A molybdenum-based alloy high-temperature oxidation resistant coating, its preparation method and application

Abstract

This invention discloses a molybdenum-based alloy high-temperature oxidation resistant coating, its preparation method, and its application. The high-temperature oxidation resistant coating has a multi-layer structure including a pure nickel binder layer, a nickel-tungsten alloy transition layer, and a platinum surface layer. A compositionally gradual transition region is formed through low-temperature interdiffusion between the pure nickel binder layer and the molybdenum-based alloy. The nickel-tungsten layer alleviates thermal expansion mismatch, and the platinum layer provides an anti-oxidation barrier. This invention also includes a method for preparing the molybdenum-based alloy high-temperature oxidation resistant coating and its application in aerospace and nuclear industry components.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, specifically to a molybdenum-based alloy high-temperature oxidation resistant coating, its preparation method, and its application. Background Technology

[0002] Molybdenum and its alloys have advantages such as high melting point, good electrical and thermal conductivity, good high-temperature strength and creep resistance. Compared with other refractory metals, molybdenum has a low coefficient of thermal expansion, good thermal shock resistance and thermal fatigue resistance, so it is widely used in the aerospace field.

[0003] However, molybdenum-based alloys are prone to generating volatile MoO3 in high-temperature oxidizing environments, resulting in a loose, porous, and easily peeling oxide layer, causing rapid component failure.

[0004] Existing high-temperature anti-oxidation coatings for molybdenum-based alloys mainly include aluminide coatings, oxide coatings, silicide coatings, and noble metal coatings. Among these, aluminide and oxide coatings have mismatched coefficients of thermal expansion with the molybdenum substrate, making them prone to cracking and even peeling. Silicide coatings offer excellent oxidation resistance but are brittle and also pose a risk of cracking. Noble metal coatings (such as single platinum coatings) have good oxidation resistance but suffer from the following fatal flaw: a large difference in coefficients of thermal expansion (Mo: ~5.5×10⁻⁶). -6 / K, Pt: 9.0×10 -6 The Mo / Pt interface suffers from severe thermal stress, leading to instability and interfacial reactions at high temperatures. This results in rapid decay of the bonding strength, making the coating prone to peeling under high-temperature cycling. Furthermore, pure platinum (Pt) coatings are extremely expensive, and increasing coating thickness to improve performance limits their engineering applications.

[0005] In existing patent literature, US3200284A proposes a method for depositing a platinum layer on a molybdenum gate electrode. This method involves first forming a roughened iron-group metal (such as Ni) interlayer on the molybdenum surface, followed by electroplating of the platinum layer. The roughened surface provides mechanical anchoring, and subsequent heat treatment promotes atomic diffusion to enhance adhesion. While this method improves the adhesion between the platinum layer and the molybdenum substrate to some extent, its transition layer is a single-layer, non-gradient, roughened Ni layer. Bonding relies solely on mechanical interlocking and limited diffusion, failing to address the issue of continuous matching of thermal expansion coefficients. Furthermore, it does not address the optimization of the coating system's oxidation resistance under long-term high-temperature oxidizing conditions. Therefore, its structure still carries the risks of interfacial stress concentration, insufficient bonding strength, and susceptibility to failure under cyclic thermal loading.

[0006] Both patent documents CN110257679B and CN110273149B employ spark plasma sintering (SPS) technology to prepare an alloy coating containing elements such as Mo, Cu, Ti, Zr, and C on the surface of a low-melting-point substrate such as an iron-based substrate. They also introduce nickel foil, copper foil, or niobium-titanium composite layer as an intermediate transition layer. By utilizing atomic diffusion between multiple metals to form a metallurgical bond, the mismatch in thermal expansion coefficients between the coating and the substrate is effectively alleviated, achieving a strong bond at temperatures below the melting point of the substrate. However, the above-mentioned technical solutions are all aimed at the preparation of high-temperature wear-resistant coatings for low-melting-point substrates such as iron-based materials. The coating composition is mainly Mo-Cu-Ti-Zr-C alloy, which aims to improve wear resistance and sintering bonding strength, rather than for anti-oxidation protection of molybdenum-based alloys under high-temperature oxidizing environments. The transition layer is nickel or composite metal foil, without introducing tungsten (W) to construct a gradient thermal expansion matching layer, and without using platinum as a surface anti-oxidation layer. The process relies on SPS sintering, which requires high pressure, high temperature, and vacuum environment. The equipment is complex and energy-intensive, making it difficult to apply to the industrial batch coating of complex-shaped molybdenum-based alloy parts. Furthermore, it cannot achieve the construction of high-precision, low-damage, and low-cost protective coatings on the surface of molybdenum-based alloys.

