KR20200121531A - Method for processing titanium alloys for reducing modulus of elasticity and low elastic modulus titanium alloy produced by the same - Google Patents

Abstract

The present invention relates to a titanium alloy processing method for reducing the modulus of elasticity by multi-pass caliber-rolling a titanium alloy at 300 °C or less and a low elastic modulus titanium alloy manufactured thereby. The titanium alloy processing method for reducing the modulus of elasticity includes: a step of heating the titanium alloy; a step of water cooling the heated titanium alloy; and a step of introducing the water-cooled titanium alloy into a multi-pass caliber-rolling processor to perform multi-pass caliber-rolling on the same.

Description

Titanium alloy processing method for reducing the modulus of elasticity and low-elasticity titanium alloy manufactured thereby.

The present invention relates to a titanium alloy processing method for reducing the modulus of elasticity and a low elastic titanium alloy manufactured thereby, and more specifically, a titanium alloy processing method for reducing the modulus of elasticity by multi-hole rolling at 300°C or less. And it relates to a low elastic titanium alloy produced thereby.

Titanium-13Niobium-13Zirconium alloy (hereinafter referred to as'TNZ alloy') is a medical implant material, and two types of thermomechanical processes are proposed according to the US ASTM F1713-08 standard.

The first method is to prepare a solution treated (hereinafter referred to as'ST') material by heat-treating the material at 800°C and then water cooling, and the second method is to heat the above ST material at 500°C for 6 hours. 'CA') materials are manufactured.

On the other hand, general medical implant materials require high strength and low elasticity at the same time, which guarantees stability of the material and freedom of design through high strength, and minimizes the stress shielding effect harmful to the human body due to its low elasticity. Because there is.

ST material has a modulus of elasticity of 65 GPa, which is somewhat higher than that of the actual bone tissue (20-40 GPa), but the Titanium-6Aluminum-4Vanadium (hereinafter referred to as'Ti64') alloy used as an implant material. Compared to the modulus of elasticity (110 GPa), it has a significantly lower advantage, but ST material has a material strength of half that of Ti64 alloy, which is difficult to use.

In the case of the CA material, the strength problem was solved by increasing the strength to 800 MPa level through heat treatment, but there is a problem that the elastic modulus increases to about 80 GPa because the high strength and high elastic alpha phase is used.

Therefore, the necessity of a thermomechanical processing process that simultaneously secures the low elastic properties of the ST material and the high strength of the CA material is on the rise.

One object of the present invention is to provide a titanium alloy processing method for reducing the modulus of elasticity by multi-hole rolling at 300° C. or less.

Another object of the present invention is to provide a low elastic titanium alloy.

The titanium alloy processing method for reducing the modulus of elasticity for one object of the present invention includes heating a titanium alloy, water cooling the heated titanium alloy, and introducing the water-cooled titanium alloy into a multi-hole rolling mill to perform multi-hole rolling. Include.

In this case, the multi-hole rolling is preferably performed at -196°C to 300°C.

In addition, the heating step is preferably performed for 30 minutes to 2 hours at 700 ℃ ~ 900 ℃.

Further, the titanium alloy may include Nb: 10 to 15% by weight, Zr: 10 to 15% by weight, and the remaining Ti and inevitable impurities.

On the other hand, in the step of multi-hole rolling, the water-cooled titanium alloy may be repeatedly introduced into the multi-hole type rolling mill for 2 to 12 times, and the water-cooled titanium alloy may be repeatedly injected into the multi-hole type mill by rotating at a predetermined angle. .

In addition, the multi-hole rolling step is preferably carried out at a cross-sectional reduction rate of 60% or more.

In an embodiment of the present invention, the modulus of elasticity of the titanium alloy obtained after the multi-hole rolling step may be 60 GPa or less, may include a martensite structure, a yield strength is 760 MPa or more, and a tensile strength of 860 MPa or more. Can have.

