阅读说明：本技术 超高温蠕变夹具用单晶合金及其制备方法 (Single crystal alloy for ultrahigh temperature creep clamp and preparation method thereof ) 是由 罗亮 秦健春 曾纪术 陈涛 何浩 刘晨 李益民 于 2021-07-20 设计创作，主要内容包括：本发明公开一种超高温蠕变夹具用单晶合金及其制备方法,涉及高温合金技术领域,它由重量百分比的Al：7.0％～7.5％；Ta：3％～5％；Mo：6.2％～8.5％；W：5％～6.8％；Cr：1.0～2.6％；其余为Ni组成；制备步骤为先制备母合金锭,再制备单晶试棒/高温蠕变夹具,最后采用固溶处理和两次时效过程的热处理,与现有技术相比,本发明合金无初熔、1200℃/1000h热暴露TCP相析出,使用合金制备的高温夹具在1200℃使用超1000h,展现优良的超高温性能,合金中未添加贵重元素Re,合金成本降低约70%,使1200℃使用的单晶合金夹具实现推广应用。(The invention discloses a single crystal alloy for an ultrahigh temperature creep fixture and a preparation method thereof, relating to the technical field of high temperature alloys and comprising the following components in percentage by weight: 7.0% -7.5%; ta: 3% -5%; mo: 6.2% -8.5%; w: 5% -6.8%; cr: 1.0-2.6%; the balance being Ni; the preparation steps comprise the steps of firstly preparing a master alloy ingot, then preparing a single crystal test bar/high-temperature creep fixture, and finally adopting solution treatment and heat treatment in two aging processes, compared with the prior art, the alloy of the invention has no primary melting, 1200 ℃/1000h of heat exposure TCP phase precipitation, the high-temperature fixture prepared by the alloy is used for more than 1000h at 1200 ℃, the excellent ultrahigh-temperature performance is shown, no noble element Re is added in the alloy, the alloy cost is reduced by about 70%, and the popularization and the application of the single crystal alloy fixture used at 1200 ℃ are realized.)

1. A single crystal alloy for an ultrahigh temperature creep clamp comprises the following components in percentage by weight:

al: 7.0% -7.5%; ta: 3% -5%; mo: 6.2% -8.5%; w: 5% -6.8%; cr: 1.0-2.6%; the balance being Ni.

2. A preparation method of a single crystal alloy for an ultrahigh temperature creep fixture is characterized in that the single crystal alloy adopts the following components by weight percent:

al: 7.0% -7.5%; ta: 3% -5%; mo: 6.2% -8.5%; w: 5% -6.8%; cr: 1.0-2.6%; the balance being Ni;

the preparation method comprises the following steps:

step 1, preparing a master alloy ingot:

preparing the single crystal alloy components into a master alloy ingot by vacuum induction melting according to a conventional method;

step 2, preparing a single crystal test bar/high-temperature creep clamp:

putting the cleaned master alloy ingot into a crucible and placing the crucible into a directional solidification furnace, and heating the directional solidification furnace to melt the master alloy ingot in the crucible to obtain a molten nickel-based alloy; refining the melted nickel-based alloy for 10-20 min at 1530-1560 ℃ to obtain a refined nickel-based alloy; the refined nickel-based alloy is cast when being cooled to 1510-1540 ℃, then is kept stand, and is pulled at the pulling speed of 4.5-8 mm/min, and finally the single crystal test bar/high-temperature creep clamp is obtained;

step 3, heat treatment:

carrying out heat treatment on the single crystal test bar/high-temperature creep clamp, wherein the heat treatment comprises solution treatment and two aging processes;

1) solution treatment: preserving the heat for 12-18 hours at the temperature of 1320-1360 ℃, and then cooling the air to the room temperature;

2) high-temperature aging treatment: preserving the heat for 2-5 hours at 1150-1190 ℃, and then air-cooling to room temperature;

3) and (3) low-temperature aging treatment: keeping the temperature at 850-930 ℃ for 25-35 hours, and then cooling to room temperature in air.

