A method for metallizing high-density graphite surface

Abstract

The present invention relates to the field of graphite surface metallization, and discloses a high-density graphite surface metallization method, in which a layer of metallization paste coating containing an active phase of an iron-based kovar alloy with a low thermal expansion coefficient and a ductile molybdenum metal phase is coated on a high-density graphite substrate whose surface has been pretreated, and the coating is prepared through process steps such as drying and vacuum firing. The active phase of the iron-based kovar alloy and the high-density graphite substrate are not only reactive but also have matching thermal expansion coefficients, forming a firm metal layer; the thermal matching problem between graphite and welding metal is improved by the ductile metal inert phase. The present invention has good metallization effect, the metallization layer is uniform, dense and firm, and has excellent thermal stability and bonding strength, providing more possibilities for the application of graphite materials.

Description

Technical Field

[0001] The invention relates to the field of graphite surface metallization, in particular to a method for high-density graphite surface metallization. Background Art

[0002] In recent years, graphite materials have shown broad application prospects in the fields of nuclear industry, electronics, aviation, etc. Graphite has a high melting point, low density, good electrical conductivity and thermal conductivity. However, compared with metal materials, its thermal expansion coefficient is relatively low, making it difficult to form a stable metallization layer with general metals, and even more difficult to directly weld with metals with large expansion coefficients.

[0003] In the prior art research, "Microstructure Analysis of Titanium Metallization on Graphite Surface" (Journal of Welding, 2005, (12): 89-92) reported that Ti would react with graphite at the interface to form titanium carbide, but due to the large difference in thermal expansion coefficient, thermal stress would be generated, resulting in cracks between titanium carbide and Ti.

[0004] "Interface Structure Analysis and Properties of Graphite / Ni-Based Metal Brazing Coating" (Journal of the China Welding Association, 2017, 38(02):120-124.) reported that due to the inevitable presence of pores in graphite itself, the diffusion speed of elements in the solder in the graphite layer is different, and the generated carbides will destroy the original dense layered structure of graphite. Therefore, an unevenly distributed and discontinuous island structure will be formed on the interface.

[0005] At the same time, publication number CN 109913696 A discloses a method for graphite surface metallization, wherein the graphite surface metallization layer is mainly composed of the following elements and mass percentages: V 0.25-7%, Cu 0-30%, Ga 0-0.5%, Ce 0-0.5%, and the balance is Sn and inevitable impurities. The process is: the above mixture is mixed evenly with a binder, coated on the graphite surface, the coating layer is scraped flat by a scraper and dried to obtain a graphite pretreatment part, the graphite pretreatment part is placed in a vacuum brazing furnace, heat-treated at 800°C for 30 minutes by a brazing process, and then cooled with the furnace to obtain surface metallized graphite. Patent 2 (CN 109023262A) invented the graphite metallization process and welding method: first use Cr target material to prime the surface of the graphite substrate, then use Ni target material to sputter, the thickness of Cr film and Ni film is controlled by the operation time to ensure a firm bond with the substrate and connection with other metals, using silver-copper solder.

[0006] However, the above-mentioned prior art still has the problem of thermal expansion matching between the graphite substrate and the metal layer and the welding metal. Therefore, the present invention proposes a method for high-density graphite surface metallization. Summary of the invention

[0007] The purpose of the present invention is to provide a method for high-density graphite surface metallization to solve the problem of thermal matching between graphite and welding metal in view of the shortcomings of the prior art.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions: A high-density graphite surface metallization method, specifically comprising the following steps:

[0009] Step 1, performing surface pretreatment on a high-density graphite substrate;

[0010] Step 2, preparing a metal powder batch material for a metallized coating;

[0011] Step 3, preparing an organic plasticizer;

[0012] Step 4, mixing the metal powder batch obtained in step 2 and step 3 with an organic plasticizer at a mass ratio of 2:1 to 4:1 to prepare a metallization paste;

[0013] Step 5, using screen printing to apply the metallization paste obtained in step 3 on the surface of the graphite substrate, the coated sample is allowed to stand at room temperature for 15 minutes, and then placed in an oven at 80° C. for 40 minutes;

[0014] Step 6, placing the sample prepared in step 4 in a vacuum furnace for heat treatment to obtain surface metallized graphite;

[0015] The high-density graphite matrix has a density greater than 1.8 g / cm 3 The metallization paste contains a low thermal expansion coefficient Kovar alloy active phase and a ductile metal phase.

