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

Abstract

The present invention relates to a method for preparing an alloy for diffusion bonding, comprising a matrix and an alloyed region having a different chemical composition from the matrix, and the method may comprise: (a) an application step of forming an alloy precursor layer containing nickel (Ni) on the surface of a base material; (b) a surface alloying step of forming an alloyed region by mixing the base material and constituent elements of the alloy precursor layer; and (c) a polishing step of preparing an alloy surface for diffusion bonding by removing at least a portion of the alloyed region.

Description

Method for preparing an alloy for diffusion bonding, diffusion bonding material manufactured using the method for preparing an alloy for diffusion bonding

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

[0002]

[0003] Bonding is categorized into liquid-phase bonding and solid-phase bonding, depending on whether the materials are melted or not during the process. Diffusion bonding is a solid-phase bonding method that uses the thermal diffusion of atoms at high temperatures to join materials.

[0004] In conventional diffusion bonding, alloys are diffusion bonded using process variables such as temperature, pressure, environment, surface treatment, post-heat treatment, and filler metal. When diffusion bonding is performed according to conventional techniques, titanium (Ti) and carbon (C) contained in the alloy react, or aluminum (Al) and oxygen (O) react, forming secondary precipitates such as Ti-rich carbides or Al-rich oxides. The secondary precipitates formed at the diffusion bonding interface restrict grain boundary movement across the diffusion bonding interface, forming planar grain boundaries. These planar grain boundaries reduce the high-temperature mechanical properties of the diffusion bonding material.

[0005]

[0006] Ti-rich carbides or Al-rich oxides formed at the diffusion bond interface do not dissolve in the matrix until the alloy melts. Therefore, when the secondary phase is formed at the diffusion bond interface, there is a limit to promoting grain boundary migration across the diffusion bond interface through post-heat treatment used in the prior art. On the other hand, when diffusion bonding an alloy by inserting a filler metal, diffusion-induced grain boundary migration can occur due to the chemical composition gradient between the filler metal and the alloy to be diffusion bonded. Accordingly, the planar grain boundary observed at the diffusion bond interface 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 or near the diffusion bond interface.

[0007]

[0008] One of the several objects of the present invention is to minimize the formation of secondary phases (e.g., Ti-rich carbides, Al-rich oxides, or Ni3(Al,Ti) intermetallic compounds) at or near the diffusion bonding interface.

[0009]

[0010] One of the several objects of the present invention is to promote grain boundary movement across the diffusion bonding material interface.

[0011]

[0012] One of the several objects of the present invention is to ensure the soundness of a diffusion bonding agent at room temperature and high temperature.

[0013]

[0014] One of the several objects of the present invention is to provide a diffusion bonding method of a diffusion bonding agent and an alloy having mechanical properties at the level of the parent material at room temperature and high temperature.

[0015]

[0016] However, the technical problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0017]

[0018] The present invention locally changes the chemical composition of an alloy at and near the surface to solve the problem of grain boundary movement across a diffusion bonding material interface being restricted by a secondary phase formed at or near the diffusion bonding material interface.

[0019]

[0020] One of the many effects of the present invention is that it can minimize the formation of a secondary phase at or near the interface of the diffusion bonding agent.

[0021]

[0022] One of the many effects of the present invention is that it can form a grain boundary migration region across the diffusion bonding material interface.

[0023]

[0024] One of the many effects of the present invention is that it can provide a diffusion bonding method for a diffusion bonding agent and alloy having mechanical properties at the level of the parent material at room temperature and high temperature.

[0025]

[0026] Figure 1 is a flow chart schematically showing a method for preparing an alloy for diffusion bonding and a diffusion bonding method of the present invention.

[0027] Fig. 2 is a cross-sectional view schematically showing an alloy for diffusion bonding of the present invention.

[0028] Fig. 3 is a cross-sectional view schematically showing the diffusion bonding material of the present invention.

[0029] Figure 4 is an image of a cross-section of an alloy for diffusion bonding of the present invention taken using a scanning electron microscope (SEM).

[0030] Figures 5 to 8 show the distribution of constituent elements (Fe (Figure 5), Ni (Figure 6), Cr (Figure 7), and Ti (Figure 8)) analyzed using the electron microprobe analysis (EPMA) method in the cross section of Figure 4.

