% compared with conventional forgings.

[0022] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically enumerates the specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0024] Figure 1This is a microstructural photograph of the sintered Ti-6Al-4V alloy sintered billet obtained in Example 1 of the present invention.

[0025] Figure 2 This is a microstructural photograph of the Ti-6Al-4V alloy part obtained by forging in Example 1 of the present invention. Detailed implementation manners

[0026] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0027] It should be understood that the terms used herein are only for the purpose of describing specific exemplary embodiments and are not intended to be limiting. Unless otherwise clearly specified in the context, the singular forms "a", "an", and "the" as used herein may also include the plural forms. The terms "comprising", "including", "containing", and "having" are inclusive and thus specify the presence of the stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is explicitly stated. It should also be understood that additional or alternative steps may be used.

[0028] In the description of the embodiments of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, "a plurality" means two or more, unless otherwise explicitly and specifically defined.

[0029] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present invention. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0030] In the description of the embodiments of the present invention, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, in this text, the character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0031] In the description of the embodiments of the present invention, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0032] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "linkage", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0033] The first aspect of the present invention provides a preparation method for a titanium alloy component with high fatigue life. The key of this preparation method lies in using hydrogenated and dehydrogenated titanium alloy powder and adding the rare earth element yttrium for two-step sintering to prepare a titanium alloy sintered blank with bimodal tissue characteristics, and obtaining a titanium alloy component with high fatigue life through a one-fire short process forging process in the two-phase region of the titanium alloy sintered blank based on tissue heredity.

[0034] The preparation method for the titanium alloy component with high fatigue life in the present invention is specifically carried out according to the following steps.

[0035] Raw material preparation

[0036] In the embodiments of the present invention, hydrogenated and dehydrogenated titanium alloy powder and yttrium powder are used as raw material powders.

[0037] In some embodiments of the present invention, the hydrogenated and dehydrogenated titanium alloy powder can be hydrogenated and dehydrogenated Ti-6Al-4V powder.

[0038] In the embodiments of the present invention, powders with appropriate particle sizes are selected as raw material powders, and the oxygen content of the hydrogenated and dehydrogenated titanium alloy powder is controlled to be lower than 2200 ppm. When the selected powder particle size is too small, the interstitial oxygen content will increase, resulting in poor titanium alloy performance; while when the powder particle size is too large, the powder activity will decrease, leading to a decrease in sintering density.

[0039] In some embodiments of the present invention, the particle size D50 of the yttrium powder is 1 μm to 5 μm, and the purity is ≥99.99%. Exemplarily, the particle size D50 of the yttrium powder can be one of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value satisfying the above range.

[0040] In some embodiments of the present invention, the particle size D50 of the hydrided-dehydrided titanium alloy powder is 15 μm to 25 μm, and the oxygen content is ≤2200 ppm. Exemplarily, the particle size D50 of the hydrided-dehydrided titanium alloy powder can be one of 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or any value satisfying the above range. The oxygen content of the hydrided-dehydrided titanium alloy powder can be one of 2200 ppm, 2000 ppm, 1800 ppm, 1600 ppm, 1500 ppm, 1400 ppm, 1200 ppm, 1000 ppm, 800 ppm, 600 ppm, 500 ppm, 400 ppm, 200 ppm, 100 ppm or any value satisfying the above range.

[0041] Powder mixing

[0042] In an embodiment of the present invention, according to the target components, the raw material powders are mechanically mixed to obtain a uniform mixed powder.

[0043] In an embodiment of the present invention, based on the mixed powder, the mass percentage of the yttrium powder is 0.1 wt.% to 0.5 wt.%. Exemplarily, the mass percentage of the yttrium powder can be one of 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.% or any value satisfying the above range.

[0044] In some embodiments of the present invention, the hydrided-dehydrided titanium alloy powder and the yttrium powder are ball-milled and mixed to obtain a mixed powder by means of ball-milling powder mixing, wherein the ball-to-material ratio is 3:1 to 9:1, the diameter of the grinding balls is 3 mm to 6 mm, the mixing speed is 70 rpm to 200 rpm, it rotates forward for 30 min and stops for 5 min and then rotates backward for 30 min, and the mixing time is 8 h to 15 h.

