A Pt-modified gradient NiCoCrFeAl high-entropy coating and its preparation method

Abstract

The present invention provides a Pt-modified gradient NiCoCrFeAl high-entropy coating and a preparation method thereof, relating to the technical field of high-temperature oxidation-resistant coating preparation. The method first electroplates a Pt layer on the surface of a high-temperature alloy substrate to enhance the selective oxidation of Al, thereby reducing the critical Al content required to form Al2O3 on the coating surface and reducing the difficulty of forming the multi-arc ion plating target. Multi-arc ion plating is then used to prepare the NiCoCrFeAl high-entropy coating, which has a slower cooling rate than laser cladding and can reduce the coating's tendency to crack. Finally, chemical vapor deposition aluminizing is performed to increase the Al content in the coating, significantly improving the oxidation resistance of the Pt-modified gradient NiCoCrFeAl high-entropy coating sample at 1200°C.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature anti-oxidation coating preparation, and in particular to a Pt-modified gradient NiCoCrFeAl high-entropy coating and a preparation method thereof. Background Art

[0002] High-entropy alloys (HEAs) are a new type of multicomponent alloy material consisting of five or more components. Due to the slow kinetic diffusion of HEAs and the presence of specific elements such as Al and Cr, HEAs have a low oxygen diffusion rate and a denser protective oxide layer, exhibiting higher oxidation resistance at high temperatures. Currently, laser cladding is the main method used to prepare NiCoCrFeAl high-entropy coatings. High-purity (99.99 wt.%) Al, Co, Cr, Fe, and Ni mixed powders are used as raw materials. These are pre-placed on the surface of a high-temperature alloy or delivered to the surface of a high-temperature alloy synchronously with the laser. A high-power laser is used to melt the mixed powders to form a coating on the surface of the high-temperature alloy.

[0003] Existing methods for preparing NiCoCrFeAl high-entropy coatings (HE-C) involve extremely rapid heating and cooling during laser cladding. This, due to the different thermal expansion coefficients of the coating and alloy substrate, leads to significant thermal stress during the coating preparation process. This can lead to defects such as pores, cracks, and deformation, which can shorten the coating's service life. Furthermore, to improve the high-temperature oxidation resistance of laser-clad HE-C coatings, the proportion of Al in the powder must be increased. However, increasing the Al content increases the coating's brittleness and tendency to thermal cracking. Consequently, achieving NiCoCrFeAl HE-C coatings with excellent oxidation resistance at 1200°C through laser cladding is difficult. Summary of the Invention

[0004] The purpose of the present invention is to provide a Pt-modified gradient NiCoCrFeAl high-entropy coating and a preparation method thereof. The method of the present invention is used to prepare the NiCoCrFeAl high-entropy coating, which can effectively reduce the cracking tendency of the coating and significantly improve the high-temperature oxidation resistance of the coating.

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

[0006] The present invention provides a method for preparing a Pt-modified gradient NiCoCrFeAl high-entropy coating, comprising the following steps:

[0007] Electroplating a Pt layer on the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy;

[0008] Using a NiCoCrFeAl alloy as a target, multi-arc ion plating is performed on the first high-temperature alloy to form a NiCoCrFeAl high-entropy coating on the surface of the Pt layer to obtain a second high-temperature alloy; the NiCoCrFeAl alloy comprises, by weight percentage, 5-30% Al, 20-25% Co, 20-25% Fe, 20-25% Cr, and 20-25% Ni;

[0009] Chemical vapor deposition aluminizing is performed on the surface of the second high-temperature alloy to form a NiAl layer on the surface of the NiCoCrFeAl high-entropy coating, thereby obtaining a Pt-modified gradient NiCoCrFeAl high-entropy coating.

[0010] Preferably, the high temperature alloy substrate comprises IC21 single crystal alloy.

[0011] Preferably, the conditions for electroplating the Pt layer include: a current density of 1 to 3 A / dm 2 , temperature is 80-95℃, time is 36-96min, and pH value of plating solution is 8-11.

[0012] Preferably, the thickness of the Pt layer is 3 to 8 μm.

[0013] Preferably, after the Pt layer is electroplated, the process further comprises subjecting the Pt-plated high-temperature alloy substrate to vacuum heat treatment; the temperature of the vacuum heat treatment is 1040° C.±10° C., and the holding time is 1 to 3 hours.

