Ultrafine nanocrystalline silver alloy and preparation method thereof

Abstract

The application provides a superfine nanocrystalline silver alloy and a preparation method thereof, and belongs to the technical field of superfine crystal preparation.The superfine nanocrystalline silver alloy is prepared by the following steps: firstly, rolling the silver alloy; secondly, breaking the original grains in the silver alloy by rolling; thirdly, transforming the broken grains into equiaxed grains by annealing; fourthly, cross-extruding under ultralow temperature to inhibit recovery recrystallization; fifthly, breaking the equiaxed grains into superfine equiaxed grains by cross-extruding; sixthly, further refining the grains by ultralow-temperature rolling; and finally, recrystallizing the broken grains by annealing after rolling, so that the superfine nanocrystalline silver alloy with nanometer grain size is obtained; the superfine nanocrystalline silver alloy has uniform microstructure, obvious strength improvement, good conductivity and ductility, and the preparation method is simple, easy to popularize in large scale, and has wide application prospect in industry.

Description

Technical Field

[0001] This invention relates to the field of ultrafine crystal preparation technology, and in particular to an ultrafine nanocrystalline silver alloy and its preparation method. Background Technology

[0002] In recent years, nanotwinned materials have received widespread attention as an extension of research on nanocrystalline metals and alloys. Uniformly structured ultrafine nanocrystalline silver alloys, due to their unique mechanical and electrical properties, as well as their ability to sputter uniformly and rapidly in sputtered thin films, have broad application prospects in the electronics industry, electrical contact materials, and silver alloy sputtering targets.

[0003] Traditional methods for preparing ultrafine grains mainly include rapid solidification, vapor deposition, mechanical alloying, and intense plastic deformation, with intense plastic deformation being the most widely used technique. Intensive plastic deformation for sheet metal preparation is further divided into: constant-diameter angular extrusion, high-pressure torsion, and multiaxial compression / forging for bulk materials; and cumulative rolling and continuous shear deformation for strip and sheet materials. However, constant-diameter angular extrusion and high-pressure torsion are only suitable for small-sample preparation and not for industrial production. Typically, grain refinement of metallic materials is achieved primarily through traditional plastic deformation processing followed by annealing. Materials prepared by conventional processes typically have a minimum grain size of approximately 10 μm, with relatively large grain sizes and inhomogeneous microstructure.

[0004] Several patents have been published and granted regarding the preparation of fine-grained silver. Among them, patents with application numbers CN202210782731, CN202111043720, CN201710981187, and CN200710304309 all provide a preparation method for fine-grained silver. These methods all involve large plastic deformation to refine the grains. However, the grain size of the fine-grained silver provided by these patents is all in the micrometer range, not reaching the nanometer scale. Furthermore, the process described in patent application number CN200710304309 is complex and has low strength.

[0005] Therefore, how to prepare a silver alloy with a grain size down to the nanoscale, and make the silver alloy have high strength, good ductility, good conductivity, uniform microstructure and simple operation, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide an ultrafine nanocrystalline silver alloy and its preparation method. The ultrafine nanocrystalline silver alloy prepared by the preparation method of this invention has a uniform microstructure, significantly improved strength, good conductivity and ductility. At the same time, the preparation method is simple, easy to promote on a large scale, and has broad application prospects in industry.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing ultrafine nanocrystalline silver alloy, comprising the following steps:

[0009] (1) Rolling the silver alloy yields a rolled silver alloy;

[0010] (2) Anneal the rolled silver alloy obtained in step (1) to obtain an equiaxed silver alloy;

[0011] (3) The equiaxed silver alloy obtained in step (2) is kept at a constant temperature in liquid nitrogen and then subjected to cross extrusion to obtain a silver alloy with broken grains.

[0012] (4) The silver alloy with broken grains obtained in step (3) is kept in liquid nitrogen and then cold rolled to obtain a cold-rolled silver alloy.

[0013] (5) The cold-rolled silver alloy obtained in step (4) is annealed to obtain an ultrafine nanocrystalline silver alloy.

