High-strength and high-plasticity metastable beta titanium alloy and preparation method thereof

Abstract

The invention discloses a high-strength and high-plasticity metastable beta titanium alloy and a preparation method thereof, and belongs to the technical field of material preparation, the general formula of the metastable beta titanium alloy is TixZryAl10Nb5, x and y are the molar percentage of Ti and Zr respectively, x is larger than or equal to 30 and smaller than or equal to 60, y is larger than or equal to 20 and smaller than or equal to 50, and the sum of x and y is 85. The high-strength and high-plasticity metastable beta titanium alloy provided by the invention shows excellent room-temperature tensile property, shows good plasticity while having strength, unifies the strength and the plasticity, and has a good application prospect in the field of aerospace.

Description

Technical Field

[0001] The invention belongs to the field of material technology preparation, and in particular relates to a high-strength and high-plasticity metastable beta titanium alloy and a preparation method thereof. Background Art

[0002] Titanium alloys have attracted extensive attention and applications in the fields of aviation, aerospace, chemical industry, and medicine due to their advantages such as high strength, strong corrosion resistance, and light weight and high strength. Studies have shown that changing the type and content of β-stabilizing elements can effectively regulate the β thermodynamic stability, which in turn directly affects the deformation mechanism of metastable β titanium alloys. As the β thermodynamic stability gradually decreases, the deformation mechanism of the alloy will sequentially change from dislocation slip to twinning, and then to stress-induced martensitic transformation (SIMT). Compared with common dislocation slip, twinning and SIMT can improve the work hardening rate of the alloy through the dynamic Hall-Petch effect, thereby giving it a higher uniform strain rate and service safety, namely twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP). However, due to the low critical excitation stress corresponding to twinning and SIMT, the yield strength of most TWIP / TRIP metastable β titanium alloys is less than 800MPa. This means that although the TWIP / TRIP effect can significantly improve the work hardening rate and uniform elongation of metastable β-titanium alloys, it is often at the expense of yield strength, which seriously hinders the widespread application of TWIP / TRIP β-titanium alloys in advanced aerospace equipment. Summary of the invention

[0003] The purpose of the present invention is to provide a high-strength and high-plastic metastable β titanium alloy to solve the low yield strength caused by the TWIP / TRIP effect in the metastable β titanium alloy mentioned in the prior art, and further expand the application range of titanium alloy. The present invention introduces the concept of "entropy engineering", which is an extension of the concept of "high entropy alloy", and refers to a new material design concept based on the complexity of the composition and resulting in a performance breakthrough. On the one hand, when the configuration entropy increment caused by the increase in the type / content of the alloying element is greater than the increment of the system enthalpy, the corresponding reduction in Gibbs free energy will enhance the thermodynamic stability of the β solid solution. Therefore, the configuration entropy can be used as a new dimension to drive the stability of the β structure, and more flexibly realize the regulation of the deformation mechanism of the metastable β titanium alloy. On the other hand, similar to other high-entropy materials, the metastable β titanium alloy (referred to as entropy-controlled titanium alloy) based on entropy engineering regulation will have multiple main elements in addition to the original main element titanium, and there are significant differences in their atomic size, electronegativity, etc., resulting in asymmetric and anisotropic charge transfer and atomic interactions, which will induce the generation of local chemical order at the atomic scale. The existence of local chemical order is expected to act as a local barrier to the nucleation / growth process of SIMT / twinning, thereby increasing the critical excitation stress and overcoming the performance bottleneck of the incompatibility of strength and plasticity in traditional titanium alloys. It has great application potential in the aerospace field.

[0004] One of the technical solutions provided by the present invention:

[0005] A high-strength and high-plasticity metastable β titanium alloy, wherein the general formula of the metastable β titanium alloy is Ti x Zr y Al 10 Nb5, wherein x and y are the molar percentages of Ti and Zr respectively, 30≤x≤60, 20≤y≤50, and x+y=85.

[0006] Preferably, 42.5≤x≤50, 35≤y≤42.5, and x+y=85.

[0007] More preferably, x is 50 and y is 35.