[0014] Preferably, the conditions of the arc ion plating include: arc current of 160-200A, bias voltage of 20-40V, vacuum degree ≤ 2×10 -3 Pa, the first high temperature alloy temperature is 300 ~ 500 ℃.

[0015] Preferably, the thickness of the NiCoCrFeAl high entropy coating is 20-40 μm.

[0016] Preferably, the conditions for chemical vapor deposition aluminizing include: vacuum degree ≤ 5×10 -3 Pa, the aluminizing temperature is 960℃±10℃, and the aluminizing time is 3~5h.

[0017] Preferably, the thickness of the NiAl layer is 10-20 μm.

[0018] The present invention provides a Pt-modified gradient NiCoCrFeAl high-entropy coating prepared by the preparation method described in the above scheme, comprising a Pt layer, a NiCoCrFeAl high-entropy coating and a NiAl layer stacked in sequence on the surface of a high-temperature alloy substrate; the Pt layer is in contact with the high-temperature alloy substrate.

[0019] The present invention provides a preparation method of a Pt-modified gradient NiCoCrFeAl high-entropy coating, comprising the following steps: electroplating a Pt layer on the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy; performing multi-arc ion plating on the first high-temperature alloy using the NiCoCrFeAl alloy as a target material to form a NiCoCrFeAl high-entropy coating on the surface of the Pt layer to obtain a second high-temperature alloy; wherein the NiCoCrFeAl alloy comprises, in percentage by mass, 5-30% Al, 20-25% Co, 20-25% Fe, 20-25% Cr, and 20-25% Ni; and performing chemical vapor deposition aluminizing on the surface of the second high-temperature alloy to form a NiAl layer on the surface of the NiCoCrFeAl high-entropy coating to obtain the Pt-modified gradient NiCoCrFeAl high-entropy coating.

[0020] The present invention first electroplates a Pt layer on the surface of a high-temperature alloy substrate to enhance the selective oxidation of Al, thereby reducing the critical Al content required for the formation of Al2O3 on the coating surface (during actual high-temperature service, the coating's oxidation resistance is mainly achieved by forming a dense alumina protective substrate. Pt reduces the minimum content of alumina generated by oxidation of Al in the coating during this process), thereby reducing the difficulty of forming a multi-arc ion plating target. Multi-arc ion plating is then used to prepare a NiCoCrFeAl high-entropy coating, which has a slower cooling rate than laser cladding and can reduce the coating's cracking tendency. Finally, chemical vapor deposition aluminizing is performed to increase the Al content in the coating, thereby significantly improving the oxidation resistance of the Pt-modified gradient NiCoCrFeAl high-entropy coating sample at 1200°C.

[0021] Compared with laser cladding, the multi-arc ion plating method used in this invention not only reduces the tendency of coating cracking, but also allows the placement of workpieces to be adjusted according to their shape and quantity during the preparation process. Combined with a substrate rotation device, it can produce workpieces with uniform coatings in large quantities.

[0022] Increasing the Al content in the coating improves the coating's high-temperature oxidation resistance. However, increasing the Al content in the laser cladding powder increases the coating's tendency to thermally crack. In the multi-arc ion plating process for preparing high-entropy alloy coatings, increasing the Al content in the high-entropy alloy target material can lead to target brittleness and cracking during the forming process. The present invention utilizes a low-Al content target material during the multi-arc ion plating process, combined with a Pt plating treatment, to reduce the critical Al content required to form Al2O3 on the coating surface, thereby reducing the difficulty of forming the multi-arc ion plating target material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flowchart for preparing Pt-modified gradient NiCoCrFeAl high-entropy coating and testing its antioxidant properties;

[0024] Figure 2Schematic diagram of the structure of Pt-modified gradient NiCoCrFeAl high-entropy coating;

[0025] Figure 3 Schematic diagram of the cross section of the Pt-modified gradient NiCoCrFeAl high-entropy coating;

[0026] Figure 4 This is the cross-sectional element distribution diagram of the Pt-modified gradient NiCoCrFeAl high-entropy coating;

[0027] Figure 5 This is the weight gain curve of Pt-modified gradient NiCoCrFeAl high-entropy coating. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a Pt-modified gradient NiCoCrFeAl high-entropy coating, comprising the following steps:

[0029] Electroplating a Pt layer on the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy;

[0030] Using a NiCoCrFeAl alloy as a target, multi-arc ion plating is performed on the first high-temperature alloy to form a NiCoCrFeAl high-entropy coating on the surface of the Pt layer to obtain a second high-temperature alloy; the NiCoCrFeAl alloy comprises, by weight percentage, 5-30% Al, 20-25% Co, 20-25% Fe, 20-25% Cr, and 20-25% Ni;

[0031] Chemical vapor deposition aluminizing is performed on the surface of the second high-temperature alloy to form a NiAl layer on the surface of the NiCoCrFeAl high-entropy coating, thereby obtaining a Pt-modified gradient NiCoCrFeAl high-entropy coating.

