A Hf and Cr co-modified platinum aluminum coating with both oxidation resistance and thermal corrosion resistance, as well as its preparation method and application

Abstract

The present invention belongs to the field of diffusion coatings of a platinum-aluminum coating series, and specifically relates to a Hf and Cr co-modified platinum-aluminum coating with both oxidation resistance and thermal corrosion resistance, as well as a preparation method and application. The Hf and Cr co-modified platinum-aluminum coating with both oxidation resistance and thermal corrosion resistance is prepared by introducing a Ni-Cr layer and a Pt-Hf layer by composite electroplating, followed by vacuum diffusion annealing and vapor phase aluminizing to obtain the coating; after the coating is modified, the oxidation resistance and thermal corrosion resistance are significantly improved, the oxidation resistance rate is reduced at 1100°C, the adhesion performance of the oxide film is improved, and the surface undulation is small. After 400 hours of thermal corrosion at 900°C, the surface oxide film is basically intact, and the Cl element intrusion is relatively small.

Description

Technical Field

[0001] The present invention belongs to the field of platinum-aluminum coating series diffusion coatings, and specifically relates to Hf and Cr co-modified platinum-aluminum with both oxidation resistance and thermal corrosion resistance, as well as a preparation method and application. Background Art

[0002] Platinum-aluminum coatings are widely used in the aerospace industry due to their excellent resistance to high-temperature oxidation. However, as the thrust-to-weight ratio of aircraft engines continues to increase, the service temperatures of hot-end components such as turbine blades are also increasing. In this increasingly complex and harsh service environment, the coating's resistance to high-temperature oxidation and thermal corrosion must be further improved.

[0003] At high temperatures, a continuous, dense, and slow-growing oxide film forms on the surface of a platinum-aluminum coating, protecting the substrate from oxidizing and corrosive atmospheres. Furthermore, the addition of Pt further enhances the high-temperature oxidation resistance of the β-NiAl phase. Adding Pt to the NiAl coating promotes oxide film formation and reduces TGO stress in the early stages of oxidation. However, due to the significant difference in elemental composition and content between the coating and the substrate, interdiffusion between the coating and substrate is prone to occur during long-term high-temperature service. Outward diffusion of dissolved elements in the substrate degrades the mechanical properties of the alloy, while inward diffusion of Al within the coating and Al consumption cause a degenerative phase transformation of the coating, from the β-NiAl phase to the γ'-Ni3Al phase. This β→γ' phase transformation causes a change in the coating volume, resulting in surface undulations. When surface undulations become severe, the oxide film can crack and flake.

[0004] In response to the problems existing in platinum aluminum coatings, the current commonly used solution is to introduce a diffusion barrier between the coating and the substrate or to modify the coating through active elements. Commonly used diffusion barriers include ceramic-based diffusion barriers (CrN, Al2O3, etc.) and metal-based diffusion barriers (Re-based, Ru-based, etc.). The thermal expansion coefficient of the ceramic-based diffusion barrier is quite different from that of the substrate and the coating. The application of the diffusion barrier will reduce the bonding strength between the coating and the substrate. Although the thermal expansion coefficient of the metal-based diffusion barrier is not much different from that of the coating and the substrate, it is easy to undergo elemental interdiffusion with the substrate and the coating under long-term high temperature, and may affect the oxidation resistance of the coating. Another solution to improve the surface undulation and interdiffusion of platinum aluminum coatings is to modify the coating. Commonly used active elements include Hf, Y, Ru, etc. Among them, the addition of Hf element can effectively improve the high-temperature oxidation resistance of the coating and reduce the interdiffusion of elements between the coating and the substrate. This is because the Hf-modified (N At high temperatures, (i,Pt)Al coatings can form continuous HfO2, preventing the diffusion of Al from the coating into the substrate and hindering the diffusion of solid-solution strengthening elements in the substrate into the coating, thereby reducing Al consumption. Although Hf-modified Pt-Al coatings exhibit excellent high-temperature oxidation resistance and diffusion resistance, the addition of Hf does not improve the coating's resistance to hot corrosion. In actual service environments, alloys are not only corroded by oxidizing atmospheres but also by salt deposits formed on the metal or alloy surface, which can be catastrophic. After the addition of Hf, the oxide film formed in the coating is thinner in the same amount of time, allowing more S and Cl elements to enter the coating more easily, causing damage. Furthermore, while the addition of Hf can reduce the surface fluctuations of the coating during service to a certain extent, the effect is not significant. Surface fluctuations in the coating are the main cause of cracking or flaking of the oxide film. Summary of the Invention

