Gradient stress buffer insulation coating system for transformer against liquid cooling thermal shock and pvd construction method thereof

Abstract

This invention relates to the field of surface protection for special power equipment and physical vapor deposition (PVD) thin film manufacturing technology, and discloses a gradient stress buffer insulation coating system for transformers resistant to liquid cooling thermal shock and its PVD construction method. The coating system is constructed on the surface of a copper winding or silicon steel core, comprising, from bottom to top, a soft substrate surface layer formed by low-pressure glass bead wet blasting and fine polishing composite pretreatment, a Ti(C,N)-HEA-ZrO₂ cermet stress transition buffer layer with a thickness of 1.5–2.5 μm, and an AlCrN / TiAlN nanolayered insulation protective layer with a total thickness of 3.0–4.0 μm, forming a multi-layered composite structure with a gradient transition in composition and mechanical properties. This design achieves high adhesion between the coating and the soft substrate while effectively mitigating interfacial thermal stress caused by thermal expansion coefficient mismatch, significantly improving the coating's thermal shock resistance life and insulation reliability in immersion liquid cooling environments.

Description

Technical Field

[0001] This invention relates to the field of surface protection for special power equipment and advanced physical vapor deposition thin film manufacturing technology, specifically to a gradient stress buffer insulation coating system for transformers resistant to liquid cooling thermal shock and its PVD construction method. Background Technology

[0002] As AI computing devices evolve towards higher power density, miniaturization, and liquid cooling, higher demands are being placed on the service stability of the insulating protective coatings of AI computing transformers. Preparing inorganic insulating protective coatings on the surface of transformer metal substrates using physical vapor deposition (PVD) technology is an important technological direction to replace traditional organic insulating impregnation.

[0003] However, when cemented carbide coatings, which are commonly used in cemented carbide cutting tools, are directly deposited onto soft substrates of transformers such as copper or silicon steel, the following problems usually arise.

[0004] On the one hand, the difference in thermal expansion coefficients between the soft substrate and the outer nitride ceramic layer is large, and the interface is prone to accumulating large residual thermal tensile stress during thermal cycling, which in turn leads to brittle spalling.

[0005] On the other hand, traditional high-pressure hard sandblasting pretreatment can easily introduce severe plastic deformation and residual compressive stress on the soft substrate surface, which not only makes it difficult to improve the film-substrate bonding state, but also reduces the coating toughness and accelerates thermal shock failure.

[0006] Furthermore, a single-layer outer insulating coating cannot simultaneously ensure film-substrate adhesion, thermal shock reliability, and long-term liquid-cooled insulation protection.

[0007] Therefore, developing a low-damage composite pretreatment process that can be adapted to the soft substrate of transformers, and constructing a gradient stress buffer structure with thermodynamic and mechanical transition functions between the soft substrate and the outer hard insulation layer, so as to obtain a composite coating system with high bonding strength, resistance to liquid cooling thermal shock and high insulation reliability, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of direct deposition of ceramic coatings on soft substrates of transformers, which are prone to thermal stress spalling, and traditional high-pressure hard sandblasting which introduces excessive residual stress. The invention provides a gradient stress buffer insulation coating system for transformers that is resistant to liquid cooling thermal shock and its PVD construction method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution.

[0010] The present invention provides a gradient stress buffer insulation coating for transformers that resists liquid cooling thermal shock. The gradient stress buffer insulation coating is constructed on the surface of a transformer metal soft substrate, wherein the transformer metal soft substrate is a copper winding or a silicon steel core.

[0011] The gradient stress buffer insulating coating comprises, from bottom to top:

[0012] A soft substrate surface layer formed by low-pressure glass bead wet sandblasting and fine polishing composite pretreatment;

[0013] A Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer is deposited on the surface of the soft substrate, the thickness of which is 1.5–2.5 μm;

[0014] An AlCrN / TiAlN nanolayered insulating protective layer is deposited on the stress transition buffer layer. The nanolayered insulating protective layer is formed by alternating AlCrN and TiAlN layers, with a single layer thickness of 10–30 nm and a total thickness of 3.0–4.0 μm.

[0015] Preferably, the surface roughness Ra of the soft substrate is 0.15 to 0.25 μm.

