WO2022270045A1 - Ｃｏ基超弾性合金材、Ｃｏ基超弾性合金材からなる板材及び線材、Ｃｏ基超弾性合金材の製造方法、ステント、ガイドワイヤならびに人工股関節 - Google Patents

Ｃｏ基超弾性合金材、Ｃｏ基超弾性合金材からなる板材及び線材、Ｃｏ基超弾性合金材の製造方法、ステント、ガイドワイヤならびに人工股関節 Download PDF

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WO2022270045A1
WO2022270045A1 PCT/JP2022/011653 JP2022011653W WO2022270045A1 WO 2022270045 A1 WO2022270045 A1 WO 2022270045A1 JP 2022011653 W JP2022011653 W JP 2022011653W WO 2022270045 A1 WO2022270045 A1 WO 2022270045A1
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phase
alloy material
superelastic alloy
based superelastic
material according
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French (fr)
Japanese (ja)
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亮介 貝沼
俊洋 大森
キョウ 許
拓実 大平
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Tohoku University NUC
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Tohoku University NUC
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Priority to US18/571,501 priority Critical patent/US20240287651A1/en
Priority to JP2023529556A priority patent/JP7669067B2/ja
Publication of WO2022270045A1 publication Critical patent/WO2022270045A1/ja
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

  • the present invention relates to a Co-based superelastic alloy material, a plate and wire made of the Co-based superelastic alloy material, a method for producing the Co-based superelastic alloy material, a stent, a guide wire, and an artificial hip joint, and is particularly suitable as a biomaterial.
  • the present invention relates to a Co-based superelastic alloy material, a plate material and a wire made of the Co-based superelastic alloy material, and a method for producing the Co-based superelastic alloy material.
  • Stainless steel, Co-Cr alloys, and Ti alloys are widely used as biomaterials.
  • biomedical materials for example, bone substitute implant materials are desired to have a Young's modulus as low as that of bone in order to prevent stress shielding.
  • stress shielding is a phenomenon in which stress is preferentially applied to the implant material when using an implant material having a Young's modulus higher than that of the living bone, and the stress applied to the surrounding bone is shielded. .
  • stress shielding occurs, there is a problem that atrophy occurs in the bones, resulting in a decrease in bone mass and the like.
  • ⁇ -Ti alloys As materials that can achieve a Young's modulus as low as 50 GPa.
  • the ⁇ -Ti alloy has a low Young's modulus, it has poor wear resistance, and there is concern that it may break due to wear when applied as a biomaterial.
  • a Co-Cr alloy is known as a material with excellent wear resistance.
  • the Co--Cr alloy has a Young's modulus as high as about 10 times that of the living bone, the problem of stress shielding occurs when the Co--Cr alloy is applied as a biomaterial.
  • shape memory alloys By the way, in various industrial and medical fields, the practical use of shape memory alloys is being promoted to take advantage of their unique functions.
  • Ti—Ni alloys, Ni—Al alloys, Cu—Zn—Al alloys, Cu—Al—Ni alloys, etc. are known as shape memory alloys having excellent superelastic properties.
  • a Ti--Ni alloy can be mentioned as a material for practical use.
  • Patent Document 1 discloses a Cu-Al-Mn alloy having a recrystallized structure consisting of a ⁇ single phase.
  • Ni-Ni alloys have been put to practical use as biomaterials with excellent superelastic properties, but their use is limited due to their poor workability.
  • Ni allergy is regarded as a problem, the development of Ni-free superelastic materials is desired.
  • the ⁇ -Ti alloy with a low Young's modulus is Ni-free, but has a very small superelastic strain of about 3%.
  • the Co--Cr--Al--Si alloys described in Non-Patent Documents 1 to 5 are difficult to coarsen grains, and large single crystals exceeding 1 cm, for example, cannot be produced. Furthermore, the Co--Cr--Al--Si alloy described in Non-Patent Document 5 is brittle and has poor workability, such as a rolling reduction of only 20%.
  • an object of the present invention is to provide a Co-based superelastic alloy material that is excellent in workability, superelastic properties and wear resistance, and is capable of exhibiting different Young's moduli depending on the crystal orientation.
  • a further object of the present invention is to provide a plate and wire made of such a Co-based superelastic alloy material, a method for producing the Co-based superelastic alloy material, a stent, a guide wire, and an artificial hip joint.
  • the inventors first focused on the composition of the Co-based alloy and studied the composition design from the viewpoint of superelastic properties, wear resistance, and Young's modulus.