[0005] To address the shortcomings and deficiencies of the prior art, the primary objective of the present invention is to provide an Hf- and Cr-modified platinum-aluminum coating that exhibits both oxidation and hot corrosion resistance, as well as a preparation method and application. The present invention introduces a Ni-Cr composite coating and a Pt-Hf composite coating onto a substrate through composite electroplating. The concentrations of Pt, Hf, Cr, and Ni within the coatings are adjusted through vacuum annealing, followed by vapor-phase aluminizing to produce an Hf-Cr co-modified platinum-aluminum coating. This coating exhibits the following structural characteristics:

[0006] (1) The Ni-Cr composite coating provides the Ni required for the growth of the NiAl coating during the aluminizing process, so that the Ni element in the substrate diffuses less outward, the γ / γ' coherent structure of the substrate can be protected to the maximum extent, there is less mutual diffusion between the coating and the substrate, and no secondary reaction zone is formed; (2) The Ni-Cr composite coating has a better ability to absorb Al atoms than the substrate. Therefore, under the same preparation process conditions, a thicker (Ni, Pt)Al coating can be obtained; (3) The Ni-Cr composite coating absorbs a small amount of Al atoms that diffuse inward during the aluminizing process, forming a γ'-Ni3Al phase region, which is a transition layer between the substrate and the (Ni, Pt)Al. It can reduce the stress generated by the difference in thermal matching performance between the substrate and the coating, and reduce the surface undulation of the coating at high temperature and the degree of oxide film peeling.

[0007] Due to the modification effect of Cr and Hf elements, the coating has the following performance characteristics compared with the platinum aluminum coating: (1) The addition of Hf element can significantly reduce the oxidation rate and improve the adhesion performance of the oxide film; (2) The addition of Cr element can reduce the critical content of Al element to form a selective oxidation film, which can ensure that the coating can still form a protective oxide film when the Al content is reduced, so the coating has a longer service life; (3) During the thermal corrosion process, Cr particles can react with S element to generate stable CrS, thereby fixing the S element, and the coating has better thermal corrosion resistance; (4) The Ni-Cr composite coating acts as a buffer layer between the substrate and the platinum aluminum coating, which can reduce the mutual diffusion tendency between the coating and the substrate, making the coating structure more stable and the mechanical properties of the substrate better maintained;

[0008] Another object of the present invention is to provide a method for preparing Hf and Cr modified platinum aluminum coatings that are both anti-oxidation and anti-hot corrosion.

[0009] Another object of the present invention is that the Hf and Cr modified platinum aluminum coating that is both resistant to oxidation and hot corrosion can maintain the mechanical properties of the high-temperature alloy substrate to the greatest extent.

[0010] Another object of the present invention is to provide an application of the Hf and Cr modified platinum aluminum coating having both oxidation resistance and thermal corrosion resistance in the aerospace field.

[0011] The purpose of the present invention is achieved through the following technical solutions:

[0012] An Hf and Cr co-modified platinum aluminum coating with both oxidation resistance and hot corrosion resistance, comprising an interdiffusion layer and an aluminide layer, wherein Hf and Cr elements are in a solid solution state in the aluminide layer;

[0013] The aluminide layer includes a γ'-Ni3Al phase region, a Pt-Ni3Al layer and a Pt-NiAl layer from bottom to top; the interdiffusion layer includes a precipitated phase caused by interdiffusion of the matrix and a γ'-Ni3Al phase.

[0014] Preferably, the substrate of the coating is a single crystal high temperature alloy, such as a nickel-based or cobalt-based single crystal high temperature alloy.

[0015] The coating is prepared by the steps of composite electroplating of Ni-Cr layer, composite electroplating of Pt-Hf layer, vacuum annealing and vapor phase aluminizing, and includes an outer gradient platinum-aluminum coating (outer layer is Pt-NiAl, inner layer is Pt-Ni3Al) and a small amount of interdiffusion zone (IDZ), in which Hf and Cr elements are in a solid solution state in the coating.

