A method for improving the oxidation resistance of low-aluminum alloys using Cr precursor films

Abstract

This invention discloses a method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film, relating to the field of high-temperature alloy surface modification technology. The method includes: S1, selecting a binary Ni-Al alloy with an Al content of 12-16 wt.% as the substrate, processing it into a 10 mm × 10 mm × 2 mm sample, and sequentially passing it through 320 and 800 grit SiC sandpaper, ultrasonically cleaning it with acetone and anhydrous ethanol solution for 15 min, and drying it with a hair dryer for later use; S2, depositing a metallic Cr film on the pretreated alloy surface using DC magnetron sputtering (DCMS), with the deposition parameters being: system base vacuum 3 × 10⁻⁶. ‑3 Pa, sputtering pressure 0.5 Pa, DC power 1.2 kW, substrate temperature 200°C o C. The sample stage rotation speed is 15 rpm, the deposition time is 25 min, and the Cr film thickness is controlled to be 480±25 nm; S3. The alloy sample with the deposited Cr film is placed in a thermogravimetric analyzer (TGA) or a box muffle furnace in dry air, and subjected to 10 o The heating rate increased to 900 °C / min. o At temperature C, isothermal oxidation is performed for 20-100 h. This invention utilizes a Cr precursor film prepared on the alloy surface to catalyze the selective oxidation of Al in the substrate, enabling alloys that previously could not form a protective oxide film to transition from non-protective oxidation to protective oxidation. This provides a new technical approach to achieving a good match between the high-temperature mechanical properties and high-temperature oxidation resistance of alloys.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy surface modification technology, and is a preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film. Background Technology

[0002] Nickel-based superalloys, with their superior creep strength, excellent resistance to oxidation and corrosion, and good formability, have become key materials for manufacturing core hot-end components such as turbine blades and guide vanes for aero-engines. With the urgent demands for propulsion efficiency and fuel economy in the aerospace field, the design of modern high-performance engines is moving towards higher turbine inlet temperatures. To meet the stringent requirements for material mechanical properties under extreme service environments, a large number of solid solution strengthening elements have been introduced into nickel-based superalloys, aiming to improve the high-temperature strength of the alloy by forming refractory phases. However, this compositional optimization often comes with side effects: the aluminum content in the alloy is far below the critical aluminum content required to form a continuous, dense, protective Al2O3 oxide film. In traditional alloy design, when the Al content is below this critical value, the alloy tends to undergo internal oxidation or form a non-protective NiO / NiAl2O4 spinel mixed oxide during high-temperature oxidation, failing to establish an effective barrier layer, thus leading to continuous catastrophic oxidation corrosion of the matrix.

[0003] To address the degradation of antioxidant performance caused by low Al content, various surface modification strategies have been explored in existing technologies. Applying protective coatings to alloy surfaces, such as aluminide coatings, is widely used due to their simple preparation process and low cost. However, these coatings have inherent differences in physicochemical properties with the alloy substrate. During long-term high-temperature service, interdiffusion of elements occurs between the coating and the substrate, leading not only to the continuous consumption of Al in the coating and its degradation, but also to the formation of brittle phases and Kirkendall voids at the interface, ultimately causing coating peeling failure. Furthermore, once the coating is damaged, the low Al content of the substrate makes it difficult to form a new protective film through selective oxidation, resulting in direct exposure of the alloy substrate to the oxidizing environment and accelerated failure. Therefore, developing a new method that produces a uniform film with strong adhesion and fundamentally solves the problem of low-Al alloys failing to form a stable α-Al₂O₃ film is a crucial technological bottleneck that urgently needs to be overcome in the field of high-temperature protective coatings. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film to solve the technical problem that low-aluminum alloys cannot form a stable α-Al2O3 protective film.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a low-aluminum alloy with an improved oxidation resistance using a Cr precursor film, comprising, S1. A binary Ni-Al alloy with an Al content of 12-16 wt.% was selected as the matrix. The alloy was machined into samples with dimensions of 10 mm × 10 mm × 2 mm. The sample surface was polished and chamfered using 320# and 800# SiC wet sandpaper in sequence. The polished sample was ultrasonically cleaned in a mixture of acetone and anhydrous ethanol for 15 min. The cleaned sample was then dried with cold air and set aside for later use. S2. Mount the pretreated sample onto the sample holder of the magnetron sputtering equipment. A DC magnetron sputtering (DCMS) process is used to deposit a metallic Cr film on the alloy sample surface. The process parameters for the deposition are set as follows: system background vacuum 3 × 10⁻⁶. -3 Pa, sputtering working pressure 0.5 Pa, DC sputtering power 1.2 kW, center heating temperature 200 Pa. o C, sample holder rotation speed 15 rpm, deposition time 25 min. By controlling these parameters, a continuous, dense Cr film with a thickness of 480±25 nm was prepared. S3, the sample with a Cr film deposited on its surface and the control sample without any treatment are suspended in the alumina reaction tube of a thermogravimetric analyzer (TGA). At 10... o A heating rate of C / min was used to heat the temperature inside the reaction tube to 900°C. o C. In 900 o The sample was oxidized for 20 h under constant temperature conditions.