[0045] Exemplarily, during the ball milling and powder mixing process, the ball-to-material ratio can be one of 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or any value within the above range. The diameter of the grinding balls can be one of 3 mm, 4 mm, 5 mm, 6 mm or any value within the above range. The mixing speed can be one of 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm or any value within the above range. The mixing time can be one of 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h or any value within the above range.

[0046] In an embodiment of the present invention, the mixing speed is 70 rpm to 200 rpm. It rotates forward for 30 minutes, stops for 5 minutes, and then rotates backward for 30 minutes. The actual mixing time is 8 h to 15 h. Powder mixing needs to follow the alternating forward and reverse rotation of the rollers and be assisted by zirconia grinding balls. Then, a lower speed and a certain interval time are adopted to ensure that cold welding of the powder does not occur while obtaining uniformly mixed powder.

[0047] In some embodiments of the present invention, the prepared raw material powder is loaded into a mixing bottle. This process is carried out in a sealed glove box protected by high-purity argon (purity ≥ 99.999%). The oxygen content in the box is ≤ 100 ppm. The powder mixing method uses a double-roller ball mill. Among them, the grinding balls used are made of zirconia, the diameter of the grinding balls is 3 mm to 6 mm, the ball-to-material ratio is 3:1 to 9:1, the mixing speed is 70 rpm to 200 rpm, it rotates forward for 30 minutes, stops for 5 minutes, and then rotates backward for 30 minutes, and the mixing time is 8 h to 15 h.

[0048] Cold isostatic pressing

[0049] In an embodiment of the present invention, the mixed powder is loaded into a cold isostatic pressing sleeve, vibrated and compacted, and then cold isostatic pressing is carried out after sealing.

[0050] In some embodiments of the present invention, the pressure holding pressure for cold isostatic pressing is 150 MPa to 300 MPa, and the pressure holding time is 5 min to 30 min. Exemplarily, the pressure holding pressure for cold isostatic pressing can be one of 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa or any value satisfying the above range. The pressure holding time for cold isostatic pressing can be one of 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min or any value satisfying the above range.

[0051] In some embodiments of the present invention, the mixed powder is filled into a cold isostatic pressing jacket, and the whole process is carried out in a sealed glove box with an oxygen content ≤ 100 ppm in the box body, and is protected by high-purity argon with a purity ≥ 99.999% to prevent the deterioration of the properties of the titanium alloy caused by powder oxygenation. The pressure holding pressure for cold isostatic pressing is 150 MPa to 300 MPa, and the pressure holding time is 5 min to 30 min. During the powder pressing process, there are mainly two stages: particle rearrangement and plastic deformation of adjacent powders. Maintaining a certain pressure holding time with the uniform pressing pressure of cold isostatic pressing helps to ensure a higher green density of the powder at a lower pressure.

[0052] Sintering

[0053] In an embodiment of the present invention, the obtained powder compact is sintered under vacuum protection to obtain a titanium alloy sintered blank.

[0054] In some embodiments of the present invention, the vacuum degree for sintering treatment is 10 -4 Pa to 10 -2 Pa. Exemplarily, the vacuum degree can be one of 10 -4 Pa, 10 -3 Pa, 10 -2 Pa or any value satisfying the above range.

[0055] In some embodiments of the present invention, two-step sintering is adopted, firstly, the powder compact is heated to a higher sintering temperature T1, then quickly cooled to a lower sintering temperature T2, and kept warm for a long time. The specific process includes: the first step of sintering, the powder compact is heated from room temperature to 1050℃~1200℃ at a rate of 5℃ / min~10℃ / min, and kept warm for 0.5h~1h; the second step of sintering, then cooled to 980℃~1030℃ at a rate of 1℃ / min~5℃ / min, and kept warm for 3h~7h. If the sintering temperature is too low, the density of the green body will be too low; if the sintering temperature is too high, the β phase will grow abnormally, which is not conducive to the subsequent hot working (forging treatment).

[0056] In some embodiments of the present invention, after the second step of sintering and holding is completed, the green body is cooled to 800° C. at a rate of 1° C. / min to 5° C. / min, held for 1 h to 4 h, and then furnace cooled to obtain a sintered green body.

[0057] For example, in the first sintering step, the heating rate of the powder compact can be one of 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any value within the above range. The sintering temperature of the first sintering step can be one of 1050°C, 1100°C, 1150°C, 1200°C, or any value within the above range. The holding time of the first sintering step can be one of 30min, 40min, 50min, 60min, or any value within the above range.

