Preparation method of tungsten-rhenium alloy surface coating

Abstract

The invention belongs to the field of tungsten-rhenium alloy surface treatment, and particularly discloses a preparation method of a tungsten-rhenium alloy surface coating. According to the method, the tungsten-rhenium alloy serves as a cathode, tungsten metal serves as a source electrode, methane and argon serve as gas sources, and a coating is deposited on the surface of the tungsten-rhenium alloy through a double-layer glow plasma alloying method; and annealing is conducted, a coating with high wear resistance and high binding force is obtained on the surface of the tungsten-rhenium alloy, the wear resistance and hardness of the tungsten-rhenium alloy can be improved, the adaptability of the tungsten-rhenium alloy and a workpiece thereof in the extreme environment is improved, and the service life of the tungsten-rhenium alloy and the workpiece thereof in the extreme environment is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of tungsten-rhenium alloy surface treatment, and in particular relates to a method for preparing a tungsten-rhenium alloy surface coating. Background Art

[0002] As the metal with the highest melting point, tungsten and its alloys are widely used in aviation, aerospace, navigation, electronic circuits, nuclear power engineering, medical equipment, weapons and equipment, etc. due to its excellent hardness, density, thermal conductivity and low thermal expansion coefficient. China has abundant tungsten resources and has become the world's largest exporter of tungsten raw materials. However, the current export products are mainly sintered billets and powders, and high-performance tungsten alloy deep-processed products still need to be imported.

[0003] Friction stir welding is a new solid phase welding technology invented by the British Welding Research Institute in 1991. It has the advantages of energy saving, environmental protection, high quality and high efficiency. Since its invention, it has received widespread attention. It is also the connection technology with the shortest time span from invention to industrial application in the history of world welding technology development. Friction stir welding has been widely used in aviation, aerospace, shipbuilding, rail transportation, automobile and other industrial fields, and has now become the preferred welding process for high-strength aluminum alloys and magnesium alloys. In addition to aluminum and magnesium alloys, friction stir welding also has advantages in high melting point metals such as copper, steel, and titanium alloys, and has received more and more widespread attention. However, in the process of high melting point metal welding, due to the intense friction of the friction stir head, the temperature can reach 1000℃, which has exceeded the recrystallization temperature of traditional iron-based materials. At such a high temperature, the strength of iron-based materials will drop rapidly, resulting in a rapid decrease in the service life of the material. Since tungsten alloys, especially tungsten-rhenium alloys, have a high recrystallization temperature, they have shown great potential in high melting point metal friction stir welding.

[0004] The high melting point, high strength and high hardness of tungsten-rhenium alloy enable the tungsten-rhenium alloy stirring head to maintain excellent stability and durability in high temperature and high pressure welding environments, thereby ensuring the efficiency and reliability of the welding process. In addition, the excellent plasticity and low ductile-brittle transition temperature of tungsten-rhenium alloy enable it to flexibly adapt to various process requirements during the welding process and reduce the risk of material fracture and failure. Therefore, tungsten-rhenium alloy is an ideal choice for stir friction welding technology, which can significantly improve welding quality and efficiency.

[0005] Although tungsten-rhenium alloy itself has extremely excellent properties, including high melting point, high strength, high hardness, etc., which make it have excellent performance in many fields, in order to meet more stringent wear resistance requirements, especially in some extreme working environments, further improving the hardness and wear resistance of tungsten-rhenium alloy is still an urgent problem to be solved. The preparation of coatings on the surface of tungsten-rhenium alloy can significantly improve the hardness and wear resistance of tungsten-rhenium alloy. As a stirring friction head, tungsten-rhenium alloy needs to face heavy loads and high temperatures. This harsh condition also puts forward requirements for the coating. The coating must have a large thickness and excellent bonding strength. The coating formed by diffusion shows great potential in this area. The coating formed by atomic diffusion has a high bonding strength due to the existence of metallurgical bonding, but the atomic diffusion rate also limits the coating thickness.

