A process for connecting ceramic particles to metals through induced spark discharge / resistance brazing

Abstract

A process for induced spark discharge / resistance brazing of ceramic particles to metals uses a special bimetallic sheet as an induced discharge layer. The sheet is fixed above a metal substrate with a certain gap. A flexible powder mass of a brazing material and an adhesive is evenly spread onto the sheet, and ceramic particles are placed on the surface of or embedded in the brazing material as needed. The sheet is connected to the positive pole of a pulse power supply, and the metal substrate is connected to the negative pole. After power is applied, relevant process parameters are adjusted to apply pressure to the ceramic particles, reducing the gap between the sheet and the metal substrate to a point where spark discharge occurs, achieving a connection between the sheet and the metal substrate. Continuous pulse discharge is then used to melt the brazing material using the resistance heat generated at the junction of the sheet and the metal substrate, thus achieving a connection between the ceramic particles and the metal substrate. This invention effectively solves the problem of particle shedding caused by particles protruding from the coating in the prior art.

Description

Technical Field

[0001] The invention relates to an induced spark discharge / resistance brazing connection process for ceramic particles and metals, belonging to the technical field of particle protrusion coating application. Background Art

[0002] Due to the excellent physical and chemical properties of ceramic particles, particle-reinforced metal matrices have been used in a variety of engineering components in recent years. Currently, particle-reinforced coatings can be produced using a variety of methods, including electrodeposition, vacuum brazing, laser cladding, and electrospark deposition. Among these methods, electrodeposition is one of the most common techniques due to its good controllability and stress-free concentration. However, coatings prepared by electrodeposition exhibit mechanical bonding between the abrasive particles and the coating matrix, as well as between the coating matrix and the substrate, which can lead to particle shedding during practical applications. Although vacuum brazing can improve the bonding strength at the particle / coating and coating / substrate interfaces, its application is limited by its demanding working environment, susceptibility to volatile elements, and high equipment costs. Laser cladding can bury the entire abrasive particle in the coating, but the coatings produced by this method have a low particle density, and the particles tend to float to the surface. In addition, as a fusion welding method, laser cladding also causes significant thermal damage to abrasives (commonly used materials such as diamond and cubic boron nitride) at high temperatures, resulting in significant loss of the abrasive's mechanical properties (strength and wear resistance), which in turn prevents the coating from fully realizing its machining performance advantages. Previously, a new method for planting ceramic abrasive particles on high-temperature alloys using electric spark discharge, known as the electrospark particle planting (EPP) process, has been proposed. This process has great potential for preparing abrasive coatings with protruding particles, but it cannot achieve a connection between non-conductive ceramic particles and the metal substrate. Furthermore, spark discharges are generated at the top of the particles during this process, causing damage to the top of the particles, thereby reducing the excellent cutting performance of the ceramic particles.

[0003] In summary, based on the problems existing in the above production methods, there is an urgent need to study a particle protrusion coating preparation process with the advantages of simple operation and economy, so as to achieve efficient preparation of particle protrusion coatings, and at the same time provide technical support for the targeted repair of local damage to the coating (such as particle shedding, etc.). Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of particles protruding from the coating and falling off in the prior art, and to propose an induced spark discharge / resistance brazing connection process for ceramic particles and metals.

[0005] The technical solution implemented by the present invention is as follows: a process for connecting ceramic particles to metal by induced spark discharge / resistance brazing, comprising polishing a metal substrate with sandpaper and ultrasonically cleaning the polished metal substrate with anhydrous ethanol or acetone; the specific steps are as follows:

[0006] (1) Prepare a special bimetallic sheet, which is made by butt-welding two metal sheets (thickness 50-100 μm) of different materials, equal width and thickness, and the same cross-sectional area and cutting them into the required shape; the two sheets are made of metal materials with good electrical conductivity and a resistivity difference of 5-20 times; the melting point of the end of the special bimetallic sheet with higher resistivity should be greater than 600°C, and the melting point must be higher than the melting point of the solder used and lower than the melting point of the ceramic particles;

