The present invention relates to a multi-component system alloy, a biocompatible material comprising the alloy, and a method of producing the alloy, in particular, the present invention relates to a multi-component system alloy having high strength and high ductility, and a biocompatible material comprising the alloy and a method of producing the alloy.
In order to respond to a wide variety of applications, so far, the goal is to improve the existing alloy base in order to improve the high functionality of metal materials. For example, high-strength materials have been developed, ranging from metal materials for biological use such as bone implants to metal materials requiring durability such as chemical plants.
On the other hand, conventional alloys are predominantly composed of a single element as the main alloying element, but recently, multi-element system alloys such as hydrogen absorbing alloys (hydrogen storage alloys) have also been developed. For example, a hydrogen absorbing alloy (a hydrogen storage alloy) represented by the general formula: TixVyMzNi1-x-y-z (M is at least one element selected from the group consisting of Al, Mn and Zn, 0.2≦ x ≦ 0.4, 0.3≦ y < 0.7, 0.1 ≦ z ≦ 0.3, 0.6 < x+y+z ≦ 0.95), and the main component of the alloy phase being a body-centered cubic structure, is known (Patent literature 1).
Patent literature 1 : JP 09-053136 A
However, in the prior art including the above-mentioned alloys, there was a limit to the alloy properties in order to respond to a wide variety of uses. This is because in alloy design, in general, there are relatively many alloys that consist of a system containing a single element, or two elements as major elements, and other elements in small amounts, thus there are problems such as not being able to dramatically improve the properties of existing alloys.
For example, in Japan, which has become a super-aging society, the development of highly functional metal materials for biomedical use in bones is demanded along with the increasing importance of bone implants. Currently, titanium and titanium alloys are used as metal materials for biomedical applications from the viewpoint of mechanical reliability and biocompatibility. However, in addition to the required mechanical functions, there are many hurdles for in vivo use represented by biocompatibility. Therefore, in order to further improve the mechanical functions of biomedical metal materials, it is difficult to make significant improvements based on existing alloys, and we are facing a situation where the development of alloys based on completely new design concepts is required.
Further, materials and parts used in chemical plants, oil wells, gas well drilling equipment, etc. are required to have higher strength and corrosion resistance because they are used in environments exposed to strong corrosive gases. For these reasons, the development of new alloys with higher strength has been desired.
Therefore, an object of the present invention is to provide a multi-component system alloy having high strength and high ductility.
In order to achieve the above object, the inventors have made intensive research on various compositions in order to express the entropy effect of the configuration (configurational entropy effect) that does not appear in conventional alloys. As a result, the present inventors have found the alloy composed of multi-component system of the present invention.
That is, an alloy composed of multi-component system is characterized in that the alloy contains titanium, zirconium, niobium, molybdenum, and tantalum, and further the multi-component system alloy contains at least one selected from the group consisting of hafnium, tungsten, vanadium, and chromium, wherein the alloy satisfies Mo equivalent ≧ 13.5, and the alloy is a single-phase solid solution, a two-phase solid solution, or an alloy in which main phase is a solid solution phase.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy contains titanium, zirconium, niobium, molybdenum, tantalum, and hafnium.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy satisfies a VEC value (valence electron concentration value) ≦ 4.7.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy comprises a BCC structure (mainly BCC phases).
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy is represented by a general formula:
wherein in the general formula; 57.2 ≦ X ≦ 85.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy is represented by a general formula:
wherein in the general formula, 57.2≦X≦85 and 12.8≦Y≦33.3.
Further, a biocompatible material of the present invention is characterized by comprising the alloy of the present invention.
Further, a method of producing a multi-component system alloy of the present invention is characterized by comprising a step of melting the alloy by a method selected from a rapid solidification method, a vacuum arc melting method, a casting method, a melting method, a three-dimensional additive manufacturing method, or a powder metallurgy method.
Further, in a preferred embodiment of the method of producing an alloy comprising a multi-component system of the present invention, it is characterized in that the method further comprise a step of annealing the alloy.
The multi-component system alloy of the present invention has the advantageous effect of providing a multi-component system alloy having high strength and high ductility. Further, according to another aspect, the multi-component system alloy of the present invention is also excellent in biocompatibility, and thus has the advantageous effect of being usable as a biocompatible material.