[0031] Figure 9 is an image of a cross-section of a diffusion bonding material according to one embodiment of the present invention, taken using an optical microscope (OM).

[0032] Figures 10 to 12 are stress-strain curves at room temperature (25°C) of the parent material, examples, and comparative examples, respectively.

[0033] Figures 13 to 15 are stress-strain diagrams at 600°C for the base material, examples, and comparative examples, respectively.

[0034]

[0035] Hereinafter, embodiments of the present invention will be described with reference to specific embodiments and the attached drawings. It should be understood that the technology described herein is not limited to specific embodiments, but rather encompasses various modifications, equivalents, and / or alternatives of the embodiments of the present invention. In connection with the description of the drawings, similar reference numerals may be used for similar components.

[0036]

[0037] And in order to clearly explain the present invention in the drawings, parts that are not related to the explanation are omitted, and the thickness is enlarged to clearly express several layers and areas, and components with the same function within the scope of the same idea can be explained using the same reference numerals.

[0038]

[0039] In this specification, expressions such as “has”, “may have”, “includes”, or “may include” indicate the presence of a feature (e.g., a component such as a number, function, operation, or part), and do not exclude the presence of additional features.

[0040]

[0041] In this specification, expressions such as "A or B," "at least one of A and / or B," or "one or more of A or / and B" can include all possible combinations of the listed items. For example, "A or B," "at least one of A and B," or "at least one of A or B" can all refer to (1) including at least one A, (2) including at least one B, or (3) including both at least one A and at least one B.

[0042]

[0043] The present invention relates to a method for preparing an alloy for diffusion bonding. The method for preparing an alloy for diffusion bonding according to the present invention comprises a method for preparing an alloy for diffusion bonding comprising a base and an alloying region having a different chemical composition from the base, the method comprising: (a) a coating step for forming an alloy precursor layer containing nickel (Ni) on the surface of a base material; (b) a surface alloying step for forming an alloying region by mixing constituent elements of the base material and the alloy precursor layer; and (c) a polishing step for preparing a surface of the alloy for diffusion bonding by removing at least a portion of the alloying region. The method for preparing an alloy for diffusion bonding may refer to a method for processing a diffusion bonding alloy for producing a diffusion bonding material, which will be described later. When diffusion bonding is performed using an alloy for diffusion bonding prepared by the method for preparing an alloy for diffusion bonding according to the present invention, the formation of a secondary phase of a carbide or oxide series at the interface of the diffusion bonding material can be suppressed, thereby providing a diffusion bonding material having excellent mechanical properties and soundness.

[0044]

[0045] At this time, at least a part of the alloying region of the diffusion bonding alloy may be exposed to the surface of the diffusion bonding alloy. That at least a part of the alloying region is exposed to the surface of the diffusion bonding alloy may mean that the alloying region is formed on the surface and a region near the surface of the alloy. The alloying region functions as an interface that is bonded to each other in a subsequent diffusion bonding process, and the presence of the alloying region exposed to the surface can suppress the formation of a secondary phase at the diffusion bonding interface, thereby forming a grain boundary movement region, and can manufacture a diffusion bonding material having high mechanical properties.

[0046]

[0047] In the present invention, "grain boundary migration" refers to a case where atoms thermally diffuse and move the diffusion bonding material interface, and is different in meaning from the commonly used term grain boundary migration. In the present invention, "grain boundary migration region" refers to a region where grain boundary migration occurs across the diffusion bonding material interface and no planar grain boundaries are observed.

[0048]

[0049] In one example, the alloy for diffusion bonding according to the present invention can satisfy the following relationship 1.

[0050]

[0051] [Relationship 1]

[0052] C m (s) ≠C m (O)

[0053]

[0054] In the above relation 1, C m (s) refers to the chemical composition of the constituent elements on the surface of the alloy for diffusion bonding, and C m (O) refers to the chemical composition of the constituent elements in the matrix of the alloy for diffusion bonding.

[0055]

[0056] That the diffusion bonding alloy according to the present invention satisfies the above relational expression 1 may mean that the chemical composition of the constituent elements on the surface of the diffusion bonding alloy and the chemical composition of the constituent elements in the diffusion bonding alloy matrix are different from each other. The difference in the chemical composition of the constituent elements may mean that the constituent elements are different, or that the content ratios of the constituent elements are different, or that the average chemical compositions are different.