[0058] For example, in the second step of sintering, the heating rate of the green body can be one of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any value satisfying the above range. The sintering temperature of the second step of sintering can be one of 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, or any value satisfying the above range. The holding time of the second step of sintering can be one of 3h, 4h, 5h, 6h, 7h, or any value satisfying the above range.

[0059] For example, the cooling rate of the green body after the second step sintering can be one of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any value satisfying the above range. The green body is furnace-cooled after being kept warm for 1h, 2h, 3h, 4h, or any value satisfying the above range.

[0060] forging

[0061] In the embodiment of the present invention, a titanium alloy sintered blank is forged to obtain a titanium alloy product with a high fatigue life.

[0062] In some embodiments of the present invention, the forging process includes: heating a sintered blank of titanium alloy powder to a two-phase region temperature and holding it in a protective atmosphere. After the holding is completed, the blank is quickly transferred to the workbench of a hydraulic forging machine for multi-directional upsetting and drawing forging in one heat treatment.

[0063] In some embodiments of the present invention, after the holding is completed, the transfer time for quickly transferring the blank to the workbench of the hydraulic forging machine is controlled within 15 s to ensure that the temperature drop amplitude on the surface of the blank does not exceed 20°C.

[0064] In some embodiments of the present invention, the multi-directional upsetting and drawing forging in one heat treatment includes completing three alternating upsetting and drawing deformations within a single heating cycle.

[0065] In some embodiments of the present invention, completing three alternating upsetting and drawing deformations within a single heating cycle includes: applying pressure along the axial direction of the blank for the first upsetting to reduce the height of the blank, and then drawing the upset blank along the radial direction. Repeat the above process, and perform the second and third upsetting and drawing along the axial and radial directions in sequence. The total cumulative deformation amount is 30% - 50%, and the time interval between each deformation does not exceed 5 s. Exemplarily, the total cumulative deformation amount can be one of 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50% or any value satisfying the above range.

[0066] In some embodiments of the present invention, the two-phase region temperature is 930°C - 980°C, the holding time is 40 min - 90 min, and the heating rate to the two-phase region temperature is 10°C / min - 15°C / min. Exemplarily, the two-phase region temperature can be one of 930°C, 940°C, 950°C, 960°C, 970°C, 980°C or any value satisfying the above range. The holding time can be one of 40 min, 50 min, 60 min, 70 min, 80 min, 90 min or any value satisfying the above range. The heating rate to the two-phase region temperature can be one of 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min or any value satisfying the above range.

[0067] In some embodiments of the present invention, the forging process is carried out in an inert gas protective atmosphere. The specific forging process is as follows: The sintered blank is heated from room temperature to the duplex zone temperature of 930°C - 980°C at a rate of 10°C / min - 15°C / min and then held for 40 min - 90 min. After that, three alternating upsetting and drawing deformations are completed within a single heating cycle, and the total deformation amount is 30% - 50%. After forging, the forging is air-cooled to room temperature. If the forging temperature is too low, cracking will occur due to exceeding the strength limit of the material during forging; if the forging temperature is too high, the structure after forging will be coarse, and fatigue cracks will rapidly expand along the grain boundaries, resulting in low fatigue strength.

[0068] In some embodiments of the present invention, after multi-directional upsetting and drawing forging in one heat treatment, the forging is air-cooled to room temperature at a rate of 20°C / min - 30°C / min.

[0069] It is worth mentioning that the "room temperature" in the present invention generally refers to the state without active heating and cooling. For example, in the embodiments of the present invention, the room temperature refers to the temperature in the range of 20°C - 30°C.

[0070] The present invention controls the particle size D50 of the hydrogenated and dehydrogenated titanium alloy powder within the range of 15 μm - 25 μm, and adds the rare earth element yttrium. Through two-step sintering, a titanium alloy with a fine duplex structure characteristic is obtained. The principle of two-step sintering lies in utilizing the exponential variation law between the grain boundary migration activation energy, the grain boundary diffusion activation energy, and the sintering temperature. By reasonably regulating the sintering temperature range and the heating rate, the coupling effect between sintering densification and grain growth is thus eliminated. However, since the sintering temperature in the first stage enters the β single-phase region, it will still cause coarsening of the structure to form a lamellar structure, resulting in a decrease in fatigue strength. As an active rare earth element, yttrium will adsorb oxygen in the titanium matrix to in-situ form high-melting-point Y-Ti-O nanoparticles, effectively pinning the grain boundary migration and inhibiting abnormal grain growth during the high-temperature sintering stage. After rapidly cooling to the two-phase region, long-time holding at low temperature promotes the closure of grain boundary pores. At the same time, fine secondary α phases precipitate in the β phase, forming a duplex structure of "equiaxed primary α + lamellar α / β".

