A cobalt-based brazing filler metal, a preparation method and application thereof

Abstract

The application belongs to the technical field of high-temperature alloy connection, and particularly discloses a novel cobalt-based filler metal for high-temperature dissimilar metal connection and a preparation method and application thereof. The cobalt-based filler metal is composed of Co 30-70%, Ni 14-27%, Cr 11-20%, Fe 3-6.5%, Mn 1-1.5%, Si 3-6%, B 2-4%, Sc 0.3-0.5%, Y 0.2-0.4% and inevitable impurities in the rest. The cobalt-based filler metal has a melting point of 950-1100 DEG C and is suitable for use in a high-temperature environment of 600 DEG C-800 DEG C. The application focuses on the smelting process and performance evaluation of the Co x NiCrFe(Si, B) cobalt-based filler metal. By adjusting the content of Co, the wettability of the filler metal is improved and the component segregation is reduced while the brazing strength of the filler metal is ensured, so that the process requirement of high-temperature dissimilar metal material brazing connection can be fully met.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy joining technology, specifically to a cobalt-based brazing filler metal for high-temperature alloy joining, its preparation method and application, which is suitable for laser brazing of high-temperature alloys. Background Technology

[0002] With the development of high thrust-to-weight ratio aero engines, some key engine components employ complex structures with titanium casings and hard alloys at local contact surfaces. This meets the demands of next-generation high thrust-to-weight ratio engines for novel lightweight, high-temperature resistant structural materials, as well as the requirements for high hardness, high strength, and high-temperature resistance at connection points. For the connection of complex and precise dual-alloy structures, brazing is currently the most common method.

[0003] The choice of brazing filler metal is crucial in the brazing process. During brazing, the filler metal wets the base metal and achieves interatomic bonding with it through capillary action. Cobalt-based brazing materials are generally composed of Co as the matrix, with alloying elements such as Ni, Cr, and W added, and B and Si as melting point reducing elements. Cobalt has a high melting point, and both Co-Cr and Co-Ni can form solid solutions, resulting in brazing materials with excellent overall mechanical properties. However, with the rapid development of high thrust-to-weight ratio engines in recent years, existing high-temperature brazing filler metals can no longer meet current requirements. Therefore, it is necessary to develop new high-temperature brazing filler metals with superior performance to solve the bonding problem between cemented carbide and titanium in high thrust-to-weight ratio engines. Summary of the Invention

[0004] The purpose of this invention is to provide a cobalt-based brazing filler metal for high-temperature alloy joining, its preparation method, and its application, in order to solve the aforementioned problems. Based on existing properties of cobalt-based brazing filler metals, this invention adjusts the alloying elements according to their properties and the influence of their interactions, resulting in a high-performance cobalt-based brazing filler metal with a suitable melting point. This filler metal possesses advantages such as high-temperature resistance, corrosion resistance, good wettability, and excellent mechanical properties, meeting the current requirements of high thrust-to-weight ratio engines for high-temperature brazing filler metals.

[0005] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a cobalt-based solder, which, by weight percentage (total 100wt%), comprises: Co 30~70%, Ni 14~27%, Cr 11~20%, Fe 3~6.5%, Mn 1~1.5%, Si 3~6%, B 2~4%, Sc 0.3~0.5%, Y 0.2~0.4%, with the balance being unavoidable impurities (small amounts of S and P).

[0007] The Co×NiCrFe(Si,B) cobalt-based solder of the present invention uses cobalt as the base material, and has a relatively high content of nickel and chromium, and contains an appropriate amount of iron and a small amount of boron, manganese and silicon. This invention relates to a brazing filler metal used at high temperatures. Chromium, an indispensable element in high-temperature alloys, improves the high-temperature performance and oxidation resistance of cobalt-based brazing filler metals. Nickel, a major austenite-forming element and also a forming element of the strengthening phase γ′, mainly segregates into the γ′ phase to stabilize it. The γ′ phase is the most important strengthening phase in high-temperature alloys, improving the strength of the brazing filler metal. Iron in the brazing filler metal strengthens the γ phase, playing a role in dispersion strengthening and precipitation strengthening. Boron causes grain boundary segregation, reduces grain boundary defects, increases grain boundary strength, significantly changes grain boundary shape, improves the plasticity of cobalt-based alloys, and improves the wettability and deoxidation properties of the brazing filler metal. The addition of silicon can lower the melting point of the brazing filler metal. The addition of rare earth elements yttrium and scandium significantly improves the high-temperature strength, structural stability, weldability, and corrosion resistance of the brazing filler metal, and reduces the embrittlement phenomenon that easily occurs during long-term operation at high temperatures. The cobalt-based brazing filler metal of this invention can be used in high-temperature, high-pressure, and corrosion-resistant environments after welding.