[0057]

[0058] A method for preparing an alloy for diffusion bonding according to the present invention may include (a) a coating step of forming an alloy precursor layer containing nickel (Ni) on the surface of a base material.

[0059]

[0060] The method for forming an alloy precursor layer containing nickel (Ni) on the surface of the base material in the above (a) coating step is not particularly limited. For example, the alloy precursor layer may be formed through physical vapor deposition, chemical vapor deposition, pack cementation, electroplating, or electroless plating, but is not limited thereto.

[0061]

[0062] The constituent elements of the alloy precursor layer including nickel (Ni) formed in the above step (a) are not particularly limited in type, and may be composed of a monoatomic system, a diatomic system, and a polyatomic system. The alloy precursor layer includes, for example, nickel (Ni), and may additionally be composed of an alloy of Al, Ag, Au, Co, Cu, or Ti, but is not limited thereto. In addition, the alloy precursor layer may include, as a constituent element, boron, silicon, or phosphorus, which are elements that cause melting point depression.

[0063]

[0064] In one example, the thickness of the alloy precursor layer is not particularly limited in its upper limit, but may 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. If the thickness of the alloy precursor layer is excessively thin, it may not be able to sufficiently provide elements that promote grain boundary movement on the surface of the alloy for diffusion bonding. In addition, it may not be able to sufficiently reduce constituent elements that form a secondary phase at the interface of the diffusion bonding material. On the other hand, if the thickness of the alloy precursor layer is excessively thick, an excessive amount of polishing or post-heat treatment processes may be required. The lower limit of the thickness of the alloy precursor layer is not particularly limited, but may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more.

[0065]

[0066] The method for preparing an alloy for diffusion bonding according to the present invention may include a surface alloying step of mixing the constituent elements of the base material and the alloy precursor layer to form an alloying region (b). As long as the constituent elements of the base material and the alloy precursor layer can be mixed in step (b), the method is not particularly limited. For example, the mixing may be performed through ion implantation, surface treatment using a laser, surface treatment using an electron beam, heat treatment, thermo-mechanical treatment, etc., but is not limited thereto.

[0067]

[0068] The conditions of the above surface alloying step, such as temperature, pressure, time, and vacuum, are not particularly limited as long as they can mix the constituent elements of the base material and the alloy precursor layer. For example, the surface alloying may be performed by applying a pressure of 0 MPa or higher or a pressure exceeding 0 MPa at a temperature higher than room temperature. In this case, the surface alloying time may be performed for 1 minute to 100 hours, and may be performed in a vacuum lower than atmospheric pressure, but is not limited thereto.

[0069]

[0070] The diffusion bonding method of the alloy according to the present invention may include a polishing step of preparing the surface of the alloy for diffusion bonding by removing at least a portion of the alloying region (c).

[0071]

[0072] The above (c) polishing step may be a step of removing at least a portion of an alloying region including impurities and / or secondary phases after the surface alloying step. In the above-described 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 cause deterioration of the physical properties of the alloy. The surface polishing may be performed so that a portion of the alloying region remains. This can suppress the formation of secondary phases at the interface of alloys for diffusion bonding when performing diffusion bonding and promote grain boundary movement.

[0073]

[0074] The above polishing thickness is not particularly limited as long as it can sufficiently remove impurities and / or secondary phases on the surface and near the surface after the surface alloying step. For example, the polishing thickness may be 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. In addition, the lower limit of the polishing thickness is not particularly limited, but may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more. The polishing method of the above polishing step is not particularly limited as long as it can remove a part of the alloyed area, and various known methods such as mechanical polishing or electrolytic polishing may be used.

[0075]

[0076] In one example, the thickness of the alloying region of the alloy for diffusion bonding according to the present invention is not particularly limited as long as it does not hinder the effect of suppressing the formation of a secondary phase described later, but may 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. If the thickness of the alloying region is excessively thick, the process cost for homogenizing the chemical composition at the interface of the diffusion bonding material and near the interface may excessively increase. The lower limit of the thickness of the alloying region is not particularly limited, but may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more.

