Method for preparing alloy for diffusion bonding, and diffusion bonding material produced by method for preparing alloy for diffusion bonding

Abstract

The present invention relates to a method for preparing an alloy for diffusion bonding, the alloy for diffusion bonding comprising a substrate and an alloyed region having a chemical composition different from that of the substrate, the method for preparing an alloy for diffusion bonding comprising: a coating step (a) for forming an alloy precursor layer comprising nickel (Ni) on the surface of a base material; a surface alloying step (b) in which the base material and the constituent elements of the alloy precursor layer are mixed to form an alloyed region; and a polishing step (c) in which at least a portion of the alloyed region is removed and an alloy surface for diffusion bonding is prepared.

Description

Technical Field

[0001] The present invention relates to a method for preparing an alloy for diffusion bonding and a diffusion bonding material produced by the method. Background Art

[0002] Bonding is divided into liquid phase bonding and solid phase bonding, depending on whether the materials are melted during the bonding process. Diffusion bonding is a method of solid phase bonding, which is a technology that uses thermal diffusion of atoms at high temperatures to bond materials.

[0003] In the prior art, the alloy is diffused and bonded using temperature, pressure, environment, surface treatment, post-heat treatment, filler metal, etc. as process variables. According to the prior art, when diffusion bonding occurs, titanium (Ti) and carbon (C) contained in the alloy react, or aluminum (Al) and oxygen (O) react, forming secondary phases such as Ti-rich carbides or Al-rich oxides. The secondary phase formed at the interface of the diffusion bonding material restricts the movement of the grain boundary across the interface of the diffusion bonding material, forming a planar grain boundary. This planar grain boundary reduces the high temperature mechanical properties of the diffusion bonding material.

[0004] Until the melting point of the alloy, the Ti-rich carbides or Al-rich oxides formed at the interface of the diffusion bonding material will not dissolve in the matrix. Therefore, when the above-mentioned secondary phase is formed at the interface of the diffusion bonding material, the grain boundary movement across the interface of the diffusion bonding material is limited by heat treatment after use in the prior art. On the other hand, when the alloy is diffused and bonded by inserting a filler metal, the chemical composition gradient between the filler metal and the alloy to be diffused and bonded may cause diffusion-induced grain boundary movement. As a result, the planar grain boundary observed at the interface of the diffusion bonding material can be changed to an equiaxed grain boundary. However, when a filler metal is used, a secondary phase that causes brittle fracture may be formed at the interface of the diffusion bonding material or near the interface. Summary of the invention

[0005] Technical issues

[0006] One of the multiple objects of the present invention is to form a secondary phase (such as Ti-rich carbide, Al-rich oxide or Ni) at or near the interface of the diffusion bonding material. 3 The formation of (Al, Ti) intermetallic compounds) is minimized.

[0007] One of the various objects of the present invention is to achieve grain boundary migration across a diffusion bonded material interface.

[0008] One of the various objects of the present invention is to ensure the soundness of diffusion bonding materials at room temperature and at high temperatures.

[0009] One of the multiple objects of the present invention is to provide a diffusion bonding material and a diffusion bonding method of an alloy having mechanical properties at the same level as the parent material at room temperature and high temperature.

[0010] However, the technical problems to be achieved by the present invention are not limited to the problems mentioned above, and ordinary technicians in the technical field to which the present invention belongs can clearly understand other problems not mentioned from the following description.

[0011] Solutions to the problem

[0012] The present invention partially changes the chemical composition of the surface and the vicinity of the surface of the alloy to solve the problem that the secondary phase formed at or near the interface of the diffusion bonding material restricts the grain boundary movement across the interface of the diffusion bonding material.

[0013] Effects of the Invention

[0014] One of the effects of the present invention is that the formation of a secondary phase at or near the interface of diffusion bonding materials can be minimized.

[0015] One of the effects of the present invention is that a grain boundary migration region can be formed across the interface of the diffusion bonding material.

[0016] One of the effects of the present invention is that it is possible to provide a diffusion bonding material and an alloy diffusion bonding method having mechanical properties at the same level as the parent material at room temperature and high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart schematically showing the method for preparing an alloy for diffusion bonding and the diffusion bonding method of the present invention.

[0018] Figure 2 This is a cross-sectional view schematically showing the alloy for diffusion bonding of the present invention.

[0019] Figure 3 It is a cross-sectional view schematically showing the diffusion bonding material of the present invention.

