Recovery smelting method of nickel-chromium alloy sputtering residual target

Abstract

The invention discloses a recycling and smelting method for nickel-chromium alloy sputtering residual targets, and belongs to the technical field of metallurgy and chemical engineering. According to the recycling and smelting method, the nickel-chromium residual target electrode is melted through a vacuum self-consuming arc remelting technology, and the nickel-chromium residual target electrode is cooled and crystallized into a cast ingot in a water-cooled copper crucible. According to the method, partial oxides of nickel and chromium are decomposed in a high-vacuum environment, so that gas impurities such as oxygen, nitrogen and hydrogen are removed, the purity of the alloy is improved, the compactness of the cast ingot is improved through sequential solidification of the cast ingot subjected to vacuum consumable melting, and the problem of shrinkage porosity of the cast ingot subjected to traditional single vacuum induction melting pouring is solved. And in addition, the cast ingot is subjected to homogenization treatment, uneven components and harmful phases in the cast ingot are eliminated, and the alloy performance of rear-end forging is improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical and chemical technology, specifically to a method for recycling and smelting nickel-chromium alloy sputtering residue targets. Background Technology

[0002] Nickel-chromium alloys are important functional materials widely used in electronics, aerospace, metallurgy, and new energy fields. Particularly in the manufacturing of magnetic recording, semiconductor, and optoelectronic materials, nickel-chromium alloys are often used as sputtering targets, forming thin films in a vacuum environment using physical vapor deposition (PVD). However, in actual production, the targets are not completely consumed; typically, 30%-70% of the target material remains (i.e., residual targets). Although the surface of the residual targets is covered with an oxide layer and a small amount of contaminants, it still contains a large amount of high-purity nickel and chromium. Directly discarding it not only wastes resources but also places a burden on the environment.

[0003] Currently, the main methods for recovering nickel-chromium alloy targets include physical crushing, hydrochemical purification, and vacuum melting. However, these methods have the following drawbacks: (1) Physical crushing + simple smelting: It is difficult to completely remove gaseous impurities (O, N, H) and non-metallic inclusions. The purity of the recovered alloy is mostly below 99.0%, which cannot meet the requirements for target preparation. (2) Chemical wet purification: strong acid / base reagents are required, which can easily cause equipment corrosion and secondary pollution. The process cycle is long (≥48h) and energy consumption is high (energy consumption per ton ≥800kWh). (3) Traditional vacuum induction melting (VIM): Ingots are prone to shrinkage cavities and porosity, resulting in low ingot density (≤98.5%), a yield of only about 80%, and limited crucible life (≤20 times), which increases industrialization costs; (4) Electron beam cold bed melting (EB): Although it can improve density and purify impurities, the energy is too concentrated, which can easily lead to element burn-off, resulting in deviation of ingot composition and failure to meet the requirements of target material composition uniformity.

[0004] Therefore, it is necessary to develop a parameter optimization scheme adapted to the VAR process. By precisely controlling key parameters such as vacuum degree, melting current, and feeding time, and by designing the electrode preparation process in a targeted manner, the problem of "insufficient purity, low yield, and many ingot defects" in target recycling can be solved, while taking into account environmental protection and industrial feasibility. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a method for recycling and smelting nickel-chromium alloy sputtering targets, so as to solve the problems of insufficient purity, low yield and many ingot defects in the existing target recycling technology.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for recycling and smelting nickel-chromium alloy sputtering residue targets is provided, comprising the following steps: (1) Pre-treatment of residual targets: ① Grind the surface of the nickel-chromium target residue to remove impurities; ② The nickel-chromium residual target from step ① is stacked and welded to form a primary consumable electrode; wherein the welding current is 100-250A and the voltage is 20-40V; (2) One VAR melting: ① The auxiliary electrode is vacuum welded to the primary consumable electrode of step (1) in the furnace, and argon is used for cooling after welding for ≥20 min; wherein, the arc starting current is 0.5-1.5kA, the voltage is 22-26V, the arc stabilizing current is 2-4A, the welding current is 2.5-4kA, and the voltage is 22-26V. ② The product obtained in step ① is smelted once; wherein the arc starting current is 1-2kA, the voltage is 24-26V, and the arc stabilizing current is 2-4A; the normal smelting current is 4.5-5.5kA, the voltage is 27-28V, and the arc stabilizing current is 2-4A. ③ When 2-4 kg of the product obtained in step ① remains, reduce the current to 4 kA until the consumable electrode is completely melted and stop smelting. Then, fill the furnace with argon at 500-1000 Pa and cool for ≥3 hours to obtain a primary ingot. ④ Connect the first and last ends of the primary ingot from step ③ and weld them together to form a secondary consumable electrode; (3) Secondary VAR melting: ① Perform vacuum welding of the auxiliary electrode and the secondary consumable electrode in step (2) in the furnace. After welding, purge with argon at 500-2000 Pa and cool for ≥20 min. The arc starting current is 0.5-1.5 kA, the voltage is 26 V, the arc stabilizing current is 2-4 A, and the welding current is 2.5-4 kA and the voltage is 26 V. ② The product obtained in step ① is subjected to secondary melting; wherein, the arc starting current is 1-2kA, the voltage is 24-26V, the arc stabilizing current is 2-4A, the normal melting current is 7.5-8.5kA, the voltage is 28-29V, and the arc stabilizing current is 2-4A. ③ When 60kg of the product obtained in step ① remains, feeding is performed. When the secondary consumable electrode is completely melted, smelting is stopped, the furnace is filled with argon, and the cooling time is ≥4h to obtain a secondary ingot. (4) Homogenization treatment of ingots: After heating the secondary ingot from step (3) to 600-650℃, hold it for 1 hour, then continue to heat it to 1050-1180℃ and hold it for 2-3 hours, then cool it to room temperature.

