CN116411200A - A kind of preparation method of rare earth oxide reinforced TiAl-based nanocomposite material - Google Patents

Abstract

The invention discloses a preparation method of a rare earth oxide reinforced TiAl-based nanocomposite material, which belongs to the technical field of TiAl-based nanocomposite material preparation. The preparation method of the composite material of the present invention includes the following steps: (1) preparing an aluminum-based intermediate composite material with a uniform distribution of strengthening phase (rare earth oxyfluoride); (2) preparing an aluminum-based rare earth oxyfluoride intermediate composite material and pure titanium (and other components) as raw materials, and prepare TiAl-based rare earth oxide nanocomposites by vacuum arc melting; (3) heat-treat TiAl-based rare earth oxide nanocomposites to obtain target structures (such as near-lamellar or full-lamellar structures) At the same time, a large number of uniformly dispersed nano-scale rare earth oxide strengthening phases are precipitated in the matrix. This method can solve the problem of nano-phase agglomeration and uneven dispersion in the process of preparing TiAl-based rare earth oxide nanocomposites by casting method, and provides a feasible preparation method for nanoscale rare earth oxide-reinforced TiAl-based composites, which is of great importance. Value.

Description

A kind of preparation method of rare earth oxide reinforced TiAl-based nanocomposite material

technical field

The invention belongs to the technical field of preparing TiAl-based nanocomposite materials, and relates to a method for preparing TiAl-based nanocomposite materials by using aluminum-based intermediate composite materials as raw materials.

Background technique

Because of its low density, high melting point, high specific strength, high specific modulus, and good high temperature oxidation resistance, TiAl alloy is considered to be an ideal lightweight high temperature structural material for the production of low pressure turbine blades. The field has important application prospects. Nano-ceramic phase composites have been proven to further improve the performance of TiAl alloys, for example, the addition of TiC and TiB ₂ can significantly improve the mechanical properties of TiAl alloys. The price of oxides is much lower than that of borides and carbides. Studies have shown that rare earth oxides (such as yttrium oxide) can significantly improve the mechanical properties of TiAl alloys. Therefore, the rare earth oxide reinforced TiAl-based nanocomposite is a promising lightweight high-temperature structural material with excellent performance and low preparation cost.

The current preparation methods of TiAl-based nanocomposites mainly include casting method, powder metallurgy method and additive manufacturing method. Powder metallurgy and additive manufacturing methods can realize the uniform distribution of nano-ceramic phases, among which the additive manufacturing method has the best effect, but at this stage, these two methods are usually relatively expensive, and have high requirements for equipment and working environment. Large-sized workpieces are difficult. In comparison, the casting method is low in cost and convenient to manufacture large-sized workpieces, and is a more economical method for preparing nanocomposites. However, in the process of preparing TiAl-based nano-ceramic phase composites by casting method, due to the poor wettability between nanoparticles and TiAl melt, and the large specific surface area and high surface energy of nanoparticles, the nanoparticles in the melt Inhomogeneous dispersion in the body. In addition, nanoparticles are easy to agglomerate under the action of van der Waals attraction, forming large-sized micron-scale aggregates, which are difficult to exist in a nano-state, which seriously weakens the strengthening effect of nano-ceramics relative to the TiAl matrix. Therefore, it has always been a major problem and challenge to prepare TiAl-based nanocomposites strengthened by nano-state ceramic phase by casting method. Solving the problem of agglomeration and uneven distribution of nano-ceramic phases is of great significance for the low-cost preparation of high-performance nano-ceramic phase-reinforced TiAl-based composites.

Contents of the invention

The present invention provides a novel preparation method for preparing TiAl-based rare earth oxide nanocomposites using aluminum-based intermediate composite materials as raw materials and subsequent heat treatment, with the purpose of improving the nanoparticle agglomeration and The problem of uneven distribution. The method has a simple process, can realize the uniform distribution of the ceramic reinforcement phase in the matrix without high-intensity stirring of the melt, and can realize micro-nano double-scale ceramic phase strengthening.

A method for preparing a rare earth oxide reinforced TiAl-based nanocomposite material, characterized in that an aluminum-based rare earth oxyfluoride intermediate composite material is used to replace pure aluminum and rare earth oxides as raw materials for the TiAl-based rare earth oxide composite material, and the rare earth fluorine The oxides are uniformly dispersed in the aluminum-based intermediate composite material, so that the rare earth oxide strengthening phase in the TiAl-based composite material can "inherit" this good dispersion; When prepared by a method with a very high melting temperature, the oxyfluoride will be dissolved in the TiAl-based alloy melt. Since the melting and boiling point of fluoride is usually very low, the fluorine element will be volatilized and removed during the smelting process of the composite material. In the subsequent heat treatment process, micron-scale and nano-scale rare earth oxides will be uniformly precipitated in the matrix, thereby obtaining a TiAl-based rare earth oxide nanocomposite material.