[0020] Figure 4 This is an image of a cross section of the diffusion bonding alloy of the present invention taken using a scanning electron microscope (SEM).

[0021] Figures 5 to 8 Electron microprobe analysis (EPMA) was used to Figure 4 The cross section of the constituent elements (Fe( Figure 5 )、Ni( Figure 6 )、Cr( Figure 7 ) and Ti( Figure 8 ) distribution analysis.

[0022] Fig. 9 The figure is an image of a cross section of a diffusion bonding material according to an embodiment of the present invention taken using an optical microscope (OM).

[0023] Figures 10 to 12 The stress-strain curves at room temperature (25°C) are respectively those of the base material, the embodiment and the comparative example.

[0024] Figures 13 to 15 These are the stress-strain rate diagrams at 600°C for the base material, the embodiment and the comparative example. DETAILED DESCRIPTION

[0025] Hereinafter, the embodiments of the present invention will be described with reference to the specific embodiments and the accompanying drawings. The techniques described in this specification are not limited to specific embodiments, but should be understood to include various modifications, equivalent technical solutions and / or alternative technical solutions of the embodiments of the present invention. In the description of the related figures, similar structural elements may be marked with similar reference numerals.

[0026] Furthermore, in the drawings, in order to clearly illustrate the present invention, parts not related to the description are omitted, and in order to clearly express multiple layers and regions, the thickness is exaggerated, and structural elements with the same function within the scope of the same concept may be described using the same figure marks.

[0027] In this specification, expressions such as "having", "may have", "including" or "may include" refer to the existence of the feature (such as a numerical value, function, action or structural element such as a component), and do not exclude the existence of additional features.

[0028] In the present specification, expressions such as "A or B", "at least one of A or / and B", or "one or more of A or / and B" may include all possible combinations of the items listed together. For example, "A or B", "at least one of A and B", or "at least one of A or B" may all mean (1) including at least one A, (2) including at least one B, or (3) including at least one A and at least one B.

[0029] The present invention relates to a method for preparing an alloy for diffusion bonding. In the method for preparing an alloy for diffusion bonding according to the present invention, the alloy for diffusion bonding includes a substrate and an alloying region having a chemical composition different from that of the substrate, and the method may include: a coating step (a) to form an alloy precursor layer including nickel (Ni) on the surface of a base material; a surface alloying step (b) to mix the constituent elements of the base material and the alloy precursor layer to form an alloying region; and a grinding step (c) to remove at least a portion of the alloying region to prepare the surface of the alloy for diffusion bonding. The method for preparing the alloy for diffusion bonding may mean a method for processing the alloy for diffusion bonding used to manufacture a diffusion bonding material described later. When diffusion bonding is performed using the alloy for diffusion bonding prepared by the method for preparing an alloy for diffusion bonding according to the present invention, the formation of secondary phases of carbides and even oxides in the interface of the diffusion bonding material can be suppressed, and a diffusion bonding material with excellent mechanical properties and soundness can be provided.

[0030] At this time, at least a portion of the alloyed region of the diffusion bonding alloy may be exposed on the surface of the diffusion bonding alloy. Exposing at least a portion of the alloyed region on the surface of the diffusion bonding alloy may mean that the alloyed region is formed on the surface of the alloy and in the region near the surface. The alloyed region functions as an interface for mutual bonding in the subsequent diffusion bonding process, and the presence of the alloyed region exposed on the surface can suppress the formation of secondary phases at the diffusion bonding interface, forming a grain boundary movement region, and can manufacture a diffusion bonding material with high mechanical properties.

[0031] In the present invention, "grain boundary migration" means the situation where atoms migrate at the interface of diffusion bonding materials by thermal diffusion, which is different from the commonly used grain boundary migration. In the present invention, "grain boundary migration region" means the region where grain boundary migration occurs across the above-mentioned diffusion bonding material interface and no planar grain boundaries can be observed.

[0032] In one example, the alloy for diffusion bonding according to the present invention may satisfy the following Relationship 1.

[0033] Relation 1

[0034] C m (s) ≠C m (O)

[0035] In the above equation 1, C m (s) It means the chemical composition of the elements in the surface of the alloy for diffusion bonding, C m (O)It means the chemical composition of the constituent elements in the matrix of the alloy for diffusion bonding.