[0071] To retain the advantages of the fine-grained duplex structure formed by two-step sintering, in the present invention, the forging temperature is in the duplex region of 930 °C to 980 °C. By precisely controlling the forging temperature and the amount of deformation, and utilizing the tissue inheritance characteristics, while improving the density and strength-plasticity of the workpiece, the grain coarsening caused by multiple heating is avoided, which may deteriorate the fatigue performance. Finally, a titanium alloy with a duplex structure composed of 30% to 50% equiaxed α phase (10 μm to 20 μm) and β transformation structure (lamellar spacing of 0.5 μm to 0.8 μm) is prepared. When the grain size of the α phase decreases from 30 μm to 15 μm, the fatigue limit of the titanium alloy is increased by 15% to 20%. The fine-grained structure effectively delays the formation of persistent slip bands and reduces the crack nucleation probability. The dense twin network in the primary α phase can force the crack propagating transgranularly to bifurcate, causing the crack tip to deflect in direction when crossing multiple twin boundaries, significantly increasing the propagation path length; the nano-scale lamellar spacing creates a high-density phase interface, and dislocations form dislocation tangles at the α / β interface under fatigue loading, increasing the critical crack propagation stress and reducing the crack propagation rate. In addition, the duplex structure causes the crack to alternately cross the equiaxed α grains and β lamellar structures during the propagation process, resulting in a deflection angle of the propagation path up to 45°. The tortuous path reduces the crack propagation rate and increases the number of dynamic fatigue cycles.

[0072] In the second aspect of the present invention, a titanium alloy workpiece with high fatigue life is provided, which is characterized in that it is prepared by using the preparation method of the titanium alloy workpiece with high fatigue life described in the first aspect.

[0073] In the embodiments of the present invention, the structure of the titanium alloy workpiece with high fatigue life includes a duplex structure composed of 30% to 50% primary α phase and β transformation structure. Among them, the primary α phase is evenly distributed in an equiaxed shape, with a grain size of 10 μm to 20 μm, and there are a large number of type tensile twins inside, and the twin lamellar thickness is 200 nm to 500 nm and shows the characteristics of parallel arrangement and cross distribution; the β transformation structure is composed of α lamellae with a lamellar spacing of 0.5 μm to 0.8 μm and residual β phase, and there are nano-scale type compressive twins inside the α lamellae.

[0074] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments and equipment used in the following embodiments can all be obtained through market purchase or can be obtained by existing methods; the dosages of the experimental reagents are all the dosages of the reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified. It should be further noted that the following description is only exemplary and not a specific limitation of the present invention.

[0075] Example 1

[0076] S1: Raw material preparation, weigh hydrogenated and dehydrogenated Ti-6Al-4V powder (D50 = 15.27 μm, oxygen content is 2100 ppm) and yttrium powder (D50 = 2 μm). Among them, the mass percentage of yttrium powder is 0.1 wt.%.

[0077] S2: Powder mixing, in a glove box protected by high-purity argon (purity 99.999%), put the above raw material powders into a mixing bottle, and use a double-roll ball mill for mixing at room temperature. Among them, the grinding balls are zirconia balls with a diameter of 6 mm, the ball-to-material ratio is 4:1, the mixing speed is 70 rpm, and the mixing time is 8 h.

[0078] S3: Cold isostatic pressing forming, in a glove box protected by high-purity argon (purity 99.999%), put the mixed powder into a rubber sleeve with an inner diameter of 55 mm and a height of 160 mm, and compact it continuously during the powder loading process; the pressure of cold isostatic pressing forming is 200 MPa, and the pressure holding time is 10 min.

