JP2003138330A - Copper-base alloy and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper-base alloy having shape memory characteristics and superelasticity and also having high yield stress even if crystal grains are so coarsened that bamboo structure is developed and also to provide its manufacturing method. SOLUTION: The copper-base alloy has shape memory characteristics and superelasticity and has recrystallized structure where bainitic phase (γ) is precipitated in at least either of austenitic (β) phase and grain boundary. A wire of the copper-base alloy has >=100 Mpa yield stress even in the bamboo structure where the ratio of the average grain size (C) to the diameter (S) of the wire, (C/S), becomes >=1.0.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a copper alloy having excellent shape memory characteristics and superelasticity, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a copper-based alloy having shape memory characteristics and superelasticity, there is, for example, one disclosed in Japanese Patent Laid-Open No. 2001-20026. And there, Al3 ~
10% by weight, Mn 5 to 20% by weight, Ni, Co, F
Additive elements such as e, Ti, misch metal 0.001-1
A copper-based alloy having a composition of 0% by weight and the balance Cu and unavoidable impurities and having a recrystallized structure of an austenite (β) phase single phase is shown. This copper-based alloy has excellent shape memory characteristics and superelasticity.

By the way, in a copper-based alloy having shape memory characteristics and superelasticity, it is required to improve the superelasticity, especially when it is used as a spring material. In order to improve the superelasticity, it is effective to coarsen the austenite (β) phase crystal grains.

[0004]

[Problems to be Solved] However, when the austenite (β) phase crystal grains are coarsened in this manner, a so-called bamboo structure, in which nodes are partially formed, occurs. Then, when such a bamboo structure is generated to increase the austenite (β) phase crystal grains as described above,
The yield stress of the copper-based alloy decreases. Therefore, there is a limit to improving superelasticity by increasing the number of austenite (β) phase grains.

In view of the above conventional problems, the present invention provides a copper-based alloy having a high yield stress, shape memory characteristics and superelasticity even if the crystal grains are coarsened to the extent that a bamboo structure is generated, and It is intended to provide the manufacturing method.

[0006]

A first aspect of the present invention is a copper-based alloy having shape memory characteristics and superelasticity, wherein the recrystallization structure is bainite () in at least one of an austenite (β) phase and a grain boundary. The copper-based alloy is characterized in that the γ) phase is precipitated (claim 1).

In the present invention, the recrystallized structure is not the austenite (β) phase single phase as in the above-mentioned conventional copper alloys, but bainite () in the austenite (β) phase or in one or both of the grain boundaries. γ) Phase is precipitated. Therefore, even if the crystal grain is coarsened and a bamboo structure is generated in order to improve the shape memory characteristic and superelasticity,
A high yield stress of 0 MPa or more can be obtained.

In the present invention, the shape memory characteristic is
Even if the material is deformed below a certain recovery temperature, it will return to its original memorized shape when heated above the recovery temperature. Superelasticity means that the load will be applied even if bent or stretched above the recovery temperature. When removed, it is a phenomenon of returning to its original shape like rubber.

According to the present invention, it is possible to provide a copper-based alloy having a high yield stress, shape memory characteristics and superelasticity even if the crystal grains are coarsened so that a bamboo structure is generated.

Next, the second invention is a copper-based alloy having shape memory characteristics and superelasticity, wherein Al3 to 10% by weight,
It consists of a composition of 5 to 20% by weight of Mn and the balance Cu and unavoidable impurities, and the recrystallization structure precipitates a bainite (γ) phase in at least one of the austenite (β) phase and the grain boundary. The copper-based alloy is characterized by being made (claim 3).

In the second invention, 3 to 10% by weight of Al is required. If it is less than 3% by weight, the copper-based alloy is unlikely to form an austenite (β) phase, while if it exceeds 10% by weight, the copper-based alloy becomes brittle. In addition, more preferably Al6 ~
It is 10% by weight. Further, Mn is necessary for expanding the composition range in which the austenite (β) phase can exist to the low Al side and improving the cold workability of the copper alloy. Mn
If less than 5% by weight, cold workability is poor and it becomes difficult to form an austenite (β) phase. On the other hand, 20
If it exceeds 5% by weight, the shape memory property is deteriorated. Further, it is more preferably 8 to 12% by weight.