[0036] The fact that the alloy for diffusion bonding according to the present invention satisfies the above-mentioned relational expression 1 may mean that the chemical composition of the constituent elements in the surface of the alloy for diffusion bonding and the chemical composition of the constituent elements in the matrix of the alloy for diffusion bonding are different from each other. The difference in the chemical composition of the constituent elements may mean that the constituent elements are different, or the content ratio of the constituent elements is different, which may mean that the average chemical composition is different.

[0037] The method for preparing an alloy for diffusion bonding according to the present invention may include a coating step (a) of forming an alloy precursor layer including nickel (Ni) on a surface of a base material.

[0038] In the coating step (a), the method of forming the alloy precursor layer including nickel (Ni) on the surface of the base material is not particularly limited. For example, the alloy precursor layer may be formed by physical vapor deposition, chemical vapor deposition, pack cementation, electroplating or electroless plating, but is not limited thereto.

[0039] The types of constituent elements of the alloy precursor layer including nickel (Ni) formed in the above step (a) are not particularly limited, and may be composed of a single atom system, a two-atom system, and a multi-atom system. The alloy precursor layer, for example, includes nickel (Ni), and may also be composed of Al, Ag, Au, Co, Cu, and Ti alloys, but is not limited thereto. In addition, the alloy precursor layer may include an element that induces a melting point depression, i.e., boron, silicon, or phosphorus, as a constituent element.

[0040] In one example, the upper limit of the thickness of the alloy precursor layer is not particularly limited, but for example, it can be less than 10 mm, less than 8 mm, less than 6 mm, less than 4 mm, less than 2 mm or less than 1 mm. When the thickness of the alloy precursor layer is too thin, it may not be possible to fully provide elements that realize grain boundary movement to the surface of the diffusion bonding alloy. Furthermore, it may not be possible to fully reduce the constituent elements of the secondary phase formed at the interface of the diffusion bonding material. On the contrary, when the thickness of the alloy precursor layer is too thick, it is possible to excessively require grinding and even post-heat treatment steps. The lower limit of the thickness of the alloy precursor layer is not particularly limited, but for example, it can be more than 1 μm, more than 2 μm or more than 3 μm.

[0041] The preparation method of the alloy for diffusion bonding according to the present invention may include a surface alloying step (b) of mixing the constituent elements of the above-mentioned base material and the alloy precursor layer to form an alloyed region. In the above-mentioned step (b), as long as the constituent elements of the base material and the alloy precursor layer can be mixed, the method is not particularly limited. For example, the above-mentioned mixing can be performed by ion implantation, surface modification using a laser, surface modification using an electron beam, heat treatment, thermomechanical treatment methods, etc., but is not limited thereto.

[0042] The temperature, pressure, time and vacuum degree of the surface alloying step are not particularly limited as long as they are within the range in which the constituent elements of the parent material and the alloy precursor layer can be mixed. For example, the surface alloying can be performed by applying a pressure of 0 MPa or more or a pressure greater than 0 MPa at a temperature above room temperature. In this case, the surface alloying time can be performed from 1 minute to 100 hours, and can be performed at a vacuum degree below atmospheric pressure, but is not limited thereto.

[0043] The method for diffusion bonding of an alloy according to the present invention may include a grinding step of removing at least a portion of the alloyed region (c) to prepare a surface of the alloy for diffusion bonding.

[0044] The grinding step (c) can be a step of removing at least a portion of the alloying region including impurities and / or secondary phases after the surface alloying step. In the surface alloying step, impurities and / or secondary phases may be formed on the alloy surface and near the surface, and such impurities and / or secondary phases may be the cause of reducing the physical properties of the alloy. The surface grinding can be performed in a manner that a portion of the alloying region remains. This can suppress the formation of secondary phases at the interface of the diffusion bonding alloy when performing diffusion bonding, and realize grain boundary movement.

[0045] The grinding thickness is not particularly limited as long as the impurities and / or secondary phases on and near the surface can be fully removed after the surface alloying step. For example, the grinding thickness can be less than 10 mm, less than 8 mm, less than 6 mm, less than 4 mm, less than 2 mm or less than 1 mm. In addition, the lower limit of the grinding thickness is not particularly limited, but for example, it can be more than 1 μm, more than 2 μm or more than 3 μm. The grinding method of the grinding step is not particularly limited as long as a part of the alloying area can be removed. For example, various known methods such as mechanical grinding or electrolytic grinding can be used.