[0007] Furthermore, in step (1), the width of the nickel-chromium residual target is ≤230mm.

[0008] Furthermore, in step (1), the density of the primary consumable electrode is 5-6.5 g / cm³, the straight deviation distance is ≤10 mm, the diagonal of the cross section of the primary consumable electrode is ≤ the diameter of the crucible, and the maximum length of the primary consumable electrode is = upper furnace chamber height + crucible depth - auxiliary electrode length - 10 cm.

[0009] Furthermore, in step (2), the vacuum degree inside the furnace during vacuum welding is ≤5pa and the leakage rate is ≤2pa / min.

[0010] Furthermore, in step (2), the shortest length of a single casting is equal to the crucible depth, the auxiliary electrode length, and the distance between the lower limit clamp of the electrode rod and the crucible plane.

[0011] Furthermore, in step (2), the auxiliary electrode is made of stainless steel; a transition electrode of the same material as the electrode being melted is welded to the end face of the auxiliary electrode; the welding area between the auxiliary electrode and the primary consumable electrode is ≥50%, and there are no sharp weld beads on the side of the electrode.

[0012] Furthermore, in step (2), the straight deviation distance of the secondary consumable electrode is ≤10mm; the maximum length of the secondary consumable electrode = upper furnace chamber height + crucible depth - auxiliary electrode length - 10cm.

[0013] Furthermore, in step (3), the vacuum degree inside the furnace during vacuum welding is ≤5pa and the leakage rate is ≤2pa / min.

[0014] Furthermore, in step (3), the current during the feeding process is reduced from 8kA to 4KA, decreasing by 1KA every 1-1.5 minutes; when the melting current is reduced to 4kA, the voltage is set to 25V and held for 2-3 minutes; when the current is reduced to 3.5KA, it is held for 2-3 minutes; when the current is reduced to 2.5-3kA, the voltage is set to 24.5V and held for ≥15 minutes; the total feeding time is ≥25 minutes.

[0015] Furthermore, the heating rate in step (3) is 5-20℃ / min.

[0016] The present invention has the following beneficial effects: (1) Improved ingot performance: Vacuum self-consumable melting (VAR) is a process in which heat generated by electrode discharge under vacuum is used to melt metal. The metal is dripped into a copper crucible for cooling and gradually forms an ingot. Ingots melted in this way have high internal density and good degassing effect, and have a certain impurity removal effect. In addition, the homogenization treatment of the ingot improves the uniformity of ingot composition and structure.

[0017] (2) Improved yield: There is no significant loss in the vacuum self-consumable melting process. The main loss comes from the riser part of the secondary ingot and the peeling of the ingot surface. By feeding the secondary ingot in the later stage and reducing the shrinkage depth, the cutting weight of the riser can be effectively increased. In addition, by controlling the process, the surface quality of the ingot can be improved, so that it can be forged without peeling, resulting in an overall yield of over 99%.

[0018] (3) Low cost: Vacuum induction furnace melting requires the preparation of crucibles, and the crucibles have a limited lifespan. They must be replaced after a certain period of use (e.g., more than 20 times, they need to be remade). Furthermore, the vacuum induction furnaces used for melting nickel-chromium alloys are small in size and have a small melting capacity per batch, resulting in higher melting costs.