[0079] S4: Sintering, under the protection of vacuum (vacuum degree is 10 -2 Pa), sinter the powder compact. The specific sintering process is as follows: the first sintering, heat the powder compact from room temperature to 1050 °C at a rate of 5 °C / min and hold for 30 min; the second sintering, then cool it to 980 °C at a rate of 3 °C / min and hold for 5 h. After the heat preservation is completed, cool the billet to 800 °C at a rate of 2 °C / min, hold for 2 h again, and then cool it in the furnace.

[0080] S5: Forging, heat the sintered billet from room temperature to 930 °C at a rate of 10 °C / min and hold for 60 min, then perform free forging deformation of three upsetting and three drawing in one heat treatment, the deformation amount is 30%, after forging is completed, air-cool the forgings to room temperature at a rate of 20 °C / min to obtain a titanium alloy part with high fatigue life.

[0081] Example 2

[0082] S1: Raw material preparation, weigh hydrogenated and dehydrogenated Ti-6Al-4V powder (D50 = 20.61 μm, oxygen content is 1800 ppm) and yttrium powder (D50 = 2 μm). Among them, the mass percentage of yttrium powder is 0.2 wt.%.

[0083] S2: Powder mixing, in a glove box protected by high-purity argon (purity 99.999%), put the above raw material powders into a mixing bottle, and use a double-roll ball mill for mixing at room temperature. Among them, the grinding balls are zirconia balls with a diameter of 3 mm, the ball-to-material ratio is 6:1, the mixing speed is 100 rpm, and the mixing time is 10 h.

[0084] S3: Cold isostatic pressing forming. In a glove box protected by high-purity argon (purity 99.999%), the mixed powder is filled into a rubber sleeve with an inner diameter of 55 mm and a height of 160 mm, and the powder is continuously tamped during the filling process. The pressure for cold isostatic pressing forming is 250 MPa, and the pressure holding time is 15 min.

[0085] S4: Sintering. Under the protection of vacuum (vacuum degree is 10 -2 Pa), the powder compact is sintered. The specific sintering process is as follows: In the first sintering step, the powder compact is heated from room temperature to 1100 °C at a rate of 7 °C / min and held for 40 min; in the second sintering step, it is then cooled to 1000 °C at a rate of 2 °C / min and held for 5 h. After the holding is completed, the billet is cooled to 800 °C at a rate of 3 °C / min, held again for 3 h, and then cooled in the furnace.

[0086] S5: Forging. The sintered billet is heated from room temperature to 940 °C at a rate of 10 °C / min and held for 55 min, and then undergoes free forging deformation of three upsetting and three drawing in one heat treatment, with a deformation amount of 30%. After forging, the forging is air-cooled to room temperature at a rate of 20 °C / min to obtain a titanium alloy part with high fatigue life.

[0087] Example 3

[0088] S1: Raw material preparation. Weigh hydrogenated and dehydrogenated Ti-6Al-4V powder (D50 = 16.97 μm, oxygen content is 2200 ppm) and yttrium powder (D50 = 3 μm). Among them, the mass percentage of yttrium powder is 0.3 wt.%.

[0089] S2: Powder mixing. In a glove box protected by high-purity argon (purity 99.999%), the above raw material powders are filled into a mixing bottle and mixed at room temperature using a double-roll ball mill. Among them, the grinding balls are zirconia balls with a diameter of 6 mm, the ball-to-material ratio is 4:1, the mixing speed is 120 rpm, and the mixing time is 13 h.

[0090] S3: Cold isostatic pressing forming. In a glove box protected by high-purity argon (purity 99.999%), the mixed powder is filled into a rubber sleeve with an inner diameter of 55 mm and a height of 160 mm, and the powder is continuously tamped during the filling process. The pressure for cold isostatic pressing forming is 220 MPa, and the pressure holding time is 15 min.

[0091] S4: Sintering. Under the protection of vacuum (vacuum degree is 10 -2Under the protection of Pa), the powder compact is sintered. The specific sintering process is as follows: In the first step of sintering, the powder compact is heated from room temperature to 1150 °C at a rate of 8 °C / min and held for 50 min; in the second step of sintering, it is then cooled to 1020 °C at a rate of 3 °C / min and held for 5 h. After the holding is completed, the compact is cooled to 800 °C at a rate of 3 °C / min, held for another 2 h, and then cooled in the furnace.

