Si-containing high-strength and low-modulus medical titanium alloy, and additive manufacturing method and use thereof

Abstract

The present invention relates to a Si-containing high-strength and low-modulus medical titanium alloy, and an additive manufacturing method and use thereof. The additive manufacturing method comprises alloy ingredient design, powder preparation, model construction and substrate preheating, and additive manufacturing molding; wherein the Si-containing high-strength and low-modulus medical titanium alloy is designed in the ingredient proportion of Ti 60-70 at. %, Nb 16-24 at. %, Zr 4-14 at. %, Ta 1-8 at. %, Si 0.1-5 at. %. The principle of the present invention is design of a medical ?-type titanium alloy having high-strength and low-modulus and good biocompatibility by using d-electron theory; reducing the difference of thermal expansion between the silicide and the ?-Ti phase by preheating, and at the same time, ensuring that there is a sufficient degree of cooling in the additive manufacturing process to promote the transition of the alloy from the divorced eutectic reaction to the precipitation reaction, thereby solving the common problems, such as the deterioration of mechanical properties caused by the continuous distribution of the Si-containing phase along the grain boundary and the cracking caused by the difference of thermal expansion coefficient between different phases.

Claims

1: An additive manufacturing method of a Si-containing high-strength and low-modulus medical titanium alloy, characterized by comprising the following steps: (1) Alloy Ingredient Design: 0.1-5 at. % bioactive element Si is added into a low elastic modulus TiNbTaZr-based alloy, then according to the d-electron theory, the average number of bonding times of the alloy Bo is calculated by $\stackrel{\_}{Bo}=\underset{i}{.Math.}{X}_i{?\left(\mathrm{Bo}\right)}_i,$ wherein (Bo) is the covalent bond energy determined by the d electronic cloud overlapping between the alloy element i and the matrix alloy element; the average d electron orbital energy level of the alloy Md is calculated by $\stackrel{\_}{Md}=\underset{i}{.Math.}{X}_i{?\left(Md\right)}_i,$ wherein (Md), is the average value of the M-d energy level of the alloy element i, i is the alloy element Nb and Ta, Xi is the atomic percentage of the alloy element i; according to the ?-Ti region of the Bo-Md relationship graph, the calculated values of Bo and Md are selected to fall in the meta-stable ?-Ti region of the Bo-Md relationship graph; then according to the TiZrSi ternary phase graph, the alloy ingredient range which is deviated from the eutectic point and close to the maximum solid solubility of Si in Ti is selected, so that the alloy ingredients of the Si-containing high-strength and low-modulus medical titanium alloy are formulated in the ingredient proportion of Ti 60-70 at. %, Nb 16-24 at. %, Zr 4-14 at. %, Ta 1-8 at. %, Si 0.1-5 at. %, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy, and elemental silicon, as raw materials; (2) Powder Preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents of step (1), melted by a Vacuum Arc Remelting furnace so as to prepare the alloy rods, the titanium alloy powders are prepared by Electrode Induction Melting Gas Atomization method (EIGA) or Plasma Rotating Electrode Processing method (PREP), and sieved so as to obtain the spherical powders having the range of particle sizes suitable for the additive manufacturing. (3) Model construction and substrate preheating: the three-dimensional model of the structural parts to be prepared is constructed, the slicing is completed and the print files are created, the preheating temperature of the substrate in the Selective Laser Melting is 150-650? C., and the preheating temperature of the substrate in the Selective Electron Beam Melting is 650-1200? C.; (4) Additive manufacturing molding: the additive manufacturing molding is carried out by a Selective Laser Melting apparatus or a Selective Electron Beam Melting apparatus so as to obtain a high-strength and low-modulus medical titanium alloy; wherein the key molding parameters are: 50%?melting channel overlapping rate ??80%, 1000 mm/s?scanning speed V?10000 mm/s; in the case of the Selective Laser Melting, the laser input power P is 140 W?P?360 W, the laser scanning pitch h is 20-80 ?m, and in the case of the Selective Electron Beam Melting, the electron gun current I is 8 mA?1?100 mA and the electron beam scanning pitch h is 20-200 ?m.

2: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (1), Bo=2.86?2.90, Md=2.45?2.47.

3: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (2), the Vacuum Arc Remelting process comprises: the formulated raw materials are pressed into an electrode, wherein the size of the electrode is controlled to be 50-70 mm less than that of the crucible; the gap between the electrode and the molten pool is controlled between 60-80 mm; the melting speed is 20 kg/min; the casting ingots are obtained by remelting twice, without significant ingredient precipitation.