[0007] (2) Keep the special bimetallic sheet under tension and fix it above the surface area of ​​the metal substrate to be implanted with an insulating pad, so that a gap of 1-5 mm is maintained between the special bimetallic sheet and the metal substrate;

[0008] (3) Spread the flexible powder mass formed by mixing solder powder and adhesive onto the special bimetallic sheet, and control the solder thickness between 0.1-0.4mm;

[0009] (4) Select ceramic particles with a particle size of 10 to 150 meshes, and spread the ceramic particles on the surface of the solder at one end of the special bimetallic sheet with high resistivity or embed them into the solder as required;

[0010] (5) Connect the end of the special bimetallic sheet with low resistivity to the positive electrode of the pulse power supply, connect the metal substrate to the negative electrode of the pulse power supply, turn on the power supply and adjust the pulse power supply parameters; fill the space between the special bimetallic sheet and the metal substrate with protective gas;

[0011] (6) Use a pressing block to apply pressure to the ceramic particles above the special bimetallic sheet, so that the gap between the special bimetallic sheet and the metal substrate is reduced to generate spark discharge, and then a molten zone is generated, completing the connection between the special bimetallic sheet and the metal substrate; maintain pressure and continue pulse discharge, so that the resistance heat at the connection between the special bimetallic sheet and the metal substrate increases, causing the brazing material to melt and accumulate heat to form a molten pool;

[0012] (7) Turn off the power supply and allow to cool naturally to complete the connection between the ceramic particles and the metal matrix.

[0013] The pulse discharge has a discharge voltage of 0-200V, a capacitance of 350-1000μF, a discharge frequency of 0-1000Hz, and a pulse width of 0-100%.

[0014] The pressing block should be made of insulating material with a smooth bottom and a certain hardness, and the pressure should be controlled at 10-100N; the melting point of the pressing block should be higher than 1500°C to avoid deformation or melting of the pressing block in a high temperature environment.

[0015] The melting point of the solder should be controlled at 400° C.-1200° C. to achieve better connection between the particles and the metal matrix and avoid excessive loss of the solder at high temperatures.

[0016] The horizontal distance between the ceramic particle placement location and the connection location of the special bimetallic sheet should be maintained at 0.3-2mm to ensure the highest resistance heat generation at the particle placement location. The ceramic particles can be pressed into the brazing material layer to achieve fixed position of the ceramic particles.

[0017] The protective gas is pure argon, and the protective gas flow rate is 15 to 30 L / min.

[0018] The induced spark discharge / resistance brazing connection process of ceramic particles and metals of the present invention has the following beneficial effects compared with the prior art:

[0019] The process of the present invention adopts a local heating method to achieve the brazing connection between the ceramic particles and the metal matrix, eliminating the tedious steps of heating the entire furnace in traditional brazing. In addition, since pressure is applied during the melting of the brazing material, the aggregation behavior of particles floating up or sinking due to density differences in the traditional brazing process is avoided.

[0020] The process of the present invention has a simple circuit. By controlling the circuit resistance, it can accurately ensure that only the solder around the ceramic particles melts, which can achieve personalized customization of the distribution morphology of ceramic particles and provide technical support for the targeted repair of local damage to the coating (such as ceramic particle shedding).

[0021] Compared with the electrospark particle planting process, the process of the present invention retains the integrity of the top of the ceramic particles when connecting the ceramic particles to the matrix, and also solves the problem that the electrospark ceramic particle planting process can only connect conductive ceramic particles to the metal matrix.