[0077]

[0078] 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 diffusion bonding an alloy prepared through the method for preparing an alloy for diffusion bonding described above.

[0079]

[0080] FIG. 1 schematically illustrates a method for preparing an alloy for diffusion bonding and a diffusion bonding method of the present invention. Referring to FIG. 1, the diffusion bonding method according to the present invention may prepare an alloy by a method for preparing an alloy for diffusion bonding, including (a) a coating step of forming a precursor layer containing nickel (Ni) on the surface of a base material; (b) a surface alloying step of mixing constituent elements of the base material and the alloy precursor layer to form an alloying region; and (c) a polishing step of removing at least a portion of the alloying region to prepare a surface of an alloy for diffusion bonding, and may include (d) a diffusion bonding step of diffusion bonding the alloy for diffusion bonding.

[0081]

[0082] At this time, the diffusion bonding step may be a step of diffusion bonding the alloying regions of a plurality of diffusion bonding alloys to each other. The diffusion bonding alloy may include an alloying region exposed to the surface, and diffusion bonding may be performed in the alloying region exposed to the surface. For example, after preparing a plurality of diffusion bonding alloys, the alloying regions of the alloys may be arranged so as to be in contact with each other, and then diffusion bonding may be performed.

[0083]

[0084] The diffusion bonding conditions of the above diffusion bonding step are not particularly limited as long as the diffusion bonding alloy can be diffusion bonded. For example, it can be performed for 5 minutes to 20 hours at a temperature higher than room temperature and a pressure exceeding 0 MPa. At this time, the vacuum level within the diffusion bonding equipment is 10 -3 It may be less than Torr. However, the diffusion bonding conditions are not limited to the above bonding temperature, bonding pressure, bonding time, and vacuum degree.

[0085]

[0086] In addition, the method for diffusion bonding an alloy according to the present invention may include, if necessary, a step of post-heat treatment at a temperature range higher than room temperature for 1 to 100 hours after the diffusion bonding. In addition, after the post-heat treatment, the alloy may be cooled to 10 to 30°C through furnace cooling, air cooling, or quenching.

[0087]

[0088] The present invention also relates to a diffusion bonding material. The diffusion bonding material according to the present invention may be formed by diffusion bonding a plurality of diffusion bonding alloys prepared by the method for preparing a diffusion bonding alloy described above, and diffusion bonding the diffusion bonding materials.

[0089]

[0090] At this time, the diffusion bonding material may include a diffusion bonding material interface where the plurality of diffusion bonding alloys are diffusion bonded to each other and a grain boundary movement region disposed on the interface.

[0091]

[0092] Figure 2 schematically illustrates a cross-section of a plurality of diffusion bonding alloys (10). An alloying region (20) is locally formed on and near the surface of the diffusion bonding alloy (10). The chemical composition of the constituent elements in the matrix below the alloying region (20) is identical to the chemical composition of the constituent elements of the parent material.

[0093]

[0094] Figure 3 is a 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). Through diffusion bonding and post-heat treatment, atoms diffuse with each other, so that the chemical composition of the constituent elements at and near the diffusion bonding material interface (30) becomes homogeneous. In particular, the chemical composition of the constituent elements within the alloying region (20) becomes at the level of the base alloy, thereby satisfying the material description standard (e.g., ASTM B409) of the base alloy.

[0095]

[0096] In one embodiment of the present invention, the diffusion bonding material according to the present invention can satisfy the following relationship 2.

[0097]

[0098] [Relationship 2]

[0099] L2 / L1≥ 0.20

[0100]

[0101] In the above relational expression 2, L1 is the total length of the diffusion bonding material interface (30), and L2 is the length of the grain boundary movement region.

[0102]

[0103] The above ratio (L1 / L2) refers to the ratio of the length of the region across the diffusion bonding material interface where grain boundary movement occurs. The upper limit of the above ratio is not particularly limited, but may be, for example, 1.0 or less.

[0104]

[0105] The above ratio may refer to 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.

[0106]

[0107] In one example, the diffusion bonding material according to the present invention can satisfy the following relationship 3.