[0014] Preferably, the silver alloy in step (1) is an Ag-X alloy, wherein X is one or more of Zn, Cr, Pd, Cu, Pt and rare earth elements.

[0015] Preferably, the total deformation during rolling in step (1) is >70%.

[0016] Preferably, the annealing temperature in step (2) is 600-750°C and the annealing time is 1-12 hours.

[0017] Preferably, the isometric silver alloy in step (3) undergoes cross-extrusion after being kept at a high temperature in liquid nitrogen, which includes the following steps:

[0018] 1) Immerse the equiaxed silver alloy in liquid nitrogen and keep it at a temperature for 10-30 minutes, then place it in a mold for the first cross extrusion to obtain a silver alloy after one extrusion.

[0019] 2) Place the silver alloy obtained in step 1) into liquid nitrogen and keep it warm for 10-30 minutes. Then rotate the silver alloy horizontally by 90° and place it into the mold for a second cross extrusion to obtain a silver alloy with a second extrusion.

[0020] 3) Repeat steps 1) and 2) 5 to 10 times to obtain a silver alloy with broken grains.

[0021] Preferably, the 90° rotation in step 2) is either clockwise or counterclockwise.

[0022] Preferably, the time for heat preservation in liquid nitrogen in step (4) is 10 to 30 minutes.

[0023] Preferably, the deformation amount of cold rolling in step (4) is 30-90%.

[0024] Preferably, the annealing temperature in step (5) is 200-350°C and the annealing time is 0.5-2 hours.

[0025] The present invention provides an ultrafine nanocrystalline silver alloy prepared by the preparation method described above, wherein the grain size of the ultrafine nanocrystalline silver alloy is <1000nm.

[0026] This invention provides a method for preparing an ultrafine nanocrystalline silver alloy, comprising the following steps: (1) rolling a silver alloy to obtain a rolled silver alloy; (2) annealing the rolled silver alloy obtained in step (1) to obtain an equiaxed crystalline silver alloy; (3) cross-extruding the equiaxed crystalline silver alloy obtained in step (2) after heat preservation in liquid nitrogen to obtain a silver alloy with broken grains; (4) cold-rolling the silver alloy with broken grains obtained in step (3) after heat preservation in liquid nitrogen to obtain a cold-rolled silver alloy; (5) annealing the cold-rolled silver alloy obtained in step (4) to obtain an ultrafine nanocrystalline silver alloy. This invention first rolls a silver alloy to break down the original grains. Then, annealing transforms the broken grains into equiaxed grains. Next, cross-extrusion is performed at ultra-low temperatures to suppress recrystallization. This cross-extrusion further breaks down the equiaxed grains into ultrafine equiaxed grains. Ultra-low temperature rolling further refines the grains. Finally, annealing allows the broken grains to recrystallize, resulting in an ultrafine nanocrystalline silver alloy with nanometer-sized grains. This ultrafine nanocrystalline silver alloy, obtained through intense plastic deformation at ultra-low temperatures combined with low-temperature annealing, exhibits a uniform microstructure, significantly improved strength, and good conductivity and ductility. Furthermore, the preparation method is simple, easy to scale up, and has broad application prospects in industry. The results of the examples show that the ultrafine nanocrystalline silver alloy obtained by the method provided by this invention has an electrical conductivity ≤54*10⁻⁶. 6 With a Ms / m, Vickers hardness of over 70HV, ductility of over 70%, and grain size of <1000nm, it not only significantly improves strength but also has good conductivity and ductility. At the same time, the grain size reaches the nanoscale, which is significantly better than the ultrafine grains prepared by existing technologies. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the mold used in the cross-extrusion process of the present invention;

[0028] Figure 2 This is an electron backscattering pattern of the ultrafine nanocrystalline silver alloy prepared in Example 1 of the present invention. Detailed Implementation

[0029] This invention provides a method for preparing ultrafine nanocrystalline silver alloy, comprising the following steps:

[0030] (1) Rolling the silver alloy yields a rolled silver alloy;

[0031] (2) Anneal the rolled silver alloy obtained in step (1) to obtain an equiaxed silver alloy;

[0032] (3) The equiaxed silver alloy obtained in step (2) is kept at a constant temperature in liquid nitrogen and then subjected to cross extrusion to obtain a silver alloy with broken grains.