3. The method for preparing the single crystal alloy for the ultra-high temperature creep jig according to claim 2, characterized in that:

in the step 1, the single crystal alloy is refined for 10min at 1530-1560 ℃; and after refining, heating to 1570-1590 ℃, and casting to obtain the master alloy ingot.

4. The method for preparing the single crystal alloy for the ultra-high temperature creep jig according to claim 2 or 3, characterized in that:

step 2, after the cleaned mother alloy ingot is placed in a crucible, a draft tube is placed below the crucible, a mould shell is fixed on a crystallization tray and is lifted to a preset position, the lower end of the draft tube just enters a riser of the mould shell, and after the casting system is filled, the directional solidification furnace is vacuumized to 3 multiplied by 10^-2Pa; the specific operation of heating the directional solidification furnace to melt the master alloy ingot in the crucible comprises the following steps: opening a temperature control switch, heating the upper end and the lower end of a heat preservation area of the directional solidification furnace, and starting a smelting power supply to preheat a master alloy ingot when the temperature of the upper end and the temperature of the lower end of the heat preservation area are both raised to 1210 ℃; and when the temperature of the upper end of the heat preservation area reaches the preset temperature of 1540 ℃ and the temperature of the lower end of the heat preservation area reaches the preset temperature of 1550 ℃, increasing the power of a smelting power supply to melt the master alloy ingot in the crucible.

Technical Field

The invention relates to the technical field of high-temperature alloys, in particular to a single crystal alloy for a creep clamp capable of being used at ultrahigh temperature and a preparation method thereof.

Background

The metal material permanent tensile test is a test for testing the permanent life of a material under constant temperature and constant load, and is also a necessary item of high-temperature components of aero-engines and gas turbines. In the process of the endurance tensile test, the endurance creep clamp of the key hot-end part is often under the conditions of high temperature, high stress and long period, so that the service life of the endurance creep clamp is generally short, and the endurance creep clamp is particularly suitable for clamps used under the condition of ultra-high temperature (more than 1100 ℃). With the development of material science, the high temperature resistance of the material is continuously improved, the test temperature of a high temperature endurance test is also improved, and the improvement of the test temperature also puts higher requirements on the high temperature performance of the clamp.

In long-term test practice, the strength of a sample clamp is greatly reduced after the test temperature of a common metal material exceeds 900 ℃, and in a high-temperature creep test in a temperature range of 900-1100 ℃, the surface of the clamp is peeled off and the clamp is bonded with the sample due to oxidation ablation at high temperature. The sample and the clamp are tightly bonded and cannot be disassembled, and finally the test fails and the clamp is scrapped. Under the condition of ultrahigh temperature, the clamp is subjected to severe oxidative ablation and is easy to generate obvious creep deformation, so that the coaxiality in the test loading process is difficult to meet the test requirement, the test is failed, and the clamp is scrapped. Meanwhile, discontinuity of scientific research endurance test is caused or timeliness of production endurance performance test is influenced.

High temperature durable fixtures are typically made from Ni-based superalloys. Currently, commonly used superalloy clamp grades include: k002, K465, DZ125, DZ22 and DD 3. Wherein K002 and K465 are equiaxial crystals, and the use temperature is below 1000 ℃ (Luqi et al, physicochemical inspection-physical division, 2014,50 (10): 735 and 737) (Yi Xiang Rong et al, casting, 2021,70(1): 53-57). DZ125 and DZ22 are directionally solidified column crystal high temperature alloy, and the use temperature is below 1050 ℃ (Chengrong chapter et al, material engineering, 1981,0(5):1-5) (Chengrong chapter et al, material engineering, 1997,0(9): 9-12); the using temperature of the first generation single crystal superalloy DD3 is generally not higher than 1100 ℃ (Wu Tang et al, materials engineering, 1987, 0(5): 1-5.). For the use temperature of over 1100 ℃, a ceramic clamp can be used for testing, but the ceramic clamp is hard and brittle, cracks are easily formed in the temperature rising and falling process of the test, the clamp is cracked and fails, and the service life is generally short. The Ni-based high-temperature alloy clamp not only has certain strength at high temperature, but also has higher toughness and plasticity, and can ensure that the Ni-based high-temperature alloy clamp is not easy to crack in the temperature rising and falling process. Therefore, Ni-based superalloys are the first choice for creep-resistant fixture materials. However, at present, there is no published report of a single crystal superalloy clamp that can be used at 1200 ℃.