[0016] When the Ni-Cr layer and the Pt-Hf layer are deposited on the substrate, the Ni-Cr composite coating provides the Ni required to combine with Al to form a coating during the aluminizing process, and Cr diffuses outward along with the Ni and enters the platinum-aluminum coating to modify the Cr element; the Pt-Hf composite coating provides the Pt required for the growth of the platinum-aluminum coating, and the Hf element diffuses outward along with the Pt and enters the platinum-aluminum coating to modify the Hf element.

[0017] During the high-temperature oxidation process of the Hf and Cr co-modified platinum-aluminum coating, the modification of the Hf element can significantly reduce the oxidation rate of the coating and improve the adhesion performance of the oxide film; during the hot corrosion process, the Cr particles can react with the S element to generate stable CrS, thereby fixing the S element and improving the hot corrosion resistance of the coating; after the Ni layer is pre-plated during the preparation process, the coating can form a gradient coating, reduce the degradation rate of the coating, reduce the surface fluctuations of the coating, and improve the coating life.

[0018] The substrate is a high-temperature alloy, such as a nickel-based single crystal high-temperature alloy.

[0019] A method for preparing an Hf and Cr modified platinum aluminum coating having both oxidation resistance and thermal corrosion resistance, characterized by comprising the following steps:

[0020] A Ni-Cr coating is introduced on the substrate, and then a Pt-Hf coating is introduced on the Ni-Cr coating by composite electroplating;

[0021] After the above steps, two composite coatings are obtained, which are subjected to vacuum diffusion annealing and vapor phase aluminizing treatment.

[0022] The methods of introducing the Pt-Hf and Ni-Cr coatings include but are not limited to electroplating, sputtering and ion implantation.

[0023] Preferably, the method of introducing the Ni-Cr layer coating is electroplating, and the specific conditions are: electroplating temperature 40-60 ° C, current density 8-12 mA / cm 2 , pH = 4-6, and the time is 2.5h-4.5h. The plating solution is a mixture of nickel plating solution and chromium powder, wherein the particle size of chromium is 1-5μm. Preferably, the composition of the nickel plating solution is NiSO4·6H2O (120-180g / L), H3BO4 (30-60g / L), Na2SO4 (60-100g / L), and NaCl (8-10g / L).

[0024] Preferably, the method of introducing the Pt-Hf modified layer is electroplating, and the specific conditions are: electroplating temperature 70-80°C, current density 4-6 mA / cm 2 , pH = 8.0-10.0, and the time is 2-4 hours. The plating solution is a mixture of platinum plating solution and Hf powder, wherein the Hf particle size is 100-500nm. Preferably, the composition of the platinum plating solution is NaNO2 (5-15g / L) and Pt(NH3)2(NO2)2 (5-15g / L).

[0025] Preferably, the thickness of the Ni-Cr layer coating is 10-15 μm; the thickness of the Pt-Hf layer coating is 1-5 μm.

[0026] Preferably, during the vacuum diffusion annealing process, the pressure is lower than 1×10 -3 Pa, the heating rate is 5-10℃ / min; the annealing temperature is 1000℃-1080℃, and the holding time is 1-4h.

[0027] Preferably, the vapor phase aluminizing is carried out at 1020-1080° C. for 4-8 hours, Ar gas is introduced as a protective gas during the aluminizing process, and the aluminizing agent is a mixed powder consisting of an iron-aluminum alloy powder and an activator NH 4 Cl, wherein the NH 4 Cl content is 1-4 wt.%. The iron content of the iron-aluminum alloy powder is 40-55%.

[0028] The Hf and Cr modified platinum aluminum coating having both oxidation resistance and thermal corrosion resistance is used in the aerospace field.

[0029] Compared with the prior art, the present invention has the following innovations and advantages:

[0030] (1) Innovation in design concept and coating structure: The present invention introduces three beneficial elements into the platinum-aluminum coating through two-step composite electroplating. The coating thickness and composite amount can be flexibly adjusted through electroplating process parameters, thus having flexibility in the preparation process.