[0033] (4) The silver alloy with broken grains obtained in step (3) is kept in liquid nitrogen and then cold rolled to obtain a cold-rolled silver alloy.

[0034] (5) The cold-rolled silver alloy obtained in step (4) is annealed to obtain an ultrafine nanocrystalline silver alloy.

[0035] This invention involves rolling a silver alloy to obtain a rolled silver alloy.

[0036] In this invention, the silver alloy is preferably an Ag-X alloy; X is preferably one or more of Zn, Cr, Pd, Cu, Pt, and rare earth elements, more preferably one of Zn, Cr, Pd, Cu, Pt, and rare earth elements; the rare earth element is preferably any one of Nd, La, and Ce; the mass percentage of Ag in the silver alloy is preferably 95-99.9%, and the mass percentage of X is preferably ≤5%. By controlling the composition of the silver alloy, this invention allows doping elements to inhibit recrystallization during the preparation process, thereby facilitating a further reduction in the grain size of the silver alloy.

[0037] In this invention, the total deformation during rolling is preferably greater than 70%. This invention does not impose specific limitations on the number of rolling passes or the deformation per pass, as long as the total deformation meets the requirements. By controlling the total deformation during rolling, this invention ensures that the grains in the aluminum alloy are broken down as much as possible.

[0038] After obtaining the rolled silver alloy, the present invention performs annealing treatment on the rolled silver alloy to obtain an equiaxed silver alloy.

[0039] In this invention, the annealing temperature is preferably 600–750°C, more preferably 680–720°C; the annealing time is preferably 1–12 hours, more preferably 5–12 hours, and even more preferably 8–12 hours. This invention does not impose any special limitations on the cooling method for the annealing process; it can be determined based on the technical knowledge of those skilled in the art. This invention, by annealing rolled silver alloys, can transform broken grains in the silver alloy into equiaxed grains; by controlling the parameters of the annealing process, the grain transformation efficiency can be improved.

[0040] After obtaining the equiaxed crystalline silver alloy, the present invention holds the equiaxed crystalline silver alloy in liquid nitrogen and then performs cross-extrusion to obtain a silver alloy with broken grains.

[0041] In this invention, the structural schematic diagram of the die used for cross-extrusion is preferably as shown below. Figure 1 As shown.

[0042] In this invention, the equiaxed crystalline silver alloy undergoes cross-extrusion after being kept at a temperature in liquid nitrogen, preferably including the following steps:

[0043] 1) Immerse the equiaxed silver alloy in liquid nitrogen and keep it at a temperature for 10-30 minutes, then place it in a mold for the first cross extrusion to obtain a silver alloy after one extrusion.

[0044] 2) Place the silver alloy obtained in step 1) into liquid nitrogen and keep it warm for 10-30 minutes. Then rotate the silver alloy horizontally by 90° and place it into the mold for a second cross extrusion to obtain a silver alloy with a second extrusion.

[0045] 3) Repeat steps 1) and 2) 5 to 10 times to obtain a silver alloy with broken grains.

[0046] In this invention, the equiaxed silver alloy is preferably inserted into liquid nitrogen and kept at a temperature for 10 to 30 minutes, and then placed in a mold for the first cross extrusion to obtain a silver alloy that has been extruded once.

[0047] In this invention, the heat preservation time is preferably 15-25 minutes, more preferably 20-25 minutes. By controlling the heat preservation time, this invention can ensure that the temperature of the equiaxed silver alloy meets the requirements.

[0048] In this invention, the time for the first cross-extrusion is preferably 5 to 15 seconds, more preferably 5 to 10 seconds.