[0008] When 42.5≤x≤50, 35≤y≤42.5, the high-strength and high-plastic metastable β titanium alloy Ti provided by the present invention x Zr y Al 10 The mixing entropy of Nb5 is between 9.096 J·mol -1 ·K -1 and 9.207 J·mol -1 ·K -1 Within this range, the high-strength and high-plasticity metastable β titanium alloy Ti of the present invention is x Zry Al 10 Nb5 can all undergo stress-induced phase transformation, namely the TRIP effect. At the same time, as the Ti content increases, the transformation temperature of the B2 phase also increases, which means that the formation of the B2 phase becomes easier as the Ti content increases, thereby precipitating more B2 phases. It is precisely because of the presence of the B2 phase that the present invention not only improves plasticity under the influence of the TRIP effect, but also exhibits excellent yield strength, thereby obtaining a high-strength and high-plasticity metastable β titanium alloy Ti with both strength and plasticity. x Zr y Al 10 Nb5.

[0009] The second technical solution provided by the present invention is:

[0010] A method for preparing the above-mentioned high-strength and high-plasticity metastable β titanium alloy comprises the following steps: weighing metal elements Ti, Zr, Al and Nb according to molar percentage, placing the above-mentioned metal elements together in a copper crucible, and evacuating the furnace chamber to a vacuum degree of 3.2×10 -3 Pa, and then filled with argon to -0.05MPa, smelting, and solidification in a water-cooled copper crucible to obtain the high-strength and high-plasticity metastable β titanium alloy.

[0011] Preferably, the purity of the metal elements Ti, Zr, Al and Nb is greater than or equal to 99.95wt.%.

[0012] Preferably, the smelting is repeated at least 6 times at a current of 450-500A, with each smelting lasting 100-120s.

[0013] Preferably, the smelting is repeated 6 times at a current of 500A, with each smelting lasting 120s.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects:

[0015] The high-strength and high-plasticity metastable β-titanium alloy provided by the present invention exhibits excellent room-temperature tensile properties, and has high strength while also exhibiting good plasticity. The metastable β-titanium alloy prepared by the present invention has a yield strength of 817MPa, an ultimate tensile strength of 1088MPa, a work hardening rate of 5315MPa, a uniform elongation and a fracture elongation of 11.2% and 16.6%, respectively, and has mechanical properties different from those of traditional titanium alloys with low strength and high plasticity or high strength and low plasticity. The phase structure of the high-strength and high-plasticity metastable β-titanium alloy prepared by the present invention is BCC phase and B2 phase. The high-strength and high-plasticity metastable β-titanium alloy prepared by the present invention is simple and reliable to melt, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 (a) is the high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Nb5 tensile engineering stress-engineering strain curve in cast state, Figure 1 (b) is the true stress-true strain / work hardening rate curve;

[0018] Figure 2 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Electron backscattered spectra (EBSD) of Nb5;

[0019] Figure 3 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 XRD spectrum of Nb5;

[0020] Figure 4 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 TEM dark field image of Nb5;

[0021] Figure 5 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Electron backscattered pattern (EBSD) of Nb5 when the strain reaches 3%;

[0022] Figure 6 (a) is the high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Nb5 tensile engineering stress-engineering strain curve in cast state, Figure 6 (b) is the true stress-true strain / work hardening rate curve;

[0023] Figure 7 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 242.5 Zr 42.5 Al 10 Electron backscattered spectra (EBSD) of Nb5;

[0024] Figure 8 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 XRD spectrum of Nb5;

[0025] Fig. 9 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 TEM dark field image of Nb5;

[0026] Fig.10 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Electron backscattered pattern (EBSD) of Nb5 when the strain reaches 6%;

[0027] Fig.11 The high-strength and high-plasticity metastable β titanium alloy (Ti 50 Zr 35 Al 10 True stress-true strain comparison curve of the cast fine-grained high-strength titanium-zirconium-aluminum-niobium alloy prepared by Examples 1-4 in Patent CN106676325A. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0031] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0032] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0033] The room temperature in the present invention refers to 25±2°C.