4: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (2), the Electrode Induction Melting Gas Atomization method comprises: the melted casting ingots are machined into the bars of ?45 mm?550 mm, without significant surface oxidation, and one end of the bar is machined into a 45? cone, under inert gas atmosphere, at the atomization pressure of 3.5-4.5 MPa, the melting power of 20-30 KW, and the feeding rate of 35-45 mm/min.

5: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (2), the Plasma Rotating Electrode Processing method comprises: the melted casting ingots are machined into the bars of ?60 mm?650 mm, without significant surface oxidization, under inert gas atmosphere, at the atomization power of 50-60 KW, and the rotation speed of 16000-18000 r/min.

6: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (4), the overlapping rate is calculated by $?=\frac{w-h}{w}?100\%,$ wherein w is the width of the molten pool (?m); and h is the scanning pitch (?m).

7: The additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy according to claim 1, characterized in that: in step (4), the powder size suitable for Selective Laser Melting is 15-53 ?m; and the powder size suitable for Selective Electron Beam Melting is 45-100 ?m.

8: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 1, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

9: Use of the Si-containing high-strength and low-modulus medical titanium alloy according to claim 8 in the preparation of human body implants.

10: The use of the Si-containing high-strength and low-modulus medical titanium alloy in the preparation of human body implants according to claim 9, characterized in that the human body implants comprise femoral head implant, hip joint implant, knee joint implant, vertebral body fusion cage, intervertebral fusion cage, spinal implant, shoulder implant, mandible implant, cranial implant, craniomaxillofacial implant, foot ankle joint implant, toe bone implant or sternal implant.

11: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 2, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

12: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 3, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

13: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 4, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

14: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 5, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

15: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 6, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

16: A Si-containing high-strength and low-modulus medical titanium alloy, characterized in that it is prepared by the method according to claim 7, and the microstructure of the alloy comprises the columnar grains of ?-Ti and the equiaxed grains of ?-Ti as matrix, the intragranular uniformly distributed spherical (Ti, Zr).sub.2Si phase and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase as reinforcing phase, wherein the size of the ?-Ti grains is 1-13 ?m, and the size of the spherical (Ti, Zr).sub.2Si phase grains is 50-300 nm; and the grain boundary discontinuously distributed (Ti, Zr).sub.2Si phase is in a strip shape, with the width of 30-200 nm, and the aspect ratio of 1-6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is the Bo-Md relationship graph in Example 1 (Scripta Materialia 158 (2019) 62-65).

DETAILED DESCRIPTION OF THE INVENTION

[0036] For better understanding of the present invention, the present invention will be further described below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0037] The test methods of the following examples are as follows: the sample density is measured by Archimedes method; the tensile properties, such as the yield strength, the tensile strength and the strain at break of the sample are tested according to the international standard (Chinese GB/T 228-2002), the elastic modulus is tested according to the American Standard (ASTM E1876-15); and the biocompatibility is evaluated according to the international standard (GB/T 16886.5-2003).

Example 1

[0038] An additive manufacturing method of a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0039] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 68.3 at. %, Nb 23.3 at. %, Zr 4.7 at. %, Ta 1.7 at. %, and Si 2 at. %, wherein Bo=2.88, Md=2.46, which satisfy the meta-stable ?-Ti region in the Bo-Md relationship graph (the arrow position in FIG. 1, determined by Bo=2.88, Md=2.46), the atomic percentage content of the alloy can be determined by

[00005]$\stackrel{\_}{Bo}=\underset{i}{.Math.}{X}_i{?\left(\mathrm{Bo}\right)}_i\mathrm{and}\stackrel{\_}{Md}=\underset{i}{.Math.}{X}_i{?\left(Md\right)}_i,$ by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy (solid solution of niobium and tantalum), and elemental silicon as raw materials. FIG. 1 shows Bo-Md relationship graph (Scripta Materialia 158 (2019) 62-65), wherein the shaded portion is the meta-stable ?-Ti region.

[0040] Table 1 Bo and Md values for different alloy elements in bcc-Ti

TABLE-US-00001 electron orbital element Bo Md/eV 3d Ti 2.790 2.447 Zr 3.086 2.934 4d Nb 3.099 2.424 5d Ta 3.144 2.531 Si 2.561 2.200

[0041] Table 1 shows the Bo and Md values of each alloy element in bcc-Ti, which belong to the inherent properties of the alloy element itself and are obtained by calculation. The average number of bonding times Bo and the average d-orbital energy level Md of the alloy can be calculated from each alloy element, wherein the average number of bonding times of the alloy is calculated by

[00006]$\stackrel{\_}{Bo}=\underset{i}{.Math.}{X}_i{?\left(\mathrm{Bo}\right)}_i$

