Ultra-high-strength double-phase titanium alloy component design method based on alpha / beta two-phase respective strengthening

Abstract

The invention provides an alpha / beta two-phase respective strengthening-based ultrahigh-strength double-phase titanium alloy component design method, and belongs to the technical field of titanium alloys. The method comprises the following steps: firstly, obtaining an alpha / beta single-phase component in a certain high-strength double-phase titanium alloy (such as Ti-5Al-5Mo-5V-3Cr); and then component optimization is conducted on the alpha phase and the beta phase through a diffusion multi-element knot method, the change rule of the single-phase strength along with the alloy element content is obtained, and the component range of the single-phase strength at the high level is obtained. Based on the component range of the single-phase strength at a high level and the two-phase proportion range, the component range of the whole alloy is preliminarily obtained. A phase diagram is used for calculating alpha / beta single-phase components under different overall components, and it is ensured that the single-phase components are located in the component range when the single-phase strength is at the high level, so that the components are preliminarily screened. And then, according to the preliminary screening result, optimizing and determining the overall component by using a diffusion multi-element knot method. By means of the method, the new alloy with the comprehensive mechanical property obviously improved can be designed.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloys, and in particular relates to a composition design method for an ultra-high strength dual-phase titanium alloy based on separate strengthening of α / β phases. Background Art

[0002] Titanium alloys have become key structural materials in the aerospace field due to their excellent properties such as high strength, low density, high temperature resistance, and corrosion resistance. With the development of the aviation industry and the implementation of my country's large aircraft projects, the demand for lightweight and high-speed new-generation aircraft has placed higher demands on the comprehensive service performance of materials. Existing high-strength titanium alloys such as Ti-5Al-5Mo-5V-3Cr (Ti-5553), Ti-10V-2Fe-3Al (Ti-1023), and Ti-5Al-4Mo-4Cr-2Zr-2Sn (TC-17) maintain high plasticity (>8%) while their strength is mainly at the level of 1100 to 1300 MPa, which cannot fully meet the development needs of cutting-edge technology. How to design ultra-high-strength titanium alloys with a strength of 1500 MPa and maintain good plasticity has become a key issue for further optimizing aircraft performance and ensuring the safe service of major aerospace equipment components. Summary of the Invention

[0003] The present invention aims to provide a method for designing the composition of an ultra-high-strength dual-phase titanium alloy based on separate strengthening of the α / β phases. The titanium alloy obtained by the method provided by the present invention has higher strength.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for designing the composition of an ultra-high-strength dual-phase titanium alloy based on separate strengthening of α / β phases, comprising the following steps:

[0006] (1) A dual-phase high-strength titanium alloy was selected as the control object, and its composition was analyzed to determine the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy;

[0007] (2) Based on the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy determined in step (1), elements that have a significant effect on the strength of the α phase and β phase are selected respectively, and a diffusion multi-node composition gradient method is used to obtain the variation pattern of the single-phase strength with the element content, and the content range of the element when the single-phase strength is more than 90% of the maximum strength is determined, and the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level is obtained;

[0008] (3) obtaining a rough composition range of the overall titanium alloy based on the composition range of the α phase and β phase containing the selected elements and the volume percentage range of the α phase and β phase when the single-phase strength is at a higher level obtained in step (2);

[0009] (4) Based on the approximate composition range of the overall titanium alloy obtained in step (3), a phase diagram thermodynamic calculation is used to further screen the alloy composition range on this basis to obtain a preliminary composition range of the overall titanium alloy. The screening principle is: the preliminary composition range of the overall titanium alloy should meet the requirements that the precipitated α phase composition falls within the composition range of the α phase containing the selected element when the single-phase strength is at a higher level obtained in step (2), and that the precipitated β phase composition also falls within the composition range of the β phase containing the selected element when the single-phase strength is at a higher level obtained in step (2);

[0010] (5) Select a component within the preliminary composition range of the overall titanium alloy obtained in step (4), select elements that have a significant impact on the strength of the overall titanium alloy, use the diffusion multi-node composition gradient method to obtain the change pattern of the overall titanium alloy strength with element content, and determine the final composition of the overall titanium alloy when the strength is the highest.

[0011] Preferably, the step (2) comprises the following steps:

[0012] 1) Select elements that have a significant impact on the strength of the α phase and β phase respectively and make diffusion couples;

[0013] 2) diffusing the diffusion couple obtained in step 1) and then cooling it to obtain a diffused diffusion couple;

[0014] 3) Measuring the composition and hardness of the diffusion couple obtained in step 2), and obtaining the variation pattern of single-phase strength with element content based on the measured hardness and composition, determining the element content range when the single-phase strength is above 90% of the maximum strength, and obtaining the composition range of the α phase and β phase containing the selected element when the single-phase strength is at a high level.

[0015] Preferably, the diffusion couple in step 1) comprises a basic block, an element x diffusion block and an element y diffusion block.

[0016] Preferably, the diffusion couples in step 1) are placed in such a manner that the basic block and the element x diffusion block are bonded together, and the element y diffusion block is placed above the bonded basic block and element x diffusion block.

[0017] Preferably, the diffusion temperature in step 2) is 1000-1100° C., and the diffusion time is 165-180 h.

[0018] Preferably, the diffusion temperature is 1050° C. and the diffusion time is 168 h.

[0019] Preferably, in step 2), for the α phase, the cooling rate is 0.5-1.5° C. / min, and for the β phase, the cooling method is water quenching.

[0020] Preferably, in step 2), for the α phase, the cooling rate is 1° C. / min.

[0021] Preferably, in step (2), the elements that have a significant effect on the strength of the α phase include two of Al, Sn, Zr and Hf, and the elements that have a significant effect on the strength of the β phase include two of Mo, V, Hf, Ta and Nb.

[0022] Preferably, the elements that have a significant impact on the overall strength of the titanium alloy in step (5) include two of Al, Mo, Zr, Ta and Nb.

