A titanium alloy with both low elastic modulus and high superelasticity and a preparation method thereof

Abstract

The present invention discloses a titanium alloy with both low elastic modulus and high superelasticity and a preparation method thereof, relating to the field of alloy materials. The alloy comprises 42% to 48% zirconium, 7% to 10% niobium, 0.2% to 1.5% tin, and the balance titanium. The alloy exhibits an initial tensile elastic modulus of 34 to 46 GPa and a maximum recoverable strain of 6.48 to 7.7%, combining the advantages of low elastic modulus, high superelasticity, and non-cytotoxicity. The alloy is obtained by multiple smelting in a vacuum non-consumable arc furnace. Through rational alloy component design, the martensitic transformation temperature of the β-titanium alloy is near room temperature. Consequently, the alloy is unstable when deformed at room temperature, requiring only a relatively low driving force for the transformation to induce the martensitic transformation, thus saving energy and reducing costs.

Description

Technical Field

[0001] The present invention relates to the field of alloy materials, and in particular to a titanium alloy with low elastic modulus and high superelasticity and a preparation method thereof. Background Art

[0002] Titanium and its alloys are widely used in aviation, biomedical materials and civil fields due to their excellent biocompatibility, high strength, low density, stable superelasticity and good corrosion resistance.

[0003] Among them, nickel-titanium alloys and α+β-type Ti-6Al-4V and Ti-6Al-7Nb have good superelasticity and low elastic modulus, and are widely used in the medical field. However, the cytotoxicity and sensitization problems of Ni, Al, and V are worrying. In recent years, the development of Ni-free superelastic β-titanium alloys, including Ti-Nb, Ti-Mo, and Ti-Ta alloys, does not contain toxic elements and is expected to replace nickel-titanium alloys. However, the recoverable strain of the currently developed Ni-free superelastic β-titanium alloys is generally low, and the elastic modulus is high, which can easily cause a "stress shielding" effect, leading to bone absorption around the implant, causing implant loosening or fracture, etc., which is not conducive to bone healing and the long-term stability of the implant. Therefore, there is an urgent need to develop a superelastic alloy with a low elastic modulus and a high strain recovery rate that is non-biotoxic.

[0004] Therefore, those skilled in the art are committed to developing a titanium alloy with low elastic modulus, high recoverable strain and no cytotoxicity. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to obtain a titanium alloy with low elastic modulus, high recoverable strain and no cytotoxicity.

[0006] To achieve the above object, the present invention provides a titanium alloy having both low elastic modulus and high superelasticity, wherein the element composition of the alloy is 42% to 48% zirconium, 7% to 10% niobium, 0.2% to 1.5% tin, and the balance is titanium.

[0007] The alloy has a cast structure of body-centered cubic β phase, an initial tensile elastic modulus of 34-46 GPa, a tensile strength of 674-750 MPa, an induced martensitic transformation stress of 222-550 MPa, and a maximum recoverable strain of 6.48-7.7% at room temperature.

[0008] And a method for preparing a titanium alloy having both low elastic modulus and high superelasticity, characterized by comprising the following steps:

[0009] Step 1, weighing raw materials: selecting zirconium raw materials, niobium raw materials, tin raw materials, and titanium raw materials according to the atomic percentages of the elemental components of the alloy and weighing and mixing them;

[0010] Step 2, alloy smelting: placing the zirconium raw material, niobium raw material, tin raw material, and titanium raw material described in step 1 into a copper crucible in a vacuum non-consumable arc furnace, and smelting them multiple times to obtain the alloy with low elastic modulus and high superelasticity.

[0011] Furthermore, the tin raw material is placed at the bottom of the copper crucible, the titanium raw material and the zirconium raw material are placed on top of the tin in sequence, and the niobium raw material is placed on the top layer.

[0012] Furthermore, the copper crucible is a water-cooled copper crucible, the alloy smelting process is carried out under the protection of argon gas, and the bottom of the water-cooled copper crucible is cooled by circulating cooling water.