[0034] Example 1 A high-strength and high-plasticity metastable β titanium alloy (Ti 50 Zr 35 Al 10 Preparation method of Nb5)

[0035] S1. Selection of raw materials: Selecting metal single substance raw materials Ti, Zr, Al and Nb with a purity of 99.95wt.%, and polishing with sandpaper to remove the oxides on the surface of the metal single substance raw materials;

[0036] S2. Ingredients: Based on the total mass of the ingot of 50g, the mass percentages are calculated by converting the molar percentages of Ti, Zr, Al and Nb required, so as to determine the required mass of each metal element raw material, which is Ti: 18.936g; Zr: 25.255g; Al: 2.314g; Nb: 3.674g. The weights are weighed by an electronic balance, and all weighing errors are within ±0.001g.

[0037] S3. Melting: Put the above metal raw materials into the copper crucible of the vacuum arc melting furnace, and evacuate the furnace chamber to a vacuum degree of 3.2×10 -3 Pa, and then filled with high-purity argon to -0.05MPa, smelted at a current of 500A for 120s, repeatedly smelted 6 times, and solidified in a water-cooled copper crucible. The obtained metal button nail is a high-strength and high-plastic metastable β titanium alloy Ti 50 Zr 35 Al 10 Nb5.

[0038] The invention measures the yield strength, ultimate tensile strength and elongation at break of the alloy through a tensile test.

[0039] Figure 1 (a) is the high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Nb5 tensile engineering stress-engineering strain curve in cast state, Figure 1 (b) is the true stress-true strain / work hardening rate curve. Figure 1 It can be seen that the metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 The yield strength of Nb5 is 817MPa, the ultimate tensile strength is 1088MPa, the elongation at break is 16.6%, the uniform elongation is 11.2%, and the work hardening rate is 5315MPa.

[0040] Figure 2 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Electron backscattered spectra (EBSD) of Nb5, Figure 2 The metastable β titanium alloy Ti prepared in Example 1 is shown 50 Zr 35 Al 10 The grain morphology of Nb5 Figure 2 It can be seen that the metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Nb5 is composed of equiaxed crystals with completely random orientation.

[0041] Figure 3 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 The XRD spectrum of Nb5 is given by Figure 3 It can be seen that the phase structure of Example 1 is composed of a BCC phase and a B2 phase.

[0042] Figure 4 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 Dark field image of Nb5 by transmission electron microscope Figure 4 This further proves the existence of the B2 phase in Example 1.

[0043] Figure 5The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 1 50 Zr 35 Al 10 The electron backscattered image (EBSD) of Nb5 when the strain reaches 3% is shown in Figure 1. Figure 5 It can be seen that in Example 1, martensitic phase transformation occurs simultaneously with strain, namely, the TRIP effect.

[0044] Example 2 A high-strength and high-plasticity metastable β titanium alloy (Ti 42.5 Zr 42.5 Al 10 Preparation method of Nb5)

[0045] S1. Selection of raw materials: Selecting metal single substance raw materials Ti, Zr, Al and Nb with a purity of 99.95wt.%, and polishing with sandpaper to remove the oxides on the surface of the metal single substance raw materials;

[0046] S2. Ingredients: Based on the total mass of the ingot of 50g, the mass percentages are calculated by converting the molar percentages of Ti, Zr, Al and Nb required, so as to determine the required mass of each metal element raw material, which is Ti: 15.309g; Zr: 29.167g; Al: 2.030g; Nb: 3.495g. The weights are weighed by an electronic balance, and all weighing errors are within ±0.001g.

[0047] S3. Melting: Put the above metal elements into the copper crucible of the vacuum arc melting furnace, and evacuate the furnace chamber to a vacuum degree of 3.2×10 -3 Pa, and then filled with high-purity argon to -0.05MPa, smelted at a current of 500A for 120s, repeatedly smelted 6 times, and solidified in a water-cooled copper crucible, and finally cooled to room temperature. The obtained metal button nail is a high-strength and high-plastic metastable β titanium alloy Ti 42.5 Zr 42.5 Al 10 Nb5.

[0048] Figure 6 (a) is the high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Nb5 tensile engineering stress-engineering strain curve in cast state, Figure 6 (b) is the true stress-true strain / work hardening rate curve. Figure 6 It can be seen that the high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10The yield strength of Nb5 is 754MPa, the ultimate tensile strength is 875MPa, the elongation at break is 18.8%, the uniform elongation is 9.3%, and the work hardening rate is 2418MPa.