The preparation of the TiAl-based rare earth oxide nanocomposite material of the present invention comprises the following steps:

(1) Using pure aluminum, fluoride molten salt and nano-rare earth oxide as raw materials, melt pure aluminum in a graphite crucible and raise the temperature to the preset melting temperature, then stir the melt and add fluoride melting to the aluminum melt Salt and nano-rare earth oxides are cast after smelting to obtain an aluminum-based rare-earth oxyfluoride intermediate composite material.

(2) Place the aluminum-based rare earth oxyfluoride intermediate composite material, pure Ti and other alloy components in a melting tank of a vacuum electric arc furnace for melting, and remelt for 3 to 5 times to ensure uniform composition.

(3) The original TiAl-based rare earth oxide composite material obtained by vacuum arc melting is subjected to high temperature heat treatment, furnace cooling or air cooling.

Further, in step (1), the preparation process of the aluminum-based rare earth oxyfluoride intermediate composite material is fluoride molten salt assisted stirring casting, and the preset melting temperature can be higher than the melting points of aluminum and fluoride molten salt at the same time, The purpose of the stirring process is to homogenize the oxyfluoride in the aluminum melt, and any stirring method can be used as long as the purpose can be achieved.

Further, in step (1), the fluoride molten salt is KAlF ₄ ; the nano rare earth oxides are yttrium oxide and cerium oxide.

Further, in step (2), the aluminum-based rare earth oxyfluoride intermediate composite material is used as a raw material, wherein the content of oxyfluoride is 0.01wt.%-0.5wt.%.

Further, in step (3), the temperature of the heat treatment is 1200°C-1400°C, the time is 5min-2h, furnace cooling or air cooling, and the specific heat treatment regime varies with the composition of the composite material.

The present invention provides a novel method for preparing TiAl-based nanocomposites using aluminum-based intermediate composites as raw materials to solve the problem of uneven phase distribution and agglomeration of nano-ceramic phases in the process of preparing TiAl-based nanocomposites by casting. clumping problem. The solution idea of the present invention is:

(1) The ceramic phase is first well dispersed in the precursor material, and then the good dispersion of the ceramic phase in the precursor material can be "inherited" by the TiAl-based composite material when the TiAl-based composite material is smelted.

(2) Ti and Al are the two main elements of TiAl alloys, so Ti-based intermediate composites and Al-based intermediate composites are suitable choices as precursor materials. The Al-based intermediate composite material is a more suitable choice of precursor material due to its low melting point, low equipment requirements, and simple preparation process.

(3) The agglomeration of nanoparticles in the metal melt is often difficult to avoid. Therefore, in addition to achieving uniform dispersion of ceramic particles in the precursor material and reducing the size of the ceramic particle agglomerates as much as possible, it is necessary to further make the agglomerates in Ceramic phase transformed into nano state in TiAl matrix.

(4) "Dissolution-precipitation" is an effective refinement mechanism, but since pure rare earth oxides usually have a high melting point, it is difficult to dissolve or the process is slow during alloy smelting, so fluorine-modified rare earth oxides are used Oxyfluorides are formed instead of rare earth oxides as "intermediate strengthening phases". The melting point of rare earth oxyfluorides is significantly lower than that of oxides, and fluorides usually have lower melting and boiling points, which can be volatilized and removed during the high-temperature melting process of composite materials. In order to facilitate the dissolution of rare earth oxyfluorides and the removal of fluorine, methods with high melting temperatures should be used to prepare TiAl-based nanocomposites, and vacuum arc melting is one of them.

In the preparation process of rare earth oxide reinforced TiAl-based nanocomposites, due to the low melting and boiling point of fluoride, F will be volatilized and removed during the melting process of TiAl alloy. During the cooling process of the melt, since the melting point of the rare earth oxide is higher than that of the TiAl matrix, it will first precipitate to form a micron-sized rare earth oxide. Due to the rapid cooling effect of the water-cooled copper mold, the rare earth elements and oxygen elements will not be completely precipitated during the cooling process, but a part of them will be solid-solved in the matrix.

The rare earth elements and oxygen elements dissolved in the matrix will precipitate nanoscale rare earth oxides in the subsequent heat treatment process, and evenly distribute in the matrix.

The present invention innovatively proposes a rare earth oxide-reinforced TiAl-based nanocomposite based on the fact that the TiAl-based nanocomposite can "inherit" the dispersion uniformity of the strengthening phase in the aluminum-based intermediate composite, the fluorine-modified rare earth oxide and the "dissolution-precipitation" mechanism. Preparation methods of nanocomposites. This method is essentially still based on the casting method, and can realize micro-nano dual-scale rare earth oxide-reinforced TiAl alloys, which has significant advantages in the preparation of high-performance rare-earth oxide-reinforced TiAl-based nanocomposites at low cost, and is also a promising example for other types of ceramic phases. Strengthening TiAl-based nanocomposites provides a reference preparation process.