In the present invention, the recrystallized structure is not the austenite (β) phase single phase as in the above-mentioned conventional copper alloys, but bainite () in the austenite (β) phase or in one or both of the grain boundaries. γ) Phase is precipitated. Therefore, even if the crystal grain is coarsened and a bamboo structure is generated in order to improve the shape memory characteristic and superelasticity,
A high yield stress of 0 MPa or more can be obtained.

Therefore, according to the present invention, it is possible to provide a copper-based alloy having a high yield stress, shape memory characteristics and superelasticity even if the crystal grains are coarsened so that a bamboo structure is generated. .

Next, the third invention is based on Al3 to 10% by weight.
5-20% by weight of Mn, Ni, Co, Fe, Ti,
V, Cr, Si, Nb, Mo, W, Sn, Sb, Mg,
A total of 0.001 to 10% by weight of an additive element consisting of one or more of P, Be, Zr, Zn, B, C, Ag and misch metal, based on 100% by weight of the entire alloy.
And a balance of Cu and unavoidable impurities, and the recrystallization structure is bainite (γ) in at least one of the austenite (β) phase and the grain boundary.
A method for producing a copper-based alloy having shape memory characteristics and superelasticity in which phases are precipitated, wherein the composition is heated and maintained at a temperature in an austenite (β) phase region,
Quench at a speed that does not produce phases, then 200-300
The method for producing a copper-based alloy is characterized by performing aging and transformation treatment in the range of ° C (claim 7).

In the present invention, the above composition is heated and maintained at a temperature in the austenite (β) phase region, and then rapidly cooled at a rate at which an α phase does not appear, and then 200 to 300 ° C.
Aging and transformation treatment are performed between. Therefore, the recrystallized structure is not the austenite (β) phase single phase, but the bainite (γ) phase precipitated in the austenite (β) phase or in one or both of the grain boundaries. Therefore, the crystal grains can be coarsened, and a high yield stress can be obtained even if a bamboo structure is generated due to the coarsened crystal grains.

Further, in the third aspect of the present invention, the above composition is used, and the composition is heated and held at a temperature in the austenite (β) phase region, and then rapidly cooled at such a rate that the α phase is not generated. If α phase appears during the rapid cooling, there is a problem that shape memory characteristics and superelasticity characteristics cannot be obtained. Further, "the speed at which the α phase does not appear" means, for example, 8.10 wt% Al-1.
In the case of 0.2 wt% Mn-0.51 wt% Co-balance Cu, the speed is 230 ° C / sec or more.

The aging and transformation treatments after the quenching are as follows:
It is carried out at 200 to 300 ° C. If the temperature is less than 200 ° C, aging and transformation treatment will be long and there will be a problem that the treatment cost will increase. On the other hand, if the temperature exceeds 300 ° C., the precipitated bainite (γ) phase becomes coarse, the copper alloy becomes brittle, and the time range of the treatment becomes narrow, which makes control difficult. The higher the temperature, the shorter the aging and transformation treatments may be. For example, at 200 ° C., 55 to 300 minutes, 2
It is preferably 8 to 30 minutes at 50 ° C. and 1 to 5 minutes at 300 ° C. (see FIG. 1).

More preferably, the aging and transformation treatment is performed at 200 to 300 ° C., and the time (t) minutes with respect to the temperature (T) ° C. is T = −26Ln (t) +304 and T =
It is performed in a range surrounded by −25Ln (t) +339. A solid line and a broken line in FIG. 1 indicate the above-mentioned relational expressions.

In the third invention, the same copper-based alloy as shown in the second invention can be obtained. Therefore, according to the present invention, it is possible to provide a copper-based alloy having a high yield stress, shape memory characteristics and superelasticity even if the crystal grains are coarsened so that a bamboo structure is generated.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the first aspect of the present invention, the copper alloy having shape memory characteristics and superelasticity is, for example, the composition shown in the above item 3 or Cu-Zn-A.
1, Cu-Al-Ni, etc. The copper-based alloy is a copper-based alloy that generates an austenite (β) phase and a bainite (γ) phase, and preferably contains Al and Mn in addition to Cu. Further, it is preferable that Al3 to 10 wt%, Mn to 5 to 20 wt%, and the balance Cu and unavoidable impurities. The bainite (γ) phase in the recrystallized structure may be precipitated in either or both of the austenite (β) phase and the grain boundaries.

