A NiAl alloy and preparation method thereof

Abstract

The present invention discloses a NiAl alloy and a preparation method thereof. This method utilizes a carbohydrate organic compound as an oxygen source. A layer of the carbohydrate organic compound is uniformly coated on the surface of the alloy powder through methods such as ultrasound, magnetic stirring, grinding, and drying. Subsequently, oxides are generated in situ during the alloy forming process through rapid hot pressing and sintering. This method is simple to operate, has low production costs, good reproducibility, and is easy to operate and control. The in-situ generated oxides exhibit good bonding with the matrix, improving the alloy's high-temperature oxidation resistance and possessing broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy preparation, and in particular relates to a NiAl alloy and a preparation method thereof. Background Art

[0002] NiAl alloys are widely used in aerospace hot-end components due to their high strength, low density, and excellent overall performance. However, materials used at high temperatures often face oxidation challenges, which hinder their application. An ideal oxidation-resistant alloy requires a slowly growing protective oxide film on its surface. However, oxidation of NiAl alloys forms a layer of Al2O3 on the surface, which is prone to spalling during long-term oxidation, leading to alloy failure. Common methods for improving the high-temperature oxidation resistance of alloys include pre-oxidation and the addition of alloying elements (such as rare earth elements). However, the pre-oxidation process is often difficult to control, and once the pre-formed oxide film is damaged, more severe oxidation often occurs. Furthermore, the pre-oxidation process is cumbersome and significantly increases costs. The addition of alloying elements can degrade mechanical properties, and complex interactions between alloying elements can affect the overall performance of the alloy. Furthermore, the addition of certain alloying elements (such as rare earth elements) can significantly increase costs. Summary of the Invention

[0003] The main purpose of the present invention is to provide a NiAl alloy and a preparation method thereof. The method uniformly coats metal powder with small molecule sugars, generates dispersed oxides in situ during hot pressing and sintering, and realizes dispersion strengthening of the alloy. The method also greatly shortens the preparation time and has low preparation cost. The in-situ generated oxide strengthening phase has good thermodynamic stability in the matrix, and the interface between the strengthening phase and the matrix is ​​clean, has good bonding, and is uniformly distributed.

[0004] To this end, the present invention provides a method for preparing a NiAl alloy, comprising the following steps:

[0005] Step 1: dissolving a specific amount of small molecule sugar in deionized water and alcohol and ultrasonically treating the mixture to obtain a mixed solution;

[0006] Step 2: slowly adding a specific amount of metal powder to the mixed solution, and performing magnetic stirring and heating;

[0007] Step 3: After the solution evaporates, grind the composite powder and dry it in a drying oven;

[0008] Step 4: vacuum hot pressing and sintering the dried composite powder to obtain an alloy;

[0009] The mass ratio of metal powder to small molecule sugar is 100:1-200:1, the hot pressing sintering temperature is 800-1200°C, the heating rate is 80-120°C / min, the holding time is 10-30 min, and the cooling rate is 10-120°C / min.

[0010] Specifically, the small molecule sugar is sucrose, glucose or fructose.

[0011] Specifically, the magnetic stirring rate was 100-500 rpm, and the heating temperature was set to 85 °C.

[0012] Specifically, the drying temperature is set to 80-120°C, and the drying time is 4 h-24 h.

[0013] Specifically, the ultrasonic treatment time is 10-60 min.

[0014] Specifically, the powder grinding time is 10-60 min.

[0015] Specifically, the volume ratio of deionized water to alcohol is 1:1-5:1.

[0016] The present invention also provides a NiAl alloy prepared by the method.

[0017] The present invention combines metal powder with a small molecule sugar in a specific ratio, uniformly coating the metal powder with the small molecule sugar. Furthermore, a special sintering process is employed, utilizing the small molecule sugar as an oxygen source. At high temperatures, the sugar decomposes into oxidizing gases such as CO2, O2, and H2O, which react with the Al element in the alloy to form dispersed Al2O3, achieving dispersion strengthening of the alloy. Vacuum hot pressing sintering also effectively exhausts gases, ensuring material densification. The in-situ grown oxides can pin to grain boundaries, hindering the growth of NiAl alloy grains after oxidation, thereby reducing the minimum Al content required to form a protective Al2O3 oxide film and ensuring the continuous formation of Al2O3. The resulting NiAl alloy exhibits excellent high-temperature oxidation resistance.