[0006] Therefore, how to prepare a coating with large thickness and excellent bonding strength on the surface of tungsten-rhenium alloy, so as to improve the wear resistance of tungsten-rhenium alloy in extreme environments, is the key to promoting the application of tungsten-rhenium alloy in the field of stirring heads. Summary of the invention

[0007] In view of the problems involved in the above-mentioned prior art, the present invention provides a method for preparing a tungsten-rhenium alloy surface coating. The coating prepared by the method of the present invention has a large thickness, high hardness and bonding strength, and can withstand high loads without falling off, thereby improving the wear resistance of the tungsten-rhenium alloy in extreme environments, and can solve the technical problem that the wear resistance of the tungsten-rhenium alloy in the prior art is difficult to meet the requirements of heavy load and high temperature service performance.

[0008] To achieve the above purpose, the following technical solutions are specifically included:

[0009] A method for preparing a tungsten-rhenium alloy surface coating comprises the following steps:

[0010] (1) Using tungsten-rhenium alloy as cathode, tungsten metal as source, methane and argon as gas sources, a double-layer glow plasma alloying method is used to deposit a coating on the surface of tungsten-rhenium alloy;

[0011] (2) The tungsten-rhenium alloy with the deposited coating is annealed to obtain a tungsten-rhenium alloy containing a tungsten carbide coating.

[0012] In the method of the present invention, a double-layer glow plasma alloying technology is first used to prepare a deposited coating on the surface of the tungsten-rhenium alloy, wherein, on the one hand, under the ionization of a methane and argon gas mixture at a high voltage, methane can be decomposed into active carbon atoms and hydrogen, and the active carbon atoms can be deposited on the surface of the tungsten-rhenium alloy substrate; on the other hand, unlike traditional ion nitriding and carburizing, the method of the present invention uses a tungsten target as a source electrode, and the tungsten target can withstand a high temperature, and it and the cathode jointly produce a hollow cathode effect, which increases the actual operating temperature of the cathode workpiece, and at the same time, the tungsten metal at the source electrode will sputter out tungsten atoms, and the tungsten atoms can be deposited on the surface of the tungsten-rhenium alloy substrate; in addition, the active carbon atoms are more likely to react with the tungsten sputtered from the source electrode to form tungsten carbide and deposit on the alloy surface; and the presence of hydrogen can remove tungsten. The impurities on the surface of the rhenium alloy activate the surface of the tungsten-rhenium alloy and accelerate the diffusion rate of carbon atoms into the matrix. Therefore, on the surface of the alloy, there are tungsten atom deposition, carbon atom deposition, carbon atom diffusion into the matrix and surface deposition of tungsten carbide at the same time, which significantly increases the thickness of the deposited coating, and deposits a thick tungsten carbide coating on the surface of the tungsten-rhenium alloy; the tungsten-rhenium alloy after the deposition coating is annealed to achieve the metallurgical bonding effect between the coating and the tungsten-rhenium alloy matrix, so that the coating and the matrix have a high bonding force, improve the wear resistance and hardness of the tungsten-rhenium alloy surface, so that the coating on the surface of the tungsten-rhenium alloy can withstand high loads without falling off, and improve the adaptability and service life of the tungsten-rhenium alloy and its products in extreme environments (such as high loads, high temperatures, etc.). In addition, the double-layer glow plasma alloying technology of the present invention is used to prepare the coating. Because the heat of the entire sample is generated by the bombardment of a large number of particles generated by the hollow cathode effect between the cathode and the source, the high-temperature area is limited to the cathode workpiece and the source, the heating area is small, and energy is saved.

[0013] Preferably, in step (1), in the double-layer glow plasma alloying method, the cathode voltage is 400-600V, the source voltage is 800-1000V, the cathode temperature is 1300-1500°C, the cathode insulation time is 4-6h, the cathode duty cycle is 0.7-0.95, the distance between the cathode and the source is 10-20mm, the mass flow ratio of methane and argon is 1:(1-4), and the gas pressure is 30-50Pa.