[0049] After obtaining the silver alloy from the first extrusion, the present invention preferably places the silver alloy from the first extrusion into liquid nitrogen and keeps it warm for 10 to 30 minutes. Then, the silver alloy from the first extrusion is rotated horizontally by 90° and placed into a mold for a second cross extrusion to obtain a silver alloy from the second extrusion.

[0050] In this invention, the heat preservation time is preferably 15-25 minutes, more preferably 20-25 minutes. By controlling the heat preservation time, this invention can ensure that the temperature of the equiaxed silver alloy meets the requirements.

[0051] In this invention, the second cross-extrusion time is preferably 5 to 15 seconds, more preferably 5 to 10 seconds.

[0052] In this invention, the 90° horizontal rotation is preferably clockwise or counterclockwise. This invention employs a multi-stage cross-extrusion process, rotating the silver alloy during each extrusion, which effectively breaks down the grains and ensures thorough processing at every location.

[0053] In this invention, the repetition is preferably 5 to 10 times, more preferably 7 to 9 times. This invention improves the extrusion effect through multiple cross-extrusions.

[0054] In this invention, the total deformation of the cross-extrusion is preferably ≥90%. This invention does not impose a specific limitation on the deformation amount of each cross-extrusion; it can be determined based on common technical knowledge and the mold. By controlling the total deformation of the cross-extrusion, this invention can further promote the breakup of equiaxed crystals into ultrafine equiaxed crystals.

[0055] This invention lowers the temperature of the equiaxed silver alloy to ultra-low temperatures by immersing it in liquid nitrogen, thereby inhibiting recrystallization. By employing a two-stage cooling method, recrystallization caused by temperature rise during cross-extrusion can be avoided.

[0056] After cross-extrusion, the present invention preferably restores the product obtained by cross-extrusion to room temperature to obtain a silver alloy with broken grains.

[0057] After obtaining the silver alloy with broken grains, the present invention cold-rolls the silver alloy with broken grains after keeping it in liquid nitrogen to obtain a cold-rolled silver alloy.

[0058] In this invention, the holding time in liquid nitrogen is preferably 10–30 min, more preferably 15–25 min. By first holding the alloy in liquid nitrogen, the temperature can be significantly reduced, thereby inhibiting grain recrystallization and resulting in finer grains.

[0059] In this invention, cooling during the cold rolling process is preferably achieved by surface injection of liquid nitrogen. By using surface injection of liquid nitrogen for cooling during cold rolling, this invention avoids recrystallization caused by the heat generated during rolling, which would otherwise lead to an increase in alloy temperature.

[0060] In this invention, the deformation amount of the cold rolling is preferably 30-90%, more preferably 50-90%. In this invention, the number of cold rolling passes is preferably 2-5; the rolling time for each pass during the cold rolling process is preferably 5-15 seconds, more preferably 5-10 seconds. By controlling the deformation amount of the cold rolling, this invention can further refine the grain size.

[0061] After cold rolling, the present invention preferably restores the cold-rolled product to room temperature.

[0062] After obtaining the cold-rolled silver alloy, the present invention performs annealing treatment on the cold-rolled silver alloy to obtain an ultrafine nanocrystalline silver alloy.

[0063] In this invention, the annealing temperature is preferably 200–350°C, more preferably 250–320°C; the annealing time is preferably 0.5–2 hours, more preferably 0.5–1.5 hours. This invention does not impose any particular limitation on the cooling method for the annealing process; it can be determined based on the technical knowledge of those skilled in the art. By controlling the parameters of the annealing process, this invention can further promote the recrystallization of broken grains, thereby obtaining nanoscale grains.

[0064] This invention first rolls a silver alloy to break down the original grains. Then, through annealing, the broken grains are transformed into equiaxed grains. Next, cross-extrusion is performed at ultra-low temperatures to suppress recrystallization. Cross-extrusion further breaks down the equiaxed grains into ultra-fine equiaxed grains. Ultra-low temperature rolling is then used to further refine the grains. Finally, annealing allows the broken grains to recrystallize, resulting in an ultra-fine nanocrystalline silver alloy with nanoscale grain size. The ultra-fine nanocrystalline silver alloy obtained by using intense plastic deformation at ultra-low temperatures combined with low-temperature annealing exhibits a uniform microstructure, significantly improved strength, good conductivity and ductility. Furthermore, the preparation method is simple, easy to scale up, and has broad application prospects in industry.