[0092] S5: Forging, the sintered blank is heated from room temperature to 950 °C at a rate of 15 °C / min and held for 65 min, and then undergoes free forging deformation of three upsetting and three drawing in one heat treatment, with a deformation amount of 50%. After forging is completed, the forging is air-cooled to room temperature at a rate of 20 °C / min to obtain a titanium alloy part with high fatigue life.

[0093] Example 4

[0094] S1: Raw material preparation, weigh hydrogenated and dehydrogenated Ti-6Al-4V powder (D50 = 18.04 μm, oxygen content is 2100 ppm) and yttrium powder (D50 = 3 μm). Among them, the mass percentage of yttrium powder is 0.4 wt.%.

[0095] S2: Powder mixing, in a glove box protected by high-purity argon (purity 99.999%), the above raw material powders are put into a mixing bottle, and room temperature mixing is carried out using a double-roll ball mill. Among them, the grinding balls are zirconia balls with a diameter of 3 mm, the ball-to-material ratio is 6:1, the mixing speed is 150 rpm, and the mixing time is 13 h.

[0096] S3: Cold isostatic pressing forming, in a glove box protected by high-purity argon (purity 99.999%), the mixed powder is put into a rubber sleeve with an inner diameter of 55 mm and a height of 160 mm, and the powder is constantly tamped during the powder loading process; the pressure for cold isostatic pressing forming is 250 MPa, and the pressure holding time is 8 min.

[0097] S4: Sintering, under the protection of vacuum (vacuum degree is 10 -2 Pa), the powder compact is sintered. The specific sintering process is as follows: In the first step of sintering, the powder compact is heated from room temperature to 1180 °C at a rate of 8 °C / min and held for 40 min; in the second step of sintering, it is then cooled to 1030 °C at a rate of 2 °C / min and held for 3 h. After the holding is completed, the compact is cooled to 800 °C at a rate of 3 °C / min, held for another 2 h, and then cooled in the furnace.

[0098] S5: Forging, the sintered blank is heated from room temperature to 960 °C at a rate of 12 °C / min and held for 50 min, and then undergoes free forging deformation of three upsetting and three drawing in one heat treatment, with a deformation amount of 50%. After forging is completed, the forging is air-cooled to room temperature at a rate of 30 °C / min to obtain a titanium alloy part with high fatigue life.

[0099] Example 5

[0100] S1: Prepare raw materials. Weigh hydrogenated and dehydrogenated Ti-6Al-4V powder (D50 = 19.23 μm, oxygen content is 2200 ppm) and yttrium powder (D50 = 1 μm). Among them, the mass percentage of yttrium powder is 0.5 wt.%.

[0101] S2: Mix the powders. In a glove box protected by high-purity argon (purity 99.999%), put the above raw material powders into a mixing bottle and use a double-roll ball mill to mix at room temperature. Among them, the grinding balls are zirconia balls with a diameter of 6 mm, the ball-to-material ratio is 4:1, the mixing speed is 180 rpm, and the mixing time is 15 h.

[0102] S3: Cold isostatic pressing forming. In a glove box protected by high-purity argon (purity 99.999%), put the mixed powder into a rubber sleeve with an inner diameter of 55 mm and a height of 160 mm, and constantly vibrate and compact during the powder loading process; the pressure of cold isostatic pressing forming is 220 MPa, and the pressure holding time is 10 min.

[0103] S4: Sintering. Under the protection of vacuum (vacuum degree is 10 -2 Pa), sinter the powder compact. The specific sintering process is as follows: The first step of sintering, heat the powder compact from room temperature to 1200 °C at a rate of 10 °C / min and hold for 60 min; the second step of sintering, then cool down to 1030 °C at a rate of 2 °C / min and hold for 4 h. After the holding is completed, cool the billet to 800 °C at a rate of 2 °C / min, hold for another 2 h and then cool in the furnace.

[0104] S5: Forging. Heat the sintered billet from room temperature to 980 °C at a rate of 10 °C / min and hold for 60 min, then perform free forging deformation of three upsetting and three drawing in one heat treatment, with a deformation amount of 50%. After forging is completed, air-cool the forgings to room temperature at a rate of 30 °C / min to obtain a titanium alloy part with high fatigue life.