  • an alloy containing Co, Cr, Al and Si hereinafter also referred to as a Co-Cr-Al-Si alloy
  • the inventors have found that it is possible to realize a Co-based superelastic alloy material that is excellent in abrasion resistance and can exhibit different Young's moduli depending on the crystal orientation, and have completed the present invention.
  • a Co-based superelastic alloy material is a Co-based superelastic alloy material made of a Co--Cr--Al--Si based alloy, wherein the composition (atomic %) is Co--Cr - On the (Al, Si) pseudo-ternary phase diagram, point A: Co 49.5 Cr 27.5 (Al, Si) 23 , point B: Co 57 Cr 27.5 (Al, Si) 15.5 , C point: Co 50 Cr 45 (Al, Si) 5 , D point: Co 45 Cr 45 (Al, Si) 10 , and E point: Co 45 Cr 32 (Al, Si) 23 It is within the region and has Al: 2.5 to 10.0 atomic % and Si: 2.5 to 13.0 atomic %.
  • the main phase of the metal structure may be the ⁇ phase of the BCC structure.
  • the volume fraction of the ⁇ phase in the BCC structure may be 50% or more.
  • the main phase in addition to the main phase, it is selected from the group consisting of a ⁇ phase with an FCC structure, an ⁇ phase with an HCP structure, and a ⁇ phase.
  • One or two or more may be included in a total amount of 50% by volume or less.
  • the crystal structure of the ⁇ phase is one or two selected from the group consisting of A2 phase, B2 phase and L21 phase . It may consist of more than seeds.
  • the proportion of the B2 phase in the ⁇ phase may be 20% by volume or more.
  • a plate material according to an embodiment of the present invention is a plate material made of the Co-based superelastic alloy material according to any one of [1] to [6] above, wherein the Co-based superelastic alloy material is is equal to or greater than the thickness of the plate material.
  • a wire according to one embodiment of the present invention is a wire made of the Co-based superelastic alloy material according to any one of [1] to [6] above, wherein the Co-based superelastic alloy material is is equal to or larger than the radius of the wire.
  • a method for producing a Co-based superelastic alloy material according to an embodiment of the present invention is the method for producing a Co-based superelastic alloy material according to any one of [1] to [6] above, , a solution heat treatment step of performing heat treatment at 1100°C to 1400°C.
  • the method for producing a Co-based superelastic alloy material according to [9] above may include a cooling step of cooling to room temperature at an average cooling rate of 5°C/sec or more after the solution heat treatment step. .
  • the temperature range in which the ⁇ phase becomes a single phase, and the ⁇ phase + ⁇ phase or ⁇ A crystal grain coarsening step may be provided in which heat treatment is repeatedly performed in a temperature range in which two phases (phase + ⁇ phase) or in a temperature range in which three phases ( ⁇ phase + ⁇ phase + ⁇ phase) are provided.
  • the temperature range in which the ⁇ -phase single phase occurs is a temperature range of 1100 to 1400 ° C.
  • the two-phase temperature range or The temperature range in which the three phases are formed may be a temperature range of 700 to 1100°C.
  • a guidewire according to an embodiment of the present invention is made of a material containing the Co-based superelastic alloy material according to any one of [1] to [6] above.
  • a stent according to an embodiment of the present invention is made of a material containing the Co-based superelastic alloy material according to any one of [1] to [6] above.
  • An artificial hip joint according to an embodiment of the present invention is made of a material containing the Co-based superelastic alloy material according to any one of [1] to [6] above.
  • a Co-based superelastic alloy material that is excellent in workability, superelastic properties, and wear resistance and that can express different Young's moduli depending on the crystal orientation
  • the Co-based superelastic alloy material can be provided.
  • the Co-based superelastic alloy material of the present invention can exhibit superelastic properties superior to those of the conventional ones, is excellent in wear resistance, and can exhibit different Young's moduli by controlling the crystal orientation.
  • a biomaterial it can be suitably used in a wide range of fields.
  • FIG. 1 is a phase diagram of a pseudo-ternary system of Co--Cr--(Al, Si).
  • Figure 2 shows alloy no. 120 is a diffraction pattern (selected area diffraction pattern) when an electron beam is incident in the [01-1] direction of the main phase ( ⁇ phase).
  • Figures 3(a) to 3(d) show alloy no. 120 is an electron microscope image.
  • FIG. 4A shows alloy no. 120 is a diagram showing the temperature profile of the grain coarsening process (cycle heat treatment) using No. 120.
  • FIG. FIG. 4B shows analysis results by EBSD in each of Sample 1 and Sample 2 shown in FIG. 4A.
  • FIG. 5A shows alloy no.
