A method for alloying and preparing a coating on the surface of pure magnesium

Abstract

The present invention discloses a method for alloying and preparing a coating on the surface of pure magnesium, comprising the following steps: (1) alloying the surface of pure magnesium: using dual-glow plasma alloying technology, the heat-insulating cover used is a pure zinc plate, connected to the cathode stage, the heat-insulating cover is connected to the target zinc sheet, the pure magnesium is connected to another cathode electrode as a substrate, and the cavity is grounded as an anode; (2) preparing a composite coating: using magnetron sputtering technology to plate the zinc-alloyed pure magnesium, using one or both of high-purity metal oxides or precious metals as targets. The present invention uses dual-glow plasma surface alloying to prepare a pure magnesium surface alloy layer, which serves as a transition layer, and then uses magnetron sputtering to prepare a functional coating on the transition layer. The method used is safe and pollution-free, and the resulting coating has uniform composition, low porosity, a large deposition area, strong bonding with the substrate, and easy control of the thickness and composition of the coating.

Description

Technical Field

[0001] The invention relates to a surface modification method, in particular to a method for alloying and preparing a coating on the surface of pure magnesium. Background Art

[0002] Magnesium and its alloys have a wide range of applications in the automotive, aerospace, and biomedical fields due to their light weight, high specific strength, excellent electromagnetic shielding properties, good shock resistance, easy processing, recyclability, and good biocompatibility and degradability. Currently, traditional biomedical metal implants, such as titanium, titanium alloys, and stainless steel, are bioinert and require secondary surgery to remove these implants, which significantly increases medical costs and delays the recovery process. Magnesium and its alloys are promising biodegradable implant materials because their elastic modulus and compressive yield strength are close to those of human bone, thus avoiding stress shielding. However, the degradation rate of magnesium and its alloys is difficult to control and their surface strength is insufficient, which limits their widespread application in the biomedical field.

[0003] To overcome the shortcomings of magnesium and its alloys, surface modification has become an effective method for improving their corrosion resistance, mechanical properties, and biocompatibility. Surface modification methods include ion implantation, plasma spraying, laser plasma technology, and physical vapor deposition (PVD). Ion implantation is a process that bombards high-energy ions into the surface of a substrate. This method allows for selective surface modification without adversely affecting the substrate, but its high cost and relatively shallow modification depth have hindered its further development. Plasma spraying involves melting a material into droplets and energetically spraying them onto a surface, causing the individual particles to adhere and solidify. This technique can form a coating from any molten material, minimally heats the substrate during deposition, and allows for the stripping and reapplying of worn or damaged coatings without altering the component's performance or dimensions. However, this technique has a limited process scope, cannot coat small, deep cavities, and requires sealing of the coating. The surface of magnesium and its alloys can be modified using high-intensity energy laser beams to achieve finer microstructures, but this is costly and complex. The double-layer glow plasma discharge phenomenon has been successfully applied to the preparation of alloying layers on different metal surfaces, but it is rarely used for alloying low-melting-point metal surfaces. Summary of the Invention

[0004] Purpose of the invention: In order to solve the technical problems existing in the prior art, the present invention aims to provide a method for alloying and preparing a coating on the surface of pure magnesium with low cost, controllable modification depth and good modification effect.

[0005] Technical solution: The method for alloying and preparing a coating on the surface of pure magnesium according to the present invention comprises the following steps:

[0006] (1) Alloying on the surface of pure magnesium: using double glow plasma alloying technology, the heat preservation cover used is made of pure zinc plate, connected to the cathode stage, the heat preservation cover is connected to the target zinc sheet, pure magnesium is used as the substrate and connected to the other cathode electrode, and the cavity is grounded as the anode; under high vacuum protection, the target zinc sheet and pure magnesium are first pre-bombarded, and then the target zinc sheet is low-glow bombarded and deposited. After rapid cooling and heat preservation, zinc alloyed pure magnesium is obtained;

[0007] (2) Preparation of composite coating: The zinc alloyed pure magnesium is plated by magnetron sputtering technology, and one or two of high-purity metal oxides or precious metals are used as targets. The zinc alloyed pure magnesium is pre-sputtered under high vacuum protection, and then the target is sputtered to obtain pure magnesium with coating and zinc alloy.