[0108]

[0109] [Relationship 3]

[0110] TS D / TS B ≥ 0.80

[0111]

[0112] In the above relational expression 3, TS D is the tensile strength of the diffusion bonding agent at room temperature and high temperature, and TS B is the tensile strength of the base material at room temperature and high temperature. In this specification, the base material means an alloy base material that has not undergone a preparatory step for manufacturing an alloy for diffusion bonding. The above relationship 3 means that the room temperature and high temperature tensile strength of the diffusion bonding agent is 80% or more of the room temperature and high temperature tensile strength of the alloy base material. The improvement in mechanical properties according to the present invention is due to the suppression of the formation of a secondary phase at the diffusion bonding agent interface.

[0113]

[0114] The diffusion bonding material according to the present invention can satisfy the following relationship 4.

[0115]

[0116] [Relationship 4]

[0117] EL D / EL B ≥ 0.60

[0118]

[0119] In the above relational expression 4, EL D is the elongation of the diffusion bonding agent at room temperature and high temperature, and EL Bis the elongation of the base material at room temperature and high temperature. The above relationship 4 means that the elongation of the diffusion bonding agent according to the present invention at room temperature and high temperature is 60% or more compared to the base material. The improvement in mechanical properties according to the present invention is due to the suppression of the formation of a secondary phase at the interface of the diffusion bonding agent, as described above.

[0120]

[0121] In this specification, room temperature may mean about 25°C, and high temperature may mean about 600°C. For example, when the diffusion bonding agent according to the present invention satisfies the above relationship 3, it may mean that the tensile strength of the diffusion bonding agent at room temperature is 80% or more of the tensile strength of the alloy base material at room temperature, and at the same time, it may mean that the tensile strength of the diffusion bonding agent at high temperature is 80% or more of the tensile strength of the alloy base material at high temperature.

[0122]

[0123] In addition, when the diffusion bonding agent according to the present invention satisfies the above relational expression 4, it may mean that the room temperature elongation of the diffusion bonding agent is 60% or more compared to the base material, and at the same time, it may mean that the high temperature elongation of the diffusion bonding agent is 60% or more compared to the base material.

[0124]

[0125] In addition, the present invention can provide a plate heat exchanger manufactured using a diffusion bonding method of the above alloy.

[0126]

[0127] The market for renewable energy and stable power generation systems has been steadily growing recently. The North American and European heat exchanger markets (2020-2025) are projected to reach $4.7 billion (CAGR of 3.4%) and $5.02 billion (CAGR of 3.2%), respectively. Considering the market trend toward improved energy efficiency, the plate heat exchanger market is also expected to grow positively. The present invention, conceived in response to this trend, is expected to have significant industrial impact, as it relates to manufacturing technologies for small nuclear reactor steam generators and heat exchangers for hydrogen stations. Furthermore, it is expected to revitalize the stagnant domestic manufacturing sector, strengthen international competitiveness, and contribute to product and technology exports.

[0128]

[0129] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are provided solely to facilitate a better understanding of the present invention, and the scope of the present invention is not limited by the following examples.

[0130]

[0131] [Example]

[0132] Preparation of alloys for diffusion bonding

[0133] Two plates of base alloy (Alloy 800H) were prepared to manufacture an alloy for diffusion bonding. The chemical compositions of the alloys used in the examples are shown in Table 1 below.

[0134]

[0135] NiCrAlTiCSiMnSPFeComposition (weight%)31.5219.710.520.580.080.320.730.0010.01745.6

[0136]

[0137] An example of the base alloy in the present invention may include, but is not limited to, Alloy 800H (UNS N08810). The base alloy may include nickel (Ni) 30.0 to 35.0 wt%; chromium (Cr) 19.0 to 23.0 wt%; aluminum (Al) 0.15 to 0.60 wt%; titanium (Ti) 0.15 to 0.60 wt%; carbon (C) 0.05 to 0.10 wt%; and the remainder being iron (Fe).

[0138]

[0139] In addition, the above-mentioned parent alloy may further include, as necessary, 0.75 wt% or less of copper (Cu), 1.0 wt% or less of silicon (Si), 1.5 wt% or less of manganese (Mn), and 0.015 wt% or less of sulfur (S), but is not limited thereto.