[0023] The present invention provides a method for designing the composition of an ultra-high-strength dual-phase titanium alloy based on separate strengthening of α / β phases, comprising the following steps: (1) selecting a dual-phase high-strength titanium alloy as a control object, performing a composition analysis on the dual-phase high-strength titanium alloy, and determining the elemental composition and content of each of the α phase and the β phase in the dual-phase high-strength titanium alloy; (2) selecting elements that have a significant effect on the strength of the α phase and the β phase according to the elemental composition and content of each of the α phase and the β phase in the dual-phase high-strength titanium alloy determined in step (1), and using a diffusion multi-node composition gradient method to obtain the variation law of single-phase strength with element content, determine the element content range when the single-phase strength is above 90% of the maximum strength, and obtain the composition range of the α phase and the β phase containing the selected element when the single-phase strength is at a higher level; (3) obtaining the composition range of the α phase and the β phase containing the selected element and the volume percentage content range of the α phase and the β phase according to the single-phase strength obtained in step (2) when the single-phase strength is at a higher level. The approximate composition range of the overall titanium alloy; (4) according to the approximate composition range of the overall titanium alloy obtained in step (3), using phase diagram thermodynamic calculation, further screening the alloy composition range on this basis to obtain the preliminary composition range of the overall titanium alloy, the screening principle is: the preliminary composition range of the overall titanium alloy should meet the requirements that the precipitated α phase composition falls within the composition range of the α phase containing the selected elements when the single-phase strength is at a higher level obtained in step (2), and the precipitated β phase composition also falls within the composition range of the β phase containing the selected elements when the single-phase strength is at a higher level obtained in step (2); (5) selecting a component within the preliminary composition range of the overall titanium alloy obtained in step (4), selecting elements that have a significant impact on the strength of the overall titanium alloy, using the diffusion multi-node composition gradient method to obtain the variation law of the overall titanium alloy strength with the element content, and determining the final composition of the overall titanium alloy when the strength is the highest. The present invention first uses the diffusion multi-node experimental method to optimize the composition of the α-phase and β-phase elements respectively, obtains the variation law of the single-phase strength with the element composition, and at the same time obtains the composition range corresponding to the α-phase and β-phase containing the selected elements when the strength is at a higher level, and combines the volume content range of the two phases to obtain the approximate composition range of the overall titanium alloy. Then, the composition range is further narrowed by using the phase diagram thermodynamic calculation. The screening principle is that the preliminary composition range of the overall titanium alloy should meet the requirements that the precipitated α-phase composition falls within the optimal composition range regulated in step (2), and the precipitated β-phase composition also falls within the optimal composition range regulated in step (2). Based on the preliminary composition range of the overall titanium alloy, a specific component is selected and the diffusion multi-node method is used again to find the exact optimal content value of the element in the overall titanium alloy, and the titanium alloy composition is completely determined. Using this method, a new alloy with significantly improved performance is designed. The results of the embodiment show that the titanium alloy with optimized composition obtained by the method provided by the present invention can increase the strength level by more than 5% compared with the original titanium alloy, and the plasticity is basically unaffected. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a typical organization diagram of α+β duplex titanium alloy;

[0025] Figure 2 Schematic diagram of the diffusion couple after diffusion in step (2) of Example 1;

[0026] Figure 3 Schematic diagram of the diffusion couple after diffusion in step (7) of Example 1;

[0027] Figure 4 Schematic diagram of the structure of a standard tensile member during mechanical property testing in the embodiment. DETAILED DESCRIPTION

[0028] The present invention provides a method for designing the composition of an ultra-high-strength dual-phase titanium alloy based on separate strengthening of α / β phases, comprising the following steps:

[0029] (1) A dual-phase high-strength titanium alloy was selected as the control object, and its composition was analyzed to determine the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy;

[0030] (2) Based on the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy determined in step (1), elements that have a significant effect on the strength of the α phase and β phase are selected respectively, and a diffusion multi-node composition gradient method is used to obtain the variation pattern of the single-phase strength with the element content, and the content range of the element when the single-phase strength is more than 90% of the maximum strength is determined, and the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level is obtained;

[0031] (3) obtaining a rough composition range of the overall titanium alloy based on the composition range of the α phase and β phase containing the selected elements and the volume percentage range of the α phase and β phase when the single-phase strength is at a higher level obtained in step (2);

[0032] (4) Based on the approximate composition range of the overall titanium alloy obtained in step (3), a phase diagram thermodynamic calculation is used to further screen the alloy composition range on this basis to obtain a preliminary composition range of the overall titanium alloy. The screening principle is: the preliminary composition range of the overall titanium alloy should meet the requirements that the precipitated α phase composition falls within the composition range of the α phase containing the selected element when the single-phase strength is at a higher level obtained in step (2), and that the precipitated β phase composition also falls within the composition range of the β phase containing the selected element when the single-phase strength is at a higher level obtained in step (2);

[0033] (5) Select a component within the preliminary composition range of the overall titanium alloy obtained in step (4), select elements that have a significant impact on the strength of the overall titanium alloy, use the diffusion multi-node composition gradient method to obtain the change pattern of the overall titanium alloy strength with element content, and determine the final composition of the overall titanium alloy when the strength is the highest.

[0034] The composition design method provided by the present invention performs composition design on the basis of the existing α+β duplex titanium alloy, and further improves the mechanical properties of the titanium alloy compared with the existing α+β duplex titanium alloy.

[0035] In the present invention, the typical structure of the α+β dual-phase titanium alloy is as follows Figure 1 As shown, it is a basket-like structure woven from dark α laths and light β matrix.

[0036] The present invention selects a dual-phase high-strength titanium alloy as a control object, performs a component analysis on the alloy, and determines the elemental composition and content of the α phase and the β phase in the dual-phase high-strength titanium alloy.

[0037] The specific type of dual-phase high-strength titanium alloy (i.e., the regulated titanium alloy) in the present invention is a metastable β-type high-strength titanium alloy with a close ratio of the two phases under normal use conditions. In an embodiment of the present invention, the regulated titanium alloy can be specifically TC-18 titanium alloy (Ti-5Al-5Mo-5V-1Cr-1Fe, mass percentage), Ti5553 titanium alloy (Ti-5Al-5Mo-5V-3Cr-0.5Fe, mass percentage), β-CEZ titanium alloy (Ti-5Al-2Sn-2Cr-4Mo-4Zr-1Fe, mass percentage) or β21S titanium alloy (Ti-15Mo-2.7Nb-3Al-0.2Si, mass percentage).

[0038] The present invention has no particular limitation on the specific method of the composition analysis. An alloy composition analysis method well known to those skilled in the art can be used to obtain the elemental composition and content of each element of the α phase and the β phase.

[0039] The present invention preferably performs composition analysis on the regulated titanium alloy by using a micro-area composition testing method EDS (Energy Dispersive Spectroscopy) to determine the elemental composition and content of each of the α phase and the β phase in the regulated titanium alloy.

[0040] The present invention has no particular limitation on the specific operation of the micro-area composition testing method EDS, and the micro-area composition testing method EDS well known to those skilled in the art can be used.

[0041] The present invention also preferably performs a composition analysis on the regulated titanium alloy to obtain the volume ratio of the α phase and the β phase in the regulated titanium alloy.

[0042] The present invention also preferably understands the processing technology of the manipulated titanium alloy, including the forging temperature, forging heat number, annealing temperature, and annealing time. The present invention also preferably obtains the volume ratio of the α-phase to the β-phase in the manipulated titanium alloy and the processing technology so that it can be compared with the processing technology used in subsequent titanium alloy preparation to avoid significant differences in process parameters.