[0032] In the present invention, unless otherwise specified, all raw materials used are commercially available products well known in the art.

[0033] The present invention electroplates a Pt layer on the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy.

[0034] Prior to electroplating the Pt layer, the present invention preferably further includes sequentially cutting, grinding, and sandblasting the high-temperature alloy. The present invention does not have any specific requirements for the cutting and grinding processes; these processes, known in the art, can be employed. In the present invention, the sandblasting pressure is preferably 0.2-0.4 MPa, more preferably 0.3 MPa, and the duration is preferably 30 seconds to 2 minutes, more preferably 1 minute. Through grinding and sandblasting, the present invention increases the surface roughness of the high-temperature alloy substrate, thereby enhancing the bonding strength between the Pt layer and the high-temperature alloy substrate.

[0035] In the present invention, the conditions for electroplating the Pt layer include: the current density is preferably 1 to 3 A / dm 2 , more preferably 2A / dm 2 ; The temperature is preferably 80-95°C, more preferably 85-90°C; The time is preferably 36-96 min, more preferably 50-90 min; The pH value of the plating solution is preferably 8-11, more preferably 9-10. In the present invention, the chemical composition of the plating solution preferably includes: [(NH3)2Pt(NO2)2·2H2O 8-12 g / L, potassium hydroxide (KOH) 10-30 g / L, saturated ammonium hydroxide (NH3·H2O) 20-100 ml / L, sodium nitrite (NaNO2) 5-10 g / L, ammonium nitrate (NH4NO3) 5-10 g / L. In the present invention, the thickness of the Pt layer is preferably 3-8 μm, more preferably 4-6 μm. The present invention electroplates a Pt layer on the surface of a high-temperature alloy substrate, enhances the selective oxidation of Al, reduces the critical Al content required to form Al2O3 on the coating surface, and reduces the difficulty of forming the multi-arc ion plating target.

[0036] After the electroplating of the Pt layer is completed, the present invention preferably performs vacuum heat treatment on the Pt-plated high-temperature alloy substrate to obtain a first high-temperature alloy. In the present invention, the temperature of the vacuum heat treatment is preferably 1040°C ± 10°C, more preferably 1040°C, the holding time is preferably 1 to 3 hours, more preferably 2 hours, and the vacuum degree is preferably ≤ 5×10 -4 Since the electroplated coating has large internal stress and weak bonding with the substrate, it is easy to peel off. In the present invention, vacuum heat treatment is used to remove the internal stress and at the same time, a certain amount of mutual diffusion is allowed between the Pt layer and the substrate to achieve a more stable bonding.

[0037] After obtaining the first high-temperature alloy, the present invention uses NiCoCrFeAl alloy as a target material to perform multi-arc ion plating on the first high-temperature alloy to form a NiCoCrFeAl high-entropy coating on the surface of the Pt layer to obtain a second high-temperature alloy.

[0038] Prior to multi-arc ion plating, the present invention preferably pre-treats the first superalloy. The pre-treatment preferably includes ion cleaning the first superalloy, preferably for at least 10 minutes. Pre-treating the first superalloy activates the surface, effectively improving the adhesion of the NiCoCrFeAl high-entropy coating.

[0039] In the present invention, the NiCoCrFeAl alloy comprises, by mass percentage, 5-30% Al, 20-25% Co, 20-25% Fe, 20-25% Cr, and 20-25% Ni, more preferably 7.7% Al, 24.1% Co, 22.8% Fe, 21.3% Cr, and 24% Ni. In the present invention, the target material has a low Al content, which can reduce the difficulty of forming the multi-arc ion plating target material.

[0040] In the present invention, the conditions of the arc ion plating include: the arc current is preferably 160-200A, more preferably 170-190A, and further preferably 180A; the bias voltage is preferably 20-40V, more preferably 25-35A, and further preferably 30V; the vacuum degree is preferably ≤2×10 -3 Pa, the first high temperature alloy temperature is preferably 300-500° C., more preferably 350-450° C., and further preferably 400° C. In the present invention, the thickness of the NiCoCrFeAl high entropy coating is preferably 20-40 μm, more preferably 25-35 μm, and further preferably 30 μm.

