Patent Application
20210395863
The present invention relates to a complex copper alloy, including a high-entropy alloy and a method of manufacturing the same.
Brass is an alloy manufactured by adding zinc (Zn) to copper (Cu), and has a golden color and thus is aesthetically pleasing. Brass is capable of precisely realizing fine shapes due to the excellent malleability and machinability thereof, and thus has come to be widely used in the faucet business and for gas piping. In particular, in order to use brass for various purposes as described above, the machinability thereof is very important. However, in the case of brass products, since the ductility thereof is very high, chips are easily formed between cutting processes, causing a problem of sharply reduced machinability.
In the related art, to solve the problem, a lead precipitate is formed in a matrix (brass) by alloying brass and lead (Pb), thereby improving machinability. Lead has a high positive (+) heat of mixing and also a large difference in melting point from copper. For this reason, Cu (brass) and lead alloy have a monotectic reaction which is represented by the liquid-phase separation at high temperature. Since lead is separated from the Cu-rich liquid phase during solidification, it is known that most of the lead precipitate is formed inside the grains rather than at grain boundaries. Moreover, since lead has a very high interfacial energy in the liquid phase thereof, the precipitate formed is grown to have a spherical shape. In general, when a film-type precipitate is formed along the grain boundaries since a rapid fracture phenomenon occurs along the grain boundaries, the lead precipitate is known to act as a lubricant during a cutting process, so the availability thereof is great.
However, recently, the demand for lead-free brass (Pb-free brass) not containing lead has rapidly increased due to environmental regulations in the international community, including the United States and the European Union. Moreover, the research and development on alternative materials have been actively conducted. Meanwhile, bismuth (Bi) exhibits similar thermodynamic behavior with lead in copper. Therefore, lead-free brass containing bismuth has been attracted so much interest, nowadays. However, there is a problem in that, unlike lead, due to the low interfacial energy of bismuth, a significant amount of film-type precipitate is formed along the grain boundaries of the brass, thereby easily leading to fractures during a cutting process.
Accordingly, the present invention has been made keeping in mind the problems occurring in the related art, and the present invention provides a complex copper alloy with excellent mechanical properties.
The present invention provides a method of manufacturing the complex copper alloy.
Other objects of the present invention will become apparent from the following detailed description and accompanying drawings.
According to Examples of the present invention, a complex copper alloy includes a metal matrix, including copper or a copper alloy, and a high-entropy alloy (HEA) 2nd phase existing inside the grains of the matrix.
The metal matrix may be composed of the first phase, and the high-entropy alloy may be composed of a second phase-separated from the first phase.
The high-entropy alloy may have a spherical shape. The high-entropy alloy may have a size of 10 μm or less. The high-entropy alloy may include one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni. The high-entropy alloy may further include one or more alloy elements selected from the group consisting of Al, Ta, Nb, V, Mo, and W.
The complex copper alloy may have the following Chemical Formula 1.
(Cu100-xZnx)y(HEA)100-y [Chemical Formula 1]
(in Chemical Formula 1, 0≤x≤45, 0<y≤10 at %, and HEA is constituted with one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni)
The copper alloy may include one or more alloy elements selected from the group consisting of Pb, Sn, Sb, As, Bi, Cd, P, Mg, and Si.
The high-entropy alloy may be homogeneously distributed inside the grains of the matrix.
The metal matrix may be composed of pure or copper alloy (brass).
A method of manufacturing a complex copper alloy, which includes a metal matrix including copper or a copper alloy, and high-entropy alloy (HEA) precipitations existing inside grains of the metal matrix, according to Examples of the present invention includes preparing a raw material of the metal matrix and raw material of the high-entropy alloy, and melting and alloying the raw material of the metal matrix and the raw material of the high-entropy alloy.
The metal matrix may be composed of the first phase, and the high-entropy alloy may be composed of a second phase-separated from the first phase.
The solidification rate when alloying the molten raw material may be controlled to form a precipitate of the high-entropy alloy. The shape and size of the high-entropy alloy may be controlled by changing the cooling rate of 10−3 K/s or more and 103 K/s or less.
The high-entropy alloy may have a spherical shape having a size of 10 μm or less. The high-entropy alloy may include one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni. The high-entropy alloy may further include one or more alloy elements selected from the group consisting of Al, Ta, Nb, V, Mo, and W.
The complex copper alloy may have the following Chemical Formula 1.
(Cu100-xZnx)y(HEA)100-y [Chemical Formula 1]
(In Chemical Formula 1, 0≤x≤45, 0<y≤10 at %, and HEA is constituted with one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni.)
The copper alloy may include one or more alloy elements selected from the group consisting of Pb, Sn, Sb, As, Bi, Cd, P, Mg, and Si.