[0022] The continuous pulse current in the process of the present invention can effectively promote the infiltration of the solder and enhance the bonding force between the particles and the matrix. The present invention has the advantages of being economical and efficient, saving energy, having a relatively simple process, a short heating time, and strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a process flow chart for connecting ceramic particles and metals by induced spark discharge / resistance brazing according to the present invention;

[0024] Figure 2 (a) to (d) are schematic diagrams of the induced spark discharge / resistance brazing process for connecting ceramic particles to metals;

[0025] In the figure, 1 is a pad; 2 is a special bimetallic sheet; 3 is a flexible powder mass formed by mixing solder powder and adhesive; 4 is ceramic particles; 5 is a pressed block; 6 is the connection between two metal sheets in the special bimetallic sheet; 7 is an electric spark; 8 is the molten pool of the special bimetallic sheet and the metal substrate; 9 is the molten pool of the solder, the special bimetallic sheet and the metal substrate. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are as follows Figure 1 shown.

[0027] This embodiment provides a process for connecting ceramic particles to metal by induced spark discharge / resistance brazing, and the steps are as follows:

[0028] (A) Use sandpaper to remove the oxide layer on the surface of the metal substrate to be processed, and use anhydrous alcohol or acetone for ultrasonic cleaning to remove surface oil and impurities.

[0029] (B) Prepare a special bimetallic sheet 2. Select two metal sheets of different materials, equal width and thickness, the same cross-sectional area, and a thickness of 50-100 μm, weld them together, and cut them into the required shape. The two sheets should be made of metal materials with good electrical conductivity and a resistivity difference of 5-20 times. The melting point of the end of the special bimetallic sheet 2 with higher resistivity should be greater than 600°C, and the melting point must be higher than the melting point of the solder used and lower than the melting point of the ceramic particles.

[0030] (C) The special bimetallic sheet 2 is kept in tension and fixed above the surface area of ​​the metal substrate to be implanted with an insulating spacer 1, so that a gap of 1-5 mm is maintained between the special bimetallic sheet 2 and the metal substrate.

[0031] (D) The flexible powder mass 3 formed by mixing solder powder and adhesive is spread flatly on the special bimetallic sheet 2. The thickness of the solder should be controlled between 0.1-0.4mm.

[0032] (E) Select ceramic particles 4 with a particle size of 10-150 mesh, and spread the ceramic particles on the surface of the brazing material at the end with high resistivity of the special bimetallic sheet 2 or embed them into the brazing material as required.

[0033] (F) The end of the special bimetallic sheet 2 with low resistivity is connected to the positive electrode of the pulse power supply, and the metal substrate is connected to the negative electrode, as shown in Figure 2 (a).

[0034] (G) Use a pressure block 5 to apply pressure to the particles above the special bimetallic sheet 2, so that the gap between the special bimetallic sheet 2 and the metal substrate is reduced until spark discharge 7 is generated, and then a molten zone 8 is generated, completing the connection between the special bimetallic sheet 2 and the metal substrate, as shown in Figures 2(b) and 2(c); maintain pressure, and continue pulse discharge to accumulate heat to melt the brazing material to form a molten pool 9, as shown in Figure 2(d).

[0035] (H) Turn off the power and allow to cool naturally to complete the connection between the ceramic particles and the metal matrix.

[0036] The relevant process parameters that need to be adjusted include: discharge voltage 0~200V, capacitance 350~1000μF, discharge frequency 0~1000Hz, pulse width 0-100%, and protective gas flow rate 15~30L / min.

[0037] Example 1

[0038] The metal substrate of this embodiment is made of Q235 stainless steel. The surface to be planted is polished with 600# and 1500# sandpaper, cleaned with anhydrous alcohol ultrasonically, and then dried with an electric hair dryer for later use.

[0039] A 50μm copper sheet and a nickel sheet with the same thickness, width and cross-sectional area (the resistivity difference is about 5.5 times) are laser welded as a special bimetallic sheet for induced discharge. The nickel sheet (melting point 1455℃) is used to place the particle end and is fixed on the metal substrate with a rubber pad to maintain a 3mm gap between the special bimetallic sheet and the metal substrate.

[0040] The solder used is silver-based HL303 with a melting point of 665-745°C. A flexible powder mass formed by mixing solder powder and adhesive is spread flat on a special bimetallic sheet. The solder thickness is 0.15mm.