[0007] Therefore, there is an urgent need to develop a high-temperature anti-oxidation coating that has good thermal compatibility with molybdenum-based alloys, stable interface, strong adhesion, and controllable cost. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a molybdenum-based alloy high-temperature oxidation resistant coating, its preparation method, and its application. In one aspect, the present invention provides a molybdenum-based alloy high-temperature oxidation resistant coating, comprising: a multi-layer gradient system in which the coating structure comprises, from the inside out: 1. Pure nickel (Ni) binder layer: Pure nickel (Ni) is used as the binder layer to directly contact the surface of the molybdenum-based alloy; through the controllable interdiffusion of Ni and Mo, a transition zone with gradual compositional change is formed, which significantly improves the interfacial bonding strength; Furthermore, the thickness of the pure nickel is 1 µm to 2 µm; 2. Nickel-Tungsten (Ni-W) Alloy Transition Layer: Located above the pure nickel (Ni) binder layer, a Ni-W alloy transition layer is provided to buffer the difference in thermal expansion coefficients between the molybdenum-based alloy and the platinum surface layer. Its thermal expansion coefficient (CTE) is between that of molybdenum and platinum (~7.0 × 10⁻⁶). -6 / K), effectively buffering stress while reducing Pt coating thickness; Furthermore, the nickel-tungsten alloy transition layer has a thickness of 12 µm to 20 µm, wherein the atomic percentage of tungsten (W) is 20–35 at.%, and the coefficient of thermal expansion (CTE) is reduced from Mo (~5.5 × 10⁻⁶) by adjusting the W content. -6 / K) to Pt (~9.0×10 -6The smooth transition of / K) alleviates thermal stress; 3. Platinum (Pt) surface layer: Located above the nickel-tungsten (Ni-W) alloy transition layer, it has excellent high-temperature oxidation resistance and is used to provide dense, high-temperature oxidation-resistant protection; Furthermore, the platinum thickness is 1.0 µm to 1.8 µm.

[0009] In another aspect, the present invention provides a method for preparing a molybdenum-based alloy high-temperature oxidation resistant coating, comprising the following steps: S1: The surface of the molybdenum-based alloy is cleaned by atmospheric pressure plasma. The treatment atmosphere is a mixture of argon and oxygen in a volume ratio of 3% to 8%. The treatment power is 80 W to 200 W and the treatment time is 15 s to 50 s. Atmospheric pressure plasma cleaning (non-acid washing) pretreatment is used to avoid molybdenum (Mo) corrosion. S2: A pure Ni bonding layer is formed by electroplating on the surface of a molybdenum-based alloy; S3: A Ni-W alloy transition layer is formed by electroplating on a pure Ni bonding layer; S4: A Pt surface layer is formed by electroplating on the Ni-W alloy transition layer; Electroplating has low energy consumption, controllable parameters, and is suitable for continuous production. S5: Post-treatment is performed on the molybdenum-based alloy after the formation of multi-layer gradient coating to allow interdiffusion between the pure Ni binder layer and the molybdenum matrix. Through limited interdiffusion, a Ni-Mo transition zone with gradually changing composition is formed, which significantly improves the interfacial bonding strength.