[0007] As a preferred embodiment of the preparation method of improving the oxidation resistance of low-aluminum alloys using Cr precursor film as described in this invention, wherein: the binary Ni-Al alloy in S1 is Ni-16Al (Al content 16.1 wt.%, corresponding to atomic percentage 29.5%) or Ni-12Al (Al content 12.6 wt.%, corresponding to atomic percentage 23.8%).

[0008] Furthermore, two representative low-aluminum binary Ni-Al alloys were selected as experimental substrates. The Al content of Ni-16Al (29.5 at.%) was close to but did not reach the critical concentration (approximately 30.7 at.%) required by classical Wagner theory for the formation of a continuous Al₂O₃ film; while the Al content of Ni-12Al was significantly lower than this critical value. The purpose of selecting these two alloys was to verify the effectiveness of the method of this invention under subcritical and far below-critical conditions, demonstrating that even for low-Al alloys that are difficult to spontaneously form an external oxide film, excellent oxidation resistance can be achieved through the treatment method of this invention.

[0009] As a preferred embodiment of the preparation method for improving the oxidation resistance of low-aluminum alloys using Cr precursor films as described in this invention, wherein: the target material for DC magnetron sputtering in S2 is a pure Cr target (purity ≥ 99.9%), and the target-substrate distance is 150 mm.

[0010] Furthermore, to ensure the purity of the precursor film and the film-substrate adhesion, this scheme strictly limits the sputtering target to a high-purity (≥99.9%) Cr target to minimize the interference of impurity elements on subsequent oxidation behavior. Simultaneously, the target-substrate distance is set to 150 mm. This specific geometric distance helps maintain a uniform distribution of plasma density during sputtering, thereby ensuring that the Cr atoms deposited on the alloy surface have consistent kinetic energy and flux, laying the physical foundation for the formation of a dense and uniformly thick film.

[0011] As a preferred embodiment of the preparation method of improving the oxidation resistance of low aluminum alloys using Cr precursor film as described in this invention, wherein: the thickness of the Cr film in S2 is controlled to be 25 min by the deposition time, and the resulting Cr film has no voids or cracks at the interface with the alloy substrate, and the film layer is continuous and dense.

[0012] Furthermore, this invention precisely controls the deposition time to 25 min, locking the thickness of the Cr precursor film within an ultrathin range of 480±25 nm. This thickness design has dual advantages: firstly, a sufficiently thick film layer can be completely transformed into a continuous Cr2O3 barrier in the early stages of oxidation; secondly, it avoids excessive internal stress caused by an excessively thick film layer, which could lead to peeling. Experimental observations confirm that the obtained Cr film has a tight bond with the substrate interface, without voids or cracks. This continuous and dense microstructure is a physical prerequisite for subsequent induced selective oxidation.

[0013] As a preferred embodiment of the preparation method for improving the oxidation resistance of low-aluminum alloys using Cr precursor film as described in this invention, wherein: the holding time for high-temperature oxidation in S3 is 20 h, and the Cr film on the sample surface is rapidly and completely converted into a continuous Cr2O3 layer in the early stage of oxidation.

[0014] Furthermore, setting the high-temperature oxidation holding time to 20 hours is based on precise control of oxidation kinetics. At this time point, the Cr precursor film deposited on the surface has been completely oxidized and depleted, transforming into a continuous and dense Cr2O3 outer layer. This transformation process effectively reduces the oxygen partial pressure on the alloy surface to an extremely low level corresponding to the Cr2O3 / Cr equilibrium, thereby thermodynamically inhibiting the formation of NiO and creating a favorable interfacial environment for the nucleation of the inner α-Al2O3 layer.