The high-entropy alloy precipitations may be homogeneously distributed in the grains of the metal matrix.
The complex copper alloy according to Examples of the present invention has excellent physical properties. For example, the complex copper alloy has excellent machinability, formability, and mechanical properties. Further, the complex copper alloy is environmentally friendly. The complex copper alloy is used to manufacture various processed products such as faucet products and pipes.
The above and other objects, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, the present invention will be described in detail through Examples. The objects, features, and advantages of the present invention will be readily understood through the following Examples. The present invention is not limited to the Examples described herein, but may be embodied in other forms. The Examples introduced here are provided to ensure that the disclosed contents are thorough and complete and that the spirit of the present invention is sufficiently transferred to a person having ordinary knowledge in the technical field to which the present invention pertains. Therefore, the present invention should not be limited by the following Examples.
When an element “includes” any other element in the specification, this means that unless otherwise indicated, other elements may be further included rather than excluded.
A complex copper alloy according to Examples of the present invention includes a metal matrix, including copper or a copper alloy, and a high-entropy alloy (HEA) existing in grains of the metal matrix.
The metal matrix may be composed of the first phase, and the high-entropy alloy may be composed of a second phase that is separated from the first phase.
The high-entropy alloy may have a spherical shape. The high-entropy alloy may have a size of 10 μm or less. The high-entropy alloy may include one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni. The high-entropy alloy may further include one or more alloy elements selected from the group consisting of Al, Ta, Nb, V, Mo, and W.
The complex copper alloy may have the following Chemical Formula 1.
(Cu100-xZnx)y(HEA)100-y [Chemical Formula 1]
(in Chemical Formula 1, 0≤x≤45, 0<y≤10 at %, and HEA is constituted with one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni)
The copper alloy may include one or more alloy elements selected from the group consisting of Pb, Sn, Sb, As, Bi, Cd, P, Mg, and Si.
The high-entropy alloy precipitations may be homogeneously distributed in the grains of the metal matrix.
The alloy may have a copper or a copper alloy (brass) matrix.
A method of manufacturing a complex copper alloy, which includes a metal matrix including copper or copper alloy, and high-entropy alloy (HEA) precipitations existing in a crystal grain of the metal matrix, according to Examples of the present invention includes preparing a raw material of the metal matrix and raw material of the high-entropy alloy and melting and alloying the raw material of the metal matrix and the raw material of the high-entropy alloy.
The metal matrix may have the first phase, and the high-entropy alloy may precipitate as a second phase that is separated from the first phase.
The solidification when alloying the molten raw material may be controlled to form a precipitate of the high-entropy alloy. The shape and size of the high-entropy alloy may be controlled by changing a cooling rate of 10−3 K/s or more and 103 K/s or less.
The high-entropy alloy precipitation may have a spherical shape having a size of 10 μm or less. The high-entropy alloy may include one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni. The high-entropy alloy may further include one or more alloy elements selected from the group consisting of Al, Ta, Nb, V, Mo, and W.
The complex copper alloy may have the following Chemical Formula 1.
(Cu100-xZnx)y(HEA)100-y [Chemical Formula 1]
(In Chemical Formula 1, 0≤x≤45, 0<y≤10 at %, and HEA includes one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni.)
The copper alloy may include one or more alloy elements selected from the group consisting of Pb, Sn, Sb, As, Bi, Cd, P, Mg, and Si.
The high-entropy alloy precipitations may be homogeneously distributed in the grains of the metal matrix.
In the preparation of the raw materials, it is preferable to prepare an alloying element that has the relationship of positive (+) heat of mixing with respect to copper, acting as the main element of the first phase, to thus influence the properties of the metal matrix and which easily constitutes a single phase of a high-entropy alloy having a face-centered cubic (FCC) structure. Thereby, the precipitate of the high-entropy alloy, having high phase stability, is separated from the metal matrix even in a liquid phase. So spherical precipitations may be easily formed in the crystal grains of the metal matrix.
In the melting and alloying of the raw materials, it is important to homogeneously melt the alloying elements. The melting and alloying may be performed using a commercial heating method including an arc-melting method, an induction-heating method, and a resistance-heating method. It is preferable to perform the melting at a sufficiently high temperature so that individual phases are separated from the liquid phase due to a monotectic reaction caused by the positive (+) heat of mixing, thereby making it easy to form a spherical shape. When a molten metal alloy is solidified to manufacture a complex copper alloy, the solidification rate may be controlled to control the shape of the composite phase (the distribution of the high-entropy alloy and the size of the precipitate). Further, the complex copper alloy may be formed into a suitable microstructure through a post-treatment process including rolling and a heat-treatment process.