Description of drawings

Fig. 1 is a microstructure diagram of the aluminum-based yttrium oxyfluoride intermediate composite material and the yttrium oxide-reinforced TiAl-based nanocomposite material in Example 1 of the present invention. Figure 1a shows the distribution of the aluminum-based intermediate composite yttrium oxyfluoride in the aluminum matrix in Example 1 of the present invention; Figure 1b and 1c are the microstructure of the as-cast TiAl-based yttrium oxide nanocomposite in Example 1 of the present invention Figure, micron-sized yttrium oxide is uniformly distributed in the matrix; Figure 1d is the low-magnification microstructure of the as-cast TiAl-based yttrium oxide nanocomposite material in Example 1 of the present invention after high-temperature heat treatment (1340 ° C, 10 min), showing a near-sheet Layer structure; Fig. 1e is the high-magnification microstructure of Fig. 1d, with nanoscale yttrium oxide uniformly distributed in the matrix.

Fig. 2 is a transmission characterization diagram of the as-cast TiAl-based yttrium oxide nanocomposite material in Example 1 of the present invention after high temperature heat treatment (1340° C., 10 min). Fig. 2a is long rod-shaped micron-scale yttrium oxide in the matrix; Fig. 2b and 2c are equiaxed nano-scale yttrium oxide in the matrix; Fig. 2d and 2e are the interplanar spacing of nano-scale yttrium oxide at high resolution, Crystal plane angles and diffraction spot features.

Fig. 3 is a high-magnification microstructure diagram of the sample in Example 2 of the present invention after high-temperature heat treatment (1300° C., 2 h), and the nanometer yttrium oxide is evenly distributed in the matrix.

Fig. 4 is a microstructure diagram of the aluminum-based cerium oxyfluoride intermediate composite material and the ceria-reinforced TiAl-based nanocomposite material in Example 3 of the present invention. Figure 4a shows the distribution of cerium oxyfluoride in the aluminum matrix in the aluminum-based intermediate composite material in Example 3 of the present invention; Figures 4b and 4c are the original cast TiAl-based cerium oxide nanocomposites in Example 3 of the present invention. Microstructure diagram, micron-sized cerium oxide is evenly distributed in the matrix; Figures 4d and 4e are high-magnification microstructures of the as-cast TiAl-based cerium oxide nanocomposite material in Example 3 of the present invention after high-temperature heat treatment (1380°C, 30min), Nanoscale cerium oxide is evenly distributed in the matrix.

specific implementation plan

The technical solutions of the present invention will be further described below in conjunction with the examples.

Embodiment 1, TiAl-based yttrium oxide nanocomposite material

Step 1. Using pure aluminum, fluoride molten salt (KAIF ₄ ) and nanometer yttrium oxide as raw materials, melt pure aluminum in a graphite crucible and keep it at 750°C for 30 minutes, then perform mechanical stirring and add fluoride melt to the aluminum melt. salt and nanometer yttrium oxide, stop mechanical stirring after 20 minutes, and cast when the melt temperature drops to 740°C to obtain an Al-based yttrium oxyfluoride intermediate composite material, the content of yttrium oxyfluoride in the composite material is 0.08wt.%.

Step 2, using Al-based yttrium oxyfluoride composite material and pure Ti as raw materials to prepare TiAl-based yttrium oxide nano-composite material by vacuum arc melting method, remelting 3 to 5 times to ensure the uniformity of sample composition, the matrix composition is Ti-45Al(at .%);

Step 3. Put the sample in a muffle furnace for heat treatment. The heat treatment system is 1340°C-10min. After the heat treatment, the sample is cooled with the furnace;

In step 4, the heat-treated sample is prepared and tested for scanning samples and transmission samples.

Embodiment 2, TiAl-based yttrium oxide nanocomposite material

Step 1. Using pure aluminum, fluoride molten salt (KAIF ₄ ) and nanometer yttrium oxide as raw materials, melt pure aluminum in a graphite crucible and keep it at 750°C for 30 minutes, then perform mechanical stirring and add fluoride melt to the aluminum melt. salt and nanometer yttrium oxide, stop the mechanical stirring after 20 minutes, and cast the Al-based yttrium oxyfluoride intermediate composite material when the temperature of the melt drops to 740° C., the content of yttrium oxyfluoride in the composite material is 0.15wt.%.