[0041] After obtaining the second high-temperature alloy, the present invention performs chemical vapor deposition aluminizing on the surface of the second high-temperature alloy to form a NiAl layer on the surface of the NiCoCrFeAl high-entropy coating to obtain a Pt-modified gradient NiCoCrFeAl high-entropy coating.

[0042] In the present invention, the conditions for chemical vapor deposition aluminizing include: vacuum degree is preferably ≤5×10 -3 Pa; the aluminizing temperature is preferably 960°C ± 10°C, more preferably 960°C; the aluminizing time is preferably 3 to 5 hours, more preferably 4 hours. In the present invention, the thickness of the NiAl layer is preferably 10 to 20 μm, more preferably 12 to 18 μm, and even more preferably 15 μm. The present invention increases the Al content in the coating by aluminizing, thereby improving the high-temperature oxidation resistance of the Pt-modified gradient NiCoCrFeAl high-entropy coating.

[0043] The present invention provides a Pt-modified gradient NiCoCrFeAl high entropy coating prepared by the preparation method described in the above scheme, such as Figure 2 As shown, it includes a Pt layer, a NiCoCrFeAl high entropy coating and a NiAl layer which are sequentially stacked on the surface of a high-temperature alloy substrate; the Pt layer is in contact with the high-temperature alloy substrate.

[0044] The Pt-modified gradient NiCoCrFeAl high-entropy coating of the present invention has a high Al content of 8 to 9 wt % and excellent oxidation resistance at 1200° C.

[0045] The Pt-modified gradient NiCoCrFeAl high-entropy coating and its preparation method provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] Figure 1 The flow chart of the preparation of Pt modified gradient NiCoCrFeAl high entropy coating and testing of its antioxidant performance is as follows: Figure 1 As shown, the present invention uses wire cutting to process IC21 single crystal alloy into a disc sample with a thickness of 3 mm and a diameter of 13 mm. A hole with a diameter of 1 mm is cut at each end of the sample. The sample is polished with sandpaper until there is no wire cutting mark on the surface. Then, the surface roughness is increased by sandblasting. The sandblasting pressure is 0.3 MPa and the time is 1 min.

[0048] The Pt layer was electroplated on the front and back surfaces of the sandblasted alloy. The plating solution composition was [(NH3)2Pt(NO2)2·2H2O 10g / L, potassium hydroxide (KOH) 30g / L, saturated ammonium hydroxide (NH3·H2O) 50ml / L, sodium nitrite (NaNO2) 5g / L, ammonium nitrate (NH4NO3) 5g / L]; the electroplating current density was 2A / dm 2 , the temperature is 90℃, and the plated samples are placed in a clean vacuum furnace (pressure ≤ 5×10 -4 Pa) at 1040°C for 2 h to form a Pt layer with a thickness of 3 μm, thereby obtaining a first high-temperature alloy;

[0049] The first high-temperature alloy was ion cleaned for 10 minutes, and multi-arc ion plating was performed on the surface of the first high-temperature alloy sample using a NiCoCrFeAl alloy target. The NiCoCrFeAl alloy target used included the following elements, by mass percentage: Al 7.7%, Co 24.1%, Fe 22.8%, Cr 21.3%, Ni 24% (atomic percentage 0.7:1:1:1:1) and trace amounts of Hf and Y. The arc current of the multi-arc ion plating was 180 A, the bias voltage was 30 V, and the vacuum degree was 2×10 -3 Pa, the substrate temperature is 400 ° C, and the NiCoCrFeAl layer is formed with a thickness of 30 μm to obtain the second high-temperature alloy;

[0050] Chemical vapor deposition aluminizing was performed on the surface of the second high-temperature alloy sample. The vacuum degree of the chemical vapor aluminizing method was 5×10 -3 Pa, aluminizing temperature of 960℃, aluminizing time of 4h, a surface NiAl layer with a thickness of 15μm was formed, and a Pt-modified gradient NiCoCrFeAl layer was obtained. The obtained sample was recorded as sample 2.