[0014] Preferably, in step (1), the tungsten-rhenium alloy is further ground and polished.

[0015] Preferably, in step (1), the tungsten-rhenium alloy is further cleaned by argon ion bombardment, and during the argon ion bombardment cleaning, the gas pressure is 15-30 Pa, the voltage is 500-600 V, and the time is 20-40 min.

[0016] Preferably, in step (1), the tungsten metal is also cleaned by argon ion bombardment, and during the argon ion bombardment cleaning, the gas pressure is 15-30 Pa, the voltage is 900-1100 V, and the time is 20-40 min.

[0017] Preferably, in step (1), in the double-layer glow plasma alloying method, when reducing the voltages of the cathode and the source, the rate of reducing the cathode voltage is 1-15 V / min, and the rate of reducing the source voltage is 5-20 V / min.

[0018] Preferably, in step (2), the annealing temperature is 900-1100° C., the annealing time is 0.5-4 h, and the annealing atmosphere is a hydrogen atmosphere.

[0019] Annealing can reduce the internal stress of the coating, and annealing in a hydrogen atmosphere can protect the substrate and coating from oxidation and prevent tungsten carbide from reacting with oxygen at high temperatures. However, the annealing time in hydrogen should not be too long. If the time is too long and / or the temperature is too high, tungsten carbide will react with hydrogen to generate methane and decarburize the coating. In the above temperature and time range, basically no obvious reaction occurs.

[0020] The present invention also provides a tungsten-rhenium alloy or a tungsten carbide coating containing a tungsten carbide coating obtained by the preparation method of the tungsten-rhenium alloy surface coating.

[0021] Preferably, in the tungsten-rhenium alloy or tungsten carbide coating containing the tungsten carbide coating, the thickness of the tungsten carbide coating is 150-300 μm.

[0022] Further preferably, in the tungsten-rhenium alloy or tungsten carbide coating containing the tungsten carbide coating, the thickness of the tungsten carbide coating is 200-250 μm.

[0023] Preferably, in the tungsten-rhenium alloy or the tungsten carbide coating containing the tungsten carbide coating, the tungsten carbide coating has a hexagonal crystal phase structure.

[0024] Preferably, the hardness of the tungsten-rhenium alloy containing the tungsten carbide coating is greater than or equal to 600 HV.

[0025] Preferably, the tungsten-rhenium alloy containing tungsten carbide coating is subjected to a friction test in a circumferential ball-disc friction high-temperature testing machine, and the friction test parameters are: temperature of 1000°C, friction radius of 3mm, rotation speed of 560rpm, load of 50N, and time of 60min. The test shows that the wear rate of the tungsten-rhenium alloy containing tungsten carbide coating is less than or equal to 10 -6 mm 3 ·N -1 ·m -1 .

[0026] The present invention also provides an application of the tungsten-rhenium alloy or tungsten carbide coating containing the tungsten carbide coating in preparing a stirring head. The stirring head made of the tungsten-rhenium alloy or tungsten carbide coating containing the tungsten carbide coating of the present invention has higher wear resistance, higher hardness, and higher coating stability than conventional tungsten-rhenium alloy without coating, and is very suitable for application in the field of stir friction welding.

[0027] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses tungsten-rhenium alloy as cathode, tungsten metal as source, methane and argon as gas sources, and adopts double-layer glow plasma alloying method to deposit coating on the surface of tungsten-rhenium alloy; and then after annealing, a coating with high wear resistance and high bonding strength is obtained on the surface of tungsten-rhenium alloy, which can improve the wear resistance and hardness of tungsten-rhenium alloy, and improve the adaptability and service life of tungsten-rhenium alloy and its products in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flow chart of the method for coating the surface of tungsten-rhenium alloy.

[0029] Figure 2 This is a metallographic image of the cross section of the tungsten-rhenium alloy surface coating in Example 1.

