Shape memory effect alloy reinforced silver-based electrical contact material and preparation method thereof

Abstract

A shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof, belonging to the technical field of silver-based electrical contact materials. The silver-based electrical contact material is composed of a reinforcing phase NiTi and a matrix silver. The reinforcing phase NiTi is evenly distributed in the matrix silver and the two-phase interface is well bonded without obvious defects. The volume fraction of NiTi is 1-80%, and the remainder is silver. The preparation method is: Ag powder and NiTi powder are evenly mixed, pressed into a block green body by a cold press, and the Ag-NiTi block green body is sintered under protective gas or vacuum conditions to obtain an Ag-NiTi electrical contact material whose mechanical properties and electrical properties can be effectively regulated to meet the requirements of different service environments for the performance of electrical contact materials. The method adopts a simple process to prepare safe and reliable Ag-NiTi electrical contact materials with low energy consumption and convenient for industrial mass production.

Description

Technical Field

[0001] The invention belongs to the technical field of silver-based electric contact materials, and in particular relates to a shape memory effect alloy-reinforced silver-based electric contact material and a preparation method thereof. Background Art

[0002] Electrical contact materials are key materials for power systems and electrical equipment to control on and off and load current, and are crucial for safe operation during current transmission and conversion. Silver is often used as an electrical contact material and is widely used as a core component of instruments, switches and electronic components due to its excellent conductivity, low and stable contact resistance and other advantages. Silver-based electrical contact materials also need to have good mechanical and electrical properties to meet service requirements, among which elastic deformation capacity is particularly important. On the one hand, silver-based electrical contact materials need to maintain close contact through elastic deformation, thereby reducing contact resistance and avoiding relaxation that leads to unstable current transmission and arc damage to equipment; on the other hand, elastic deformation capacity can also help reduce the damage accumulation caused by plastic deformation, greatly improving the service life of silver-based electrical contact materials. NiTi alloy is used in machinery, medical and aerospace fields because of its high shape recovery strain and high elasticity. It has good wettability with silver and does not react to form intermetallic compounds. It can be used as one of the ideal reinforcing phases of silver-based electrical contact materials, effectively improving the mechanical properties (such as strength, hardness and elastic deformation capacity) and service performance (such as wear resistance and arc erosion resistance) of electrical contact materials.

[0003] At present, the related technologies retrieved about a silver-based electrical contact material reinforced with a shape memory effect alloy and its preparation method are as follows: Patent Publication No. CN 110499435 A The invention name is a silver-based composite material and its preparation method. The preparation process of the above-mentioned silver-based composite material is to prepare nickel-titanium alloy powder into a skeleton; put the skeleton, silver block or silver alloy block together to obtain a mixed block; heat the mixed block under vacuum or protective atmosphere conditions, raise the temperature to a set temperature, and keep it at the set temperature for a set time, and then cool it to obtain a silver-based composite material. The preparation process is prepared by a two-step method, namely hot pressing sintering and metal infiltration. Because the hot pressing sintered NiTi alloy powder is continuous in three-dimensional space and according to the embodiment of the patent, the volume fraction of the NiTi phase in the silver-based composite material has a limited adjustable range and the volume fraction is not less than 70%, resulting in a small adjustable range of the silver content of the composite material, which limits the conductivity of the composite material and the conductivity is not higher than 16MS / m. Summary of the invention

[0004] In view of the problems in the prior art, the present invention provides a shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof, the main purpose of which is to prepare a silver-based electrical contact material with good elasticity, strength and electrical conductivity by a simple process. In addition, the shape memory effect alloy reinforced silver-based electrical contact material provided by the present invention can arbitrarily and effectively adjust the volume ratio of NiTi and Ag phases in the composite material, and can meet the requirements of the mechanical properties (strength, hardness, elasticity) of the silver-based electrical contact material under different service environments without significantly reducing the electrical conductivity, and is expected to be widely used as a new type of silver-based electrical contact material in the fields of circuits, electrical appliances, etc. In addition, the present invention adopts a simple process to prepare a safe, reliable, low-energy-consuming, and easy-to-industrial mass-produced high-conductivity, high-elasticity Ag-NiTi electrical contact material.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a shape memory effect alloy-reinforced silver-based electrical contact material of the present invention comprises the following steps:

[0007] Step 1, prepare mixed powder:

[0008] The NiTi powder and the Ag powder are ball-milled, and after the ball-milling is completed, the mixed slurry is allowed to settle, the solid-liquid is separated, and the mixture is dried to obtain an Ag-NiTi mixed powder;

[0009] Step 2, preparing Ag-NiTi bulk green body:

[0010] The Ag-NiTi mixed powder is cold pressed, and the corresponding pressure and holding time are matched according to the volume fraction of NiTi powder in the Ag-NiTi mixed powder to obtain an Ag-NiTi bulk green body;

[0011] Step 3, high temperature sintering treatment:

[0012] The Ag-NiTi bulk green body is loaded into a crucible, placed in a high-temperature sintering furnace in a vacuum environment or a protective atmosphere, and subjected to high-temperature sintering treatment, so as to finally obtain a silver-based electrical contact material reinforced with a shape memory effect alloy.

[0013] In the step 1, the ball milling mixing time is at least 24 hours, and the ball milling speed is 20 to 120 rpm, preferably 50 to 100 rpm.

[0014] In the step 1, the ball milling is performed by dry or wet ball milling, more preferably wet ball milling. The solvent used in the wet ball milling is acetone, the ball milling medium is zirconium balls, and the material-to-ball ratio is 10:1.

[0015] In step 1, the raw material powders are NiTi powder and silver powder, wherein the particle size of the NiTi powder is 10-20 μm, the particle size of the silver powder is 3-25 μm, the volume fraction of the NiTi powder is 1%-80%, and the remainder is Ag powder.

[0016] In step 2, the cold pressing pressure is 5 to 40 MPa, preferably 10 to 30 MPa, the holding time is at least 0.5 h, preferably 0.5 to 2 h, and the pressure mold used for cold pressing is made of stainless steel.

[0017] In the step 2, the density of the Ag-NiTi green block is 85%-90%.

[0018] In step 3, the vacuum degree is 10 -3 Pa, the protective atmosphere is argon.

[0019] In step 3, the high temperature sintering furnace is heated from room temperature to a sintering temperature of 800-900° C. at a heating rate of 5-10° C. / min, the holding time is at least 10 minutes, and the furnace is cooled to room temperature. The crucible material is corundum.

[0020] The shape memory effect alloy reinforced silver-based electrical contact material of the present invention is prepared by the above method. The shape memory effect alloy reinforced silver-based electrical contact material comprises a reinforcing phase NiTi and a matrix silver; the reinforcing phase NiTi is evenly distributed in the matrix silver, the two phase interfaces are well bonded and have no defects, wherein the volume fraction of NiTi is 1% to 80%, preferably 5 to 75%, and the remainder is Ag.

[0021] Preferably, the hardness of the shape memory effect alloy reinforced silver-based electrical contact material is 0.2 to 1.8 GPa.

[0022] Preferably, the electrical conductivity of the shape memory alloy reinforced silver-based electrical contact material is 15-45 MS / m.

[0023] Compared with the prior art, the shape memory alloy reinforced silver-based electrical contact material and the preparation method thereof of the present invention have the following beneficial effects:

[0024] The present invention provides a shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof. A powder metallurgy process is adopted to wet-mix a certain proportion of silver powder and NiTi powder to prepare Ag-NiTi mixed powder, and a corresponding pressure and holding time are matched according to the volume fraction of NiTi powder in the Ag-NiTi mixed powder to obtain an Ag-NiTi block green body, and finally a sintering treatment is performed to obtain a shape memory effect alloy reinforced silver-based electrical contact material. Among them, the volume fractions of silver powder and NiTi powder can be effectively regulated to obtain a good match of hardness, elasticity and electrical conductivity, so as to be suitable for more service environments. Compared with the silver-based composite material obtained by prefabricating NiTi skeleton and then infiltrating silver, the present invention adopts simple operation processes such as cold pressing and sintering that are more suitable for industrial production in terms of process, greatly reducing the high cost problems caused by pre-sintering skeleton and infiltration above the melting point of silver; secondly, the volume fraction of the composite material occupied by the NiTi skeleton is significantly higher than the volume fraction of silver. Although the mechanical properties of the composite material are improved, the adjustable range of the two-phase volume fraction is small, and it is difficult to significantly improve the conductivity of the material, thereby affecting the current transmission and conversion efficiency. The Ag-NiTi mixed powder prepared by the present invention can effectively control the NiTi volume fraction in the range of 1-80 vol%, and can meet the requirements of strength, hardness and elasticity of silver-based electrical contact materials under different service environments while ensuring high electrical conductivity of the electrical contact material.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a microstructure diagram of the silver-based electrical contact material reinforced with the shape memory effect alloy of Ag-10 vol% NiTi prepared in Example 1 of the present invention;

[0027] Figure 2 This is a microstructure diagram of a silver-based electrical contact material reinforced with a shape memory alloy of Ag-20 vol% NiTi prepared in Example 2 of the present invention;

[0028] Figure 3 This is a microstructure diagram of a silver-based electrical contact material reinforced with a shape memory alloy of Ag-25 vol% NiTi prepared in Example 3 of the present invention;

[0029] Figure 4 This is a microstructure diagram of a silver-based electrical contact material reinforced with a shape memory alloy of Ag-70 vol% NiTi prepared in Example 4 of the present invention;

[0030] Figure 5This is an XRD diagram of the silver-based electrical contact material reinforced with the shape memory alloy of Ag-70 vol% NiTi prepared in Example 4 of the present invention;

[0031] Figure 6 These are macroscopic photographs of Ag-NiTi shape memory alloy-reinforced silver-based electrical contact materials prepared in all embodiments of the present invention. DETAILED DESCRIPTION

[0032] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention application are described in detail below in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0033] The specific scheme of the present invention is as follows:

[0034] The embodiment of the present invention provides a shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof. The shape memory effect alloy reinforced silver-based electrical contact material is prepared by uniformly mixing micron-level silver powder and NiTi powder, and obtaining an Ag-NiTi bulk green body through a cold pressing process, and finally undergoing a sintering process to obtain a two-phase uniformly distributed shape memory effect alloy reinforced silver-based electrical contact material; wherein, the mixing ratio of silver powder and NiTi powder can be adjusted within a wide range, and in the cold pressing process, the corresponding cold pressing pressure and holding time are matched according to the addition amount of NiTi powder to ensure the preparation of the Ag-NiTi bulk green body, and after sintering, an electrical contact material in which NiTi is uniformly distributed in the silver matrix is ​​obtained. The preferred cold pressing pressure is 5-40MPa, and the preferred pressure is 10-30MPa and the holding time is 0.5-2h; the preferred sintering temperature is 800-900℃ for the mixed powder.

[0035] The present invention is further described below by specific experimental examples:

[0036] In the following examples, the same cold pressing device, cold pressing mold and heating furnace are used to prepare Ag-NiTi bulk green body and sintering treatment of Ag-NiTi electrical contact material respectively.

[0037] Example 1

[0038] This embodiment adopts a method for preparing a shape memory effect alloy-reinforced silver-based electrical contact material, which includes the following preparation steps:

[0039] Step 1, preparing Ag-10vol%NiTi mixed powder:

[0040] Weigh 10 g of NiTi powder with an average particle size of 10 to 20 μm and 146.25 g of silver powder with an average particle size of 3 μm, add acetone and a small amount of zirconium balls, the liquid level of acetone is higher than the NiTi powder and the Ag powder, mix for 24 hours on a rolling ball mill, after the mixing is completed, pour the mixed slurry into a beaker, remove the upper acetone after powder precipitation, and then place it in a fume hood for natural drying. After the acetone is volatilized, Ag-NiTi mixed powder is obtained;

[0041] Step 2, preparing Ag-NiTi bulk green body:

[0042] The Ag-NiTi mixed powder is loaded into a stainless steel pressure mold and placed in a cold pressing device, a pressure of 10 MPa is applied and the pressure is maintained for 0.5 h, and an Ag-NiTi bulk green body can be obtained;

[0043] Step 3, high temperature sintering treatment:

[0044] The Ag-NiTi green body was placed in a corundum crucible and the vacuum was evacuated to 10 -3 Pa, close the vacuum, introduce flowing argon, heat in a protective atmosphere, first at a heating rate of 5°C / min, from room temperature to 800°C and keep warm for 1h, cool to room temperature with the furnace and take out to obtain Ag-10vol%NiTi electrical contact material;

[0045] Figure 1 The microstructure of the Ag-10 vol% NiTi shape memory alloy reinforced silver-based electrical contact material obtained in Example 1 of the present invention is characterized. The electrical conductivity of the Ag-10 vol% NiTi electrical contact material is 42±0.4 MS / m, and the hardness is 0.3±0.01 GPa. Figure 6 This is a macroscopic photograph of the Ag-NiTi shape memory effect alloy reinforced silver-based electrical contact material prepared in all embodiments of the present invention. From this picture, it can be seen that the Ag-NiTi sample prepared by this patent has no obvious defects and can be directly machined into electrical contact material products.

[0046] Example 2

[0047] This embodiment adopts a method for preparing a shape memory effect alloy-reinforced silver-based electrical contact material, which includes the following preparation steps:

[0048] Step 1, preparing Ag-20 vol% NiTi mixed powder:

[0049] Weigh 20 g of NiTi powder with an average particle size of 10 to 20 μm and 130.1 g of silver powder with an average particle size of 10 μm, add acetone and a small amount of zirconium balls, the liquid level of acetone is higher than that of NiTi powder and Ag powder, mix on a rolling ball mill for 24 hours, after the mixing is completed, pour the mixed slurry into a beaker, remove the upper acetone after powder precipitation, and then place it in a fume hood for natural drying. After the acetone is volatilized, Ag-NiTi mixed powder is obtained;

[0050] Step 2, preparing Ag-NiTi bulk green body:

[0051] The Ag-NiTi mixed powder is loaded into a stainless steel pressure mold and placed in a cold pressing device, a pressure of 20 MPa is applied and the pressure is maintained for 1 hour to obtain an Ag-NiTi bulk green body;

[0052] Step 3, high temperature sintering treatment:

[0053] The Ag-NiTi green body was placed in a corundum crucible and the vacuum was evacuated to 10 -3 Pa, close the vacuum, introduce flowing argon, heat in a protective atmosphere, first at a heating rate of 5°C / min, from room temperature to 800°C and keep warm for 1h, cool to room temperature with the furnace and take out to obtain Ag-20vol%NiTi electrical contact material;

[0054] Figure 2 This is the microstructure of the silver-based electrical contact material reinforced by the shape memory effect alloy of Ag-20 vol% NiTi obtained in Example 2 of the present invention. Through characterization, it is found that the conductivity of the silver-based electrical contact material reinforced by the shape memory effect alloy of Ag-20 vol% NiTi is 37±0.5MS / m, and the hardness value is 0.43±0.02GPa.

[0055] Example 3

[0056] This embodiment uses a shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof, comprising the following preparation steps:

[0057] Step 1, preparing Ag-25vol%NiTi mixed powder:

[0058] Weigh 20 g of NiTi powder with an average particle size of 10 to 20 μm and 97.58 g of silver powder with an average particle size of 24 μm, add acetone and a small amount of zirconium balls, the liquid level of acetone is higher than that of NiTi powder and Ag powder, mix on a rolling ball mill for 24 hours, after the mixing is completed, pour the mixed slurry into a beaker, remove the upper acetone after powder precipitation, and then place it in a fume hood for natural drying. After the acetone is volatilized, Ag-NiTi mixed powder is obtained;

[0059] Step 2, preparing Ag-NiTi bulk green body:

[0060] The Ag-NiTi mixed powder is loaded into a stainless steel pressure mold and placed in a cold pressing device, a pressure of 20 MPa is applied and the pressure is maintained for 2 h, and an Ag-NiTi bulk green body can be obtained;

[0061] Step 3, high temperature sintering treatment:

[0062] The Ag-NiTi green body was placed in a corundum crucible and the vacuum was evacuated to 10 -3 Pa, close the vacuum, introduce flowing argon, heat under protective atmosphere, first at a heating rate of 5°C / min, from room temperature to 850°C and keep warm for 1h, cool to room temperature with the furnace and take out to obtain Ag-25vol%NiTi electrical contact material;

[0063] Figure 3 This is the microstructure of the silver-based electrical contact material reinforced with the shape memory effect alloy of Ag-25 vol% obtained in Example 3 of the present invention. Through characterization, it is found that the conductivity of the silver-based electrical contact material reinforced with the shape memory effect alloy of Ag-25 vol% NiTi is 32±0.4MS / m, and the hardness value is 0.48±0.01GPa.

[0064] Example 4

[0065] This embodiment uses a shape memory effect alloy reinforced silver-based electrical contact material and a preparation method thereof, comprising the following preparation steps:

[0066] Step 1, preparing Ag-25vol%NiTi mixed powder:

[0067] Weigh 80g of NiTi powder with an average particle size of 10-20μm and 55.76g of silver powder with an average particle size of 24μm, add acetone and a small amount of zirconium balls, the liquid level of acetone is higher than that of NiTi powder and Ag powder, mix on a rolling ball mill for 24h, after the mixing is completed, pour the mixed slurry into a beaker, remove the upper acetone after powder precipitation, and then place it in a fume hood for natural drying. After the acetone is volatilized, Ag-NiTi mixed powder is obtained;

[0068] Step 2, preparing Ag-NiTi bulk green body:

[0069] The Ag-NiTi mixed powder is loaded into a stainless steel pressure mold and placed in a cold pressing device, a pressure of 30 MPa is applied and maintained for 2 h, and an Ag-NiTi bulk green body can be obtained;

[0070] Step 3, high temperature sintering treatment:

[0071] The Ag-NiTi green body was placed in a corundum crucible and the vacuum was evacuated to 10-3 Pa, close the vacuum, introduce flowing argon, heat under protective atmosphere, first at a heating rate of 5°C / min, from room temperature to 850°C and keep warm for 1h, cool to room temperature with the furnace and take out to obtain Ag-70vol%NiTi electrical contact material;

[0072] Figure 4 The microstructure of the Ag-70 vol% NiTi shape memory alloy reinforced silver-based electrical contact material obtained in Example 4 of the present invention is shown in FIG. Figure 5 This is an XRD result diagram of the silver-based electrical contact material reinforced by the shape memory effect alloy of Ag-70vol%NiTi. Through characterization, it was found that the conductivity of the silver-based electrical contact material reinforced by the shape memory effect alloy of Ag-70vol%NiTi was 18±0.4MS / m and the hardness value was 1.7±0.01GPa.

[0073] Example 5

[0074] The same as Example 1, except that dry ball milling is used, and the ball milling speed is preferably 20-40 rpm to avoid the silver powder with high density from agglomerating, agglomerating and other uneven dispersions due to the rotation of the container during the mixing process due to too fast a speed. Dry ball milling is more time-consuming than wet ball milling.

[0075] Comparative Example 1

[0076] The same as Example 1, except that step 2 adopts hot pressing, and the hot pressing temperature is 100°C. Silver powder is easily oxidized. Since silver powder has a large specific surface area, it is easier to generate a surface oxide film under the action of temperature and oxygen, thereby affecting the sintering efficiency and density of the composite material, and further affecting the conductivity and mechanical properties of the composite material.

[0077] Comparative Example 2

[0078] The same as Example 1, except that there is no ball milling process in Example 1, only a simple mixing of the two phases, and the uniformity of the mixed powder is poor, so that the silver-rich area of ​​the composite material is not resistant to arc erosion and arc erosion pits appear, and the wear resistance is poor, and it is easy to be worn and cause poor contact.