[0016] Preferably, the surface of the soft substrate is free of deep grooves and sharp peaks.

[0017] The present invention also provides a PVD method for constructing the above-mentioned gradient stress buffer insulating coating, comprising the following steps:

[0018] Step 1: Perform composite pretreatment on the transformer's soft metal substrate. This composite pretreatment includes wet sandblasting, fine polishing with sandpaper, and cleaning and drying. In the wet sandblasting, glass beads are used as abrasive, the sandblasting pressure is 0.15–0.25 MPa, and the sandblasting time is 3–5 minutes. After sandblasting, fine polishing is performed using 1000–1500 grit water-resistant sandpaper. The treated substrate is then ultrasonically cleaned in 95% alcohol or acetone solution for 5–15 minutes and dried.

[0019] Step 2: Deposition of Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer. The pretreated substrate is placed in a multi-arc ion plating machine, evacuated to a base vacuum of 5.0 × 10⁻⁴ Pa, Ar gas is introduced, and the chamber pressure is adjusted to 0.1–0.5 Pa. Simultaneously, it is heated to 350–450 °C, and an argon ion sputtering cleaning is performed for 10 min under a negative bias of -400 V to -500 V. Subsequently, the substrate negative bias is adjusted to -150 V, the Ti(C,N)-HEA-ZrO2 composite cathode target is turned on, and the Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer is deposited in a nitrogen-argon mixed atmosphere. The working pressure is 0.5–1.0 Pa, and the deposition time is 40–60 min.

[0020] Step 3: AlCrN and TiAlN layers are deposited alternately to form a nano-layered insulating protective layer. The substrate negative bias voltage is adjusted to -100 V, pure N2 is introduced and the gas pressure is adjusted to 2.0 Pa, and the temperature is controlled at 500 ℃. When depositing the AlCrN layer, the aluminum target and the chromium target are turned on, and the target current is 50-60 A for both. When depositing the TiAlN layer, the chromium target is turned off and the titanium target is turned on. The aluminum target and the titanium target work together, and the target current is 50-60 A for both. The above deposition process is repeated so that the AlCrN layer and the TiAlN layer are stacked alternately. The total deposition time is 100-120 min. After the deposition is completed, the workpiece is cooled with the furnace to below 150 ℃ and then removed.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0022] 1. By combining sandblasting and fine polishing as a pretreatment, a surface state conducive to coating deposition can be formed while avoiding excessive surface damage, thereby improving the film-substrate bonding state on soft substrates;

[0023] 2. By setting a Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer between the soft substrate and the outer nitride layer, the interfacial thermal stress caused by the mismatch between the coefficient of thermal expansion and the elastic modulus can be relieved, reducing the risk of thermal shock peeling of the coating.

[0024] 3. By constructing an AlCrN / TiAlN nanolayered insulating protective layer, multiple interfaces can be used to deflect, branch, and block microcracks, thereby improving the insulation protection capability and service life in liquid-cooled environments. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 SEM images of the microstructure of the transformer metal soft substrate surface after pretreatment under different sandblasting methods, abrasive types and sandblasting pressures;

[0027] in, Figure 1 (a) shows the surface microstructure under dry blasting, glass bead, and 0.2 MPa conditions. Figure 1 (b) shows the surface microstructure of corundum under dry blasting conditions and 0.5 MPa. Figure 1 (c) shows the surface microstructure under wet blasting, glass bead, and 0.5 MPa conditions. Figure 1 (d) shows the surface microstructure of corundum under wet blasting conditions of 0.2 MPa.

[0028] Figure 2SEM image of the cross-sectional continuous structure of the gradient stress buffer insulation coating;

[0029] Among them, 1 is the matrix, 2 is the Ti(C,N)-HEA-ZrO2 stress transition buffer layer, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 are AlCrN layers, and 4, 6, 8, 10, 12, 14, 16, 18, 20, and 22 are TiAlN layers.

[0030] Figure 3 (a) ~ Figure 3 (g) SEM images of the surface morphology of the samples under different polishing sandpaper mesh numbers;

[0031] in, Figure 3 (a) ~ Figure 3 (g) The surface morphology of the sample after polishing with 5000 mesh, 3000 mesh, 1000 mesh, 600 mesh, 240 mesh, 120 mesh and 80 mesh sandpaper, respectively. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment illustrates the method for constructing a gradient stress buffer insulating coating under the preferred process conditions of the present invention.