(i is the alloy element, for example, Nb and Ta, X.sub.i is the atomic percentage of the alloy element i, (Bo) is the covalent bond energy determined by the d-electronic cloud overlapping between the alloy element i and the matrix alloy element), and the average d-electron orbital energy level of the alloy is calculated by

[00007]$\stackrel{\_}{Md}=\underset{i}{.Math.}{X}_i{?\left(Md\right)}_i$

(i is the alloy element, for example, Nb and Ta, X.sub.i is the atomic percentage of the alloy element i, and (Md).sub.i is the average value of the M-d energy level of the alloy element i). The Bo-Md relationship graph shows the ranges of Bo and Md of various titanium alloy types (?, ?+?, ?+?, ?), which can be used as references for designing the meta-stable ?-type titanium alloy ingredients. The specific design method is as follows: according to the TiZrSi phase graph, the content which is away from the eutectic point of the ingredient and close to the maximum solid solubility of Si in Ti is selected, the atomic percentage of Si is 2%, then the contents of other alloy elements are determined from Bo=2.88, Md=2.46, wherein the ingredients of Example 1 are shown at the arrow position. [0042] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents in step (1), melted by a Vacuum Arc Remelting furnace at melting speed of 20 kg/min, remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round bars of ?45 mm?550 mm, and the surface oxide skins are removed. The alloy powders are prepared by Electrode Induction Melting Gas Atomization method (EIGA) under inert gas atmosphere, at the atomization pressure of 4.0 MPa, the melting power of 25 KW, and the feeding rate of 40 mm/min. Then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 15-53 ?m.

[0043] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is inputted into Magics 15.01 for setting the position and the printing directions. Then, the processed data are imported into the EOSRPtools software to perform slicing and generate the print files. Then, the substrate is leveled, and the titanium alloy powders with a thickness in the range of 50-100 ?m are previously uniformly laid on the Ti-6Al-4V substrate by a powder laying device. The molding chamber is vacuumized to less than 0.6 mbar by a vacuum pump, and Ar gas is charged into the molding chamber, until the oxygen content in the forming chamber is reduced to 0.1% or less. The preheating temperature of the substrate is 180? C. The preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, at the same time the thermal stress caused by the difference of thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible, so as to avoid cracking. [0044] (4) Additive manufacturing molding: the additive manufacturing molding is carried out by a selective laser melting apparatus, under the selective laser melting parameters of the overlapping rate of 50%, the laser scanning speed of 2200 mm/s, the laser power, P, of 250 W, the scanning pitch of 50 ?m, the powder thickness of 30 ?m, and the laser scanning strategy of 67?. The addition of the non-metallic element Si is beneficial to improve biocompatibility, but very easy to form the brittle phase continuously distributed along the grain boundary. The high cooling rate under high speed scanning is used to promote the transition of the alloy ingredients from the divorced eutectic reaction to the precipitation reaction, and in turn, suppress the formation of the brittle phase continuously distributed along the grain boundary and the generation of cracking, promote the intragranular diffusion and precipitation of the second phase, and at the same time, the high overlapping rate is used to compensate the defect of easy formation of holes due to high-speed scanning, thus preparing the titanium alloy sample having fine grain structure or even ultrafine grain structure.

[0045] In this example, the titanium alloy formed in step (4) has a density of up to 99.5%, which is nearly full density. The microstructure of the alloy is consisted of columnar grains of ?-Ti and equiaxed grains of ?-Ti and (Ti, Zr).sub.2Si phase, wherein the columnar grains of ?-Ti are epitaxially grown along the boundary of the molten pool, with the grain size of about 3-12 ?m; and the equiaxed grains of ?-Ti are mainly distributed at the periphery of the molten pool and at the boundary of the molten pool, with the grain size of 1-3 ?m. The (Ti, Zr).sub.2Si phase is mainly distributed in the intragranular form and the grain boundary form, wherein the intragranular (Ti, Zr).sub.2Si phase is mainly spherical, with the size of 50-200 nm; and the grain boundary (Ti, Zr).sub.2Si phase is mainly in the interrupted strip shape, with the width of 30-150 nm, and the aspect ratio of 1-4.

[0046] Although the addition of the bioactive element Si can achieve the purpose of refining grains and improving biocompatibility, the intermetallic compound (Ti, Zr).sub.2Si phase is readily continuously precipitated at the grain boundary, thus weakening the mechanical properties. The high speed scanning and the high overlapping rate are used to, on one hand, refine the grains, reduce the formation of holes and in turn improve the mechanical properties, and on the other hand, suppress the divorced eutectic reaction and promote the precipitation reaction, and in turn suppress the continuous precipitation of (Ti, Zr).sub.2Si at the grain boundary, thus achieving the effects of strengthening the solid solution and strengthening the second phase. Therefore, the medical titanium alloy excellent in mechanical compatibility and biocompatibility can be obtained only when the combination of high speed scanning and high overlapping rate is used.