[0008] Furthermore, in step (1), the parameters of the pre-bombardment are: working pressure of 20-35 Pa, two cathode voltages of 100-250 V, bombardment time of 1-10 min; the parameters of the low-glow bombardment are: insulation cover voltage of 200-450 V, working temperature of 200-350 ° C, bombardment time of 5-60 min; the parameters of the high vacuum are: vacuum degree of 3×10 -4 -6×10 -4 Pa; the parameters for rapid cooling and insulation are: working pressure of 10-25Pa, insulation of 10-60min, the pure magnesium substrate is suspended and placed in the center of the insulation cover without contacting the target.

[0009] Furthermore, in step (2), the metal oxide is titanium dioxide, and the noble metal is tantalum, niobium or zirconium; the distance between the target and the zinc-alloyed pure magnesium is 5-8 cm, and the pre-sputtering time is 5-10 min. The functions of the pre-sputtering are: on the one hand, it can clean the surface of the sample to be sputtered, and on the other hand, it can activate the surface of the sample to be sputtered to facilitate the adsorption of active atoms; the sputtering time of the target is 10-120 min, the RF power of sputtering the metal oxide is 100-350 W, and the DC power of sputtering the noble metal is 100-200 W. The coated and zinc-alloyed pure magnesium has a zinc layer as an intermediate layer and a metal oxide layer or a noble metal layer or a composite layer of metal oxide and noble metal as a coating.

[0010] Principle of the invention: The present invention utilizes the double glow discharge phenomenon and uses high-purity, low-melting-point metal zinc as the target material. First, a magnesium-zinc alloy layer is prepared on the surface of pure magnesium that has been simply mechanically polished. This alloy layer not only plays a role in surface mechanical reinforcement, but also can improve the surface structure of pure magnesium. This is used as a transition layer, and then titanium dioxide and precious metal tantalum are used as target elements. With the help of magnetron sputtering technology, a coating is sputtered and deposited on the surface of the metal substrate, further improving the mechanical properties and degradation properties of pure magnesium.

[0011] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0012] (1) The pure magnesium material with coating and zinc alloy prepared by the present invention not only has excellent biocompatibility, mechanical properties and corrosion resistance, but also has controllable degradation. Experimental data show that the hardness of the pure magnesium is only 38HV compared with that of the untreated pure magnesium. 10 The hardness of the modified pure magnesium is increased to 185HV 10 , increased by 4.9 times;

[0013] (2) The present invention combines dual-glow plasma alloying technology with magnetron sputtering technology to perform surface treatment on pure magnesium. The process is simple, safe and environmentally friendly, the degree of modification is controllable, the raw material utilization rate is high, the cost is low, and it is suitable for the surface treatment of large quantities of pure magnesium substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The microstructure and element distribution of the material obtained in Example 1 of the present invention;

[0015] Figure 2 The microstructure and element distribution of the material obtained in Example 3 of the present invention;

[0016] Figure 3 The cross-sectional morphology and element distribution diagram of the material obtained in Example 3 of the present invention;

[0017] Figure 4 The microstructure and element distribution of the material obtained in Example 4 of the present invention;

[0018] Figure 5 This is the cross-sectional morphology of the material obtained in Example 4 of the present invention;

[0019] Figure 6 The microscopic morphology and element distribution diagram of the material obtained in Comparative Example 2 of the present invention;

[0020] Figure 7 The cross-sectional morphology and element distribution diagram of the material obtained in Comparative Example 2 of the present invention;

[0021] Figure 8 This is a comparison chart of the hardness of the materials obtained in Comparative Example 1, Comparative Example 2, and Example 2 of the present invention;

[0022] Figure 9 Polarization curves of the materials obtained in Comparative Example 1, Comparative Example 2, and Example 2 of the present invention;

[0023] Figure 10 This is a schematic top view of the dual-glow plasma equipment used in the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below with reference to specific embodiments and accompanying drawings.

[0025] Example 1: The method for alloying and preparing a coating on the surface of pure magnesium according to the present invention comprises the following steps:

[0026] (1) Alloying on pure magnesium surface:

[0027] ①Put the base pure magnesium wiped with anhydrous ethanol into a heat preservation cover made of pure zinc plate. The heat preservation cover is connected to a cathode stage in a double-layer glow plasma furnace. The target zinc sheet is placed around the heat preservation cover. The base pure magnesium is connected to another cathode electrode. The cavity is grounded as an anode.

