TWI540211B - Equiaxed grain nickel-base casting alloy for high stress application - Google Patents

Description

High stress equiaxed crystal nickel base alloy

This invention relates to a nickel based alloy, and more particularly to a high stress equiaxed nickel based alloy.

Nickel has high strength, corrosion resistance and oxidation resistance at high temperatures, making it one of the most widely used materials for today's advanced turbine engine high temperature components. Traditionally, the forming methods of nickel-based alloys include casting, forging and powder metallurgy. The casting technology has the advantages of being able to produce complex shapes. Therefore, if the shape of the workpiece is complicated, the casting method will be selected. To make a workpiece.

Under the conditions of use of nickel-based alloy at room temperature to about 760 ° C (medium temperature), the grain boundary strength can still be maintained, so polycrystalline castings with equiaxed crystal structure will be used in design and use. However, at a high temperature of about 760 ° C or higher, the grain boundary will begin to weaken, and the higher the temperature, the more obvious the degree of grain boundary weakening. Therefore, under high temperature use conditions, directional solidification crystal or single crystal will be used. (Single Crystal) organized castings to provide the strength required for high temperature use. Although castings of single-direction crystal or single crystal structure have high high-temperature strength, it is still impossible to produce complex shapes and integrally formed castings (such as turbine rotors for turbine engines) by the current casting technology, so that single-direction crystals are used. Casting or The use of single crystal castings is limited. Since the current equiaxed crystal casting technology can produce complex shapes and integrally formed castings, castings of equiaxed crystal structures are generally used under the conditions of use below about 760 °C.

The latent change becomes a phenomenon of plastic deformation slowly under the action of medium and high temperature, which is the main reason for the material to be damaged by medium and high temperature. Among them, the turbine engine used in aerospace industry needs to be in medium and high temperature environment. Maintaining good mechanical strength, it is extremely necessary in the industry to develop a nickel-based alloy with excellent mechanical properties such as resistance to creep, fatigue, and high stress. In this way, both cost and mechanical properties can be simultaneously prepared. A high-stress nickel-based alloy.

In view of the above disadvantages of the prior art, the main object of the present invention is to provide a high stress equiaxed nickel base alloy, integrating a vacuum melting, a vacuum casting, and an appropriate element addition to prepare a high stress equiaxed nickel base. alloy.

In order to achieve the above object, according to one aspect of the present invention, there is provided a high stress equiaxed nickel base alloy having the following composition in terms of weight percent: Cr is 8.0 to 9.0 wt%, and W is 9.5 to 10.5 wt%, Co is 9.5 to 10.5 wt%, Al is 5.0 to 6.0 wt%, Ti is 0.5 to 1.5 wt%, Mo is 0.5 to 1.0 wt%, Ta is 2.5 to 3.5 wt%, Hf is 1.0 to 2.0 wt%, and Re is 4.0 to 5.0 wt%, Ru is 2.0 to 3.0 wt%, C is 0.12 to 0.18 wt%, and the balance is composed of Ni and unavoidable impurities.

The above high stress equiaxed crystal nickel base alloy is vacuum induction furnace After the smelting, vacuum precision casting is carried out in a vacuum environment, the molten alloy liquid is poured into the ceramic mold, and cooling is performed to complete the ingot working of the nickel-based alloy.

The above-mentioned nickel-based alloy ingot is a polycrystalline casting of an equiaxed crystal structure, and a further heat treatment process is required; the nickel-based alloy is subjected to a two-stage heat treatment in the present invention, wherein the first-stage heat treatment is performed at 1100-1300 ° C The ingot of the nickel-based alloy is subjected to heat treatment for at least one hour, and then the nickel-based alloy is cooled and cooled by argon gas; and the second-stage heat treatment is performed by heat-treating the nickel-based alloy ingot at 800-1000 ° C. After ten hours or more, the high-stress equiaxed nickel-based alloy was cooled by natural cooling to prepare a high-stress equiaxed nickel-based alloy.

The above summary and the following detailed description are intended to further illustrate the manner, means and effects of the present invention to achieve the intended purpose. Other purposes and advantages of this creation will be explained in the following description and drawings.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily understand the advantages and effects of the present invention from the disclosure of the present disclosure.