[0010] Further, in step S2, a pure nickel bonding layer is deposited using electroplating: the electroplating solution is a conventional Watt's nickel system or a nickel sulfamate system, and the current density is 0.8–1.5 A / dm³. 2 ; Furthermore, the transition time between step S2 and step S3 is less than 5 minutes to prevent re-oxidation of the molybdenum substrate surface; Further, in step S3, a Ni-W alloy transition layer is deposited using an electroplating method: a modified Watt's nickel system is used, with an average current density of 0.8–1.2 A / dm³. 2 The pulse duty cycle is 30%–50%, the pH value of the electroplating solution is 7.0–8.2, and the composition of the plating solution includes: 30–60 g / L NiSO4·7H2O, 70–90 g / L Na3C6H5O7·H2O, 55–135 g / L Na2WO4·2H2O, 0.2–0.35 g / L Ti(SO4)2, and 0.1–0.15 g / L LaCl3; the Ni-W electroplating solution containing Ti(SO4)2 and LaCl3 is used to improve the density of the coating and reduce internal stress. Further, in step S4, a Pt surface layer is formed by electroplating: a weakly acidic Pt plating solution is used, with a current density of 0.5–1.0 A / dm³. 2 The electroplating solution has a pH of 5.0–5.8 and contains: 10–15 g / L dinitrodiammineplatinum, 42–46 g / L glycine, 12–18 g / L diaminotriacetic acid, and 0.06–0.12 g / L cerium trichloride. The Pt electroplating solution containing cerium trichloride is used to inhibit the coarsening of Pt grains during electroplating and heat treatment, and to improve the density of the coating.

[0011] Furthermore, the post-treatment described in step S5 is a heat treatment: under a nitrogen atmosphere, the heating rate is 3-5 °C / min, the heat treatment temperature is 480-550 °C, and the heat treatment time is 100-150 min. This range of heat treatment temperature and time can promote limited interdiffusion between Ni and Mo while avoiding coarsening of the Pt layer.

[0012] In another aspect of the present invention, the molybdenum-based alloy with the above-mentioned multilayer structure and high-temperature oxidation resistant coating is applied to aerospace components or nuclear industry components in high-temperature oxidation environments.

[0013] Compared with the prior art, the present invention has the following advantages: 1) Significantly enhanced bonding strength: By inserting a pure nickel bonding layer between the molybdenum substrate and the Ni-W transition layer, and subjecting it to heat treatment at 480–550℃, the pure nickel and the molybdenum substrate undergo limited interdiffusion, forming a Ni-Mo transition zone with a gradually changing composition. This effectively alleviates the stress concentration at the interface, resulting in a bonding strength of 38 N, which is much higher than that of structures without a Ni layer (18 N) and single Pt coatings (15 N).

[0014] 2) Significantly improved thermal cycling resistance: The thermal expansion coefficient of the Ni-W transition layer is ~7.0×10⁻⁶. -6 The K group (Ti(SO4)2) is positioned between Mo and Pt, forming a gradient buffer. Adding Ti(SO4)2 and LaCl3 to the Ni-W coating improves its density and reduces internal stress. Adding cerium trichloride to the Pt coating inhibits grain coarsening and maintains its density. The synergistic effect of these three components results in a thermal cycle life >200 cycles, which is 6.7 times that of a single Pt coating.

[0015] 3) Excellent antioxidant properties: The ultrathin Pt layer (1.0–1.8 µm) provides a dense, inert antioxidant barrier. Combined with atmospheric pressure plasma pretreatment (avoiding surface re-oxidation), it significantly inhibits MoO3 volatilization, with an oxidation weight gain of only 0.65 mg / cm³ at 1400℃ / 100h. 2 .

[0016] 4) Significantly reduced precious metal usage: Under the same Pt ​​thickness (1.4 µm), the coating of this invention achieves a leap in performance through structural optimization, although the cost is the same as that of a single Pt coating (26.4 yuan / dm). 2 However, its performance far exceeds that of other materials, achieving the engineering economy of "replacing materials with structure".