[0018] The present invention generates oxides in situ during the rapid hot-pressing sintering process, reducing the number of steps required compared to traditional methods, significantly shortening preparation time and lowering costs. Furthermore, the in-situ generated oxide strengthening phase has good thermodynamic stability within the matrix, and the interface between the strengthening phase and the matrix is ​​clean, well-bonded, and evenly distributed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 This is the microstructure of the in-situ grown oxide of the alloy of Example 1;

[0021] Figure 2 This is a cross-sectional view of the sample after long-term high-temperature oxidation of the alloy in Example 1;

[0022] Figure 3 This is the alloy structure diagram of comparative example 4. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Example

[0024] Atomized Ni50Al (wt.%) was used as the base metal powder, and sucrose was used as the low-molecule oxygen source. 24 g of Ni50Al and 0.16 g of sucrose were weighed and dissolved in a mixture of deionized water (40 ml) and ethanol (20 ml). The mixture was ultrasonicated for 30 minutes to completely dissolve the sucrose. The dissolved sucrose was then placed on a magnetic stirrer at 300 rpm and heated to 85°C. Ni50Al powder was then slowly poured into the mixture. After the solution evaporated, the powder was milled for 30 minutes and dried in a drying oven for 8 hours. Finally, the dried composite powder was subjected to rapid vacuum hot pressing to in-situ generate oxides and synthesize the composite material. The sintering temperature was set at 900°C, the heating rate was 100°C / min, the holding time was 10 minutes, and the cooling rate was 100°C / min.

[0025] The structure after hot pressing sintering is as follows Figure 1 As shown in the figure, it can be seen that the alloy is dense and has no holes. Al2O3 particles are dispersed at the grain boundaries and are tightly bonded to the matrix. Subsequently, the high-temperature oxidation performance test of pure Ni50Al and the alloy with in-situ generated Al2O3 was carried out at a test temperature of 1050 ℃ for 100 h. The cross-sectional morphology after oxidation is shown in the figure. Figure 2As shown in the figure, the oxidation product of the Ni50Al alloy is loose and porous, with a thickness of approximately 40 μm. However, the oxidation product of the alloy after in-situ growth of Al2O3 is continuous and dense, with a thickness of less than 5 μm, forming a protective oxide film, which further improves the alloy's resistance to high-temperature oxidation. The improved oxidation resistance is due to the ability of the in-situ grown oxide to pin at the grain boundaries, hindering the growth of the NiAl alloy grains after oxidation, thereby reducing the minimum Al content required to form the protective Al2O3 oxide film and ensuring the continuous formation of Al2O3.

[0026] In addition, the microhardness of pure NiAl alloy and in-situ generated Al2O3 alloy was tested, and the average microhardness of the two was 941.8 HV 0.2 and 1103.1 HV 0.2 , the microhardness is significantly improved, which is due to the dispersion strengthening effect of Al2O3 particles, thereby improving the hardness of the alloy. Example

[0027] Different from Example 1, glucose was used as the small molecule oxygen source, the Ni50Al content was 20 g, the glucose content was 0.18 g, the sintering temperature was set to 1100 °C, the heating rate was 110 °C / min, the holding time was 20 min, and the cooling rate was 80 °C / min. Analysis of the microstructure after hot pressing sintering showed that the alloy was dense and free of pores, and the Al2O3 particles were dispersed in the matrix and tightly bonded to the matrix. The average microhardness of the samples was 1073.5 HV, ... 0.2 . Example

[0028] Different from Example 1, the sintering temperature was set at 800°C, the heating rate was 120°C / min, the holding time was 20 min, and the cooling rate was 120°C / min. Analysis of the microstructure after hot pressing sintering showed that the alloy was dense and free of pores, and the Al2O3 particles were dispersed in the matrix and tightly bonded to the matrix. The average microhardness of the samples was 1098.7HV. 0.2 .