The alloy of the present invention is designed from a nickel base having an equiaxed crystal structure Starting from gold, aluminum and titanium elements are added thereto, and the mechanical strength is enhanced by the γ' precipitation strengthening phase of Ni3 (Al, Ti) formed by Al and Ti and Ni. Since the γ' phase has an L12 structure, unlike the general metal, the mechanical strength decreases with temperature, and its mechanical strength has a property proportional to temperature, and the higher the temperature, the better the strength. Although the increase of Al and Ti content can be the number of γ' phase, if the amount of γ' phase is too large, the alloy fragility will increase, which is easy to cause the alloy to be brittle during the casting process or during use. Therefore, the nickel base in the present invention The optimum content of Al in the alloy should be between 5.0 and 6.0 wt%, and the content of Ti should be between 0.5 and 1.5 wt%. When the nickel-based alloy is used in medium and high temperature for a long time, it increases with time. 'The phase coarsening and the volume fraction are gradually reduced, and the strength of the nickel-based alloy is lowered. To improve this phenomenon, the Ta element in the alloy of the present invention is used to improve the stability of the γ' phase in the medium and high temperature for a long time, but Too much addition of Ta element, easy to produce coarse TaC type carbide, this type of carbide is easy to become the origin of cracking crack, so that the strength of the alloy is reduced, so the Ta element content of the nickel-based alloy in the present invention is controlled at 2.7 ~ 3.2wt.%; In the present invention, Co mainly plays a function of increasing the solidus temperature of the γ' phase and reducing the solubility of Al and Ti in the γ base, so as to increase the volume fraction of the γ' precipitate, resulting in an increase in the strength of the alloy at medium and high temperatures. But after Co adds a certain amount, its The effect of increasing the number of γ' phases becomes inconspicuous. Although Co can provide a solid solution strengthening effect, the atomic size of Co and Ni is similar, which provides a solid solution strengthening effect, so the nickel base alloy in the present invention. The Co content is controlled between 9.5 and 10.5 wt%.

Carbon (C) in the nickel-based alloy of the present invention, and other alloying elements The carbides form carbides with high atomic bonding strength, which are distributed in the grains and on the grain boundaries. If the distribution of carbides on the grain boundary is uniform, discontinuous, and M23C6 type granular carbides, it will help to inhibit the slippage of grain boundaries at medium and high temperatures, strengthen the grain boundary strength and improve the creep life, but carbonization. If the material precipitates on the grain boundary in a continuous film form, it will not only have no strengthening effect on the grain boundary, but will cause cracking along the crystal; in general, when the carbon content of the nickel-based alloy is low, the grain boundary carbide distribution is uneven and easy. The film formation may be caused by the uneven distribution of carbon atoms at the grain boundaries due to the low carbon content, and the precipitation of carbides only in the localized regions of the grain boundaries, and since the grain boundaries cannot provide a certain amount of carbon atoms for their growth, Therefore, it is possible to continue to maintain its original film-like appearance. Therefore, in the present invention, the carbon content of the nickel-based alloy needs to be at least 0.12% by weight. If the carbon content is too high, it is easy to form a large-grained MC type (M represents a metal atom, C represents a carbon atom), a block or a strip. Carbide, which makes the carbide easy to be the origin of cracks. When the carbon content is too high, the temperature of the initial melting phase of the alloy is lowered. In order to avoid the generation of the initial melting phase, heat treatment conditions with a lower solution temperature must be used. After the alloy is cast, the subsequent effect of strengthening the alloy by heat treatment is compromised. Therefore, the carbon content of the nickel-based alloy in the present invention should be between 0.12 and 0.18 wt%; the main role of Cr in this experiment is to improve the alloy. The oxidation resistance and the hot corrosion resistance, but in addition to the above advantages, in the alloy of the present invention, there is still an effect of the precipitation agent of the M23C6 carbide. After a series of experiments, it is found that the Cr content of the nickel-based alloy in the present invention should be The limit is between 8.0 and 9.0 wt%.