[0035] Transformer copper busbars were selected as the substrate. Wet sandblasting with glass beads as abrasive was employed, with a sandblasting pressure controlled at 0.2 MPa and a treatment time of 3 minutes. After sandblasting, the substrate surface was finely polished with 5000-grit water-resistant sandpaper, followed by ultrasonic cleaning in 95% alcohol for 5 minutes and drying. After this composite pretreatment, the surface roughness Ra of the substrate stabilized at approximately 0.18 μm, with no obvious deep scratches or residual compressive stress accumulation.

[0036] The pretreated copper busbar was loaded into a multi-arc ion plating machine, evacuated to 5.0 × 10⁻⁴ Pa, and heated to 400 °C. After negative bias sputtering cleaning, the Ti(C,N)-HEA-ZrO₂ composite cathode target was turned on, and deposition was carried out for 60 min in a nitrogen-argon mixed atmosphere at 0.8 Pa to obtain a Ti(C,N)-HEA-ZrO₂ cermet stress transition buffer layer with a thickness of approximately 2.1 μm.

[0037] Then, pure N2 was introduced, the working pressure was controlled at 2.0 Pa, and the temperature was maintained at 500 ℃. Chromium, aluminum, and titanium targets were alternately turned on, and AlCrN and TiAlN layers were deposited alternately. The thickness of a single layer was about 20 nm, and the total alternating deposition time was 110 min, forming an AlCrN / TiAlN nanolayered insulating protective layer with a thickness of about 3.45 μm.

[0038] Comprehensive performance characterization results show that, using the MST scratch test, the film-substrate adhesion of the coating is 53.95 N; cross-sectional SEM indicates that there are no obvious pores or microcracks in the coating, and the film-substrate interface is clear, dense, and has good continuity. Figure 2 It can be seen that the interface between the matrix and the Ti(C,N)-HEA-ZrO2 stress transition buffer layer is continuous, the outermost AlCrN layer and TiAlN layer grow alternately, the layer boundaries are relatively clear, and no obvious through cracks and pores are observed in the overall cross section, indicating that the gradient structure has good integrity and compactness.

[0039] Comparative Example 1

[0040] Compared with Example 1, the only difference is that the pretreatment step is changed to: dry sandblasting is used, glass beads are used as abrasive, and the sandblasting pressure is controlled at 0.2 MPa; the remaining fine polishing, cleaning and drying, Ti(C,N)-HEA-ZrO2 stress transition buffer layer deposition and AlCrN / TiAlN nanolayered insulating protective layer deposition steps are the same as in Example 1.

[0041] Depend on Figure 1 (a) It can be seen that under this condition, relatively uniform micro-impact pits are formed on the substrate surface, but obvious directional impact marks can still be seen in local areas, indicating that the uniformity of particle impact under dry sandblasting conditions is relatively weak.

[0042] Comparative Example 2

[0043] Compared with Example 1, the only difference is that the pretreatment step is changed to: dry sandblasting is used, corundum is used as the abrasive, and the sandblasting pressure is controlled at 0.5 MPa; the rest of the steps are the same as in Example 1.

[0044] Depend on Figure 1 (b) It can be seen that under this condition, the substrate surface shows obvious coarse erosion marks and irregular protrusions, and the surface damage in local areas is more significant, indicating that high-pressure corundum dry sandblasting is more likely to introduce strong impact damage to the soft substrate surface.

[0045] Comparative Example 3

[0046] Compared with Example 1, the only difference is that the pretreatment step is changed to: wet sandblasting is used, glass beads are used as abrasive, and the sandblasting pressure is controlled at 0.5 MPa; the rest of the steps are the same as in Example 1.

[0047] Depend on Figure 1 (c) It can be seen that under the buffering effect of the liquid medium, the overall surface of the substrate is relatively uniform, but higher sandblasting pressure will still lead to the superposition of local micro-pits and increased surface undulation, indicating that sandblasting pressure is still an important factor affecting the degree of damage to the soft substrate surface.

