JP6621977B2 - β-type Ti-based superelastic alloy and method for producing β-type Ti-based superelastic alloy - Google Patents

Description

  The present invention relates to a method for producing a β-type Ti-based superelastic alloy and a β-type Ti-based superelastic alloy, and in particular, a β-type Ti capable of suitably producing an alloy having a desired shape such as a plate material or a wire by cold working. The present invention relates to a method for producing a superelastic alloy and a β-type superelastic alloy.

  Shape memory alloys generally exhibit shape memory properties, superelasticity, or both properties due to martensitic transformation. When the shape memory alloy exhibits superelasticity at room temperature, the repeated deformation characteristics are remarkably improved as compared with a normal spring metal. Therefore, it can be said that one of the preferable results from the viewpoint of material design is that the shape memory alloy exhibits superelasticity at room temperature.

  It has been clarified that a Ti—Ni-based shape memory metal exhibits both the above characteristics at room temperature.

  However, other Ti-based shape memory alloys rarely have both shape memory characteristics and superelastic characteristics at room temperature, and generally exhibit either one of the characteristics. This is because the number of elements composing the Ti-based shape memory alloy is often 3 or more, and the concentration is severe enough that the desired characteristics may not occur if the concentration of the additive element changes even at 0.1%. It is thought that this is because it is very difficult to find an ideal alloy composition, processing method, etc. .

  In addition, the inventor of the present application has clarified in the past that a β-type Ti-based alloy composed of a predetermined composition exhibits shape memory characteristics (see Patent Document 1).

JP 2009-215650 A

  However, there has been a problem that it has not yet been clarified that a β-type Ti alloy composed of the above-described predetermined composition exhibits superelasticity.

  Accordingly, the present invention has been made in view of these points, and provides a β-type Ti-based superelastic alloy that exhibits superelasticity with a β-type Ti-based alloy and a method for producing a β-type Ti-based superelastic alloy. It is an object of the present invention.

  (1) In order to achieve the object described above, the β-type Ti superelastic alloy of the present invention is Ti—X1 mol% Cr—X2 mol% Sn, and 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and 0.8 ≦ X1 / X2 ≦ 1.5 are all satisfied.

  Thereby, the Ti-based alloy can exhibit superelasticity with a shape recovery rate of 10% or more at room temperature.

  (2) Further, the β-type Ti-based superelastic alloy of the present invention has 4.5 ≦ X1 ≦ 5.5, 4.5 ≦ X2 ≦ 5.5, 9.5 <X1 + X2 <10.5, and 0 It is preferable that all the conditions of .8 ≦ X1 / X2 ≦ 1.2 are further satisfied.

  Thereby, the Ti-based alloy can exhibit superelasticity with a shape recovery rate of 40% or more at room temperature.

  (3) Further, in order to achieve the above-described object, the production method of the β-type Ti-based superelastic alloy of the present invention has the same composition as the β-type Ti-based superelastic alloy described in (1) or (2) above. The intermediate material manufacturing process for manufacturing the intermediate material, which is an alloy in the state before cold working, and the temperature of the processed member in the part in contact with the intermediate material is 313 to 353K, and the average temperature of the intermediate material during cold working is 293K to 393K, including a cold working process for cold working the intermediate material.

  Thereby, it can cold-work into a desired shape, without producing a crack and a crack with respect to the intermediate material of (beta) type | system | group Ti superelastic alloy as described in said (1) or (2).

  (4) Further, in the cold working step of the method for producing a β-type Ti-based superelastic alloy of the present invention, it is preferable to perform cold working on the intermediate material at a working speed of 20 m / min or less for the intermediate material.

  As a result, a rapid temperature rise in the intermediate material can be suppressed and brittle precipitates can be prevented from being generated inside the intermediate material, so that the intermediate material has a desired shape without causing cracks or cracks. Can be cold worked.

  (5) Further, in the method for producing a β-type Ti-based superelastic alloy according to the present invention, the total working rate with respect to the initial thickness of the intermediate material in the cold working process is 40% or more and before the intermediate material is cracked or cracked. And an intermediate annealing step for annealing the intermediate material.

  Thereby, it is possible to perform cold working with a total working rate of 97% or more at the maximum with respect to the intermediate material.

  (6) Further, in the cold working step of the method for producing a β-type Ti-based superelastic alloy according to the present invention, the average working rate per one time with respect to the intermediate material is set to 32.5% or less, and the cold working is performed on the cold working material. It is characterized by performing.