[0017] 5) Environmentally friendly process and suitable for mass production: Atmospheric pressure plasma cleaning is used instead of acid washing to avoid substrate corrosion; aqueous solution electroplating method is used, which does not require high temperature, vacuum or complex equipment, and the process parameters are stable, making it suitable for continuous and mass production of complex shaped parts. Attached Figure Description

[0018] Figure 1 This is a cross-sectional SEM image of the high-temperature oxidation resistant coating of the molybdenum-based alloy of the present invention. Specific implementation examples: Example 1 (Basic Example) S1: The surface of the molybdenum-based alloy was treated with an atmospheric pressure plasma cleaner with a power of 80 W and an atmosphere of Ar + 3% O2 ​​(volume ratio) for 15 seconds. S2: Electroplated pure Ni bonding layer: Watt's nickel system, current density 0.8 A / dm 2 Thickness 1 µm, transfer to S3 < 5 min; S3: Ni-W plating: 0.8 A / dm 2 The plating solution had a duty cycle of 30%, pH = 7.0, and contained 30 g / L NiSO4·7H2O, 70 g / L Na3C6H5O7·H2O, 55 g / L Na2WO4·2H2O, 0.2 g / L Ti(SO4)2, and 0.1 g / L LaCl3. The plating thickness was 12 µm, and the W content was 20 at.%. S4: Pt plating: 0.5 A / dm 2 The pH value is 5.0. The plating solution contains 10 g / L dinitrodiammineplatinum, 42 g / L glycine, 12 g / L diaminotriacetic acid, and 0.06 g / L cerium trichloride. The thickness is 1.0 µm. S5: Heat treatment: Nitrogen gas, 3℃ / min, 480℃, 100 min.

[0019] Example 2 (Optimized Example) S1: Molybdenum-based alloy atmospheric pressure plasma cleaning, power 120W, Ar+5% O2, processing time 30s; S2: Electroplated pure Ni bonding layer: Watt's nickel system, current density 1.2 A / dm 2 Thickness 1.5 µm, transfer to S3 < 5 min; S3: Ni-W plating: 1.0 A / dm2 The plating solution had a duty cycle of 40%, pH = 7.8, and contained 45 g / L NiSO4·7H2O, 80 g / L Na3C6H5O7·H2O, 95 g / L Na2WO4·2H2O, 0.28 g / L Ti(SO4)2, and 0.12 g / L LaCl3. The plating thickness was 16 µm, and the W content was 30 at.%. S4: Pt plating: 0.8 A / dm 2 The pH value is 5.4. The plating solution contains 12 g / L dinitrodiammineplatinum, 44 g / L glycine, 15 g / L diaminotriacetic acid, and 0.09 g / L cerium trichloride, with a thickness of 1.4 µm. S5: Heat treatment: 4℃ / min, 510℃, 120 min.

[0020] Example 3 (High W Content Example) S1: Molybdenum-based alloy atmospheric pressure plasma cleaning, power 200W, Ar+8% O2, processing time 50s; S2: Electroplated pure Ni bonding layer: Watt's nickel system, current density 1.5 A / dm 2 Thickness 2 µm, transfer to S3 < 5 min; S3: Ni-W plating: 1.2 A / dm 2 The plating solution had a duty cycle of 50%, pH = 8.2, and contained 60 g / L NiSO4·7H2O, 90 g / L Na3C6H5O7·H2O, 135 g / L Na2WO4·2H2O, 0.35 g / L Ti(SO4)2, and 0.15 g / L LaCl3. The plating thickness was 20 µm, and the W content was 35 at.%. S4: Pt plating: 1.0 A / dm 2 The pH value is 5.8, and the plating solution contains 15 g / L dinitrodiammineplatinum, 46 g / L glycine, 18 g / L diaminotriacetic acid, and 0.12 g / L cerium trichloride, with a thickness of 1.8 µm. S5: Heat treatment: 5℃ / min, 550℃, 150 min.

[0021] Comparative Example 1 (without Ni binder layer) S1: Same as Example 1; S2: Electroplating a Ni-W transition layer directly onto the molybdenum-based alloy body (same parameters as in Example 1, thickness 12 µm, W 20 at.%). S3: Electroplated Pt layer (same as in Example 1, thickness 1.0 µm); S4: The heat treatment conditions are the same as in Example 1.