[0015] As a preferred embodiment of the preparation method for improving the oxidation resistance of low-aluminum alloys using Cr precursor films as described in this invention, in step S3, after high-temperature oxidation, a double-layer protective film of outer Cr2O3 and inner α-Al2O3 is formed on the alloy surface. The inner α-Al2O3 directly nucleates and grows through the crystal isomorphism effect of Cr2O3, without the formation of metastable phases such as γ-Al2O3 or θ-Al2O3.

[0016] Furthermore, the isomorphic catalytic mechanism is utilized. Since Cr2O3 and α-Al2O3 both belong to the corundum crystal structure, the Cr2O3 layer formed in the early stage of oxidation can provide a template for heterogeneous nucleation of α-Al2O3, significantly reducing the nucleation energy barrier of α-Al2O3. Therefore, when Al elements diffuse outward from the alloy, they can directly grow into the thermodynamically stable α-Al2O3 below the outer Cr2O3 layer, completely skipping the formation of metastable phases such as γ or θ in the traditional oxidation process, and avoiding the drawbacks of volume shrinkage and microcracks caused by phase transformation.

[0017] As a preferred embodiment of the preparation method of improving the oxidation resistance of low-aluminum alloys using Cr precursor film as described in this invention, wherein: after high-temperature oxidation in S3, the oxidation kinetics of the low-aluminum alloy with Cr film deposited on the surface follows a parabolic law, and its parabolic rate constant is reduced by 80% compared with the untreated alloy.

[0018] Furthermore, testing showed that the parabolic rate constant of the treated Ni-16Al alloy decreased from the original 3.0 × 10⁻⁶. - 13 g 2 ·cm -4 ·s -1 Reduced to 6.0×10 -14 g 2 ·cm -4 ·s -1 This data shows that, thanks to the effective barrier of the double-layer protective film, the oxidation weight gain rate of the alloy decreased by about 80%, and its steady-state oxidation resistance is even better than that of the high-aluminum-content Ni-22Al alloy, achieving a leapfrog improvement in the oxidation resistance of low-aluminum alloys.

[0019] As a preferred embodiment of the preparation method of improving the oxidation resistance of low-aluminum alloys using Cr precursor film as described in this invention, in which: after high-temperature oxidation in S3, the thickness of the inner α-Al2O3 layer is about 0.4±0.1 μm, and the depth of the aluminum-poor region of the alloy matrix is ​​only 0.4±0.1 μm (far smaller than the 3.2±0.6 μm of untreated Ni-16Al).

[0020] Further microstructural analysis revealed that after 20 h of oxidation, a bilayer oxide film with a total thickness of approximately 0.4 μm was formed on the alloy surface. Crucially, the Al-depleted zone thickness on the substrate side was reduced to 0.4 ± 0.1 μm, while the untreated Ni-16Al alloy exhibited a depleted zone thickness as high as 3.2 ± 0.6 μm under the same conditions. This significant comparison demonstrates that this invention, by promoting efficient Cr2O3 / α-Al2O3 bilayer growth, greatly reduces the ineffective consumption of Al elements and maintains the structural integrity of the substrate surface.

[0021] As a preferred embodiment of the preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in this invention, wherein: after high-temperature oxidation in step S3, the oxidation is detected by photoexcited fluorescence piezoelectric spectroscopy (PLPS) at only 14402 cm⁻¹. -1 With 14432 cm -1 Two characteristic peaks belonging to α-Al2O3 were detected at the location, but no characteristic peaks of θ-Al2O3 were found.

[0022] Furthermore, photoluminescent piezoelectric spectroscopy (PLPS) was used to identify the phase composition of the oxidation products, and the results showed that only at 14402 cm⁻¹... -1 and 14432 cm -1 The characteristic double peak of α-Al₂O₃ appeared at 14575 cm⁻¹, while at 14575 cm⁻¹... -1 and 14645 cm -1 No signal belonging to θ-Al2O3 was found. This spectroscopic evidence conclusively confirms that the method of this invention induces a single, thermodynamically stable α-Al2O3 phase, completely eliminating the existence of metastable phases and ensuring the long-term microstructural stability of the oxide film.

