Method for controlling the structure of magnesium-containing metal materials and medical devices

Abstract

To control the magnesium crystal structure without adding other metals to magnesium, and to obtain a magnesium-containing metal material with superior strength. [Solution] A method for controlling the microstructure of a magnesium-containing metal material, comprising step 1 of performing a hydrogenation treatment on one or more metal materials selected from magnesium, etc., to form MgH2(1) on the grain boundaries(2) of the metal material.

Description

Technical Field

[0001] The present invention relates to a method for controlling the structure of a magnesium-containing metal material and a medical device.

Background Art

[0002] Medical prostheses such as stents are medical devices that are inserted into the lumen of tubular tissues such as blood vessels, tracheas, esophaguses, and intestinal tracts to expand and hold the lumen. The stent is often a cylindrical member having a metal mesh structure, and a stent corresponding to the treatment site is used.

[0003] A self-degradable stent, which is one type of stent, is a medical device used to expand blood vessels. It is inserted into an occluded blood vessel, expands the blood vessel to restore blood flow to the heart, and then gradually decomposes and is absorbed. The self-degradable stent has the merit of not only restoring blood vessel occlusion but also eliminating the need for removal surgery.

[0004] In recent years, the use of magnesium in self-degradable stents has been spreading and some have been put into practical use. Magnesium is an essential element in the human body and has the property of being stably decomposed and absorbed in the human body, so it is suitable as a material for the self-degradable stent.

[0005] However, magnesium materials have the drawback of insufficient mechanical strength. Therefore, as a method for improving the mechanical strength of magnesium materials, methods using magnesium and other metals, such as alloying, precipitate strengthening, and crystal refinement, have been attempted.

[0006] For example, Patent Document 1 discloses a method in which an alloy powder containing magnesium is hydrogenated and subjected to predetermined dehydrogenation, and a large number of fine crystal grains are precipitated by holding the alloy powder in an atmosphere heated to a predetermined temperature. Patent Document 1 describes that the durability of the alloy can be improved according to this method.

[0007] Furthermore, Patent Document 2 describes the preparation of a biodegradable stent with increased yield strength and ultimate tensile strength by alloying pure magnesium with 8% scandium and 2.7% yttrium. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-80801 [Patent Document 2] Special Publication No. 2013-509217 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, prior art, including Patent Documents 1 and 2, requires the addition of other metals to magnesium. The addition of other metals must be done in a way that does not involve selecting metals undesirable to the body and using amounts that do not adversely affect the body, thus limiting the improvement of the strength of the magnesium material. In practice, the strength is compensated for by increasing the thickness of the stent, but since the thickness can only be increased to a extent that does not adversely affect the insertability into blood vessels, etc., there are still limits to the improvement of the strength.

[0010] Therefore, one aspect of the present invention aims to provide a method for controlling the microstructure of a magnesium-containing metal material, which controls the crystal structure of magnesium without adding other metals to magnesium, or while reducing the content of other metals as much as possible. [Means for solving the problem]

[0011] To solve the above problems, a method for controlling the microstructure of a magnesium-containing metal material according to one aspect of the present invention includes step 1 of performing a hydrogenation treatment on one or more metal materials selected from the group consisting of magnesium and magnesium alloys, thereby forming MgH2 on the grain boundaries of the metal material.

[0012] Furthermore, a medical device according to one aspect of the present invention comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloy is magnesium in which MgH2 is formed on the grain boundaries.

[0013] Furthermore, a medical device according to one aspect of the present invention comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys includes magnesium derived from MgH2 formed on the grain boundaries. [Effects of the Invention]

[0014] According to one aspect of the present invention, the crystal grain size of magnesium can be controlled without adding other metals to magnesium, or while minimizing the content of other metals. Therefore, a magnesium-containing metal material with excellent strength can be obtained while reducing the content of metals other than magnesium. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows the results of observing the inside of a magnesium crystal in a magnesium-containing metal material whose structure was controlled by the method of the present invention using an optical microscope. [Figure 2] This is a schematic diagram illustrating the growth of magnesium crystals in a magnesium-containing metal material. Figure 1001 shows the growth of magnesium crystals without hydrogenation treatment, and figure 1002 shows the growth of magnesium crystals after hydrogenation treatment. [Figure 3]It is a schematic diagram explaining a method for determining crystal grains to be used for calculating crystal grain size among the crystal grains of magnesium crystals observed with an optical microscope. [Figure 4] It is a diagram showing the result of observing the surface of magnesium with an optical microscope after performing hot rolling on magnesium twice. [Figure 5] It is a diagram showing the X-ray diffraction profile of the internal cross-section of magnesium that was subjected to hot rolling twice, had palladium vapor-deposited on its surface, and then was heat-treated at 673K in a hydrogen atmosphere of 4.0 MPa. [Figure 6] It is a diagram showing the result of etching the observation surface inside magnesium that was heat-treated at 673K in an argon atmosphere of 0.1 MPa or in a hydrogen atmosphere of 1.0 MPa or 4.0 MPa and then observing the etched observation surface with an optical microscope. [Figure 7] It is a diagram showing the change over time of the average crystal grain size of magnesium that was heat-treated at 673K in an argon atmosphere of 0.1 MPa or in a hydrogen atmosphere of 1.0 MPa or 4.0 MPa. [Figure 8] It is a diagram showing the result of performing a tensile test on a tensile test piece of pure magnesium that was hydrogenated, after dehydrogenation, together with a control. [Figure 9] It is a diagram showing the result of performing a tensile test on a tensile test piece of pure magnesium whose surface was polished until a metallic luster appeared after hydrogenation (treatment time: 18h). [Figure 10] It is a diagram showing the result of performing a tensile test on a tensile test piece of pure magnesium whose surface was polished until a metallic luster appeared after hydrogenation (treatment time: 192h).

Embodiments for Carrying Out the Invention

[0016] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more, B or less".

[0017] [1. Method for controlling the microstructure of magnesium-containing metal materials] A method for controlling the microstructure of a magnesium-containing metal material according to one embodiment of the present invention (hereinafter also referred to as "the method of the present invention") is a method for controlling the microstructure of a magnesium-containing metal material, comprising step 1 of performing a hydrogenation treatment on one or more metal materials selected from the group consisting of magnesium and magnesium alloys, thereby forming MgH2 on the grain boundaries of the metal material.