[0051] After preparation, the structure of sample 2 is as follows Figure 2 As shown, the cross-sectional appearance is Figure 3 As shown, the cross-sectional element distribution diagram is as follows Figure 4 shown. Figure 3 The outer side is NiAl layer, the middle is NiCoCrFeAl high entropy coating, the inner side is Pt layer, the white dots in the middle are Al-Ni-Pt-rich phase, and the dots at the junction of Pt layer and substrate are Mo-rich phase. Figure 4 It can be seen that the outer side of the high entropy coating is an Al-rich region, and the inner side is a Cr-rich region.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that no Pt plating and no Al infiltration are performed. The obtained sample is recorded as Sample 1.

[0054] Comparative Example 2

[0055] The only difference from Example 1 is that no Al is infiltrated. The obtained sample is recorded as Sample 3.

[0056] IC21 single crystal alloy samples 1 and 3 with NiCoCrFeAl high entropy coatings, and IC21 single crystal alloy sample 2 with Pt modified gradient NiCoCrFeAl high entropy coatings were subjected to a 1200°C standard cyclic oxidation test (referring to a cyclic test at 1200°C, where the sample was heated for 50 minutes and air-cooled for 10 minutes, and the mass change of the sample was recorded during the test until weight loss was achieved, at which point the test was terminated). Complete antioxidant test data were obtained, and the test results are shown in Tables 1 and Figure 5 As shown, the high temperature oxidation resistance of the Pt modified gradient NiCoCrFeAl high entropy coating was judged.

[0057] Table 1 High temperature oxidation resistance of sample 1 and sample 2

[0058]

[0059] According to HB5258-2000 "Test method for determination of oxidation resistance of steel and high temperature alloys", the spalling amount of sample 1 is 17.78g / m 2 , reaching the secondary antioxidant level, the peeling amount of sample 2 is 0.77g / m 2 , reaching the complete anti-oxidation level, the peeling amount of sample 3 is 2.58g / m 2 , reaching the anti-oxidation level, indicating that the high-temperature anti-oxidation performance of the Pt-modified gradient NiCoCrFeAl high-entropy coating prepared by the present invention is significantly improved.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a Pt-modified gradient NiCoCrFeAl high-entropy coating, comprising the following steps: Electroplating a Pt layer on the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy; The first high-temperature alloy is subjected to multi-arc ion plating using NiCoCrFeAl alloy as a target to form a NiCoCrFeAl high-entropy coating on the surface of the Pt layer to obtain a second high-temperature alloy; the NiCoCrFeAl alloy is Includes: Al 5~30%, Co 20~25%, Fe 20~25%, Cr 20~25% and Ni 20~25%; Chemical vapor deposition aluminizing is performed on the surface of the second high-temperature alloy to form a NiAl layer on the surface of the NiCoCrFeAl high-entropy coating, thereby obtaining a Pt-modified gradient NiCoCrFeAl high-entropy coating.

2. The preparation method according to claim 1, characterized in that The high temperature alloy substrate includes IC21 single crystal alloy.

3. The preparation method according to claim 1, characterized in that The conditions for electroplating the Pt layer include: a current density of 1-3 A / dm2, a temperature of 80-95°C, a time of 36-96 minutes, and a plating solution pH of 8-11.

4. The preparation method according to claim 1 or 3, characterized in that The thickness of the Pt layer is 3-8 μm.

5. The preparation method according to claim 1 or 3, characterized in that After the Pt layer is electroplated, the high-temperature alloy substrate after the Pt plating is subjected to vacuum heat treatment; the temperature of the vacuum heat treatment is 1040°C±10°C, and the holding time is 1-3 hours.

6. The preparation method according to claim 1, characterized in that The conditions for the multi-arc ion plating include: arc current of 160-200 A, bias voltage of 20-40 V, vacuum degree ≤ 2×10-3 Pa, and first high-temperature alloy temperature of 300-500°C.

7. The preparation method according to claim 1 or 6, characterized in that The thickness of the NiCoCrFeAl high entropy coating is 20-40 μm.

8. The preparation method according to claim 1, characterized in that The conditions for the chemical vapor deposition aluminizing include: vacuum degree ≤5×10-3Pa, aluminizing temperature of 960°C±10°C, and aluminizing time of 3-5h.

9. The preparation method according to claim 1 or 8, characterized in that The thickness of the NiAl layer is 10-20 μm.

10. The Pt-modified gradient NiCoCrFeAl high-entropy coating prepared by the preparation method according to any one of claims 1 to 9 comprises a Pt layer, a NiCoCrFeAl high-entropy coating, and a NiAl layer stacked in sequence and attached to the surface of a high-temperature alloy substrate; the Pt layer is in contact with the high-temperature alloy substrate.

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