The alloy composed of multi-component system of the present invention is characterized in that the alloy contains titanium, zirconium, niobium, molybdenum, and tantalum, and further the multi-component system alloy contains at least one selected from the group consisting of hafnium, tungsten, vanadium, and chromium, wherein the alloy satisfies Mo equivalent ≧ 13.5, and the alloy is a single-phase solid solution, a two-phase solid solution, or an alloy in which main phase is a solid solution phase. In the present invention, from the viewpoint of high ductility, it is characterized in that the alloy satisfies Mo equivalent ≥ 13.5. In the present invention, the formula (1) proposed by Kiyohito Ishida based on the thermodynamic database of Ti alloys was used for the Mo equivalent (Moeq). Moeq is given by the following formula (1) (Schaeffler-type phase diagram of Ti-based alloys).
Also, the alloy of the present invention is a single-phase solid solution, a two-phase solid solution, or an alloy in which main phase is a solid solution phase. That is, the alloy of the present invention can mean a so-called high-entropy alloy (hereinafter also referred to as HEA), which exhibits an entropy effect of arrangement that does not originally appear in conventional alloys. The alloy of the present invention preferably consists of a quinary system or higher multi-component system. From the viewpoint of the effects of ΔSmix and ΔHmix, the composition of each constituent element can be preferably 0.1 to 35 at%, more preferably 7 to 25 at%, still more preferably 10 to 22 at%.
The high-entropy alloy of the present invention differs from other multi-component alloys in that the high-entropy alloy is a single-phase solid solution, a two-phase solid solution, or an alloy in which main phase is a solid solution phase, and has high mixing entropy.
Although the alloy of the present invention is a solid solution with a simple crystal structure by maximizing the entropy effect of the configuration that does not appear in conventional alloys, it is a high entropy alloy (hereafter HEA) that exhibits a high strength, a high ductility, a low Young’s modulus, a heat resistance and other special physical properties. In addition, a biocompatibility can be imparted in the present invention. In addition, in the present invention, in the search for the alloy composition in which HEA exists, it is novel in that it established a systematic alloy development method for HEA alloys that can also be applied to living organisms, using the entropy of configuration (ΔSmix), the entropy of mixing (ΔHmix), the atomic radius ratio factor (8 parameter), the valence electron concentration (VEC parameter), and if necessary, biotoxicity of constituent elements as parameters. In the present invention, the complex arrangement of different atomic species in high-entropy alloys allows the emergence of several beneficial characteristics that differ from common alloys. For example, characteristics include improved ductility due to solid solution formation and increased strength due to strained lattices.
The principle of the present invention is as follows. It is necessary to increase the number of constituent elements of the HEA and select a composition that maximizes the entropy effect of the configuration. In the present invention, it was found that HEA can be obtained in a composition that satisfies -15 ≦ ΔHmix and 7 ≧ δ while placing the highest priority on the condition of 1.5R ≦ΔSmix (R is the gas constant).
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy contains titanium, zirconium, niobium, molybdenum, tantalum, and hafnium. Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy satisfies a VEC value (valence electron concentration value) ≦ 4.7 from the viewpoint of high ductility.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy comprises a BCC structure, from the viewpoint of achieving high ductility.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy is represented by a general formula:
wherein in the general formula, 57.2 ≦ X ≦ 85. In the above general formula, it is not particularly limited as long as it satisfies -15 ≦ ΔHmix, 7 ≧ δ, 4.7 ≧ VEC, but the range of x is preferably 57.2 ≦ X ≦ 85, more preferably 70 (70% titanium group) ≦ X ≦ 85, and further preferably, 78.1 ≦ X ≦ 85, from the viewpoint that high properties can be expected from alloy design based on entropy of mixing (ΔSmix), Mo equivalent, and VEC, and it is a composition range where the entropy effect can be expressed more.