[0018] (1-1) Technical concept of the present invention As mentioned above, conventional attempts have been made to improve the strength of magnesium-containing metallic materials by obtaining alloys of magnesium with other metals. However, as previously stated, there are limitations to improving the strength of such materials by adding other metals to magnesium. The method of the present invention employs a method of hydrogenating magnesium without adding other metals to magnesium, or while minimizing the content of other metals. As a result, it was found that in hydrogenated magnesium, MgH2 is generated not only on the surface but also inside, and that this MgH2 exists on the grain boundaries, inhibiting dislocation movement and thus inhibiting the growth of magnesium crystals. The fact that magnesium crystal growth can be inhibited by hydrogenating magnesium is a fact that has been revealed for the first time by the present invention. It is said that as the grain size decreases, the strength of a metallic material improves inversely proportional to the square root of the grain size (Hall-Petch's Law). Therefore, according to the method of the present invention, it is possible to improve the strength of magnesium materials. This is demonstrated in Example 2, which will be described later.

[0019] The method of the present invention is completely different from the conventional method in that it can improve the strength of magnesium materials based on the previously nonexistent concept of inhibiting magnesium crystal growth through hydrogenation treatment.

[0020] (1-2) Process 1 In step 1, one or more metallic materials selected from the group consisting of magnesium and magnesium alloys are subjected to hydrogenation treatment to form MgH2 on the grain boundaries of the metallic materials.

[0021] The term "magnesium" as used above refers to pure magnesium. While a purity close to 100% is preferable, it is not required to be 100%, and it may contain unavoidable impurities. Examples of unavoidable impurities include one or more selected from the group consisting of Li, Na, P, K, Fe, B, Al, S, Ca, Cu, F, Si, Cl, Mn, and Zn.

[0022] From the viewpoint of facilitating the formation of MgH2 internally, the purity of the magnesium is preferably 95% by weight or higher, more preferably 97% by weight or higher, and even more preferably 99% by weight or higher.

[0023] A "magnesium alloy" refers to a material obtained by melting and solidifying two or more metallic elements, including magnesium. Other metals can be one or more selected from the group consisting of, for example, Al, Zn, Mn, and Zr. The most basic of these other metals are aluminum and zinc, and examples of magnesium alloys include AZ31 and AZ91.

[0024] From the viewpoint of facilitating the formation of MgH2 internally, the proportion of magnesium in the alloy is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 98% by weight or more. Although data is not shown, the inventors have confirmed that MgH2 can be formed on the grain boundaries of the alloy by subjecting a magnesium alloy comprising 6% by weight of Al, 1% by weight of Zn, and 93% by weight of Mg to step 1.

[0025] The proportion of metals other than magnesium in the alloy is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 2% by weight or less. By setting the proportion of the other metals to 10% by weight or less, the amount of the other metals in the magnesium alloy can be kept as small as possible.

[0026] In the aforementioned prior art, it was necessary to add a large amount of other metals to give magnesium material sufficient strength. On the other hand, the microstructure control method of the present invention inhibits the growth of magnesium crystals by forming MgH2 on the grain boundaries of magnesium, thereby improving the strength of the magnesium material while reducing the content of metals other than magnesium.

[0027] The alloy can be manufactured, for example, by placing magnesium and another metal in a crucible and melting and casting them at 650°C to 800°C.

[0028] The hydrogenation treatment is a process for obtaining MgH2 by reacting magnesium with hydrogen. The hydrogenation treatment preferably includes a step of pressurizing and heating the metal material in a hydrogen atmosphere. This step, for example, involves placing the metal material in a pressure-resistant and high-temperature-resistant container, evacuating the container, then performing hydrogen displacement by sealing hydrogen into the container, saturating the container with hydrogen, pressurizing it, and heating it.

[0029] For example, a stainless steel container can be used as the container. The process can be carried out using, for example, a Sieberts-type apparatus. That is, first, the container containing the metal material is placed in the electric furnace of the Sieberts-type apparatus. Next, the container is evacuated using a rotary pump, and then, while checking the hydrogen pressure with a pressure gauge, hydrogen is introduced from a gas cylinder into the container until the desired pressure is reached, and then heated by the electric furnace. The temperature of the metal material can be measured, for example, by a thermocouple installed inside the container.

[0030] To ensure that the reaction Mg + H2 → MgH2 proceeds quickly and that the Mg crystal grain size is reliably controlled by MgH2, it is preferable that the hydrogen be as pure as possible.

[0031] The hydrogenation treatment coats the surface of the metal material with MgH2, generates MgH2 within the metal material, and forms MgH2 on the grain boundaries of the metal material. One reason why MgH2 is formed on the grain boundaries by the hydrogenation treatment is thought to be the rapid diffusion of hydrogen atoms at the grain boundaries. "The grain boundaries of the metal material" refers to the magnesium grain boundaries if the metal material is magnesium. If the metal material is a magnesium alloy, it refers to the grain boundaries of magnesium and the other metals forming the magnesium alloy.

[0032] Figure 1 shows the results of observing the interior of a magnesium crystal in a magnesium-containing metal material whose structure was controlled by the method of the present invention using an optical microscope. In the figure, 1 is MgH2, 2 is a grain boundary, and 3 is a crystal grain. As shown in Figure 1, MgH2 exhibits granularity and exists on the grain boundaries. The fact that the granular material indicated by 1 is MgH2 can be confirmed by X-ray diffraction, as will be described later.

[0033] Figure 2 is a schematic diagram showing the growth of magnesium crystals in a magnesium-containing metal material. 1001 shows the growth of magnesium crystals without hydrogenation treatment, and 1002 shows the growth of magnesium crystals after hydrogenation treatment. In the figure, the base of the arrow indicates the state of the magnesium crystal immediately after hydrogenation treatment, and the lower part of the arrow indicates the state of the magnesium crystal after a certain period of time has elapsed since hydrogenation treatment. In the figure, symbols 1 to 3 are equivalent to those shown in Figure 1, and 4 indicates MgH2 formed on the surface of the magnesium.

[0034] As shown in 1002, magnesium crystals with MgH2 present at the grain boundaries exhibit inhibited grain growth and smaller grain size compared to magnesium crystals without MgH2 at the grain boundaries (shown in 1001). From this, it is considered that in the magnesium-containing metal material, the grains are pinned by the MgH2 at the grain boundaries, and this pinning effect suppresses recrystallization, inhibits grain growth, and reduces grain size.

[0035] In Figure 1, the larger particles are located at the triple point of the crystal, while the smaller particles are located at the double point. As shown in Figure 1, according to the method of the present invention, the amount of MgH2 present at the triple point, where the grain boundary exists stably, is greater than the amount of MgH2 present at the double point and the quadruple point. Therefore, according to the method of the present invention, the aforementioned pinning effect can be effectively achieved.

[0036] In step 1, MgH2 is formed on the grain boundaries of the metal material, but it is not necessary to form MgH2 on all the grain boundaries of the crystals in the metal material. For example, by adjusting the reaction temperature during the hydrogenation treatment and the Gibbs free energy of the reaction, as will be described later, an appropriate amount of MgH2 can be formed on the grain boundaries, and the desired pinning effect can be obtained.