[0028] ② High vacuum protection: Turn on the double-layer glow plasma alloying water pump equipment, use a mechanical pump to pump the furnace pressure to 3Pa, and then use a molecular pump to further pump the furnace pressure to 4×10 -4 Pa, to keep the furnace in high vacuum state;

[0029] ③ Low-glow bombardment and deposition: fill with argon gas to 25Pa, turn on the two cathode power supplies and apply 250V voltage respectively, pre-bombard the target zinc sheet and the substrate pure magnesium for 10 minutes. After the pre-bombardment, gradually adjust the insulation cover voltage to the test value of 300V, so that the target zinc sheet reaches the working temperature of 200℃, stabilize the process parameters and start insulation for 5min-10min;

[0030] ④ Rapid cooling and heat preservation: quickly turn off the power supply of the target and workpiece substrate, and adjust the argon gas to the working pressure of 15Pa, and continue to maintain it for 10-60 minutes;

[0031] ⑤Turn off the cathode power supply and argon gas source in sequence, and evacuate the vacuum furnace to 3×10 -4 Pa vacuum, cooled to room temperature and taken out of the furnace to obtain pure magnesium alloyed with zinc, namely MgZn;

[0032] (2) Preparation of composite coating:

[0033] ① Place Mg-Zn on the magnetron sputtering stage and install a high-purity titanium dioxide target. The distance between the target and the sample is kept at 6 cm.

[0034] ② High vacuum protection: Turn on the plasma sputtering equipment and its supporting cooling system, use a mechanical pump to pump the pressure of the coating furnace to below 3Pa, and then use a molecular pump to further pump the pressure of the furnace to 5×10 -4 Pa, to keep the furnace in high vacuum state;

[0035] ③ Fill the furnace with argon gas to 2Pa and pre-sputter the sample for about 10 minutes;

[0036] ④ After pre-sputtering, turn on the RF power supply, adjust the RF power to 200W, and sputter titanium dioxide for 60 minutes;

[0037] ⑤ After sputtering is completed, the target baffle, DC power supply, and argon gas source are turned off in sequence, the furnace is cooled to room temperature, and then the gas is vented and sampled to obtain pure magnesium with titanium dioxide coating and zinc alloy, which is marked as MgZn-TiO2.

[0038] Example 2: The method for alloying and preparing a coating on the surface of pure magnesium according to the present invention comprises the following steps:

[0039] (1) Alloying on pure magnesium surface:

[0040] ①Pure magnesium wiped with anhydrous ethanol is placed in a heat preservation cover made of pure zinc plate. The heat preservation cover is connected to a cathode stage in a double-layer glow plasma furnace. Four zinc targets are placed around the heat preservation cover. The base pure magnesium is connected to another cathode electrode. The cavity is grounded as an anode.

[0041] ② High vacuum protection: Turn on the double-layer glow plasma alloying water pump equipment, use a mechanical pump to pump the pressure of the coating furnace to 2Pa, and then use a molecular pump to further pump the pressure of the furnace to 3×10-4Pa to keep the furnace in a high vacuum state;

[0042] ③ Low-glow bombardment and deposition: fill the chamber with argon to 20Pa, turn on the two cathode power supplies and apply 100V voltage, bombard the target zinc sheet and the substrate pure magnesium for 1-10 minutes. After the pre-bombardment, gradually adjust the insulation cover voltage to the test value of 250V, so that the target zinc sheet reaches the working temperature of 300℃, stabilize the process parameters and start insulation for 5 minutes;

[0043] ④ Rapid cooling and heat preservation: quickly turn off the power supply of the target and workpiece substrate, and adjust the argon gas to the working pressure of 20Pa, and continue to maintain it for 60 minutes;

[0044] ⑤Turn off the cathode power supply and argon gas source in sequence, and evacuate the vacuum furnace to 4×10 -4 Pa vacuum, cooled to room temperature and taken out of the furnace to obtain pure magnesium alloyed with zinc, namely MgZn;

[0045] (2) Preparation of composite coating:

[0046] ① Place Mg-Zn on the magnetron sputtering stage, install a high-purity titanium dioxide target and a precious metal tantalum target, and keep the distance between the two targets and the sample at the same distance as the workpiece's inter-electrode spacing at 6 cm;

[0047] ② High vacuum protection: Turn on the plasma sputtering equipment and its supporting cooling system, use a mechanical pump to pump the pressure of the coating furnace to below 5Pa, and then use a molecular pump to further pump the pressure of the furnace to 6×10 -4Pa, to keep the furnace in high vacuum state;

[0048] ③ Fill the furnace with argon gas to 3 Pa and pre-sputter the sample for 10 minutes;

[0049] ④ After pre-sputtering, turn on the DC power supply and the baffle of the titanium dioxide target, first adjust the RF power to 200W, and sputter the titanium dioxide for 60 minutes; close the baffle of the titanium dioxide target, open the baffle of the tantalum target, adjust the DC power to 200W, and sputter the tantalum target for 30 minutes;

[0050] ⑤ After sputtering is completed, the tantalum metal baffle, DC power supply, and argon gas source are turned off in sequence, the furnace is cooled to room temperature, and then the gas is vented and sampled to obtain pure magnesium with a composite coating of titanium dioxide and metallic tantalum and zinc alloy, marked as Mg-Zn-TiO2 / Ta.

[0051] Example 3: The difference from Example 1 is that in step (2), the target material used is tantalum metal, the DC power is adjusted to 200 W, the tantalum target is sputtered for 30 minutes, and the obtained material is MgZn-Ta.

[0052] Example 4: The difference from Example 2 is that in step (2), ④ is repeated twice, and the material obtained is MgZn-TiO2 / Ta-TiO2 / Ta.

[0053] Comparative Example 1: pure magnesium, marked as Mg.

[0054] Comparative Example 2: The difference from Example 1 is that step (2) is not included, and pure magnesium alloyed with zinc is obtained, which is marked as MgZn.

[0055] The performance test of the materials obtained in Example 1 to Example 4 and Comparative Example 1 to Comparative Example 2 is shown in FIG. Figures 1-9 .

[0056] Figure 1 The SEM image and element distribution diagram of MgZn-TiO2 prepared in Example 1 are shown in FIG. Figure 1 As shown in the left figure, the use of magnetron sputtering technology to sputter oxides increases the number of surface defects, which is also conducive to the subsequent nucleation and growth; Figure 1 The right figure shows the ratio of each element in MgZn-TiO2. Therefore, MgZn-TiO2 is actually MgZn 86.59 -Ti 5.52 O 7.89 .

[0057] Figure 2 The SEM image and element distribution diagram of MgZn-Ta prepared in Example 3 are shown in FIG. Figure 2 As shown in the left figure, the surface of the noble metal tantalum target sputtered by magnetron sputtering technology is cellular with obvious gaps; Figure 2The right figure shows the ratio of each element in MgZn-Ta. Therefore, MgZn-Ta is actually MgZn 0.06 -Ta 99.94 .

[0058] Figure 3 The cross-sectional morphology and element distribution diagram of MgZn-Ta prepared in Example 3 are shown in FIG. Figure 3 As can be seen from the left figure, Ta atoms are deposited into the MgZn alloy layer, and it is obvious that the surface is dense and tightly bonded, with a coating thickness of 3.98um.

[0059] Figure 4 The microstructure and element distribution of MgZn-TiO2 / Ta-TiO2 / Ta prepared in Example 4 are shown in FIG. Figure 4 As can be seen from the left figure, the surface is a continuous cellular structure with a dense structure; Figure 4 The ratio of each element of MgZn-TiO2 / Ta-TiO2 / Ta can be obtained from the figure on the right. Therefore, MgZn-TiO2 / Ta-TiO2 / Ta is actually Mg 0.36 Zn 0.58 -TiO 2.11 / Ta-TiO 2.11 / Ta 96.96 .

[0060] Figure 5 This is the cross-sectional morphology of MgZn-TiO2 / Ta-TiO2 / Ta prepared in Example 4. The coating is 5.63 μm, with a smooth surface and a dense structure.

[0061] Figure 6 The microstructure and element distribution of MgZn prepared in Comparative Example 2 are shown in FIG. Figure 6 As shown in the left figure, the magnesium-zinc alloy layer is prepared on the surface of pure magnesium using the double glow plasma technology, and the surface is curled; Figure 6 As can be seen from the figure on the right, the ratio of each element in MgZn, so MgZn is actually Mg / Mg 1.82 Zn 98.18 .