  Thereby, it is possible to prevent the intermediate material from being cracked or cracked at a low total processing rate such as 40% or less.

  According to the β-type Ti-based superelastic alloy and the β-type Ti-based superelastic alloy manufacturing method of the present invention, a material having a desired shape such as a plate material or a wire that exhibits superelasticity at room temperature can be manufactured by cold working. There is an effect that a possible Ni-free superelastic alloy can be provided.

  Hereinafter, the present Example regarding the manufacturing method of (beta) type | system | group Ti type | system | group superelastic alloy and (beta) type Ti type | system | group superelastic alloy of this invention is demonstrated. In this example, a β-type Ti alloy showing superelasticity with a shape recovery rate of 5% or more at room temperature (293K to 297K) and exhibiting a shape memory effect mainly at other than room temperature is referred to as “β-type Ti-based”. It is called “superelastic alloy”. A β-type Ti-based alloy that exhibits superelasticity with a shape recovery rate of less than 5% and exhibits a shape memory effect mainly at other than room temperature is referred to as a “β-type Ti-based shape memory alloy”.

[1] Composition First, the β-type Ti-based superelastic alloy of this example will be described.

[1-1] Selection Criteria for Metal Additive Elements [1-1-1] Melting Point Nb (melting point: 2468 ° C.) in other β-type Ti-based shape memory alloys such as Ti—Nb alloys and Ti—Mo alloys The β-stable element such as Mo (melting point: 2620 ° C.) has a melting point higher than that of Ti (melting point: 1668 ° C.) by 800 ° C. There is. Therefore, the melting point of the metal-added element is preferably 2000 ° C. or less, which can be easily dissolved by the metal melting method.

[1-1-2] Boiling point When the boiling point of the additive element is equal to or lower than the melting point of Ti (1668 ° C.), there is a problem that the additive element is vaporized (evaporated) during dissolution of Ti. Therefore, the boiling point of the additive element is preferably equal to or higher than the melting point of Ti (1668 ° C.).

[1-1-3] Lattice strain The mechanism by which the β-type Ti-based alloy exhibits superelasticity is between two phases of a body-centered cubic β called a parent phase and an orthorhombic α ″ called a thermoelastic martensite phase. This lattice deformation causes a phase transformation, and the maximum value of the strain that causes the phase transformation (hereinafter referred to as “phase transformation strain”) is the maximum value of the superelastic strain. In order to increase the elastic strain, it is necessary to increase the phase transformation strain.

  Here, the maximum value of the phase transformation strain in the Ti—Ni based superelastic alloy is 10.5%, and the maximum value of the phase transformation strain in the β-type Ti based superelastic alloy such as the Ti—Nb based superelastic alloy is 3%. % (Ti-16Nb-4.8Sn: 3.3%, Ti-24Nb-3Al: 3.0%). Therefore, it can be said that a β-type Ti superelastic alloy having a maximum phase transformation strain exceeding 3% exhibits superior superelasticity as compared with a conventional β-type Ti superelastic alloy.

[1-2] Composition of the present alloy The compositions of the β-type Ti-based superelastic alloy and β-type Ti-based shape memory alloy (hereinafter referred to as “the present alloy”) manufactured in this example are Ti—X1 mol% Cr. -X2 mol% Sn. The reason for selecting Cr and Sn as the metal additive element of this alloy is that the melting point and boiling point of the metal additive element of this alloy are the above-mentioned “(1-1-1) melting point” and “(1-1-2) boiling point”. In addition to satisfying the selection criteria, an impression is obtained that the Ti—Cr—Sn-based alloy may satisfy the selection criteria of “(1-1-3) lattice strain” in a preliminary experiment performed before this example. This is because.

[1-2-1] Ti selection reason and concentration (mol%)
Ti is a base element in this alloy. This is because Ti is lightweight and has excellent strength, corrosion resistance, and biocompatibility. The concentration of Ti (mol%) is 100 mol% to Cr concentration X1 (mol%) and Sn concentration X2 (mol%), and when inevitable impurities are mixed, the concentration α (mol%) of the inevitable impurities is added. The concentration is 100− (X1 + X2 + α) (mol%) obtained by dividing the total concentration X1 + X2 + α (mol%) obtained.