  • FIG. 120 shows the temperature profile of the grain coarsening step (cyclic heat treatment) and the subsequent solution heat treatment step using 120.
  • FIG. FIG. 5B shows alloy no. 120 is an EBSD observation result of a cross section parallel to the plate surface.
  • FIG. 6 shows alloy no. 118 is a stress-strain curve of a single crystal sample obtained from No. 118.
  • FIG. 7A shows alloy no. 120 is a stress-strain curve of a single crystal sample obtained from No. 120;
  • FIG. 7B is a schematic diagram showing a tensile test piece used for measuring the stress-strain curve (SS curve) in this example.
  • FIG. 8A shows alloy no. 118 and no. 120 is a stress-strain curve of a single crystal sample obtained from No. 120;
  • FIG. 8B is a relationship diagram between Young's modulus and strain obtained from the stress-strain curve of FIG. 8A.
  • Figure 9 shows alloy no. 120 is a stress-strain curve of a single crystal sample obtained from No. 120, and a relationship diagram between Young's modulus and strain obtained from the stress-strain curve.
  • FIG. 10 is a photograph of the abrasion trace after the abrasion test and a photograph of its cross section.
  • the Co-based superelastic alloy material according to the present embodiment the plate material and wire made of the Co-based superelastic alloy material, and the method for manufacturing the Co-based superelastic alloy material will be described.
  • the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the gist of the present invention.
  • the Co-based superelastic alloy material of this embodiment consists of Co, Cr, Al, Si, and unavoidable impurities. That is, the Co-based superelastic alloy material of this embodiment is made of a Co--Cr--Al--Si alloy.
  • the composition (atomic %) of the Co-based superelastic alloy material of the present embodiment is Co--Cr--(Al, Si) ("(Al, Si)" is the sum of the compositions of Al and Si) shown in FIG.
  • point A Co 49.5 Cr 27.5 (Al, Si) 23
  • point B Co 57 Cr 27.5 (Al, Si) 15.5
  • point C Co 50 Cr 45 (Al, Si) 5
  • point D Co 45 Cr 45 (Al, Si) 10
  • point E Co 45 Cr 32 (Al, Si) 23 .
  • a composition in which Al is in the range of 2.5 to 10.0 atomic % and Si is in the range of 2.5 to 13.0 atomic %.
  • a composition surrounded by a pentagon means a composition on and inside each side of the pentagon.
  • each vertex of the triangle corresponds to 100% A, 100% B, and 100% C, respectively.
  • the three sides are defined to correspond to Co, Cr, and the sum of Al and Si.
  • Use state diagrams are atomic %, "40% Co-0% Cr-60% (Al, Si)" (Al, Si)", and "40% Co-60% Cr-0% (Al, Si)".
  • each vertex may also be described as " Co40 ( Al,Si) 60 ", " Co100 ", and " Co40Cr60 ".
  • the Co-based superelastic alloy material of this embodiment does not substantially contain components other than Cr, Al, Si and Co.
  • substantially free means to include the presence of unavoidable impurities to the extent that they do not impair the effects and characteristics of the present invention.
  • the unavoidable impurities are components that are mixed in due to various factors in the manufacturing process including raw materials when industrially manufacturing an alloy material, and include components that are unavoidably mixed.
  • the content of unavoidable impurities is preferably as small as possible, it is preferably less than 1.0% by mass with respect to the total mass of the alloy material.
  • a Co-based superelastic alloy material that can exhibit excellent workability, superelastic properties, and wear resistance, and can express different Young's moduli depending on the crystal orientation. can be provided. If the composition is outside the sides EA and AB, the workability is lowered, and coarse grains and single crystals are difficult to form. When the composition falls outside the side BC, the superelastic properties and Young's modulus properties are degraded. Superelastic properties, Young's modulus and workability all deteriorate when the composition falls outside of sides CD and DE.
  • Al is an element that has the effect of affecting the phase stability and workability of the ⁇ phase.
  • hot workability can be improved by adjusting the Al content.
  • the Al content is set to 2.5 atomic % or more, preferably 4.5 atomic % or more, and more preferably 5.0 atomic % or more.
  • the Al content is set to 10.0 atomic % or less, preferably 9.0 atomic % or less, and more preferably 8.0 atomic % or less.
  • Si is an element that has the effect of affecting the phase stability and workability of the ⁇ phase.
  • hot workability it is necessary to control the Si content. That is, hot workability can be improved by adjusting the Si content. If the Si content is less than 2.5 atomic percent, there is a risk that a sufficient ⁇ phase will not be obtained. Therefore, the Si content is set to 2.5 atomic % or more, preferably 6.5 atomic % or more, and more preferably 7.0 atomic % or more. On the other hand, if the Si content exceeds 13.0 atomic %, the hot workability may deteriorate. Therefore, the Si content is set to 13.0 atomic % or less, preferably 12.0 atomic % or less, and more preferably 11.0 atomic % or less.
