NiAl alloy and preparation method thereof

Abstract

The invention discloses a NiAl alloy and a preparation method thereof.The method comprises the steps that carbohydrate organic matter serves as an oxygen source, and the surface of alloy powder is evenly coated with a layer of carbohydrate organic matter through ultrasonic treatment, magnetic stirring, grinding, drying and other methods in advance. And then, through rapid hot pressed sintering, oxide is generated in situ in the alloy forming process. The method is easy to operate, low in production cost, good in repeatability and easy to operate and control, the binding property of the oxide generated in situ and the matrix is good, the high-temperature oxidation performance of the alloy is improved, and the wide application prospect is achieved.

Description

Technical Field

[0001] The 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 hot-end components of aerospace due to their high strength, low density and excellent comprehensive properties. However, materials used at high temperatures often face problems such as oxidation, which hinders the application of NiAl alloys. An ideal anti-oxidation alloy needs to form a slowly growing protective oxide film on the surface. After oxidation, NiAl alloy will form a layer of Al2O3 on the surface, which is prone to peeling during long-term oxidation, causing the alloy to fail. Common methods to improve the high-temperature oxidation performance of alloys include pre-oxidation and adding alloying elements (such as rare earth elements). The pre-oxidation process is often difficult to control, and once the pre-generated oxide film is damaged, more severe oxidation often occurs. The pre-oxidation process is cumbersome and greatly increases costs. Adding alloying elements may cause deterioration of mechanical properties, and there may be complex interactions between alloying elements, which may affect the overall performance of the alloy. In addition, adding certain alloying elements (such as rare earth elements) will cause a large increase in 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, realizes dispersion strengthening of the alloy, greatly shortens the preparation time, has low preparation cost, and 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 NiAl alloy preparation method provided by the present invention comprises the following steps: Step 1, dissolving a specific amount of small molecule sugar in deionized water and alcohol and performing ultrasonic treatment to obtain a mixed solution; Step 2: slowly adding a specific amount of metal powder into the mixed solution, and performing magnetic stirring and heating; Step 3: After the solution evaporates, grind the composite powder and put it into a drying oven for drying; Step 4: performing vacuum hot pressing sintering on 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.

[0005] Specifically, the small molecule sugar is sucrose, glucose or fructose.

[0006] Specifically, the magnetic stirring rate was 100-500 rpm, and the heating temperature was set to 85 °C.

[0007] Specifically, the drying temperature is set to 80-120°C, and the drying time is 4 h-24 h.

[0008] Specifically, the ultrasonic treatment time is 10-60 min.

[0009] Specifically, the powder grinding time is 10-60 min.

[0010] Specifically, the volume ratio of deionized water to alcohol is 1:1-5:1.

[0011] The invention also provides a NiAl alloy prepared by the method.

[0012] The present invention mixes metal powder with small molecule sugar in a specific ratio so that the small molecule sugar uniformly covers the metal powder, and cooperates with a special sintering process system, using the small molecule sugar as an oxygen source, decomposing into oxidizing gases such as CO2, O2, H2O at high temperature, and reacting with the Al element in the alloy to generate dispersed Al2O3, thereby achieving dispersion strengthening of the alloy. At the same time, vacuum hot pressing sintering can effectively discharge gas to ensure the densification of the material. The in-situ grown oxide can be pinned at the grain boundary, hindering the growth of NiAl alloy grains after oxidation, thereby reducing the minimum Al content required to form a protective Al2O3 oxide film, ensuring the continuous formation of Al2O3, and the prepared NiAl alloy has excellent high-temperature oxidation performance.

[0013] The present invention generates oxides in situ during the rapid hot pressing sintering process, which reduces the steps required compared to the traditional method, greatly shortens the preparation time and reduces the cost. In addition, the oxide strengthening phase generated in situ has good thermodynamic stability in the matrix, and the interface between the strengthening phase and the matrix is ​​clean, has good bonding and is evenly distributed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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.

