Patent Application
20250084506
The present invention generally relates to the field of material science. more specifically, the present invention provides an ultra-strong and ductile multifunctional titanium alloy and methods for preparing the same.
Titanium alloys are promising materials used in multi-domain applications. As featured by high specific strength, titanium alloys such as the typical Ti-6Al-4V (TC4) have specific advantages in the aerospace and automotive industries1. For biological applications, titanium alloys with a low elastic modulus and high corrosion resistance are highly desirable as biomedical materials, such as surgical implants2. Recently, biomedical titanium alloys containing non-toxic elements and exhibiting higher biocompatibility have garnered significant interest. To function as smart or functional materials, titanium alloys can be engineered, such as the conventional Ti—Ni or metastable β-Ti alloys, to exhibit shape memory effects or pseudoelasticity3,4.
To achieve superior mechanical performance, a key focus in the development of titanium alloys lies in enhancing their plastic behavior. In order to address the inadequate work hardening observed in many titanium alloys, notably TC4, alternative deformation mechanisms like twinning- or transformation-induced plasticity (TWIP/TRIP) present in metastable titanium alloys have garnered significant attention5,6. However, the elevation of the work hardening rate in TRIP/TWIP alloys is commonly accompanied by a reduction in yield strength, specifically the stress level required to initiate mechanical twinning or martensitic transformation. Consequently, the equilibrium between yield strength and strain hardening remains a prominent topic of interest in the recent and forthcoming research endeavors7.
In a medical field, researchers are actively exploring alternatives to surgical implants made from commercial titanium alloys due to growing concerns about the presence of toxic and allergenic elements in these materials. The demand for biocompatible titanium alloys has led to the development of β-Ti alloys such as Ti—Nb and Ti—Nb—Zr, challenging the TC4 and Ti—Ni implants that are most commercial but dangerous once corrupted8,9. However, these β-Ti alloys have limited strength and are thereby unsuitable for multi-environment applications. Similar limitations are also evident in titanium alloys used for smart functional materials, impeding their broader application across various scenarios.
Consequently, designing a titanium alloy capable of meeting the requirements of these diverse applications is a complex task, demanding the harmonious integration of superior strength, biocompatibility, and functional properties.
Accordingly, the present invention aims to address the challenges associated with existing β-Ti alloys.
In a first aspect, the present invention provides an ultra-strong and ductile multifunctional titanium alloy made from two or more metal elements. The titanium alloy has a molecular formula of TiaZrbHfcNbdSne, a, b, c, d, and e represent atomic percentages of the metal elements, falling within the ranges of 45≤a≤55, 36≤b≤43,3≤c≤6, 3.5≤d≤7.5, and 1.5≤e≤3. The titanium alloy exhibits an initial microstructure characterized by an equiaxed ultra-fine grain (UFG) structure, which is reinforced by hierarchical nanostructures formed during subsequent deformation.
In accordance with one embodiment, the titanium alloy includes 48 at. % of Ti, 39 at. % of Zr, 4.5 at. % of Hf, 6.3 at. % of Nb, and 2.2 at. % of Sn.
In accordance with one embodiment, the hierarchical nanostructures include nanotwins, and wherein one or more nanobands are confined within the nanotwins.
In accordance with one embodiment, the UFG structure has an average size of 300 nm to 2 μm.
In accordance with one embodiment, the titanium alloy demonstrates a tensile strength of approximately 1.75 GPa, coupled with a uniform elongation of at least 20%.
In accordance with one embodiment, the titanium alloy endures over 1000 fatigue cycles under a constant tensile stress of 1.4 GPa.
In accordance with one embodiment, the titanium alloy exhibits an almost-complete recovery from deformation ranging between 4% and 5%.
In accordance with one embodiment, the titanium alloy achieves a maximum recoverable strain of approximately 7%.