[0043] After determining the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy, the present invention selects elements that have a significant impact on the strength of the α phase and β phase based on the determined elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy, and adopts the diffusion multi-node composition gradient method to obtain the variation pattern of single-phase strength with element content, determine the element content range when the single-phase strength is above 90% of the maximum strength, and obtain the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level.

[0044] In the present invention, based on the determined elemental composition and content of each of the α phase and β phase in the regulated titanium alloy, elements that have a significant impact on the strength of the α phase and β phase are selected respectively, and a diffusion multi-node composition gradient method is used to obtain the variation pattern of single-phase strength with element content, and the content range of the element when the single-phase strength is above 90% of the maximum strength is determined. The composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level is preferably obtained by the following steps:

[0045] 1) Select elements that have a significant impact on the strength of the α phase and β phase respectively and make diffusion couples;

[0046] 2) diffusing the diffusion couple obtained in step 1) and then cooling it to obtain a diffused diffusion couple;

[0047] 3) Measuring the composition and hardness of the diffusion couple obtained in step 2), and obtaining the variation pattern of single-phase strength with element content based on the measured hardness and composition, determining the element content range when the single-phase strength is above 90% of the maximum strength, and obtaining the composition range of the α phase and β phase containing the selected element when the single-phase strength is at a high level.

[0048] In the present invention, elements that have a significant impact on the strength of the α phase and the β phase are preferably selected to produce diffusion couples.

[0049] In the present invention, the elements significantly affecting the strength of the α phase and the β phase are preferably included in two independent amounts.

[0050] In the present invention, the element having a significant effect on the strength of the α phase and the β phase is preferably an element that does not have a linear effect on the strength of the α phase and the β phase or an element that does not form an intermetallic compound when added in a large amount.

[0051] In the present invention, the elements that have a significant impact on the strength of the α-phase and β-phase preferably include elements contained in the regulated titanium alloy and / or elements not contained in the regulated titanium alloy.

[0052] In the present invention, the elements having a significant effect on the α phase strength preferably include two of Al, Sn, Zr and Hf; the elements having a significant effect on the β phase strength preferably include two of Mo, V, Hf, Ta and Nb.

[0053] As an embodiment, when TC-18 high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the α-phase strength are preferably Al and Sn; and the elements that have a significant impact on the β-phase strength are preferably Mo and V.

[0054] As another embodiment, when Ti5553 high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the α-phase strength are preferably Al and Sn; and the elements that have a significant impact on the β-phase strength are preferably Mo and Hf.

[0055] As another embodiment, when β-CEZ high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the α phase strength are preferably Al and Zr; and the elements that have a significant impact on the β phase strength are preferably Mo and Ta.

[0056] As another embodiment, when β21S high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the α phase strength are preferably Al and Hf; and the elements that have a significant impact on the β phase strength are preferably Mo and Nb.

[0057] In the present invention, the diffusion couple preferably includes a basic block, an element x diffusion block, and an element y diffusion block.

[0058] In the present invention, the chemical composition of the base block is preferably the chemical composition of the α phase or β phase after removing elements that significantly affect the strength of the α phase or β phase.

[0059] In the present invention, the chemical composition of the element x diffusion block is preferably a chemical composition obtained by replacing Ti element with an element having a significant effect on the strength of the α phase or β phase in the basic block component.

[0060] In the present invention, the mass percentage of the element x in the element x diffusion block is preferably 1 to 35%.

[0061] In the present invention, the chemical composition of the element y diffusion block is preferably a chemical composition obtained by replacing Ti element in the basic block composition with another element that has a significant effect on the strength of the α phase or β phase.

[0062] In the present invention, the mass percentage of the element y in the element y diffusion block is preferably 1 to 35%.

[0063] The present invention has no special limitation on the manufacturing method of the basic block, the element x diffusion block and the element y diffusion block. They can be manufactured by conventional manufacturing methods according to their chemical composition.

[0064] The present invention has no particular limitation on the size of the diffusion couple, which can be selected according to actual needs. In an embodiment of the present invention, the sizes of the basic block, the element x diffusion block, and the element y diffusion block are 10mm*10mm*5mm respectively.

[0065] In the present invention, the diffusion couple is preferably placed in such a manner that the basic block and the element x diffusion block are bonded together, and the element y diffusion block is placed above the bonded basic block and element x diffusion block.

[0066] In the present invention, the base block and the element x diffusion block are preferably joined using a fixture, and vacuum heated at 1000-1100°C for 5-7 hours to obtain a joined block, and then the element y diffusion block is joined to the joined block using a fixture, and vacuum heated at 1000-1100°C for 5-7 hours to obtain a diffusion couple. More preferably, the base block and the element x diffusion block are joined using a fixture, and vacuum heated at 1050°C for 6 hours to obtain a joined block, and then the element y diffusion block is joined to the joined block using a fixture, and vacuum heated at 1050°C for 6 hours to obtain a diffusion couple. The present invention does not particularly limit the vacuum degree of the vacuum, and vacuum conditions familiar to those skilled in the art can be used.

[0067] After obtaining the diffusion couple, the present invention preferably diffuses the diffusion couple and then cools it to obtain a diffused diffusion couple.

[0068] In the present invention, the diffusion temperature is preferably 1000-1100°C, more preferably 1050°C; the diffusion time is preferably 165-180 hours, more preferably 168 hours. During the diffusion process, elements form a composition gradient at the interface between different blocks, which can be used for subsequent composition and hardness measurements.

[0069] In the present invention, for the α phase, the cooling rate is preferably 0.5-1.5°C / min, more preferably 1°C / min. For the β phase, the cooling method is preferably water quenching. The present invention does not specifically limit the specific operation of the water quenching, and the water quenching technical solution familiar to those skilled in the art can be used.

[0070] After obtaining the diffused diffusion couple, the present invention measures the composition and hardness of the diffused diffusion couple. Based on the measured hardness and composition, the variation pattern of single-phase strength with element content is obtained, the element content range when the single-phase strength is above 90% of the maximum strength is determined, and the composition range of the α phase and β phase containing the selected element when the single-phase strength is at a higher level is obtained.

[0071] The hardness and strength of titanium alloys are positively correlated. The higher the hardness, the higher the strength. Therefore, the present invention preferably uses the hardness of titanium alloys to represent the strength of titanium alloys.

[0072] In the present invention, the diffused diffusion couple is preferably cut, ground, and polished in sequence before measuring composition and hardness. Cutting is preferably performed along the alignment line between the base block and the element x diffusion block. The grinding and polishing procedures are not particularly limited in the present invention; grinding and polishing techniques familiar to those skilled in the art may be employed.