[0140]

[0141] Below, we will explain the role and effect of each element:

[0142] (1) Iron (Fe)

[0143] The iron above serves as a base metal. The iron content in the alloy includes at least 39.5 wt%. In nickel-based heat-resistant alloys, iron is used to replace expensive elements such as nickel or cobalt. Adding iron to nickel-based heat-resistant alloys can improve the material's workability.

[0144]

[0145] (2) Nickel (Ni)

[0146] 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 wt%. At this time, if the nickel content is less than 30.0 wt%, the stability, corrosion resistance, and strength of the structure may deteriorate at high temperatures.

[0147]

[0148] (3) Chromium (Cr)

[0149] The above chromium is an element for increasing high-temperature oxidation resistance, and the chromium content in the alloy may be 19.0 to 23.0 wt%. At this time, if the chromium content is less than 19.0 wt%, an oxide film may not be stably formed at high temperatures, and if the chromium content exceeds 23.0 wt%, a secondary phase may be formed due to heat aging.

[0150]

[0151] (4) Aluminum (Al)

[0152] The above aluminum is an element that increases high-temperature corrosion resistance and increases the strength of the material at high temperatures due to the precipitate strengthening effect. The aluminum content in the alloy may be 0.15 to 0.60 wt%. At this time, if the aluminum content is less than 0.15 wt%, high-temperature corrosion resistance and precipitate strengthening effects may not be obtained, and if it exceeds 0.60 wt%, secondary phases may be formed due to heat aging.

[0153]

[0154] (5) Titanium (Ti)

[0155] The titanium content above is an element for strengthening precipitates, and the titanium content in the alloy may be 0.15 to 0.60 wt%. If the titanium content is less than 0.15 wt%, creep strength and oxidation resistance may be reduced, and if it exceeds 0.60 wt%, a secondary phase may be formed due to heat aging.

[0156]

[0157] Meanwhile, the alloy for diffusion bonding according to the present invention may further contain, as necessary, 0.75 wt% or less of copper (Cu), 1.0 wt% or less of silicon (Si), 1.5 wt% or less of manganese (Mn), and 0.015 wt% or less of sulfur (S), but is not limited thereto. The above elements may be a type of impurity that is inevitably included during the production of a material, but when the above content range is satisfied, physical properties such as high-temperature strength can be improved.

[0158]

[0159] (a) Application stage

[0160] An alloy precursor layer containing nickel (Ni) was applied to the surface of the above two base alloys. The thickness of the applied alloy precursor layer is not particularly limited as long as it is to a degree necessary for the surface alloying step described later, but may 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 may be 1 μm or more, 2 μm or more, or 3 μm or more, but is not limited thereto.

[0161]

[0162] (b) Surface alloying step

[0163] Surface alloying was performed by heat-treating an alloy coated with an alloy precursor layer containing nickel. The heat treatment was performed at a temperature near (±150°C) the solution heat treatment temperature (minimum 1149°C), and the heat treatment was terminated after sufficient alloying had occurred. The heat treatment time is not particularly limited as long as the surface alloying can proceed sufficiently, but may be performed for, for example, 1 minute to 100 hours. After the heat treatment was completed, the alloyed alloy base material was cooled under conditions in which no surface oxidation occurred.

[0164]

[0165] (c) Polishing stage

[0166] The surface of the alloy precursor material having the above surface alloyed is mechanically polished in the depth direction to remove the surface. The mechanical polishing can be performed within the thickness range of the alloy precursor layer formed in the above-described coating step. The thickness of the surface removed through the mechanical polishing 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, but is not limited to, 1 μm or more, 2 μm or more, or 3 μm or more.

[0167]

[0168] Figure 4 is a SEM image of a cross-section of an alloy for diffusion bonding. Referring to Figure 4, after surface polishing, no Cr-rich carbides are observed in the t3 region. This is because the Cr-rich carbides in the t3 region have been incorporated into the matrix. Conversely, referring to Figure 4, precipitates that have not been incorporated into the matrix are observed in regions deeper than t3.