[0030] Figure 3 The XRD spectrum of the tungsten-rhenium alloy surface coating in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels. The tungsten-rhenium alloys used below are all W-25Re alloys (Re content is 25wt%). The Re content in the tungsten-rhenium alloy is not specifically limited. The purpose of the present invention can be achieved by using conventional tungsten-rhenium alloys. Specifically, a tungsten-rhenium alloy with a Re content of 1-26wt% can be used.

[0032] Example 1

[0033] A method for preparing a tungsten-rhenium alloy surface coating, the specific process flow chart is as follows Figure 1 As shown, the specific steps include:

[0034] (1) Pretreatment of substrate materials:

[0035] Prepare tungsten-rhenium alloy, grind it step by step on 180#, 300#, 600#, 1000#, 1200#, 1500#, and 2000# metallographic sandpaper, polish it with flannel cloth until it reaches a scratch-free mirror surface, then place it in alcohol for ultrasonic cleaning and set aside.

[0036] (2) Cleaning and placing workpieces:

[0037] The tungsten-rhenium alloy cleaned in step (1) is loaded into the furnace. Before loading, the inner wall of the furnace body and the surface of the target material are polished with fine sandpaper. After removing the surface oxide film and impurities, they are wiped with a dust-free cloth dipped in anhydrous ethanol. The tungsten-rhenium alloy is used as the cathode and the pure tungsten target is used as the source. The distance between the cathode and the source is 15 mm.

[0038] (3) Vacuuming:

[0039] Turn on the mechanical pump and open the mechanical pump exhaust valve. When the air pressure is pumped below 5Pa, open the electromagnetic isolation valve. When the air pressure is pumped below 1Pa, turn on the molecular pump to pump the air pressure in the furnace to 1×10 -3 Pa. Then, argon gas was introduced and the molecular pump and electromagnetic isolation valve were closed.

[0040] (4) Gas washing:

[0041] Close the mechanical pump valve, control the Ar flowmeter to adjust the Ar flow, raise the gas pressure to normal pressure, then close the Ar flow, open the mechanical pump valve and pump the gas to below 10Pa. Repeat this operation three times to complete the gas washing step.

[0042] (5) Source and cathode cleaning:

[0043] Turn on the equipment circulation water and adjust the argon pressure in the furnace to 20Pa, turn on the cathode power supply, increase it to 550V, and keep it at this voltage for 30 minutes. After that, turn on the source power supply, increase it to 1000V, and keep it for 20 minutes. In this process, the bombardment of Ar ions can remove pollutants on the surface of the substrate and target, including oil stains and oxides.

[0044] (6) Boosting process:

[0045] By adjusting the argon mass flow meter and the mechanical pump valve, the gas pressure is adjusted to below 10Pa, the source voltage and cathode voltage are slowly increased to the set voltage, and then methane is introduced by adjusting the mass flow rate, and the methane and argon flow ratio is adjusted to 1:1. The mechanical pump valve is used to slowly increase the gas pressure and finally adjust it to a working pressure of 40Pa;

[0046] (7) Tungsten-rhenium alloy surface deposition coating process:

[0047] The workpiece (cathode) voltage was set to 600 V, the target voltage (source) was set to 900 V, the workpiece duty cycle was adjusted to 0.9, the workpiece temperature was maintained at 1400°C, the holding time was 4 hours, and a coating was deposited on the tungsten-rhenium alloy surface.

[0048] (8) Depressurization process:

[0049] Slowly reduce the source and cathode voltages, with the source voltage reduction rate of 10V / min and the cathode voltage reduction rate of 6V / min. The entire voltage reduction process needs to last for more than half an hour. When the voltage drops to a lower value, it can be directly turned off. This process needs to avoid the voltage reduction rate being too fast, which will cause the temperature to drop rapidly and cause greater thermal stress on the coating.

[0050] (9) Annealing treatment:

[0051] The tungsten-rhenium alloy after the deposition coating is placed in a hydrogen furnace for high-temperature annealing treatment. The annealing temperature is 1000°C and the annealing time is 1 hour. Finally, a high-hardness and wear-resistant carbide coating is prepared on the surface of the tungsten-rhenium alloy.