[1-2-2] Reason for addition of Cr and its concentration X1 (mol%)
Cr is a β-phase stabilizing element in this alloy. The β-phase stabilizing element is an additive element for the present alloy to exhibit superelasticity at room temperature by lowering the Ms point (martensitic transformation start temperature) of the present alloy. In other words, the Cr concentration is directly related to the superelastic performance difference of the present alloy in order to adjust the Ms point to a desired temperature. Therefore, the present inventor set the concentration X1 (mol%) of Cr added to the alloy so as to satisfy 0.0 ≦ X1 ≦ 9.0 based on past experience.

[1-2-3] Reason for addition of Sn and its concentration X2 (mol%)
Sn is an ω brittleness suppressing element in the present alloy. The ω brittleness suppressing element is an additive element for suppressing ω brittleness due to the ω phase that is likely to occur as an intermediate product from the residual β phase to the α phase. When a large number of ω phases are formed, reverse transformation is inhibited and superelasticity is not exhibited. In addition, when the Sn concentration is increased, the effect of suppressing the ω brittleness is enhanced, but the present inventor considers that the second phase other than the ω phase is formed and the shape memory characteristics are deteriorated. Therefore, the present inventor has set the concentration X2 (mol%) of Sn added to the alloy so as to satisfy 0.0 ≦ X2 ≦ 6.0 based on past experience.

[1-2-4] Total concentration of additive elements (Cr, Sn) X1 + X2 (mol%)
When Sn is added to this alloy (Ti—Cr—Sn superelastic alloy), Sn also has the effect of lowering Ms, like Cr. Therefore, when Cr and Sn are added to the β-type Ti-based superelastic alloy, the total concentration X1 + X2 (mol%) of the additive element that is the sum of the concentrations of Cr and Sn is also an important factor in adjusting the Ms point. The inventor thinks. Therefore, the present inventor has set the total concentration X1 + X2 (mol%) of the additive element added to the alloy so as to satisfy 3.0 ≦ X1 + X2 ≦ 12.0 based on past experience.

[1-2-5] Concentration ratio X1 / X2 of additive elements (Cr, Sn)
The present inventor considers that the balance between the adjustment of the Ms point and the effect of suppressing the ω phase is also important for the present alloy to exhibit superelasticity. The present inventor considers that the factor for determining whether this balance is appropriate is the concentration ratio X1 / X2 of the additive element. Therefore, the present inventor has set the concentration ratio X1 / X2 of the additive element added to the alloy so as to satisfy 0.1 <X1 / X2 <10.0 based on past experience.

[2] Manufacturing Process Next, a manufacturing method of the β-type Ti superelastic alloy in the present embodiment will be described.

  The manufacturing method of the β-type Ti-based superelastic alloy in the present embodiment includes an intermediate material manufacturing process and a cold working process. Moreover, it is preferable that the manufacturing method of the β-type Ti-based superelastic alloy in the present embodiment further includes a homogenization treatment, an intermediate annealing step, and a solution treatment step.

[2-1] Intermediate Material Manufacturing Process The intermediate material of this alloy was produced in an ingot shape by melting the raw materials of each composition element using a non-consumable tungsten electrode type argon arc melting furnace. In this embodiment, the intermediate material refers to an alloy having the same composition as that of the present alloy manufactured before the cold working process.

[2-2] Cold working step [2-2-1] Shape of the main alloy The intermediate material after the homogenization treatment was processed into the main alloy having a desired shape by the cold working step. The shape of the alloy can be selected from plate materials, wire materials, and other desired shapes. Also, the shape of the intermediate material after processing can be selected from plate materials, wire materials, and other desired shapes. That is, the shape before and after processing is not limited to a specific shape such as a plate material or a wire material. In this example, the intermediate material and the present alloy were processed into plate materials.

[2-2-2] Processing temperature [2-2-2-1] Definition of cold processing The upper limit of the processing temperature in cold processing is generally called recrystallization temperature. That is, when the processing temperature is ½ of the melting point of the alloy, the processing is classified as cold processing.

  In this example, even when the alloy was heated at about 1273 K (1000 ° C.) for 2 hours, the alloy did not dissolve at all. From this, the melting point of this alloy is at least about 1273 K (1000 ° C.) at least. Therefore, the recrystallization temperature of this alloy is at least 637K (364 ° C.), which is half that temperature, at the lowest. That is, processing performed at a processing temperature of 637 K (364 ° C.) or less for this alloy is classified as cold processing.