[0037] By reducing the grain size, the proportion of grain boundaries increases, and dislocation movement is suppressed. Therefore, according to the method of the present invention, the strength of the magnesium material can be improved. Furthermore, since it is said that the strength of a metallic material improves inversely proportional to the square root of the grain size (Hall-Petch's Law), the method of the present invention can also improve the strength of the magnesium material.

[0038] Thus, the method of the present invention can improve the strength of magnesium materials by reducing the size of magnesium crystal grains through hydrogenation of magnesium. This is demonstrated in Examples 2 and 3 described later.

[0039] Therefore, unlike methods that improve the strength of magnesium materials by using magnesium and other metals (such as alloying, precipitate strengthening, and crystal refinement), there is no limitation on the content of other metals, which would hinder the improvement of strength in the aforementioned method. As a result, the strength of magnesium materials can be improved more easily than with conventional techniques.

[0040] The grain size of magnesium can be controlled by adjusting the reaction temperature and Gibbs free energy of the reaction during the hydrogenation treatment. From the viewpoint of improving the strength of the magnesium material, the average grain size of magnesium is preferably 150 μm or less, preferably 100 μm or less, preferably 80 μm or less, preferably 60 μm or less, preferably 40 μm or less, and preferably 20 μm or less, with the latter being more preferable. The lower limit of the average grain size may be on the submicron order, preferably 100 nm or more, preferably 300 nm or more, preferably 500 nm or more, preferably 800 nm or more, preferably 1 μm or more, and more preferably 10 μm or more.

[0041] The average grain size of magnesium can be determined, for example, as follows: First, a photograph of the etched magnesium material is taken using an optical microscope, and the area of ​​the crystal grains is determined using image analysis software. Next, assuming that the crystal grains are perfectly round, the grain size d is calculated from the obtained cross-sectional area of ​​the crystal (cross-sectional area = πd). 2 (4) At this time, crystals in which the entire grain boundary is not visible in the field of view are excluded, and the area is calculated only for those in which the entire grain boundary is visible.

[0042] Figure 3 is a schematic diagram illustrating the method for determining the crystal grain size of magnesium crystals observed with an optical microscope. The symbols in the figure are the same as in Figure 1. As shown in the left diagram of Figure 3, there are crystals in the microscope field of view where the entire grain boundary is not visible. However, as shown in the right diagram of Figure 3, only those where the entire grain boundary is visible are selected, the area of ​​each crystal is determined, and the crystal grain size d is calculated as πd 2 The average crystal grain size is calculated by approximating it to a circular shape based on / 4.

[0043] The step of pressurizing and heating the metal material under a hydrogen atmosphere is preferably carried out under conditions such that the Gibbs free energy of the reaction is less than -1.2 kJ / mol, given that the enthalpy of the reaction Mg + H2 → MgH2 is -74.7 kJ / mol and the entropy of the reaction is -135.6 J / (K·mol).

[0044] The control factors for the frequency of MgH2 production are the reaction temperature and the Gibbs free energy of the reaction. The aforementioned conditions are preferable because they are appropriate conditions that take into account the relationship between the reaction temperature and the Gibbs free energy of the reaction, and by performing hydrogenation under these conditions, MgH2 can be efficiently produced inside the magnesium crystal.

[0045] The enthalpy of the above reaction is set to -74.7 kJ / mol and the entropy to -135.6 J / (K·mol) due to the thermodynamic conditions for producing MgH2 from Mg and hydrogen gas.

[0046] Specific conditions that result in a reaction Gibbs free energy being less than -1.2 kJ / mol include, for example, a reaction temperature of 340°C to 440°C and a hydrogen pressure of 0.6 MPa to 5 MPa.

[0047] Preferably, the metal material has a hydrogen-absorbing metal deposited on part or all of its surface. That is, it is preferable that the hydrogen-absorbing metal is deposited on part or all of the surface of the metal material before the hydrogenation treatment.

[0048] "Having a hydrogen-absorbing metal deposited on part or all of the surface" means that the surface treatment of the metal material is performed with a hydrogen-absorbing metal. The metal material may be an alloy of magnesium and another metal as described above, but since it is preferable that the content of other metals other than magnesium be as low as possible, it is preferable that it be magnesium (pure magnesium).

[0049] Hydrogen-storing metals are metals that can reversibly absorb and release hydrogen at or near room temperature and atmospheric pressure. Examples include one or more metals selected from the group consisting of palladium, titanium, zirconium, and vanadium.

[0050] Because hydrogen-absorbing metals possess these properties, when a hydrogen-absorbing metal is deposited onto part or all of the surface of a metal material, hydrogen can be more easily distributed into the interior of the metal material compared to when the hydrogen-absorbing metal is not deposited. Therefore, MgH2 can be easily generated inside the metal material.

[0051] In view of the effects of depositing hydrogen-absorbing metals, even if the hydrogen-absorbing metal is deposited on only a part of the surface, MgH2 can be generated more easily than when the hydrogen-absorbing metal is not deposited. However, in order to achieve the above effect more effectively, it is preferable that the proportion of the surface on which the hydrogen-absorbing metal is deposited is higher, and it is preferable that the hydrogen-absorbing metal is deposited on the entire surface.

[0052] Examples of deposition methods include vacuum deposition, sputtering, and molecular beam epitaxy. Among these, sputtering is preferred because it offers advantages such as strong adhesion, no change in the composition ratio of the metal material to be deposited, the ability to control the film thickness over time, and the ability to create a uniform film even over a large area.

[0053] The thickness of the hydrogen-absorbing metal film formed on the surface of the metal material by vapor deposition is preferably 50 to 200 nm, more preferably 50 to 150 nm, and even more preferably 50 to 100 nm, from the viewpoint of facilitating hydrogen penetration into the interior of the metal material.

[0054] Conventionally, one method for distributing hydrogen into the interior of a metal material involves polishing the material with SiC abrasive paper in a gas glove box having a predetermined dew point and oxygen concentration. However, this method is more labor-intensive than vapor deposition, and vapor deposition utilizes the properties of hydrogen-absorbing metals, allowing for more efficient distribution of hydrogen into the interior of the metal material. Therefore, vapor deposition is more advantageous than the aforementioned method. A surface-treated metal material can be obtained by the vapor deposition method described above.

[0055] In the present invention, it is preferable that the method includes a step of hot rolling one or more metallic materials selected from the group consisting of magnesium and alloys of magnesium and other metals, prior to step 1. It is preferable that the hot rolling is performed on metallic materials that do not have the hydrogen-absorbing metal deposited on them.