[0013] Furthermore, the vacuum non-consumable arc furnace is evacuated before the alloy is smelted. When the vacuum degree reaches 5×10 -3 Pa, and then argon gas is introduced for washing to remove residual air, and finally the alloy is smelted under the protection of argon gas.

[0014] Furthermore, the alloy is smelted at a current of 370 to 400 A, a voltage of 20 to 60 V, and a smelting time of 50 to 70 s.

[0015] Furthermore, the multiple smelting is repeated smelting 5 to 7 times, and smelting again after each flip.

[0016] Furthermore, the zirconium raw material, niobium raw material, tin raw material and titanium raw material are respectively industrial sponge zirconium, niobium block, tin block and sponge titanium with a purity exceeding 99.0 wt%.

[0017] Furthermore, the low elastic modulus and high superelastic alloy obtained in step 2 is a button-shaped alloy ingot, and the button-shaped alloy ingot is cast to obtain a titanium alloy rod;

[0018] Furthermore, during the casting, the button-shaped alloy ingot is placed in a crucible cavity with a bottom pouring hole, a copper ingot mold is placed under the pouring hole, and a non-consumable electrode is used to scan and heat the button-shaped alloy ingot. The molten metal flows from the pouring hole into the copper ingot mold to obtain the titanium alloy rod.

[0019] The technical effects of the present invention are as follows:

[0020] (1) The present invention integrates d-electron alloy design and valence electron concentration design, and takes into account the role of zirconium and tin in stabilizing the β phase in the alloy system, reduces the content of niobium, and prepares a titanium alloy with both low elastic modulus and high recoverable strain. The tensile initial elastic modulus of the alloy of the present invention is 34 to 46 GPa, which is closer to the elastic modulus of human bone (10 to 30 GPa), and can effectively alleviate the implant failure problem caused by the mismatch between the elastic modulus between the implant and human bone. In the cyclic loading-unloading experiment, the unloading recovery rate of some alloys was still above 80% when 8% strain occurred, which is similar to that of Ni-Ti shape memory alloy. In addition, because of its high strength and low modulus, it can also be used in fields such as sports and industrial parts, such as golf club surface materials, springs, etc. In particular, the tensile elastic modulus of the Ti-Zr-Nb alloy microalloyed with an appropriate amount of Sn can be as low as 34 to 46 GPa.

[0021] (2) The β-Ti stabilizing element niobium content added in the present invention is very low, which reduces the occurrence of smelting segregation and niobium inclusions compared to traditional Ti-Nb alloys, and reduces the smelting difficulty and preparation cost.

[0022] (3) The alloy of the present invention has a simple preparation process and can be used in the cast state without the need for subsequent deformation processing and heat treatment, which not only reduces the preparation cost but also allows parts with complex shapes to be directly cast from the melt.

[0023] (4) The alloying elements titanium, zirconium, niobium, and tin used in the alloy of the present invention are all non-cytotoxic elements, which effectively avoids the cytotoxicity problem of elements such as Ni, Mo, and V in certain medical alloys. In addition, the alloy has better biocompatibility than Ni-Ti alloys because zirconium, niobium, and tin all have good biocompatibility while Ni does not. This provides a new material for biomedical implants such as orthopedic implants, and can be widely used in fields such as biomedical materials, such as prostheses, artificial joints, and bone trauma products.

[0024] (5) The present invention is based on d electrons calculated from first principles, while taking into account the solid solution strengthening effect of each alloying element on the titanium alloy. By fitting the Bo-Md (bond order-d electron energy level) value of the alloy system and taking into account the valence electron concentration theory related to the elastic modulus, the martensitic phase transition temperature of the β-titanium alloy is made to be near room temperature. Therefore, the alloy is in an unstable state when deformed at room temperature, and only a relatively low phase transition driving force is required to induce the martensitic phase transition, thereby saving energy and reducing costs.