[0169]

[0170] Figures 5 to 8 are the results of analyzing the cross-section of the alloy for diffusion bonding using the EPMA method. Figure 5 shows the content of iron (Fe), Figure 6 shows the content of nickel (Ni), Figure 7 shows the content of chromium (Cr), and Figure 8 shows the content of titanium (Ti), respectively. Referring to Figures 5 and 7, it can be confirmed that the contents of iron and chromium in the alloy for diffusion bonding according to the present invention do not show a large deviation from the surface in the depth direction. In addition, referring to Figure 8, in the case of titanium, it can be confirmed that there is a region where the peak intensity is measured to be large, but the content does not show a tendency to constantly increase or decrease with depth.

[0171]

[0172] In contrast, referring to FIG. 6, nickel has a gradient toward the matrix from the surface of the diffusion bonding alloy of the present invention to a predetermined depth. Specifically, the nickel content decreases from the surface and reaches the level of the base material at a predetermined depth. The chemical composition of the alloy constituent elements other than nickel at and near the surface of the diffusion bonding alloy according to the present embodiment is somewhat reduced compared to the chemical composition of the constituent elements in the matrix.

[0173]

[0174] Diffusion bonding of alloys for diffusion bonding

[0175] The surface of the above diffusion bonding alloy was washed with ethanol, and two sheets of diffusion bonding alloy were placed facing each other and then diffusion bonded. Diffusion bonding was performed at a bonding temperature of 1150°C, a bonding pressure of 10 MPa, and a bonding temperature of 10 -5 It was performed for 1 hour at a vacuum of 10 Torr.

[0176]

[0177] Fig. 9 is an image of a cross-section of a diffusion bonding agent according to the present embodiment, taken using an optical microscope (OM). In Fig. 9, the arrow indicates the diffusion bonding agent interface. Region A of Fig. 9 represents a grain boundary migration region. Referring to region A of Fig. 9, it can be confirmed that grain boundary migration occurred across the diffusion bonding agent interface. On the other hand, region B can be confirmed that grain boundary migration did not occur across the diffusion bonding agent interface.

[0178]

[0179] [Comparative example]

[0180] 60 sheets of alloy (Alloy 800H) were diffusion bonded under conditions similar to those of the example (1150°C / 10 MPa / 1 hour) without performing steps (a) to (c) above.

[0181]

[0182] Exam example

[0183] Tensile tests were performed on the diffusion bonding materials manufactured in the Examples and Comparative Examples. Specifically, tensile test specimens were collected from the diffusion bonding materials manufactured in the Examples and Comparative Examples, and tensile tests were performed at room temperature (25°C) and 600°C according to ASTM E8 / E8M.

[0184]

[0185] Figures 10 to 12 are stress-strain curves at room temperature for the parent material, examples, and comparative examples, respectively.

[0186]

[0187] The tensile strength of the base material at room temperature is 547 ± 6 MPa, and the elongation is 50.2 ± 1.3%. The diffusion bonding material according to the example has a tensile strength of 518 ± 13 MPa at room temperature, and an elongation of 52.2 ± 5.1%. Meanwhile, the tensile strength of the comparative example at room temperature is 395 ± 49 MPa, and the elongation is 10.5 ± 4.4%.

[0188]

[0189] Through the above results, it can be confirmed that at room temperature, the diffusion bonding material of the example has a tensile strength of about 95% of that of the base material, while the comparative example has a tensile strength of about 72% of that of the base material. In addition, it can be confirmed that the elongations of the diffusion bonding material of the example and the comparative example at room temperature are about 103% and 21% of that of the base material, respectively.

[0190]

[0191] The tensile test results above demonstrate that the mechanical properties of the diffusion bonding material manufactured using the present invention are improved at room temperature compared to diffusion bonding materials manufactured using conventional techniques. Furthermore, the mechanical properties of the diffusion bonding material manufactured using the present invention were confirmed to be comparable to those of the base material at room temperature.

[0192]

[0193] Figures 13 to 15 are stress-strain curves at 600°C for the base material, examples, and comparative examples, respectively.

[0194]

[0195] The tensile strength of the base material at 600°C is 441 ± 4 MPa, and the elongation is 50.8 ± 1.0%. The tensile strength of the diffusion bonding material according to the embodiment of the present invention at 600°C is 421 ± 1 MPa, and the elongation is 67.8 ± 3.6%. Meanwhile, the tensile strength of the diffusion bonding material of the comparative example at 600°C is 220 ± 23 MPa, and the elongation is 3.7 ± 1.8%.