[0056] By performing hot rolling before step 1, the magnesium crystals can be refined. This increases the number of grain boundaries per unit area, making it easier for larger grain sizes of MgH2 to be present on these grain boundaries compared to the case where hot rolling is not performed in step 1. Alternatively, cold rolling and annealing can be performed instead of hot rolling.

[0057] The conditions for hot rolling are preferably a temperature of 150 to 500°C and a reduction ratio of 80% or less.

[0058] [2. Medical Devices] A medical device according to one embodiment of the present invention (hereinafter also referred to as the medical device of the present invention) comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and the magnesium alloy is magnesium in which MgH2 is formed on the grain boundaries.

[0059] Magnesium in which MgH2 is formed on the grain boundaries exhibits inhibited grain growth and smaller grain size compared to magnesium crystals without MgH2 on the grain boundaries. Since the strength of the aforementioned magnesium is higher than that of magnesium that has not undergone MgH2 formation, one embodiment of the present invention can provide a medical device with excellent strength.

[0060] The "one or more metallic materials selected from the group consisting of magnesium and magnesium alloys" are as described in [1.] above.

[0061] "Magnesium with MgH2 formed on the grain boundaries" can be obtained by a method that includes a step of hydrogenating one or more metallic materials selected from the group consisting of magnesium and magnesium alloys to form MgH2 on the grain boundaries of the metallic materials. At this time, it is preferable to deposit a hydrogen-absorbing metal onto part or all of the surface of the metallic material before the hydrogenation treatment, as this makes it easier for hydrogen to penetrate into the interior of the metallic material during the hydrogenation treatment. Therefore, it is preferable to obtain "magnesium with MgH2 formed on the grain boundaries" by the method described in [1.] above. Furthermore, it is preferable that "magnesium with MgH2 formed on the grain boundaries" has a hydrogen-absorbing metal deposited on part or all of its surface.

[0062] As described in [1.] above, the hydrogenation treatment preferably includes a step of pressurizing and heating the metal material in a hydrogen atmosphere. Furthermore, it is preferable that the step of pressurizing and heating the metal material in a hydrogen atmosphere is carried out under conditions such that the Gibbs free energy of the reaction is less than -1.2 kJ / mol, given that the enthalpy of the reaction Mg + H2 → MgH2 is -74.7 kJ / mol and the entropy of the reaction is -135.6 J / (K·mol).

[0063] Furthermore, the method preferably includes a step of hot rolling of one or more metallic materials selected from the group consisting of magnesium and alloys of magnesium and other metals before the hydrogenation treatment. If a hydrogen-absorbing metal is deposited on part or all of the surface of the metallic material before the hydrogenation treatment, it is preferable to include a step of hot rolling before depositing the hydrogen-absorbing metal. In addition, the hydrogen-absorbing metal is preferably one or more metals selected from the group consisting of palladium, titanium, zirconium, and vanadium.

[0064] The medical device of the present invention may also be a medical device comprising one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and the magnesium alloy is magnesium obtained by dehydrogenating magnesium on which MgH2 is formed at the grain boundaries.

[0065] The phrase "obtained by dehydrogenating magnesium on which MgH2 has been formed at the grain boundaries" means that the magnesium and magnesium alloy contained in the medical device are magnesium obtained by dehydrogenating MgH2 formed at the grain boundaries. The dehydrogenation is performed with the aim of avoiding hydrogen embrittlement and / or fracture of the grain boundaries.

[0066] As mentioned above, magnesium with MgH2 formed on the grain boundaries has higher strength than magnesium crystals without MgH2 on the grain boundaries. Therefore, high-strength magnesium can be obtained without performing the dehydrogenation process. On the other hand, the MgH2 layer deposited on the surface of magnesium by hydrogenation is brittle and can serve as a crack initiation point. By performing the dehydrogenation process, the MgH2 layer deposited on the surface can be removed, making it easier to obtain high-strength magnesium.

[0067] One possible method of dehydrogenation is vacuum high-temperature degassing. The completion of the dehydrogenation can be confirmed by mass spectrometry.

[0068] The magnesium before dehydrogenation and the magnesium forming the magnesium alloy are magnesium in which MgH2 has formed on the grain boundaries, and therefore have crystals in which a pinning effect is observed. Although the MgH2 becomes Mg through dehydrogenation, the grain size of the crystal grains in which the pinning effect was observed remains smaller than the grain size of magnesium that has not undergone MgH2 formation. The crystals in which the pinning effect is observed are crystals after grain growth and have a stable shape, so the growth rate of the interface is slow. Also, since the time required for dehydrogenation is very short, the effect of dehydrogenation on interface growth is negligible. Therefore, there is almost no grain growth due to the heat added during dehydrogenation. Thus, even after the MgH2 becomes Mg through dehydrogenation, the grain size of the crystal grains remains smaller than the grain size of magnesium that has not undergone MgH2 formation.

[0069] Therefore, according to Hol-Petch's law, the strength of the aforementioned metal material is higher than that of a metal material containing magnesium that has not undergone the formation of MgH2. Thus, the medical device of the present invention can provide a medical device with superior strength. The aforementioned medical device is a novel medical device that can exhibit high strength without increasing the content of other metals besides magnesium, and without increasing the thickness of the device itself. Therefore, it can be suitably used in applications where high strength is required, such as stents inserted into bones.

[0070] Furthermore, magnesium obtained by dehydrogenating magnesium in which MgH2 has formed on the grain boundaries has a smaller grain size than magnesium that has not undergone the formation of MgH2, but it is still magnesium. Moreover, it is difficult to define the grain size in general terms. For this reason, magnesium obtained by dehydrogenating magnesium in which MgH2 has formed on the grain boundaries cannot be directly identified by its structure or properties, or it is not practical to do so.

[0071] The method for removing the MgH2 layer deposited on the surface is not limited to dehydrogenation. For example, a method of polishing the surface of magnesium on which MgH2 has formed on the grain boundaries can be mentioned. For example, a method of polishing the surface until the metallic luster of magnesium appears can be mentioned. For example, a method of polishing the surface using a micromotor control device equipped with a rotary tool; a method of polishing the surface using abrasive paper and / or chemical fibers can be mentioned.

[0072] The medical device of the present invention preferably has a surface roughness Ra of 0.7 μm or less for the metal material. By subjecting the medical device of the present invention to a method of polishing the surface of magnesium on which MgH2 has formed on the grain boundaries, for example, and removing the MgH2 layer deposited on the surface, a medical device of the present invention having a surface roughness Ra of 0.7 μm or less for the metal material can be obtained. When the surface roughness Ra of the metal material is 0.7 μm or less, the MgH2 layer deposited on the surface is sufficiently removed, resulting in high-strength magnesium, which is preferable. Note that even when the surface of magnesium on which MgH2 has formed on the grain boundaries is subjected to polishing, the MgH2 on the grain boundaries remains. This can be confirmed by observation with an optical microscope and X-ray diffraction as described above.