[0029] Comparative Example 1

[0030] The difference from Example 1 is that the content of Ni50Al is 15 g and the content of sucrose is 0.16 g. The other process parameters are the same as those in Comparative Example 1. The alloy after hot pressing and sintering was analyzed, and it was found that some Al2O3 particles aggregated and grew, deteriorating the interface bonding. This is because too much oxygen source was added, resulting in oxygen source enrichment on the alloy surface, which promoted the nucleation, aggregation, and growth of a large amount of Al2O3 during the hot pressing process. The oxide was not tightly bonded to the matrix interface, forming a large number of pores, resulting in a decrease in alloy performance, and O2 easily diffused inward along defects such as pores, causing serious internal oxidation.

[0031] Comparative Example 2

[0032] The difference from Example 1 is that the content of Ni50Al is 48 g and the content of sucrose is 0.16 g. The other process parameters are the same as those of Comparative Example 1. Analysis of the microstructure and properties of the alloy after hot pressing and sintering shows that there are fewer Al2O3 particles at the grain boundaries and no obvious oxide dispersion distribution. This is because too little oxygen source is added, the amount of oxide is insufficient, and there is no obvious strengthening effect.

[0033] Comparative Example 3

[0034] The difference from Example 1 is that the sintering temperature is set to 1400 ° C, the heating rate is 70 ° C / min, and the other process parameters are the same as those in Comparative Example 1. The microstructure and properties of the alloy after hot pressing and sintering are analyzed, and it is found that the alloy cannot be formed. This is because a large amount of liquid phase will appear during hot pressing and sintering at this temperature, resulting in liquid phase extrusion and inability to form.

[0035] Comparative Example 4

[0036] The difference from Example 1 is that the sintering temperature is set to 700 ° C and the holding time is 5 min. The other process parameters are the same as those in Comparative Example 1. The microstructure and properties of the alloy after hot pressing sintering are analyzed. Figure 3 As shown in the figure, there are a large number of pores in the alloy and the microhardness of the alloy is greatly reduced. The main reason is that the sintering temperature is too low and the holding time is too short, resulting in insufficient sintering strength and poor density.

[0037] The above embodiments are merely examples to clearly illustrate the present invention and are not intended to limit its implementation. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to provide an exhaustive list of all embodiments. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a NiAl alloy, characterized in that: The steps include: Step 1: dissolving a specific amount of small molecule sugar in deionized water and alcohol and ultrasonically treating the mixture to obtain a mixed solution; Step 2: slowly adding a specific amount of metal powder to the mixed solution, and performing magnetic stirring and heating; Step 3: After the solution evaporates, grind the composite powder and dry it in a drying oven; Step 4: vacuum hot pressing and sintering the dried composite powder to obtain an alloy; The mass ratio of metal powder to small molecule sugar is 100:1-200:1, the hot pressing sintering temperature is 800-1200°C, the heating rate is 80-120°C / min, the holding time is 10-30 min, and the cooling rate is 10-120°C / min.

2. The method for preparing a NiAl alloy according to claim 1, wherein: Small molecule sugars include sucrose, glucose or fructose.

3. The method for preparing NiAl alloy according to claim 1, wherein: The magnetic stirring rate was 100-500 rpm and the heating temperature was set to 85 °C.

4. The method for preparing NiAl alloy according to claim 1, wherein: The drying temperature is set at 80-120 ℃ and the drying time is 4 h-24 h.

5. The method for preparing NiAl alloy according to claim 1, wherein: The ultrasonic treatment time is 10-60 min.

6. The method for preparing NiAl alloy according to claim 1, wherein: The powder grinding time is 10-60 min.

7. The method for preparing NiAl alloy according to claim 1, wherein: The volume ratio of deionized water to alcohol is 1:1-5:

1.

8. A NiAl alloy, characterized in that: The NiAl alloy is prepared by the method for preparing the NiAl alloy according to any one of claims 1 to 6.

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