[0046] In one example, the thickness of the alloyed region of the diffusion bonding alloy according to the present invention is not particularly limited as long as it is within the range that does not hinder the effect of inhibiting the formation of secondary phases described later, but can be, for example, 10 mm or less, 8 mm or less, 6 mm or less, 4 mm or less, 2 mm or less, or 1 mm or less. When the thickness of the alloyed region is too thick, the process cost for homogenizing the chemical composition at the interface of the diffusion bonding material and near the interface may increase excessively. The lower limit of the thickness of the alloyed region is not particularly limited, but can be, for example, 1 μm or more, 2 μm or more, or 3 μm or more.

[0047] The present invention also relates to a diffusion bonding method. The diffusion bonding method according to the present invention may include a diffusion bonding step of performing diffusion bonding on an alloy prepared by the method for preparing the alloy for diffusion bonding.

[0048] Figure 1 The method for preparing the alloy for diffusion bonding and the diffusion bonding method of the present invention are schematically shown. Figure 1 According to the diffusion bonding method of the present invention, the alloy can be prepared by a method for preparing an alloy for diffusion bonding, and the method for preparing the alloy for diffusion bonding may include: a coating step (a), forming a precursor layer including nickel (Ni) on the surface of a base material; a surface alloying step (b), mixing constituent elements of the base material and the alloy precursor layer to form an alloyed region; a grinding step (c), removing at least a portion of the alloyed region to prepare the surface of the alloy for diffusion bonding, and may include a diffusion bonding step (d) of diffusion bonding the alloy for diffusion bonding.

[0049] At this time, the diffusion bonding step may be a step of mutually diffusion bonding the alloyed regions of the diffusion bonding alloys of the plurality of diffusion bonding alloys. The diffusion bonding alloy may include an alloyed region exposed on the surface, and diffusion bonding may be achieved in the alloyed region exposed on the surface. For example, after preparing a plurality of diffusion bonding alloys, the alloyed regions of the alloys may be arranged so as to be in contact with each other, and then diffusion bonding may be performed.

[0050] The diffusion bonding conditions of the above-mentioned diffusion bonding step are not particularly limited as long as they are within the range in which the diffusion bonding alloy can be diffusion bonded. For example, the diffusion bonding step can be performed for 5 minutes to 20 hours at a temperature above room temperature and a pressure greater than 0 MPa. At this time, the vacuum degree in the diffusion bonding equipment can be 10 -3 However, the diffusion bonding conditions are not limited to the above-mentioned bonding temperature, bonding pressure, bonding time and vacuum degree.

[0051] Furthermore, the alloy diffusion bonding method according to the present invention may include, as required, a step of performing a post-heat treatment at a temperature range above room temperature for 1 to 100 hours after the above-mentioned diffusion bonding. Furthermore, after the above-mentioned post-heat treatment, the alloy may be cooled to 10° C. to 30° C. by furnace cooling, air cooling or quenching.

[0052] The present invention also relates to a diffusion bonding material. The diffusion bonding material according to the present invention can be formed by diffusion bonding a plurality of diffusion bonding alloys prepared by the method for preparing the above-mentioned diffusion bonding alloy and then bonding them to each other.

[0053] In this case, the diffusion bonding material may include a diffusion bonding material interface formed by diffusion bonding the plurality of diffusion bonding alloys to each other and a grain boundary migration region disposed on the interface.

[0054] Figure 2 The cross sections of a plurality of diffusion bonding alloys 10 are schematically shown. An alloyed region 20 is partially formed on the surface and near the surface of the diffusion bonding alloy 10. In the matrix below the alloyed region 20, the chemical composition of the constituent elements is the same as the chemical composition of the base material constituent elements.

[0055] Figure 3 Schematic diagram of a cross section of a diffusion bonding material according to the present invention. The diffusion bonding material of the present invention includes a plurality of diffusion bonding alloys 10 and a diffusion bonding material interface 30 disposed between the plurality of diffusion bonding alloys 10. After diffusion bonding and post-heat treatment, atoms diffuse mutually, and the chemical composition of the constituent elements at the diffusion bonding material interface 30 and near the interface becomes homogeneous. In particular, the chemical composition of the constituent elements in the alloying region 20 reaches the level of the parent alloy, meeting the raw material specification (such as ASTM B409) of the parent alloy.

[0056] In one embodiment of the present invention, the diffusion bonding material according to the present invention may satisfy the following Relationship 2.

[0057] Relation 2

[0058] L 2 / L 1 ≥0.20

[0059] In the above equation 2, L 1 is the total length of the diffusion bonding material interface 30, L 2 is the length of the grain boundary movement region.