[0073] The present invention cuts, grinds and polishes the diffusion couple after diffusion, measures the internal composition and hardness of the diffusion couple after diffusion, and can avoid the influence of oxygen oxidation on the surface of the diffusion couple, so that the measurement result is accurate.

[0074] The present invention preferably uses a Vickers microhardness tester to evenly mark points in the diffusion area to measure the alloy hardness in different areas.

[0075] The present invention has no particular limitation on the operation of using a Vickers microhardness tester to uniformly mark the diffusion area to measure the alloy hardness in different areas, and a technical solution well known to those skilled in the art can be used.

[0076] The present invention preferably uses an EDS micro-area composition test method to determine the alloy composition corresponding to different hardness points within the diffusion zone. The present invention does not specifically limit the method of using the EDS micro-area composition test method to determine the alloy composition corresponding to different hardness points within the diffusion zone, and can use technical solutions familiar to those skilled in the art.

[0077] The present invention has no special restrictions on the operations of obtaining the variation pattern of single-phase strength with element content based on the measured hardness and composition, determining the element content range when the single-phase strength is above 90% of the maximum strength, and obtaining the composition range of α-phase and β-phase containing the selected elements when the single-phase strength is at a higher level, and can adopt technical solutions familiar to those skilled in the art.

[0078] After obtaining the composition range of the α phase and β phase containing selected elements when the single-phase strength is at a higher level, the present invention obtains the approximate composition range of the overall titanium alloy based on the composition range of the α phase and β phase containing selected elements when the single-phase strength is at a higher level and the volume percentage range of the α phase and β phase.

[0079] In the present invention, the volume percentage of the α phase and the β phase is preferably in the range of 40 to 65%.

[0080] The present invention does not specifically limit the operation of obtaining the approximate composition range of the overall titanium alloy based on the composition range of the α phase and β phase containing selected elements when the single-phase strength is at a higher level, and the volume percentage range of the α phase and β phase is obtained. Conventional calculation methods can be used to calculate the composition range.

[0081] After obtaining the approximate composition range of the overall titanium alloy, the present invention uses phase diagram thermodynamic calculations based on the approximate composition range of the overall titanium alloy, and further screens the alloy composition range on this basis to obtain the preliminary composition range of the overall titanium alloy. The screening principle is: the preliminary composition range of the overall titanium alloy should be consistent with the requirement that the precipitated α-phase composition falls within the composition range of the α-phase containing the selected elements when the single-phase strength is at a higher level obtained by the above technical solution, and the precipitated β-phase composition also falls within the composition range of the β-phase containing the selected elements when the single-phase strength is at a higher level obtained by the above technical solution.

[0082] The present invention preferably performs phase diagram thermodynamic calculations using Pandat or JMatPro. The present invention does not specifically limit the operation of performing the phase diagram thermodynamic calculations; technical solutions familiar to those skilled in the art may be employed. In the present invention, the temperature at which two phases are precipitated from the preliminary alloy composition can also be obtained during the phase diagram thermodynamic calculations.

[0083] After obtaining the preliminary composition range of the overall titanium alloy, the present invention selects a component within the preliminary composition range of the overall titanium alloy, selects elements that have a significant impact on the strength of the overall titanium alloy, and adopts the diffusion multi-node composition gradient method to obtain the change pattern of the overall titanium alloy strength with element content, and determines the final composition of the overall titanium alloy when the strength is the highest.

[0084] The present invention can select any specific component within the initial composition range of the overall titanium alloy, because the content variation range of each element within the initial composition range of the overall titanium alloy is small. Within this small range, the specific content of each element will not have a significant impact on the strength of the final titanium alloy.

[0085] In the present invention, the elements having a significant impact on the overall strength of the titanium alloy preferably include two of Al, Mo, Zr, Ta and Nb.

[0086] As an embodiment, when TC-18 high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the strength of the overall titanium alloy are preferably Al and Mo.

[0087] As another embodiment, when the Ti5553 high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the strength of the entire titanium alloy are preferably Al and Mo.

[0088] As another embodiment, when the β-CEZ high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the strength of the entire titanium alloy are preferably Zr and Ta.

[0089] As another embodiment, when the β21S high-strength titanium alloy is used as the object of composition control, the elements that have a significant impact on the strength of the entire titanium alloy are preferably Al and Nb.

[0090] In the present invention, the cooling method in the diffusion multi-node component gradient method is preferably: water cooling to 510-518° C. and maintaining the constant temperature for 5-7 hours, and then water cooling to room temperature.

[0091] In the present invention, elements that have a significant impact on the strength of the overall titanium alloy are selected, and the diffusion multi-node composition gradient method is used to obtain the variation pattern of the overall titanium alloy strength with the element content. Other operations of determining the final composition of the overall titanium alloy when the strength is the highest are preferably the same as the above-mentioned operations of selecting elements that have a significant impact on the strength of the α phase and β phase, and using the diffusion multi-node composition gradient method to obtain the variation pattern of the single-phase strength with the element content, determining the element content range when the single-phase strength is above 90% of the maximum strength, and obtaining the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level, and will not be repeated here.

[0092] After determining the final composition of the overall titanium alloy when the strength is the highest, the present invention preferably prepares the titanium alloy according to the determined final composition of the overall titanium alloy when the strength is the highest.

[0093] The present invention has no particular limitation on the preparation method of the titanium alloy, and any preparation method of the titanium alloy well known to those skilled in the art may be used.

[0094] The present invention first uses the diffusion multi-node experimental method to optimize the composition of the α-phase and β-phase elements respectively, obtains the variation law of single-phase strength with elemental composition, and obtains the composition range corresponding to the α-phase and β-phase containing the selected elements when the strength is at a higher level. According to the volume percentage range of the α-phase and β-phase, the approximate composition range of the overall titanium alloy is obtained. Then, using the phase diagram thermodynamic calculation, based on the single-phase optimal composition and the approximate composition range of the overall titanium alloy, the alloy composition of the two precipitated single-phase compositions falling within the optimized optimal single-phase composition range is preliminarily calculated. A specific alloy composition is taken within the more precise range that has been screened, and the specific alloy composition is the preliminary alloy composition. Then, based on the preliminary alloy composition, the diffusion multi-node method is used again to find the exact optimal content value of the element in the overall alloy, and the alloy composition is completely determined. Using this method, a new alloy with significantly improved performance is designed.