[0031] Composite Ni-Cr electroplating between the substrate and the coating: The Ni-Cr composite coating provides Cr element modification to the Pt-Al coating and, during the aluminizing process, provides the Ni necessary for NiAl coating growth. This prevents the outward diffusion of large amounts of Ni from the substrate from destroying the substrate's γ / γ' coherent structure. Interdiffusion between the coating and the substrate is minimal, and no secondary reaction zones form. The Ni-Cr composite coating has a better ability to absorb Al atoms than the substrate, allowing for thicker (Ni, Pt)Al coatings to be obtained under the same preparation conditions. During the aluminizing process, the Ni-Cr composite coating forms a γ'-Ni3Al phase region, which serves as a transition layer between the substrate and the Pt-Al coating. This reduces stress caused by thermal mismatch between the substrate and coating, and reduces surface roughness and oxide film flaking at high temperatures.

[0032] A Pt-Hf composite coating is introduced above the Ni-Cr composite coating: the Pt-Hf composite coating provides the Pt required for the growth of the platinum-aluminum coating. At the same time, the Hf element diffuses outward with the Pt during the aluminizing process and enters the platinum-aluminum coating for Hf element modification.

[0033] (2) Significant improvement in coating performance: During the high-temperature oxidation process of the Hf and Cr co-modified platinum aluminum coating, the modification of the Hf element can significantly reduce the oxidation rate of the coating and improve the adhesion performance of the oxide film; during the thermal corrosion process, the Cr particles can react with the S element to generate stable CrS, thereby fixing the S element and improving the thermal corrosion resistance of the coating; after the Ni layer is pre-plated during the preparation process, the coating can form a gradient coating, reduce the degradation rate of the coating, reduce the surface undulation of the coating, and improve the coating life.

[0034] (3) The preparation method of the Hf and Cr modified platinum aluminum coating with both oxidation resistance and thermal corrosion resistance provided by the present invention is simple and efficient, harmless to the substrate performance, and has good thermal corrosion resistance and reliability, which is of great significance to improving the service life of the hot end components of aviation and aerospace engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Cross-sectional morphology of deposited Ni-Cr and Pt-Hf composite electroplating;

[0036] Figure 2 Surface (a) and cross-sectional (b) morphologies of Hf and Cr co-modified Pt-Al coatings;

[0037] Figure 3 a is the cross-sectional morphology of the Pt-plated deposited state. Figure 3 b is the cross-sectional morphology of the composite electroplated Pt-Hf deposited state;

[0038] Figure 4 a、4b Surface and cross-sectional morphology of ordinary (Ni, Pt) Al coating, Figure 4c, 4d are the surface and cross-sectional morphologies of Hf-modified (Ni,Pt)Al coatings;

[0039] Figure 5 a is the weight gain curve of the three coatings after oxidation at 1100℃ for 500h. Figure 5 b Oxidation rate constants of the three coatings after oxidation at 1100 °C for 500 h;

[0040] Figure 6 a is the surface profile curve of ordinary (Ni, Pt) Al coating after oxidation at 1100℃ for different times. Figure 6 b is the surface profile curve of Hf modified (Ni, Pt) Al coating after oxidation at 1100℃ for different times. Figure 6 c is the surface profile curve of the (Ni, Pt) Al coating modified by Hf and Cr after oxidation at 1100℃ for different times;

[0041] Figure 7 a is the surface morphology of ordinary (Ni, Pt) Al coating after 400h of hot corrosion. Figure 7 b is the surface morphology of Hf-modified (Ni, Pt)Al coating after hot corrosion for 400 h; Figure 7 c is the surface morphology of the (Ni,Pt)Al coating co-modified by Hf and Cr after hot corrosion for 400 h;

[0042] Figure 8 a and b are cross-sectional morphologies of ordinary (Ni, Pt) Al coating after 400h of hot corrosion. Figure 8 c, d are the cross-sectional morphologies of Hf-modified (Ni, Pt)Al coatings after 400 h of hot corrosion; Figure 8 e, f are the cross-sectional morphologies of the (Ni,Pt)Al coating modified by Hf and Cr after hot corrosion for 400 h;