[0052] Example 2

[0053] A method for preparing a tungsten-rhenium alloy surface coating, the specific process flow chart is as follows Figure 1 As shown, the specific steps include:

[0054] (1) Pretreatment of substrate materials:

[0055] Prepare tungsten-rhenium alloy, grind it step by step on 180#, 300#, 600#, 1000#, 1200#, 1500#, and 2000# metallographic sandpaper, polish it with flannel cloth until it reaches a scratch-free mirror surface, then place it in alcohol for ultrasonic cleaning and set aside.

[0056] (2) Cleaning and placing workpieces:

[0057] The tungsten-rhenium alloy cleaned in step (1) is loaded into the furnace. Before loading, the inner wall of the furnace body and the surface of the target material are polished with fine sandpaper. After removing the surface oxide film and impurities, they are wiped with a dust-free cloth dipped in anhydrous ethanol. The tungsten-rhenium alloy is used as the cathode and the pure tungsten target is used as the source. The distance between the cathode and the source is 15 mm.

[0058] (3) Vacuuming:

[0059] Turn on the mechanical pump and open the mechanical pump exhaust valve. When the air pressure is pumped below 5Pa, open the electromagnetic isolation valve. When the air pressure is pumped below 1Pa, turn on the molecular pump to pump the air pressure in the furnace to 1×10 -3 Pa. Then, argon gas was introduced and the molecular pump and electromagnetic isolation valve were closed.

[0060] (4) Gas washing:

[0061] Close the mechanical pump valve, control the Ar flowmeter to adjust the Ar flow, raise the gas pressure to normal pressure, then close the Ar flow, open the mechanical pump valve and pump the gas to below 10Pa. Repeat this operation three times to complete the gas washing step.

[0062] (5) Source and cathode cleaning:

[0063] Turn on the equipment circulation water and adjust the gas pressure in the furnace to 20Pa, turn on the cathode power supply, increase it to 550V, and keep it at this voltage for 30 minutes. After that, turn on the source power supply, increase it to 1000V, and keep it for 20 minutes. In this process, the bombardment of Ar ions can remove pollutants on the surface of the substrate and target, including oil stains and oxides.

[0064] (6) Boosting process:

[0065] By adjusting the argon mass flow meter and the mechanical pump valve, the gas pressure is adjusted to below 10Pa, the source voltage and cathode voltage are slowly increased to the set voltage, and then methane is introduced by adjusting the mass flow rate, and the methane and argon flow ratio is adjusted to 1:1. The mechanical pump valve is used to slowly increase the gas pressure and finally adjust it to a working pressure of 40Pa;

[0066] (7) Tungsten-rhenium alloy surface deposition coating process:

[0067] The workpiece (cathode) voltage was set to 600 V, the target voltage (source) was set to 900 V, the workpiece duty cycle was adjusted to 0.8, the workpiece (cathode) temperature was maintained at 1300°C, the holding time was 4 hours, and a coating was deposited on the tungsten-rhenium alloy surface.

[0068] (8) Depressurization process:

[0069] Slowly reduce the source and cathode voltages, with the source voltage reduction rate of 10V / min and the cathode voltage reduction rate of 6V / min. The entire voltage reduction process needs to last for more than half an hour. When the voltage drops to a lower value, it can be directly turned off. This process needs to avoid the voltage reduction rate being too fast, which will cause the temperature to drop rapidly and cause greater thermal stress on the coating.

[0070] (9) Annealing treatment:

[0071] The tungsten-rhenium alloy after the deposition coating is placed in a hydrogen furnace for high-temperature annealing treatment. The annealing temperature is 1000°C and the annealing time is 1 hour. Finally, a high-hardness and wear-resistant carbide coating is prepared on the surface of the tungsten-rhenium alloy.