[0041] Diamond ceramic particles with a particle size of 45-55 mesh are selected and placed on the brazing material at the end of the nickel sheet and at a horizontal distance of 1.5 mm from the connection position of the copper sheet and the nickel sheet as required.

[0042] Connect one end of the copper sheet to the positive electrode of the pulse power supply, and connect the metal substrate to the negative electrode of the pulse power supply. Adjust the process parameters: discharge voltage 80V, capacitance 350μF, discharge frequency 70Hz, pulse width 30%, shielding gas (99.95% pure argon) flow rate 18-23L / min, and use a corundum ceramic pressing block (melting point 2050℃) to apply pressure to press the special bimetallic sheet until spark discharge is generated with the metal substrate to achieve connection between the special bimetallic sheet and the stainless steel metal substrate. Then maintain pressure to ensure continuous pulse discharge, melt the brazing material, and complete the connection between the particles and the metal substrate after natural cooling.

[0043] Example 2

[0044] The metal substrate of this embodiment is made of high-temperature alloy Incone 1625. The surface to be implanted is polished with 600# and 1500# sandpaper, cleaned with anhydrous alcohol ultrasonically, and then dried with an electric hair dryer for later use.

[0045] A copper sheet of 80μm with the same thickness, width and cross-sectional area and a 304 stainless steel sheet (with a resistivity difference of about 8 times) are laser welded as a special bimetallic sheet for induced discharge. The stainless steel sheet (melting point 1420℃) is used to place the particle end and is fixed above the metal substrate with a rubber pad to maintain a 2mm gap between the special bimetallic sheet and the metal substrate.

[0046] The brazing material used is nickel-based brazing material BNi-5, with a melting point of 1079-1135°C. A flexible powder mass formed by mixing brazing material powder and adhesive is spread flat on a special bimetallic sheet. The brazing material thickness is 0.2mm.

[0047] Select TiC ceramic particles with a particle size of 30-40 mesh and place them on the brazing material at the end of the stainless steel sheet and at a horizontal distance of 2 mm from the connection between the copper sheet and the stainless steel sheet.

[0048] Connect one end of the copper sheet to the positive electrode of the pulse power supply, and connect the metal substrate to the negative electrode of the pulse power supply. Adjust the process parameters: discharge voltage 100V, capacitance 450μF, discharge frequency 100Hz, pulse width 45%, shielding gas (99.95% pure argon) flow rate 18-23L / min, and use a corundum ceramic pressing block (melting point 2050℃) to apply pressure to press the special bimetallic sheet until spark discharge is generated with the metal substrate to achieve connection between the special bimetallic sheet and the metal substrate. Then maintain pressure to ensure continuous pulse discharge, melt the brazing material, and complete the connection between the particles and the metal substrate after natural cooling.

[0049] Example 3

[0050] The metal matrix of this embodiment is made of high-temperature alloy DZ125L. The surface to be implanted is polished with 600# and 1500# sandpaper, cleaned with anhydrous alcohol ultrasonically, and then dried with an electric hair dryer for later use.

[0051] A 100μm copper sheet and an iron sheet with the same thickness, width and cross-sectional area (the resistivity difference is about 5.6 times) are laser welded as a special bimetallic sheet for induced discharge. The iron sheet (melting point 1536℃) is used to place the particle end and is fixed above the metal substrate with a rubber pad to maintain a 3mm gap between the special bimetallic sheet and the metal substrate.

[0052] The brazing material used is nickel-based brazing material BNi-2, with a melting point of 970-1000°C. A flexible powder mass formed by mixing brazing material powder and adhesive is spread flat on a special bimetallic sheet. The brazing material thickness is 0.1mm.

[0053] Select Al2O3 ceramic particles with a particle size of 55-65 mesh. Place the Al2O3 ceramic particles on the solder at the end of the iron sheet and at a horizontal distance of 1 mm from the connection between the copper sheet and the iron sheet.