[2-2-2-2] Setting of processing temperature The processing member temperature of the part which contacts an intermediate material is room temperature (293K (20 degreeC)), 313-353K (40-80 degreeC), and 373K (100 degreeC). The intermediate material was cold worked. This is for controlling the temperature of the intermediate material during processing. The processed member is a member that comes into direct contact with an intermediate material in a cold processing apparatus, such as a roller for rolling or extrusion, a slitter or die for drawing, and a die for pressing.

  In the cold working step, the average temperature of the intermediate material during cold working was set to 293K (20 ° C.) to 393 K (120 ° C.). This is to prevent the occurrence of brittle fracture inside the intermediate material due to excessive decrease or increase in the intermediate material temperature.

[2-2-3] Processing rate The inventor set the total processing rate of the entire intermediate material before and after the cold working to 97% or more. The processing rate calculation method is a reduction rate of the cross-sectional thickness before and after processing. The reason why the total working rate is set to 97% or more is that the present inventor considered that it can be a reference value for judging whether or not the cold workability of the Ti-based alloy is excellent.

  When the initial thickness of the intermediate material before cold working is 10 mm and the total working rate is set to about 97%, the final thickness of the alloy (the plate material in this embodiment), which is the intermediate material after cold working. Is 0.3 mm.

  The number of cold workings performed from the initial thickness of the intermediate material to its final thickness was set to 10 to 30 times based on the experience of cold working of the intermediate material by the inventor. In addition, the average processing rate X per time, the number N of cold processings, and the total processing rate Z which occupies for the whole intermediate material are as the following formula | equation (Formula 1).

  That is, when the above total processing rate and the number of cold processing are applied to the above formula, the average processing rate per time can be calculated to be 11.5% to 32.5%. In other words, the present inventor can also paraphrase that the average processing rate per process for the intermediate material is set to 32.5% or less.

[2-2-3] Processing speed The inventor set the processing speed of the cold processing to either 20 m / min or 10 m / min. The reason for changing the processing speed is that when the processing speed of cold processing was 20 m / min, there was an intermediate material that was too fast and caused brittle fractures such as cracks and cracks.

[2-3] Heat treatment process [2-3-1] Homogenization process After the intermediate material manufacturing process and before the cold working process, the intermediate material is homogenized for 2 hours at 1273 K (1000 ° C.). Was given. The change in composition accompanying dissolution and heat treatment was ± 0.3 mol% or less for each concentration.

[2-3-2] Intermediate annealing step In the intermediate annealing step, the total working rate with respect to the initial thickness of the intermediate material in the cold working step is 40% or more, and before the intermediate material is cracked or cracked, the intermediate material Was subjected to intermediate annealing. This is because the working pressure generated inside the intermediate material during the cold working is reduced to facilitate the working. The conditions for the intermediate annealing are an annealing temperature of 1173 K (900 ° C.) and an annealing time of 30 minutes in an Ar atmosphere. Then, cold working was continued on the intermediate material until the desired total working rate was achieved after the intermediate annealing.

[2-3-3] Solution Treatment Step This solution was subjected to solution treatment in a vacuum atmosphere at 1073 K (800 ° C.) to 1473 K (1200 ° C.) for 30 minutes, and then quenched into water. It was conducted.

[3] Evaluation Table 1 shows the composition and characteristics of this alloy produced as this example.

  In the “sample number” column shown in Table 1, the presence / absence of superelasticity and physical properties of the alloys named as sample numbers 1 to 26 are described.

[3-1] Superelasticity Evaluation The present inventor performed superelasticity evaluation by a tensile test on the alloy using a tensile tester (AG-500N, load cell maximum load: 1 kN) manufactured by Shimadzu Corporation. It was.

[3-1-1] Evaluation method The method of the tensile test is as follows. First, the inventor applied a load to the alloy at room temperature (293 to 298 K (20 to 25 ° C.) at a constant speed of 5 × 10 ⁻⁴ m / min until the tensile strain reached 4%. Was applied. Thereafter, the present inventor obtained the shape recovery rate of the alloy by superelasticity by unloading the alloy and measuring the residual strain. The shape recovery rate due to superelasticity is as shown in Equation 2 below.

  Here, plastic strain = tensile strain (4%) − elastic strain, recovery strain = plastic strain−residual strain.