[0019] (4) Improved forging performance: By homogenizing the secondary ingot, the uniformity of the ingot structure and composition is improved, and cracking during the forging process is eliminated. Attached Figure Description

[0020] Figure 1 Image of a sputtered nickel-chromium alloy target residue; Figure 2 This is a diagram of a single consumable electrode. Figure 3 A diagram of a single ingot prepared for a single VAR melting process; Figure 4 Diagram of a secondary ingot prepared for secondary VAR melting. Detailed Implementation

[0021] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0022] This invention adapts parameters to an existing 1t-class VAR furnace, with core hardware specifications shown in Table 1, ensuring spatial matching between the electrode, crucible, and furnace chamber. Table 1 Core hardware specifications of embodiments of the present invention

[0023] This invention uses vacuum consumable arc remelting (VAR) to recycle used nickel-chromium alloy targets into high-purity, high-quality nickel-chromium alloy ingots. The process route is as follows: target pretreatment → primary consumable electrode preparation → primary VAR melting → secondary consumable electrode preparation → secondary VAR melting → homogenization treatment. The parameters of each step are adapted to 1t-level hardware.

[0024] Example 1: A method for recycling and smelting nickel-chromium alloy sputtering residue targets is disclosed in this embodiment. The primary smelting crucible in the vacuum consumable arc furnace used in this embodiment has a diameter of φ280*1600mm, and the secondary smelting crucible has a diameter of φ380*2000mm. The specific steps include: (1) Pre-treatment of residual targets: ① Grind the nickel-chromium alloy target scraps to remove surface impurities. Cut nickel-chromium alloy target scraps with a size exceeding 220mm to a width ≤220mm (see...). Figure 1 ); ② Stack the nickel-chromium alloy target residues from step ① layer by layer, and then weld them together using argon arc welding to form a primary consumable electrode (see...). Figure 2 The welding current is 150A and the welding voltage is 36V. One end of the primary consumable electrode is flat to facilitate the welding of the auxiliary electrode. The size of the primary consumable electrode is controlled within φ150-220*2200-2600mm, and its maximum cross-sectional size is ≤220mm, that is, a margin of ≥30mm is left on one side (maximum length of primary consumable electrode = upper furnace chamber height + crucible depth - auxiliary electrode length - 10cm). (2) One VAR melting: ① A φ80mm diameter nickel-chromium dummy electrode is welded onto the end face of the auxiliary electrode using manual argon arc welding; the auxiliary electrode is made of 304 stainless steel, has a diameter of φ80mm, a length of 450mm, and a flat-headed chamfered end face (30°, 20mm). ② The auxiliary electrode of step ① is vacuum welded with the primary consumable electrode of step (1) in the furnace (vacuum degree ≤2pa before welding, leakage rate ≤2pa), argon is purged at 600pa after welding, cooling time ≥20min (temperature ≤300℃), welding area ≥60%; wherein, the arc starting current is 1kA, the voltage is 24V, and the welding current is 3kA during welding; ③ The product obtained in step ② is smelted once. When 4 kg of the product obtained in step ② remains, the smelting current is reduced to 3 kA and smelting is stopped. Then, argon is charged to 600 Pa, and the cooling time is ≥3 hours (temperature ≤300℃) to obtain a primary ingot (see...). Figure 3 The arc-starting current is set to 1kA, the voltage to 24V, and the arc-stabilizing current to 3A DC; the normal melting current is set to 5kA, the voltage to 27V, and the arc-stabilizing current to 3A; the minimum length of a single ingot casting = crucible depth - auxiliary electrode length - distance between the lower limit clamp of the electrode rod and the crucible plane; the minimum weight to be melted is calculated based on the minimum length, i.e., the minimum melting weight G = L * ρ * D 2 / 4*π, where the shortest length of the primary ingot is L, the density of the nickel-chromium alloy is ρ, the diameter of the crucible is D, and π is approximately 3.14; ④ Connect the first ingot from step ③ to the second ingot using argon arc welding to form a secondary consumable electrode (maximum length of the secondary consumable electrode = upper furnace chamber height + crucible depth - auxiliary electrode length - 10cm), without using welding wire, with a welding depth of 10mm. (3) Secondary VAR melting: ① Perform vacuum welding in the furnace on the auxiliary electrode of step (2) and the secondary consumable electrode of step (2) (vacuum degree ≤2pa, leakage rate ≤2pa before welding), purge with argon 500pa after welding, cool for ≥20min (temperature ≤300℃), and then open the furnace to check. The welding area of ​​the auxiliary electrode is ≥50%, and there are no sharp weld beads on the side of the electrode. The arc starting current is set to 1kA, the voltage is set to 26V, the arc stabilizing current is set to 2-4A, the welding current is set to 2.5-4kA, and the voltage is set to 26V. ② Reseal the furnace chamber, evacuate to ≤1pa, with a leakage rate ≤1pa / min, and then perform secondary melting; wherein, the arc ignition current is set to 1kA, the voltage is set to 24V, and the arc stabilization current is set to 3A; the normal melting current is set to 8kA, the voltage is set to 28V, and the arc stabilization current is set to 3-4A. ③ When the remaining product from step ① is 60 kg, begin the feeding operation. Specifically, during feeding, the current is reduced from 8 kA to 4 kA, decreasing by 1 kA every minute. Simultaneously, the voltage is set according to the actual voltage. When the melting current drops to 4 kA, the voltage is set to 25 V and maintained for 2.5 minutes. Then, it is reduced to 3.5 kA and maintained for 2.5 minutes. The current continues to decrease to 2.5-3 kA, and the voltage is set to 24.5 V and maintained for at least 17 minutes (total feeding time ≥ 25 minutes). Melting is stopped when the weight of the product from step ① is 0 kg. Then, argon is charged to 700 Pa, and the cooling time is ≥ 4 hours. The product is then removed, and its top ingot crown is removed to obtain a secondary ingot (see...). Figure 4 ); (4) Homogenization treatment of ingots: Place the secondary ingot from step (3) into a vacuum heat treatment furnace with a vacuum degree of <5pa. Heat it to 600°C at a rate of 8°C / min and hold for 1 hour. Then heat it to 1100°C at a rate of 5°C / min and hold for 2 hours. After completion, stop heating and cool it with the furnace.