[0060] The above ratio (L 1 / L 2) means the ratio of the length of the region that crosses the diffusion bonding material interface and undergoes grain boundary migration. The upper limit of the above ratio is not particularly limited, but may be, for example, 1.0 or less.

[0061] The above ratio may mean the ratio of the length of the region where grain boundary movement occurs across the diffusion bonding material interface, and the upper limit is not particularly limited, but may be, for example, 1.0 or less. When the diffusion bonding material according to the present invention satisfies the above relational expression 2, the formation of planar grain boundaries can be suppressed, and the mechanical properties of the diffusion bonding material can be improved.

[0062] In one example, the diffusion bonding material according to the present invention may satisfy the following equation 3.

[0063] Relation 3

[0064] TS D / TS B ≥0.80

[0065] In the above equation 3, TS D is the tensile strength of the diffusion bonded material at room temperature and high temperature, TS B It is the tensile strength of the base material at room temperature and high temperature. In this specification, the base material means the alloy base material that has not undergone the preparation steps for manufacturing the diffusion bonding alloy. The above relationship 3 means that the room temperature and high temperature tensile strength of the diffusion bonding material is more than 80% of the room temperature and high temperature tensile strength of the alloy base material. The mechanical properties are improved according to the present invention because the formation of the secondary phase at the interface of the diffusion bonding material is suppressed.

[0066] The diffusion bonding material according to the present invention can satisfy the following Relationship 4.

[0067] Relation 4

[0068] EL D / EL B ≥0.60

[0069] In the above equation 4, EL D is the elongation of the diffusion bonding material at room temperature and high temperature, EL B The above relational expression 4 means that the room temperature and high temperature elongation of the diffusion bonding material according to the present invention is more than 60% of that of the base material. The mechanical properties of the present invention are improved because the formation of the secondary phase at the interface of the diffusion bonding material is suppressed as described above.

[0070] In this specification, normal temperature may mean about 25° C., and high temperature may mean about 600° C. For example, when the diffusion bonding material according to the present invention satisfies the above-mentioned relational expression 3, it may mean that the room temperature tensile strength of the diffusion bonding material is more than 80% of the room temperature tensile strength of the alloy parent material, and it may mean that the high temperature tensile strength of the diffusion bonding material is more than 80% of the high temperature tensile strength of the alloy parent material.

[0071] Furthermore, when the diffusion bonding material according to the present invention satisfies the above relational expression 4, it means that the room temperature elongation of the diffusion bonding material is 60% or more than that of the base material, and it also means that the high temperature elongation of the diffusion bonding material is 60% or more than that of the base material.

[0072] Furthermore, the present invention can provide a plate-type heat exchanger manufactured by the diffusion bonding method of the above alloy.

[0073] Recently, the growth momentum of the market for introducing renewable energy and stable power generation systems has been increasing. The growth forecast results of the North American and European heat exchanger markets (2020-2025) are US$4.7 billion (3.4% annual growth rate) and US$5.02 billion (3.2% annual growth rate), respectively. Considering the market trend aimed at improving energy efficiency, the growth momentum of the plate heat exchanger market is also predicted to be positive. The present invention has been developed based on this trend of the times, and it is expected to have a high industrial impact on the manufacturing technology of small nuclear reactor steam generators and the manufacturing technology of heat exchangers for hydrogen stations. Furthermore, it is expected to activate the stagnant domestic manufacturing sector in South Korea, strengthen external competitiveness, and contribute to product / technology exports.

[0074] In order to help understand the present invention, preferred embodiments are presented below. However, the following embodiments are provided to make it easier to understand the present invention, and the content of the present invention is not limited to the following embodiments.

[0075] Example

[0076] Preparation of alloy for diffusion bonding

[0077] In order to prepare the alloy for diffusion bonding, two plates of base alloy (Alloy 800H) were prepared. The chemical composition of the alloy used in the examples is shown in Table 1 below.

[0078] Table 1

[0079]

[0080] In the present invention, the example of the parent alloy may be Alloy 800H (UNS N08810), but is not limited thereto. The parent alloy may include 30.0 to 35.0 weight percent of nickel (Ni), 19.0 to 23.0 weight percent of chromium (Cr), 0.15 to 0.60 weight percent of aluminum (Al), 0.15 to 0.60 weight percent of titanium (Ti), 0.05 to 0.10 weight percent of carbon (C), and the balance of iron (Fe).