[0079] Comparative Example 3

[0080] The same as Example 1, except that the cold pressing pressure used is 2 MPa, the obtained Ag-NiTi block has low green density, and is prone to produce holes in the subsequent high-temperature sintering process, which is not conducive to improving the comprehensive performance of the composite material.

[0081] Comparative Example 4

[0082] The same as Example 1, except that, in the high-temperature sintering process, the Ag-NiTi bulk green body is directly placed at 800°C. When the Ag-NiTi bulk green body is sintered at high temperature, without a vacuum environment and argon protection, the silver powder in the composite material is first oxidized, and its composition changes, causing the conductivity and mechanical properties of the composite material to deteriorate.

[0083] Comparative Example 5

[0084] The same as Example 1, except that the sintering temperature used in the high-temperature sintering process is 500° C., the sintering efficiency of the composite material is low, the densification degree is almost unchanged, and the conductivity and mechanical properties thereof are not effectively improved.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a shape memory effect alloy reinforced silver-based electrical contact material, characterized in that: The NiTi powder and the Ag powder are ball-milled and mixed, the Ag-NiTi mixed powder is cold-pressed to obtain an Ag-NiTi bulk green body, and the green body is placed in a vacuum environment or a protective atmosphere for high-temperature sintering to obtain a shape memory effect alloy-reinforced silver-based electrical contact material; The method specifically comprises the following steps: Step 1, prepare mixed powder: The NiTi powder and the Ag powder are ball-milled, and after the ball-milling is completed, the mixed slurry is allowed to settle, the solid-liquid is separated, and the mixture is dried to obtain an Ag-NiTi mixed powder; Step 2, preparing Ag-NiTi bulk green body: The Ag-NiTi mixed powder is cold pressed, and the corresponding pressure and holding time are matched according to the volume fraction of NiTi powder in the Ag-NiTi mixed powder to obtain an Ag-NiTi bulk green body; Step 3, high temperature sintering treatment: The Ag-NiTi bulk green body is loaded into a crucible, placed in a high-temperature sintering furnace in a vacuum environment or a protective atmosphere, and subjected to high-temperature sintering treatment, thereby finally obtaining a silver-based electrical contact material reinforced with a shape memory effect alloy; In the step 1, the raw material powders are NiTi powder and silver powder, wherein the particle size of the NiTi powder is 10 to 20 μm, the particle size of the silver powder is 3 to 25 μm, the volume fraction of the NiTi powder is 1% to 25%, and the remainder is Ag powder; In step 2, the cold pressing pressure is 5-40 MPa, and the holding time is at least 0.5 h; The shape memory effect alloy reinforced silver-based electrical contact material comprises a reinforcement phase NiTi and a matrix silver; the reinforcement phase NiTi is uniformly distributed in the matrix silver and has no defects; The shape memory effect alloy reinforced silver-based electrical contact material has a hardness of 0.2 to 1.8 GPa and a conductivity of 18 to 45 MS / m.

2. The method for preparing the shape memory effect alloy reinforced silver-based electrical contact material according to claim 1, characterized in that: In the step 1, the ball milling mixing time is at least 24 hours, the ball milling speed is 20-120 rpm; the ball milling is performed by dry or wet ball milling; the solvent used in the wet ball milling is acetone, the ball milling medium is zirconium balls, and the material-to-ball ratio is 10:

1.

3. The method for preparing the shape memory effect alloy reinforced silver-based electrical contact material according to claim 1, characterized in that: In the step 2, the density of the Ag-NiTi green block is 85%-90%.

4. The method for preparing the shape memory effect alloy reinforced silver-based electrical contact material according to claim 1, characterized in that: In step 3, the vacuum degree is 10 -3 Pa, the protective atmosphere is argon.

5. The method for preparing the shape memory effect alloy reinforced silver-based electrical contact material according to claim 1, characterized in that: In step 3, the high temperature sintering furnace is heated from room temperature to a sintering temperature of 800-900° C. at a heating rate of 5-10° C. / min, the holding time is at least 10 minutes, and the furnace is cooled to room temperature.

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