[0025] Ingot test results: Ni content 79.8%, Cr content 20.1% (total purity 99.9%), oxygen content 35ppm, density 99.86%, shrinkage cavity depth 40mm, yield 99.2%.

[0026] Experimental example: To verify the impact of parameters on quality, using a φ380mm secondary casting ingot as the target specification and Ni80Cr20 residual target as the raw material (original purity 99.0%, oxygen content 140ppm), two sets of experiments were designed: Experiment 1: Secondary melting was set with three vacuum gradients (0.5Pa, 2Pa, and 6Pa), and other parameters were the same as in Example 1 (normal current 8kA, feeding time 25min); Experiment 2: Primary melting vacuum degree 2pa, with three sets of currents (4kA / 5kA / 6kA); Secondary melting vacuum degree 2pa, with three sets of currents (7kA / 8kA / 9kA) and three sets of feeding times (10min / 25min / 35min); other parameters were the same as in Example 1.

[0027] See Table 2 for specific parameters.

[0028] Table 2 Experimental Parameter Settings

[0029] The test results are shown in Tables 3 and 4.

[0030] Table 2 shows that when the vacuum degree is ≤2Pa, the removal effect of gaseous impurities is optimal, and the purity and density are significantly improved. Table 3 shows that when the primary current is set to 5kA and the secondary current is set to 8kA, combined with a feeding time of ≥25min, both the ingot yield and density can be balanced.