In addition, it is preferable that the titanium alloy obtained after the multi-hole rolling step has an average grain size of 1 μm or less.

On the other hand, the low-elasticity titanium alloy for another object of the present invention is manufactured according to the titanium alloy processing method of the present invention, and has an elastic modulus of 60 GPa or less.

In addition, the low-elasticity titanium alloy may include a martensitic structure, a yield strength of 760 MPa or more, a tensile strength of 860 MPa or more, and an average grain size of 1 μm or less.

According to the present invention, the martensitic structure of the titanium alloy is not destroyed by multi-pass caliber-rolling process at 300°C or less, and the UFG structure can be successfully induced, thereby securing high strength. In addition, it has the effect of reducing the modulus of elasticity of the titanium alloy.

Therefore, the low-elasticity titanium alloy of the present invention can be variously used in medical materials that require high strength and low elasticity at the same time.

In addition, as the low-elasticity titanium alloy of the present invention is processed and manufactured through a multi-hole rolling process, there is an advantage that large-scale production is possible.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present invention, various modifications may be made and various forms may be applied, and specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific form of disclosure, it is to be understood as including all changes, equivalents, or substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

The terms used in the present application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the existence of features, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features or steps It is to be understood that it does not preclude the possibility of addition or presence of, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

The titanium alloy processing method for reducing the modulus of elasticity of the present invention includes heating a titanium alloy, water cooling the heated titanium alloy, and introducing the water-cooled titanium alloy into a multi-hole rolling mill to perform multi-hole rolling.

Here, the multi-pass caliber-rolling process means digging a caliber of various sizes between two rolling rolls, gradually decreasing the size from the largest cross-sectional area, and inserting the water-cooled titanium alloy between each hole. It means a way of performing rolling.

Specifically, in the present invention, the step of heating the titanium alloy first proceeds.

The heating step is to allow the beta phase transformation of the titanium alloy to occur, and is preferably performed at 700°C to 900°C for 30 minutes to 2 hours. When the heating temperature is less than 700° C., the phase transformation does not occur smoothly due to the beta transformation temperature of the titanium alloy, and when the heating temperature exceeds 900° C., there is no additional microstructure control effect, resulting in a large economic loss. In addition, when the heating time is less than 30 minutes, stability of the transformed phase can be achieved, and when the heating time exceeds 2 hours, economical loss is large.

Therefore, the heating step is most preferably performed at 800° C. for 1 hour.

In addition, the titanium alloy is preferably Nb: 10 to 15% by weight, Zr: 10 to 15% by weight, and the remaining Ti and inevitable impurities are preferably included, but are not limited thereto, for example, Ti-13Ni-13Zr ( Hereinafter,'TNZ alloy') titanium alloy may be used.

This titanium alloy may be used for medical purposes, and the reason for including Nb and Zr in the weight% is as follows.

Niobium (Nb) is a gray metal that is easy to mold from a soft material. It is known as a bio-friendly metal material because it does not exhibit harmful reactivity with fibrous cells, corrosion products, and biological solutions in the human body, but exhibits stability. In addition, it is very stable at room temperature and is an element with excellent corrosion resistance, such as no erosion by oxygen or strong acid.

The niobium (Nb) is preferably added in an amount of 10 to 15% by weight to the titanium alloy of the present invention, because if it is out of the above range, the elastic modulus rapidly increases, making it difficult to apply to a living body.

Zirconium (Zr) is a metal having very high corrosion resistance in high-temperature water in an acid and base atmosphere, and an oxide film is generated even in air, showing strong corrosion resistance. It is also a non-cytotoxic element and is a bio-friendly metal material.

The zirconium (Zr) is also preferably added in an amount of 10 to 15% by weight to the titanium alloy of the present invention, because if it is out of this range, the elastic modulus rapidly increases, making it difficult to apply to a living body.