[0048] Comparative Example 4

[0049] Compared with Example 1, the only difference is that the pretreatment step is changed to: wet sandblasting is used, corundum is used as the abrasive, and the sandblasting pressure is controlled at 0.2 MPa; the rest of the steps are the same as in Example 1.

[0050] Depend on Figure 1 (d) It can be seen that wet sandblasting conditions have a certain mitigating effect on impact, but due to the high hardness of corundum particles, obvious coarse particle adhesion and irregular pit morphology can still be observed on the surface, indicating that high hardness sand is still not conducive to obtaining a low-damage pre-treated surface.

[0051] Example 2

[0052] This embodiment illustrates the effect of the grit size of fine polishing sandpaper on surface morphology and film-substrate adhesion.

[0053] The pretreatment and PVD deposition steps were the same as in Example 1, except that the fine polishing step was performed using 5000 grit, 3000 grit, 1000 grit, 600 grit, 240 grit, 120 grit, and 80 grit water-resistant sandpaper, respectively. The surface morphology of the samples after PVD coating following different sandpaper pretreatments is shown in the figures below. Figure 3 (a)~ Figure 3 (g) The results of the membrane-substrate bonding test are shown in Table 1.

[0054] serial number a b c d e f g Sandpaper grit 5000 3000 1000 600 240 120 80 Matrix bonding force / N 53.95 50.90 50.7 45.15 44.45 41.70 40.10

[0055] Table 1. Test results of film-substrate adhesion for different polishing sandpaper grits

[0056] Depend on Figure 3 (a) ~ Figure 3 (g) It can be seen that the surface morphology corresponding to different grits of sandpaper is significantly different: the surface treated with 5000 grit and 3000 grit sandpaper is relatively smooth with only a few fine grinding marks; the surface treated with 1000 grit and 600 grit sandpaper begins to show more obvious parallel polishing marks; the surface treated with 240 grit, 120 grit and 80 grit sandpaper has more obvious grooves and scratches, and the surface undulation is intensified.

[0057] Table 1 shows that the film-substrate adhesion forces corresponding to different polishing grit numbers are: 80 mesh 40.10 N, 120 mesh 41.70 N, 240 mesh 44.45 N, 600 mesh 45.15 N, 1000 mesh 50.70 N, 3000 mesh 50.90 N, and 5000 mesh 53.95 N. The results indicate that under the current experimental conditions of this application, as the polishing grit number increases, the substrate surface morphology gradually becomes smoother, and the overall film-substrate adhesion force shows an upward trend, with the highest film-substrate adhesion force corresponding to 5000 mesh sandpaper.

[0058] Comparative Example 5

[0059] The substrate pretreatment is the same as in Example 1, but the Ti(C,N)-HEA-ZrO2 stress transition buffer layer is omitted in the multi-arc ion plating process. Instead, an AlCrN / TiAlN nanolayered insulating protective layer is directly deposited on the surface of the pretreated copper substrate, and the deposition time is extended to ensure consistent total film thickness.

[0060] The results show that, due to the lack of a gradual transition layer with varying coefficients of thermal expansion and elastic modulus, the residual thermal tensile stress at the film-substrate interface increases significantly. During thermal shock cycling, the coating edges are more prone to cracking and brittle spalling, indicating that the intermediate stress transition buffer layer plays an important role in improving interface stability.

[0061] Comparative Example 6

[0062] Compared with Example 1, the difference in process is that the substrate pretreatment uses corundum abrasive for dry sandblasting, the sandblasting pressure is increased to 0.5 MPa, and the subsequent 5000-grit fine polishing is not performed; the remaining coating steps are the same as in Example 1.

[0063] The results show that high-pressure corundum blasting is more likely to cause significant plastic distortion and large residual compressive stress on the copper surface, and the resulting coating is more prone to interfacial spalling under thermal shock conditions.

[0064] in conclusion

[0065] As can be seen from the above embodiments and comparative embodiments, the present invention, through the composite pretreatment of low-pressure glass bead wet sandblasting and fine polishing, the synergistic construction of Ti(C,N)-HEA-ZrO2 stress transition buffer layer and AlCrN / TiAlN nanolayered insulating protective layer, can improve the film-substrate bonding state on soft substrates, suppress film-substrate thermal mismatch stress concentration, and improve the coating's thermal shock resistance and insulation reliability in liquid-cooled environments.