[0054] Connect one end of the copper sheet to the positive electrode of the pulse power supply, and connect the metal substrate to the negative electrode of the pulse power supply. Adjust the process parameters: discharge voltage 200V, capacitance 420μF, discharge frequency 150Hz, pulse width 50%, shielding gas (99.95% pure argon) flow rate 18-23L / min, and use a corundum ceramic pressing block (melting point 2050℃) to apply pressure to press the special bimetallic sheet until spark discharge is generated with the metal substrate to achieve connection between the special bimetallic sheet and the metal substrate. Then maintain pressure to ensure continuous pulse discharge, melt the brazing material, and complete the connection between the particles and the metal substrate after natural cooling.

Claims

1. A process for connecting ceramic particles to metal by induced spark discharge / resistance brazing, comprising polishing and cleaning the surface of the metal substrate to be processed, characterized in that: The process steps are as follows: (1) Prepare a special bimetallic sheet, which is made by butt-welding two metal sheets of different materials, equal width and thickness, the same cross-sectional area, and thickness of 50-100 μm, and then cutting them into the required shape; the two sheets are metal materials with good electrical conductivity and a resistivity difference of 5-20 times; the melting point of the end of the special bimetallic sheet with higher resistivity should be greater than 600°C, and the melting point must be higher than the melting point of the solder used and lower than the melting point of the ceramic particles; (2) The special bimetallic sheet is kept in tension and fixed above the surface area of ​​the metal substrate to be implanted with an insulating pad, so that a gap of 1-5 mm is maintained between the special bimetallic sheet and the metal substrate; (3) Spread the flexible powder mass formed by mixing solder powder and adhesive onto the special bimetallic sheet, and control the solder thickness between 0.1-0.4mm; (4) Select ceramic particles with a particle size of 10 to 150 meshes, and spread the ceramic particles on the surface of the solder at one end of the special bimetallic sheet with high resistivity or embed them into the solder as required; (5) Connect the end of the special bimetallic sheet with low resistivity to the positive electrode of the pulse power supply, and connect the metal substrate to the negative electrode of the pulse power supply; fill the space between the special bimetallic sheet and the metal substrate with protective gas; (6) Use a pressure block to apply pressure to the particles above the special bimetallic sheet, so that the gap between the special bimetallic sheet and the metal matrix is ​​reduced to generate spark discharge, and then a molten zone is generated to complete the connection between the special bimetallic sheet and the metal matrix; maintain pressure, and continue pulse discharge to accumulate heat to melt the brazing material to form a molten pool; (7) Turn off the power supply and allow to cool naturally to complete the connection between the ceramic particles and the metal matrix.

2. The induced spark discharge / resistance brazing connection process of ceramic particles and metal according to claim 1, characterized in that: The pulse discharge has a discharge voltage of 0-200V, a capacitance of 350-1000μF, a discharge frequency of 0-1000Hz, and a pulse width of 0-100%.

3. The induced spark discharge / resistance brazing connection process of ceramic particles and metal according to claim 1, characterized in that: The pressing block should be made of insulating material with a smooth bottom and a certain hardness, and the pressure should be controlled at 10-100N; the melting point of the pressing block should be higher than 1500℃.

4. The process for connecting ceramic particles to metals by induced spark discharge / resistance brazing according to claim 1, characterized in that: The melting point of the solder should be controlled at 400° C.-1200° C. to achieve better connection between the ceramic particles and the metal matrix and avoid excessive loss of the solder at high temperatures.

5. The induced spark discharge / resistance brazing connection process of ceramic particles and metal according to claim 1, characterized in that: The horizontal distance between the placement position of the ceramic particles and the connection position of the special bimetallic sheet should be ensured to be 0.3-2 mm.

6. The process for connecting ceramic particles to metals by induced spark discharge / resistance brazing according to claim 1, characterized in that: The protective gas is pure argon, and the protective gas flow rate is 15 to 30 L / min.

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