In a second aspect, the present invention provides a method for preparing an ultra-strong and ductile multifunctional titanium alloy sheet, including weighing at least two raw materials with a purity higher than 95%, wherein the at least two raw materials comprise Ti, Zr, Hf, Nb, and Sn; melting the at least two raw materials through arc melting under a pure argon atmosphere to obtain a molten alloy; drop casting the molten alloy into a water-cooled copper mold; cold rolling the as-cast alloy to achieve a thickness reduction ranging from 97% to 99% to obtain a cold-rolled alloy sheet; wrapping the cold-rolled alloy sheet in an iron sheet and annealed between 800° C. to 900° C. for an annealing time under a continuous flow of argon atmosphere, followed by air cooling to obtain the titanium alloy sheet.
In accordance with one embodiment, the titanium alloy containing the at least two raw materials has a molecular formula of TiaZrbHfcNbdSne, and wherein a, b, c, d, and e represent atomic percentages of the metal elements, falling within the ranges of 45≤a≤55, 36≤b≤43, 3≤c≤6, 3.5≤d≤7.5, and 1.5≤e≤3.
In accordance with one embodiment, the step of melting the at least two raw materials through arc melting under a pure argon atmosphere to obtain a molten alloy includes a series of melting and remelting processes, amounting to a total of 7-8 cycles.
In accordance with one embodiment, the annealing time is between 20 seconds to 20 minutes. When the annealing time is in a range of 25 to 45 seconds, the titanium alloy demonstrates a tensile strength of approximately 1.75 GPa, coupled with a uniform elongation of at least 20%. When the annealing time is in a range of 45 to 75 seconds, the titanium alloy demonstrates a tensile strength of approximately 1.5 GPa, coupled with a uniform elongation of at least 15%. When the annealing time is in a range of 12 to 20 minutes, the titanium alloy demonstrates a tensile strength of approximately 1.2 GPa, coupled with a uniform elongation of at least 17%.
The current invention offers a β-Ti alloy sheet composed of non-toxic elements, resulting in enhanced biocompatibility. This alloy sheet features an equiaxed ultra-fine grain (UFG) structure fortified by hierarchical nanostructures formed during deformation. The alloy is initially reinforced by its UFG structure, resulting in a first yielding point of approximately 1.36 GPa. Subsequently, this initial yielding is followed by a reversible TRIP effect, which contributes to significant strain hardening and the large pseudoelasticity of approximately 7% upon loading. Further deformation gives rise to the formation of nanotwins, with the nanobands being confined within them. This ongoing process continuously enhances strain hardening, ultimately resulting in an exceptional tensile strength of around 1.75 GPa, coupled with a uniform elongation of at least 20%.
Compared to the existing technology, the present inventions offer significant advantages, which include:
Embodiments of the present invention are described in more detail hereinafter with reference to the drawings, in which:
The present invention will be described in detail through the following embodiments with appending drawings. It should be understood that the specific embodiments are provided for an illustrative purpose only, and should not be interpreted in a limiting manner. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.
The invention includes all such variation and modifications. The invention also includes all of the steps and features referred to or indicated in the specification, individually or collectively, and any and all combinations or any two or more of the steps or features. Other aspects and advantages of the invention will be apparent to those skilled in the art from a review of the ensuing description.
It might draw upon potential candidates from recently developed gum metals and Ti—Nb—Ta—Zr (TNTZ) alloys, which showcase high yield strength nearing 1.2 GPa and a relatively low elastic modulus. It could also derive inspiration from the realm of metastable titanium high-entropy alloys, which possess functional properties originating from the reversible TRIP effect.
Accordingly, the present invention provides an ultra-strong and ductile multifunctional titanium alloy made from two or more metal elements. The titanium alloy has a molecular formula of TiaZrbHfcNbdSne, a, b, c, d, and e represent atomic percentages of the metal elements, falling within the ranges of 45≤a≤55, 36≤b≤43,3≤c≤6, 3.5≤d≤7.5, and 1.5≤e≤3. The titanium alloy exhibits an initial microstructure characterized by an equiaxed ultra-fine grain (UFG) structure, which is reinforced by hierarchical nanostructures formed during subsequent deformation.
Preferably, the titanium alloy comprises 48 at. % of Ti, 39 at. % of Zr, 4.5 at. % of Hf, 6.3 at. % of Nb, and 2.2 at. % of Sn.