Next, it is preferable that the bainite (γ) phase has not completed bainite transformation (claim 2). In this case, due to the appropriate amount of bainite (γ) phase, a high yield stress of, for example, 100 MPa or more can be obtained while maintaining the superelastic property.

Next, in the second invention, the unavoidable impurities include, for example, O and N.

Next, the above copper-based alloy is further mixed with Ni and C.
o, Fe, Ti, V, Cr, Si, Nb, Mo, W, S
n, Sb, Mg, P, Be, Zr, Zn, B, C, Ag
And an additive element consisting of one or two or more types of misch metal, with the total alloy being 100% by weight, a total of 0.00
It is preferable to contain 1 to 10% by weight (claim 4).

As the additive element, one or more of the above-listed elements are used. Among them, Ni and / or Co are particularly preferable. These elements exert the effect of improving the strength of the copper-based alloy by performing solid solution strengthening while maintaining cold workability. The total content of the above-mentioned additional elements is preferably 0.001 to 10% by weight, and more preferably 0.001 to 5% by weight, based on 100 parts by weight of the entire alloy. If the total content of these elements exceeds 10% by weight, the martensitic transformation temperature lowers and the β single phase structure becomes unstable.

Next, the above Ni, Co, Fe, Sn and Sb are effective elements for strengthening the matrix structure. The preferable contents of Ni and Fe are 0.001 to 3% by weight, respectively.
Is. Co strengthens the precipitation by forming CoAl, but if it becomes excessive, it reduces the toughness of the alloy. The preferable content of Co is 0.001 to 2% by weight. Sn and S
The preferable content of b is 0.001 to 1% by weight, respectively.

Ti combines with N and O, which are elements that hinder alloy properties, to form oxides and nitrides. Also,
When added together with B, boride is formed and contributes to precipitation strengthening. The preferable content of Ti is 0.001 to 2% by weight.

W, V, Nb, Mo and Zr have the effect of improving hardness and wear resistance. Further, since these elements hardly form a solid solution in the alloy matrix, they are precipitated as bcc crystals and are effective for precipitation strengthening. W, V, N
The preferable contents of b, Mo and Zr are each 0.00
It is 1 to 1% by weight.

Cr is an element effective in maintaining wear resistance and corrosion resistance. The preferable content of Cr is 0.001
~ 2% by weight. Si has the effect of improving corrosion resistance. The preferable content of Si is 0.001 to 2% by weight.

Mg removes N and O, which are elements that hinder alloy properties, and fixes S, which is an hindrance element, as a sulfide, and is effective in improving hot workability and toughness.
Addition of a large amount causes segregation of grain boundaries, which causes embrittlement. Mg
The preferable content of is 0.001 to 0.5% by weight.

P acts as a deoxidizing agent and has the effect of improving toughness. The preferable content of P is 0.01 to 0.5% by weight. Be has the effect of strengthening the base organization. B
The preferred content of e is 0.001 to 1% by weight.

Zn has the effect of raising the shape memory temperature. The preferable content of Zn is 0.001 to 5% by weight. B and C segregate at the grain boundaries, strengthening the grain boundaries,
It also has the effect of precipitating boride and carbide at the grain boundaries and refining the crystal grains. The preferred contents of B and C are 0.001 to 0.5% by weight, respectively.

Ag has the effect of improving cold workability. The preferable content of Ag is 0.001 to 2% by weight. Misch metal acts as a deoxidizer and has the effect of improving toughness. The preferred content of misch metal is 0.
001 to 5% by weight.

Next, the copper alloy is a wire rod, and the wire rod has a bamboo structure in which the ratio (C / S) of the average crystal grain size (C) to the wire diameter (S) is 1.0 or more. Also, it is preferable that the yield stress is 100 MPa or more, and that the material has shape memory characteristics and superelasticity (claim 5).

In this case, the yield stress is 100 MP.
It is possible to obtain a copper-based alloy wire having excellent properties of a or more and having shape memory characteristics and superelasticity. The wire diameter (S) has a unit of μm, and the average crystal grain size (C) has a unit of μm.