[0047] The titanium alloy parts manufactured by using the high speed scanning method described in this example have the yield strength of up to 810 MPa, the tensile strength of 1120 MPa, the strain at break of 6.4%, and the elastic modulus of ?59 GPa. Compared with Ti-6Al-4V ELI (ASTM F136), the alloy of this example is slightly increased in the yield strength, increased in the tensile strength by 260 MPa, and decreased in the elastic modulus by 51 GPa. Compared with the medical ?-type titanium alloy Ti-13Nb-13Zr (ASTM F1713), the alloy of this example is increased in the yield strength by 85 MPa, increased in the tensile strength by 260 MPa, and decreased in the elastic modulus by 20 GPa. Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy in example 1 has higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect caused by the mismatching of the elastic modulus, and avoid the functional degradation and the body absorption of the original bone tissue caused by long-term implantation of human body, and the implanting failure resulted therefrom. In addition, the cell proliferation experiment of Example 1 shows that the absorbance (OD value) detected by the microplate reader at 1 day, 4 days and 7 days is 0.07, 0.8, 2.1, respectively, which is significantly superior to those in Ti-6Al-4V ELI (0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiments of Example 1 shows that the cell surviving number after 24 h (live cell staining area per unit area) is 15.3%, which is also higher than that of Ti-6Al-4V ELI (11.3%). Compared with Ti-6Al-4V ELI, the alloy of Example 1, which contains the bioactive element Si and does not contain the toxic elements such as Al and V, greatly promotes the cell proliferation and exhibits lower biotoxicity, therefore, has better mechanical compatibility and biocompatibility than those in the traditional medical titanium alloys.

Example 2

[0048] An additive manufacturing method of a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0049] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 68.3 at. %, Nb 23.3 at. %, Zr 4.7 at. %, Ta 1.7 at. %, and Si 2 at. %, wherein Bo=2.88, Md=2.46, which satisfy the meta-stable ?-Ti region in the Bo-Md relationship graph, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy, and elemental silicon as raw materials. [0050] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents in step (1), melted by a Vacuum Arc Remelting furnace at melting speed of 20 kg/min, remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round bars of ?60 mm?650 mm, and the surface oxide skins are removed. The alloy powders are prepared by Plasma Rotating Electrode Processing method (PREP) under inert gas atmosphere, with the atomization power of 55 KW, the rotation speed of 17000 r/min. Then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 45-100 ?m. [0051] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is input into Magics 15.01 for setting the position and the printing direction, then the processed data are imported into BuildAssembler software to perform slicing and generate the print files. The substrate is leveled, and the amount of powders in the powder boxes on both sides is adjusted. Then the molding chamber is vacuumized to less than 5?10.sup.?3 Pa by a vacuum pump. The substrate is preheated to 650? C. The preheating temperature of the substrate is 180? C. The preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, and the same time the thermal stress caused by the difference of the thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible so as to avoid cracking. [0052] (4) 3D printing molding: 3D printing molding is carried out by an selective electron beam melting apparatus, with the selective electron beam melting parameters of: the overlapping rate of 80%, the electron beam scanning speed of 4530 mm/s, the current I of 38 mA, the scanning pitch of 20 jam, the scanning strategy of 90?, and powder thickness of 50 ?m. The addition of the non-metallic element Si is beneficial to improve biocompatibility, but easy to form the brittle phase continuously distributed along the grain boundary. The high cooling rate under high speed scanning is used to promote the transition of the alloy ingredients from the divorced eutectic reaction to the precipitation reaction, and in turn, suppress the formation of the brittle phase continuously distributed along the grain boundary and the generation of cracking, promote the intragranular diffusion and precipitation of the second phase, and at the same time, the high overlap rate is used to compensate the defect of easy formation of holes due to high-speed scanning, thereby preparing the titanium alloy sample having fine grain structure or even ultrafine grain structure.