[0066] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 gradient stress buffer insulation coating for transformers resistant to liquid cooling thermal shock, characterized in that, The gradient stress buffer insulation coating is constructed on the surface of the transformer metal soft substrate, which is a copper winding or a silicon steel core. The gradient stress buffer insulating coating comprises, from bottom to top: A soft substrate surface layer formed by low-pressure glass bead wet sandblasting and fine polishing composite pretreatment; A Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer is deposited on the surface of the soft substrate, the thickness of which is 1.5–2.5 μm; And an AlCrN / TiAlN nanolayered insulating protective layer deposited on the stress transition buffer layer, wherein the nanolayered insulating protective layer is formed by alternating AlCrN layers and TiAlN layers, with a single layer thickness of 10-30 nm and a total thickness of 3.0-4.0 μm.

2. The gradient stress buffer insulating coating according to claim 1, characterized in that, The surface roughness Ra of the soft substrate is 0.15–0.25 μm.

3. The gradient stress buffer insulating coating according to claim 1 or 2, characterized in that, The surface of the soft substrate is free of deep grooves and sharp peaks.

4. A PVD method for building up a gradient stress buffer insulation coating according to any one of claims 1 to 3, characterized in that The steps include the following: S1. A composite pretreatment of the transformer metal soft substrate is performed, including: using glass beads as abrasive, wet sandblasting the transformer metal soft substrate in deionized water medium, with a sandblasting pressure of 0.15-0.25 MPa and a sandblasting time of 3-5 min; then fine polishing with 1000-1500 grit water-resistant sandpaper; and then ultrasonic cleaning in 95% alcohol or acetone solution for 5-15 min followed by drying. S2. The transformer metal soft substrate treated in step S1 is placed into a multi-arc ion plating machine. Under the condition of a base vacuum of 5.0×10^-4 Pa, Ar gas is introduced and the chamber pressure is adjusted to 0.1~0.5 Pa. At the same time, it is heated to 350~450 ℃ and a negative bias voltage of -400 V~-500 V is applied for argon ion sputtering cleaning for 10 min. Then, the substrate negative bias voltage is adjusted to -150 V, the Ti(C,N)-HEA-ZrO2 composite cathode target is turned on, and a Ti(C,N)-HEA-ZrO2 metal ceramic stress transition buffer layer is deposited in a nitrogen-argon mixed atmosphere. The working pressure is 0.5~1.0 Pa and the deposition time is 40~60 min. S3. AlCrN and TiAlN layers are alternately deposited on the surface of the stress transition buffer layer obtained in step S2 to form an AlCrN / TiAlN nanolayered insulating protective layer.

5. The PVD method according to claim 4, characterized in that, In step S1, the glass bead has high roundness and a hardness lower than that of corundum sand.

6. The PVD method according to claim 4 or 5, characterized in that, In step S1, the fine polishing is performed using 1000-grit water-resistant sandpaper.

7. The PVD method according to any one of claims 4 to 6, characterized in that, In step S2, the thickness of the Ti(C,N)-HEA-ZrO2 cermet stress transition buffer layer is 1.5 to 2.5 μm.

8. The PVD method according to any one of claims 4 to 7, characterized in that, In step S3, when depositing the AlCrN / TiAlN nanolayered insulating protective layer, the substrate negative bias voltage is adjusted to -100 V, pure N2 is introduced and the gas pressure is adjusted to 2.0 Pa, and the temperature is controlled at 500 ℃.

9. The PVD method according to claim 8, characterized in that, In step S3, when depositing the AlCrN layer, both the aluminum and chromium targets are turned on, and the target currents are both 50–60 A; when depositing the TiAlN layer, the chromium target is turned off and the titanium target is turned on, with the aluminum and titanium targets working together, and the target currents are both 50–60 A.

10. The PVD method according to claim 8 or 9, characterized in that, In step S3, the total deposition time for the AlCrN layer and TiAlN layer is 100-120 min. After deposition, the workpiece is cooled to below 150 °C in the furnace and then removed.

Images