Meanwhile, inevitable impurities are inevitably included in the process of manufacturing the titanium alloy, and may be metal oxides, metal nitrides, Cu, Fe, Si, etc., and these elements are 1% by weight or less, preferably 0.1% by weight or less, More preferably, it may be included in an amount of 0.01% by weight or less.

Next, the step of water cooling the heated titanium alloy proceeds.

Specifically, by water-cooling the heated titanium alloy, the microstructure of the titanium alloy can include a martensite structure having a fine layered structure.

Thereafter, the water-cooled titanium alloy may be introduced into a multi-hole rolling mill to perform a multi-hole rolling.

Specifically, the water-cooled titanium alloy may be repeatedly introduced into the multi-hole mill and into the multi-hole mill from 2 to 12 times, more preferably from 4 to 12 times, and at this time, the water-cooled titanium alloy is at a predetermined angle for each repeated injection. It is preferable to rotate at (for example, 90°C) and put into a multi-hole rolling mill.

In addition, the step of multi-hole rolling is preferably performed at 300°C or less, and by performing multi-hole rolling in this temperature range, the martensite structure of the titanium alloy is not destroyed, and the resulting titanium alloy The modulus of elasticity can be reduced. On the other hand, when the heating temperature exceeds 300° C., the martensitic structure disappears, so that an effect of reducing the modulus of elasticity cannot be expected.

On the other hand, since the effect of reducing the modulus of elasticity was maintained even in the case of the titanium alloy obtained after performing at -196°C, which is the maximum limit that can be cooled with liquid nitrogen, the lower limit of the temperature in the multi-hole rolling step of the present invention may not be specifically set. have.

However, since the effect of sufficiently reducing the modulus of elasticity appears even at room temperature, it is most preferable to perform the step of multi-hole rolling near room temperature (0°C to 100°C) in order to prevent energy loss and productivity decrease due to heating or cooling. .

On the other hand, the step of multi-hole rolling is preferably performed at a cross-sectional reduction ratio of 60% or more, and when applying a cross-sectional reduction ratio of less than 60%, sufficient plastic deformation is not applied, making it difficult to create an ultrafine-grained (UFG) area. There is a problem.

That is, since the cross section of the titanium alloy obtained after processing is reduced by more than 60% compared to the cross section before the titanium alloy processing, sufficient plastic deformation is applied, so that the UFG structure of the titanium alloy can be successfully induced.

As the titanium alloy obtained through the above-described processing method performs the step of multi-hole rolling at 300°C or less, it contains a martensite structure even after multi-hole rolling, so that the elastic modulus is reduced, thereby exhibiting a low modulus of elasticity of 60 GPa or less. do.

In addition, the titanium alloy obtained by the above method has a UFG structure having an average grain size of 1 μm or less, so that the yield strength is 760 MPa or more, and the tensile strength is 860 MPa or more.

Therefore, according to the present invention, the martensitic structure of the titanium alloy is not destroyed by multi-pass caliber-rolling process at 300°C or less, and the UFG structure can be successfully induced, It has the effect of not only securing the Titanium, but also reducing the elastic modulus of the titanium alloy.

On the other hand, in another embodiment of the present invention, it is possible to provide a low-elastic titanium alloy manufactured by the processing method of the present invention.

The low elastic titanium alloy may have an elastic modulus of 60 GPa or less, and exhibit low elastic properties.

Further, the low-elasticity titanium alloy includes a martensitic structure, includes a UFG structure having an average grain size of 1 μm or less, and has a yield strength of 760 MPa or more, and a tensile strength of 860 MPa or more.

That is, the low-elasticity titanium alloy of the present invention not only secures high strength, but also exhibits low elasticity due to excellent elasticity modulus reduction effect, thereby ensuring the stability of the material and the degree of freedom of design, and at the same time, the stress shielding effect harmful to the human body. effect) can be minimized, so it is highly applicable to medical materials that require high strength and low elasticity.

In addition, as the low-elasticity titanium alloy of the present invention is processed and manufactured through a multi-hole rolling process, there is an advantage that large-scale production is possible.