The solid solution strengthening in general alloys is mainly to improve the bonding force between atoms, to generate lattice distortion (Lattice Distortion), to reduce the diffusion ability of elements in solid solution, etc., to achieve the purpose of strengthening the alloy base, however, when the working temperature When the melting temperature of the alloy exceeds 0.6 times or more, the diffusion rate of the solid solution element is greatly increased, so that the effective strengthening of the γ phase cannot be formed. Therefore, an element having a large atomic radius and a high temperature diffusion rate, such as a high temperature resistant metal element such as tantalum or tungsten, It has become the most effective strengthening element. It has been found that the content of elements such as tantalum and tungsten cannot be increased without limit. If the content is too high, the composition will be unevenly distributed, and the serious point will form TCP (Topologically-close-packed) harmful in the alloy. Phase, TCP phase is a very brittle phase, which is easy to be caused by the accumulation of stresses, which makes it the origin of cracks, which leads to the decrease of material strength. When TCP phase is formed, it will consume a lot of solid solution strengthening elements in γ base. , reduce the strength γ base; to improve the tungsten-nickel-based alloy of the present invention, the solid-solution strengthening elements rhenium of the solid solution strengthening effect, The invention adds the appropriate content of bismuth, can increase the uniformity of the distribution of the components, and inhibit the formation of the TCP phase; based on the above considerations, the content of tungsten, lanthanum and cerium in the nickel-based alloy of the invention should be limited to 9.5 to 10.5 wt% of tungsten, respectively.铼4~5wt%, 钌2~3wt%; the main effect of Hf in the invention is to form a large amount of γ-γ' rose-like eutectic structure, the eutectic structure has good toughness and precipitates on the grain boundary Increasing the intrinsic toughness of the grain boundary, preventing the high-speed expansion of the crack, and thus toughening the grain boundary, but the addition of Hf element is excessive, and it is easy to produce coarse HfC-type carbide, which is easy to become the origin of the crack and the alloy strength is lowered. Therefore, in the present invention, the Hf content of the nickel-based alloy is preferably controlled within a range of 1.0 to 2.0% by weight; in the present invention, Mo can increase the stable temperature of the γ' phase, that is, increase the dissolution temperature of the γ' phase, but the Mo content is excessive. There is also a problem of causing the TCP phase and the large-sized bulk carbonization type. Therefore, the Mo element content of the nickel-based alloy in the present invention is controlled to be 0.5 to 1.0 wt.%.

Based on the foregoing experimental results, the present invention develops a nickel-based alloy for polycrystalline casting which can be used in an environment of about 760 ° C (medium temperature) and has excellent latent life, the chemical composition of which is (in percentage by weight): Cr is 8.0 to 9.0 wt%, W is 9.5 to 10.5 wt%, Co is 9.5 to 10.5 wt%, Al is 5.0 to 6.0 wt%, Ti is 0.5 to 1.5 wt%, Mo is 0.5 to 1.0 wt%, and Ta is 2.5 to 3.5 wt%, Hf is 1.0 to 2.0 wt%, Re is 4.0 to 5.0 wt%, Ru is 2.0 to 3.0 wt%, C is 0.12 to 0.18 wt%, and the balance is composed of Ni and unavoidable impurities.

Embodiment 1

The nickel-based alloy of the present invention is smelted in a vacuum induction furnace according to its chemical composition ratio, and then vacuum precision casting is performed, and the molten alloy liquid is poured into the ceramic mold, and the alloy sample is prepared to ensure the components are correct and simultaneously sampled. The Hf, Re and Ru were analyzed by ICP/AES, and the remaining components were analyzed by SPARK-AES. The results (in weight percent) were as follows: Cr: 8.38 wt%

W: 9.69wt%

Re: 4.87wt%

Ru: 2.79wt%

Co: 10.04wt%

Al: 5.47wt%

Ta: 2.98wt%

Hf: 1.43wt%

C: 0.15wt%

Ti: 0.98wt%

Mo: 0.74wt%

Ni: Rem.

The nickel-based alloy is subjected to heat treatment after casting to optimize the microstructure inside the alloy. The heat treatment procedure is as follows: (1) vacuum solid solution treatment at 1185 ° C / 2 h, quenching with argon to room temperature, (2) It was then subjected to vacuum aging treatment at 871 ° C / 20 h, followed by furnace cooling to room temperature. The test rod was subjected to a 760 ° C / 724 MPa creep test after heat treatment, and the test result has a creep life of 185.1 hours.

Embodiment 2

The nickel-based alloy of the present invention is smelted in a vacuum induction furnace according to its chemical composition ratio, and then vacuum precision casting is performed, and the molten alloy liquid is poured into the ceramic mold, and the alloy sample is prepared to ensure the components are correct and simultaneously sampled. The Hf, Re and Ru were analyzed by ICP/AES, and the remaining components were analyzed by SPARK-AES. The results (in weight percent) were as follows: Cr: 8.21% by weight

W: 9.56wt%

Re: 4.93wt%

Ru: 2.02wt%

Co: 10.32wt%

Al: 5.46wt%

Ta: 2.96wt%

Hf: 1.25wt%

C: 0.15wt%

Ti: 0.95wt%

Mo: 0.72wt%

Ni: Rem.