[0022] Comparative Example 2 (Single Pt Coating) S1: Same as Example 2 S2: A single Pt coating with the same Pt ​​thickness (1.4 µm) as in Example 2 is directly electroplated onto the surface of a molybdenum-based alloy.

[0023] S3: The heat treatment conditions are the same as in Example 2.

[0024] Comparative Example 3 (MoSi2 coating) An embedded MoS2 coating with a thickness of approximately 20 µm was used.

[0025] Comparative Example 4 (Al2O3 coating) An Al2O3 coating with a thickness of approximately 10 µm was applied by magnetron sputtering.

[0026] Comparison of the effects of this invention and the comparative example: Test metrics: 1. Adhesion test: According to GB / T 30707-2014 "Determination of adhesion strength of thermal spray coating", the tensile test of the paired specimens was adopted, the loading rate was 1 mm / min, and the average value of three specimens was taken. 2. Oxidation weight gain test: Isothermal oxidation was performed at 1400℃ in still air for 100 hours. The weight gain per unit area of ​​the sample before and after oxidation was measured using a balance with an accuracy of 0.01 mg. 3. Thermal Cycling Life Test: The sample was held at 1400℃ for 10 minutes, and then forced to cool to room temperature (approximately 25℃). This constitutes one cycle. The number of cycles when visible cracks or peeling areas on the coating surface exceeded 5% was recorded. The average value of 5 samples in each group was taken.

[0027] Table 1: Test Tables for Examples and Comparative Examples

[0028] Note: In Table 1, the thickness of Pt in Example 2 and Comparative Example 2 is the same (1.4 μm), and the amount of Pt used is 0.12 g / dm. 2 The cost of Pt material is approximately 26.4 yuan / dm². 2 (Based on platinum at 220 yuan / gram); As can be seen from Table 1 above: (1) Structural advantages (In both Embodiment 2 and Comparative Example 2 of this invention, the Pt thickness is the same, 1.4 µm) The invented coating showed a 153% improvement in adhesion (38 N vs 15 N) and a 0.65 mg / cm³ weight gain during oxidation at 1400℃ / 100h. 2 vs 1.4 mg / cm 2In terms of both thermal cycling life (>200 cycles vs 30 cycles, extending by 566%), it is significantly better than coatings of the same Pt ​​thickness. The only variable between the two is the presence or absence of a Ni bonding layer and a Ni-W transition layer. The performance parameters of Example 2 of the present invention are also significantly better than those of Comparative Example 1, which confirms the core role of the multilayer gradient structure of the present invention in interface strengthening, thermal stress buffering and antioxidant performance improvement.

[0029] (2) Comparison of antioxidant properties (comparison of this invention with MoSi2 coating) The oxidative weight gain of this invention is 0.65 mg / cm³. 2 Slightly higher than the MoSi2 coating (0.45 mg / cm³). 2 However, due to its inherent brittleness and significant difference in thermal expansion coefficient compared to the molybdenum substrate, the MoSi2 coating has a thermal cycling life of only 20 cycles, far lower than the >200 cycles of the present invention. The present invention solves the key bottleneck of poor thermal shock resistance in silicide coatings while ensuring good oxidation resistance.

[0030] (3) Overall performance comparison (comparison of this invention with Al2O3 coating) This invention outperforms Al2O3 coatings in both adhesion (38 N vs 20 N) and thermal cycling life (>200 cycles vs 40 cycles), and also exhibits lower oxidative weight gain (0.65 mg / cm³) compared to Al2O3 coatings. 2 vs 1.1 mg / cm 2 This demonstrates the comprehensive advantages of multilayer metal gradient coatings over single oxide coatings.

[0031] (4) Engineering economics This invention replaces the thick Pt layer increment required for enhanced functionality with a Ni or Ni-W non-precious metal transition layer, minimizing the amount of Pt used (1.0~1.8μm) while ensuring high performance, and has good engineering economics and prospects for mass application.

[0032] At the same time, from Figure 1 As you can see, from bottom to top in the image are: molybdenum substrate (molybdenum-based alloy body), pure nickel bonding layer (Ni), nickel-tungsten transition layer (Ni-W), and platinum surface layer (Pt). The interfaces are clear, the interlayer bonding is dense, there are no macroscopic cracks or pores, and the transition zone has a gradual change characteristic.