[0062] Figure 7 The cross-sectional morphology and element distribution of the material obtained in Comparative Example 2 are shown in FIG. Figure 7 As can be seen from the left figure, the cross-section of the MgZn alloying layer is loose and the number of defects increases.

[0063] Figure 8 The hardness comparison chart of the materials obtained in comparative example 1, comparative example 2 and embodiment 2 is shown in FIG. The hardness of Mg, MgZn alloy layer and MgZn-TiO2-Ta is 38HV respectively when measured by microhardness tester. 10 、57HV 10 、138HV10 , indicating that the composite coating prepared on pure magnesium is beneficial to the improvement of its mechanical properties.

[0064] Figure 9 As shown in the polarization curves of the materials obtained in Comparative Example 1, Comparative Example 2 and Example 2, it can be seen from the figure that the corrosion current of MgZn-TiO2-Ta is the smallest and the corrosion voltage is the largest, indicating that this composite coating can delay the corrosion of pure magnesium.

[0065] Figure 10 This is a top view of the dual-glow plasma equipment used in the present invention. The pure magnesium substrate is placed in a protective cover for surface treatment.

[0066] In summary, the present invention utilizes dual-glow plasma sputtering technology to prepare a zinc alloy layer on the surface of pure magnesium. The alloy elements are adsorbed, deposited, and diffused into the surface of the substrate to form a loose film. Titanium dioxide and tantalum coatings are then prepared by magnetron sputtering. In the initial nucleation stage, titanium dioxide and tantalum nucleate at defect sites. After the defect site nucleation process is completed, titanium dioxide and tantalum begin to deposit and grow. Finally, in the secondary nucleation stage, new defects appear, and titanium dioxide and tantalum nucleate again on the surface, ultimately forming a coating on the surface of pure magnesium.

Claims

1. A method for alloying and preparing a coating on the surface of pure magnesium, characterized in that: The following steps are involved: (1) Alloying on the surface of pure magnesium: using double glow plasma alloying technology, the heat preservation cover is made of pure zinc plate, connected to the cathode stage, the heat preservation cover is connected to the target zinc sheet, pure magnesium is connected to the other cathode electrode as the substrate, and the cavity is grounded as the anode; under high vacuum protection, the target zinc sheet and pure magnesium are pre-bombarded first, and then the target zinc sheet is low-glow bombarded and deposited. After rapid cooling and heat preservation, zinc alloyed pure magnesium is obtained; the parameters of the pre-bombardment are: The working pressure is 20-35 Pa, the voltages of both cathodes are 100-250 V, and the bombardment time is 1-10 min. The parameters of the low-glow bombardment are: the voltage of the heat preservation cover is 200-450 V, the working temperature is 200-350° C., and the bombardment time is 5-60 min. The parameters of the rapid cooling and heat preservation are: the working pressure is 10-25 Pa, and the heat preservation time is 10-60 min. The pure magnesium substrate is suspended and placed in the center of the heat preservation cover. (2) Preparation of composite coating: The zinc alloyed pure magnesium is plated by magnetron sputtering technology. High-purity metal oxide or one or two of the metals are used as targets. The zinc alloyed pure magnesium is pre-sputtered under high vacuum protection, and then the target is sputtered to obtain zinc alloyed pure magnesium with a coating. The metal is tantalum, niobium or zirconium, and the metal oxide is titanium dioxide.

2. The method according to claim 1, characterized in that In step (1), the high vacuum parameters are: vacuum degree is 3×10 -4 -6×10 -4 Pa.

3. The method according to claim 1, characterized in that In step (2), the distance between the target material and the zinc-alloyed pure magnesium is 5-8 cm.

4. The method according to claim 1, wherein In step (2), the time for sputtering the target is 10-120 minutes, the radio frequency power for sputtering the metal oxide is 100-350W, and the direct current power for sputtering the metal is 100-200W.

5. The method according to claim 1, characterized in that The zinc-alloyed pure magnesium with coating has a zinc layer as an intermediate layer and a metal oxide layer or a metal layer or a composite layer of metal oxide and metal as a coating layer.

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