Hereinafter, various embodiments and experimental examples of the present invention will be described in detail. However, the following examples are only some examples of the present invention, and the present invention should not be construed as being limited to the following examples.

[Example]

Nb: 13% by weight, Zr: 0.5% by weight, Ti-13Nb-13Zr alloy consisting of the remaining Ti and inevitable impurities was processed into a bar having a diameter of 12.5 mm and a length of 50 mm. The bar thus processed was heated at 800° C. for 1 hour using an electric furnace and then cooled with water to induce a martensite structure.

Next, the water-cooled rods were put into a multi-hole rolling mill and multi-hole rolling at room temperature. In this example, four types of titanium alloys were fabricated according to the size and number of the balls, and the rods were rotated by 90°C for each rolling pass, and the operation of putting them into the multi-hole rolling mill was performed at 2, 4, 8 and 12 times. Each was repeated.

The change in cross-sectional diameter of the titanium alloy according to the number of multi-hole rolling in each example is shown below. Here,'Φ' means the cross-sectional diameter of the titanium alloy rolled through each hole of the multi-hole rolling machine, and the unit is'mm'. The last number refers to the cross-sectional diameter of the finally manufactured low-elastic titanium alloy.

[Example 1 (CCR-2P)]

Φ12.5 → Φ11.9 → Φ11.29

[Example 2 (CCR-4P)]

Φ12.5 → Φ11.9 → Φ11.29 → Φ10.79 → Φ10.14

[Example 3 (CCR-8P)]

Φ12.5 → Φ11.9 → Φ11.29 → Φ10.79 → Φ10.14 → Φ9.64 → Φ9.15 → Φ8.67 → Φ8.23

[Example 4 (CCR-12P)]

Φ12.5 → Φ11.9 → Φ11.29 → Φ10.79 → Φ10.14 → Φ9.64 → Φ9.15 → Φ8.67 → Φ8.23 → Φ7.8 → Φ7.4 → Φ7.2 → Φ6. 66

[Comparative Example]

A titanium alloy was fabricated and manufactured in the same manner as in Example 3, except that multi-hole rolling was performed at a temperature of 650°C.

Mechanical properties

In order to compare the mechanical properties of the two conventional materials (ST, CA) prepared in Examples 1 to 4, Comparative Examples and 4 CCR materials according to the US ASTM standard, a tensile test was performed using a conventional tensile tester. .

Specific test results are shown in Table 1 below.

Material Yield strength (MPa) Tensile strength (MPa) ST (ASTM) 544.6 ± 5 734 ± 8.3 CA (ASTM) 771.6 ± 12 850.9 ± 9.7 Comparative example 810 ± 2 960 ± 2 Example 1 (CCR-2P) 767.1 ± 7.1 866.2 ± 7.2 Example 2 (CCR-4P) 858.1 ± 4.6 942.6 ± 3.9 Example 3 (CCR-8P) 902.2 ± 10.6 999.9 ± 5.5 Example 4 (CCR-12P) 962.7 ± 25.4 1043.3 ± 1.4

As shown in Table 1, it was confirmed that all examples compared to the ST material, all examples except for Example 1 compared to the CA material, and Examples 3 and 4 compared to the comparative example obtained clearly improved yield strength and tensile strength.

Elastic modulus measurement

In order to compare the elastic modulus of the two conventional materials (ST, CA) prepared according to the US ASTM standards for Examples 1 to 4, Comparative Examples and 4 types of CCR materials, two types of tensile curve-based measurement and ultrasonic-based measurement were used. Another experimental method was introduced to accurately measure the modulus of elasticity, and the results are shown in Table 2 below.