  • the elements described above are basic components contained in the Co-based superelastic alloy material according to this embodiment. That is, the Co-based superelastic alloy material of this embodiment does not substantially contain components other than Cr, Al, Si and Co. Inevitable impurities, such as ingredients derived from raw materials, may be mixed due to various factors in the manufacturing process. As described above, the content of such unavoidable impurities is preferably as small as possible.
  • the metallic structure of the Co-based superelastic alloy material of the present embodiment has a ⁇ phase, which is a BCC structure, as the main phase.
  • the term "main phase" as used herein means that it accounts for 50% by volume or more of the total metal structure in the Co-based superelastic alloy material.
  • the volume fraction of the ⁇ phase is less than 50%, sufficient superelastic properties may not be obtained. Furthermore, it may be difficult to precisely control the Young's modulus for each crystal orientation. Therefore, it is more desirable that the volume fraction of the ⁇ phase is 50% or more.
  • the Co-based superelastic alloy material of the present embodiment since the degree of order of the ⁇ phase, which is the main phase, is lowered, it is considered that the hot workability described later is improved. Also, the Co-based superelastic alloy material may be a single crystal having no crystal grain boundaries between ⁇ phases.
  • the crystal structure of the ⁇ phase which is the main phase, is a group consisting of A2 type (A2 phase), B2 type (B2 phase) and L2 1 type (L2 1 phase) from the viewpoint of sufficiently exhibiting superelastic properties and workability. It is preferable that the crystal structure is one or two or more selected from the above. In order to exhibit the effect more effectively, the crystal structure of the main phase more preferably contains a large amount of B2 type. In order to ensure sufficient superelastic properties, the crystal structure of the ⁇ phase is preferably basically composed of fine phases of one or both of B2 type and L21 type. The fine phases in this case are for example less than 10 nm.
  • the crystal structure of the ⁇ -phase may contain the A2 type, but if the volume fraction of the A2 type increases, the superelastic properties will deteriorate.
  • the crystal structure of the ⁇ -phase is preferably basically composed of fine phases of one or both of A2 type and B2 type. The fine phases in this case are for example less than 10 nm.
  • the L2 1 type may be included, but if the volume fraction increases, the workability will deteriorate. Therefore, the crystal structure of the ⁇ phase may contain a small amount of A2 type and L21 type , but more preferably contains a large amount of B2 type.
  • the proportion of the B2 type in the ⁇ phase is preferably 20% by volume or more. More preferably, the proportion of the B2 type in the ⁇ phase is 30% by volume or more, and still more preferably 40% by volume or more.
  • a small amount of one or more of the FCC-structured ⁇ -phase, the HCP-structured ⁇ -phase, and the ⁇ -phase may be precipitated.
  • the ⁇ phase contributes to the improvement of hot workability and the effect of facilitating the formation of coarse grains.
  • the ⁇ phase contributes to the improvement of wear resistance and the effect of facilitating the formation of coarse grains, but if it appears in a large amount, it may impair the superelastic properties.
  • the ⁇ phase contributes to the improvement of wear resistance and the effect of facilitating the formation of coarse grains.
  • the total is 50 It is preferable to set it as vol% or less.
  • the Co-based superelastic alloy material can be manufactured by conventional methods, such as melting and casting, hot working (hot forging, hot rolling, etc.), and then solution treatment in a specific temperature range, which will be described later. .
  • the manufacturing conditions in each step are not particularly limited, but for example, the temperature in hot working can be 1100 to 1400° C. and the hot working rate can be 10% or more.
  • solution treatment is performed after hot working.
  • the solution treatment is carried out by heating a Co-based superelastic alloy material formed by melting and casting and forming by hot working or the like to a solution temperature to convert the structure into a single ⁇ -phase with a BCC structure, followed by quenching.
  • the solution treatment is carried out at a temperature range of 1100 to 1400°C. The higher the temperature of the solution treatment, the easier it is to obtain a single phase of ⁇ phase.
  • the holding time at the solution temperature is not particularly limited, it is preferably 60 minutes or more from the viewpoint of sufficiently raising the temperature. However, if the holding time exceeds 24 hours, there is a risk of oxidation, so the holding time is preferably 24 hours or less.