[0196]

[0197] Through the above results, it can be confirmed that the tensile strength of the diffusion bonding material of the example at 600℃ is about 95% of that of the base material, but the tensile strength of the comparative example is only about 49% of that of the base material. Meanwhile, it can be confirmed that the elongation of the diffusion bonding material of the example and the diffusion bonding material of the comparative example at 600℃ is about 133% and 7% of that of the base material, respectively.

[0198]

[0199] The above results confirm that the diffusion bonding agent of the present invention has mechanical properties that correspond to the mechanical properties of the base material at 600°C, not only at room temperature but also at a temperature of 600°C. In addition, it can be confirmed that the mechanical properties of the diffusion bonding agent produced using the present invention are improved at high temperatures compared to conventional technologies.

[0200]

[0201] The foregoing description of the present invention is provided for illustrative purposes only. Those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0202]

[0203] One of the many effects of the present invention is that it can minimize the formation of a secondary phase at or near the interface of the diffusion bonding agent.

[0204]

[0205] One of the many effects of the present invention is that it can form a grain boundary migration region across the diffusion bonding material interface.

[0206]

[0207] One of the many effects of the present invention is that it can provide a diffusion bonding method for a diffusion bonding agent and alloy having mechanical properties at the level of the parent material at room temperature and high temperature.

Claims

1. A method for preparing an alloy for diffusion bonding including a base and an alloying region having a different chemical composition from the base, (a) a coating step of forming an alloy precursor layer containing nickel (Ni) on the surface of a base material; (b) a surface alloying step of forming an alloying region by mixing the constituent elements of the above-mentioned parent material and alloy precursor layer; and (c) a polishing step of preparing an alloy surface for diffusion bonding by removing at least a portion of the alloyed region; A method for preparing an alloy for diffusion bonding, comprising:

2. In paragraph 1, A method for preparing an alloy for diffusion bonding, wherein at least a portion of the alloying region is exposed to the surface of the alloy for diffusion bonding.

3. In paragraph 1, A method for preparing an alloy for diffusion bonding satisfying the following relational expression 1: [Relationship 1] C m (s) ≠C m (O) In the above relation 1, C m (s) refers to the chemical composition of the constituent elements on the surface of the alloy for diffusion bonding, and C m (O) refers to the chemical composition of the constituent elements in the matrix of the alloy for diffusion bonding.

4. In paragraph 1, A method for preparing an alloy for diffusion bonding, wherein the coating thickness of the above alloy precursor layer is 10 mm or less.

5. In paragraph 1, A method for preparing an alloy for diffusion bonding, wherein the polishing step removes a portion of an alloying region containing impurities and / or secondary phases.

6. In paragraph 1, A method for preparing an alloy for diffusion bonding, further comprising a diffusion bonding step of diffusion bonding the above-mentioned alloy for diffusion bonding.

7. In paragraph 6, The above diffusion bonding step is a method for preparing a diffusion bonding alloy, which is a step of diffusion bonding alloying regions of a plurality of diffusion bonding alloys to each other.

8. In a diffusion bonding material in which a plurality of diffusion bonding alloys prepared by the method for preparing a diffusion bonding alloy of Article 6 are diffusion bonded, A diffusion bonding material comprising a diffusion bonding material interface in which the plurality of diffusion bonding alloys are diffusion bonded to each other and a grain boundary movement region disposed on the interface.

9. In Article 8 Diffusion bonding agent satisfying the following relationship 2: [Relationship 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 movement region located on the diffusion bonding material interface.

10. In paragraph 8, Diffusion bonding agent satisfying the following relational expression 3: [Relationship 3] TS D / TS B ≥ 0.80 In the above relational expression 3, TS D is the tensile strength of the diffusion bonding agent at room temperature and high temperature, and TS B is the tensile strength of the parent material at room temperature and high temperature.

11. In paragraph 8, Diffusion bonding agent satisfying the following relational expression 4: [Relationship 4] HE D / HE B ≥ 0.60 In the above relational expression 4, EL D is the elongation of the diffusion bonding agent at room temperature and high temperature, and EL B is the elongation of the parent material at room temperature and high temperature.

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