[0073] The surface roughness Ra of the aforementioned metal material can be determined by measuring the arithmetic surface height Ra using a surface roughness meter (Mitutoyo Corporation "SURFTEST SJ-400 Compact Surface Roughness Measuring Instrument"). The measurement conditions are as follows. Cutoff value = 0.8mm Measurement length = 4mm Measurement speed=0.5mm / s Vertical magnification = 50x Horizontal magnification = 5000x The surface roughness Ra is more preferably 0.65 μm or less, and even more preferably 0.6 μm or less.

[0074] Therefore, the magnesium and the magnesium forming the magnesium alloy may be magnesium obtained by surface polishing magnesium on which MgH2 has been formed at the grain boundaries. For the same reasons as magnesium obtained by dehydrogenating magnesium on which MgH2 has been formed at the grain boundaries, it is impossible or impractical to directly identify such magnesium by its structure or properties.

[0075] Magnesium decomposes in the presence of water through the following reaction. Therefore, the medical device of the present invention is biodegradable. Mg + 2H2O → Mg 2+ +2OH - +H2 The medical device in question may be, for example, a prosthesis, and an example of such a prosthesis is a stent. A stent is inserted into the body to expand the lumen of tubular tissues such as coronary arteries and restore blood flow. The medical device of the present invention can be used as a stent and, as described above, is biodegradable, so it is gradually broken down and absorbed in the body. Therefore, there is no need to perform a removal surgery after the completion of its use in the body, and even if the patient experiences repeated restenosis of the tubular tissue, a new stent can be placed in the same location where the original stent was installed.

[0076] The medical device of the present invention can be manufactured, for example, by melting and casting the metal material at 650 to 800°C, subjecting the resulting ingot to hot extrusion, and then laser-processing the resulting tube material to a desired shape (for example, a mesh shape).

[0077] It is preferable to remove oxides adhering to the surface of the obtained medical device using, for example, an acidic solution. Furthermore, it is preferable to immerse the medical device, from which the oxides have been removed, as the anode in an electrolyte solution, connect it to a metal plate acting as the cathode via a DC power supply, and apply a voltage to polish the medical device to a mirror finish.

[0078] The aforementioned medical device can be placed, for example, around the balloon of a balloon catheter, inserted into a tubular tissue such as a coronary artery, and then left in place within the tubular tissue by expanding the balloon and then removing the balloon catheter.

[0079] The medical device of the present invention may be a medical device comprising one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and the magnesium alloy includes magnesium derived from MgH2 formed on the grain boundaries.

[0080] "Magnesium derived from MgH2 formed on the grain boundary" does not mean MgH2 itself formed on the grain boundary, but rather magnesium from which MgH2 has been formed on the grain boundary and which has been dehydrogenated. Furthermore, "magnesium derived from MgH2 formed on the grain boundary" may also refer to magnesium obtained by surface polishing magnesium from which MgH2 has been formed on the grain boundary.

[0081] The aforementioned "MgH2 formed on the grain boundaries" can be obtained, for example, by a method that includes a step of hydrogenating one or more metallic materials selected from the group consisting of magnesium and magnesium alloys. Before the hydrogenating treatment, it is preferable to deposit a hydrogen-absorbing metal onto part or all of the surface of the metallic material, as this makes it easier for hydrogen to penetrate into the interior of the metallic material during the hydrogenating treatment. Therefore, it is preferable to obtain the "MgH2 formed on the grain boundaries" by the method described in [1.] above.

[0082] "Magnesium derived from MgH2 formed on the grain boundaries" can be obtained, for example, by dehydrogenating the MgH2 or by surface polishing. Dehydrogenation and surface polishing are as described above. Preferably, the "magnesium derived from MgH2 formed on the grain boundaries" has a hydrogen-absorbing metal deposited on its surface.

[0083] Because the medical device of the present invention has the features described above, it contributes, for example, to achieving United Nations Sustainable Development Goals (SDGs) Goal 3, "Ensure healthy lives and promote well-being for all," and Goal 12, "Ensure responsible consumption and production."

[0084] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0085] 〔summary〕 The present invention includes the following embodiments.

[0086] <1> A method for controlling the microstructure of a magnesium-containing metallic material, comprising step 1, which involves hydrogenating one or more metallic materials selected from the group consisting of magnesium and magnesium alloys to form MgH2 on the grain boundaries of the metallic materials.

[0087] <2> The hydrogenation treatment includes the step of pressurizing and heating the metal material in a hydrogen atmosphere. <1> A method for controlling the microstructure of a magnesium-containing metal material as described above.

[0088] <3> The process of pressurizing and heating the aforementioned metal material under a hydrogen atmosphere is carried out under conditions such that, given the enthalpy of the reaction Mg + H2 → MgH2 is -74.7 kJ / mol and the entropy of the reaction is -135.6 J / (K·mol), the Gibbs free energy of the reaction is less than -1.2 kJ / mol. <2> A method for controlling the microstructure of a magnesium-containing metal material as described above.

[0089] <4> The aforementioned metal material is formed by depositing a hydrogen-absorbing metal onto a part or all of the surface of the metal material. <1> A method for controlling the microstructure of a magnesium-containing metal material as described above.

[0090] <5> Prior to step 1, the process includes hot rolling of one or more metallic materials selected from the group consisting of magnesium and magnesium alloys. <1> from <4> A method for controlling the microstructure of a magnesium-containing metal material as described in any of the following.

[0091] <6> The hydrogen storage metal is one or more metals selected from the group consisting of palladium, titanium, zirconium, and vanadium. <4> or <5> A method for controlling the microstructure of a magnesium-containing metal material as described above.

[0092] <7> A medical device comprising one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys is magnesium in which MgH2 is formed on the grain boundaries.

[0093] <8> The surface roughness Ra of the metal material is 0.7 μm or less. <7> The medical devices listed. <9> A medical device comprising one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys is magnesium obtained by dehydrogenating magnesium on which MgH2 is formed at the grain boundaries. <10> The magnesium and the magnesium forming the magnesium alloy have a hydrogen storage metal deposited on part or all of their surfaces. <7> from <9> A medical device listed in any one of the following categories. <11> A medical device comprising one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys includes magnesium derived from MgH2 formed on the grain boundaries. <12> The magnesium and the magnesium forming the magnesium alloy have a hydrogen storage metal deposited on part or all of their surfaces. <11> The medical devices listed. [Examples]

[0094] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0095] [Example 1] (Microstructure control of magnesium-containing metallic materials) As a sample, Mg (manufactured by Niraco Co., Ltd., purity: 97.0%) was used. To adjust the grain size, the Mg was held at atmospheric pressure and 427K for 30 minutes, and then hot-rolled by repeating a 25% reduction process twice.