  Further, in the “Superelastic” column of Table 1, “◯” indicates “shape recovery rate is 40% or more”, “Δ” indicates “shape recovery rate is 5% to 40%”, and “×” indicates “shape recovery rate”. Is less than 5%, or the alloy breaks during the tensile test.

[3-1-2] Evaluation of the presence or absence of superelasticity This alloy exhibits superelasticity in the “superelasticity” column in sample numbers 3 to 5, 8 to 10, 15, 16 and 20 shown in Table 1. It is shown. That is, this alloy (Ti—X1 mol% Cr—X2 mol% Sn) is 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and When all the conditions of 8 ≦ X1 / X2 ≦ 1.5 are satisfied, it has been revealed that this alloy exhibits superelasticity. Assuming that the composition error of each additive element is ± 0.2 mol%, the above conditions are 3.8 <X1 <6.2, 3.8 <X2 <6.2, 8.8 <X1 + X2 <10.7. And 0.6 <X1 / X2 <1.7.

  Further, as shown in the “superelasticity” column in sample numbers 5, 10 and 15 shown in Table 1, this alloy (Ti—X1 mol% Cr—X2 mol% Sn) is 4.5 ≦ X1 ≦ 5.5, 4 It is clear that this alloy exhibits superelasticity when all the conditions of 0.5 ≦ X2 ≦ 5.5, 9.5 <X1 + X2 <10.5, and 0.8 ≦ X1 / X2 ≦ 1.2 are satisfied. It became. As above, assuming that the composition error of each additive element is ± 0.2 mol%, the above conditions are 4.3 <X1 <5.7, 4.3 <X2 <5.7, 9.3 <X1 + X2. Even if <10.7 and 0.6 <X1 / X2 <1.4, it is considered to hold.

  When the composition of this alloy is Ti-5 mol% Cr-5 mol% Sn (X1≈X2≈5.0, X1 + X2≈10.0, and X1 / X2≈1.0), the shape recovery rate is maximum. It showed 90% or more.

  Furthermore, when the phase transformation strain of Ti-5 mol% Cr-5 mol% Sn, which is an example of this alloy, was calculated based on the experimental results, the maximum value of the phase transformation strain was 8.7%. This approximates the maximum value (10.5%) of the phase transformation strain in the Ti—Ni superelastic alloy and the theoretical maximum value (9.3%) of the lattice strain in the Ti-based alloy. That is, it has been clarified that the superelasticity of the Ti—Cr—Sn based superelastic alloy, which is the present alloy, exhibits performance close to that of the Ti—Ni based alloy.

[3-2] Workability evaluation The inventor evaluated the workability of the present alloy based on the cold work described above.

[3-2-1] Evaluation Method “Processability” in Table 1 means that the intermediate member in this example has an intermediate member temperature of 313 to 353 K (40 ° C. to 80 ° C.) and an intermediate member during cold working. This alloy obtained by performing cold working (hereinafter referred to as “main cold working”) at an average temperature of 293 K to 393 K (20 ° C. to 120 ° C.) and a working speed of 20 m / min or 10 m / min or less. Is cold workability. In the “Workability” column of Table 1, “◎” indicates that “the total processing rate of the main cold processing (hereinafter referred to as“ the main cold processing rate ”) is 40% or more and the processing speed is 10 m / min to 20 m / min. "The alloy in which cracking did not occur in this alloy in the case of minutes", "○" was "the alloy in which cracking did not occur in this alloy when the main cold working rate was 40% or more and the processing speed was 10 m / min or less" , “△” means “alloy where the main cold working rate is 10% to 40%, and this alloy is cracked or cracked”, and “×” means “when the main cold working rate is 0% to 10%. Shows an alloy in which the alloy is cracked or cracked.

  On the other hand, the “comparative workability” in Table 1 is that the cold working conditions are set to room temperature (about 297 K = 20 ° C.) for an alloy having the same composition as this alloy, and the average temperature of the intermediate material during cold working is set. And cold workability exhibited by an alloy (hereinafter referred to as “comparative alloy”) obtained by performing cold working (hereinafter referred to as “comparative alloy”) at a processing speed of 20 m / min. . In the “comparative workability” column of Table 1, “◯” indicates “an alloy in which cracking did not occur in the comparative alloy when the total processing rate by comparative processing (hereinafter referred to as“ comparative processing rate ”) is 40% or more”, Δ Is “an alloy in which cracks and cracks occur in the comparative alloy when the comparative processing rate is 10% to 40%”, and “X” is a crack and cracks in the comparative alloy when the comparative processing rate is 0% to 10% "Alloy". That is, if the evaluation of “workability” is superior to the evaluation of “comparative workability”, this means that the present cold work is more suitable than the comparative work for this alloy.