Next, the copper alloy is a plate material, and the plate material has a bamboo structure in which the ratio (C / P) of the average crystal grain size (C) to the plate material thickness (P) is 1.0 or more. Also, it is preferable that the yield stress is 100 MPa or more, and that it has shape memory characteristics and superelasticity (claim 6). In this case, it is possible to obtain a copper-based alloy plate material similar to the case of the wire material. The unit of the plate material thickness (P) is μm.

Next, in the manufacturing method of the third invention, it is preferable to obtain a copper alloy having a yield stress of 100 MPa or more and having shape memory characteristics and superelasticity (claim 8). In this case, a copper-based alloy having excellent yield stress and elongation, shape memory characteristics and superelasticity can be obtained.

[0037]

EXAMPLES Experimental Example 1 A wire of a copper-based alloy consisting of 8.07% by weight Al-9.68% by weight Mn-0.51% by weight Co-balance Cu (diameter 1 m
m), heat and hold at 850 ° C. (austenite (β) phase region) for 5 minutes to coarsen the crystal grains, perform air cooling treatment 4 times, and heat at 850 ° C. (austenite (β) phase region) for 5 minutes. Post water quenching was performed. As a result, the sample 1 which was austenite (β) phase single phase, as-quenched
Prepared many.

Next, the sample 1 was subjected to aging and transformation treatments at various temperatures and times. That is, the sample 1 is heated to the target aging and transformation temperature of 99 ° C.
The temperature is raised at a rate of / min, and that temperature is kept isothermal for a predetermined time.
The transformation was confirmed and the measurement was completed. The start and end of the transformation is D
It was measured by SC (differential scanning calorimeter). The amount of each sample 1 was 23 to 25 mg.

The isothermal holding of the above aging and transformation treatment is 2
00, 230, 250, 260, 270, 280, 29
0,300,320,400,500 degreeC was used, respectively. At 320 ° C. or higher, the transformation starts during the temperature rise, so the start and end times of transformation cannot be measured. Bainite transformation T in the above aging and transformation treatment
The TT diagram is shown in FIG.

In FIG. 1, the left line shows the start of transformation, the right line shows the end of transformation, and the black circles (●) and triangles (Δ) show the temperatures of the above measurements. From FIG. 1, it can be seen that the higher the isothermal transformation temperature, the faster the time from the start of transformation to the end. In addition, although aging and transformation treatment time can be shortened by increasing the temperature, it becomes difficult to control the precipitation amount of bainite (γ) phase.

Next, in order to observe the bainite (γ) phase in each of the above Samples 1, the cross section of Sample 1 after the above measurement was etched with a corrosive solution and observed using a SEM (scanning electron microscope). did. The SEM photograph (magnification 100
0 times) is shown in FIG. 2 and FIG. Both figures show the above 200
Each isothermal aging and transformation treatment temperature in the range of ℃ to 500 ℃ is shown. As is known from both figures, it can be seen that the bainite (γ) phase is precipitated (acicular crystals) in Sample 1, and the precipitated bainite (γ) phase is denser as the aging and transformation treatment temperatures are lower. Further, the coarser the precipitation phase becomes, the more brittle it becomes. Therefore, it is better to perform the aging and transformation treatment at a low temperature of 200 to 300 ° C.

Further, FIG. 4 shows the DS of the sample 1 above.
The relationship between the time when C measurement is performed and DSC (mw) is illustrated. In the figure, Ms is the martensite transformation start temperature, Mf is the martensite transformation end temperature, As is the martensite reverse transformation start temperature, and Af is the martensite reverse transformation end temperature. And in this example,
It can be seen that the bainite transformation starts at about 250 ° C.

Next, with respect to the sample 1 which was aged and transformed at each of the above temperatures, its isothermal transformation temperature and hardness (H
v0.1) is shown in FIG. The hardness was measured at 3 to 5 points with a load of 100 g using a micro Vickers. From the figure, between 200 and 300 ℃,
Hardness does not decrease so much, but when it exceeds 300 ℃,
It can be seen that the hardness is remarkably reduced. In addition, 200-25
It can be seen that almost the same hardness is maintained at 0 ° C.