[0043] Figure 9 a is the cross-sectional element distribution of ordinary (Ni, Pt) Al coating after 400h of hot corrosion. Figure 9 b is the cross-sectional element distribution of Hf-modified (Ni, Pt)Al coating after hot corrosion for 400 h; Figure 9 c is the cross-sectional element distribution of the (Ni,Pt)Al coating co-modified by Hf and Cr after hot corrosion for 400h. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0045] Example 1 (composite electroplating of Ni-Cr and Pt-Hf layers on the surface of a second-generation nickel-based single crystal high-temperature alloy, vacuum annealing and vapor-phase aluminizing (Hf and Cr modified platinum-aluminum coating)):

[0046] (1) The substrate sample used is the second-generation nickel-based single crystal high-temperature alloy N5, with a sample size of Φ15×2mm. Before electroplating, the sample needs to be polished with 600#, 1000#, 1500#, and 2000# SiC sandpaper in sequence, and then wet sandblasted with quartz sand particles. After sandblasting, the sample is ultrasonically degreased with acetone for 15 minutes, and ultrasonically cleaned with alcohol and deionized water for 15 minutes respectively.

[0047] (2) Deposition of Ni-Cr layer: Add Cr powder with a particle size of 1 to 5 μm to the nickel plating solution, add 20 g / L of Cr powder, and perform magnetic stirring. The composition of the nickel plating solution is NiSO4·6H2O (150 g / L), H3BO4 (45 g / L), Na2SO4 (80 g / L), and NaCl (9 g / L). The cleaned sample is suspended in the electroplating tank with copper wire. The sample serves as the cathode and the nickel mesh serves as the anode. During electroplating, the water temperature in the water bath is maintained at 40 to 60 ° C, and the current density is 8 to 12 mA / cm 2 , pH is in the range of 4 to 6, and the deposition time is 2.5h; the electroplated samples are washed with deionized water, ultrasonically cleaned with alcohol, and then blown dry.

[0048] (3) Deposition of Pt-Hf layer: Add Hf powder with a particle size of 100-500nm to the platinum plating solution, the added mass is 10g / L, and magnetic stirring is performed. The composition of the platinum plating solution is NaNO2 (10g / L), Pt(NH3)2(NO2)2 (10g / L). The sample coated with Ni-Cr layer is suspended in the electroplating tank with copper wire, the sample is used as the cathode, and the platinum mesh is used as the anode. During electroplating, the water temperature in the water bath is kept at 70-80℃ and the current density is 5mA / cm 2 , pH is in the range of 8 to 10, and the deposition time is 2 h; the electroplated samples are washed with deionized water, ultrasonically cleaned with alcohol, and then blown dry. Figure 1 This is the cross-sectional morphology of the deposited Ni-Cr and Pt-Hf composite electroplating. It can be seen that the coating consists of Ni-Cr layer and Pt-Hf layer, and the coatings are well bonded.

[0049] (4) The electroplated samples were annealed in a vacuum tube furnace (1050 ° C for 1 h, vacuum degree of 10 - 3 Pa, heating rate is less than 10℃ / min), vacuum annealing treatment can eliminate the hydrogen introduced in the preparation process and reduce the stress of the coating, and make the Pt element fully dissolved in the alloy matrix. During the annealing process, the temperature is first maintained at 600℃ for 2h to remove the residual hydrogen in the coating during electroplating and prevent the occurrence of bulging and other phenomena. After the vacuum annealing treatment is completed, the sample is cooled to room temperature with the furnace.

[0050] (5) The annealed sample was placed in a chemical vapor deposition vacuum furnace for vapor phase aluminizing. The aluminizing was carried out at 1060°C, the holding time was 6 hours, and the heating rate was about 10°C / min. Ar gas was introduced as a protective gas during the aluminizing process. The aluminizing agent was a mixed powder consisting of iron-aluminum alloy powder (49wt.% Fe) and activator NH4Cl (3wt.%). After the aluminizing was completed, the sample was taken out after cooling to room temperature in the furnace. The surface and cross-sectional morphology of the coating after aluminizing is shown in Figure 2. Figure 2 As shown, it can be seen that the coating surface is composed of equiaxed grains, and the cross section consists of two layers: NiAl layer and interdiffusion zone (IDZ).