[0095] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0096] Example 1

[0097] A composition design method for an ultra-high strength dual-phase titanium alloy based on separate strengthening of α / β phases: (1) The elemental composition and content of each element in the α phase and β phase of TC-18 titanium alloy (Ti-5Al-5Mo-5V-1Cr-1Fe, mass percentage) are determined by using the micro-area composition testing method EDS. In the α phase, Al is 7.5%, V is 1.7%, Mo is 0.8%, Cr is 0.25%, Fe is 0%, and the balance is Ti, that is, the composition of the α phase is Ti-7.5Al-1.7V-0.8Mo-0.25Cr; in the β phase, Al is 3.5%, V is 8.5%, Mo is 13%, Cr is 2%, Fe is 1.8%, and the balance is Ti, that is, the composition of the β phase is Ti-3.5Al-8.5V-13Mo-2Cr-1.8Fe;

[0098] (2) Select Al and Sn, which have a significant effect on the strength of the α phase, and prepare three diffusion couples by melting and wire cutting. The composition of the basic block is Ti-1.7V-0.8Mo-0.25Cr, the composition of the Al variable block is Ti-1.7V-0.8Mo-0.25Cr-15Al, and the composition of the Sn variable block is Ti-1.7V-0.8Mo-0.25Cr-10Sn. The size of the three diffusion couples is 10mm*10mm*5mm. First, the basic block and the Al variable block are used. The two blocks were joined using a fixture and placed in a tube furnace under vacuum heating at 1050°C for 6 hours to weld the contact surfaces together by diffusion welding to form a 10mm*10mm*10mm cubic block. The Sn variable block was then placed on top of the cubic block, joined using a fixture, and placed in a tube furnace under vacuum heating at 1050°C for 6 hours to form a diffusion couple. The diffusion couple was sealed in a vacuum quartz tube and diffused at 1050°C for 168 hours. The diffusion couple was then cooled to room temperature at a cooling rate of 1°C / min to make the entire structure α-phase, thereby obtaining a diffusion couple after diffusion.

[0099] (3) Selecting elements Mo and V that have a significant effect on the strength of the β phase, three diffusion couples are prepared by smelting and wire cutting, wherein the composition of the basic block is Ti-3.5Al-2Cr-1.8Fe, the composition of the Mo variable block is Ti-3.5Al-30Mo-2Cr-1.8Fe, and the composition of the V variable block is Ti-3.5Al-2Cr-1.8Fe-25V. Except that the cooling method is water quenching to room temperature so that the structure is all β phase, other parameters are the same as step (2), and the diffusion couple after diffusion is obtained;

[0100] (4) The diffusion couples obtained in steps (2) and (3) after diffusion are cut along the fitting surface of the base block and the variable block, polished, and evenly marked in the diffusion area using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition testing method EDS to obtain the variation law of single-phase strength with element content, determine the element content when the single-phase strength is more than 90% of the highest strength, and obtain the composition of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level, wherein the composition range of the α phase is Ti-1.7V-0.8Mo-0.25Cr-(5.9~6.5)Al-(3.8~4.2)Sn, and the composition of the β phase is Ti-(10~11)V-(10.6~11.4)Mo-2Cr-3.5Al-1.8Fe;

[0101] (5) According to the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level obtained in step (4), the volume percentage range of the α phase and the β phase is 40-65%, respectively, and the composition range of the overall titanium alloy can be roughly obtained as Ti-(4.3-5.3)Al-(4.8-5.8)Mo-(4.5-6.4)V-(0.9-1.3)Cr-(1.8-2.5)Sn-(0.5-1.1)Fe;

[0102] (6) Using the Pandat phase diagram thermodynamic calculation, the two single-phase compositions of the precipitated titanium alloy are calculated to fall within the optimal single-phase composition range optimized in step (4), which is the preliminary composition range of Ti-(4.3-4.9)Al-(4.7-4.9)Mo-(5.5-6.4)V-(0.9-1.1)Cr-(1.8-2.1)Sn-(0.5-0.7)Fe;

[0103] (7) Select the elements Al and Mo that have a significant impact on the overall strength of titanium alloy, and prepare three diffusion couples by melting and wire cutting. The composition of the basic block is Ti-6.1V-2Sn-1Cr-0.5Fe, the composition of the Al variable block is Ti-6.1V-2Sn-1Cr-0.5Fe-10Al, and the composition of the Mo variable block is Ti-6.1V-2Sn-1Cr-0.5Fe-10Mo. Except for the treatment method after diffusion, which is water cooling + constant temperature at 518℃ for 6h + water cooling, the other parameters are The same as step (2), the diffusion couple after diffusion is obtained, the diffusion couple after diffusion is cut along the bonding surface of the base block and the variable block, polished, and the diffusion area is evenly marked with points using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition test method EDS to obtain the change law of the overall titanium alloy strength with the element content, and it is determined that the final composition of the overall titanium alloy when the strength is the highest is Ti-6.1V-4.4Mo-1Cr-4.8Al-2Sn-1Fe;

[0104] (8) According to the final composition of the overall titanium alloy at the highest strength determined in step (7), a titanium alloy is prepared with a forging temperature of 830°C, a total forging deformation of 300%, three forging cycles, and then solution treatment at 810°C for 1.5 hours, followed by annealing at 520°C for 6 hours.

[0105] The schematic diagram of the diffusion couple after diffusion in step (2) of Example 1 is as follows Figure 2 shown. Figure 2 The lower left corner shows an alloy containing the α-phase components of TC-18 alloy except Al. The lower right corner shows an alloy with 15% more Al added to the lower left corner. The top corner shows an alloy with 10% more Sn added to the lower left corner. After long-term high-temperature diffusion (1050°C / 168h), a composition gradient can be formed in the interface region of the ternary diffusion couple. At the binary interface, the effects of changes in Al and Sn content on alloy strength can be studied separately. In the triangular region, the effects of simultaneous changes in Al and Sn content on alloy strength can be studied. The T-junction of the metal blocks is the main diffusion region.

[0106] The schematic diagram of the diffusion couple after diffusion in step (7) of Example 1 is as follows Figure 3 shown.

[0107] The titanium alloy prepared in Example 1 was cut into standard tensile pieces (size as shown in FIG. Figure 4Mechanical property testing (as shown in Figure 1) revealed that the titanium alloy prepared in Example 1, with a chemical composition of Ti-6.1V-4.4Mo-1Cr-4.8Al-2Sn-1Fe, achieved a strength of 1312 MPa, a 5% increase compared to the original TC-18 titanium alloy's 1250 MPa. Its elongation was 7%, essentially the same as the original alloy. Overall performance, especially strength, was significantly improved.