[0081] Furthermore, the above-mentioned base alloy may further include less than 0.75 weight percent of copper (Cu), less than 1.0 weight percent of silicon (Si), less than 1.5 weight percent of manganese (Mn), and less than 0.015 weight percent of sulfur (S) as required, but is not limited thereto.

[0082] The following describes the functions and effects of each element.

[0083] (1) Iron (Fe)

[0084] The iron is an element that acts as a base metal. The iron content in the alloy is at least 39.5 weight percent. In nickel-based heat-resistant alloys, iron is used to replace expensive elements such as nickel and even cobalt. When iron is added to nickel-based heat-resistant alloys, the workability of the raw materials may become easier.

[0085] (2) Nickel (Ni)

[0086] The nickel is an element added to stabilize the austenite structure, and the nickel content in the alloy may be 30.0 to 35.0 weight percent. At this time, when the nickel content is less than 30.0 weight percent, the stability, corrosion resistance and strength of the structure at high temperatures may be reduced.

[0087] (3) Chromium (Cr)

[0088] The chromium is an element used to increase high temperature oxidation resistance, and the chromium content in the alloy may be 19.0 to 23.0 weight percent. At this time, when the chromium content is less than 19.0 weight percent, an oxide film may not be stably formed at high temperatures, and when the chromium content is greater than 23.0 weight percent, a secondary phase according to thermal aging may be formed.

[0089] (4) Aluminum (Al)

[0090] The aluminum is an element that increases high temperature corrosion resistance and increases the strength of the raw material at high temperatures according to the precipitation strengthening effect. The aluminum content in the alloy may be 0.15 to 0.60 weight percent. At this time, when the aluminum content is less than 0.15 weight percent, high temperature corrosion resistance and precipitation strengthening effect may not be obtained, and when it is greater than 0.60 weight percent, a secondary phase according to thermal aging may be formed.

[0091] (5) Titanium (Ti)

[0092] The titanium is an element for the precipitation strengthening effect, and the titanium content in the alloy can be 0.15 to 0.60 weight percent. When the titanium content is less than 0.15 weight percent, the creep strength and oxidation resistance may be reduced, and when it is greater than 0.60 weight percent, a secondary phase according to thermal aging may be formed.

[0093] On the other hand, the alloy for diffusion bonding according to the present invention may further include copper (Cu) 0.75 weight percent or less, silicon (Si) 1.0 weight percent or less, manganese (Mn) 1.5 weight percent or less, sulfur (S) 0.015 weight percent or less as needed, but is not limited thereto. The above elements may be one of the impurities inevitably included when making the raw materials, but when the above content range is met, physical properties such as high temperature strength can be improved.

[0094] (a) Coating step

[0095] An alloy precursor layer including nickel (Ni) is applied to the surfaces of the two base alloys. The thickness of the alloy precursor layer applied is not particularly limited as long as it is the thickness required in the surface alloying step described later, but can be, for example, 10 mm or less, 8 mm or less, 6 mm or less, 4 mm or less, 2 mm or less, or 1 mm or less, and the lower limit of the thickness can be 1 μm or more, 2 μm or more, or 3 μm or more, but is not limited thereto.

[0096] (b) Surface alloying step

[0097] The alloy coated with the alloy precursor layer including nickel is subjected to heat treatment to perform surface alloying. The heat treatment is performed at a solution heat treatment temperature (at least 1149°C) or so (±150°C), and the heat treatment is terminated after sufficient alloying is performed. The heat treatment time is not particularly limited as long as the surface alloying can be fully performed, but can be performed for 1 minute to 100 hours, for example. After the heat treatment is completed, the alloyed alloy base material is cooled under the condition that no surface oxidation occurs.

[0098] (c) Grinding step

[0099] The surface of the alloy matrix material whose surface is alloyed is mechanically ground in the depth direction to remove the surface. The mechanical grinding can be performed within the thickness range of the alloy precursor layer formed in the coating step. The thickness of the surface removed by the mechanical grinding can be, for example, less than 10 mm, less than 8 mm, less than 6 mm, less than 4 mm, less than 2 mm, or less than 1 mm, and the lower limit of the thickness can be more than 1 μm, more than 2 μm, or more than 3 μm, but is not limited thereto.