[0051] Example 2 (performance comparison):

[0052] (1) The substrate sample used is a second-generation nickel-based single crystal high-temperature alloy with a sample size of Φ15×2mm. Before electroplating, the sample needs to be polished with 600#, 1000#, 1500#, and 2000# SiC sandpaper in sequence, and then wet sandblasted with quartz sand particles. After sandblasting, the sample is ultrasonically degreased with acetone for 15 minutes, and ultrasonically cleaned with alcohol and deionized water for 15 minutes respectively.

[0053] (2) In order to facilitate the comparison of coating structure and performance, two other ordinary Pt-plated samples and composite electroplated Pt-Hf samples were prepared respectively:

[0054] Deposition of ordinary Pt-plated samples: Place the platinum plating solution in a water bath and heat it. Hang the sample in the plating tank with a copper wire. The sample serves as the cathode and the platinum mesh serves as the anode. The composition of the platinum plating solution is NaNO2 (10g / L), Pt(NH3)2(NO2)2 (10g / L). Maintain the water temperature in the water bath at 70-80°C and the current density at 5mA / cm 2 , pH is in the range of 8 to 10, and the deposition time is 2 h; the electroplated samples are washed with deionized water, ultrasonically cleaned with alcohol, and then blown dry. Figure 3 a is the cross-sectional morphology of the Pt-plated deposited state, and the coating and the substrate are well bonded.

[0055] Deposition of composite electroplated Pt-Hf sample: Add Hf powder with a particle size of 100-500nm to the platinum plating solution, add a mass of 10g / L, and stir magnetically. The composition of the platinum plating solution is NaNO2 (10g / L), Pt(NH3)2(NO2)2 (10g / L). The sample is suspended in the electroplating tank with copper wire, the sample is used as the cathode, and the platinum mesh is used as the anode. During electroplating, the water temperature in the water bath is maintained at 70-80℃, and the current density is 5mA / cm 2 , pH is in the range of 8 to 10, and the deposition time is 2 h; the electroplated samples are washed with deionized water, ultrasonically cleaned with alcohol, and then blown dry. Figure 3b is the cross-sectional morphology of the composite electroplated Pt-Hf deposited state. It can be seen that the coating and the substrate are well bonded and the Hf particles are evenly distributed in the coating.

[0056] (3) After electroplating, the two samples were annealed in a vacuum tube furnace (1050℃ for 1h, vacuum degree of 10 -3 Pa, heating rate is less than 10℃ / min), vacuum annealing treatment can eliminate the hydrogen introduced in the preparation process and reduce the stress of the coating, and make the Pt element fully dissolved in the alloy matrix. During the annealing process, the temperature is first maintained at 600℃ for 2h to remove the residual hydrogen in the coating during electroplating and prevent the occurrence of bulging and other phenomena. After the vacuum annealing treatment is completed, the sample is cooled to room temperature with the furnace.

[0057] (4) The two annealed samples were placed in a chemical vapor deposition vacuum furnace for vapor aluminizing. Aluminizing was performed at 1060°C for 6 hours at a heating rate of approximately 10°C / min. Ar gas was introduced as a protective gas during the aluminizing process. The aluminizing agent was a mixed powder consisting of an iron-aluminum alloy powder (49 wt.% Fe) and an activator, NH4Cl (3 wt.%). After aluminizing, the samples were removed from the furnace after cooling to room temperature.

