Preparation method of hard nitride ceramic coating on surface of magnesium alloy

Abstract

The invention provides a preparation method of a hard nitride ceramic coating on the surface of a magnesium alloy, and belongs to the technical field of magnesium alloy coatings. According to the method, intermittent plasma flow is formed by controlling intermittent discharge of a cathode target in the PVD process, heat accumulation generated by continuous bombardment of matrix-coating interface ions is reduced by regulating and controlling the discharge / arc extinguishing period of the target, so that thermal expansion of the matrix-coating interface is reduced, and the thermal conductivity of the matrix-coating interface is improved. And growth defects (pores and cracks) caused by thermal expansion difference between the nitride ceramic coating and the substrate are reduced, and the method has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy coatings, and in particular to a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy. Background Art

[0002] Depositing hard nitride ceramic coating on the surface of magnesium alloy by physical vapor deposition (PVD) technology is an important method to improve the corrosion resistance and wear resistance of magnesium alloy. However, due to the large difference in thermal expansion coefficient (CTE) between magnesium alloy and nitride (the CTE of magnesium alloy is about 25×10 -6 ~30×10 -6 / ℃; the CET of common nitrides such as TiN, AlTiN, AlN, CrN, etc. is approximately 5×10 -6 ~10×10 -6 / ℃), resulting in the presence of a large number of growth defects such as pores and cracks in the PVD nitride coating on the surface of the magnesium alloy substrate, which seriously affects the microstructure and mechanical properties of the coating.

[0003] Currently, the main approach to improving growth defects in PVD nitride coatings on magnesium alloy substrates is to optimize process parameters, such as target power, preheat temperature, reaction gas pressure, reaction gas flow, and substrate bias voltage. However, these methods cannot effectively reduce the thermal expansion difference between the substrate and coating caused by target ion and nitrogen ion bombardment, and therefore have limited control over growth defects in the coating structure. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy. By controlling the intermittent discharge of the cathode during the PVD process to form an intermittent plasma flow, the thermal expansion fluctuations caused by ion bombardment on the substrate surface are effectively controlled, thereby solving the problem of many growth defects of the hard nitride ceramic coating on the surface of the magnesium alloy substrate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy, comprising the following steps:

[0007] 1) pretreating the magnesium alloy substrate to obtain a pretreated magnesium alloy substrate;

[0008] 2) Vacuum to 2×10 -3 Pa below, after preheating the PVD chamber, etching and cleaning the pretreated magnesium alloy substrate;

[0009] 3) Setting intermittent discharge of target material and performing intermittent plasma deposition;

[0010] The target material includes a Ti target, an AlTi alloy target, an Al target or a Cr target.

[0011] Preferably, the pretreatment includes grinding, polishing and ultrasonic cleaning the surface of the magnesium alloy substrate in sequence.

[0012] Preferably, the preheating is performed to a temperature of 100 to 250°C.

[0013] Preferably, the etching and cleaning conditions include: substrate bias voltage of -100 to -300 V, and cleaning time of 5 to 30 minutes.

[0014] Preferably, the duration of a single discharge of the intermittent plasma deposition is independently 10 to 120 seconds, the discharge current of a single target material is independently 80 to 130 A, the arc extinguishing gap of a single target material is independently 10 to 300 seconds, and the cumulative discharge time is 60 to 600 minutes.

[0015] Preferably, the intermittent plasma deposition is performed in a nitrogen atmosphere; the purity of the nitrogen is 99.999%, the nitrogen flow rate is 100-500 sccm, and the chamber pressure is 0.5-2.0 Pa.

[0016] Preferably, the intermittent plasma deposition is provided with an intermittent substrate bias, the bias cycle is synchronized with the discharge cycle, and the substrate bias value is -30 to -200V.

[0017] Preferably, during the intermittent plasma deposition, the chamber temperature is 50-250°C.

[0018] Preferably, after the intermittent plasma deposition is completed, a heat preservation treatment is performed, the temperature of the heat preservation treatment is 50 to 250° C., and the heat preservation time is 30 to 120 minutes.

[0019] The present invention provides a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy. The present invention controls the intermittent discharge of a cathode target during the PVD process to form an intermittent plasma flow. By regulating the target discharge / arc extinguishing cycle, the heat accumulation generated by the continuous ion bombardment at the substrate-coating interface is reduced, thereby reducing the thermal expansion of the substrate-coating interface and reducing the growth defects (pores, cracks, etc.) of the nitride ceramic coating caused by the thermal expansion difference between the nitride ceramic coating and the substrate. The present invention has good industrial application prospects.