  • the crystal grain coarsening step (cycle heat treatment) described below is performed after the solution heat treatment step described above. is preferably applied. That is, after the solution heat treatment step, there is a temperature range in which a single ⁇ phase occurs, a temperature range in which two phases of ⁇ phase + ⁇ phase or ⁇ phase + ⁇ phase occur, or a temperature range in which three phases of ⁇ phase + ⁇ phase + ⁇ phase occur.
  • Co-based superelastic alloy material can be made into coarse grains or single crystals by repeatedly heat-treating .
  • the number of times of the crystal grain coarsening step is not limited to a plurality of times, and the effect can be obtained even if it is performed only once. That is, after the solution heat treatment, it is cooled to a temperature range where two phases of ⁇ phase + ⁇ phase or ⁇ phase + ⁇ phase, or three phases of ⁇ phase + ⁇ phase + ⁇ phase, at an average cooling rate of the level described later. , after holding for a certain period of time, the temperature may be raised to a temperature range in which the single ⁇ phase is obtained, and the temperature may be held only. As a result, the Co-based superelastic alloy material can be made into coarse grains or single crystals. However, in order to make the crystal grains coarser or to produce a larger single crystal, it is preferable to perform the crystal grain coarsening step multiple times after the solution heat treatment step. A case where the crystal grain coarsening step is performed multiple times will be described in detail below.
  • the steel is cooled from the above-mentioned solution temperature to the temperature range in which the two phases are obtained or the temperature range in which the three phases are obtained. Specifically, it is cooled to a temperature range of 700 to 1100° C., which is the temperature range for the two phases or the temperature range for the three phases.
  • the average cooling rate at this time is preferably 0.1° C./min or more, more preferably 1° C./min or more.
  • the upper limit of the average cooling rate is not particularly limited, it may be 20° C./min or less. Cooling is performed by immersing in a coolant such as water or by forced air cooling.
  • the holding time is preferably from 1 minute to 24 hours. If the holding time is too long, oxidation may occur, so 24 hours or less is preferable. On the other hand, if the holding time is too short, the ⁇ phase, the ⁇ phase, or the precipitates of the ⁇ phase and the ⁇ phase cannot be sufficiently formed, so holding in the temperature range of the two phases or the temperature range of the three phases
  • the time is preferably 1 minute or more.
  • the temperature is raised to the single-phase ⁇ -phase temperature range and held. Specifically, the temperature is raised to a temperature range of 1100 to 1400° C., which is the temperature range in which the single ⁇ phase is obtained.
  • the average heating rate at this time is not particularly limited, but from the viewpoint of easily obtaining coarse grains or single crystals, it is preferably 20° C./min or less, more preferably 10° C./min or less. If the average heating rate is too low, the efficiency may decrease, so it is preferably 0.1° C./min or more.
  • the “average cooling rate” in the present embodiment is a value obtained by dividing the temperature drop width of the alloy material from the start of cooling to the end of cooling by the time required from the start of cooling to the end of cooling.
  • the “average temperature rise rate” is a value obtained by dividing the temperature rise range of the alloy material from the start of heating to the end of heating by the time required from the start of heating to the end of heating.
  • the temperature range in which the ⁇ phase is single phase and the temperature range in which two phases, ⁇ phase + ⁇ phase or ⁇ phase + ⁇ phase, or ⁇ It is preferable to repeat the heat treatment in the three phases of phase + ⁇ phase + ⁇ phase, and the number of repetitions is about 1 to 20 cycles. That is, "cooling from the temperature range of single ⁇ phase to the temperature range of two phases or three phases and holding, then raising the temperature again to the temperature range of single ⁇ phase and holding" heat treatment. is one cycle, by repeating 1 to 20 cycles, the Co-based superelastic alloy material can be easily formed into coarse grains or single crystals, and as a result, the effect of being able to produce coarse grains or single crystals is obtained. be able to.
  • the temperature is maintained in the ⁇ -phase single-phase temperature range, and then room temperature (about 25 ° C.). Cool (cooling process).
  • the Co-based superelastic alloy material of this embodiment can be manufactured by performing rapid cooling (for example, water cooling) at the time of cooling.
  • rapid cooling for example, water cooling
  • the average cooling rate during rapid cooling is preferably 5° C./second or more.
  • the crystal structure can be one or more selected from the group consisting of types. Specifically, by setting the average cooling rate to 5° C./second or more, the proportion of the B2 phase in the ⁇ phase can be set to 20% by volume or more. Furthermore, in order to obtain a ⁇ -single-phase structure and further increase the proportion of the B2 type in the ⁇ -phase crystal structure, it is more preferable to set the average cooling rate during rapid cooling to 100° C./second or more. By setting the average cooling rate during quenching to 100° C./second or more, a B2-type fine phase of less than 10 nm can be obtained. As a result, superelastic properties, low Young's modulus properties and workability can be sufficiently secured.