Material Tensile curve-based measurement modulus of elasticity (GPa) Ultrasonic based measurement
Modulus of elasticity (GPa) ST (ASTM) 61.2 ± 2.7 63.9 CA (ASTM) 78.0 ± 0.7 76.8 Comparative example 78.0 ± 0.1 - Example 1 (CCR-2P) 56.2 ± 0.1 63.0 Example 2 (CCR-4P) 54.5 ± 0.1 59.0 Example 3 (CCR-8P) 53.1 ± 1.5 55.7 Example 4 (CCR-12P) 47.2 ± 2.1 51.4

Referring to Table 2, it was found that Examples 1 to 4 clearly exhibited a lower modulus of elasticity compared to the two existing materials (ST, CA material).

In particular, in the case of Example 4 (CCR-12P), the modulus of elasticity was reduced by 20%-40% compared to the two existing materials (ST, CA material), which is a whopping 53-57% decrease compared to the Ti64 alloy. .

Such a low modulus of elasticity is a value close to that of a beta-based titanium alloy (Ti-29Nb-13Ta, 4.6Zr, or Ti-35Nb-4Sn, etc.) manufactured by using a large amount of expensive alloying elements. It was confirmed that the titanium alloy prepared accordingly has an excellent elastic modulus reduction effect.

On the other hand, in the case of the comparative example in which the multi-hole rolling was performed at a temperature of 650°C, the elastic modulus showed a similar value to that of the existing material (CA material), and through this, when the multi-hole rolling was performed at a temperature exceeding 300°C, It was found that the effect of reducing the modulus of elasticity did not appear due to the disappearance of the martensite structure.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the present invention described in the following claims. You will understand that you can.

Claims (15)

Heating the titanium alloy;
Water cooling the heated titanium alloy; And
Including a step of multi-hole rolling by introducing the water-cooled titanium alloy into a multi-hole type rolling machine, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 1,
The multi-hole rolling step is characterized in that performed at -196 ℃ to 300 ℃, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 2,
The heating step is characterized in that performed for 30 minutes to 2 hours at 700 ℃ ~ 900 ℃, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 2,
The titanium alloy is Nb: 10 to 15% by weight, Zr: 10 to 15% by weight, and titanium alloy processing method for reducing the modulus of elasticity, characterized in that it contains the remaining Ti and inevitable impurities.
The method of claim 4,
In the multi-hole rolling step, characterized in that the water-cooled titanium alloy is repeatedly introduced into the multi-hole rolling mill for 2 to 12 times, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 5,
In the multi-hole rolling step, the water-cooled titanium alloy is rotated at a predetermined angle and introduced into the multi-hole rolling mill.
The method of claim 6,
The multi-hole rolling step is characterized in that performed at a cross-sectional reduction rate of 60% or more, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 7,
The titanium alloy processing method for reducing the elastic modulus, characterized in that the elastic modulus of the titanium alloy obtained after the multi-hole rolling step is 60 GPa or less.
The method of claim 7,
The titanium alloy obtained after the multi-hole rolling step is characterized in that it comprises a martensite (martensite) structure, titanium alloy processing method for reducing the modulus of elasticity.
The method of claim 7,
The titanium alloy processing method for reducing the modulus of elasticity, characterized in that the yield strength of the titanium alloy obtained after the multi-hole rolling step is 760 MPa or more, and the tensile strength is 860 MPa or more.
The method of claim 7,
The titanium alloy obtained after the multi-hole rolling step is characterized in that the average grain size is less than 1㎛, titanium alloy processing method for reducing the modulus of elasticity.
Processed by the processing method according to claim 7,
A low-elasticity titanium alloy, characterized in that the modulus of elasticity is 60 GPa or less.
The method of claim 12,
The low elastic titanium alloy is characterized in that it comprises a martensite (martensite) structure, low elastic titanium alloy.
The method of claim 12,
The low-elastic titanium alloy has a yield strength of 760 MPa or more, and a tensile strength of 860 MPa or more.
The method of claim 12,
The low-elasticity titanium alloy, characterized in that the average grain size of less than 1㎛, low-elasticity titanium alloy.