[0053] In this example, the titanium alloy formed under the above ranges of processing parameters has a density of up to 99.7%, which is a nearly full density. The phase composition of the titanium alloy comprises ?-Ti as a matrix, with the grain size of 1-9 ?m, which size is less than that in Example 1; the (Ti, Zr).sub.2Si phase mainly precipitated in intragranular form and grain boundary form, wherein the intragranular (Ti, Zr).sub.2Si phase is spherical, with the size of 50-150 nm; the grain boundary (Ti, Zr).sub.2Si phase is interruptedly distributed along the grain boundary, with the width of 30-100 nm, and the aspect ratio of 1-3. The titanium alloy in this example has the tensile strength of 1090 MPa, the yield strength of 790 MPa, the elastic modulus of ?57 GPa. Compared with Ti-6Al-4V ELI (ASTM F136), the medical titanium alloy prepared in this example is slightly increased in the yield strength, increased in the tensile strength by 230 MPa, and decreased in the elastic modulus by 53 GPa. Compared with the medical ?-type titanium alloy Ti-13Nb-13Zr (ASTM F1713), the alloy in this example is increased in the yield strength by 65 MPa, increased in the tensile strength by 230 MPa, and decreased in the elastic modulus by 22 GPa. In addition, the cell proliferation experiment of Example 2 shows that the absorbance (OD values) detected by the microplate reader at 1 day, 4 days and 7 days is 0.07, 0.8, 2.0, respectively, which is significantly superior to those in Ti-6Al-4V ELI (0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiment of Example 2 shows that the cell surviving number after 24 h (live cell staining area per unit area) is 15.1%, which is also higher than that in Ti-6Al-4V ELI (11.3%). Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy of Example 2 has higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect caused by the mismatching of the elastic modulus, avoid the functional degradation and body absorption of the original bone tissue caused by long-term implantation of the human body, and the implanting failure resulted therefrom, and at the same time, has significantly better biocompatibility than that of the traditional medical titanium alloy.

Example 3

[0054] An additive manufacturing method of a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0055] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 69.6 at. %, Nb 23.7 at. %, Zr 4.8 at. %, Ta 1.7 at. %, Si 0.1 at. %, wherein Bo=2.88, Md=2.47, which satisfy the meta-stable ?-Ti region in the Bo-Md relationship graph, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy as raw materials. [0056] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents in step (1), melted by a vacuum arc remelting furnace at melting speed of 20 kg/min, remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round bars of ?45 mm?550 mm, and the surface oxide shins are removed. The alloy powders are prepared by Electrode Induction Melting Gas Atomization (EIGA) under inert gas atmosphere, with the atomization pressure of 4.0 MPa, the melting power of 25 KW, and the feeding rate of 40 mm/min. Then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 15-53 ?m. [0057] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is inputted into Magics 15.01 for setting the position and the printing direction. Then, the processed data are imported into the EOSRPtools software to perform slicing and generate the print files. Then, the substrate is leveled, and the titanium alloy powders with a thickness in the range of 50-100 ?m are previously uniformly laid on the Ti-6Al-4V substrate by a powder laying device. The molding chamber is vacuumized to less than 0.6 mbar by a vacuum pump, and Ar gas is charged into the molding chamber, until the oxygen content in the molding chamber is reduced to 0.1% or less; The preheating temperature of the substrate is 180? C. The preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, and at the same time the thermal stress caused by the difference of the thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible, so as to avoid cracking. [0058] (4) Additive manufacturing molding: additive manufacturing molding is carried out by a selective laser melting apparatus, under the selective laser melting parameters of: the overlapping rate of 70%, the laser scanning speed of 3000 mm/s, the laser power, P, of 360 W, the scanning pitch of 40 ?m, the powder thickness of 40 ?m, and the laser scanning strategy of 67?. In the Example 3, although no Si element is added, the high overlapping rate and high scanning speed can be used to achieve the effects of refining grains as well, thereby improving the mechanical properties and biocompatibility of the alloy.

[0059] In this example, the titanium alloy formed in the above range of processing parameters has a density of up to 99.7%, which is nearly full density. The phase composition of the titanium alloy comprises the columnar grains of ?-Ti as a matrix, with the grain size of 2-13 ?m, the tensile strength of 932 MPa, the yield strength of 896 MPa, and the plasticity at break of 19%. Compared with the Ti-30Nb-5Ta-3Zr alloy prepared by SLM in Reference 1, since the grains are finer under high speed scanning, the medical titanium alloy prepared in this example is increased in the tensile strength by 252 MPa, increased in the yield strength by 232 MPa, increased in the plasticity by 3.7%, and decreased in the elastic modulus by 12 GPa. Compared with Ti-6Al-4V ELI (ASTM F136), the alloy in this example is reduced in the elastic modulus by 58 GPa. In addition, the cell proliferation experiment of Example 3 shows that the absorbance (OD value) detected by the microplate reader at 1 day, 4 days and 7 days is 0.06, 0.7, 1.8, respectively, which is slightly superior over that in Ti-6Al-4V ELI (0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiment of Example 3 shows that the cell surviving number after 24 h (live cell staining area per unit area) is 13.7%, which is also higher than that in Ti-6Al-4V ELI (11.3%). Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy of Example 3 has smaller grains, higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect caused by the mismatching of elastic modulus, and avoid the functional degradation and body absorption of the original bone tissue caused by long-term implantation of the human body, and the implantation failure resulted therefrom, and at the same time due to the absence of biotoxic elements such as Al and V, exhibits relatively good biocompatibility.