  • the average cooling rate during rapid cooling is 100 ° C./second or more
  • the A2 type and the L21 type do not exist or their volume fractions are extremely small, which is preferable.
  • the average cooling rate during quenching is less than 100 ° C./sec
  • a coarse phase of 10 nm or more consisting of one or both of A2 type and L21 type and having a volume fraction of less than 80% appears.
  • less than 50% by volume of precipitates composed of one or more of ⁇ phase, ⁇ phase, and ⁇ phase appear from the grain boundaries of the ⁇ phase. Even in such cases, relatively good superelastic properties, low Young's modulus properties and workability are obtained, but these properties are better with the fine phase of B2 type.
  • the average cooling rate during rapid cooling it is more preferable to set the average cooling rate during rapid cooling to 100° C./second or more.
  • the average cooling rate during quenching is less than 5° C./sec, a coarse phase of 10 nm or more and having a volume fraction of 80% or more consisting of one or both of A2 type and L21 type appears.
  • 50% by volume or more of precipitates composed of one or more of ⁇ phase, ⁇ phase, and ⁇ phase emerge from both the grain boundaries and grain interiors of the ⁇ phase.
  • superelastic properties, low Young's modulus properties and workability may be significantly degraded.
  • the Co-based superelastic alloy material according to this embodiment exhibits the following characteristics.
  • the Co-based superelastic alloy material of this embodiment has strong elastic anisotropy. That is, in the Co-based superelastic alloy material of this embodiment, the Young's modulus strongly depends on the crystal orientation. Therefore, the Co-based superelastic alloy material of this embodiment has different Young's moduli depending on the crystal orientation. Specifically, in directions such as the ⁇ 100> direction, it has a Young's modulus close to that of living bone of 10 to 30 GPa, while in directions such as the ⁇ 110> and ⁇ 111> directions, it has a high rigidity of 80 to 150 GPa.
  • the Young's modulus of the Co-based superelastic alloy material of this embodiment differs depending on the crystal orientation.
  • the Young's modulus of living bone is about 10 to 30 GPa. That is, if the Young's modulus of the Co-based superelastic alloy material can be lowered to the same level as that of living bone, the Young's modulus will be close to that of living bone, and the Co-based superelastic alloy material can be used as a biomaterial such as a bone substitute implant material. can prevent stress shielding. In other words, when the Co-based superelastic alloy material of the present embodiment is applied to a biomedical material such as a bone substitute implant material, a Co-based superelastic alloy in which the ⁇ 100> direction is dominant among the crystal orientations is used. By doing so, the Young's modulus can be lowered.
  • members such as stents and guide wires are required to have a high Young's modulus of about 80 to 150 GPa. Therefore, when the Co-based superelastic alloy material of the present embodiment is applied to a member such as a stent or a guide wire, the Co-based superelastic alloy in which the ⁇ 110> direction and the ⁇ 111> direction are dominant among the crystal orientations can be used to increase the Young's modulus.
  • the Co-based superelastic alloy material according to the present embodiment there is a correlation between the crystal orientation and the appearing Young's modulus. , can express different Young's moduli.
  • the Young's modulus of each crystal orientation can be calculated from the gradient of the stress-strain curve using a strain gauge. Specifically, a single crystal sample having a specific crystal orientation is prepared, a strain gauge is attached to the sample, and a stress-strain curve is experimentally determined by a tensile test or a compression test. Then, the Young's modulus at that strain is obtained from the gradient of the stress-strain curve at that strain.
  • the Co-based superelastic alloy material of this embodiment exhibits stable and excellent superelasticity. Specifically, the superelastic strain is 3% or more, and very large superelasticity can be exhibited.
  • the term “superelastic strain” in this embodiment is defined as the amount of strain in the plateau region in the stress-strain diagram shown in FIG. 6, which will be described later.
  • the "plateau region” is the region after the elastic deformation region, which is the region of constant stress after yielding.
  • the Co-based superelastic alloy material of this embodiment has excellent wear resistance due to the optimization of the composition. Therefore, it can be suitably used as a biological material. Improvement in wear resistance can be achieved by optimizing the composition.
  • the Co-based superelastic alloy material of this embodiment is excellent in hot workability in addition to the above characteristics. It is considered that this is because the degree of order of the BCC structure is lowered.
  • Conventional Co--Cr--Al--Si alloys have good superelastic properties, but they are very brittle and are not easy to work.
  • hot workability can be improved by suppressing the contents of Al and Si and lowering the degree of order of the ordered alloy.