[0025] (6) Advantages of the metal selected in the present invention:

[0026] Titanium: It is selected as the matrix element, and through the addition of other alloying elements, a metastable body-centered cubic β alloy is finally obtained, which lays the foundation for the subsequent stress-induced martensitic phase transformation. This crystal form can make the alloy undergo stress-induced martensitic phase transformation when the external stress reaches a certain value, thereby making the alloy superelastic with a recoverable strain of 6.48-7.7%.

[0027] Zirconium: Zirconium and titanium belong to the same element family, share the same crystal form, and are completely miscible. However, the lattice parameters of titanium and zirconium differ to some extent. The addition of zirconium can significantly distort the alloy's lattice, providing solid solution strengthening. Furthermore, zirconium has a weak β-stabilizing effect in the Ti-Nb-Zr system, enhancing the β-stabilizing effect of niobium and stabilizing the high-temperature β phase of the titanium alloy to room temperature.

[0028] Niobium: Niobium stabilizes the high-temperature body-centered cubic phase of titanium alloys to room temperature, stabilizing the β phase. Furthermore, the addition of niobium also contributes to solid solution strengthening and improves the toughness of the alloy.

[0029] Tin: With a high solid solubility in both α-Ti and β-Ti, it can simultaneously improve tensile strength at both room and elevated temperatures. By stabilizing the ω phase, it lowers the martensitic transition temperature and reduces the room-temperature aging effect. The addition of tin inhibits the formation of the athermal ω phase, thereby reducing the elastic modulus and improving superelastic properties.

[0030] At the same time, because the density of titanium (4.51g / cm 3 ) is much lower than zirconium (6.51g / cm 3 While maintaining performance, the present invention utilizes a higher titanium content, reducing the alloy's density and increasing its specific strength. Under the same load-bearing capacity, the alloy components of the present invention are significantly lighter, resulting in a significant weight reduction. Furthermore, because pure titanium is significantly less expensive than other pure metals, the present invention utilizes a "microalloying" strategy to add tin, controlling the atomic percentage of tin to 0.2-1.5%. While also strictly controlling the zirconium and niobium content, the alloy's cost is relatively low.

[0031] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is an X-ray diffraction pattern of an embodiment of the present invention;

[0033] Figure 2 is a room temperature tensile stress-strain curve of a preferred embodiment of the present invention;

[0034] Figure 3is a room temperature cyclic tensile stress-strain curve of an embodiment of the present invention;

[0035] Among them: 1#—Ti-42Zr-10Nb-0.2Sn, 2#—Ti-44Zr-8Nb-0.5Sn, 3#—Ti-44Zr-7Nb-1.5Sn, 4#—Ti-48Zr-9Nb-0.2Sn. DETAILED DESCRIPTION

[0036] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0037] Example

[0038] Industrially pure metals with a purity of 99% or more were used as raw materials. The alloy's raw material composition and atomic percentages were: zirconium 42% to 48%, niobium 7% to 10%, tin 0.2% to 1.5%, and the remainder titanium. The alloy compositions in each embodiment are shown in Table 1.

[0039] Table 1 Example alloy composition (atomic percentage)

[0040]

[0041] In the following examples, the Ti-Zr-Nb superelastic alloy was prepared according to the following steps:

[0042] (1) Raw material preparation: Industrial pure metals with a purity of 99% or more are selected as raw materials. The pure metal raw materials used in the β-type Ti-Zr-Nb alloy of the present invention are as follows: zirconium 42% to 48%, niobium 7% to 10%, tin 0.2% to 1.5%, and the balance titanium.