[3-2-2] Evaluation of good workability Good workability of the present cold work on the present alloy exhibiting superelasticity is good because of sample numbers 3 to 5, 8 to 10, 15 shown in Table 1, 16 and 20 indicate “２０” or “◯” in the “cold workability” column. In addition, the fact that the present cold working for the present alloy exhibiting superelasticity is superior to the comparative working is that “△” in the “Comparative workability” column in the same sample number as described above in Table 1 or “ "X" indicates.

  That is, this alloy (Ti—X1 mol% Cr—X2 mol% Sn) is 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and When all the conditions of 8 ≦ X1 / X2 ≦ 1.5 are satisfied, it has been revealed that the present alloy exhibits a good workability in the cold working. And if the temperature of the processing member of the part which contacts an intermediate material shall be 313-353K (40-80 degreeC) and the average temperature of the intermediate material at the time of cold work shall be 293K-393K (20-120 degreeC), this alloy It became clear that the workability of the was improved.

  On the other hand, if the temperature of the processed member was less than 313K, the intermediate material cracked or cracked during cold working. The inventor believes that this is because the average temperature of the intermediate material during cold working is less than 293 K (20 ° C.), and hydrogen embrittlement is likely to be induced inside the intermediate material. Similarly, even when the temperature of the processed member exceeded 353 K, cracks and cracks occurred on the surface of the intermediate material that was in contact with the roll during cold processing. The inventor believes that this is because the average temperature of the intermediate material during cold working exceeds 393 K (120 ° C.), so that ω brittleness is easily induced inside the intermediate material.

  Further, as shown in the “cold workability” column in sample numbers 5, 10 and 15 shown in Table 1, this alloy (Ti—X1 mol% Cr—X2 mol% Sn) is 4.5 ≦ X1 ≦ 5.5. 4.5 ≦ X2 ≦ 5.5, 9.5 <X1 + X2 <10.5, and 0.8 ≦ X1 / X2 ≦ 1.2, this alloy has a workpiece temperature of It was 313 to 353 K (40 ° C. to 80 ° C.) and when the processing speed was reduced from 20 m / min to 10 m / min or less, it was revealed that good cold workability was exhibited. This can be said to show the superiority of slowing the processing speed. That is, the present inventor believes that it is easy to suppress a rapid increase in the average temperature of the intermediate material during the cold working by slowing the working speed.

  From the above, even if this alloy has a composition in which ω embrittlement is likely to occur due to a low concentration of Sn among all the compositions of this alloy, the present It has become clear that it is possible to perform cold working on an alloy without giving an undesirable thermal history.

In the same manner as described above, when the composition error of each additive element is taken into consideration, it is considered that the above condition is established even if the condition is ± 0.2 mol%.
[3-2] Ductility evaluation The present inventor conducted a tensile test on the alloy at room temperature (293 to 298K (20 to 25 ° C)) to evaluate the ductility of the alloy.

The conditions of the tensile test in the ductility evaluation are as follows. The present inventor measured the maximum tensile strength and elongation at break when the alloy was broken at room temperature until it was broken at a constant rate of 5 × 10 ⁻⁴ m / min.

  Each column of “Maximum tensile strength”, “Elongation at break” and “Ductility” in Table 1 shows the results of ductility evaluation. Here, “◯” described in the ductility column indicates “the breaking elongation of the alloy is 10% or more”, and “x” indicates “the breaking elongation of the alloy is less than 10%”.

  The good ductility of the present alloy exhibiting superelasticity is indicated by “◯” in the “Ductility” column in sample numbers 3 to 5, 8 to 10, 15, 16 and 20 shown in Table 1. That is, this alloy (Ti—X1 mol% Cr—X2 mol% Sn) is 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and When all the conditions of 8 ≦ X1 / X2 ≦ 1.5 were satisfied, it was revealed that this alloy exhibits a ductility of 10% or more.