Chinese patent document No. CN101706391A discloses "an anti-adhesion shoulder clamp for improving endurance test efficiency", which effectively prevents adhesion between the clamp and a sample and improves the use temperature of the clamp to a certain extent by the structural design of high temperature clamps such as DZ22 and DD 3. However, only an anti-adhesive effect can be achieved by the design of the clamp structure, and the failure of the clamp not only results from adhesion to the test specimen, but also includes creep deformation of the clamp itself. The creep deformation of the clamp is closely related to the components and microstructure of the clamp, so that the problem of optimizing the microstructure is difficult to solve, and the service temperature of the clamp can be increased only through reasonable component and microstructure design. In addition, experimental practice shows that the high-temperature clamps such as DZ22 and DD3 have creep deformation of different degrees after being used for more than 500 hours at 1200 ℃, and are difficult to continue to use.

The document "Yi Ru. script material 147 (2018) 21-26" records a high gamma' phase fraction Ni-based single crystal alloy exhibiting excellent ultra-high temperature durability properties with a endurance life of more than 100 hours at 1200 ℃/80 MPa. However, 3wt.% of noble metal Re is added into the alloy, and the alloy is high in cost when used for preparing a high-temperature durable clamp and is difficult to popularize and apply.

Disclosure of Invention

The invention aims to solve the problem that the existing clamp is easy to deform, oxidize and ablate and crack when used under an ultrahigh temperature condition.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the single crystal alloy for the ultrahigh-temperature creep fixture comprises the following components in percentage by weight:

al: 7.0% -7.5%; ta: 3% -5%; mo: 6.2% -8.5%; w: 5% -6.8%; cr: 1.0-2.6%; the balance being Ni.

The preparation method of the single crystal alloy for the ultrahigh-temperature creep fixture comprises the following steps: the single crystal alloy comprises the following components in percentage by weight:

al: 7.0% -7.5%; ta: 3% -5%; mo: 6.2% -8.5%; w: 5% -6.8%; cr: 1.0-2.6%; the balance being Ni;

the preparation method comprises the following steps:

step 1, preparing a master alloy ingot:

preparing the single crystal alloy components into a master alloy ingot by vacuum induction melting according to a conventional method;

step 2, preparing a single crystal test bar/high-temperature creep clamp:

putting the cleaned master alloy ingot into a crucible and placing the crucible into a directional solidification furnace, and heating the directional solidification furnace to melt the master alloy ingot in the crucible to obtain a molten nickel-based alloy; refining the melted nickel-based alloy for 10-20 min at 1530-1560 ℃ to obtain a refined nickel-based alloy; the refined nickel-based alloy is cast when being cooled to 1510-1540 ℃, then is kept stand, and is pulled at the pulling speed of 4.5-8 mm/min, and finally the single crystal test bar/high-temperature creep clamp is obtained;

step 3, heat treatment:

carrying out heat treatment on the single crystal test bar/high-temperature creep clamp, wherein the heat treatment comprises solution treatment and two aging processes;

1) solution treatment: preserving the heat for 12-18 hours at the temperature of 1320-1360 ℃, and then cooling the air to the room temperature;

2) high-temperature aging treatment: preserving the heat for 2-5 hours at 1150-1190 ℃, and then air-cooling to room temperature;

3) and (3) low-temperature aging treatment: keeping the temperature at 850-930 ℃ for 25-35 hours, and then cooling to room temperature in air.

In the above technical solution, a more specific solution may also be: in the step 1, the single crystal alloy components are refined for 10min at 1530-1560 ℃; and after refining, heating to 1570-1590 ℃, and casting to obtain the master alloy ingot.