[0108] Example 2

[0109] A composition design method for an ultra-high strength dual-phase titanium alloy based on α / β phase strengthening is proposed: (1) The elemental composition and content of each element of the α phase and β phase in Ti5553 (Ti-5Al-5Mo-5V-3Cr-0.5Fe) are determined by using the micro-area composition testing method EDS. In the α phase, Al≈7.8%, V≈1%, Mo≈0%, Cr≈0.6%, Fe≈0%, and the balance is Ti, that is, the composition of the α phase is Ti-7.8Al-1V-0.6Cr; in the β phase, Al≈4%, V≈7%, Mo≈10%, Cr≈6%, Fe≈0.8%, and the balance is Ti, that is, the composition of the β phase is Ti-4Al-7V-10Mo-6Cr-0.8Fe; the volume percentages of the α phase and the β phase are 57% and 43% respectively;

[0110] (2) Selecting elements Al and Sn that have a significant effect on the strength of the α phase, three diffusion couples were prepared by smelting and wire cutting, wherein the composition of the base block was Ti-1V-0.6Cr, the composition of the Al variable block was Ti-1V-0.6Cr-15Al, and the composition of the Sn variable block was Ti-1V-0.6Cr-15Sn. Other parameters were the same as those in step (2) of Example 1, and a diffusion couple after diffusion was obtained;

[0111] (3) Selecting elements Mo and Hf that have a significant effect on the strength of the β phase, and preparing three diffusion couples by smelting and wire cutting, wherein the composition of the basic block is Ti-4Al-7V-6Cr-0.8Fe, the composition of the Mo variable block is Ti-4Al-7V-6Cr-0.8Fe-20Mo, and the composition of the Hf variable block is Ti-4Al-7V-6Cr-0.8Fe-25Hf. Except that the cooling method is water quenching to room temperature so that the structure is all β phase, other parameters are the same as step (2), and the diffusion couple after diffusion is obtained;

[0112] (4) The diffusion couples obtained in steps (2) and (3) after diffusion are cut along the fitting surface of the base block and the variable block, polished, and evenly marked in the diffusion area using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition testing method EDS to obtain the variation law of the α-phase and β-phase strength with the composition, determine the content of elements when the single-phase strength is more than 90% of the maximum strength, and obtain the composition of the α-phase and β-phase containing the selected elements when the single-phase strength is at a higher level, wherein the composition of the α-phase is Ti-1V-0.6Cr-(8-8.4)Al-(3-4.3)Sn, and the composition of the β-phase is Ti-7V-6Cr-0.8Fe-4Al-(6.6-7.5)Mo-(11-13.3)Hf;

[0113] (5) According to the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level obtained in step (4), the volume percentage range of the α phase and the β phase is 40-65%, respectively, and the composition range of the overall titanium alloy can be roughly obtained as Ti-(4.9-5.8)Al-(3.3-4.5)Mo-(4.5-5.5)V-(2.6-3.4)Cr-(0.4-0.7)Fe-(10.5-14.2)Hf;

[0114] (6) Using the Pandat phase diagram thermodynamic calculation, the two single-phase compositions of the precipitated titanium alloy are calculated to fall within the optimal single-phase composition range optimized in step (4), which is the preliminary composition range of Ti-(5.4-5.8)Al-(3.3-3.9)Mo-(4.8-5.4)V-(3-3.4)Cr-(0.4-0.5)Fe;

[0115] (7) Select the elements Al and Mo that have a significant impact on the overall strength of titanium alloy, and prepare three diffusion couples by melting and wire cutting. The composition of the basic block is Ti-5V-3Cr-0.5Fe-12Hf, the composition of the Al variable block is Ti-5V-3Cr-0.5Fe-12Hf-12Al, and the composition of the Mo variable block is Ti-5V-3Cr-0.5Fe-12Hf-10Mo. Except for the treatment method after diffusion, which is water cooling + constant temperature at 510℃ for 6h + water cooling, all other parameters are the same as those of the original. The same as step (2), the diffusion couple after diffusion is obtained, the diffusion couple after diffusion is cut along the bonding surface of the base block and the variable block, polished, and the diffusion area is evenly marked with points using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition testing method EDS to obtain the change law of the overall titanium alloy strength with the element content, and it is determined that the final composition of the overall titanium alloy when the strength is the highest is Ti-3.3Mo-5.6Al-5V-3Cr-0.5Fe-12Hf;

[0116] (8) According to the final composition of the overall titanium alloy at the highest strength determined in step (7), a titanium alloy is prepared, with a forging temperature of 805°C, a total forging deformation of 300%, three forging cycles, and then annealing at 500°C for 6 hours.

[0117] The titanium alloy prepared in Example 2 was cut into standard tensile parts using wire cutting and subjected to mechanical property testing. The titanium alloy prepared in Example 2, with a chemical composition of Ti-3.3Mo-5.6Al-5V-3Cr-0.5Fe-12Hf, had a strength of 1507 MPa, a yield strength increase of approximately 12% compared to the original Ti5553 titanium alloy's 1350 MPa. The elongation was 7.9%, almost identical to the original alloy's 8%. Overall performance, especially strength, was significantly improved.

[0118] Example 3

[0119] A composition design method for an ultra-high strength dual-phase titanium alloy based on separate strengthening of α / β phases: (1) The elemental composition and content of each element of the α phase and β phase in the β-CEZ titanium alloy (Ti-5Al-2Sn-2Cr-4Mo-4Zr-1Fe) are determined by using the micro-area composition testing method EDS. In the α phase, Al≈8%, Sn≈2.9%, Cr≈0.4%, Zr≈3.9%, and the balance is Ti, that is, the composition of the α phase is Ti-8Al-2.9Sn-0.4Cr-3.9Zr; in the β phase, Al≈3.8%, Sn≈0.7%, Cr≈4.1%, Mo≈8.6%, Zr≈4.0%, Fe≈2.3%, and the balance is Ti, that is, the composition of the β phase is Ti-3.8Al-0.7Sn-8.6Mo-4.1Cr-4Zr-2.3Fe;

[0120] (2) Selecting elements Al and Zr that have a significant effect on the strength of the α phase, three diffusion couples were prepared by smelting and wire cutting, wherein the composition of the base block was Ti-2.9Sn-0.4Cr, the composition of the Al variable block was Ti-2.9Sn-0.4Cr-15Al, and the composition of the Zr variable block was Ti-2.9Sn-0.4Cr-12Zr. Other parameters were the same as those in step (2) of Example 1, and diffusion couples were obtained;

[0121] (3) Selecting elements Mo and Ta that have a significant effect on the strength of the β phase, and preparing three diffusion couples by smelting and wire cutting, wherein the composition of the basic block is Ti-3.8Al-0.7Sn-4.1Cr-4Zr-2.3Fe, the composition of the Mo variable block is Ti-3.8Al-0.7Sn-4.1Cr-4Zr-2.3Fe-15Mo, and the composition of the Ta variable block is Ti-3.8Al-0.7Sn-4.1Cr-4Zr-2.3Fe-10Ta. Except that the cooling method is water quenching to room temperature so that the structure is all β phase, other parameters are the same as step (2), and the diffusion couple after diffusion is obtained;