[3-4] Concentration evaluation of additive elements [3-4-1] Cr concentration X1 (mol%)
Presuming from the results in the “superelastic” column and “phase” column of Table 1, when the Cr concentration X1 is less than 3.5 mol%, the thermoelastic martensite phase necessary for exerting superelasticity is present in the alloy. The inventor believes that it is not generated or induced. The same applies when the Cr concentration X1 is higher than 6.5 mol%. The reason for this is that even if stress is applied to the alloy, the thermoelastic martensite phase necessary to exert superelasticity is not induced, and the β phase of the parent phase is stably present in the alloy. This inventor thinks that it originates in doing.

[3-4-2] Sn concentration X2 (mol%)
As shown by the results in the “cold workability” column of sample numbers 2, 6, 12, and 17 shown in Table 1, when the concentration X2 of Sn added to the alloy is 3.0 mol% or less, It became clear that the inter-workability was not good. The present inventor believes that this is caused by insufficient suppression of ω brittleness.

  Further, as shown in the results of the “cold workability” column of Sample No. 11 shown in Table 1, when the concentration X2 of Sn added to the alloy exceeds 6.0 mol%, the precipitate phase containing Sn is The present inventor thinks that this is because the alloy is embrittled by precipitation in the alloy.

[3-5] Analysis of crystal structure [3-5-1] Relationship between shape memory effect and superelasticity and crystal structure In Ti metal or Ti alloy, the stress-induced transformation phase (metastable phase) is hexagonal ω. Phase, hexagonal α ′ phase and orthorhombic α ″ phase. Of these three types, the martensite phase that causes shape memory effect or superelasticity is thermoelastic Only α ”phase, which is a type martensite phase. In other words, in order for a Ti-based alloy to exhibit a shape memory effect or superelasticity, it is necessary that the Ti-based alloy not only cause stress-induced transformation but also generate an α ″ phase of a thermoelastic martensite phase. is there.

[3-5-2] Analysis of Crystal Structure As shown in the “Phase” column of sample numbers 3 to 5, 8 to 10, 15, 16 and 20 in Table 1, the present alloy (Ti—X1 mol% Cr—X2 mol%) Sn) is 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and 0.8 ≦ X1 / X2 ≦ 1.5. When all of these conditions are satisfied, it was revealed that the alloy is a β phase in which the parent phase β single phase or the thermoelastic martensite phase α ″ phase remains. In other words, the alloy is a β single phase at room temperature. Alternatively, when the α ″ phase indicates a remaining β phase, it has been found that the present alloy may exhibit superelasticity or a shape memory effect.

  Assuming that the composition error of each additive element is ± 0.2 mol%, the above conditions are 3.8 <X1 <6.2, 3.8 <X2 <6.2, 8.8 <X1 + X2 <10. .7 and 0.6 <X1 / X2 <1.7.

[4] Effects Next, effects related to the manufacturing method of the β-type Ti-based superelastic alloy and the β-type Ti-based superelastic alloy of this example will be described.

  (1) The β-type Ti-based superelastic alloy of this example is Ti—X1 mol% Cr—X2 mol% Sn, and 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, All of the conditions of 9.0 ≦ X1 + X2 ≦ 10.5 and 0.8 ≦ X1 / X2 ≦ 1.5 are satisfied.

  Thereby, the Ti-based alloy can exhibit superelasticity with a shape recovery rate of 10% or more at room temperature.

  (2) Further, the β-type Ti-based superelastic alloy of this example has 4.5 ≦ X1 ≦ 5.5, 4.5 ≦ X2 ≦ 5.5, 9.5 <X1 + X2 <10.5, and It is preferable that all the conditions of 0.8 ≦ X1 / X2 ≦ 1.2 are further satisfied.

  Thereby, the Ti-based alloy can exhibit superelasticity with a shape recovery rate of 40% or more at room temperature.

  (3) Moreover, the manufacturing method of the β-type Ti-based superelastic alloy of this example has the same composition as that of the β-type Ti-based superelastic alloy described in (1) or (2) above, and before the cold working. Intermediate material production process for producing an intermediate material that is an alloy in the state, the temperature of the processed member in the part contacting the intermediate material is 313 to 353K, the average temperature of the intermediate material during cold working is 293K to 393K, the intermediate material And a cold working step for performing cold working.

  Thereby, it can cold-work into a desired shape, without producing a crack and a crack with respect to the intermediate material of (beta) type | system | group Ti superelastic alloy as described in said (1) or (2).

  (4) Further, in the cold working step of the method for producing the β-type Ti-based superelastic alloy of the present embodiment, it is preferable that the working speed for the intermediate material is 20 m / min or less and the intermediate material is cold worked. .