Further, in a preferred embodiment of the multi-component system alloy of the present invention, it is characterized in that the alloy is represented by a general formula:
wherein in the general formula, 57.2≦X≦85 and 12.8≦Y≦33.3. In the above general formula, it is not particularly limited as long as it satisfies -15 ≦ ΔHmix, 7 ≧ 8, 4.7 ≧ VEC, but the range of x is preferably 57.2 ≦ X ≦ 85, more preferably 70 (70% titanium group) ≦ X ≦ 85, and further preferably, 78.1 ≦ X ≦ 85, and the range of Y is preferably 12.8 ≦ Y ≦ 33.3, more preferably 12.8 ≦ Y ≦ 20 (sum of Nb and Ta is 20), more preferably in the range of 12.8 ≦ Y ≦ 13.5, from the viewpoint that high properties can be expected from alloy design based on entropy of mixing (ΔSmix), Mo equivalent, and VEC, and it is a composition range where the entropy effect can be expressed more. The concept of notating the composition of these alloys makes it possible to realize 1) in order to reduce the VEC value, the elements are classified into three groups based on Ti, Zr, Hf (VEC=4) and Nb, Ta (VEC=5), Mo (VEC=6), 2) in order to lower the Mo equivalent, the ratio of Ti, Zr, Hf, and the ratio of Nb and Ta can be calculated by considering not only the same but also different cases, to find a composition range wherein high properties can be expected and a more entropy effect exhibits.
Further, a biocompatible material of the present invention is characterized by comprising the multi-component system alloy of the present invention. As for the multi-component system alloy of the present invention, the above description can be referred to as it is. This is because Ti, Zr, Nb, Ta, Mo, and Hf is able to realize high-entropy alloys, as is clear from the Examples described later. Furthermore, this is because it has low cytotoxicity and can be sufficiently exhibited as a biocompatible material.
Further, the method of producing an alloy comprising a multi-component system of the present invention will be described below. That is, from the viewpoint of producing a uniform alloy, a method of producing a multi-component system alloy of the present invention is characterized by comprising a step of melting the alloy by a method selected from a rapid solidification method, a vacuum arc melting method, a casting method, a melting method, a three-dimensional additive manufacturing method, or a powder metallurgy method.
Further, in a preferred embodiment of the method of producing an alloy comprising a multi-component system of the present invention, from the viewpoint of reforming the solidified structure, it is characterized in that the method further comprise a step of annealing the alloy. The temperature of the annealing treatment is preferably 100 to 1500° C., more preferably 800 to 1200° C., still more preferably 950 to 1050° C., from the viewpoint of the diffusion coefficient of constituent atoms. Further, as to the annealing treatment time, the heat treatment can be preferably carried out for 5 minutes to 1 month, more preferably 24 hours to 10 days, still more preferably 6 days to 8 days, from the viewpoint of the time to reach an equilibrium state.
At this point, an example of the present invention will now be described, but the present invention should not be construed as being limited to the example below. Further, it goes without saying that appropriate modifications can be made without departing from the gist of the present invention.
First, TiZrHfNbTaMo HEA (Ti16.67Zr16.67Hf16.67Nb16.67Ta16.67Mo16.67 at%, hereinafter referred to as TZHNTM-Eq) with an equiatomic composition ratio was used as a starting composition. Finally, for the development of living HEA that exhibits ductility at room temperature, the following three policies were adopted: (1) To satisfy the entropy-based definition of HEA, the entropy of mixing (ΔSmix) become ΔSmix ≧ 1.5 R; (wherein R is the gas constant), (2) the melting point should be lowered to suppress macroscopic casting defects such as cold shut, and (3) the VEC value should be lowered. TiB+AxZrB+AxHfB+AxNbB+AxTaB+AxMoB+Ax alloy was devised to design Ti—Zr—Hf—Nb—Ta—Mo alloys having a non-equiatomic composition ratio. At this point, A is a parameter related to the pure substance’s melting point, B is a parameter related to the pure substance’s VEC, and x is a variable. In order to lower the melting point of the alloy, A was defined as A = (Tm-Tm(i))/Tm. Here, Tm(i) is the melting point of a pure substance of element i, and Tm is expressed by the following formula.
Tm is the average melting point of Ti, Zr, Hf, Nb, Ta and Mo. The parameters A are A(Ti)=0.251, A(Zr)=0.167, A(Hf)=0.033, A(Nb)=-0.062, A(Ta)=-0.270 and A(Mo)=-0.118. The composition average melting point of the alloy is shown by the following formula.