Referring to
In order to ensure excellent machinability, it is necessary to limit precipitation at the grain boundary of the precipitate not containing lead as the main element so that the precipitate having a spherical shape is homogeneously distributed in the grain.
The complex copper alloys according to the Examples of the present invention include novel alloyed elements. In the case of the alloy included in the complex copper alloys, to ensure excellent properties, the alloy needs to have a large positive (+) heat of mixing with respect to a brass matrix, particularly copper determining properties of brass, and a deterioration in properties of the brass must not occur in the alloying with the brass matrix. In consideration thereof, element groups for use in alloying were selected, as shown in Table 2 below.
The element group I shown in Table 2 includes Ni, Mn, Co, Cr, and Fe, which are five kinds of elements forming a single phase of a high-entropy alloy having an FCC crystal structure among alloys having a large positive heat of mixing with respect to copper. The high-entropy alloy is an alloy system in which various kinds of elements act as main elements, has high phase stability even at high temperatures, and may easily cause a liquid-phase separation with a copper matrix.
The element group II includes elements that do not form the FCC high-entropy alloy, has a positive heat of mixing with respect to copper to be separated from brass, and is alloyed with the FCC high-entropy alloy, thus improving mechanical properties such as the strength of a precipitation phase. The following Table 3 shows various Comparative Examples of the present invention, including an alloy including a combination of the element group I to easily form the FCC crystal structure (Comparative Examples 7 to 11) and an alloy system in which a small amount of element group II is added to the corresponding alloy (Comparative Examples 12 and 13).
It can be confirmed that the high-entropy alloy phase having high phase stability even at high temperatures exhibits a phase separation phenomenon even in a liquid phase, as in a conventional lead-copper phase diagram. Further, in general, an alloy including transition metals exhibits greater interfacial energy than lead (copper: 1360 dynes/cm2, nickel: 1770 dynes/cm2, and lead: 442 dynes/cm2—based on a substrate having low surface energy). Accordingly, the precipitation phase including the transition metal may have a spherical shape that is easily maintained during a solidification process and may be homogeneously distributed in the form of a precipitate in the crystal grain.
The brass is an alloy of copper and zinc, and the atomic radius of the two alloy elements are very similar to each other; specifically, copper has a radius of 145 pm and zinc has a radius of 142 pm. Accordingly, the brass may form a substituted solid solution in a wide composition range. In particular, brass generally contains a larger amount of copper than zinc, so the brass may exhibit thermodynamic properties similar to the thermodynamic properties of copper, which acts as a matrix. Therefore, when copper and brass are used as the matrix, the thermodynamic behaviors of the alloys constituting the pseudo-binary system between alloyed phase-separable elements are considered to be similar to each other.
In order to prove this, a thermodynamic simulation was performed. The result of calculation in
The complex copper alloys according to the Examples of the present invention were manufactured and the properties thereof were analyzed. The complex copper alloys were melted using induction casting method, which has a stirring effect by an electromagnetic field making it easy to manufacture a homogeneous microstructure, and then rapidly cooled. In addition to the induction casting method, it is possible to manufacture the complex copper alloys through a commercial casting process using an arc-melting method in which a bulk homogeneous solid solution is rapidly manufactured and impurities such as oxides and pores are minimized because high temperatures are capable of being achieved using arc plasma, a resistance-heating method in which a temperature is capable of being precisely controlled, and a rapid-cooling solidification method that is useful for the formation of a homogeneous solid solution. Further, the complex copper alloys may be manufactured using the commercial casting method, in which high-melting-point metals of raw metals are capable of being melted and may be manufactured by sintering raw materials manufactured in a powder form according to spark plasma sintering or hot isostatic pressing sintering using a powder metallurgy method at high temperatures under high pressure. In the case of the sintering method, it is easy to more precisely control a microstructure and to manufacture parts having desired shapes. The alloy that is manufactured may be cold rolled, hot rolled, or heat-treated for recrystallization.
The alloy compositions of the complex copper alloys according to the Examples of the present invention may be represented by Chemical Formula 1 below, and the high-entropy alloy (HEA) represents the composition of the precipitate alloy constituting the second phase.
(Cu100-xZnx)y(HEA)100-y [Chemical Formula 1]
(0≤x≤45, 0<y≤10 at %, and the high-entropy alloy includes one or more alloy elements selected from the group consisting of Cr, Mn, Fe, Co, and Ni.)