[0008] In one embodiment of the present invention, the solder composition, by weight percentage, is: Co 35%, Ni 27%, Cr 20%, Fe 6.5%, Mn 1.5%, Si 6%, B 3%, Sc 0.5%, Y 0.4%, with the balance being unavoidable impurities.

[0009] In one embodiment of the present invention, the solder composition, by weight percentage, is: Co 50%, Ni 20%, Cr 15%, Fe 6%, Mn 1%, Si 5%, B 2%, Sc 0.5%, Y 0.4%, with the balance being unavoidable impurities.

[0010] In one embodiment of the present invention, the solder composition, by weight percentage, is: Co 65%, Ni 14%, Cr 11%, Fe 3%, Mn 1%, Si 3%, B 2%, Sc 0.5%, Y 0.4%, with the balance being unavoidable impurities.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned cobalt-based solder, comprising the following steps:

[0012] (1) Batching: Weigh the raw materials to be melted according to the weight percentage of the brazing filler metal;

[0013] (2) Melting: The weighed raw materials are melted at high temperature using a high-vacuum non-consumable arc melting furnace. After melting, the materials are cooled to room temperature and samples are taken to obtain the alloy ingot of the brazing filler metal.

[0014] (3) Cutting: Cut the alloy master ingot into the required shape and size by wire cutting.

[0015] Furthermore, in step (1), all the raw materials of each component are particles with a purity greater than 99.99%.

[0016] Furthermore, in step (2), the non-consumable arc furnace is evacuated before melting to below -4Pa, and then filled with argon gas of 99.99% purity until the pressure is -0.05MPa.

[0017] Further, in step (2), the high-temperature smelting process is as follows: hold at 1500~1600℃ for 3 minutes, hold at 1400~1500℃ for 3 minutes, hold at 1300~1400℃ for 3 minutes, and turn on the electromagnetic stirrer to stir during the process. The current is controlled at 400~600 A, and the casting is carried out at 1400℃.

[0018] Thirdly, the present invention provides the application of the above-mentioned cobalt-based brazing filler metal, which can be used for brazing connections of dissimilar high-temperature alloys such as cemented carbide and titanium or cemented carbide and steel, with a brazing temperature (melting point) of 950°C to 1100°C.

[0019] Furthermore, the brazing connection method is as follows: the brazing filler metal is placed between two base materials to be brazed, and after being fixed with a clamp, the sample is laser brazed with a laser power of 1400 W, a laser scanning speed of 0.012 m / s, a defocusing amount of -0.8 mm, and argon (99.99%) as the protective gas with a gas flow rate of 23 L / min.

[0020] The present invention has the following beneficial effects:

[0021] 1. This invention ensures the brazing strength and hardness of the brazing filler metal while improving its wettability and reducing component segregation, thus fully meeting the process requirements for brazing connections of dissimilar metal materials at high temperatures.

[0022] 2. The brazing connection using the filler metal of this invention has good compressive strength and corrosion resistance, and has a better high-temperature service temperature (600℃~800℃). It can effectively solve the connection and repair problem of high-temperature alloy parts in harsh environments and has important application value. Attached Figure Description

[0023] Figure 1 : Appearance images of the Co×NiCrFe(Si,B) cobalt-based ingots prepared in Examples 1-3. In the figures: (a) front of A1 solder; (b) front of A2 solder; (c) front of A3 solder; (d) back of A1 solder; (e) back of A2 solder; (f) back of A3 solder.

[0024] Figure 2XRD patterns of Co×NiCrFe(Si,B) cobalt-based solders prepared in Examples 1-3.

[0025] Figure 3 DSC curves of Co×NiCrFe(Si,B) cobalt-based solders prepared in Examples 1-3.

[0026] Figure 4 The spread area of ​​the Co×NiCrFe(Si,B) cobalt-based solder prepared in Examples 1-3 on the base materials (titanium and cemented carbide).

[0027] Figure 5 Microhardness of the Co×NiCrFe(Si,B) cobalt-based solders prepared in Examples 1-3. In the figure, (a) cobalt-based solders of group A1; (b) cobalt-based solders of group A2; (c) cobalt-based solders of group A3. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific examples.