In [Math. 2], xi indicates the mole fraction of the i element. Here, when B=1 for all elements, it was found that the ΔSmix and the compositional average melting points of alloys monotonously decrease as x increases. TiZr0.86Hf0.58Nb0.40Ta0.28Mo0.01 (Ti32.07Zr27.58Hf18.49Nb12.70Ta0.19Mo8.97 at%, hereafter also called TZHNTM-1.) was designed; as an alloy with a reduced composition average melting point while satisfying the condition of ΔSmix ≧ 1.5R.
Next, in order to simultaneously reduce the melting point and VEC, a case was examined in which the parameter B was set to the following values: B(Ti)=1.5, B(Zr)=1.5, B(Hf)=1.5, B(Nb)=1.25, B(Ta)=1.25 and B(Mo)=1. The parameter B can be examined using the relationship of the VEC value ratio 6:5:4=1.5:1.25:1, for reasons such as lowering the VEC value of the entire alloy. When B (Ti, Zr, Hf) = 1.5, B (Nb, Ta) = 1.25, B (Mo) = 1, it was found that ΔSmix, compositional average melting point and VEC all decreased monotonically with increasing x in a TiB + AxZrB + AxHfB + AxNbB + AxTaB + AxMoB + Ax alloy. TiZr0.88Hf0.63Nb0.37Ta0.24Mo0.02 (Ti32.61Zr28.58Hf20.39Nb12.05Ta0.80Mo5.57 at %, hereinafter TZHNTM-2) was designed as an alloy that satisfies the condition of ΔSmix ≧ 1.5R and minimizes the average compositional melting point and VEC. Tix1Zrx1Hfx1Nbx2Tax2Mox3 was studied as an alloy considering only VEC without considering melting point.
Here, x1, x2 and x3 are variables. TiZrHfNb0.24Ta0.24Mo0.05 (Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 at%, hereafter TZHNTM-3) was designed with x1, x2, and x3 set to 1, 0.24, and 0.05, respectively, as an alloy that satisfies the condition of ΔSmix ≧ 1.5R and has a minimum VEC. Both TiZrHfNbTaMo (TZHNTM-Eq) having an equiatomic composition ratio and Ti—Zr—Hf—Nb—Ta—Mo (TZHNTM—X, (X = 1, 2, 3) having a non-equiatomic composition ratio alloys showed a high propensity for solid solution formation in ΔHmix (entropy of mixing), Ω (omega parameter: it is a dimensionless parameter that includes both ΔSmix and ΔHmix, and is a parameter that evaluates the relative relationship between ΔSmix and ΔHmix. ), and δ ( Atomic radius ratio factor) which are empirical parameters for high-entropy alloys.
Next, in order to study the solid solution formation tendency and the crystal structure of the constituent phases in more detail, the crystal structure was examined using new alloy parameters, a ground state diagram based on the first-principles calculation database, and the results of thermodynamic calculations (CALPHAD). The results are shown in
Here, [M] is the mass fraction of component M.
The ground-state diagram predicted by the Materials Project (A. Jain, S.P. Ong, G. Hautier, W. Chen, W.D. Richards, S. Dacek, S. Cholia, D. Gunter, D. Skinner, G. Ceder, K.A. Persson, APL Materials, 1, 1 (2013) 011002.) has been found to be useful for designing super multi-component alloys such as liquid-phase separated type amorphous alloys and high-entropy alloys.
In the Ti—Zr—Hf—Mo (
The TD of TZHNTM-Eq (
Next, we attempted to actually produce ingots with various compositions using the vacuum arc melting method. Arc-melted ingots of TZHNTM-X (X = Eq, 1, 2, 3) alloys were made from mixtures of pure elemental base materials. The cooling rate in the arc melting method is estimated to be about 2000 Ks-1, which is about one order of magnitude higher than the cooling rate for general die casting. and about three order of magnitude higher than the cooling rate for crucible melting and cooling. The texture and constituent phases were investigated by XRD (X-ray diffraction). SEM (Scanning Electron Microscopy), EDS (Energy Dispersive x-ray Spectroscopy).