  • the superelastic properties of the Co-based superelastic alloy material may depend not only on the crystal structure but also on the size of the crystal grains. For example, in the case of a plate material or a wire material, if the average crystal grain size of the crystal grains is greater than the thickness T of the plate material or the radius R of the wire material, the superelasticity is greatly improved. This is probably because the binding force between crystal grains is reduced when the average crystal grain size of the crystal grains is greater than the thickness T of the plate or the radius R of the wire.
  • the plate material made of the Co-based superelastic alloy material preferably has an average grain size of crystal grains equal to or larger than the thickness T of the plate material.
  • a plate material having such crystal grains is in a state in which individual crystal grains are released from grain boundaries on the surface of the plate material.
  • the sheet material since the average crystal grain size is equal to or greater than the thickness T, the sheet material exhibits excellent superelasticity because the restraining force between crystal grains is reduced, as in the case of the wire material described above.
  • the average crystal grain size of the crystal grains of the plate material is 2T or more. It is more preferable that the average crystal grain size of the crystal grains is equal to or larger than the width W of the plate material.
  • a plate material made of a Co-based superelastic alloy material can be used for various spring materials, contact members, clips, etc. by utilizing its superelasticity.
  • the wire made of the Co-based superelastic alloy has an average crystal grain size equal to or larger than the radius R of the wire.
  • the average crystal grain size of the crystal grains is 2R or more in diameter.
  • a wire made of a Co-based superelastic alloy material can be used, for example, for stents and guidewires. Further, when the wire material made of the Co-based superelastic alloy material is a fine wire with a diameter of 1 mm or less, a plurality of fine wires may be twisted to form a stranded wire. Furthermore, the wire can be used as a spring material.
  • a plate material made of the Co-based superelastic alloy material of the present embodiment is subjected to hot rolling, and then to punching and/or pressing into a desired shape. After that, it can be manufactured by performing the above-mentioned solution treatment at least once, and performing quenching treatment and aging treatment as necessary.
  • the wire made of the Co-based superelastic alloy material of this embodiment is made into a wire by hot forging and drawing. After that, the above-mentioned solution heat treatment is performed at least once, and quenching treatment and aging treatment are performed as necessary.
  • a wire rod By producing a wire rod by performing the same treatment as for the plate material, it is possible to produce a wire rod in which the crystal grains are coarsened so that the average crystal grain size is greater than or equal to the radius.
  • the Co-based superelastic alloy material of this embodiment can maintain a Young's modulus close to that of living bones, it is suitable as a biological material such as an artificial hip joint.
  • the Co-based superelastic alloy material of the present embodiment has different Young's moduli depending on the crystal orientation, by giving priority to the ⁇ 110> direction, the ⁇ 111> direction, etc., which show a relatively high Young's modulus, It can be suitably used for stents, guide wires, and the like.
  • An alloy material having the composition shown in Table 1 was melted in an Ar atmosphere by high-frequency induction melting, and the melted material was cast into a mold to prepare a round bar-shaped sample ( ⁇ 10 mm).
  • the obtained round-bar-shaped sample was subjected to hot rolling at 1200° C. to a plate thickness of 4 mm to obtain a Co-based superelastic alloy material.
  • the hot workability of the Co-based superelastic alloy material was evaluated as described later.
  • the Co-based superelastic alloy material formed by hot rolling was subjected to solution treatment.
  • Alloy No. Alloy materials other than 122 were heated to 1200° C. (solution temperature) to convert the structure into a single ⁇ phase, and then water-cooled (average cooling rate: 1700° C./sec).
  • Alloy no. The No. 122 alloy material was heated to 1300° C. (solution temperature) to convert the structure into a ⁇ -phase single phase, and then water-cooled (average cooling rate: 1700° C./sec).
  • Table 1 shows the phase state after water cooling and the volume fraction of the ⁇ phase.
  • " ⁇ + ⁇ " is the ⁇ phase (alloy No. In the case of 105, it means that 26% by volume of ⁇ phase) was observed.
  • alloy No. 1 which is a comparative example
  • All of Nos. 124 to 129 had cracks during hot rolling and could not be rolled to a rolling reduction of 60%.
  • all the alloy materials of the present invention examples could be hot rolled without cracking.
  • FIG. 2 is a diffraction pattern (selected area diffraction pattern) when an electron beam is incident in the [01-1] direction of the main phase ( ⁇ phase).
  • FIGS. 3(a) to 3(d) show alloy No. 120 is an electron microscope image.
  • FIG. 3(a) is a bright field image obtained using the transmission spot
  • FIG. 3(b) is a dark field image obtained using the 111 diffraction spot in the same field.