[0023] As a preferred embodiment of the preparation method for improving the oxidation resistance of low-aluminum alloys using Cr precursor film as described in this invention, in which: after the high-temperature oxidation in S3 is extended to 100 h, the alloy surface still maintains a complete Cr2O3 / α-Al2O3 double-layer structure, with no oxide film peeling or cracks, the thickness of the α-Al2O3 layer increases to 0.9±0.1 μm, and the depth of the aluminum-depleted zone is maintained within 1.2±0.1 μm.

[0024] Furthermore, to verify the reliability of this invention under actual long-term service conditions, the oxidation time was extended to 100 hours. The results showed that the alloy surface maintained a complete and intact outer Cr2O3 + inner α-Al2O3 double-layer structure, without any peeling or cracking. At this time, the thickness of the inner α-Al2O3 layer increased to 0.9 ± 0.1 μm, while the thickness of the Al-depleted zone remained within 1.2 ± 0.1 μm. This fully demonstrates that the protective film formed by this invention has excellent adhesion and growth stability, and can continuously and effectively protect the low-aluminum alloy substrate from high-temperature oxidation corrosion.

[0025] The beneficial effects of this invention are as follows: By selecting a binary Ni-Al alloy with a specific Al content and pre-treating it with fine grinding and ultrasonic cleaning, the surface activity and surface quality of the substrate are ensured, providing an ideal nucleation substrate for subsequent film growth; an ultrathin and continuous dense metallic Cr precursor film is deposited on the substrate using DC magnetron sputtering technology. This Cr film preferentially transforms into a continuous Cr2O3 layer in the early stage of high-temperature oxidation, effectively reducing the oxygen partial pressure on the alloy surface and inducing α-Al2O3 to directly nucleate and grow steadily under Cr2O3 based on the crystal isomorphism effect. Thus, a dual protective film structure of outer Cr2O3 + inner α-Al2O3 is successfully constructed on the surface of low-Al alloys, reducing the oxidation rate of low-aluminum alloys by about 80%, inhibiting internal oxidation of the alloy and the expansion of the aluminum-depleted region, and completely avoiding the drawbacks of easy particle shedding and metastable phase transformation in traditional spraying methods, thereby improving the oxidation stability and protective reliability of the material under high-temperature long-term service environment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 Flowchart of a method for improving the oxidation resistance of low-aluminum alloys using Cr precursor films. Figure 2 The cross-sectional morphology of Ni-12Al and Ni-16Al after oxidation for 20 h without any surface treatment is shown in Figure (a), which is the Ni-12Al alloy and Figure (b) is the Ni-16Al alloy.

[0028] Figure 3 The cross-sectional morphology and elemental distribution of the oxide film of Ni-12Al alloy modified with Cr precursor film after 20 h of oxidation are shown.

[0029] Figure 4The cross-sectional morphology and elemental distribution of the oxide film of Ni-16Al alloy modified with Cr precursor film after 20 h of oxidation are shown. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0033] Reference Figure 1-4 This is one embodiment of the present invention, which provides a method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film, comprising the following steps: Example 1: Preparation of Cr precursor film on Ni-16Al alloy surface and its high-temperature oxidation experiment This embodiment demonstrates a significant improvement in oxidation resistance achieved by the method of the present invention on Ni-16Al alloys near the critical Al content.

[0034] Matrix pretreatment: A binary Ni-16Al alloy (Al content 16.1 wt.%, atomic percentage 29.5%) was selected and machined into a sample of 10 mm × 10 mm × 2 mm. The sample was polished with 320 and 800 grit SiC sandpaper in sequence, followed by ultrasonic cleaning in acetone and anhydrous ethanol for 15 min each, and finally dried for later use.

[0035] Preparation of Cr precursor film: A metallic Cr film was deposited on the surface of the above sample using DC magnetron sputtering. The process parameters were: system base vacuum 3 × 10⁻⁶. -3 Pa, sputtering pressure 0.5 Pa, DC power 1.2 kW, equipment center heating temperature 200 o C, sample stage rotation speed 15 rpm, target-substrate distance 150 mm, deposition time 25 min. Finally, a continuous and dense Cr film with a thickness of approximately 480±25 nm was obtained, with no voids or cracks at the interface.

[0036] High-temperature oxidation: The alloy sample with the deposited Cr film was placed in a thermogravimetric analyzer and subjected to oxidation at 10 °C. o The heating rate increased to 900 °C / min. o C, and keep at that temperature for 20 h for constant temperature oxidation.