[0096] Subsequently, the hot-rolled Mg was cut with a microcutter, dry-polished, and shaped into a 4mm x 8mm x 5mm specimen. Sputter deposition of Ar (nominal purity 99.9999%) with a current of 20mA, deposition time of 20 seconds, and 8Pa was performed on the top and bottom surfaces of the shaped Mg specimen using an auto fine coater, so that the Pd film thickness was 100nm.

[0097] Subsequently, the sample was placed in a sample tube and connected to a Sieberts apparatus. After evacuating the sample tube, hydrogen (nominal purity 99.99999%) was sealed into the sample tube four times to perform hydrogen replacement. Then, heat treatment was carried out under the following conditions: treatment temperature T=673K, treatment time t=86.4~691.2ks, and hydrogen pressure (PH2)=4.0MPa or 1.0MPa. In other words, hydrogenation treatment was performed.

[0098] Furthermore, as a standard annealing procedure, the sample tube containing Mg without Pd deposition was evacuated, and then Ar (nominal purity 99.9999%) was sealed in four times to replace the Ar. Then, the temperature was set to T=673K, processing time t=86.4~691.2ks, and argon pressure (P Ar Heat treatment was performed at 0.1 MPa.

[0099] The surface of each sample was wet-polished using SiC abrasive paper in the order of #320, #800, #1000, #1500, and #2000. Anhydrous methanol was used as the spreading agent. Next, mirror polishing was performed using the synthetic fiber Chemomet (registered trademark, manufactured by Buehler) with colloidal silica as the abrasive. After polishing, the samples were cleaned in an ultrasonic cleaner with anhydrous methanol and dried with dry nitrogen gas (99.9999%). Then, the observation surfaces obtained by cutting each sample with a rotary cutting wheel were etched using Nital.

[0100] Using an optical microscope and a laser microscope, photographs were taken of the etched sample surface, and the area of ​​the crystal grains was determined using image analysis software. Next, assuming that the crystal grains were perfectly round, the crystal grain size d was calculated from the determined crystal area. At this time, crystals in which the entire grain boundary was not visible in the field of view were excluded, and the area was calculated only for those in which the entire grain boundary was visible. An X-ray diffractometer was used to identify the constituent phases. The measurement conditions were: divergence slit: 0.625°, scattering slit: open, receiving slit: open, scan speed 2° / min, sampling width 0.05°. A Cu X-ray tube was used, with a tube voltage of 30kV and a tube current of 15mA. A Ni filter was used as the filter.

[0101] (Formation of MgH2 inside magnesium and crystal grain size) Figure 4 shows the results of observing the surface of magnesium under an optical microscope after two hot-rolling processes. As shown in Figure 4, no crystals were observed in the magnesium microstructure. Taking this point as processing time t=0, heat treatment was performed as described in "Microstructure Control of Magnesium-Containing Metal Materials".

[0102] Figure 5 shows the X-ray diffraction profile of the internal cross-section of magnesium that underwent two hot-rolling processes, had palladium deposited on its surface, and then was heat-treated at 673 K under a hydrogen atmosphere at 4.0 MPa. In the figure, the numbers such as "86.4 ks" represent the heat treatment time. In all heat treatment times, peaks of MgH2 with high intensity ratios are observed at 27.9° ((110) diffraction line) and 35.8° ((101) diffraction line). The area ratio of MgH2 inside the magnesium (hereinafter referred to as MgH2(int)) is small, so the intensity appears weak, but Figure 5 shows that MgH2(int) is being generated.

[0103] Figure 6 shows the results of etching the observation surface inside magnesium that had been heat-treated at 673K ​​under an argon atmosphere of 0.1 MPa, or a hydrogen atmosphere of 1.0 MPa or 4.0 MPa, and then observing the said observation surface with an optical microscope. In the figure, "0.1MPaAr" represents the results under an argon atmosphere of 0.1 MPa, "1.0MPaH2" represents the results under a hydrogen atmosphere of 1.0 MPa, and "4.0MPaH2" represents the results under a hydrogen atmosphere of 4.0 MPa.

[0104] As shown in Figure 6, MgH2(int) formed on the magnesium grain boundaries was observed on the observation surface of the magnesium interior represented by 4.0 MPaH2. On the other hand, no precipitates were observed on the observation surfaces of the magnesium interior represented by 0.1 MPaAr and 1.0 MPaH2. Furthermore, it was confirmed that the microstructure of the observation surface of the magnesium interior represented by 4.0 MPaH2 was finer than that of the observation surfaces of the magnesium interior represented by 0.1 MPaAr and 1.0 MPaH2 in all time axes.

[0105] From these tissue images, image analysis software was used to determine the area of ​​the number of crystal grains shown in "Number of Measured Grains (grains)" in Table 1 below, using 300 as the baseline. Furthermore, the magnesium crystal grain size d was calculated using the method described above. The results are shown in Table 1.

[0106] [Table 1]

[0107] In the table, for example, "Mg-0.1MPaAr(673K,86.4ks)" means magnesium that has been heat-treated (annealed) at 673K ​​for 86.4ks under an argon atmosphere of 0.1MPa. From Table 1, the results showed that, for the same heat treatment time, the average and median grain sizes inside magnesium heat-treated at 4.0MPaH2 were smaller than those inside magnesium heat-treated at 0.1MPaAr or 1.0MPaH2. In addition, the magnesium heat-treated at 4.0MPaH2 tended to have a smaller standard deviation than the other test groups. This trend indicates that the grain size distribution inside the magnesium heat-treated at 4.0MPaH2 was narrow, meaning that the grains did not grow significantly.

[0108] Figure 7 shows the change in average grain size over time of magnesium that was heat-treated at 673K ​​under an argon atmosphere of 0.1 MPa or a hydrogen atmosphere of 1.0 MPa or 4.0 MPa. From Figure 7, it can be seen that the average grain size of magnesium heat-treated at 4.0 MPaH2 decreases at each heat treatment time. Furthermore, it can be seen that as the heat treatment time increases, the difference in average grain size between magnesium heat-treated at 4.0 MPaH2 and magnesium heat-treated at 0.1 MPaAr widens. From these results, it is thought that the pinning effect of MgH2 generated inside the magnesium by hydrogenation treatment controls the crystalline structure of magnesium, and thus reduces the average grain size.