[0043] (2) Alloy melting and casting methods

[0044] The alloy was melted in a water-cooled copper crucible vacuum non-consumable arc furnace. During the first melting, the low-melting-point tin raw material was placed at the bottom of the copper crucible, the titanium and zirconium raw materials were placed on top of the tin raw material, and finally the niobium raw material was placed on the top. After the raw materials were placed in the crucible, vacuum treatment was carried out. When the vacuum degree reached 5×10 -3 Pa, argon gas was introduced for purge to remove the remaining air. Then the vacuum was re-evacuated to 5×10 -3Pa, high-purity argon is then filled in, and smelting is carried out under argon protection. The smelting current is controlled between 370 and 400 A; the smelting voltage is 20 to 60 V, maintained for 50 to 70 seconds. During smelting, circulating cooling water is passed through the bottom of the copper crucible to cool it. To ensure uniform composition, the melted buttons are flipped over and re-smelted, repeating the smelting process 5 to 7 times. The melted button ingot is placed in a crucible cavity with a bottom pouring hole. A copper ingot mold is placed below the pouring hole. A non-consumable electrode is used to scan and heat the button ingot. Initially, the surface tension of the melted metal prevents it from flowing out of the pouring hole. Only after the molten pool temperature rises and the metal's fluidity increases, does the molten metal quickly and completely flow out of the pouring hole. A suction casting process can also be used to improve mold filling quality. Cooled by circulating cooling water, the alloy melt solidifies in the copper mold, resulting in a rectangular sample with a cross-sectional dimension of 10 mm × 10 mm and a length of 45 mm.

[0045] X-ray diffraction test and phase composition analysis

[0046] After cutting the sample into small pieces with a cross-sectional size of 10 mm × 10 mm using a wire-cut electric discharge machine, the sample was then ground using 100#, 500#, 1000#, 1500#, and 2000# metallographic sandpaper. Phase composition analysis of the metallographic samples was performed using an X-ray diffractometer with a scanning speed of 2° / min and a scanning range of 20° to 70°.

[0047] Figure 1 The XRD patterns of the as-cast alloys 1#, 2#, 3#, and 4# are shown in Table 1. The analysis results show that the alloys are mainly composed of β body-centered cubic phase and a small amount of α″ martensite.

[0048] Room temperature quasi-static tensile test

[0049] The prepared alloy was cut into dog-bone tensile specimens with a working section thickness of 1.5 mm and a width of 4 mm using an electric spark wire cutting machine. The gauge length was 10 mm, and the surface was polished with metallographic sandpaper to eliminate surface defects. The tensile test was carried out on a Z20 universal material testing machine with a uniform tensile rate of 1×10 -3 s, at least three alloy samples were selected for testing for each alloy composition. Figure 2 This is a typical room temperature tensile engineering stress-strain curve of alloy 3# in the example.

[0050] In the room temperature tensile test, alloys No. 1#, 2#, 3#, and 4# all exhibited a "double yield" phenomenon. Table 2 lists the room temperature mechanical properties of alloys No. 1#, 2#, 3#, and 4#.

[0051] Table 2 Room temperature mechanical properties of alloys No. 1#, 2#, 3#, and 4#

[0052]

[0053] Room temperature loading-unloading experiments

[0054] The specimens with the same size as those in the room temperature tensile test were subjected to a loading-unloading test on the Z20 universal material testing machine. The specimens were stretched to a certain deformation and then unloaded. The deformation of the specimen gauge section was recorded by an extensometer to obtain the recovery amount (recoverable strain) and calculate the recovery rate. The unloading curves of alloys No. 1#, 2#, 3#, and 4# at different deformation amounts are shown in Figure 2. Figure 3 As shown in Table 3, the superelastic properties of the alloy are listed.

[0055] Comprehensive Table 2, Table 3, Figure 2 and Figure 3 It can be seen that Alloy No. 3 exhibits the typical "double yield" phenomenon of superelastic alloys, that is, the alloy first yields at 222 MPa, and further deformation causes the transformation of the body-centered cubic β phase to the orthorhombic α" martensite phase. As shown in Table 3, the recovery rate of the alloy is greater than 90% when the deformation does not exceed 8%. When the deformation reaches 9%, the newly formed martensite rearranges and the alloy slips, resulting in the inability to recover some of the deformation after unloading, and the recovery rate decreases.