[0015] Figure 1 This is the organization diagram of the in-situ grown oxide of the alloy of Example 1; Figure 2 This is a cross-sectional view of the sample after long-term high-temperature oxidation of the alloy in Example 1; Figure 3 This is the alloy structure diagram of comparative example 4. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0017] Gas atomized Ni50Al (wt.%) was selected as the base metal powder, and sucrose was used as the small molecule oxygen source. 24g Ni50Al and 0.16g sucrose were weighed, and the sugar was dissolved in a mixed solution of deionized water (40 ml) and alcohol (20 ml) and ultrasonicated for 30 min to completely dissolve the sucrose. Subsequently, the dissolved sucrose was placed on a magnetic stirring table, the speed was adjusted to 300 rpm, and heated to 85 ℃, and Ni50Al powder was slowly poured into the solution. After the solution evaporated, the powder was ground for 30 min and placed in a drying oven for 8 h. Finally, the dried composite powder was sintered by rapid vacuum hot pressing to generate oxides in situ and synthesize composite materials. The sintering temperature was set to 900 ℃, the heating rate was 100 ℃ / min, the holding time was 10 min, and the cooling rate was 100 ℃ / min.

[0018] 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. Dispersed Al2O3 particles appear at the grain boundaries and are closely integrated with the matrix. Subsequently, the high-temperature oxidation performance of pure Ni50Al and the alloy with in-situ Al2O3 was tested at 1050 ℃ and 100 h. The cross-sectional morphology after oxidation is shown in Figure 2 As shown in the figure, it can be seen that the oxidation product of Ni50Al alloy is loose and porous, with a thickness of about 40 μm, while 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, and the alloy has better high-temperature oxidation resistance. The reason for the increase in oxidation resistance is that the in-situ grown oxide can be pinned at the grain boundary, 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.

[0019] 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 HV0.2 , the microhardness is significantly improved, which is due to the dispersion strengthening effect of Al2O3 particles, thereby improving the hardness of the alloy. Example

[0020] Different from Example 1, glucose is used as a small molecule oxygen source, the Ni50Al content is 20 g, the glucose content is 0.18 g, the sintering temperature is set to 1100 ℃, the heating rate is 110 ℃ / min, the holding time is 20 min, and the cooling rate is 80 ℃ / min. Analysis of the microstructure after hot pressing sintering shows that the alloy is dense and has no holes, and the Al2O3 particles are dispersed in the matrix structure and are closely combined with the matrix. The average microhardness of the samples is 1073.5 HV 0.2 . Example

[0021] Different from Example 1, the sintering temperature is set to 800 ℃, the heating rate is 120 ℃ / min, the holding time is 20 min, and the cooling rate is 120 ℃ / min. Analysis of the microstructure after hot pressing sintering shows that the alloy is dense and has no holes, and the Al2O3 particles are dispersed in the matrix structure and are closely combined with the matrix. The average microhardness of the samples is 1098.7HV 0.2 .

[0022] Comparative Example 1 Different from Example 1, the content of Ni50Al is 15 g, the content of sucrose is 0.16 g, and 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 prompted Al2O3 to nucleate, aggregate, and grow in large quantities during the hot pressing process. The oxide is not tightly bonded to the matrix interface, forming a large number of pores, resulting in a decrease in alloy performance, and O2 is easy to diffuse inward along defects such as pores, causing serious internal oxidation.

[0023] Comparative Example 2 The difference from Example 1 is that the content of Ni50Al is 48 g, the content of sucrose is 0.16 g, and the other process parameters are the same as those of Comparative Example 1. The microstructure and properties of the alloy after hot pressing and sintering are analyzed, and it is found 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.

[0024] Comparative Example 3 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 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, which makes it impossible to form.

[0025] Comparative Example 4 The difference from Example 1 is that the sintering temperature is set to 700 °C, the holding time is 5 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 sintering are analyzed. Figure 3 As shown in the figure, there are a large number of holes 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.

[0026] The above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived therefrom are still 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 performing ultrasonic treatment to obtain a mixed solution; Step 2: slowly adding a specific amount of metal powder into the mixed solution, and performing magnetic stirring and heating; Step 3: After the solution evaporates, grind the composite powder and put it into a drying oven for drying; Step 4: performing vacuum hot pressing sintering on 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 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, characterized in that: 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, characterized in that: The drying temperature is set at 80-120 °C and the drying time is 4 h-24 h.

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

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

7. The method for preparing NiAl alloy according to claim 1, characterized in that: 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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