[0072] The tungsten-rhenium alloy containing the coating in the above Example 1 was subjected to metallographic test and XRD test. The test results are shown in the attached Figure 2-3 Among them. From Figure 2 It can be observed that on the surface of the tungsten-rhenium alloy, the coating and the substrate are well bonded, no cracks are seen at the bonding point, and the entire coating thickness is above 200μm. Figure 3 From the XRD analysis, it can be seen that the surface layer of the coating is tungsten carbide, which is a hard phase and belongs to the hexagonal crystal phase, which can well improve the hardness of the surface of the tungsten-rhenium alloy.

[0073] The tungsten-rhenium alloy with coating and the tungsten-rhenium alloy without coating in Example 1-2 were subjected to hardness test and friction test respectively, wherein the friction test used a circular ball-disc friction high temperature tester, and the friction test parameters were: temperature of 1000°C, friction radius of 3mm, rotation speed of 560rpm, load of 50N, and time of 60min. The test results are shown in Table 1.

[0074] Table 1

[0075] Alloy Type Hardness / HV <![CDATA[Wear rate / 10 -6 mm 3 ·N -1 ·m -1 > W-25Re alloy 530 141.03 Example 1 1032 25.91 Example 2 973 46.91

[0076] It can be seen from Table 1 that the hardness of the coated tungsten-rhenium alloy in Example 1-2 is much higher than that of the W-25Re alloy without coating, and the wear rate is also much lower than that of the W-25Re alloy without coating. The method of preparing a coating on the surface of the tungsten-rhenium alloy of the present invention enables the surface of the tungsten-rhenium alloy to be covered with a tungsten carbide coating, which can significantly improve the hardness and wear resistance of the surface of the tungsten-rhenium alloy.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a tungsten-rhenium alloy surface coating, characterized in that: The steps include: (1) Using tungsten-rhenium alloy as cathode, tungsten metal as source, methane and argon as gas sources, a double-layer glow plasma alloying method is used to deposit a coating on the surface of tungsten-rhenium alloy; (2) The tungsten-rhenium alloy with the deposited coating is annealed to obtain a tungsten-rhenium alloy containing a tungsten carbide coating.

2. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (1), in the double-layer glow plasma alloying method, the cathode voltage is 400-600V, the source voltage is 800-1000V, the cathode temperature is 1300-1500°C, the cathode insulation time is 4-6h, the cathode duty cycle is 0.7-0.95, the distance between the cathode and the source is 10-20mm, the mass flow ratio of methane and argon is 1:(1-4), and the gas pressure is 30-50Pa.

3. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (2), the annealing temperature is 900-110° C., the annealing time is 0.5-4 h, and the annealing atmosphere is a hydrogen atmosphere.

4. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (1), the tungsten-rhenium alloy is further ground and polished.

5. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (1), the tungsten-rhenium alloy is also cleaned by argon ion bombardment. During the argon ion bombardment cleaning, the gas pressure is 15-30 Pa, the voltage is 500-600 V, and the time is 20-40 min.

6. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (1), the tungsten metal is also cleaned by argon ion bombardment. During the argon ion bombardment cleaning, the gas pressure is 15-30 Pa, the voltage is 900-1100 V, and the time is 20-40 min.

7. The method for preparing the tungsten-rhenium alloy surface coating according to claim 1, characterized in that: In step (1), in the double-layer glow plasma alloying method, when reducing the voltages of the cathode and the source, the rate of reducing the cathode voltage is 1-15V / min, and the rate of reducing the source voltage is 5-20V / min.

8. A tungsten-rhenium alloy or tungsten carbide coating containing a tungsten carbide coating obtained by the method for preparing a tungsten-rhenium alloy surface coating according to any one of claims 1 to 7.

9. The tungsten-rhenium alloy or tungsten carbide coating containing a tungsten carbide coating according to claim 8, characterized in that: In the tungsten-rhenium alloy or tungsten-carbide coating containing a tungsten-carbide coating, the thickness of the tungsten-carbide coating is 150-300 μm.

10. Use of the tungsten-rhenium alloy containing tungsten carbide coating or tungsten carbide coating according to claim 8 or 9 in preparing a stirring head.

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