Further: step 2, after the cleaned mother alloy ingot is placed in a crucible, a draft tube is placed below the crucible, a mould shell is fixed on a crystallization tray and is lifted to a preset position, the lower end of the draft tube just enters a riser of the mould shell, and after the casting system is filled, the directional solidification furnace is vacuumized to 3 multiplied by 10^-2Pa; the specific operation of heating the directional solidification furnace to melt the master alloy ingot in the crucible comprises the following steps: opening a temperature control switch, heating the upper end and the lower end of a heat preservation area of the directional solidification furnace, and starting a smelting power supply to preheat a master alloy ingot when the temperature of the upper end and the temperature of the lower end of the heat preservation area are both raised to 1210 ℃; and when the temperature of the upper end of the heat preservation area reaches the preset temperature of 1540 ℃ and the temperature of the lower end of the heat preservation area reaches the preset temperature of 1550 ℃, increasing the power of a smelting power supply to melt the master alloy ingot in the crucible.

The technical scheme of the invention is that according to the action of each element in the alloy, a noble element Re is not added, and a cheap W element is added for substitution, so as to ensure that the alloy has better creep property and reduce the cost of the alloy; the content of Al and Ta is controlled to be between 10.0 and 12.5 percent, the volume fraction of a single crystal alloy precipitated phase is still higher than 50 percent at 1200 ℃, and meanwhile, the phenomenon that excessive precipitated phases form abnormal rattan-shaped structures to deteriorate the high-temperature mechanical property of the alloy is avoided.

The method adopts the solid solution treatment and two-time aging treatment in the heat treatment, and improves the temperature of the solid solution treatment, so that the eutectic in the as-cast structure is fully dissolved, the full diffusion of elements is promoted, the element segregation in the alloy is reduced, the content of refractory elements in a matrix is reduced, the precipitation tendency of a TCP phase is reduced, and the structure stability of the alloy is improved. Meanwhile, elements in the alloy are fully diffused, so that the cubic gamma' phases are similar in size, uniform in distribution and regular in arrangement, the precipitation strengthening effect is favorably improved, and the overall mechanical property of the alloy is improved.

The chemical components of the invention are designed mainly based on the following reasons:

al and Ta are the forming elements in nickel-base superalloys that form the gamma prime phase, and their content determines the strength and volume fraction of the gamma prime phase in the superalloy. Under the condition of ultrahigh temperature, the gamma' phase in the Ni-based single crystal alloy can be subjected to significant dissolution, and the high-temperature creep property of the alloy is seriously damaged. The method can keep enough gamma' phase strengthening phase under the condition of ultrahigh temperature, and is an important guarantee that the alloy has excellent high-temperature performance. However, too high Al and Ta contents not only increase the eutectic content and increase the difficulty of heat treatment, but also form abnormal rattan-like structures and deteriorate the performance of the alloy. Therefore, the Al content is controlled to be 7.0-7.5 percent, and the Ta content is controlled to be 3-5 percent.

Re is an important strengthening element in the nickel-based single crystal superalloy, has an extremely low diffusion coefficient, and can effectively prevent the tissue degradation and vacancy aggregation caused by diffusion at high temperature. However, the segregation of the element Re is serious, which brings great difficulty to the solution treatment, and at the same time, the precipitation of the TCP phase in the alloy is strongly promoted, and the reserve of Re is rare and the price is very expensive. Therefore, no Re element is added to the alloy. The segregation ratio of W in gamma and gamma 'phases is close to 1, the gamma' phase can be strengthened while the gamma matrix phase is strengthened, and the creep life of the alloy can be effectively prolonged due to the lower diffusion coefficient. When the element Re is not added, the W strengthening effect needs to be sufficiently exhibited. However, the excessive content of W can promote the alloy to separate out a TCP phase and destroy the structural stability; meanwhile, the casting performance of the alloy is influenced, and defects such as freckles are caused. Therefore, the content of W is controlled to be 5% to 6.8%. Mo is a solid solution strengthening element, can increase the mismatching degree of gamma/gamma', promote the formation of a dense dislocation network, effectively block dislocation motion and improve the alloy performance; however, Mo adversely affects the hot corrosion resistance of the alloy and tends to promote the precipitation of the TCP phase in the alloy. Therefore, the content of Mo is controlled to be 6.2-8.5%.