[0037] Results and beneficial effects: Using the method described in this embodiment, the Cr film on the sample surface is rapidly oxidized into a continuous Cr2O3 layer, significantly reducing the oxygen partial pressure on the alloy surface and inhibiting NiO formation. After oxidation, a double-layer protective film structure of outer Cr2O3 and inner α-Al2O3 is formed. The inner α-Al2O3 layer directly nucleates and grows through the isomorphic effect of Cr2O3, avoiding the formation of metastable phases such as θ-Al2O3. Measurements show that its parabolic rate constant is reduced by approximately 80% compared to the untreated Ni-16Al alloy, and the Al-depleted region depth is only 0.4 ± 0.1 µm, far smaller than the 3.2 ± 0.6 µm of the untreated alloy.

[0038] Example 2: Preparation of Cr precursor film on Ni-12Al alloy surface and its high-temperature oxidation experiment This embodiment demonstrates that the method of the present invention can still achieve selective oxidation on Ni-12Al alloys with lower Al content (far below the critical aluminum content value for the formation of external alumina).

[0039] Matrix pretreatment: A binary Ni-12Al alloy (Al content 12.6 wt.%, atomic percentage 23.8%) was selected, and the remaining pretreatment steps were the same as in Example 1.

[0040] Preparation of Cr precursor film: Using the same DC magnetron sputtering parameters as in Example 1, a Cr film with a thickness of about 480 nm was prepared on the Ni-12Al surface.

[0041] High-temperature oxidation: The sample is placed in a dry air thermogravimetric analyzer and subjected to oxidation at 10°C. o C / min increased to 900 o C, keep warm for 20 hours.

[0042] Results and beneficial effects: Although the Al content of the Ni-12Al matrix itself is insufficient to form an external Al2O3 film, the Cr precursor film surface modification method in this embodiment lowers the nucleation energy barrier of the protective oxide, and a continuous protective Al2O3 film is formed on the alloy surface after 20 h of oxidation. Photoexcited fluorescence piezoelectric spectroscopy (PLPS) detection shows that α-Al2O3 has a nucleation energy barrier at 14402 cm⁻¹. -1 and 14432cm -1The presence of a characteristic bimodal pattern confirms the absence of metastable phase formation. Its oxidation weight gain is two orders of magnitude lower than that of untreated Ni-12Al, demonstrating the effectiveness of this method for alloys with extremely low Al content.

[0043] Example 3: Verification of long-term oxidation stability of Cr precursor film on Ni-16Al alloy surface This embodiment demonstrates the stability of the method of the present invention under long-term high-temperature service conditions.

[0044] Substrate pretreatment and Cr film preparation: Ni-16Al alloy was selected, and Cr precursor film was prepared according to the process in Example 1.

[0045] High-temperature oxidation: Place the sample in a dry air muffle furnace at 10°C. o C / min increased to 900 o C, and extend the heat preservation time to 100 h.

[0046] Results and beneficial effects: After 100 hours of long-term oxidation, the alloy surface maintained a complete Cr2O3 / α-Al2O3 bilayer structure without peeling or cracking. The thickness of the α-Al2O3 layer increased to 0.9±0.1 µm, and the depth of the Al-depleted zone remained within 1.2±0.1 µm. In contrast, the untreated Ni-22Al alloy formed a thicker oxide film and a deeper depleted zone under the same conditions. This indicates that the method of the present invention not only reduces the initial oxidation rate but also maintains excellent oxidation resistance under prolonged high-temperature exposure.

[0047] In summary, this invention selects a binary Ni-Al alloy with a specific Al content and pre-treats it with fine grinding and ultrasonic cleaning to ensure the surface activity and quality of the substrate, providing an ideal nucleation substrate for subsequent film growth. A thin and continuous dense metallic Cr precursor film is deposited on this substrate using DC magnetron sputtering technology. This Cr film rapidly transforms into a continuous Cr2O3 layer in the early stages of high-temperature oxidation, effectively reducing the oxygen partial pressure on the alloy surface. Based on the crystal isomorphism effect, α-Al2O3 is induced to directly nucleate and grow steadily beneath the Cr2O3 layer. This successfully constructs a dual protective film structure of outer Cr2O3 and inner α-Al2O3 on the surface of a low-Al alloy, significantly reducing the oxidation rate of low-aluminum alloys, inhibiting internal oxidation and excessive expansion of the aluminum-depleted region, and completely avoiding the drawbacks of metastable phase transformation. This improves the oxidation stability and protective reliability of the material under high-temperature, long-term service conditions.