[0122] (4) The diffusion couples obtained in steps (2) and (3) after diffusion are cut along the fitting surface of the base block and the variable block, polished, and evenly marked in the diffusion area using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition testing method EDS to obtain the variation law of single-phase strength with element content, determine the element content range when the single-phase strength is above 90% of the highest strength, and obtain the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level, wherein the composition range of the α phase is Ti-(7.2-7.8)Al-2.9Sn-0.4Cr-(3.2-3.7)Zr, and the composition range of the β phase is Ti-3.8Al-0.7Sn-4.1Cr-(7.4-8.2)Mo-4Zr-2.3Fe-(3.2-4)Ta;

[0123] (5) According to the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level obtained in step (4), the volume percentage range of the α phase and the β phase is 40-65%, respectively, and the composition range of the overall titanium alloy can be roughly obtained as Ti-(4.4-5.8)Al-(1.5-2.4)Sn-(3.3-4.2)Mo-(1.6-2.4)Cr-(0.7-1.3)Fe-(3-4.1)Zr-(3-4.2)Ta;

[0124] (6) Using the Pandat phase diagram thermodynamic calculation, the two single-phase compositions of the precipitated titanium alloy are calculated to fall within the optimal single-phase composition range optimized in step (4), which is the preliminary composition range of Ti-(4.4-4.7)Al-(2-2.4)Sn-(3.4-3.7)Mo-(1.6-1.9)Cr-(0.7-1)Fe-(3.4-3.8)Zr-(1.8-2.4)Ta;

[0125] (7) The elements Zr and Ta that have a significant impact on the overall strength of titanium alloy were selected, and three diffusion couples were prepared by smelting and wire cutting. The composition of the basic block was Ti-4.6Al-2Sn-2Cr-3.5Mo-0.7Fe, the composition of the Zr variable block was Ti-4.6Al-2Sn-2Cr-3.5Mo-0.7Fe-12Zr, and the composition of the Ta variable block was Ti-4.6Al-2Sn-2Cr-3.5Mo-0.7Fe-8Ta. The treatment after diffusion was water cooling at a constant temperature of 510℃ for 6h+water cooling. The other parameters are the same as those in step (2), and the diffusion couple after diffusion is obtained. The diffusion couple after diffusion is cut along the fitting surface of the base block and the variable block, polished, and evenly marked in the diffusion area using a Vickers microhardness tester to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition test method EDS to obtain the variation law of the overall titanium alloy strength with the element content, and the final composition of the overall titanium alloy when the strength is the highest is determined to be Ti-4.6Al-2Sn-2Cr-3.5Mo-4.8Zr-1Fe-1.5Ta;

[0126] (8) According to the final composition of the overall titanium alloy at the highest strength determined in step (7), a titanium alloy is prepared, with a forging temperature of 850°C, a total forging deformation of 300%, three forging cycles, and then annealing at 560°C for 6 hours.

[0127] The titanium alloy prepared in Example 3 was cut into standard tensile parts using wire cutting and mechanical property testing was performed. The titanium alloy prepared in Example 3 with a chemical composition of Ti-4.6Al-2Sn-2Cr-3.5Mo-4.8Zr-1Fe-1.5Ta had a strength level of 1296 MPa, which was 8% higher than the 1200 MPa of the original β-CEZ titanium alloy; and the elongation was 11.4%, which was 14% higher than the 10% of the original β-CEZ titanium alloy; the overall performance including strength and plasticity was significantly improved.

[0128] Example 4

[0129] A composition design method for an ultra-high strength dual-phase titanium alloy based on separate strengthening of α / β phases: (1) The elemental composition and content of each element of the α phase and β phase in β21S titanium alloy (Ti-15Mo-2.7Nb-3Al-0.2Si) are determined by using the micro-area composition testing method EDS. In the α phase, Al≈4.1%, Mo≈2%, Nb≈0.6%, Si≈0.2%, and the balance is Ti, that is, the composition of the α phase is Ti-2Mo-0.6Nb-4.1Al-0.2Si; in the β phase, Al≈2%, Mo≈27.7%, Nb≈4.7%, Si≈0.2%, and the balance is Ti, that is, the composition of the β phase is Ti-27.7Mo-4.7Nb-2Al-0.2Si; the volume percentages of the α phase and the β phase are 60% and 40% respectively;

[0130] (2) Selecting elements Al and Hf that have a significant effect on the strength of the α phase, three diffusion couples were prepared by smelting and wire cutting, wherein the composition of the base block was Ti-2Mo-0.6Nb-0.2Si, the composition of the Al variable block was Ti-2Mo-0.6Nb-0.2Si-12Al, and the composition of the Hf variable block was Ti-2Mo-0.6Nb-0.2Si-12Hf. Other parameters were the same as those in step (2) of Example 1, and a diffusion couple after diffusion was obtained;

[0131] (3) Selecting elements Mo and Nb that have a significant effect on the strength of the β phase, and preparing three diffusion couples by melting and wire cutting, wherein the composition of the base block is Ti-2Al-0.2Si, the composition of the Mo variable block is Ti-2Al-0.2Si-35Mo, and the composition of the Nb variable block is Ti-2Al-0.2Si-12Nb. Except that the cooling method is water quenching to room temperature so that the structure is all β phase, other parameters are the same as step (2), and the diffusion couple after diffusion is obtained;

[0132] (4) The diffusion couples obtained in steps (2) and (3) after diffusion are cut along the fitting surface of the base block and the variable block, polished, and evenly marked in the diffusion area using a Vickers microhardness tester to test the hardness of the alloy in different areas. The alloy composition corresponding to different hardness is tested using the micro-area composition testing method EDS to obtain the variation law of single-phase strength with element content, determine the element content range when the single-phase strength is above 90% of the maximum strength, and obtain the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level, wherein the composition range of the α phase is Ti-(4.8-5.6)Al-(4.4-5)Hf-2Mo-0.6Nb-0.2Si, and the composition range of the β phase is Ti-2Al-(19-23.5)Mo-(4.4-5)Nb;

[0133] (5) According to the composition range of the single phase obtained in step (4) at a higher level containing the selected elements of α phase and β phase, the volume percentage range of α phase and β phase is 40-65%, respectively, and the composition range of the overall titanium alloy can be roughly obtained as Ti-(2.8-3.8)Al-(11-16)Mo-(2.5-3.6)Nb-(4-5.2)Hf-0.2Si