[0056] The results show that within the compositional system of the present invention, the yield strength of the alloy can be adjusted between 222 MPa and 550 MPa by adjusting the composition. Alloys 1#, 2#, 3#, and 4 all exhibit elongation exceeding 25%, and elastic moduli ranging from 34 to 46 GPa, approaching the elastic modulus of bone. The recovery strain rate after unloading at 8% strain remains above 80%, demonstrating excellent superelasticity and high strength. Furthermore, the elastic modulus of the alloys with appropriate Sn microalloying is as low as 34 GPa, significantly lower than that of alloys without Sn addition or those with higher Sn content. This indicates that appropriate Sn microalloying can simultaneously reduce the elastic modulus and enhance the superelasticity of the alloys, resulting in excellent superelasticity and high strength, which has important implications for applications in smart materials.

[0057] Table 3 Superelastic properties of alloys No. 1#, 2#, 3#, and 4# at different deformations

[0058]

[0059] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A titanium alloy having both low elastic modulus and high superelasticity, characterized in that: The element composition of the alloy is 42% to 48% zirconium, 7% to 10% niobium, 0.2% to 1.5% tin, and the balance is titanium. The alloy has a cast structure of body-centered cubic β phase, an initial tensile elastic modulus of 34-46 GPa, a tensile strength of 674-750 MPa, an induced martensitic transformation stress of 222-550 MPa, and a maximum recoverable strain of 6.48-7.7% at room temperature.

2. A method for preparing a titanium alloy having both low elastic modulus and high superelasticity as claimed in claim 1, characterized in that: The following steps are involved: Step 1, weighing raw materials: selecting zirconium raw materials, niobium raw materials, tin raw materials, and titanium raw materials according to the atomic percentages of the elemental components of the alloy and weighing and mixing them; Step 2, alloy smelting: placing the zirconium raw material, niobium raw material, tin raw material, and titanium raw material described in step 1 into a copper crucible in a vacuum non-consumable arc furnace, and smelting them multiple times to obtain the alloy with low elastic modulus and high superelasticity.

3. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The tin raw material is placed at the bottom of a copper crucible, the titanium raw material and the zirconium raw material are placed on top of the tin raw material, and the niobium raw material is placed on the top layer.

4. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The copper crucible is a water-cooled copper crucible, the alloy smelting process is carried out under the protection of argon gas, and the bottom of the water-cooled copper crucible is cooled by circulating cooling water.

5. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: Before the alloy is smelted, the vacuum non-consumable arc furnace is evacuated. When the vacuum degree reaches 5×10 -3 Pa, and then argon gas is introduced for washing to remove residual air, and finally the alloy is smelted under the protection of argon gas.

6. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The alloy is smelted at a current of 370 to 400 A, a voltage of 20 to 60 V, and a smelting time of 50 to 70 seconds.

7. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The multiple smelting is repeated smelting 5 to 7 times, and smelting again after each flip.

8. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The zirconium raw material, niobium raw material, tin raw material and titanium raw material are respectively industrial sponge zirconium, niobium block, tin block and sponge titanium with a purity exceeding 99.0wt%.

9. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 2, wherein: The alloy with low elastic modulus and high superelasticity obtained in step 2 is a button-shaped alloy ingot, and the button-shaped alloy ingot is cast to obtain a titanium alloy rod.

10. The method for preparing a titanium alloy having both low elastic modulus and high superelasticity according to claim 9, wherein: During the casting, the button-shaped alloy ingot is placed in a crucible cavity with a bottom pouring hole, a copper ingot mold is placed under the pouring hole, and a non-consumable electrode is used to scan and heat the button-shaped alloy ingot. The molten metal flows from the pouring hole into the copper ingot mold to obtain the titanium alloy rod.

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