The present invention features an ultra-fine grain structure capable of undergoing a reversible Transformation-Induced Plasticity (TRIP) effect and being reinforced by hierarchical nanostructures during deformation. The hierarchical nanostructures may be nanotwins, and one or more nanobands are confined within the nanotwins. Furthermore, the alloy offers additional advantages due to its competitive corrosion resistance, coupled with compositions carefully chosen from non-toxic elements.
In another embodiments, the TRIP effect, along with other subsequent strengthening mechanisms, should be capable of occurring within the UFG structure.
In one of the embodiments, the UFG structure has an average size of 300 nm to 2 μm. When the annealing time is in a range of 25 to 45 seconds, the UFG structure has an average size of 400 nm. When the annealing time is in a range of 45 to 75 seconds, the UFG structure has an average size of 1.7 μm.
Strengthened by a reversible transformation-induced plasticity (TRIP) effect in an early stages of deformation, the alloy displays pseudoelasticity at lower levels of deformation, allowing it to recover from a strain of approximately 5% and extend to around 7% under more substantial deformations. In particular, the recoverable strain (RS) of sample prepared in Example 1 achieves a maximum recoverable strain of approximately 7%. The RS of sample 2 is approximately 5.6%. The RS of sample 3 is approximately 4.3%.
In one of the embodiments, the alloy endured over one thousand fatigue cycles under a constant tensile stress of 1.4 GPa.
In one of the embodiments, the alloy contained non-toxic elements and exhibited corrosion resistance comparable to that of the commercial TC4 alloy.
In another aspect, the present invention provides a method for preparing an ultra-strong and ductile multifunctional titanium alloy sheet, including weighing at least two raw materials with a purity higher than 95%, wherein the at least two raw materials comprise Ti, Zr, Hf, Nb, and Sn; melting the at least two raw materials through arc melting under a pure argon atmosphere to obtain a molten alloy; drop casting the molten alloy into a water-cooled copper mold; cold rolling the as-cast alloy to achieve a thickness reduction ranging from 97% to 99% to obtain a cold-rolled alloy sheet; wrapping the cold-rolled alloy sheet in an iron sheet and annealed between 800° C. to 900° C. for an annealing time under a continuous flow of argon atmosphere, followed by air cooling to obtain the titanium alloy sheet.
In one of the embodiments, the step of melting the at least two raw materials through arc melting under a pure argon atmosphere to obtain a molten alloy contains a series of melting and remelting processes, amounting to a total of 7-8 cycles.
In one of the embodiments, the annealing time is between 20 seconds to 20 minutes. when the annealing time is in a range of 25 to 45 seconds, the titanium alloy demonstrates a tensile strength of approximately 1.75 GPa, coupled with a uniform elongation of at least 20%.
In another embodiment, when the annealing time is in a range of 45 to 75 seconds, the titanium alloy demonstrates a tensile strength of approximately 1.5 GPa, coupled with a uniform elongation of at least 15%. For example, the titanium alloy demonstrates a tensile strength of approximately 1.5 GPa, coupled with a uniform elongation of 18%.
In yet another embodiment, when the annealing time is in a range of 12 to 20 minutes, the titanium alloy demonstrates a tensile strength of approximately 1.2 GPa, coupled with a uniform elongation of at least 17%. For example, the titanium alloy demonstrates a tensile strength of approximately 1.2 GPa, coupled with a uniform elongation of 17.3%.
The following examples illustrate the present invention and are not intended to limit the same.
In this example, the designed β-Ti alloy (referred to as TiZrHfNbSn), with the composition specified in Table 1, was manufactured using high-purity raw materials through arc melting under a pure argon atmosphere. The alloy underwent a series of melting and remelting processes, totaling 7-8 cycles, to ensure chemical homogeneity, followed by a dropped cast into a water-cooled copper mold featuring a cross-sectional area of 10×10 mm2. The as-cast alloy underwent cold rolling until the thickness reduction reached approximately 99%, without undergoing any intermediate annealing steps. The cold-rolled alloy sheet was then wrapped in an iron sheet and annealed at 800° C. for recrystallization, followed by air cooling. The flowing argon atmosphere was provided to prevent oxidation during annealing.