[0100] Figure 4 This is a SEM image of a cross section of a diffusion bonding alloy. Figure 4 , after grinding the surface, at t 3 No Cr-rich carbides were observed in the region. This is because t 3 The Cr-rich carbides in the region are dissolved in the matrix. Figure 4 , at a depth deeper than t 3 Precipitates that were not dissolved in the matrix were observed in the region.

[0101] Figures 5 to 8 The following are the results of analyzing the cross section of the diffusion bonding alloy using the EPMA method. Figure 5 Indicates the content of iron (Fe), Figure 6 Indicates the content of nickel (Ni), Figure 7 Indicates the content of chromium (Cr), Figure 8 Indicates the content of titanium (Ti). Figure 5 and Figure 7 It can be confirmed that the content of iron and chromium in the alloy for diffusion bonding according to the present invention does not vary greatly from the surface to the depth direction. Figure 8 It can be confirmed that titanium exists in an area with a large peak intensity, but there is no tendency for the content to increase or decrease in a predetermined manner according to the depth.

[0102] In comparison, reference Figure 6 , from the surface of the diffusion bonding alloy of the present invention to a predetermined depth, nickel has a gradient toward the substrate. Specifically, the nickel content decreases from the surface and reaches the parent material level at a predetermined depth. The chemical composition of the remaining alloy constituent elements other than nickel on and near the surface of the diffusion bonding alloy according to this embodiment is reduced compared to the chemical composition of the constituent elements in the substrate.

[0103] Diffusion bonding of alloys for diffusion bonding

[0104] The surfaces of the above-mentioned diffusion bonding alloys were cleaned with ethanol, and two diffusion bonding alloys were arranged to face each other and then diffusion bonding was performed. Diffusion bonding was performed at a bonding temperature of 1150°C, a bonding pressure of 10 MPa and a bonding pressure of 10 -5 The vacuum was carried out at 2000 Torr for 1 hour.

[0105] Fig. 9 This is an image of a cross section of the diffusion bonding material according to this embodiment taken using an optical microscope (OM). Fig. 9 In the figure, the arrows indicate the diffusion bonding material interfaces. Fig. 9 The A region means the grain boundary migration region. Fig. 9 In the A region, it was confirmed that grain boundary movement occurred across the diffusion bonding material interface. On the contrary, it was confirmed that grain boundary movement did not occur across the diffusion bonding material interface in the B region.

[0106] Comparative Example

[0107] Without performing the above step (a) or step (c), 60 sheets of the alloy (Alloy 800H) were diffusion-bonded under conditions similar to those of the example (1150° C. / 10 MPa / 1 hour).

[0108] Test example

[0109] Tensile tests were performed on the diffusion bonded materials produced in the examples and comparative examples. Specifically, after taking out tensile test pieces from the diffusion bonded materials produced in the examples and comparative examples, tensile tests were performed at room temperature (25° C.) and 600° C. according to ASTM E8 / E8M.

[0110] Figures 10 to 12 They are the stress-strain curves at room temperature of the base material, the embodiment and the comparative example.

[0111] The tensile strength of the base material at room temperature is 547±6MPa, and the elongation is 50.2±1.3%. The tensile strength of the diffusion bonding material according to the embodiment at room temperature is 518±13MPa, and the elongation is 52.2±5.1%. On the other hand, at room temperature in the comparative example, the tensile strength is 395±49MPa, and the elongation is 10.5±4.4%.

[0112] The above results confirm that the diffusion bonding material of the embodiment has a tensile strength of 95% of the base material at room temperature, while the comparative example has a tensile strength of 72% of the base material at room temperature. In addition, it can be confirmed that the elongation of the diffusion bonding material of the embodiment and the diffusion bonding material of the comparative example at room temperature is 103% and 21% respectively compared to the base material.

[0113] The tensile test results show that the mechanical properties of the diffusion bonding material produced by the present invention at room temperature are improved compared to the diffusion bonding material produced by the prior art. Furthermore, it is confirmed that the mechanical properties of the diffusion bonding material produced by the present invention at room temperature reach the mechanical properties of the base material at room temperature.

[0114] Figures 13 to 15 The stress-strain curves at 600°C are respectively those of the base material, the embodiment and the comparative example.

[0115] At 600°C, the tensile strength of the base material is 441±4MPa, and the elongation is 50.8±1.0%. The diffusion bonding material according to the embodiment of the present invention has a tensile strength of 421±1MPa at 600°C, and an elongation of 67.8±3.6%. On the other hand, the diffusion bonding material of the comparative example has a tensile strength of 220±23MPa at 600°C, and an elongation of 3.7±1.8%.