The precipitated bainite (γ) phase is denser and the acicular precipitates are smaller as the temperature is lower as described above. Considering these facts, it is considered that higher hardness is better for utilizing the precipitated bainite (γ) phase as a pinning effect for dislocations and stress-induced martensite phases. Therefore, it is easy to control the transformation amount. Considering the minuteness of the organization, 200-
Aging and transformation treatment temperatures at 270 ° C are more desirable.

Next, FIG.
Regarding the copper-based alloy according to the present invention which has been subjected to the aging and transformation treatment at 3 ° C. for 3 minutes and the comparative sample 1 of the austenite (β) single phase which has been subjected to the aging and transformation treatment at 200 ° C. for 15 minutes for the above sample 1, It shows the tensile cycle characteristics of strain and stress. From the figure, the copper alloy according to the present invention (solid line) has a high stress of 100 MPa or more at a strain of 1% or more. On the other hand, the copper-based alloy (dotted line) according to the comparative example has a slight strain of 100% at a strain of 5% or more.
It only exerts about MPa. Thus, it can be seen that the copper alloy of the present invention has excellent superelasticity.

Experimental Example 2 A bending experiment was conducted on the sample 1 shown in Experimental Example 1 above. The sample 1 was subjected to each aging and transformation treatment at 200 ° C. for 15,178 minutes. The result is shown in FIG. 7.
First, in the bending experiment, a copper-based alloy wire 1 having a length of 80 mm and a diameter of 1 mm was bent in an arc shape having a radius of 49.5 mm between the fixed frames 2 and 2 arranged at a distance of 71.5 mm. Fixed When the wire rod 1 is bent uniformly, the strain corresponds to 1%.

As is known from FIG.
The specimens that had been aged and transformed for 8 minutes did not have local folds, while those that had been aged and transformed for 15 minutes at 200 ° C had local folds. From this, 2
When aging is performed at 00 ° C for 178 minutes, the bainite (γ) phase is precipitated in the austenite (β) phase or in one or both of the crystal grain boundaries. When aging at 15 ° C. for 15 minutes, it is considered that the bainite (γ) phase is not precipitated, and therefore local breakage occurs.

Next, FIG. 8 explains the coarsening of crystal grains. That is, in the figure, when the crystal grains 10 of the copper-based alloy wire rod 1 shown in FIG.
As shown in (B), a node is formed between the coarsened crystal grains 10, and the copper-based alloy wire has a so-called bamboo structure. FIG. 3B shows that the ratio (C / S) of the average crystal grain diameter (C) to the wire diameter (S) is 1.0 or more.

According to the present invention, even if a bamboo structure is formed, as described above, the bainite (γ) phase is precipitated in the austenite (β) phase or at the grain boundary, and the austenite (β) phase is formed.
By not using a single phase, the yield stress is prevented from decreasing.

Experimental Example 3 A wire of a copper-based alloy consisting of 8.12% by weight Al-9.73% by weight Mn-0.52% by weight Co-balance Cu (diameter: 1 m).
m) in the same manner as in Experimental Example 1, in order to coarsen the crystal grains, heat and hold at 850 ° C. for 5 minutes, and perform air cooling treatment 4 times.
After heating at 50 ° C. for 5 minutes, water quenching was performed. As a result, a large number of as-quenched Samples 2 to 6 having an austenite (β) single phase were prepared.

Next, regarding these, as shown in Table 1,
Aging and transformation treatment were performed at various temperatures and times. In this treatment, the above wire was placed in a furnace set to the temperature of the target aging and transformation treatment, and kept at that temperature for a predetermined time.

After the above treatment, the tensile cycle characteristics of strain and stress of each sample were measured in the same manner as that shown in FIG. With this, superelasticity characteristics were measured. The results are shown in Table 1. From Table 1, sample No. 3 and N
o. In No. 6, the treatment time at 200 ° C. or 300 ° C. was too long, the bainite transformation was completed, and superelastic properties were not obtained.

[0053]

[Table 1]

[Brief description of drawings]

FIG. 1 is a bainite transformation TTT diagram in Experimental Example 1.

FIG. 2 is an SEM photograph (magnification: 1000 times) showing metal compositions after various aging and transformation treatments in Experimental Example 1.