  • FIG. 3(c) is a bright field image obtained using a transmission spot at another observation location
  • 3(d) is a dark field image obtained using a 200 diffraction spot in the same field of view. be. From the selected area diffraction pattern of [01-1] incidence of the main phase ( ⁇ phase) shown in FIG. It can be seen that the main phase of 120 is the BCC structure. Furthermore, in FIG. 2, the intensity of the diffraction spot at 111 is very weak, suggesting that the reduction in the degree of order of the BCC structure results in excellent hot workability.
  • Sample 1 has a four-phase structure of ⁇ phase (BCC) as a parent phase, ⁇ phase, ⁇ phase, and ⁇ phase transformed by cooling. Moreover, from the misorientation map (GROD map), it can be seen that Sample 1 has strain in the parent phase between the precipitates. On the other hand, in Sample 2, as shown in FIG. 4B, it can be seen that it is a ⁇ -phase single phase, which is the mother phase. However, we observed the formation of sub-boundaries in the grains, which are presumed to have been formed by the strain induced by the precipitates.
  • plate material The hot rolled alloy no. A plate material having a thickness of 1.5 mm, a width of 8 mm, and a length of 70 mm was cut from 120 and subjected to cycle heat treatment (dotted line area) shown in FIG. 5A. After that, the plate material after the cycle heat treatment was solution heat treated at 1200° C. for 8 hours, and then quenched in water (W.Q.) (see FIG. 5A). When the cross section of the plate material after quenching parallel to the plate surface was observed by EBSD, it was observed that the crystal grains were coarsened as shown in FIG. Indeed, some grains were growing. In addition, in FIG. 5B, the single crystal is shown in dark gray.
  • alloy No. 2 which is an example of the present invention
  • 115, 117 to 120, and 123 to 125 which are comparative examples, were subjected to the cycle heat treatment shown in FIG.
  • alloy No The orientation dependence of the superelastic properties of the single crystal sample obtained from 120 is shown in FIG. 7A.
  • the critical stress increased and the amount of deformation strain decreased compared to the ⁇ 100> oriented sample.
  • the ⁇ 111> orientation on the other hand, superelasticity was not obtained because the critical stress exceeded the breaking stress of the material itself.
  • alloy No. Alloy Nos. 115, 117 and 119 also 118 and No. Good results similar to 120 were obtained.
  • alloy No. 1 which is a comparative example
  • In Nos. 123 to 125 single crystals could not be produced as shown in Table 4, and polycrystals were obtained, so superelastic properties could not be obtained due to intergranular fracture.
  • the stress-strain curve (SS curve) in this example was obtained as follows. First, a tensile test piece having the dimensions shown in FIG. 7B was repeatedly stress-loaded and unloaded twice by a tensile test to obtain a stress-strain curve.
  • Fig. 9 shows alloy No. 120 is a stress-strain curve of a single crystal sample obtained from No. 120, and a relationship diagram between Young's modulus and strain obtained from the stress-strain curve.
  • alloy no. The Young's modulus of 120 differs depending on the orientation, and the samples near ⁇ 110> and ⁇ 111> showed high values of 80 GPa and 120 GPa, respectively. It is expected that an even higher Young's modulus can be obtained by moving the orientation closer to the ⁇ 111> direction.
  • FIG. 10 shows a photograph of the abrasion trace after the abrasion test and a photograph of the cross section.
  • the amount of wear is very small.
  • a specific wear amount wear volume/sliding distance/load
  • the specific wear amount was calculated from the cross-sectional area and wear radius calculated from the cross-sectional image shown in FIG. 10, the wear volume was calculated, and the sliding distance and load were calculated.
  • Table 5 shows the results. Further, the unit of the specific wear amount shown in Table 5 is " ⁇ 10 -8 (mm 2 /N)".
  • alloy no. 120 was used to investigate the effect of the average cooling rate in the cooling process after the solution treatment on the crystal structure of the ⁇ phase. Specifically, alloy No. 120 was heated to 1200° C. (solution temperature) to convert the structure into a ⁇ -phase single phase, and then cooled at the average cooling rate shown in Table 6. Table 6 shows the phase state after cooling, the volume fraction of the ⁇ phase, and the ratio (% by volume) of the B2 phase in the ⁇ phase. In addition, in the notation of "phase” in Table 6, for example, " ⁇ + ⁇ + ⁇ " is the ⁇ phase of the main phase and the fraction obtained by subtracting the " ⁇ phase volume fraction" from 100% ( ⁇ + ⁇ phase) is observed. It means that it was done.

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