[0065] The present invention provides an ultrafine nanocrystalline silver alloy prepared by the preparation method described above, wherein the grain size of the ultrafine nanocrystalline silver alloy is <1000nm.

[0066] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0067] Example 1

[0068] A method for preparing an ultrafine nanocrystalline silver alloy comprises the following steps:

[0069] (1) The silver alloy is rolled to obtain a rolled silver alloy; the silver alloy is an Ag-Zn alloy, the mass percentage of Ag in the silver alloy is 99.2%, and the mass percentage of Zn is 0.8%; the total deformation of the rolling is 60%;

[0070] (2) The rolled silver alloy obtained in step (1) is annealed to obtain an equiaxed silver alloy; the annealing temperature is 700℃ and the annealing time is 12h.

[0071] (3) The equiaxed silver alloy obtained in step (2) is kept at a temperature in liquid nitrogen and then subjected to cross extrusion to obtain a silver alloy with broken grains; the total deformation of the cross extrusion is 90%.

[0072] (4) The silver alloy with broken grains obtained in step (3) is placed in liquid nitrogen for 20 minutes, and then quickly placed into a rolling mill for cold rolling. During the cold rolling process, liquid nitrogen is injected into the surface for cooling to obtain a cold-rolled silver alloy. The deformation of the cold rolling is 90%, the number of cold rolling passes is 3, and the rolling time of each pass during the cold rolling process is 10 seconds.

[0073] (5) The cold-rolled silver alloy obtained in step (4) is annealed to obtain an ultrafine nanocrystalline silver alloy; the annealing temperature is 300℃ and the annealing time is 0.5h.

[0074] The specific steps of cross-extrusion at ultra-low temperature in step (3) are as follows:

[0075] 1) Immerse the equiaxed crystal silver alloy in liquid nitrogen for 20 minutes, then place it in a mold for the first cross extrusion for 10 seconds to obtain the silver alloy after one extrusion.

[0076] 2) Place the silver alloy obtained in step 1) into liquid nitrogen and keep it warm for 20 minutes. Then rotate the silver alloy in a clockwise direction by 90° and place it into the mold for a second cross extrusion for 10 seconds to obtain a silver alloy with broken grains.

[0077] 3) Repeat steps 1) and 2) a total of 8 times to obtain a silver alloy with broken grains.

[0078] The electron backscattering pattern of the ultrafine nanocrystalline silver alloy prepared in Example 1 of this invention is shown below. Figure 2 As shown. By Figure 2 It can be seen that the microstructure of the ultrafine nanocrystalline silver alloy prepared by this invention is uniform and the grain size is small.

[0079] Example 2

[0080] A method for preparing an ultrafine nanocrystalline silver alloy comprises the following steps:

[0081] (1) The silver alloy is rolled to obtain a rolled silver alloy; the silver alloy is an Ag-Zn alloy, the mass percentage of Ag in the silver alloy is 99.2%, and the mass percentage of Zn is 0.8%; the total deformation of the rolling is 60%;

[0082] (2) The rolled silver alloy obtained in step (1) is annealed to obtain an equiaxed silver alloy; the annealing temperature is 700℃ and the annealing time is 12h.

[0083] (3) The equiaxed silver alloy obtained in step (2) is kept at a temperature in liquid nitrogen and then subjected to cross extrusion to obtain a silver alloy with broken grains; the total deformation of the cross extrusion is 90%.

[0084] (4) The silver alloy with broken grains obtained in step (3) is placed in liquid nitrogen for 20 minutes, and then quickly placed into a rolling mill for cold rolling. During the cold rolling process, liquid nitrogen is injected into the surface for cooling to obtain a cold-rolled silver alloy. The deformation of the cold rolling is 70%, the number of cold rolling passes is 3, and the rolling time of each pass during the cold rolling process is 10 seconds.