Example 4

[0060] An additive manufacturing method of a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0061] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 67 at. %, Nb 21.8 at. %, Zr 6 at. %, Ta 4.2 at. %, and Si 1 at. %, wherein Bo=2.86, Md=2.45, which satisfy the meta-stable ?-Ti region in the Bo-Md relationship graph, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy, and elemental silicon as raw materials. [0062] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents in step (1), melted by a Vacuum Arc Remelting furnace at melting speed of 20 kg/min, remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round bars of ?60 mm?650 mm, and the surface oxide skins are removed. The alloy powders are prepared by Plasma Rotating Electrode Processing method (PREP) under inert gas atmosphere, at the atomization power of 55 KW, the rotation speed of 17000 r/min. Then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 45?100 ?m. [0063] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is input into Magics 15.01 for setting the position and the printing direction, then the processed data are imported into BuildAssembler software to perform slicing and generate print files. Then the substrate is leveled, and the amount of powders in the powder boxes on both sides is adjusted. Then the molding chamber is vacuumized to less than 5?10.sup.?3 Pa by a vacuum pump, and the substrate is pre-heated to 650? C. The preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, and at the same time, the thermal stress caused by the difference in the thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible, so as to avoid cracking. [0064] (4) 3D printing molding: 3D printing molding is carried out by an Selective electron beam melting apparatus, under the selective electron beam melting parameters of: the overlapping rate of 50%, the electron beam scanning speed of 8000 mm/s, the current I of 56 mA, the scanning pitch of 60 jam, the scanning strategy of 90?, and the powder thickness of 50 ?m. The addition of the non-metallic element Si is beneficial to improve biocompatibility, but very easy to form the brittle phase continuously distributed along the grain boundary. The high cooling rate under high speed scanning is used to promote the transition of the alloy ingredients from the divorced eutectic reaction to the precipitation reaction, and in turn, suppress the formation of the brittle phase continuously distributed along the grain boundary and the generation of cracking, promote the intragranular diffusion and precipitation of the second phase, and at the same time, the high overlapping rate is used compensate the defect of easy formation of holes due to high-speed scanning, thereby preparing the titanium alloy sample having fine grain structure or even ultrafine grain structure.

[0065] In this example, the titanium alloy formed under the above range of processing parameters has a density of up to 99.7%, which is nearly full density. The phase composition of the alloy comprises ?-Ti as a matrix, with the grain size of 1-8 ?m, which size is less than that in Example 1; the (Ti, Zr).sub.2Si phase mainly precipitated in intragranular form and grain boundary form, wherein the intragranular (Ti, Zr).sub.2Si phase is spherical, with the size of 50-100 nm; and the grain boundary (Ti, Zr).sub.2Si phase is interruptedly distributed along the grain boundary, with the width of 30-100 nm, and the aspect ratio of 1-3. Compared with Ti-6Al-4V ELI (ASTM F136), the medical titanium alloy prepared in this example is comparable in the yield strength, increased in the tensile strength by 190 MPa, and decreased in the elastic modulus by 56 GPa. Compared with the medical ?-type titanium alloy Ti-13Nb-13Zr (ASTM F1713), the medical titanium alloy prepared in this example is increased in the yield strength by 50 MPa, increased in the tensile strength by 190 MPa, and decreased in the elastic modulus by 25 GPa. In addition, the cell proliferation experiment of Example 2 shows that the absorbance (OD value) detected by the microplate reader at 1 day, 4 days and 7 days is 0.07, 0.8, 1.9, respectively, which is significantly superior to those of Ti-6Al-4V ELI (i.e., 0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiment of Example 4 shows that the cell surviving number after 24 h (live cell staining area per unit area) is 14.2%, which is also higher than that in Ti-6Al-4V ELI (11.3%). Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy of Example 4 has higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect caused by the mismatching of the elastic modulus, and avoid the functional degradation and body absorption of the original bone tissue caused by long-term implantation of the human body and the implanting failure resulted therefrom, and has significantly better mechanically compatibility and biocompatibility than those in the traditional medical titanium alloys.