[0105] Comparative Example 1

[0106] In Comparative Example 1, the specific operation refers to Example 1, and the only difference is that in Comparative Example 1, a single sintering temperature is used. The specific sintering process is as follows: Heat the powder compact from room temperature to 1200 °C at a rate of 8 °C / min and hold for 5 h. After the holding is completed, then cool down to 800 °C at a rate of 2 °C / min, hold for 2 h and then cool in the furnace.

[0107] Comparative Example 2

[0108] For Comparative Example 2, the specific operations refer to Example 1, with the only difference being that in Comparative Example 2, the forging temperature is increased to the β single-phase region. The specific forging process is as follows: The sintered blank is heated from room temperature to 1050°C at a rate of 10°C / min and held for 60 min, and then undergoes free forging deformation of three upsetting and three drawing in one heat, with a deformation amount of 30%. After forging, the forging is air-cooled to room temperature at a rate of 20°C / min to obtain a titanium alloy workpiece.

[0109] Comparative Example 3

[0110] For Comparative Example 3, the specific operations refer to Example 1, with the only difference being that in Comparative Example 3, a single sintering temperature is used while the forging temperature is increased to the β single-phase region. Specifically: During sintering, the powder compact is heated from room temperature to 1200°C at a rate of 8°C / min, held for 5 h, then cooled to 800°C at a rate of 2°C / min and held for 2 h, and then furnace-cooled; the sintered blank is heated from room temperature to 1100°C at a rate of 10°C / min and held for 60 min, and then undergoes free forging deformation of three upsetting and three drawing in one heat, with a deformation amount of 30%. After forging, the forging is air-cooled to room temperature at a rate of 20°C / min to obtain a titanium alloy workpiece.

[0111] Comparative Example 4

[0112] For Comparative Example 4, the specific operations refer to Example 1, with the only difference being that in Comparative Example 4, two-heat forging is used during forging. Specifically: The sintered blank is heated from room temperature to 980°C at a rate of 10°C / min and held for 40 min, the initial forging deformation amount is 30%, after deformation, it is reheated to 940°C and held for 60 min, and the final forging deformation amount is 20%. After forging, the forging is air-cooled to room temperature at a rate of 20°C / min to obtain a titanium alloy workpiece.

[0113] Performance testing

[0114] (1) Mechanical property testing: The titanium alloy workpieces prepared in Examples 1 to 5 and Comparative Examples 1 to 4 are respectively subjected to the determination of room temperature tensile strength, room temperature yield strength and elongation in accordance with the standard of GB / T 228.1-2021. The test results are shown in Table 1 for details.

[0115] (2) High-cycle fatigue testing: The titanium alloy workpieces prepared in Examples 1 to 5 and Comparative Examples 1 to 4 are respectively subjected to room temperature high-cycle fatigue testing in accordance with the standard of GB / T 3075-2021. The test results are shown in Table 1 for details.

[0116] (3) Detection of organizational structure: The titanium alloy parts prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were respectively cut into metallographic samples of 8 mm × 8 mm × 4 mm by wire cutting. The surfaces of the specimens were polished step by step with 240#, 400#, 800#, 1200#, 2000#, and 3000# sandpapers and then mechanically polished. Then, they were etched with an etching solution of HF:HNO3:H2O = 1:2:17. The microscopic morphology of the surface of the etched samples was observed using a scanning electron microscope. The test results are shown in Table 1 in detail.

[0117] Table 1 Summary of the properties of the titanium alloy parts prepared in Examples 1 to 5 and Comparative Examples 1 to 4

[0118]

[0119]

[0120] It can be seen from the data in Table 1 that the structures of the titanium alloy parts prepared by the preparation method of the present invention are all duplex structures, specifically composed of 30% - 50% equiaxed α phase (10 μm - 20 μm) and β transformation structure (lamellar spacing 0.5 μm - 0.8 μm).

[0121] In Comparative Examples 1 to 4, whether it is the room temperature tensile strength, room temperature yield strength, elongation after fracture or fatigue limit, they are all much lower than the corresponding data in Examples 1 to 5 of the present invention. This is because in Comparative Example 1, the sintering temperature was too high, resulting in abnormal growth of β grains and it was difficult to completely break and eliminate the coarse β grains during the subsequent forging process. In Comparative Example 2, since the forging temperature increased and entered the β single-phase region, a fully lamellar Widmanstätten structure was formed after forging. In Comparative Example 3, the double temperature rise aggravated the coarsening of the β phase and grain boundary migration, forming continuous grain boundaries. Compared with the duplex organizational structures obtained in Examples 1 to 5 of the present invention, the structures in Comparative Examples 1 to 3 are mainly composed of coarse lamellar structures, causing fatigue cracks to rapidly expand along the grain boundaries and reducing the fatigue strength. Although in Comparative Example 4, equiaxed structures were formed by refining grains through multi-pass forging, repeated heating made the process flow longer and the energy consumption increased.