[0058] Figure 3 a is the cross-sectional morphology of the Pt-plated deposited state. Figure 3 b is the cross-sectional morphology of the composite electroplated Pt-Hf deposited state; it can be seen that the surfaces of both coatings are composed of equiaxed grains, and the cross-section consists of two layers: the NiAl layer and the interdiffusion zone (IDZ). The dark black particles in the coating are the aluminum oxide particles remaining after sandblasting. The thickness of the ordinary (Ni, Pt) Al coating and the Hf-modified (Ni, Pt) Al coating is basically the same, while the NiAl layer of the Hf and Cr co-modified (Ni, Pt) Al coating is the thickest, about 51 μm, and the IDZ layer is the thinnest, about 12 μm. Figure 2 As shown in b. The reason for the different coating thicknesses is that the Hf and Cr co-modified platinum aluminum coating has a 15μm Ni-Cr layer electroplated between the substrate and the platinum layer. During the Al infiltration process, the Ni-Cr layer can provide a Ni source for the formation of the NiAl phase, and the Ni consumption in the substrate will be reduced. Therefore, compared with the other two coatings, the Hf and Cr co-modified platinum aluminum coating has the thinnest interdiffusion zone. This shows that the coating obtained by the present invention has less interdiffusion with the substrate, and the beneficial Al elements in the coating can be used more to form oxides because of less interdiffusion consumption; the Ni elements in the substrate also diffuse less into the coating, keeping the strengthening elements solid-dissolved in Ni, avoiding the precipitation of solid-dissolved elements, and destroying the mechanical properties of the substrate. It is worth noting that there is no obvious difference in the cross-sectional morphology of the three coatings, which shows that electroplating the Ni-Cr layer between the substrate and the platinum layer does not change the final morphology of the coating.

[0059] (5) The three coatings were oxidized at 1100℃ for 500h. Figure 5 a is the weight gain curve of the three coatings after oxidation at 1100℃ for 500h. Figure 5 b Oxidation rate constants of the three coatings after oxidation at 1100°C for 500 h. It can be seen that the oxidation patterns of the three coatings all conform to the parabolic law, that is, the weight gain is rapid in the initial stage and enters a stable weight gain stage after oxidation for a period of time. It is worth noting that the Hf and Cr co-modified Pt-Al coating has the smallest oxidation weight gain and the smallest oxidation rate constant. Figure 6 The following are the surface profile curves of the three coatings after oxidation at 1100°C for different times. After 500 hours of oxidation, the surface fluctuations of the ordinary Pt-Al coating are the largest, while the surface fluctuations of the Pt-Al coating modified with Hf and Cr are the smallest. This indicates that the coating degradation rate is slowed down and the internal stress is reduced after modification, resulting in the smallest surface fluctuations. The reason for the slower degradation is that a Ni-Cr layer is electroplated between the substrate and the Pt-Hf layer during the electroplating process. Ni provides a Ni source for the formation of the β-(Ni,Pt)Al phase, resulting in a gradient coating. From top to bottom, the β-(Ni,Pt)Al phase gradually decreases, while the γ-(Ni,Pt)Al phase gradually increases. Therefore, the degradation of the β phase can be slowed down.

[0060] (6) Place the samples of ordinary (Ni, Pt) Al coating, Hf modified (Ni, Pt) Al coating, and Hf and Cr co-modified (Ni, Pt) Al coating on an iron plate at 120°C for heating. Then, a layer of Na2SO4 / NaCl (mass fraction ratio of 75%:25%) mixed salt is evenly coated on the surface of the coating. The amount of salt applied is 1-1.5 mg / cm 2 The sample coated with mixed salt was placed in a muffle furnace for a period of time and then taken out for air cooling at a holding temperature of 900°C. After the sample cooled, it was boiled twice in deionized water to remove the residual salt on the surface. After cleaning, it was then applied with salt again.

[0061] Figure 7 、 Figure 8 The surface and cross-sectional morphologies of the three coatings after thermal corrosion at 900℃ for 400h are shown respectively. Figure 7 It can be seen from a that after 400h of hot corrosion, the surface oxide film of the ordinary (Ni, Pt) Al coating peeled off in a large area, and the morphology was quite different from that of the other two samples. Figure 8c It can be seen that the oxide film of the Hf-modified (Ni, Pt) Al coating also underwent severe peeling, while after 400 h of hot corrosion, no obvious peeling was found in the surface and cross-sectional morphology of the Hf- and Cr-modified (Ni, Pt) Al coatings. The oxide film was granular, showing the typical morphology of α-Al2O3, and was relatively dense, indicating that the hot corrosion resistance of the coating was significantly improved compared with that of the ordinary (Ni, Pt) Al coating and the Hf-modified (Ni, Pt) Al coating. Figure 9 The element distribution of the cross section of three coatings after hot corrosion at 900℃ for 400h. Figure 9 It can be seen from a that the insoluble elements such as Co and Ta in the ordinary β-(Ni,Pt)Al coating diffuse outward, which will lead to insufficient strengthening elements in the matrix and reduce the mechanical properties of the matrix alloy to a certain extent. In addition, the Cl element content in the coating is the highest. Figure 9 b It can be seen that the Al element signal in the Hf modified (Ni, Pt) Al coating is weak, and CrS is widely distributed in the coating, which is not conducive to the hot corrosion resistance of the coating. In addition, there are also more Cl elements in the coating. It is worth noting that the Al element signal in the Hf and Cr co-modified (Ni, Pt) Al coating is very strong, the Al2O3 film formed is more dense, and the Co element is evenly distributed without segregation. Figure 9 c. Therefore, it can be shown that after the simultaneous addition of Hf and Cr elements, the diffusion of insoluble elements in the matrix is suppressed, the coating is less corroded by the molten salt, the S element remaining in the coating is less, and the Cl element is basically undetectable in the coating.