Cr is a key element for improving the hot corrosion resistance of the alloy and is mainly distributed in a matrix, but Cr is one of main components of a TCP phase, and the structural stability of the alloy is reduced due to the increase of the Cr content, so that the Cr content is controlled to be 1.0-2.6%.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention adopts the reduced component design, and the alloy has the advantages of high initial melting temperature, large heat treatment window, low segregation degree and the like;

2. the alloy of the invention has higher ultra-high temperature durability: the creep life is more than or equal to 100h at 1200 ℃/80 MPa; the high-temperature clamp prepared by the alloy has the service life of over 1000h at 1200 ℃ and higher than that of directional solidification high-temperature clamps such as DZ22 and DZ 125;

3. the alloy does not contain rare and noble element Re, the alloy cost is reduced by about 70 percent, and the single crystal alloy clamp used at 1200 ℃ is popularized and applied;

4. the alloy of the invention is verified by 1200 ℃/1000h thermal exposure, has no TCP phase precipitation and has good structure stability.

Drawings

FIG. 1 is a microstructure of a single crystal alloy of the present invention after heat treatment.

FIG. 2 is the morphology of the single crystal alloy of the present invention after 1000 hours of thermal exposure at 1200 ℃.

FIG. 3 is a creep curve of the single crystal alloy of the present invention at 1200 deg.C/80 MPa.

FIG. 4 is a graph showing the evolution of the gamma prime strengthening phase of the single crystal alloy of the present invention at 1200 ℃ over time.

FIG. 5 is the initial melting temperature of the alloy as determined by Differential Scanning Calorimetry (DSC).

FIG. 6 is a graph of the rattan morphology formed in single crystal alloys with excessively high Al or Ta contents.

Detailed Description

The present invention will be further described with reference to the following drawings and specific embodiments, but the present invention is not limited to these embodiments.

The alloy compositions of examples 1 to 7 of the present invention and comparative examples 1 to 3 are shown in Table 1.

TABLE 1

The preparation processes of examples 1 to 7 and comparative examples 1 to 3 were:

step 1, preparing a master alloy ingot: the alloy compositions of examples 1-7 and comparative examples 1-5 in Table 1 were compounded. The master alloy is prepared by vacuum induction melting by a conventional method. Refining the alloy at 1530-1560 ℃ for 10 min; after refining, heating to 1570-1590 ℃, and casting to obtain a master alloy ingot; polishing the obtained master alloy ingot to remove oxide skin, and ultrasonically cleaning the master alloy ingot by alcohol to prepare a single crystal rod;

step 2, preparing a single crystal test bar/high-temperature creep clamp on the directional solidification furnace by adopting a spiral crystal selection method: placing the cleaned mother alloy ingot in a crucible, placing a flow guide pipe below the crucible, fixing a mould shell on a crystallization tray, lifting the mould shell to a preset position to enable the lower end of the flow guide pipe to just enter a mould shell riser, and vacuumizing the directional solidification furnace to 3 x 10 < -2 > Pa after the casting system is filled; opening a temperature control switch, and heating the upper end and the lower end of a heat preservation area of the directional solidification furnace to ensure that the temperature of the upper end of the heat preservation area is 1540 ℃ and the temperature of the lower end of the heat preservation area is 1550 ℃; when the temperature of the upper end and the temperature of the lower end of the heat preservation area are both raised to 1210 ℃, starting a smelting power supply to preheat the master alloy ingot; and when the temperature of the upper end of the heat preservation area reaches the preset temperature of 1540 ℃ and the temperature of the lower end of the heat preservation area reaches the preset temperature of 1550 ℃, increasing the power of a smelting power supply to melt the mother alloy ingot in the crucible to obtain the melted nickel-based single crystal alloy. The melted nickel-based alloy is refined for 10min to 20min at 1530 ℃ to 1560 ℃, and casting is carried out when the temperature of the melt reaches 1510 ℃ to 1540 ℃. And (3) standing the melt in a mould shell for 15min, and drawing at a drawing speed of 4.5-8 mm/min to prepare the single crystal test bar/high-temperature creep clamp. The parameters of the single crystal production process of each example and comparative example of the present invention are shown in Table 2.