[0020] The process provided by the present invention is simple and feasible, has high processing efficiency, and has strong applicability to substrates and parent materials, and has good application prospects. The method of the present invention also provides a reference for the PVD hard coating process of metal substrates with high thermal expansion coefficients. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Schematic diagram of conventional continuous plasma deposition (a) and schematic diagram of gap plasma deposition of the present invention (b);

[0022] Figure 2 Comparison of scanning electron microscope structures of AlTiN and CrN coatings prepared by traditional continuous deposition process and intermittent plasma deposition process: (a) Traditional continuous deposition AlTiN coating in comparative example 1; (a1) intermittent plasma deposition AlTiN coating in embodiment 1; (b) Traditional continuous deposition CrN coating in comparative example 5; (b1) intermittent plasma deposition CrN coating in embodiment 5. DETAILED DESCRIPTION

[0023] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0024] like Figure 1 As shown, the present invention provides a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy, comprising the following steps:

[0025] 1) pretreating the magnesium alloy substrate to obtain a pretreated magnesium alloy substrate;

[0026] 2) Vacuum to 2×10 -3 Pa below, after preheating the PVD chamber, etching and cleaning the pretreated magnesium alloy substrate;

[0027] 3) Setting intermittent discharge of target material and performing intermittent plasma deposition;

[0028] The target material includes a Ti target, an AlTi alloy target, an Al target or a Cr target.

[0029] The present invention has no particular limitation on the specific specifications and types of the magnesium alloy substrate, and any magnesium alloy well known in the art can be used. In the embodiment of the present invention, the substrate is specifically AZ31B commercial magnesium alloy rolled plate (thickness 5 mm).

[0030] In the present invention, the pretreatment preferably includes grinding, polishing and cleaning the surface of the magnesium alloy substrate in sequence. The present invention has no particular limitation on the grinding, polishing and cleaning, and they can be performed according to processes well known in the art.

[0031] The present invention preferably evacuates the PVD chamber to a vacuum of 2×10 -3 Pa or less, the PVD chamber is preheated to a temperature preferably of 100-250°C, more preferably of 150-200°C.

[0032] In the present invention, the etching and cleaning conditions preferably include: a substrate bias voltage of -100 to -300 V, more preferably -100 to -200 V, and a cleaning time of 5 to 30 minutes, more preferably 5 to 10 minutes. The present invention has no particular limitation on the etching and cleaning process, and etching and cleaning can be performed using the above conditions according to methods well known in the art.

[0033] In the present invention, the target material includes a Ti target, an AlTi alloy target, an Al target or a Cr target.

[0034] In the present invention, the purity of the Ti target is preferably 99.99%; the AlTi atomic ratio in the AlTi alloy target is preferably 50%:50%, and the purity of the AlTi alloy target is preferably 99.99%; the purity of the Al target is preferably 99.99%; and the purity of the Cr target is preferably 99.99%.

[0035] The present invention has no particular limitation on the specific source of the target material, and any commercially available product well known in the art may be used.

[0036] In the present invention, the duration of a single discharge of the intermittent plasma deposition is preferably independently 10 to 120 s, more preferably 15 to 60 s, and further preferably 20 to 30 s; the discharge current of a single target material is preferably independently 80 to 130 A, more preferably 90 to 120 A, and further preferably 100 to 110 A; the arc extinguishing gap of a single target material is preferably independently 10 to 300 s, more preferably 20 to 200 s, and further preferably 30 to 120 s; the cumulative discharge time is preferably 60 to 600 min, more preferably 80 to 300 min, and further preferably 120 to 180 min.

[0037] In the present invention, the intermittent plasma deposition is preferably carried out in a nitrogen atmosphere; the purity of the nitrogen is preferably 99.999%, the nitrogen flow rate is preferably 100-500 sccm, more preferably 150-400 sccm, and further preferably 200-300 sccm; the chamber pressure is preferably 0.5-2.0 Pa, more preferably 0.6-1.5 Pa, and further preferably 1.0-1.2 Pa.

[0038] In the present invention, the intermittent plasma deposition is preferably set with an intermittent substrate bias, and the bias cycle is synchronized with the discharge cycle (that is, the substrate is negatively biased when the target material discharges, and the substrate bias is canceled when the target material extinguishes the arc). The bias duration is preferably 10 to 120 s, more preferably 15 to 60 s, and further preferably 20 to 30 s; the bias gap is preferably 10 to 300 s, more preferably 20 to 200 s, and further preferably 30 to 120 s; the substrate bias value is preferably -30 to -200 V, more preferably -40 to -150 V, and further preferably -50 to -100 V.