[0049] Figure 7 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Electron backscattered spectra (EBSD) of Nb5, Figure 7 The metastable β titanium alloy Ti prepared in Example 2 is shown 42.5 Zr 42.5 Al 10 The grain morphology of Nb5 Figure 7 It can be seen that the metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Nb5 is composed of equiaxed crystals with completely random orientation.

[0050] Figure 8 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 The XRD spectrum of Nb5 is given by Figure 8 It can be seen that the phase structure of Example 2 is composed of a BCC phase and a B2 phase.

[0051] Fig. 9 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 Dark field image of Nb5 by transmission electron microscope Fig. 9 This further proves the existence of the B2 phase in Example 2.

[0052] Fig.10 The high-strength and high-plasticity metastable β titanium alloy Ti prepared in Example 2 42.5 Zr 42.5 Al 10 The electron backscattered image (EBSD) of Nb5 when the strain reaches 6% is shown in Figure 1. Fig.10 It can be seen that Example 2 produces a martensitic phase transformation, i.e., the TRIP effect, while strain occurs. Patent CN106676325A discloses a cast fine-grained high-strength titanium-zirconium-aluminum-niobium alloy and a preparation method thereof. Examples 1-4 of the invention are used as comparative examples to compare the performance of the alloy prepared by Example 1 of the present invention. Fig.11 The high-strength and high-plasticity metastable β titanium alloy (Ti 50 Zr 35 Al10 Nb5) and the true stress-true strain comparison curve of the cast fine-grained high-strength titanium-zirconium-aluminum-niobium alloy prepared in Examples 1-4 of the patent CN106676325A. Table 1 is a high-strength and high-plastic metastable β titanium alloy Ti prepared in Example 1 of the present invention. 50 Zr 35 Al 10 Comparison results of the mechanical properties of the alloys prepared by Nb5 and Examples 1-4 in Patent CN106676325 A, wherein the yield strength and ultimate tensile strength of Comparative Examples 1-4 are the measurement results of the corresponding examples in Patent CN106676325 A.

[0053] Table 1

[0054]

[0055] The composition of the raw metal species proposed in patent CN106676325A is similar to that of the present invention, but the mechanical properties of the prepared titanium alloy are high strength and low plasticity, and its application potential in the aerospace field is limited. The elongation at break of the alloy prepared by Examples 1-4 of patent CN106676325 A is significantly lower than that of the present invention.

[0056] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A high-strength and high-plasticity metastable β titanium alloy, It is characterized in that The general formula of the metastable β titanium alloy is Ti x Zr y Al 10 Nb 5 , wherein x and y are the molar percentages of Ti and Zr respectively, 30≤x≤60, 20≤y≤50, and x+y=85.

2. The high-strength and high-plasticity metastable β titanium alloy according to claim 1, It is characterized in that 42.5≤x≤50, 35≤y≤42.5, and x+y=85.

3. The high-strength and high-plasticity metastable β titanium alloy according to claim 2, It is characterized in that x is 50 and y is 35.

4. A method for preparing the high-strength and high-plasticity metastable β titanium alloy according to any one of claims 1 to 3, It is characterized in that The following steps are involved: Weigh the metal elements Ti, Zr, Al and Nb according to the molar percentage, put the above metal elements into a copper crucible, and evacuate the furnace chamber to a vacuum degree of 3.2×10 -3 Pa, and then filled with argon to -0.05MPa, smelting, and solidification in a water-cooled copper crucible to obtain the high-strength and high-plasticity metastable β titanium alloy.

5. The method for preparing the high-strength and high-plasticity metastable β titanium alloy according to claim 4, It is characterized in that The purity of the metal elements Ti, Zr, Al and Nb is greater than or equal to 99.95wt.%.

6. The method for preparing the high-strength and high-plasticity metastable β titanium alloy according to claim 4, It is characterized in that The smelting is repeated at least 6 times at a current of 450-500A, with each smelting lasting 100-120s.

7. The method for preparing the high-strength and high-plasticity metastable β titanium alloy according to claim 6, It is characterized in that The smelting is repeated 6 times at a current of 500A, with each smelting lasting 120s.

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