TABLE 2 Single Crystal production Process parameters of inventive examples and comparative examples

And 3, carrying out heat treatment on the obtained single crystal test bar/high-temperature creep clamp: the heat treatment comprises solution treatment and two aging processes;

solution treatment: keeping the temperature at 1320-1360 ℃ for 12-18 hours, taking out the test bar after the temperature is kept, and cooling the test bar to room temperature in air to obtain a single crystal test bar/high-temperature creep clamp subjected to solution treatment; in the temperature rise process of the single crystal test bar/high-temperature creep clamp from room temperature to 1360 ℃, the temperature rise rate is 5 ℃/min;

high-temperature aging treatment: placing the single crystal test bar/high-temperature creep clamp subjected to solution treatment in a tube furnace, preserving heat for 2-5 hours at 1150-1190 ℃, taking out the test bar after heat preservation, and air-cooling to room temperature to obtain a single crystal test bar/high-temperature creep clamp subjected to primary aging;

and (3) low-temperature aging treatment: and (3) preserving the heat of the single crystal test bar/high-temperature creep clamp subjected to primary aging at 850-930 ℃ for 25-35 hours, and then air-cooling to room temperature.

The heat treatment process parameters of the examples and comparative examples of the present invention are shown in table 3:

TABLE 3 Heat treatment Process parameters of inventive examples and comparative examples

FIG. 1 shows the structure and morphology of the single crystal alloy in example 1 after heat treatment.

The heat treatment of the invention is adopted to prepare the cubic gamma' phase with the element diffusion sufficient and the precipitation size of 0.4-0.5 mm, the distribution is uniform, the arrangement is regular, and the alloy has no primary melting after the heat treatment. FIG. 2 shows the morphology of the single crystal alloy in example 2 after 1000 hours of heat exposure at 1200 ℃. It can be found that the coarsening degree of the gamma' phase in the alloy is low, and meanwhile, no TCP phase is separated out, and good structure stability is shown. The durability test was conducted after the nickel-based single crystal alloy test piece was completely heat-treated, and the durability of each of the examples and comparative examples of the present invention is shown in Table 4.

TABLE 4 permanence properties of the examples and comparative examples

As can be seen from Table 4, the alloy of each example has a endurance life of more than 100h under the condition of 1200 ℃/80MPa, and an elongation of 19.4-21.6%. The alloy of each comparative example has the endurance life of less than 100h under the condition of 1200 ℃/80MPa, the elongation of 18.6-19.8%,

FIG. 3 is a creep curve of the single crystal alloy in example 3 at 1200 deg.C/80 MPa. The figure shows that the alloy undergoes more distinct three stages of creep, with steady state strain amounts below 4%, exhibiting excellent creep performance. The isothermal quenching test at 1200 ℃ shows that after the single crystal alloy reaches a thermal equilibrium state, the gamma' strengthening phase in the alloy is still higher than 50 percent and is equivalent to the third generation Ni-based single crystal alloy.

FIG. 4 shows the evolution of the gamma-prime phase of the alloy of example 5 at 1200 ℃ with the holding time. As shown in fig. 5, the initial melting temperature of the alloy of example 7 was determined by Differential Scanning Calorimetry (DSC) and was as high as 1379.5 ℃. The higher initial melting temperature is an important reason for keeping enough gamma 'strengthening phase at high temperature, and the condition for keeping a large amount of gamma' strengthening phase at high temperature is a necessary condition for the single crystal alloy to have excellent ultrahigh temperature durability. FIG. 6 shows the morphology of the rattan-like structure formed by the single crystal alloy in comparative example 1. As the excessive Ta element is added into the alloy, a plurality of rattan-shaped structures are formed in the microstructure, and the rattan-shaped structures are easy to generate micro cracks to promote the fracture failure of the alloy. The alloy of the invention reasonably controls the contents of Al and Ta, and is one of the important reasons for the excellent ultrahigh temperature durability.