[0039] In the present invention, during the intermittent plasma deposition, the chamber temperature is preferably 50-250°C, more preferably 80-200°C, and even more preferably 100-150°C.

[0040] In the present invention, after the intermittent plasma deposition is completed, a heat preservation treatment is performed, the temperature of the heat preservation treatment is 50-250°C, preferably 80-200°C, and more preferably 100-150°C; the heat preservation time is 30-120min, more preferably 40-90min, and further preferably 60-70min.

[0041] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0042] The following experimental methods and detection methods, unless otherwise specified, are conventional methods; the following reagents and raw materials, unless otherwise specified, are commercially available.

[0043] In the following examples, the magnesium alloy substrate is AZ31B commercial magnesium alloy rolled plate (manufacturer: Henan Jimitai New Materials Co., Ltd.; plate thickness: 5 mm);

[0044] The purity of nitrogen is 99.999%.

[0045] Example 1

[0046] The ground, polished and cleaned magnesium alloy substrate was placed in the PVD chamber, and the chamber was vacuumed to 2×10 -3 Pa below, the chamber is preheated to a temperature of 150 ° C; the substrate is etched and cleaned, the substrate bias voltage is -100 V during cleaning, and the cleaning time is 5 minutes;

[0047] like Figure 1As shown in (b), a high-purity AlTi alloy target (atomic ratio of composition 50%:50%; purity 99.99%) was selected as the target material, and intermittent discharge of the target was set. The single discharge duration was 30s, the target discharge current was 110A, and the target arc extinguishing gap was 30s. Intermittent plasma deposition was performed, and the nitrogen flow rate during the deposition process was 300sccm, and the chamber pressure was 1.0Pa; during the deposition process, an intermittent bias was set on the substrate, and the bias cycle was synchronized with the discharge cycle. The bias duration was 30s, the bias gap was 30s, and the bias value was -50V; during the deposition process, the chamber temperature was set to 150℃; after a cumulative discharge time of 120min, the deposition was completed, the chamber temperature was set to 150℃, and the holding time was 60min to obtain an AlTiN coating.

[0048] Comparative Example 1

[0049] The only difference from Example 1 is that: Figure 1 As shown in (a), a continuous deposition process is adopted, the deposition process parameters are the same as those in Example 1, and the cumulative discharge time is the same.

[0050] According to the results of scanning electron microscopy on the coating surface, the surface density of pores (pore size 1 μm or more) in the AlTiN coating deposited by intermittent plasma in Example 1 is P Every 100μm 2 The area is 0.41, and the surface density of macro cracks (length over 50 μm) is ρ C per mm 2 Area 0. Compared with the AlTiN coating defects under the same continuous deposition process in Comparative Example 1: ρ P Every 100μm 2 Area 4.6, ρ C per mm 2 The area is 1.2 lines. The intermittent plasma deposition process effectively reduces the growth defects of AlTiN coating on the surface of magnesium alloy.

[0051] Example 2

[0052] The ground, polished and cleaned magnesium alloy substrate was placed in the PVD chamber, and the chamber was vacuumed to 2×10 -3 Pa below, the chamber is preheated to a temperature of 150 ° C, and the substrate is etched and cleaned. During cleaning, the substrate bias voltage is -100 V and the cleaning time is 5 minutes;

[0053] A high-purity Ti target (purity 99.99%) was selected as the target material, and intermittent discharge of the target was set. The single discharge duration was 20s, the target discharge current was 110A, and the target arc extinguishing gap was 60s. Intermittent plasma deposition was performed, and the nitrogen flow rate during the deposition process was 300sccm, and the chamber pressure was 1.0Pa; during the deposition process, an intermittent bias was set on the substrate, and the bias cycle was synchronized with the discharge cycle. The bias duration was 20s, the bias gap was 60s, and the bias value was -100V; during the deposition process, the chamber temperature was set to 150°C; after a cumulative discharge time of 60min, the deposition was completed, the chamber temperature was set to 150°C, and the insulation time was 60min to obtain a TiN coating.

[0054] Comparative Example 2

[0055] The only difference from Example 2 is that a continuous deposition process is adopted, the deposition process parameters are the same as those of Example 2, and the accumulated discharge time is the same.