The nickel-based alloy is subjected to heat treatment after casting to optimize the microstructure inside the alloy. The heat treatment procedure is as follows: (1) vacuum solid solution treatment at 1185 ° C / 2 h, quenching with argon to room temperature, (2) It was then subjected to vacuum aging treatment at 871 ° C / 20 h, followed by furnace cooling to room temperature. The test rod was subjected to a 760 ° C / 724 MPa creep test after heat treatment, and the test result had a creep life of 208 hours.

Embodiment 3

The nickel-based alloy of the present invention is smelted in a vacuum induction furnace according to its chemical composition ratio, and then vacuum precision casting is performed, and the molten alloy liquid is poured into the ceramic mold, and the alloy sample is prepared to ensure the components are correct and simultaneously sampled. The Hf, Re and Ru were analyzed by ICP/AES, and the remaining components were analyzed by SPARK-AES. The results (in weight percent) were as follows: Cr: 8.38 wt%

W: 9.77wt%

Re: 4.16wt%

Ru: 2.69wt%

Co: 9.88wt%

Al: 5.54wt%

Ta: 2.94wt%

Hf: 1.39wt%

C: 0.14wt%

Ti: 0.97wt%

Mo: 0.72wt%

Ni: Rem.

The nickel-based alloy is subjected to heat treatment after casting to optimize the microstructure inside the alloy. The heat treatment procedure is as follows: (1) vacuum solid solution treatment at 1185 ° C / 2 h, quenching with argon to room temperature, (2) It was then subjected to vacuum aging treatment at 871 ° C / 20 h, followed by furnace cooling to room temperature. The test rod was subjected to a 760 ° C / 724 MPa creep test after heat treatment, and the test result has a creep life of 168.9 hours.

The latent deformation of metal is often the interaction between poor displacement and grain boundary slip. The high stress equiaxed nickel-based alloy of the present invention has a metamaterial-like precipitation, which greatly inhibits the difference in latent discharge and the addition of carbon. Helping to resist the image before the grain boundary slip, and the high stress equiaxed nickel base alloy of the present invention is more appropriately added with other anti-potential elements, so that the high stress equiaxed nickel base alloy of the invention has excellent anti-potential change Therefore, the present invention evaluates the creep performance of five high-strength nickel-based alloys suitable for equiaxed casting in the market. The results are shown in Table 1, in which a uniform evaluation standard is adopted, and medium temperature/ The high stress (760 ° C / 724 MPa) creep test conditions were evaluated. The results show that the creep life is best performed by the high stress equiaxed nickel base alloy of the present invention, which satisfies the requirements of today's high turbine engines.

The above-described embodiments are merely illustrative of the features and functions of the present invention and are not intended to limit the scope of the technical content of the present invention. Any person skilled in the art can modify and change the above embodiments without departing from the spirit and scope of the creation. Therefore, the scope of protection of this creation should be as listed in the scope of the patent application described later.

Claims (8)

A high stress equiaxed crystal nickel-based alloy having the following composition in terms of weight percent. Cr is 8.0 to 9.0 wt%, W is 9.5 to 10.5 wt%, Co is 9.5 to 10.5 wt%, and Al is 5.0 to 6.0 wt%. Ti is 0.5 to 1.5 wt%, Mo is 0.5 to 1.0 wt%, Ta is 2.5 to 3.5 wt%, Hf is 1.0 to 2.0 wt%, Re is 4.0 to 5.0 wt%, and Ru is 2.0 to 3.0 wt%, C. It is 0.12~0.18wt%, and the rest is composed of Ni and unavoidable impurities. The high stress equiaxed nickel base alloy has a creep life of more than 160 hours at 760 °C and 724Mpa. A method for producing a high stress equiaxed nickel-based alloy according to claim 1, wherein the high stress equiaxed nickel base alloy is smelted in a vacuum induction furnace. The method for producing a high-stress equiaxed nickel-based alloy according to claim 2, wherein the high-stress equiaxed nickel-based alloy is cast in a vacuum environment. The method for manufacturing a high stress equiaxed nickel base alloy according to claim 3, wherein the high stress equiaxed nickel base alloy is subjected to a two-stage heat treatment after casting. The method for producing a high-stress equiaxed nickel-base alloy according to claim 4, wherein the first-stage heat treatment is performed at 1000 ° C or higher. The method for fabricating a high stress equiaxed nickel base alloy according to claim 5, wherein the first stage heat treatment is to cool the high stress equiaxed nickel base alloy by argon gas. The method for producing a high-stress equiaxed nickel-based alloy according to claim 6, wherein the second-stage heat treatment is performed at 800 ° C or higher. The method for producing a high stress equiaxed nickel base alloy according to claim 7, wherein the second stage heat treatment is performed by natural cooling.