Example 5

[0066] An additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0067] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 67.6 at. %, Nb 23 at. %, Zr 4.7 at. %, Ta 1.7 at. %, and Si 3 at. %, wherein Bo=2.88, Md=2.46, which satisfy the meta-stable ?-Ti region of the Bo-Md relationship graph, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy, and elemental silicon as raw materials. [0068] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents of step (1), melted by a Vacuum Arc Remelting furnace at melting speed of 20 kg/min, remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round bars of ?45 mm?550 mm, and the surface oxide skins are removed. The alloy powders are prepared by Electrode Induction Melting Gas Atomization method (EIGA) under inert gas atmosphere, at the atomization pressure of 4.0 MPa, the melting power of 25 KW, and the feeding rate of 40 mm/min And then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 15-53 ?m. [0069] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is inputted into Magics 15.01 for setting the position and the printing direction. Then, the processed data are imported into the EOSRPtools software to perform slicing and generate the print files. Then, the substrate is leveled, and the titanium alloy powders with a thickness in the range of 50-100 ?m are previously uniformly laid on the Ti-6Al-4V substrate by a powder laying device. The molding chamber is vacuumized to less than 0.6 mbar by a vacuum pump, and Ar gas is charged into the molding chamber, until the oxygen content in the molding chamber is reduced to 0.1% or less. The preheating temperature of the substrate is 180? C. The preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, at the same time, the thermal stress caused by the difference in the thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible, so as to avoid cracking. [0070] (4) Additive manufacturing molding: additive manufacturing molding is carried out by a Selective Laser Melting apparatus, under the Selective Laser Melting parameters of: the overlapping rate of 60%, the laser scanning speed of 2200 mm/s, the laser power, P, of 250 W, the scanning pitch of 40 ?m, the powder thickness of 30 ?m, and the laser scanning strategy of 67?. The addition of the non-metallic element Si is beneficial to improve biocompatibility, but very easy to form the brittle phase continuously distributed along the grain boundary. The high cooling rate under high speed scanning is used to promote the transition of the alloy ingredients from the divorced eutectic reaction to the precipitation reaction, and in turn, suppress the formation of the brittle phase continuously distributed along the grain boundary and the generation of cracking, promote the intragranular diffusion and precipitation of the second phase, and at the same time, the high overlapping rate is used to compensate the defect of easy formation of holes due to high-speed scanning, thereby preparing the titanium alloy sample having fine grain structure or even ultrafine grain structure.

[0071] In this example, the titanium alloy formed in the above range of processing parameters has a density of up to 99.6%, which is nearly full density. The phase composition of the alloy comprises ?-Ti as a matrix, with the grain size of 1-8 ?m, which size is less than that in Example 1; the (Ti, Zr).sub.2Si phase mainly precipitated in the intragranular form and the grain boundary form, wherein the intragranular (Ti, Zr).sub.2Si phase is spherical, with the size of 50-300 nm; and the grain boundary (Ti, Zr).sub.2Si phase is interruptedly distributed along the grain boundary, with the width of 50-200 nm, and the aspect ratio of 1-3. Compared with Ti-6Al-4V ELI (ASTM F136), the medical titanium alloy prepared in this example is increased in the yield strength by 30 MPa, increased in the tensile strength by 290 MPa, and decreased in the elastic modulus by 46 GPa. Compared with the medical ?-type titanium alloy Ti-13Nb-13Zr (ASTM F1713), the medical titanium alloy prepared in this example is increased in the yield strength by 105 MPa, increased in the tensile strength by 290 MPa, and decreased in the elastic modulus by 15 GPa. In addition, the cell proliferation experiment of Example 2 shows that the absorbance (OD value) detected by the microplate reader at 1 day, 4 days and 7 days is 0.07, 0.9, 2.3, respectively, which is significantly superior to those in Ti-6Al-4V ELI (0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiment of Example 5 shows that the cell surviving number after 24 h (live cell staining area per unit area) is 15.6%, which is also higher than that in Ti-6Al-4V ELI (11.3%). Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy in Example 5 has higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect due to the mismatching of the elastic modulus, avoid the functional degradation and body absorption of the original bone tissue caused by long-term implantation of the human body, and the implanting failure resulted therefrom, and has significantly better mechanically compatibility and biocompatibility than those in the traditional medical titanium alloy.