[0029] Example 1

[0030] This embodiment provides a cobalt-based solder A1, whose composition, by weight percentage, is: Co 35%, Ni 27%, Cr 20%, Fe 6.5%, Mn 1.5%, Si 6%, B 3%, Sc 0.5%, Y 0.4%, and trace amounts of S and P impurities, with the sum of the weight percentages of all components being 100 wt%. This cobalt-based solder is prepared by the following method:

[0031] (1) Batching: According to the weight percentage of the brazing filler metal, use a high-precision electronic balance to accurately weigh each component raw material to be melted, with the error controlled within ±5mg to ensure the accuracy of the test. The total weight of the raw materials is 200g, and each component raw material is a particle with a purity greater than 99.99%.

[0032] (2) Melting: The high vacuum non-consumable arc melting furnace (model DHL500) is evacuated to below -4Pa, and then filled with 99.99% pure argon gas until the pressure is -0.05MPa. The weighed raw materials are placed in the melting furnace and melted according to the following process: 1500~1600℃ for 3min, 1400~1500℃ for 3min, 1300~1400℃ for 3min, and the electromagnetic stirrer is turned on for stirring during the process. The current is controlled at 400-600 A. The casting is done at 1400℃. After the melting is completed, the sample is cooled to room temperature and a sample is taken to obtain the alloy ingot of the brazing filler metal.

[0033] (3) Cutting: Cut the alloy master ingot into the required brazing filler blocks by wire cutting.

[0034] Example 2

[0035] This embodiment provides a cobalt-based solder A2, which, by weight percentage, comprises Co 50%, Ni 20%, Cr 15%, Fe 6%, Mn 1%, Si 5%, B 2%, Sc 0.5%, Y 0.4%, and trace amounts of S and P impurities, with the sum of the weight percentages of all components being 100 wt%. The preparation method of this cobalt-based solder is the same as in Example 1, except for the weighing of the raw materials.

[0036] Example 3

[0037] This embodiment provides a cobalt-based solder A3, whose composition by weight percentage is: Co 65%, Ni 14%, Cr 11%, Fe 3%, Mn 1%, Si 3%, B 2%, Sc 0.5%, Y 0.4%, and trace amounts of S and P impurities, with the sum of the weight percentages of all components being 100 wt%. The preparation method of this cobalt-based solder is the same as in Example 1, except for the weighing of the raw materials.

[0038] The solders prepared in Examples 1-3 were characterized and their performance was tested, as follows:

[0039] 1. Metallographic observation of the brazing filler metal block was performed, and the results are as follows: Figure 1 As shown, the brazing filler metals of Examples 1-3 are dense in metallographically and have no obvious defects. Moreover, compared with Examples 1 and 2, the surface morphology of the cobalt-based ingot of Example 3 is more uniform.

[0040] 2. XRD tests were performed on the brazing filler metal block, and the results were as follows: Figure 2 As shown, the Co×NiCrFe(Si,B) cobalt-based solders in Examples 1-3 mainly contain Co, Cr, FeNi3 and Cr2B phases.

[0041] 3. DSC curve testing was performed on the brazing filler metal block, and the results are as follows: Figure 3 As shown, the melting points of the brazing filler metal blocks are A1 < A2 < A3; the melting range of the cobalt-based brazing filler metal is 60.6℃ when the Co content is 35 wt.%; when the Co content increases to 50 wt.%, the melting range of the cobalt-based brazing filler metal is 102.8℃; when the Co content increases to 65 wt.%, the melting range of the cobalt-based brazing filler metal shrinks to 80.2℃. The brazing filler metals in Examples 1-3 all have relatively small melting ranges. The reduction in the melting range can improve the fluidity of the cobalt-based brazing filler metal during brazing and prevent component segregation.

[0042] 4. A wettability test was conducted on the brazing filler metal block, and the results are as follows: Figure 4 As shown: In Example 1, the spread area of ​​the brazing filler metal on the cemented carbide was 76.38 mm². 2 The titanium spreading area is 70.32 mm².2 Example 2: The brazing filler metal spread over the cemented carbide area was 91.86 mm². 2 The titanium spreading area is 82.28 mm². 2 Example 3: The brazing filler metal spread over the cemented carbide area was 100.58 mm². 2 The titanium spreading area is 83.71 mm². 2 All three groups of solders exhibited good wettability, with Example 3 showing the best wetting effect.