The metal matrix of the complex copper alloy according to the Example of the present invention may include copper and zinc, and the amount of zinc may be up to 45 at % based on the entire metal matrix. This is because the brass alloy commonly used includes an FCC single-phase or a composite structural alloy having an FCC phase including a BCC phase. As shown in
Further, the high-entropy alloy (HEA) of Chemical Formula 1 includes an alloy of one or more elements selected from the element group I consisting of Cr, Mn, Fe, Co, and Ni, among the elements constituting the FCC high-entropy alloy. The following Table 4 shows Examples of various kinds of alloys satisfying Chemical Formula 1.
From the result of alloying pure copper and one to five elements selected from alloy elements included in the element group I, as shown in Table 4, it could be confirmed that spherical precipitations were formed in the grains of the related alloy.
In particular, the above result can be confirmed from the results of optical microscope analysis shown in
It can be confirmed that this phenomenon is a property that may be expressed in all of the various alloys of the present invention precipitated based on the above-described mechanism as well as in the alloy of Example 12 (Table 4), and these results are shown in detail in
Therefore, as shown in
The form (shape and size) of the precipitate that is capable of being formed in the complex copper alloys according to the Examples of the present invention may be controlled by varying the process conditions. As shown in Table 5, it can be confirmed that when the composition alloy of the present invention as in Example 15 is solidified using furnace cooling (cooling speed: less than 10−3 K/s) (Comparative Example 14), a coarse second phase having a size of several tens of μm or more is formed so as to have a dendritic pattern, unlike a precipitate having a size of 10 μm or less formed using conventional water cooling (cooling speed: 10−3 K/s or more and 103 K/s or less). That is, the control of process conditions may significantly affect the control of the shape and size of the precipitate.
Further, when a coarse precipitate having a size of more than 10 μm is precipitated in a spherical or dendritic shape, the total interface length between the matrix and the precipitate is reduced. Accordingly, during processing, a stress concentration phenomenon may occur, which may lead to rapid fractures. Therefore, it is preferable that the precipitate be formed so as to have a size of 10 μm or less.
As shown in Comparative Example 15 of Table 6, in the case of the alloy that contains the high-entropy alloy phase in an amount of more than 10 at %, a large amount of precipitate having a size of several tens of μm or more is obtained in the form of dendritic-pattern branches throughout the material even during rapid cooling, thereby decreasing the machinability, as in the case where the coarse precipitate is formed. Accordingly, it is preferable that the high-entropy alloy element forming the precipitate be used in an amount of 10 at % or less in order to perform the alloying. That is, the results based on Example 15 and Comparative Examples 14 and 15 above mean that the amount of the high-entropy alloy phase shown in Chemical Formula 1 must be 10 at % or less based on the entirety of each of the alloy compositions during the alloying. It is preferable that the cooling speed be controlled to be 10−3 K/s or more and 103 K/s or less.
The following Table 7 shows that the phase separation phenomenon can be confirmed not only in the alloy of the pure copper matrix, but also in the brass matrix. When checking the microstructure of Example 19 shown in
In order to improve the properties of the precipitate, the high-entropy alloy composition in Chemical Formula 1 may include one or more alloy elements selected from the element group II consisting of Al, Ta, Nb, V, Mo, and W, which are easily solid-solved in the high-entropy alloy phase without reducing the properties of the free cutting lead-free brass according to the Examples of the present invention, in an amount of up to 10 at % based on the high-entropy alloy. The composition is as shown in Examples 21 to 26 of the following Table 8.
Examples 27 to 35 shown in Table 9 below are for improving the machinability of the matrix, and one or more alloy elements selected from the alloy group consisting of Pb, Sn, Sb, As, Bi, Cd, P, Mg, and Si, which are known to improve machinability when added in small amounts to the material brass, may be used in alloying in respective amounts of 2 at % or less based on the total amount of the alloy elements.
Hereinabove, specific Examples of the present invention have been described. A person having ordinary knowledge in the technical field to which the present invention pertains will understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed Examples should be considered in terms of explanation rather than limitation. The present invention's scope is as set forth in the claims rather than in the previous description, and all variations within the equivalent range should be interpreted as being included in the present invention.
The complex copper alloy according to Examples of the present invention has excellent physical properties. For example, the complex copper alloy has excellent machinability (machinability), formability, and mechanical properties. Further, the complex copper alloy is environmentally friendly. The complex copper alloy is used to manufacture various processed products such as faucet products and pipes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2018-0126132 | Oct 2018 | KR | national |
This application is a Section 371 National Stage Application of International Application No. PCT/KR2019/013869, filed Oct. 22, 2019 and published as WO2020/085755 on Apr. 30, 2020, in Korean, which claims priority to KR Patent Application Serial No. 10-2018-012632, filed Oct. 22, 2018 the contents of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2019/013869 | 10/22/2019 | WO | 00 |