[0048] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film, characterized in that: include, S1. A binary Ni-Al alloy with an Al content of 12-16 wt.% was selected as the matrix. The alloy was machined into samples with dimensions of 10 mm × 10 mm × 2 mm. The sample surface was polished and chamfered using 320# and 800# SiC wet sandpaper in sequence. The polished sample was ultrasonically cleaned in a mixture of acetone and anhydrous ethanol for 15 min. The cleaned sample was then dried with cold air and set aside for later use. S2. Mount the pretreated sample onto the sample holder of the magnetron sputtering equipment. A DC magnetron sputtering (DCMS) process is used to deposit a metallic Cr film on the alloy sample surface. The process parameters for the deposition are set as follows: system background vacuum 3 × 10⁻⁶. -3 Pa, sputtering working pressure 0.5 Pa, DC sputtering power 1.2 kW, center heating temperature set at 200°C. o C, sample holder rotation speed 15 rpm, deposition time 25 min. By controlling these parameters, a continuous, dense Cr film with a thickness of 480±25 nm was prepared. S3, the sample with the Cr film deposited on its surface and the control sample without any treatment are suspended in the alumina reaction tube of a thermogravimetric analyzer (TGA). The thermogravimetric analyzer is started at 10... o A heating rate of C / min was used to heat the temperature inside the reaction tube to 900°C. o C. In 900 o The sample was oxidized for 20 h under constant temperature conditions.

2. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 1, characterized in that: The binary Ni-Al alloy described in S1 is Ni-16Al (Al content 16.1 wt.%, corresponding to atomic percentage 29.5%) or Ni-12Al (Al content 12.6 wt.%, corresponding to atomic percentage 23.8%).

3. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 2, characterized in that: The target material for DC magnetron sputtering described in S2 is a pure Cr target (purity ≥ 99.9%), and the target-substrate distance is 150 mm.

4. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 3, characterized in that: The thickness of the Cr film described in S2 is controlled by the deposition time, which is set to 25 min. The resulting Cr film has no voids or cracks at the interface with the alloy substrate, and the film layer is continuous and dense.

5. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 4, characterized in that: The high-temperature oxidation described in S3 involves a holding time of 20 h. In the initial stage of oxidation, the Cr film on the sample surface will rapidly and completely transform into a continuous Cr2O3 layer.

6. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 5, characterized in that: After high-temperature oxidation as described in S3, a double protective film of outer Cr2O3 and inner α-Al2O3 is formed on the alloy surface. The inner α-Al2O3 directly nucleates and grows through the crystal isomorphism effect of Cr2O3, without the formation of metastable phases such as γ-Al2O3 or θ-Al2O3.

7. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 6, characterized in that: After high-temperature oxidation as described in S3, the oxidation kinetics of the low-aluminum alloy with a Cr film deposited on the surface follow a parabolic law, and its parabolic rate constant is reduced by 80% compared with the untreated alloy.

8. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 7, characterized in that: After high-temperature oxidation as described in S3, the thickness of the inner α-Al2O3 layer is approximately 0.4±0.1 μm, and the depth of the aluminum-poor region of the alloy matrix is ​​only 0.4±0.1 μm (far smaller than the 3.2±0.6 μm of untreated Ni-16Al).

9. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 8, characterized in that: Following the high-temperature oxidation described in S3, the fluorescence was detected using photoexcited fluorescence piezoelectric spectroscopy (PLPS) at only 14402 cm⁻¹. -1 With 14432 cm -1 Two characteristic peaks belonging to α-Al2O3 were detected at the location, but no characteristic peaks of θ-Al2O3 were found.

10. The preparation method for improving the oxidation resistance of low-aluminum alloys using a Cr precursor film as described in claim 9, characterized in that: After the high-temperature oxidation described in S3 was extended to 100 h, the alloy surface still maintained a complete Cr2O3 / α-Al2O3 double-layer structure, with no oxide film peeling or cracks. The thickness of the α-Al2O3 layer increased to 0.9±0.1 μm, and the depth of the aluminum-depleted zone remained within 1.2±0.1 μm.

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