[0043] 5. Microhardness test was performed on the brazing filler metal block, and the results are as follows: Figure 5 As shown, the microhardness was 273.53 HV when the Co content was 35 wt.%; when the Co content increased to 50 wt.%, the microhardness increased to 284.43 HV; however, when the Co content continued to increase to 65 wt.%, the microhardness decreased to 229.03 HV. All three groups of solders exhibited good hardness, with Example 2 showing the highest hardness.

[0044] Application Example 1

[0045] Brazing of dissimilar metals was performed using the brazing filler block A1 prepared in Example 1. The base materials to be brazed were cemented carbide (WC-20Co) and titanium (TA2). The specific brazing method is as follows:

[0046] Before welding, the surfaces of the cemented carbide (WC-20Co) and titanium (TA2) samples were polished with 800-grit sandpaper and ultrasonically cleaned in acetone for 15 minutes to remove oil stains from the sample surfaces. Then, the cut brazing filler metal blocks were placed between the base materials to be welded and fixed with a clamp. Nicorobraz White Stop Off Type II solder resist alumina powder was applied to the outer surface of the samples to prevent solder loss during brazing. The samples were then laser brazed with a laser power of 1400 W, a laser scanning speed of 0.012 m / s, a defocusing amount of -0.8 mm, and argon (99.99%) as the shielding gas with a flow rate of 23 L / min.

[0047] Application Example 2

[0048] Brazing between dissimilar metals was performed using the brazing filler block A2 prepared in Example 2. The base materials to be brazed were cemented carbide (WC-20Co) and titanium (TA2). The specific brazing method was the same as in Application Example 1.

[0049] Application Example 3

[0050] Brazing between dissimilar metals was performed using the brazing filler block A3 prepared in Example 3. The base materials to be brazed were cemented carbide (WC-20Co) and titanium (TA2). The specific brazing method was the same as in Application Example 1.

[0051] In Application Examples 1-3, the brazing blocks can achieve brazing of dissimilar metals. Among them, Application Example 3 has the best brazing effect. The wettability of the brazing block is A3 > A2 > A1.

[0052] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A cobalt-based solder, characterized in that, The brazing filler metal is composed of the following components by weight percentage: Co 50%, Ni 20-27%, Cr 11-15%, Fe 3-6.5%, Mn 1-1.5%, Si 3-5%, B 2-4%, Sc 0.3-0.5%, Y 0.2-0.4%, with the balance being unavoidable impurities. The cobalt-based brazing filler metal mainly contains Co, Cr, FeNi3, and Cr2B phases.

2. The cobalt-based solder according to claim 1, characterized in that, The solder composition by weight percentage is: Co 50%, Ni 20%, Cr 15%, Fe 6%, Mn 1%, Si 5%, B 2%, Sc 0.5%, Y 0.4%, with the balance being unavoidable impurities.

3. The method for preparing the cobalt-based solder according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Batching: Weigh the raw materials to be melted according to the weight percentage of the brazing filler metal; (2) Melting: The weighed raw materials are melted at high temperature using a high-vacuum non-consumable arc melting furnace. After melting, the materials are cooled to room temperature and samples are taken to obtain the alloy ingot of the brazing filler metal. (3) Cutting: Cut the alloy master ingot into the required shape and size by wire cutting.

4. The method for preparing cobalt-based solder according to claim 3, characterized in that, In step (1), all the raw materials are particles with a purity greater than 99.99%.

5. The method for preparing cobalt-based solder according to claim 3, characterized in that, In step (2), the non-consumable arc furnace is evacuated before melting to below -4Pa, and then filled with argon gas of 99.99% purity until the pressure is -0.05MPa.

6. The method for preparing cobalt-based solder according to claim 5, characterized in that, In step (2), the high-temperature smelting process is as follows: hold at 1500~1600℃ for 3 minutes, hold at 1400~1500℃ for 3 minutes, hold at 1300~1400℃ for 3 minutes, turn on the electromagnetic stirrer to stir during the process, control the current at 400~600 A, and cast at 1400℃.

7. The application of the cobalt-based solder according to any one of claims 1-2, characterized in that, This brazing filler metal is used for brazing dissimilar high-temperature alloys such as cemented carbide to titanium or cemented carbide to steel, with a brazing temperature of 950℃~1100℃.

8. The application of the cobalt-based solder according to claim 7, characterized in that, The brazing connection method is as follows: place the brazing filler metal between two base materials to be brazed, fix it with a clamp, and then perform laser brazing on the sample. The laser power is 1400 W, the laser scanning speed is 0.012 m / s, the defocusing amount is -0.8 mm, the protective gas is argon, and the gas flow rate is 23 L / min.

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