[0033] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A molybdenum-based alloy high-temperature oxidation resistant coating, characterized in that: The coating structure is a multi-layer gradient system, which includes, in sequence: a pure nickel bonding layer, which directly contacts the surface of the molybdenum-based alloy; a nickel-tungsten alloy transition layer, which is located above the pure nickel bonding layer; and a platinum surface layer, which is located above the nickel-tungsten alloy transition layer.

2. The molybdenum-based alloy high-temperature oxidation resistant coating according to claim 1, characterized in that, The thickness of the pure nickel bonding layer is 1.2 µm to 1.8 µm.

3. The molybdenum-based alloy high-temperature oxidation resistant coating according to claim 1, characterized in that, The nickel-tungsten alloy transition layer has a thickness of 12 µm to 20 µm, wherein the atomic percentage of tungsten is 20 to 35 at.%.

4. The molybdenum-based alloy high-temperature oxidation resistant coating according to claim 1, characterized in that, The thickness of the platinum surface layer is 1.0µm to 1.8µm.

5. The method for preparing a high-temperature oxidation resistant coating for a molybdenum-based alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Perform atmospheric pressure plasma cleaning on the surface of molybdenum-based alloys. The treatment atmosphere is a mixture of argon and oxygen in a volume ratio of 3% to 8%. The treatment power is 80 watts to 200 watts, and the treatment time is 15 seconds to 50 seconds. S2: A pure nickel bonding layer is deposited on the surface of the molybdenum-based alloy treated with S1 by electroplating. S3: A nickel-tungsten alloy transition layer is deposited on the surface of the nickel bonding layer by electroplating. S4: A platinum surface layer is deposited on the surface of the nickel-tungsten alloy transition layer by electroplating. S5: Heat treatment is performed on the molybdenum-based alloy with a multi-layer coating structure formed by S1 to S4.

6. The method for preparing a high-temperature oxidation-resistant coating for molybdenum-based alloys according to claim 5, characterized in that, The electroplating solution of S2 is a conventional Watt's nickel system or a nickel sulfamate system, with a current density of 0.8–1.5 A / dm³. 2 .

7. The method for preparing a high-temperature oxidation-resistant coating for a molybdenum-based alloy according to claim 5, characterized in that, The transition time between S2 and S3 is less than 5 minutes; the electroplating solution of S3 is a modified Watt's nickel system with an average current density of 0.8–1.2 A / dm³. 2 The pulse duty cycle is 30%–50%, and the pH value of the electroplating solution is 7.0–8.

2. The electroplating solution composition includes: 30–60 g / L NiSO4·7H2O, 70–90 g / L Na3C6H5O7·H2O, 55–135 g / L Na2WO4·2H2O, 0.2–0.35 g / L Ti(SO4)2, and 0.1–0.15 g / L LaCl3.

8. The method for preparing a high-temperature oxidation-resistant coating for molybdenum-based alloys according to claim 5, characterized in that, The S4 electroplating solution is a weakly acidic platinum plating system with a current density of 0.5–1.0 A / dm³. 2 The electroplating solution has a pH value of 5.0–5.8; the composition of the electroplating solution includes: 10–15 g / L dinitrodiammineplatinum, 42–46 g / L glycine, 12–18 g / L diaminotriacetic acid, and 0.06–0.12 g / L cerium trichloride.

9. The method for preparing a high-temperature oxidation resistant coating of molybdenum-based alloy according to claim 5, characterized in that the S5 heat treatment is performed under a nitrogen atmosphere, with a heating rate of 3℃ / min to 5℃ / min, a heat treatment temperature of 480℃ to 550℃, and a heat treatment time of 100 min to 150 min.

10. The molybdenum-based alloy high-temperature oxidation resistant coating according to any one of claims 1 to 4, characterized in that, The multi-layered coated molybdenum-based alloy is used in aerospace or nuclear industry components in high-temperature oxidizing environments.

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