[0016] Furthermore: the mass percentage composition of the low thermal expansion coefficient Kovar alloy active phase in the metallized paste coating is C 0-0.05%, Mn 0-0.5%, Si 0-0.3%, Ni 32.1-33.6%, Co 14.0-15.2%, and the balance is Fe.

[0017] Furthermore, the ductile metal phase in the metallized paste coating is metal molybdenum powder;

[0018] Further: In the step 1, the surface pretreatment method of the high-density graphite substrate is: grinding the graphite substrate surface roughness by a polishing machine to 0.8-3.2, placing it in an acetone solution for ultrasonic cleaning for 15 minutes, taking it out, rinsing it with deionized water, and then placing it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, taking it out and drying it for standby use.

[0019] Furthermore, the process flow of preparing the metal powder batch material of the metallized coating in step 2 is as follows: the mass ratio of the active phase of the low thermal expansion coefficient Kovar alloy to the ductile metal phase is 9 / 1 to 3 / 7; the batch powder is placed in a ceramic ball mill, and then corundum balls and ethanol are added according to the ratio of material: ball: anhydrous ethanol = 1:2:0.8, and ground for 4 to 6 hours.

[0020] Further: in step 3, the mass percentage composition of the organic plasticizer is 40-44% butyl acetate, 50-54% terpineol, 2-3% ethyl cellulose, 1%-2% acrylic resin, 2%-3% castor oil; 1%-2% acrylic resin, and these components will form a plasticizer with good adhesion and fluidity after mixing.

[0021] Further: in step 6, the vacuum degree of the vacuum furnace is 0.01-1 Pa, the sintering temperature range is 1450-1480° C., the holding time is 50-70 min, and the heating rate is 5-10° C. / min.

[0022] According to the above scheme,

[0023] Compared with the prior art, the beneficial effects are as follows:

[0024] The graphite surface metallization layer obtained by the method of the present invention is uniform and dense, and has excellent thermal stability and bonding strength, providing a good technical basis for the application of graphite material metallization coating or metal joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 .SEM photo of the cross section of graphite metallization layer;

[0026] Figure 2 .SEM photo of the cross section of graphite copper welding. DETAILED DESCRIPTION

[0027] The invention will be further described in detail below with reference to the accompanying drawings and through specific embodiments. The following embodiments are merely illustrative and are not intended to limit the scope of protection of the present invention.

[0028] Example 1

[0029] A high-density graphite surface metallization method has the following specific steps:

[0030] (1) Preparation of graphite matrix: The block graphite sample was polished with a polishing machine to a surface roughness range of 3.2 to 0.8, then ultrasonically cleaned in an acetone solution for 15 min, taken out, rinsed with deionized water, ultrasonically cleaned in anhydrous ethanol for 15 min, and dried in an oven at 80°C.

[0031] (2) Preparation of graphite surface metallization coating batch material: metal powder C 0.03g, Mn 0.5g, Si 0.3g, Ni 33g, Co 14g, Fe 52.17g were weighed according to weight percentage to prepare Kovar alloy 4J33 raw material, which was placed in a ball mill and ball milled for 5 hours according to the ratio of raw material, alcohol and corundum grinding ball of 1:0.8:2, and then taken out and dried at 80°C. Kovar alloy 4J33 phase and molybdenum (Mo) powder were weighed in a mass ratio of 6 / 4, a total of 10g, and mixed and ball milled in a ball mill for 5 hours to obtain the graphite surface metallization coating metal powder batch material;

[0032] (3) preparing an organic plasticizer: preparing an organic plasticizer composed of 42% butyl acetate, 50% terpineol, 3% ethyl cellulose, 3% castor oil, and 3% acrylic resin by mass percentage;

[0033] (4) Preparation of metallization paste: Mix metal powder batch material and organic plasticizer in a mass ratio of 3 / 1 to prepare metallization paste, stir thoroughly, and ball mill for 4 to 6 hours;.

[0034] (5) The prepared graphite surface metallization coating paste was applied to the cleaned graphite surface by screen printing technology (200 mesh sieve, scraper angle of 45-60°), left to stand at room temperature for 15 min, then placed in an oven at 80°C for 40 min, heated in a vacuum tube furnace at a heating rate of 10°C / min, sintered at 1450°C, and sintered for 60 min to obtain a surface metallized graphite sample (see the attached figure for the cross-sectional morphology of the metallized layer). Figure 1 ). The surface metallized graphite sample was welded to copper using AgCu28 solder, and the shear strength could reach 51MPa.