Tensile tests were performed at room temperature at a strain rate of 1.67×10-4 s-1. The function of the fabricated TZHNTM-X (X = Eq, 1, 2, 3) alloys as biomaterials was evaluated by analyzing the cell adhesion behavior controlled by the interaction between the alloy surface and cells at the molecular level.
Here, the calculated intensity was obtained by VESTA (K. Momma, F. Izumi, J. Appl. Crystallogr., 41 (2008) 653-658.,). The sharp diffraction peaks observed in the TZHNTM-Eq with an equiatomic composition ratio were identified as two BCC phases. On the other hand, the sharp diffraction peak of TZHNTM-3 was identified as a single-phase BCC phase.
In addition, it was thought that the difference in the degree of segregation between the TZHNTM-Eq with an equiatomic composition ratio and the TZHNTM-3 with a non-equiatomic composition ratio corresponds to the temperature difference between TL and TS (that is, the temperature range in the solid-liquid coexistence region) predicted by thermodynamic calculations and the partition coefficient (k) at TL. The partition coefficients of Ti (kTi) and the partition coefficients of Zr (kZr) in the TZHNTM-Eq with an equiatomic composition ratio were calculated to be 0.76 and 0.55, respectively. On the other hand, the kTi and kZr of the TZHNTM-3 with a non-equiatomic composition ratio were calculated to be 0.85 and 0.93, respectively. It was thought that the kZr in the TZHNTM-Eq with an equiatomic composition ratio is much smaller than 1, unlike the kzr in the TZHNTM-3 with a non-isoatomic composition ratio, which seems to correspond to the development of a large compositional distribution. Formation of Mo-related intermetallic compounds was not confirmed by microstructural observation by XRD and SEM in any of TZHNTM-X (X = Eq, 1, 2, 3).
Next, the results of the tensile test of the alloy in one example of the present invention were examined.
Next, a biocompatibility evaluation was performed in one example of the present invention.
In addition, focusing on cell morphology, which directly affects the construction of living tissues and organs, different characteristic cell morphologies were shown depending on the type of substrate material.
In addition, it can be seen that on the fabricated alloy, well elongated and developed focal adhesions (molecular groups that control cell adhesion to metal substrates; although it is difficult to distinguish from the figure, the red part (colored part labeled as vinculin) in
Next, an attempt was made to produce a cast material and a heat-treated material as an alloy in one embodiment of the present invention. As a composition, Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 (at%) alloy was obtained by vacuum arc melting method. When the crystal structure of the obtained alloy was observed by XRD, it was confirmed to be a solid solution with a simple structure (bcc structure in this example), which is the most distinctive feature of HEA (
As to the obtained alloy, the bcc structure was maintained even after heat treatment at 1000° C. for 1 week (1273 K, 168 h). As for the microstructure, an equiaxed dendrite structure peculiar to high-entropy alloys, which has been previously reported, was observed in the cast material (
As shown in
These results indicate that the alloy exhibits extremely low cytotoxicity due to the formation of an oxide film on the surface, and support the validity of the constituent elements as a biomaterial. Based on the above, it was found that the biocompatibility of the developed TZHNTM alloy is superior to that of SUS-316L and Co—Cr—Mo alloys and is even comparable to that of pure titanium, which is generally used as a metallic material for living organisms.
As described above, we have succeeded in developing non-equiatomic composition Ti—Zr—Hf—Nb—Ta—Mo bio-HEA with a non-equiatomic composition ratio that can be stretched at room temperature and has excellent biocompatibility. Arc-melted ingots with a BCC structure without intermetallic compound were obtained in Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 (TZHNTM-3) alloy with a non-equiatomic composition ratio. The TZHNTM-3 with a non-equiatomic composition ration has room-temperature tensile ductility and its yield stress is larger than that of CP—Ti. Moeq and VEC were effective for alloy design of bio-MEA and bio-HEA with BCC structure. The TZHNTM-3 with a non-equiatomic composition ratio showed as high biocompatibility as CP—Ti.
Since the HEA obtained by the present invention has high strength, high ductility, and high biocompatibility, which has not been found so far, a new market is created using HEA alloys for biomedical use, along with this, there is a large ripple effect on a wide range of industries and product groups.
Number | Date | Country | Kind |
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JP2020-100743 | Jun 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/020045 | 5/26/2021 | WO |