The initial microstructure was highly sensitive to annealing time, which exerted a significant influence on the mechanical and functional performance. In this example, three different samples (sample 1, sample 2 and sample 3) were prepared based on varying annealing times. The annealing time was set as 30 seconds, 45 seconds, and 15 minutes, for samples 1 to 3, respectively.
In sample 1, the annealing time was 25-45 seconds, and the sample exhibited an average grain size of approximately 400 nm. The ultimate tensile strength (UTS), uniform elongation (UE) and recoverable strain (RS) of sample 1 were 1.75 GPa, 20% and 7.0%, respectively.
In sample 2, the annealing time was 45-75 seconds, and the sample exhibited an average grain size of approximately 1.7 μm. The UTS, UE and RS of sample 2 were 1.55 GPa, 18% and 5.6%, respectively.
In sample 3, the annealing time was 12-20 minutes, and the sample exhibited an average grain size of approximately 31 μm. The UTS, UE and RS of sample 3 were 1.20 GPa, 17.3% and 4.3%, respectively.
The microstructures were characterized by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The fundamental principle of EBSD is that when an electron beam strikes the material's surface, the electrons scattered back will have specific energy and directional distributions, which depend on the material's crystal structure and lattice orientation. By detecting these backscattered electrons, crystallographic information about the material can be obtained. EBSD technology is employed to collect and analyze diffraction patterns, allowing for the inference of properties like crystal orientation, grain boundary distribution, grain size, and crystal deformation.
The alloy sheet used for the EBSD test was electropolished until the surface became mirror-bright. The solution for electropolishing was HNO3:Methanol (1:4), where the voltage was set to 25 V and the temperature was kept below −40° C. The EBSD test was conducted by the FEI Scios microscope equipped with an EDAX Velocity camera, at an accelerating voltage of 20 kV and current of 13 nA.
The TEM sample was initially prepared through mechanical grinding and polishing, resulting in a thickness of approximately 30 μm. Subsequently, a disc with a diameter of 3 mm (@3 mm) was extracted from the sheet and underwent further thinning until a thickness of electron transparency by the precision ion polishing system (PIPS II, Model 695, Gatan). The milling temperature was maintained at −100° C. to preserve the metastable or deformation microstructure. The TEM analysis was conducted using the JEOL-2100F microscope operating at 200 kV.
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Flat dog-bone-shaped tensile samples with gauge dimension of 12.5×3.2×0.1 mm3 were cut from the alloy sheet by the ProtoMAX Abrasive Waterjet Cutter machine. The tensile tests were conducted on the Instron Series 3382 Universal Testing Machine at room temperature. For the mechanical property test, the sample was stretched until fracture with a strain rate of 0.001 s−1. The functional property was examined by the cyclic load-unload-reload (LUR) test at a strain rate of 0.001 s−1, where the strain increases by 1% in each cycle until reaching 8%. In addition, individual tensile tests were also conducted with different pre-strain ranging from 1%-10%. The fatigue test was conducted with a strain rate of 0.002 s−2, using the LUR test with a constant applied stress of 1.4 GPa.
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As sample 1 exhibited superior mechanical performance compared to the other two, its microstructure during deformation was of significant interest and was therefore thoroughly investigated to delve into the underlying mechanism.
The TEM characterization at strain of 10%, 15%, and fracture were carried out to investigate the microstructural evolution. Commencing with a 10% strain was motivated by the reinforcement of the initial plastic behavior through the reversible β α″ martensitic transformation. Insufficient deformation below 10% would fail to adequately stabilize the α″ phase via dislocation activity.
Further investigation was carried out, with a focus on the nanobands confined within the individual α″ twins. Although the nanobands exhibited different contrast (
Since the plastic behavior of the TiZrHfNbSn alloy was strengthened by the reversible TRIP effect in the early stages of deformation, pseudoelasticity was consequently anticipated, in addition to the real elasticity upon unloading. Therefore, cyclic tensile tests were carried out for samples 1-3.