[0056] According to the results of scanning electron microscopy on the coating surface, the surface density of pores (pore size 1 μm or more) in the intermittent plasma deposited TiN coating in Example 2 is P Every 100μm 2 The area is 0.54, and the surface density of macro cracks (length above 50μm) is ρ C per mm 2 Area 0. Compared with the TiN coating defects under the same continuous deposition process in Comparative Example 2: (ρ P Every 100μm 2 Area 6.3, ρ C per mm 2 The area is 1.4 lines. The intermittent plasma deposition process effectively reduces the growth defects of TiN coating on the surface of magnesium alloy.

[0057] Example 3

[0058] The ground, polished and cleaned magnesium alloy substrate was placed in the PVD chamber, and the chamber was vacuumed to 2×10 -3 Pa below, the chamber is preheated to a temperature of 150 ° C, and the substrate is etched and cleaned. During cleaning, the substrate bias voltage is -100 V and the cleaning time is 5 minutes;

[0059] A high-purity Ti target (purity 99.99%) was selected as the target material, and intermittent discharge of the target was set. The single discharge duration was 30s, the target discharge current was 90A, and the target arc extinguishing gap was 120s, and intermittent plasma deposition was performed. During the deposition process, the nitrogen flow rate was 300sccm and the chamber pressure was 1.0Pa. During the deposition process, an intermittent bias was set on the substrate, and the bias cycle was synchronized with the discharge cycle. The bias duration was 30s, the bias gap was 120s, and the bias value was -50V. During the deposition process, the chamber temperature was set to 100°C. After a cumulative discharge time of 120min, the deposition was completed, the chamber temperature was set to 100°C, and the insulation time was 60min to obtain a TiN coating.

[0060] Comparative Example 3

[0061] The only difference from Example 3 is that a continuous deposition process is adopted, the deposition process parameters are the same as those of Example 3, and the accumulated discharge time is the same.

[0062] According to the results of scanning electron microscopy on the surface structure of the coating, the surface density of pores (pore size 1 μm or more) in the intermittent plasma deposited TiN coating in Example 3 is P Every 100μm 2 Area 0.21, macro crack (length 50μm or more) surface density ρ C per mm 2 Area 0. Compared with the defects of TiN coating under the same continuous deposition process in Comparative Example 3: ρ P Every 100μm 2 Area 3.2, ρ C per mm 2 The area is 0.9, and the intermittent plasma deposition process effectively reduces the growth defects of TiN coating on the surface of magnesium alloy.

[0063] Example 4

[0064] The ground, polished and cleaned magnesium alloy substrate was placed in the PVD chamber, and the chamber was vacuumed to 2×10 -3 Pa, the chamber is preheated to a temperature of 150°C, and the substrate is etched and cleaned. The substrate bias voltage during cleaning is -100 V, and the cleaning time is 5 minutes.

[0065] A high-purity Al target (purity 99.99%) was selected as the target material, and intermittent discharge of the target was set. The single discharge duration was 20s, the target discharge current was 90A, and the target arc extinguishing gap was 120s. Intermittent plasma deposition was performed, and the nitrogen flow rate during the deposition process was 200sccm, and the chamber pressure was 0.8Pa; during the deposition process, the substrate was set with an intermittent bias, the bias cycle was synchronized with the discharge cycle, the bias duration was 20s, the bias gap was 120s, and the bias value was -50V; during the deposition process, the chamber temperature was set to 100℃; after a cumulative discharge time of 120min, the deposition was completed, the chamber temperature was set to 100℃, and the insulation time was 60min to obtain an AlN coating.

[0066] Comparative Example 4

[0067] The only difference from Example 4 is that a continuous deposition process is adopted, the deposition process parameters are the same as those of Example 4, and the accumulated discharge time is the same.

[0068] According to the results of scanning electron microscopy on the coating surface, the surface density of pores (pore size 1 μm or more) in the intermittent plasma deposited AlN coating in Example 4 is P Every 100μm 2 Area 0.14, macro crack (length 50μm or more) surface density ρ C per mm 2 Area 0. Compared with the AlN coating defects under the same continuous deposition process in Comparative Example 4: ρ P Every 100μm 2 Area 1.9, ρ C per mm 2 The area is 1.5 lines, and the intermittent plasma deposition process effectively reduces the growth defects of AlN coating on the surface of magnesium alloy.