[0085] (5) The cold-rolled silver alloy obtained in step (4) is annealed to obtain an ultrafine nanocrystalline silver alloy; the annealing temperature is 320°C and the annealing time is 0.5h.

[0086] The specific steps of cross-extrusion at ultra-low temperature in step (3) are as follows:

[0087] 1) Immerse the equiaxed crystal silver alloy in liquid nitrogen for 20 minutes, then place it in a mold for the first cross extrusion for 10 seconds to obtain the silver alloy after one extrusion.

[0088] 2) Place the silver alloy obtained in step 1) into liquid nitrogen and keep it warm for 20 minutes. Then rotate the silver alloy in a clockwise direction by 90° and place it into the mold for a second cross extrusion for 10 seconds to obtain a silver alloy with broken grains.

[0089] 3) Repeat steps 1) and 2) a total of 8 times to obtain a silver alloy with broken grains.

[0090] The properties of the ultrafine nanocrystalline silver alloys obtained in Examples 1 and 2 were tested, and the results are shown in Table 1:

[0091] Table 1. Properties of the ultrafine nanocrystalline silver alloys obtained in Examples 1 and 2

[0092] Conductivity / Ms / m Vickers hardness / HV Extensibility / % Grain size / nm Example 1 <![CDATA[54*10 6 ]]> 80 70 700 Example 2 <![CDATA[52*10 6 ]]> 70 72 900

[0093] As can be seen from Table 1, the ultrafine nanocrystalline silver alloy prepared by the present invention not only has significantly improved strength, but also good conductivity and ductility. At the same time, the grain size reaches the nanoscale, which is significantly better than the ultrafine crystals prepared by the prior art.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-fine nanocrystalline silver alloy, comprising the following steps: (1) rolling silver alloy to obtain rolled silver alloy; (2) annealing the rolled silver alloy obtained in step (1) to obtain equiaxed silver alloy; (3) cross-extruding the equiaxed silver alloy obtained in step (2) after keeping in liquid nitrogen to obtain silver alloy with broken grains; (4) cold-rolling the silver alloy with broken grains obtained in step (3) after keeping in liquid nitrogen to obtain cold-rolled silver alloy; (5) annealing the cold-rolled silver alloy obtained in step (4) to obtain ultra-fine nanocrystalline silver alloy; the cross-extruding the equiaxed silver alloy after keeping in liquid nitrogen in step (3) comprises the following steps: 1) inserting the equiaxed silver alloy into liquid nitrogen for 10-30 min, and then putting it into a mold for first cross-extrusion to obtain once-extruded silver alloy; 2) putting the once-extruded silver alloy obtained in step 1) into liquid nitrogen for 10-30 min, and then putting the once-extruded silver alloy into a mold for second cross-extrusion after rotating it horizontally by 90° to obtain twice-extruded silver alloy; 3) repeating steps 1) and 2) for 5-10 times in turn to obtain silver alloy with broken grains; the horizontal rotation by 90° in step 2) is clockwise rotation or counterclockwise rotation; the keeping in liquid nitrogen in step (4) is for 10-30 min; and the deformation amount of cold-rolling in step (4) is 30-90%. The silver alloy in step (1) is Ag-X alloy, wherein X is one or more of Zn, Cr, Pd, Cu, Pt and rare earth elements. The total deformation amount of rolling in step (1) is >70%. The annealing temperature in step (2) is 600-750℃, and the annealing time is 1-12 h. The annealing temperature in step (5) is 200-350℃, and the annealing time is 0.5-2 h.

6. The ultra-fine nanocrystalline silver alloy prepared by the method of any one of claims 1-5, wherein the grain size of the ultra-fine nanocrystalline silver alloy is <1000 nm. ​ ​ ​ ​ ​ ​ 2. The production method according to claim 1, characterized by, ​ 3. The preparation method according to claim 1, characterized in that, ​ 4. The method of claim 1, wherein, ​ 5. The preparation method according to claim 1, characterized in that, ​ ​

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