[0031] Table 3 Detection results of experimental group 1

[0032] Table 4 Detection results of experimental group 2

[0033] The results above show that: 1. Vacuum degree: A higher vacuum degree can significantly reduce gas solubility. A high smelting vacuum degree needs to be maintained, and "in-furnace vacuum welding" should be used to avoid secondary gas intake. 2. Melting current: 7.8-8.2kA matching φ380mm crucible. Too low a current will result in insufficient molten pool temperature and poor fluidity; too high a current will easily cause arc instability, increase spatter and affect the surface quality of the ingot. 3. Compensation process: Stepped cooling can avoid "concentration of shrinkage cavities caused by rapid cooling", and low current heat preservation can fill tiny shrinkage cavities, thereby reducing the depth of shrinkage cavities; 4. Homogenization temperature: Homogenization treatment reduces compositional deviation. 1050-1180℃ is the recrystallization temperature range of nickel-chromium alloys, which can eliminate segregation of the as-cast structure and avoid grain coarsening caused by excessive temperature.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling and smelting nickel-chromium alloy sputtering residue targets, characterized in that, Includes the following steps: (1) Pre-treatment of residual targets: ① Grind the surface of the nickel-chromium target residue to remove impurities; ② The nickel-chromium residual target from step ① is stacked and welded to form a primary consumable electrode; wherein the welding current is 100-250A and the voltage is 20-40V; (2) One VAR melting: ① The auxiliary electrode is vacuum welded to the primary consumable electrode of step (1) in the furnace, and argon is used for cooling after welding for ≥20 min; wherein, the arc starting current is 0.5-1.5kA, the voltage is 22-26V, the arc stabilizing current is 2-4A, the welding current is 2.5-4kA, and the voltage is 22-26V. ② The product obtained in step ① is smelted once; wherein the arc starting current is 1-2kA, the voltage is 24-26V, and the arc stabilizing current is 2-4A; the normal smelting current is 4.5-5.5kA, the voltage is 27-28V, and the arc stabilizing current is 2-4A. ③When the product obtained in step ① is 2-4kg, reduce the current to 4kA until the consumable electrode is completely melted and stop the melting process. Then, fill the furnace with argon at 500-1000pa and cool for ≥3h to obtain a primary ingot. ④ Connect the first and last ends of the primary ingot from step ③ and weld them together to form a secondary consumable electrode; (3) Secondary VAR melting: ① Perform vacuum welding of the auxiliary electrode and the secondary consumable electrode in step (2) in the furnace. After welding, purge with argon at 500-2000 Pa and cool for ≥20 min. The arc starting current is 0.5-1.5 kA, the voltage is 26 V, the arc stabilizing current is 2-4 A, and the welding current is 2.5-4 kA and the voltage is 26 V. ② The product obtained in step ① is subjected to secondary melting; wherein, the arc starting current is 1-2kA, the voltage is 24-26V, the arc stabilizing current is 2-4A, the normal melting current is 7.5-8.5kA, the voltage is 28-29V, and the arc stabilizing current is 2-4A. ③ When 60kg of the product obtained in step ① remains, feeding is performed. When the secondary consumable electrode is completely melted, smelting is stopped, the furnace is filled with argon, and the cooling time is ≥4h to obtain a secondary ingot. (4) Homogenization treatment of ingots: After heating the secondary ingot from step (3) to 600-650℃, hold it for 1 hour, then continue to heat it to 1050-1180℃ and hold it for 2-3 hours, then cool it to room temperature.

2. The recycling and smelting method according to claim 1, characterized in that, The width of the nickel-chromium residual target mentioned in step (1) is ≤230mm.

3. The recycling and smelting method according to claim 1, characterized in that, The density of the primary consumable electrode in step (1) is 5-6.5 g / cm³, and the straight deviation distance is ≤10 mm; the diagonal of the cross section of the primary consumable electrode is ≤ the diameter of the crucible; the maximum length of the primary consumable electrode is = upper furnace chamber height + crucible depth - auxiliary electrode length - 10 cm.

4. The recycling and smelting method according to claim 1, characterized in that, When performing vacuum welding in the furnace as described in step (2), the vacuum level inside the furnace is ≤5pa and the leakage rate is ≤2pa / min.

5. The recycling and smelting method according to claim 1, characterized in that, The shortest length of a single casting in step (2) is equal to the crucible depth, the auxiliary electrode length, and the distance between the lower limit clamp of the electrode rod and the crucible plane.

6. The recycling and smelting method according to claim 1, characterized in that, The auxiliary electrode in step (2) is made of stainless steel; a transition electrode of the same material as the electrode being melted is welded to the end face of the auxiliary electrode; the welding area between the auxiliary electrode and the primary consumable electrode is ≥50%, and there are no sharp weld beads on the side of the electrode.

7. The recycling and smelting method according to claim 1, characterized in that, The linear deviation distance of the secondary consumable electrode in step (2) is ≤10mm; the maximum length of the secondary consumable electrode = upper furnace chamber height + crucible depth - auxiliary electrode length - 10cm.

8. The recycling and smelting method according to claim 1, characterized in that, The vacuum degree inside the furnace during the vacuum welding process described in step (3) is ≤5pa, and the leakage rate is ≤2pa / min.

9. The recycling and smelting method according to claim 1, characterized in that, In step (3), the current during the feeding process is reduced from 8kA to 4KA, decreasing by 1KA every 1-1.5 minutes; when the melting current is reduced to 4kA, the voltage is set to 25V and held for 2-3 minutes; when the current is reduced to 3.5KA, it is held for 2-3 minutes; when the current is reduced to 2.5-3kA, the voltage is set to 24.5V and held for ≥15 minutes; the total feeding time is ≥25 minutes.

10. The recycling and smelting method according to claim 1, characterized in that, The heating rate in step (3) is 5-20℃ / min.

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