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To examine the functional stability, a tensile fatigue test was conducted with a constant applied stress of 1.4 GPa (
The as-cast alloy was cold-rolled to achieve an appropriate thickness of 0.8 mm to 1.0 mm. Subsequently, it underwent recrystallization at a temperature of 800° C. for a duration of one minute. A cylinder with a diameter of @12 mm was then cut from the alloy sheet using the ProtoMAX Abrasive Waterjet Cutter machine.
The surface of the cylinder, which was to undergo an electrochemical test, was mechanically ground and polished to ensure surface roughness. For comparison, a commercial TC4 alloy was provided and subjected to the same pretreatment. The electrochemical test was conducted in the Simulated Body Fluid (SBF) solution at 37° C. and pH 7.4 using the CHI 760E. The electrochemical cell was a standard three-electrode device equipped with a platinum sheet as a counter electrode (CE), a saturated calomel electrode as reference electrode (SCE), and the alloy as working electrode (WE). The exposed area of WE was 1 cm2. Prior to conducting the test, the WE was immersed in the SBF for 2 hours to reach a steady state for open-circuit potential (OCP).
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In summary, the present invention develops a metastable titanium alloy capable of multifunctional use. The initial microstructure is characterized by an equiaxed UFG structure, which is further reinforced by hierarchical nanostructures during deformation. The alloy in the present invention possesses an ultra-high strength and pseudoelasticity, indicating its capability to absorb high energy. The alloy demonstrates continuous strain hardening, resulting in a high tensile strength of approximately 1.75 GPa and a ductility exceeding 20%. Strengthened by a reversible transformation-induced plasticity (TRIP) effect in the early stages of deformation, the alloy displays pseudoelasticity at lower levels of deformation, with a maximum recoverable strain reaching 7%. Regarding the biocompatibility, the alloy shows an electrochemical corrosion resistance comparable to that of the Ti-6Al-4V in the simulated body fluid (SBF) environment.
Combined with its resistance to high-stress fatigue testing, the alloy is expected to be used as advanced damping devices and shock or vibration absorbers in aerospace or automotive industries. In biomedical applications, the alloy can serve as stent grafts, orthodontic, and orthopedic implants. With its absence of toxic elements and demonstrated competitive corrosion resistance, this alloy could emerge as a robust contender against the commercial biomedical TC4 and Ti—Ni alloys.
The present invention has potential applications in the biomedical, aerospace, and automotive fields. In biomedical applications, it can serve as a biological implant that is safer and more biocompatible compared to existing titanium alloy implants. As a result, the alloy could emerge as a strong competitor against commercial biomedical β-Ti alloys and Ti—Ni SMAs.
For aerospace and automotive applications, its ultra-high strength, pseudoelasticity, and fatigue resistance allow it to be used as damping devices, shock absorbers, and vibration dampeners. Therefore, it can serve as a new and advanced functional material in areas with challenging and harsh conditions.
Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.
Furthermore, throughout the specification and claims, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
As used herein and not otherwise defined, the terms “substantially,” “substantial,” “approximately” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can encompass instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.
In the methods of preparation described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately.
“TRIP effect” refers to a phenomenon in materials science where the deformation and mechanical properties of a material change due to a phase transformation that occurs during plastic deformation. In the context of alloys, such as certain steels, when they undergo plastic deformation, a phase transformation from one crystal structure to another can occur, leading to enhanced ductility, strain hardening, and energy absorption capabilities.
“TC4” refers to a type of titanium alloy, commonly known as the Ti-6Al-4V alloy. This alloy is a combination of titanium and aluminum, containing 6% aluminum and 4% vanadium. It possesses high strength and excellent corrosion resistance, often used in aerospace and medical device applications.
Other definitions for selected terms used herein may be found within the detailed description of the present invention and apply throughout. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the present invention belongs.
It will be appreciated by those skilled in the art, in view of these teachings, that alternative embodiments may be implemented without undue experimentation or deviation from the spirit or scope of the invention, as set forth in the appended claims. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.