[0116] The above results confirm that the tensile strength of the diffusion bonding material of the embodiment is 95% of that of the base material at 600°C, while the tensile strength of the comparative example is only 49% of that of the base material. On the other hand, it can be confirmed that the elongation of the diffusion bonding material of the embodiment and the diffusion bonding material of the comparative example at 600°C is 133% and 7% of that of the base material, respectively.

[0117] The above results confirm that the mechanical properties of the diffusion bonding material of the present invention correspond to those of the base material at 600°C not only at room temperature but also at 600°C. Furthermore, it can be confirmed that the mechanical properties of the diffusion bonding material produced by the present invention at high temperatures are improved compared to the prior art.

[0118] The above description of the present invention is for illustration only, and those skilled in the art should understand that the present invention can be easily transformed into other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above described embodiments are illustrative in all aspects and not limiting.

[0119] Industrial Applicability

[0120] One of the effects of the present invention is that the formation of a secondary phase at or near the interface of diffusion bonding materials can be minimized.

[0121] One of the effects of the present invention is that a grain boundary migration region can be formed across the interface of the diffusion bonding material.

[0122] One of the effects of the present invention is that it is possible to provide a diffusion bonding material and an alloy diffusion bonding method having mechanical properties at the same level as the parent material at room temperature and high temperature.

Claims

1. A method for preparing a diffusion bonding alloy, the diffusion bonding alloy comprising a matrix and an alloyed region having a chemical composition different from that of the matrix, characterized in that: The coating step (a) forms an alloy precursor layer including nickel (Ni) on the surface of the base material; a surface alloying step (b) of mixing the constituent elements of the parent material and the alloy precursor layer to form an alloyed region; as well as The grinding step (c) removes at least a portion of the alloyed region to prepare an alloy surface for diffusion bonding.

2. The method for preparing an alloy for diffusion bonding according to claim 1, characterized in that: At least a portion of the alloyed region is exposed on the surface of the diffusion bonding alloy.

3. The method for preparing an alloy for diffusion bonding according to claim 1, characterized in that: Satisfies the following relationship 1, Relation 1 C m (s) ≠C m (O) In the above equation 1, C m (s) It means the chemical composition of the elements in the surface of the alloy for diffusion bonding, C m (O) It means the chemical composition of the constituent elements in the matrix of the alloy for diffusion bonding.

4. The method for preparing an alloy for diffusion bonding according to claim 1, characterized in that: The coating thickness of the alloy precursor layer is 10 mm or less.

5. The method for preparing an alloy for diffusion bonding according to claim 1, characterized in that: In the above-mentioned grinding step, a portion of the alloyed region including impurities and / or secondary phases is removed.

6. The method for preparing an alloy for diffusion bonding according to claim 1, characterized in that: The method further includes a diffusion bonding step of performing diffusion bonding on the above-mentioned alloy for diffusion bonding.

7. The method for preparing an alloy for diffusion bonding according to claim 6, characterized in that: The diffusion bonding step is a step of diffusion bonding alloyed regions of a plurality of diffusion bonding alloys to one another.

8. A diffusion bonding material obtained by diffusion bonding a plurality of diffusion bonding alloys prepared by the method for preparing a diffusion bonding alloy according to claim 6, characterized in that: The invention includes a diffusion bonding material interface formed by mutual diffusion bonding of the plurality of diffusion bonding alloys and a grain boundary migration region arranged on the interface.

9. The diffusion bonding material according to claim 8, characterized in that Satisfies the following relationship 2, Relation 2 L2 / L1≥0.20 In the above relational expression 2, L1 is the total length of the diffusion bonding material interface, and L2 is the length of the grain boundary migration region located on the diffusion bonding material interface.

10. The diffusion bonding material according to claim 8, characterized in that Satisfies the following relationship 3, Relation 3 TS D / TS B ≥0.80 In the above equation 3, TS D is the tensile strength of the diffusion bonded material at room temperature and high temperature, TS B It is the tensile strength of the base material at room temperature and high temperature.

11. The diffusion bonding material according to claim 8, characterized in that Satisfies the following relationship 4, Relation 4 HE D / HE B ≥0.60 In the above equation 4, EL D is the elongation of the diffusion bonding material at room temperature and high temperature, EL B It is the elongation of the base material at room temperature and high temperature.

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