[0035] Embodiment 2:

[0036] A high-density graphite surface metallization method has the following specific steps:

[0037] The difference from Example 1 is that:

[0038] Preparation of graphite surface metallization coating paste, in which Kovar alloy 4J33 phase and molybdenum (Mo) powder are weighed in a mass ratio of 5 / 5, and a total of 10g is taken.

[0039] The surface metallized graphite sample was welded to copper using AgCu28 solder, and the shear strength reached 56MPa (see the attached figure for the weld fracture morphology). Figure 2 ).

[0040] The technical solution of the present invention is summarized as follows: a method for metallizing a high-density graphite surface, wherein the density of the pretreated surface is greater than 1.8 g / cm 3A metallized paste coating containing an active phase of an iron-based Kovar alloy with a low thermal expansion coefficient and a ductile molybdenum metal phase is coated on a high-density graphite substrate, and the coating is prepared through drying and vacuum firing.

[0041] The bonding strength is generated by the high-temperature reaction of the active phase of the iron-based Kovar alloy with the graphite matrix, which has good thermal matching and wettability with the graphite matrix; the thermal matching problem of the graphite metallization coating is improved by the ductile metal phase.

[0042] The active phase of the low thermal expansion coefficient Kovar alloy and the ductile metal inert phase are Kovar alloy-like 4J33 phase and molybdenum phase, respectively.

[0043] The graphite surface metallization layer obtained by the method of the present invention is uniform and dense, and has excellent thermal stability and bonding strength, providing a good technical basis for the application of graphite material metallization coating or metal joints.

[0044] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A high-density graphite surface metallization method, characterized in that; Specifically, it includes the following steps: step 1, surface pretreatment of high-density graphite substrate; step 2, preparing metal powder batch material of metallized coating; specifically, preparing the batch material according to the mass ratio of low thermal expansion coefficient Kovar alloy active phase to ductile metal phase: 9 / 1 to 3 / 7; step 3, preparing organic plasticizer; step 4, mixing the metal powder batch material obtained in step 2 and step 3 with the organic plasticizer in the mass ratio of 2:1 to 4:1 to prepare metallized paste; step 5, using screen printing to apply the metallized paste obtained in step 4 on the surface of graphite substrate, and the coated sample is allowed to stand at room temperature for 15 minutes, and then placed in an oven at 80°C for 40 minutes; step 6, placing the sample prepared in step 5 in a vacuum furnace for heat treatment to obtain surface metallized graphite; the density of the high-density graphite substrate is greater than 1.8g / cm3, and the metallized paste contains low thermal expansion coefficient Kovar alloy active phase and ductile metal phase; the mass percentage composition of the low thermal expansion coefficient Kovar alloy active phase in the metallized paste coating is C 0~0.05%, Mn 0~0.5%, Si 0~0.3%, Ni32.1~33.6%, Co 14.0~15.2%, and the balance is Fe; the ductile metal phase in the metallized paste coating is metal molybdenum powder, and the vacuum furnace sintering temperature range is 1450~1480℃.

2. A high-density graphite surface metallization method according to claim 1, characterized in that: In step 1, the surface pretreatment method of the high-density graphite substrate is: grinding the graphite substrate surface roughness by a polishing machine to 0.8-3.2, placing it in an acetone solution for ultrasonic cleaning for 15 minutes, taking it out, rinsing it with deionized water, and then placing it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, taking it out and drying it for standby use.

3. A high-density graphite surface metallization method according to claim 1, characterized in that: The process flow of preparing the metal powder batch material of the metallized coating in step 2 is as follows: placing the batch powder in a ceramic ball mill, then adding corundum balls and ethanol according to the ratio of material: ball: anhydrous ethanol = 1:2:0.8, and grinding for 4 to 6 hours.

4. A high-density graphite surface metallization method according to claim 1, characterized in that: In step 3, the mass percentage composition of the organic plasticizer is 40-44% butyl acetate, 50-54% terpineol, 2-3% ethyl cellulose, 1%-2% acrylic resin, 2%-3% castor oil, and 1%-2% acrylic resin.

5. A high-density graphite surface metallization method according to claim 1, characterized in that: In step 6, the vacuum degree of the vacuum furnace is 0.01-1 Pa, the insulation time is 50-70 min, and the heating rate is 5-10° C. / min.

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