FIG. 3 is a similar SEM photograph continued from FIG.

FIG. 4 is an explanatory diagram of DSC measurement in Experimental Example 1.

FIG. 5 is a diagram showing hardness after completion of isothermal transformation in Experimental Example 1.

FIG. 6 is a stress-strain diagram in Experimental Example 1.

FIG. 7 is an explanatory diagram of a bending experiment in Experimental Example 2.

FIG. 8 is an explanatory diagram of crystal grain coarsening and a bamboo structure in Experimental Example 2.

[Explanation of symbols]

1. ． ． Copper alloy wire rod, 10. ． ． Crystal grain,

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 623 C22F 1/00 623 625 625 625 630 630L 691 691B 692 692A (72) Inventor Takayuki Okamoto Aichi prefecture 68 Kamishiota, Narumi-cho, Midori-ku, Nagoya City, Chuo-jou Co., Ltd. (72) Inventor, Masami Wakita 68, Kamioshida, Narumi-cho, Midori-ku, Midori-ku, Nagoya, Aichi Prefecture Kiyohito 3-5-20 Uesugi, Aoba-ku, Sendai-shi, Miyagi Prefecture (72) Inventor Ryosuke Kainuma 172-1 Kurane, Kurata, Natori-shi, Miyagi (72) Inventor Yuji Sudo 4-4-Kunimi, Aoba-ku, Sendai-shi, Miyagi Prefecture 1 Kunimi Heights Building No. 205

Claims (8)

[Claims] 1. A copper-based alloy having shape memory characteristics and superelasticity, wherein the recrystallized structure precipitates a bainite (γ) phase in at least one of an austenite (β) phase and a grain boundary. A copper-based alloy characterized by being present. 2. The copper-based alloy according to claim 1, wherein the bainite (γ) phase has not completely completed bainite transformation. 3. A copper-based alloy having shape memory characteristics and superelasticity, comprising a composition comprising 3 to 10% by weight of Al, 5 to 20% by weight of Mn, and the balance Cu and unavoidable impurities. A copper-based alloy having a crystal structure in which a bainite (γ) phase is precipitated in at least one of an austenite (β) phase and a grain boundary. 4. The copper-based alloy according to claim 3, further comprising Ni, Co, Fe, Ti, V, Cr, Si, Nb,
Mo, W, Sn, Sb, Mg, P, Be, Zr, Zn,
A copper-based alloy characterized by containing 0.001 to 10% by weight in total of an additive element consisting of one or more of B, C, Ag and misch metal, based on 100% by weight of the entire alloy. . 5. The copper alloy according to claim 3 or 4, wherein the copper-based alloy is a wire, and the wire has a ratio (C / S) of the average crystal grain size (C) to the wire diameter (S) of 1.0. Even in the above bamboo structure, a copper alloy having a yield stress of 100 MPa or more, shape memory characteristics and superelasticity. 6. The copper alloy according to claim 3 or 4, wherein the copper alloy is a plate, and the plate has a ratio (C / P) of the average crystal grain size (C) to the plate thickness (P) of 1.0. Even in the above bamboo structure, a copper alloy having a yield stress of 100 MPa or more, shape memory characteristics and superelasticity. 7. Al3-10 wt%, Mn5-20 wt%, Ni, Co, Fe, Ti, V, Cr, Si, N
b, Mo, W, Sn, Sb, Mg, P, Be, Zr, Z
The additive element consisting of one or more of n, B, C, Ag and misch metal is 0.001 to 10 wt% in total, with the total alloy being 100 wt%, and the balance is Cu and unavoidable impurities. A copper alloy having a shape memory property and superelasticity, which is composed of a composition and has a recrystallization structure in which a bainite (γ) phase is precipitated in at least one of an austenite (β) phase and a grain boundary. A method of producing a composition comprising: heating the composition to a temperature in the austenite (β) phase region, quenching the composition at a rate at which an α phase does not appear, and then aging and aging in a range of 200 to 300 ° C. A method for producing a copper-based alloy, which comprises performing a transformation treatment. 8. The yield stress of 100 MPa according to claim 7.
a) A method for producing a copper-based alloy, characterized in that the copper-based alloy having shape memory characteristics and superelasticity is obtained.