[0134] (6) Using the Pandat phase diagram thermodynamic calculation, it is calculated that the two single-phase compositions of the precipitated titanium alloy fall within the optimal single-phase composition range optimized in step (4) and are within the preliminary composition range of the overall titanium alloy Ti-(3.4-3.7)Al-(12-14)Mo-(2.9-3.4)Nb-(4.5-5)Hf-0.2Si;

[0135] (7) Select the elements Al and Nb that have a significant impact on the overall strength of titanium alloy, and prepare three diffusion couples by melting and wire cutting. The composition of the basic block is Ti-13Mo-4.7Hf-0.2Si, the composition of the Al variable block is Ti-13Mo-4.7Hf-0.2Si-10Al, and the composition of the Nb variable block is Ti-13Mo-4.7Hf-0.2Si-10Nb. Except for the treatment method after diffusion, which is water cooling + constant temperature at 510℃ for 6h + water cooling, the other parameters are the same as those of step 1. The same as step (2) is used to obtain a diffusion couple after diffusion, and the diffusion couple after diffusion is cut along the bonding surface of the base block and the variable block, and polished. A Vickers microhardness tester is used to evenly mark points in the diffusion area to test the alloy hardness in the diffusion area. The alloy composition corresponding to different hardness points is tested using the micro-area composition testing method EDS to obtain the change law of the overall titanium alloy strength with the element content, and it is determined that the final composition of the overall titanium alloy when the strength is the highest is Ti-3.9Al-13Mo-3.8Nb-4.7Hf-0.2Si;

[0136] (8) According to the final composition of the overall titanium alloy at the highest strength determined in step (7), a titanium alloy is prepared, with a forging temperature of 750°C, a total forging deformation of 300%, three forging cycles, and then annealing at 480°C for 6 hours.

[0137] The titanium alloy prepared in Example 4 was cut into standard tensile parts using wire cutting and subjected to mechanical property testing. The titanium alloy prepared in Example 4, with a chemical composition of Ti-3.9Al-13Mo-3.8Nb-4.7Hf-0.2Si, exhibited a strength of 1224 MPa, a 6.4% increase compared to the 1150 MPa of the original β21S titanium alloy. Its elongation was 11%, essentially the same as the original alloy. This marked a significant improvement in overall performance.

[0138] In summary, the present invention optimizes the composition design of the α-phase and β-phase elements respectively, obtains the variation pattern of the single-phase strength with the element content, and thus analyzes the content range of the elements when the strength of each single phase is at a higher level, and then obtains the composition range corresponding to the α-phase and β-phase. Based on the single-phase optimal composition range and volume percentage range, a rough alloy composition range is obtained. On this basis, the phase diagram thermodynamic calculation is used to screen out the alloy compositions whose precipitated two-phase components fall within the optimal single-phase composition range. From the screened range, any specific composition is selected as the preliminary alloy composition, and the diffusion multi-node method is used again to find the exact optimal content value of the element in the overall alloy, and the alloy composition is completely determined. Compared with the original titanium alloy, the mechanical properties of the titanium alloy are further improved.

[0139] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for designing the composition of an ultra-high-strength dual-phase titanium alloy based on separate α / β phase strengthening, comprising the following steps: (1) A dual-phase high-strength titanium alloy was selected as the control object, and its composition was analyzed to determine the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy; (2) Based on the elemental composition and content of the α phase and β phase in the dual-phase high-strength titanium alloy determined in step (1), elements that have a significant effect on the strength of the α phase and β phase are selected respectively, and a diffusion multi-node composition gradient method is used to obtain the variation pattern of the single-phase strength with the element content, and the content range of the element when the single-phase strength is more than 90% of the maximum strength is determined, and the composition range of the α phase and β phase containing the selected elements when the single-phase strength is at a higher level is obtained; (3) obtaining a rough composition range of the overall titanium alloy based on the composition range of the α phase and β phase containing the selected elements and the volume percentage range of the α phase and β phase when the single-phase strength is at a higher level obtained in step (2); (4) Based on the approximate composition range of the overall titanium alloy obtained in step (3), a phase diagram thermodynamic calculation is used to further screen the alloy composition range on this basis to obtain a preliminary composition range of the overall titanium alloy. The screening principle is: the preliminary composition range of the overall titanium alloy should meet the requirements that the precipitated α phase composition falls within the composition range of the α phase containing the selected element when the single-phase strength is at a higher level obtained in step (2), and that the precipitated β phase composition also falls within the composition range of the β phase containing the selected element when the single-phase strength is at a higher level obtained in step (2); (5) Select a component within the preliminary composition range of the overall titanium alloy obtained in step (4), select elements that have a significant impact on the strength of the overall titanium alloy, use the diffusion multi-node composition gradient method to obtain the change pattern of the overall titanium alloy strength with element content, and determine the final composition of the overall titanium alloy when the strength is the highest.

2. The design method according to claim 1, characterized in that: The step (2) comprises the following steps: 1) Select elements that have a significant impact on the strength of the α phase and β phase respectively and make diffusion couples; 2) diffusing the diffusion couple obtained in step 1) and then cooling it to obtain a diffused diffusion couple; 3) Measuring the composition and hardness of the diffusion couple obtained in step 2), and obtaining the variation pattern of single-phase strength with element content based on the measured hardness and composition, determining the element content range when the single-phase strength is above 90% of the maximum strength, and obtaining the composition range of the α phase and β phase containing the selected element when the single-phase strength is at a high level.

3. The design method according to claim 2, characterized in that: The diffusion couple in step 1) includes a basic block, an element x diffusion block and an element y diffusion block.

4. The design method according to claim 3, characterized in that: The diffusion couples in step 1) are placed in the following manner: the basic block and the element x diffusion block are bonded together, and the element y diffusion block is placed above the bonded basic block and element x diffusion block.

5. The design method according to claim 2, characterized in that: The diffusion temperature in step 2) is 1000-1100° C., and the diffusion time is 165-180 hours.

6. The design method according to claim 5, characterized in that: The diffusion temperature is 1050° C., and the diffusion time is 168 h.

7. The design method according to claim 2, characterized in that: In the step 2), for the α phase, the cooling rate is 0.5-1.5° C. / min, and for the β phase, the cooling method is water quenching.

8. The design method according to claim 7, characterized in that: In the step 2), for the α phase, the cooling rate is 1° C. / min.

9. The design method according to claim 1, characterized in that: In the step (2), the elements that have a significant effect on the strength of the α phase include two of Al, Sn, Zr and Hf, and the elements that have a significant effect on the strength of the β phase include two of Mo, V, Hf, Ta and Nb.

10. The design method according to claim 1, characterized in that: The elements that have a significant impact on the overall strength of the titanium alloy in step (5) include two of Al, Mo, Zr, Ta and Nb.

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