Step 2, using Al-based yttrium oxyfluoride composite material and pure Ti as raw materials to prepare TiAl-based yttrium oxide nano-composite material by vacuum arc melting method, remelting 3 to 5 times to ensure the uniformity of sample composition, the matrix composition is Ti-45Al(at .%);

Step 3. Put the sample in a muffle furnace for heat treatment. The heat treatment system is 1300°C-2h. After the heat treatment, the sample is cooled with the furnace;

In step 4, the heat-treated sample is prepared and tested for scanning samples.

Embodiment 3, high Nb-TiAl based cerium oxide nanocomposite material

Step 1, using pure aluminum, fluoride molten salt (KAIF ₄ ) and nano-cerium oxide as raw materials, melt pure aluminum in a graphite crucible and keep it at 750°C for 30 minutes, then mechanically stir and add fluoride melt to the aluminum melt salt and nano-cerium oxide, stop the mechanical stirring after 20 minutes, and cast the Al-based cerium oxyfluoride intermediate composite material when the temperature of the melt is lowered to 740° C., the content of cerium oxyfluoride in the composite material is 0.3wt.%.

Step 2, using Al-based cerium oxyfluoride composite materials, pure Ti and Al-Nb alloys as raw materials to prepare high-Nb-TiAl-based cerium oxide nanocomposites by vacuum arc melting, and remelting 3 to 5 times to ensure the uniformity of the sample composition, The matrix composition is Ti-45Al-8Nb(at.%);

Step 3. Put the sample in a muffle furnace for heat treatment. The heat treatment system is 1380°C-30min. After the heat treatment, the sample is cooled with the furnace;

In step 4, the heat-treated sample is prepared and tested for scanning samples.

The above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described through the above embodiments, those skilled in the art should understand that changes and equivalent replacements made in form and details It will not deviate from the scope defined by the claims of the present invention.

Claims (5)

1. A method for preparing a rare earth oxide reinforced TiAl-based nanocomposite material, characterized in that, using an aluminum-based rare earth oxyfluoride intermediate composite material to replace pure aluminum and rare earth oxides as a raw material for a TiAl-based rare earth oxide composite material, and The rare earth oxyfluoride is uniformly dispersed in the aluminum-based intermediate composite material, so that the rare earth oxide strengthening phase in the TiAl-based composite material can "inherit" this good dispersion; the rare earth oxyfluoride with a lower melting point is used in vacuum When prepared by arc melting with extremely high melting temperature, oxyfluoride will dissolve in the TiAl-based alloy melt. Since fluoride usually has a low melting and boiling point, fluorine will be volatilized and removed during the smelting process of the composite material. During solidification and subsequent heat treatment, micron-scale and nano-scale rare earth oxides will be uniformly precipitated in the matrix, thereby obtaining a TiAl-based rare earth oxide nanocomposite material; the preparation of the TiAl-based rare earth oxide nanocomposite material includes the following steps: (1) Using pure aluminum, fluoride molten salt and nano-rare earth oxide as raw materials, melt pure aluminum in a graphite crucible and raise the temperature to the preset melting temperature, then stir the melt and add fluoride melting to the aluminum melt Salt and nano-rare earth oxides, casting after smelting to obtain aluminum-based rare earth oxyfluoride intermediate composite materials; (2) Melting the aluminum-based rare earth oxyfluoride intermediate composite material, pure Ti and other alloy components in a melting tank of a vacuum electric arc furnace, and remelting 3 to 5 times to ensure uniform composition; (3) The original TiAl-based rare earth oxide composite material obtained by vacuum arc melting is subjected to high temperature heat treatment, furnace cooling or air cooling. 2. the preparation method of rare earth oxide reinforced TiAl-based nano-composite material as claimed in claim 1, is characterized in that in step (1), the preparation process of aluminum-based rare earth oxyfluoride intermediate composite material is fluoride molten salt assisted stirring casting , the preset smelting temperature needs to be higher than the melting point of aluminum and fluoride molten salt at the same time. The purpose of the stirring process is to homogenize the oxyfluoride in the aluminum melt. The stirring method can be used as long as this purpose can be achieved. 3. the preparation method of rare earth oxide reinforced TiAl-based nanocomposite material as claimed in claim 1, is characterized in that in step (1), described fluoride molten salt is KAlF ₄ ; Described nanometer rare earth oxide is yttrium oxide, Ceria. 4. the preparation method of rare earth oxide reinforced TiAl-based nanocomposite material as claimed in claim 1, is characterized in that in step (2), described with aluminum base rare earth oxyfluoride intermediate composite material as raw material, wherein the oxyfluoride The content is 0.01wt.%～0.5wt.%. 5. The preparation method of rare earth oxide reinforced TiAl-based nanocomposites as claimed in claim 1, characterized in that in step (3), the temperature of the heat treatment is 1200 ° C ~ 1400 ° C, the time is 5 min ~ 2 h, furnace cooling Or air cooling, the specific heat treatment regime varies depending on the composition of the composite material.

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