Claims

1. A Hf and Cr co-modified platinum aluminum coating with both oxidation resistance and hot corrosion resistance, characterized in that It includes an interdiffusion layer and an aluminide layer, and Hf and Cr elements are in a solid solution state in the aluminide layer; The aluminide layer includes, from bottom to top, a γ'-Ni3Al phase region, a Pt-Ni3Al layer, and a Pt-NiAl layer; the interdiffusion layer includes a precipitated phase caused by interdiffusion of the matrix and a γ'-Ni3Al phase; The preparation method of the Hf and Cr co-modified platinum aluminum coating having both oxidation resistance and hot corrosion resistance comprises the following steps: A Ni-Cr coating is introduced on the substrate, and then a Pt-Hf coating is introduced on the Ni-Cr coating by composite electroplating; the Ni-Cr coating is introduced by electroplating, and the plating solution is a mixture of a nickel plating solution and Cr powder; the Pt-Hf coating is introduced by electroplating, and the plating solution is a mixture of a platinum plating solution and Hf powder; After the above steps, two composite coatings are obtained, which are subjected to vacuum diffusion annealing and vapor phase aluminizing treatment.

2. The coating according to claim 1, characterized in that: The substrate of the coating is a single crystal high temperature alloy.

3. A method for preparing the Hf and Cr modified platinum aluminum coating having both oxidation resistance and hot corrosion resistance according to claim 1 or 2, characterized in that: The steps include: A Ni-Cr coating is introduced on the substrate, and then a Pt-Hf coating is introduced on the Ni-Cr coating by composite electroplating; After the above steps, two composite coatings are obtained, which are subjected to vacuum diffusion annealing and vapor phase aluminizing treatment.

4. The preparation method according to claim 3, wherein: The method comprises the following steps: the method of introducing the Pt-Hf and Ni-Cr coatings is electroplating, sputtering or ion implantation.

5. The preparation method according to claim 3, wherein: The method of introducing the Ni-Cr layer coating is electroplating, and the specific conditions are: electroplating temperature 40-60 ° C, current density 8-12 mA / cm 2 , pH=4~6, time is 2.5 h~4.5 h; the plating solution is a mixture of nickel plating solution and Cr powder.

6. The preparation method according to claim 3, wherein: The method for introducing the Pt-Hf modified layer is electroplating, and the specific conditions are: electroplating temperature 70-80 ° C, current density 4-6 mA / cm 2 , pH=8.0~10.0, time is 2 h~4 h; the plating solution is a mixture of platinum plating solution and Hf powder.

7. The preparation method according to claim 3, wherein: The thickness of the Ni-Cr layer coating is 10-15 μm; the thickness of the Pt-Hf layer coating is 1-5 μm.

8. The preparation method according to claim 3, wherein: During the vacuum diffusion annealing process, the gas pressure is lower than 1×10 -3 Pa, annealing temperature is 1000℃-1080℃, and holding time is 1-4 h.

9. The preparation method according to claim 3, wherein: The vapor phase aluminizing is carried out at 1020-1080°C with a holding time of 4-8 hours; the aluminizing agent is a mixed powder consisting of iron-aluminum alloy powder and activator NH4Cl.

10. Application of the Hf and Cr modified platinum aluminum coating having both oxidation resistance and hot corrosion resistance according to claim 1 or 2 in the aerospace field.

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