[0122] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a titanium alloy part with a high fatigue life, characterized in that: The following steps are involved: The mixed powder of hydrogenated dehydrogenated titanium alloy powder and yttrium powder is cold isostatically pressed, and the obtained powder compact is subjected to two-step sintering treatment under vacuum protection to obtain a sintered compact; The sintered blank is heated to a two-phase region temperature under a protective atmosphere, and then subjected to a single-fire multi-directional upsetting forging after being kept warm, so as to obtain the titanium alloy product with a high fatigue life.

2. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: Based on the mixed powder, the mass percentage of the yttrium powder is 0.1wt.% to 0.5wt.%; Preferably, the particle size D50 of the yttrium powder is 1 μm to 5 μm, and the purity is ≥99.99%.

3. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The particle size D50 of the hydrogenated dehydrogenated titanium alloy powder is 15 μm to 25 μm, and the oxygen content is ≤2200 ppm.

4. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The holding pressure of the cold isostatic pressing is 150 MPa to 300 MPa, and the holding time is 5 min to 30 min.

5. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The two-step sintering process includes: a first step of sintering, heating the powder compact from room temperature to 1050°C to 1200°C at a rate of 5°C / min to 10°C / min, and keeping the temperature for 0.5h to 1h; a second step of sintering, then cooling the powder compact to 980°C to 1030°C at a rate of 1°C / min to 5°C / min, and keeping the temperature for 3h to 7h; Preferably, after the second step of sintering and heat preservation is completed, the green body is cooled to 800°C at a rate of 1°C / min to 5°C / min, kept at this temperature for 1h to 4h, and then furnace cooled; Preferably, the vacuum degree of the two-step sintering process is 10 -4 Pa~10 -2 Pa.

6. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The temperature of the two-phase region is 930° C. to 980° C., the insulation time is 40 min to 90 min, and the heating rate to the temperature of the two-phase region is 10° C. / min to 15° C. / min.

7. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The one-time multi-directional upsetting and drawing forging includes completing three alternating upsetting and drawing deformations in a single heating cycle; Preferably, after the multi-directional upsetting forging, the forging is air-cooled to room temperature at a rate of 20° C. / min to 30° C. / min.

8. The method for preparing a titanium alloy product with a high fatigue life according to claim 7, characterized in that: The three alternating upsetting and stretching deformations completed within a single heating cycle include: applying pressure along the axial direction of the blank during the first upsetting to reduce the height of the blank, then stretching the upset blank along the radial direction, repeating the above process, and performing the second and third upsetting and stretching along the axial direction and radial direction in sequence, with a total cumulative deformation of 30% to 50%, and the interval time between each deformation not exceeding 5s.

9. The method for preparing a titanium alloy product with a high fatigue life according to claim 1, characterized in that: The hydrogenated dehydrogenated titanium alloy powder and the yttrium powder are ball-milled and mixed to form the mixed powder, wherein the ball-to-material ratio is 3:1-9:1, the grinding ball diameter is 3mm-6mm, the mixing speed is 70rpm-200rpm, the powder is rotated forward for 30min, stopped for 5min, and then reversed for 30min, and the mixing time is 8h-15h.

10. A titanium alloy product with high fatigue life prepared by the method for preparing a titanium alloy product with high fatigue life according to any one of claims 1 to 9, characterized in that: The structure of the titanium alloy product includes a dual-state structure consisting of 30% to 50% of the primary α phase and the β transformation structure, wherein: The primary α phase is evenly distributed in an equiaxed shape, with a grain size of 10μm to 20μm, and a large amount of Type tensile twins, the twin layer thickness is 200nm~500nm and is characterized by parallel arrangement and cross distribution; The β-transformed structure is composed of α-lamellae with a lamella spacing of 0.5μm to 0.8μm and residual β-phase. Type compression twins.

Images