[0069] Example 5

[0070] The ground, polished and cleaned magnesium alloy substrate was placed in the PVD chamber, and the chamber was vacuumed to 2×10 -3 Pa below, the chamber is preheated to a temperature of 150 ° C, and the substrate is etched and cleaned. During cleaning, the substrate bias voltage is -100 V and the cleaning time is 5 minutes;

[0071] A high-purity Cr target (purity 99.99%) was selected as the target material, and intermittent discharge of the target was set. The single discharge duration was 10s, the target discharge current was 100A, and the target arc extinguishing gap was 120s. Intermittent plasma deposition was performed, and the nitrogen flow rate during the deposition process was 300sccm, and the chamber pressure was 1.2Pa; during the deposition process, an intermittent bias was set on the substrate, and the bias cycle was synchronized with the discharge cycle. The bias duration was 10s, the bias gap was 120s, and the bias value was -100V; during the deposition process, the chamber temperature was set to 150℃; after a cumulative discharge time of 120min, the deposition was completed, the chamber temperature was set to 150℃, and the insulation time was 70min to obtain a CrN coating.

[0072] Comparative Example 5

[0073] The only difference from Example 5 is that a continuous deposition process is adopted, the deposition process parameters are the same as those of Example 5, and the accumulated discharge time is the same.

[0074] According to the results of SEM microstructure measurement on the coating surface, the surface density of pores (pore size above 1 μm) in the intermittent plasma deposited CrN coating in Example 5 is P Every 100μm 2 Area 0.26, macro crack (length 50μm or more) surface density ρ C per mm 2 Area 0. Compared with the CrN coating defects under the same continuous deposition process in Comparative Example 5: ρ P Every 100μm 2 Area 2.3, ρ C per mm 2 The area is 0.6, and the intermittent plasma deposition process effectively reduces the growth defects of CrN coating on the surface of magnesium alloy.

[0075] Figure 2 Comparison of scanning electron microscope structures of AlTiN and CrN coatings prepared by traditional continuous deposition process and intermittent plasma deposition process: (a) Traditional continuous deposition AlTiN coating in comparative example 1; (a1) intermittent plasma deposition AlTiN coating in embodiment 1; (b) Traditional continuous deposition CrN coating in comparative example 5; (b1) intermittent plasma deposition CrN coating in embodiment 5. Figure 2 It can be seen that the intermittent plasma deposition process effectively reduces growth defects such as pores and cracks on the surface of magnesium alloys.

[0076] It can be seen from the above embodiments that the present invention provides a method for preparing a hard nitride ceramic coating on the surface of a magnesium alloy. By controlling the intermittent discharge of the cathode during the PVD process and controlling the thermal expansion fluctuations on the substrate surface caused by ion bombardment, the problem of many growth defects (pores and cracks) in the hard nitride ceramic coating on the surface of the magnesium alloy substrate is solved, and the method has good industrial application prospects.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a hard nitride ceramic coating on a magnesium alloy surface, characterized in that: The following steps are involved: 1) pretreating the magnesium alloy substrate to obtain a pretreated magnesium alloy substrate; 2) Vacuum to 2×10 -3 Pa below, after preheating the PVD chamber, etching and cleaning the pretreated magnesium alloy substrate; 3) Setting intermittent discharge of target material and performing intermittent plasma deposition; The target material includes a Ti target, an AlTi alloy target, an Al target or a Cr target.

2. The preparation method according to claim 1, characterized in that The pretreatment includes grinding, polishing and ultrasonic cleaning the surface of the magnesium alloy substrate in sequence.

3. The preparation method according to claim 1, characterized in that Preheat to a temperature of 100-250°C.

4. The preparation method according to claim 1, characterized in that The etching and cleaning conditions include: substrate bias voltage of -100 to -300 V, and cleaning time of 5 to 30 minutes.

5. The preparation method according to claim 1, characterized in that The duration of a single discharge of the intermittent plasma deposition is independently 10 to 120 seconds, the discharge current of a single target material is independently 80 to 130A, the arc extinguishing gap of a single target material is independently 10 to 300 seconds, and the cumulative discharge time is 60 to 600 minutes.

6. The preparation method according to claim 5, characterized in that The intermittent plasma deposition is performed in a nitrogen atmosphere; the purity of the nitrogen is 99.999%, the nitrogen flow rate is 100-500 sccm, and the chamber pressure is 0.5-2.0 Pa.

7. The preparation method according to claim 6, characterized in that The intermittent plasma deposition is provided with an intermittent substrate bias, the bias cycle is synchronized with the discharge cycle, and the substrate bias value is -30 to -200V.

8. The preparation method according to claim 7, characterized in that During the intermittent plasma deposition, the chamber temperature is 50-250°C.

9. The preparation method according to claim 8, characterized in that After the intermittent plasma deposition is completed, a heat preservation treatment is performed. The temperature of the heat preservation treatment is 50 to 250° C. and the heat preservation time is 30 to 120 minutes.

Images