Example 6

[0072] An additive manufacturing method for a Si-containing high-strength and low-modulus medical titanium alloy, comprising the following steps: [0073] (1) Alloy Ingredient Design: the alloy ingredients are formulated in the ingredient proportion of Ti 60 at. %, Nb 20.6 at. %, Zr 5 at. %, Ta 9.4 at. %, and Si 5 at. %, where Bo=2.9, Md=2.47, which satisfy the meta-stable ?-Ti region of the Bo-Md relationship graph, by using sponge titanium, sponge zirconium, tantalum niobium intermediate alloy, and elemental silicon as raw materials. [0074] (2) Powder preparation: the elements Ti, Nb, Zr, Ta and Si are compounded according to the contents in step (1), melted by a Vacuum Arc Remelting furnace, with the melting speed of 20 kg/min, and remelted twice so as to obtain the casting ingots without significant ingredient precipitation. The metal ingots are machined into the round rods of ?60 mm?650 mm, and the surface oxide skins are removed. The alloy powders are prepared by Plasma Rotating Electrode Processing method (PREP) under inert gas atmosphere, with the atomization power of 55 KW, the rotation speed of 17000 r/min. Then the resulting powders are subjected to airflow classification and screening treatment, so as to obtain the powders having particle size in the range of 45-100 ?m. [0075] (3) Model construction and substrate preheating: the cuboid structure of 50?10?10 is constructed. The constructed cuboid structure is input into Magics 15.01 for setting the position and the printing direction, then the processed data are imported into BuildAssembler software to perform slicing and generate the print files. Then the substrate is leveled, and the amount of powders in the powder boxes on both sides is adjusted. Then the molding chamber is vacuumized to below 5?10 Pa by a vacuum pump. The substrate is preheated to 1200? C., wherein the preheating temperature is selected to ensure that there is a sufficiently high degree of undercooling in the precipitation reaction, and at the same time, the thermal stress caused by the difference in the thermal expansion coefficient between the second phase and the matrix phase is reduced as much as possible, so as to avoid cracking. [0076] (4) 3D printing molding: 3D printing molding is carried out by an Selective electron beam melting apparatus, with the Selective electron beam melting parameters of: the overlapping rate of 70%, the electron beam scanning speed of 1000 mm/s, the current I of 64 mA, the scanning pitch of 40 jam, the scanning strategy of 90?, and the powder thickness of 50 ?m. The addition of the non-metallic element Si is beneficial to improve biocompatibility, but very easy to form the brittle phase continuously distributed along the grain boundary. The high cooling rate under high speed scanning is used to promote the transition of the alloy ingredients from the divorced eutectic reaction to the precipitation reaction, and in turn, suppress the formation of the brittle phase continuously distributed along the grain boundary and the generation of cracking, promote the intragranular diffusion and precipitation of the second phase, and at the same time, the high overlapping rate is used to compensate the defect of easy formation of holes due to high-speed scanning, thereby preparing the titanium alloy sample having fine grain structure or even ultrafine grain structure.

[0077] In this example, the titanium alloy formed in the above range of processing parameters has a density of up to 99.7%, which is nearly full density. The phase composition of the titanium alloy comprises ?-Ti as a matrix, with the grain size of 1-7 ?m, which size is less than that in Example 1; the (Ti, Zr).sub.2Si phase mainly precipitated in the intragranular form and the grain boundary form, wherein the intragranular (Ti, Zr).sub.2Si phase is spherical, with the size of 50-200 nm; the grain boundary (Ti, Zr).sub.2Si phase is interruptedly distributed along the grain boundary, with the width of 30-150 nm, and the aspect ratio of 1-6. Compared with Ti-6Al-4V ELI (ASTM F136), the medical titanium alloy prepared in this example is increased in the yield strength by 45 MPa, increased in the tensile strength by 320 MPa, and decreased in the elastic modulus by 41 GPa. Compared with the medical ?-type titanium alloy Ti-13Nb-13Zr (ASTM F1713), the medical titanium alloy prepared in this example is increased in the yield strength by 120 MPa, increased in the tensile strength by 320 MPa, and decreased in the elastic modulus by 10 GPa. In addition, the cell proliferation experiment of Example 2 shows that the absorbance (OD value) detected by the microplate reader at 1 day, 4 days and 7 days is 0.07, 0.9, 2.3, respectively, which is significantly superior to those in Ti-6Al-4V ELI (0.04, 0.6 and 1.6). Meanwhile, the cytotoxicity experiment of Example 6 shows that the cells surviving number after 24 h (live cell staining area per unit area) is 16.7%, which is also higher than that in Ti-6Al-4V ELI (11.3%). Obviously, compared with the medical titanium alloy implant of the current clinical application, the alloy in Example 6 has higher strength and lower elastic modulus, which can effectively reduce the stress shielding effect caused by the mismatching of the elastic modulus, avoid the functional degradation and body absorption of the original bone tissue caused by long-term implantation of the human body, and implanting failure resulted therefrom, and has significantly better mechanically compatibility and biocompatibility than those in the traditional medical titanium alloy.

[0078] It should be noted that the above examples do not constitute limitations on the scope of protection of the present invention, and equivalent replacements or changes are made according to the technical solutions of the present invention and the inventive concepts thereof, which all belong to the scope of protection of the present invention.