[0109] (Amount of MgH2(int) produced) The amount of MgH2(int) produced is important for controlling the microstructure of Mg. Table 2 shows the number and magnitude of MgH2(int) produced when the heat treatment conditions are changed. The number of MgH2(int) produced is given by the unit area (mm²). 2The number of MgH2(int) particles per unit area is expressed as the number of MgH2(int) particles. The number of MgH2(int) particles generated was measured using image analysis software. The size of MgH2(int) particles is expressed as the average grain size and the median grain size. The average grain size and median grain size were measured using image analysis software.

[0110] In the table, for example, "Mg-4.0MPaH2 (673K, 86.4ks)" means magnesium that has been heat-treated (annealed) at 673K ​​for 86.4 ks (24 hours) under a hydrogen atmosphere of 4.0 MPa. From Table 2, the average grain size of MgH2(int) is increased in Mg-4.0MPaH2 (693K, 86.4ks) compared to Mg-4.0MPaH2 (673K, 86.4ks), indicating that temperature has a significant impact on the growth of MgH2(int). In Mg-6.0MPaH2 (673K, 86.4ks), the number of MgH2(int) generated per unit area is increased compared to Mg-4.0MPaH2 (673K, 86.4ks), indicating that hydrogen pressure affects the frequency of MgH2(int) generation. While the average grain size of Mg-6.0MPaH2 (673K, 86.4ks) is increased compared to Mg-4.0MPaH2 (673K, 86.4ks), the average roundness remains almost unchanged from 0.78 to 0.76.

[0111] [Table 2]

[0112] The greater the amount of MgH2(int) produced, the better the pinning effect by MgH2(int) is achieved, which allows for a smaller grain size of magnesium crystals and, consequently, an improvement in the strength of the magnesium material. Therefore, the amount of MgH2(int) produced is important when controlling the structure of Mg. In particular, the number density of MgH2(int) has a significant impact on the pinning effect, and a higher number density results in a better pinning effect.

[0113] Mg-6.0MPaH2 (673K, 86.4ks) has the highest number of MgH2(int) particles per unit area (amount produced) and the largest grain size of MgH2(int) particles, but its average roundness is not significantly different from that of Mg-4.0MPaH2. Therefore, under the conditions listed in Table 2, Mg-4.0MPaH2 (693K, 86.4ks) and Mg-6.0MPaH2 (673K, 86.4ks) are preferred.

[0114] Thus, it is preferable to perform the magnesium hydrogenation treatment under conditions that maximize the amount of MgH2(int) produced. As for the conditions, when the enthalpy of the reaction Mg+H2→MgH2 is -74.7 kJ / mol and the entropy of the reaction is -135.6 J / (K·mol), the Gibbs free energy of the reaction is less than -1.2 kJ / mol.

[0115] [Example 2] (Tensile test) Pure magnesium (nominal purity: 99.8%) was used as the sample. The pure magnesium was cut to a size of 30 mm (length) x 80 mm (width) x 60 mm (height), held at atmospheric pressure and 523 K for 600 seconds, and then hot-rolled twice with a reduction ratio of 25%.

[0116] Subsequently, plate-shaped tensile test specimens were cut from the hot-rolled Mg using a surface grinder. The shape of these test specimens was determined by referring to the following formula specified in the ISO standard (standard number: ISO-6892-1-2009), with a parallel length of 21.5 mm and a rectangular cross-section with sides of 3 mm.

[0117]

number

[0118] Next, sputter deposition was performed on the upper and lower surfaces of the tensile test specimen with Ar (nominal purity 99.9999%) at a current of 20 mA, a deposition time of 20 seconds, and an 8 Pa pressure, so that the Pd film thickness was 100 nm.

[0119] Next, the tensile test specimen was placed in a sample tube and connected to a Sieberts apparatus. After evacuating the sample tube, hydrogen (nominal purity 99.99999%) was sealed into the sample tube four times to perform hydrogen replacement. Then, heat treatment was carried out under the conditions of a treatment temperature T=673K, a treatment time of 691.2ks (192 hours), and a hydrogen pressure (PH2) of 4.0MPa. In other words, a hydrogenation treatment was performed. As a control, a system was also prepared in which the argon pressure (PAr) was set to 0.1MPa instead of the hydrogen pressure, and the heat treatment was carried out under the same conditions as before.

[0120] Since the MgH2 precipitated by the aforementioned hydrogenation can serve as a crack initiation site, it was subjected to dehydrogenation treatment by vacuum degassing. The control sample was also subjected to the same dehydrogenation treatment as the hydrogen sample, with the aim of matching the heat treatment time to that of the hydrogen sample. The dehydrogenation treatment was performed for 10 -2 The experiment was conducted under conditions of an atmosphere below Pa, with a holding time of 3.6 ks at 673 K.

[0121] The gauge length of the tensile test specimen after the dehydrogenation treatment was set to 17 mm. Before the tensile test, the width of the parallel section of the tensile test specimen and the thickness of the tensile test specimen were determined using a micrometer. The tensile test was performed at room temperature using a Shimadzu Autograph AGS-J5KN as the apparatus, with a stroke speed of 0.5 mm / min.

[0122] The results are shown in Figure 8. In the figure, "192hH2" indicates the results when the hydrogenation was carried out for 192 hours, and "192hAr" indicates the results when the heat treatment using argon was carried out for 192 hours.

[0123] As shown in Figure 8, when heat treatment is performed using argon, the strength decreases significantly when the crosshead displacement is around 0.92δ / mm, but when hydrogenation is performed, the strength does not decrease until around 1.4δ / mm. Therefore, the strength of magnesium material can be improved according to the method of the present invention.

[0124] [Example 3] (Tensile test) Pure magnesium (nominal purity: 99.8%) was used as the sample. The sample was cut from a 9.0 mm thick sheet of pure magnesium to a size of 60 mm (length) x 40 mm (width) x 9 mm (height), and then processed by hot rolling. Hot rolling was performed by subjecting the sample to processing at a reduction ratio of 25% twice, while holding it at 523 K under atmospheric pressure for 1.8 ks (30 minutes). Holding at 523 K for 1.8 ks was done to ensure a uniform temperature distribution and stabilize the structure.

[0125] From the sample that had undergone hot rolling, a plate-shaped tensile test specimen was cut out using a surface grinder. The shape of the test specimen was set to a rectangular shape with a parallel length of 21.5 mm and a cross-sectional shape of 3 mm on each side, referring to the formula described in Example 2.

[0126] Pd sputter deposition was performed on the upper and lower surfaces of the test specimen. The sputtering conditions were 8 Pa of Ar (nominal purity 99.9999%), a current of 20 mA, and a deposition time of 20 seconds, resulting in a Pd film thickness of approximately 100 nm.