  As a result, a rapid temperature rise in the intermediate material can be suppressed and brittle precipitates can be prevented from being generated inside the intermediate material, so that the intermediate material has a desired shape without causing cracks or cracks. Can be cold worked.

  (5) Further, in the method for producing a β-type Ti-based superelastic alloy of this example, the total working rate with respect to the initial thickness of the intermediate material in the cold working process is 40% or more, and the intermediate material is cracked or cracked. An intermediate annealing step of annealing the intermediate material before is further provided.

  Thereby, it is possible to perform cold working with a total working rate of 97% or more at the maximum with respect to the intermediate material.

  (6) Further, in the cold working step of the method for producing the β-type Ti-based superelastic alloy of this example, the average working rate per one time with respect to the intermediate material is set to 32.5% or less, It is characterized by processing.

  Thereby, it is possible to prevent the intermediate material from being cracked or cracked at a low total processing rate such as 40% or less.

  That is, according to the manufacturing method of the β-type Ti-based superelastic alloy and β-type Ti-based superelastic alloy of the present embodiment, it is possible to manufacture a material having a desired shape, such as a plate material or a wire material, that exhibits superelasticity at room temperature. As a result, a practical Ni-free superelastic alloy can be provided.

  In addition, this invention is not limited to the Example mentioned above, A various change is possible as needed.

  For example, for the β-type Ti-based superelastic alloy of the present invention, Sc, Y, La, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Al, Ga, In, Si, Ge, B, C, N, and O can be added as additional elements. The reason is as follows. When Sc, Y, and La are added to the alloy, the additive elements take up oxygen in the alloy and contribute to precipitation hardening. When Zr and Hf are added to this alloy, the additive element replaces Ti of this alloy, contributing to solid solution strengthening and β stabilization. When V, Nb, Ta, W, or Mn is added to this alloy, the additive element replaces Cr and contributes to β stabilization. When Fe, Co, or Ni is added to the alloy, the additive element replaces Cr of the alloy, contributing to β stabilization and strengthening. When Al, Ga, In, Si, or Ge is added to the alloy, the additive element replaces Sn of the alloy and suppresses ω brittleness of the alloy. When B, C, N, and O are added to this alloy, the additive elements B, C, N, and O strengthen the solid solution as interstitial interstitial elements.

Claims (6)

A β-type Ti-based superelastic alloy which is Ti—X1 mol% Cr—X2 mol% Sn and satisfies all the following conditions (A) and (B).
(A) 4.0 ≦ X1 ≦ 6.0, 4.0 ≦ X2 ≦ 6.0, 9.0 ≦ X1 + X2 ≦ 10.5, and 0.8 ≦ X1 / X2 ≦ 1.5,
(B) The β-type Ti-based superelastic alloy exhibits superelasticity with a shape recovery rate of 5% or more at room temperature (293K to 297K). 2. The β-type Ti superelastic alloy according to claim 1, wherein in addition to the conditions (A) and (B), the following condition (C) is also satisfied.
(C) 4.5 ≦ X1 ≦ 5.5, 4.5 ≦ X2 ≦ 5.5, 9.5 <X1 + X2 <10.5, and 0.8 ≦ X1 / X2 ≦ 1.2. An intermediate material manufacturing step of manufacturing an intermediate material that is the same composition as the β-type Ti-based superelastic alloy according to claim 1 or 2 and is an alloy in a state before cold working,
A cold working step of performing cold working on the intermediate material, assuming that the temperature of the processing member in contact with the intermediate material is 313 to 353K, and the average temperature of the intermediate material during cold working is 293K to 393K;
The method for producing a β-type Ti-based superelastic alloy according to claim 1 or 2, characterized by comprising: 4. The method for producing a β-type Ti superelastic alloy according to claim 3, wherein in the cold working step, the intermediate material is cold worked at a working speed of 20 m / min or less. . An intermediate annealing step of annealing the intermediate material before the intermediate material has a total processing rate of 40% or more with respect to the initial thickness of the intermediate material in the cold working step and cracking or cracking occurs in the intermediate material,
The method for producing a β-type Ti-based superelastic alloy according to claim 3 or 4, further comprising: 6. The cold working process according to claim 3, wherein in the cold working step, cold working is performed on the cold material with an average working rate per one time of the intermediate material set to 32.5% or less. A method for producing a β-type Ti-based superelastic alloy according to claim 1.