[0127] Next, the obtained sample was placed in a sample tube and connected to a Sieberts apparatus. After evacuating the sample tube, hydrogen (nominal purity 99.99999%) was sealed into the sample tube four times to perform hydrogen displacement. Subsequently, heat treatment was carried out under the following conditions: processing temperature T=673K, processing times of 64.8ks (18 hours) and 691.2ks (192 hours), and hydrogen pressure (PH2)=4.0MPa.

[0128] A brittle MgH2 layer forms on the surface of the sample after heat treatment in an H2 atmosphere; therefore, mechanical polishing was performed to remove the MgH2 layer. A micromotor control device (Premo-V35 (manufactured by Nakanishi Co., Ltd.)) was used for polishing, and a felt buff wheel (outer diameter φ20 mm, thickness 5 mm, shaft diameter φ3 mm) was attached as the rotating tool. The rotation speed was 4000 min⁻¹. -1 The surface was polished using a set setting until a metallic luster appeared. After polishing, the sample was ultrasonically cleaned in anhydrous methanol to completely remove any powder residue and oil from the surface.

[0129] The surface roughness Ra of the polished sample was measured using a surface roughness meter (Mitutoyo Corporation "SURFTEST SJ-400 Compact Surface Roughness Measuring Instrument"), and the arithmetic surface height Ra was measured. The measurement conditions were as follows. Cutoff value = 0.8mm Measurement length = 4mm Measurement speed=0.5mm / s Vertical magnification = 50x Horizontal magnification = 5000x.

[0130] The surface roughness measurement results are shown in Table 3.

[0131] [Table 3]

[0132] In the table, "sample with MgH2 layer formed on the surface" refers to a sample that underwent the heat treatment under the conditions of heat treatment temperature T=673K, treatment time 5 hours, and hydrogen pressure (PH2)=4.0MPa, but without surface polishing. "sample with surface polished until metallic luster appears" refers to a sample that underwent the heat treatment under the conditions of heat treatment temperature T=673K, treatment time 5 hours, and hydrogen pressure (PH2)=4.0MPa, and then underwent surface polishing.

[0133] Subsequently, tensile tests and microstructure observations were performed on the obtained tensile specimens. Tensile tests were conducted using an AGS-5kNX tensile testing machine (manufactured by Shimadzu Corporation) at a stroke speed of 0.5 mm / min at room temperature.

[0134] The results are shown in Figures 9 and 10. In Figure 9, "Mg(4MPaH2)18h" shows the results of a tensile test specimen manufactured under the same conditions as in Example 2, except that the heat treatment time was 18 hours. "Mg(0.1MPaAr)18h" shows the results of a tensile test specimen manufactured under the same conditions as the control used in Example 2, except that the heat treatment time was 18 hours. "Mg(4MPaH2)18h with MgH2(int)" shows the results of a tensile test specimen manufactured in this example. In Figure 10, "Mg(4MPaH2)192h" shows the results of a tensile test specimen manufactured under the same conditions as in Example 2, and "Mg(0.1MPaAr)192h" shows the results of a tensile test specimen manufactured under the same conditions as the control used in Example 2. "Mg(4MPaH2)192h with MgH2(int)" shows the results of a tensile test specimen manufactured in this example.

[0135] As shown in Figure 9, the tensile test specimens manufactured in Example 2 showed high nominal stress up to a nominal strain of approximately 0.065. Furthermore, the tensile test specimens manufactured in this example showed nominal stress equivalent to that of the tensile test specimens manufactured in Example 2 up to a nominal strain of approximately 0.02. As shown in Figure 10, the tensile test specimens manufactured in this example showed significantly higher nominal stress than the tensile test specimens manufactured under the same conditions as in Example 2 up to a nominal strain of approximately 0.032. [Industrial applicability]

[0136] The method of the present invention allows for the control of magnesium crystal structure and the acquisition of a magnesium-containing metal material with superior strength, without adding other metals to magnesium, or while minimizing the content of other metals. Therefore, the method of the present invention can be used in the manufacture of medical devices with superior strength containing the aforementioned material.

[0137] Furthermore, according to one aspect of the present invention, when designing medical devices such as stents, it is possible to control the metallic structure of magnesium without adding other metals to magnesium, or while reducing the content of other metals as much as possible, and thereby improve the strength of the medical device. [Explanation of Symbols]

[0138] 1 ···MgH2 2 ···Grain boundaries 3 ···crystal grains 4. MgH2 formed on the surface of magnesium

Claims

1. One or more metallic materials selected from the group consisting of magnesium and magnesium alloys are subjected to hydrogenation treatment, and MgH is applied to the grain boundaries of the metallic materials. ２ A method for controlling the microstructure of a magnesium-containing metal material, comprising step 1 of forming a structure.

2. The method for controlling the microstructure of a magnesium-containing metal material according to claim 1, wherein the hydrogenation treatment includes a step of pressurizing and heating the metal material in a hydrogen atmosphere.

3. The process of pressurizing and heating the aforementioned metal material in a hydrogen atmosphere is called Mg + H ２ →MgH ２ A method for controlling the microstructure of a magnesium-containing metal material according to claim 2, wherein the reaction is carried out under conditions such that the Gibbs free energy of the reaction is less than -1.2 kJ / mol, when the enthalpy of the reaction is -74.7 kJ / mol and the entropy of the reaction is -135.6 J / (K·mol).

4. The method for controlling the structure of a magnesium-containing metal material according to claim 1, wherein the metal material is formed by depositing a hydrogen-absorbing metal onto a part or all of the surface of the metal material.

5. A method for controlling the microstructure of a magnesium-containing metallic material according to claim 1, further comprising the step of hot-rolling one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, prior to step 1.

6. The method for controlling the microstructure of a magnesium-containing metal material according to claim 4, wherein the hydrogen storage metal is one or more metals selected from the group consisting of palladium, titanium, zirconium, and vanadium.

7. The collection comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys has MgH on the grain boundaries. ２ A medical device made of magnesium that has been formed.

8. The medical device according to claim 7, wherein the surface roughness Ra of the metal material is 0.7 μm or less.

9. The collection comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys has MgH on the grain boundaries. ２ A medical device made of magnesium obtained by dehydrogenating magnesium that has been formed.

10. The medical device according to any one of claims 7 to 9, wherein the magnesium and the magnesium forming the magnesium alloy have a hydrogen storage metal deposited on part or all of their surfaces.

11. The collection comprises one or more metallic materials selected from the group consisting of magnesium and magnesium alloys, wherein the magnesium forming the magnesium and magnesium alloys is MgH formed on the grain boundaries. ２ A medical device containing magnesium derived from [a certain substance].

12. The medical device according to claim 11, wherein the magnesium and the magnesium forming the magnesium alloy have a hydrogen storage metal deposited on part or all of their surfaces.

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