Fine-grained high-density TiAl alloy parts and preparation method thereof

Abstract

The present invention provides a fine-grained, high-density TiAl alloy part and a preparation method thereof. The preparation method is based on powder injection molding technology. By introducing a SnAl sintering aid system and utilizing the pilot diffusion effect of Al between TiAl solid-phase powder and SnAl liquid-phase melt, more diffusion channels are formed between the solid and liquid phases, resulting in more liquid phase during the sintering process, accelerating the formation of a sintering neck, reducing the sintering temperature, and thus accelerating sintering densification.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy, and in particular to a fine-grained high-density TiAl alloy part and a preparation method thereof. Background Art

[0002] TiAl alloys, with their low density, high specific strength, high thermal conductivity, and excellent high-temperature oxidation and corrosion resistance, represent an ideal new lightweight, high-temperature structural material, positioned between nickel- and cobalt-based superalloys and advanced ceramics. They hold great potential as a replacement for traditional superalloys and can meet the growing demand for lightweight materials. Currently, low-pressure turbine blades in aircraft engines are the primary application of TiAl alloys, with service temperatures reaching 800°C. This enables lightweight engine manufacturing and improves thrust-to-weight ratios. Current TiAl alloy manufacturing processes primarily rely on precision casting. However, due to the high degree of TiAl alloying, defects such as composition segregation, microstructure inhomogeneity, inclusions, and porosity inevitably occur during the casting process, resulting in low yields and poor mechanical properties. Furthermore, the inherent brittleness of TiAl alloys makes them difficult to machine and form, leading to high manufacturing costs, which severely limits their industrial application. Compared to casting, powder injection molding offers unique advantages in alloy composition design, microstructure homogeneity, and near-net-shape formation. This technology can directly prepare three-dimensional complex-shaped parts, avoiding or reducing the machining process. The material utilization rate is close to 100%, and it is easy to achieve mass production of thin-walled blade parts. It is a low-cost manufacturing technology that saves resources and energy.

[0003] The sintering densification behavior of powder injection molding is primarily controlled by elemental diffusion processes. For TiAl alloys, the significant difference in the interdiffusion coefficients between Ti and Al makes pressureless sintering of powder TiAl alloys extremely difficult. To improve the degree of sintering densification, sintering is typically performed near the liquidus temperature of the TiAl alloy. However, high-temperature sintering results in rapid grain boundary migration, often leading to abnormal grain growth. Combined with the inherently poor plasticity of TiAl alloys, this severely limits the mechanical properties of the finished part. Furthermore, pressure sintering methods such as hot isostatic pressing (HIP) and hot pressing make it difficult to produce complex-shaped parts and are associated with high production costs.

[0004] In summary, how to achieve pressureless high-densification sintering of fine-grained TiAl alloy is an urgent problem to be solved in the high-quality preparation of TiAl alloy products. Summary of the Invention

[0005] In order to overcome the deficiencies in the prior art, the main purpose of the present invention is to provide a fine-grained, high-density TiAl alloy part and a preparation method thereof. The preparation method is based on powder injection molding technology. By introducing a SnAl sintering aid system and utilizing the pilot diffusion effect of Al between the TiAl solid phase powder and the SnAl liquid phase melt, more diffusion channels are formed between the solid and liquid phases, so that more liquid phase is produced during the sintering process, the formation of a sintering neck is accelerated, the sintering temperature is reduced, and thus the sintering densification is accelerated.

[0006] In order to achieve the above object, according to a first aspect of the present invention, a method for preparing a fine-grained and high-density TiAl alloy part is provided.

[0007] The preparation method of the fine-grained high-density TiAl alloy part comprises the following steps:

[0008] TiAl pre-alloyed powder and SnAl pre-alloyed powder are used as raw materials to prepare TiAl / SnAl composite powder; wherein the content of the SnAl pre-alloyed powder in the TiAl / SnAl composite powder is 0.5-1.5% by atomic percentage;

[0009] TiAl / SnAl composite powder and binder are used as raw materials, which are mixed and crushed into granular feed;

[0010] Then the granular feed is subjected to injection molding, degreasing and sintering treatments in sequence to obtain a TiAl alloy product.

[0011] Furthermore, the preparation of the TiAl / SnAl composite powder includes:

[0012] Premixing the TiAl pre-alloyed powder and the SnAl pre-alloyed powder to obtain a premixed powder;

[0013] Performing a composite treatment on the premixed powder using PCS to obtain the TiAl / SnAl composite powder;

[0014] Preferably, the rotation speed of the PCS treatment is 2500-3200 r / min, the time is 10-50 min, and the protective atmosphere is high-purity argon.

[0015] Preferably, the rotation speed of the premixing treatment is 100-200 r / min, the time is 6-10 h, the ball-to-material ratio is 1-5:1, and the protective atmosphere is high-purity argon.

[0016] Furthermore, the TiAl pre-alloyed powder comprises, in atomic percentage, 45-50% Al, 1-5% Cr, 1-8% Nb, and the balance Ti;

[0017] The SnAl pre-alloyed powder comprises, by mass percentage, 85-95% Sn and 5-15% Al;

[0018] Preferably, the particle size of the TiAl pre-alloyed powder is in the range of 0 to 20 μm;

[0019] Preferably, the particle size of the SnAl pre-alloyed powder is in the range of 0 to 10 μm.

[0020] Furthermore, the binder comprises, by mass percentage, 75-85% polyoxymethylene, 2-10% high-density polyethylene, 2-8% ethylene-vinyl acetate copolymer, and 5-10% stearic acid;

[0021] Preferably, the volume percentage of the TiAl / SnAl composite powder in the particle size feed is 60-65%;

[0022] Preferably, the mixing temperature is 170-200° C., the mixing time is 1-2 hours, and the mixing speed is 10-30 r / min.

[0023] Furthermore, the injection molding has an injection temperature of 170-200°C, an injection pressure of 110-130 MPa, a holding pressure of 100-120 MPa, a holding time of 3-10s, a mold temperature of 100-120°C, and an injection speed of 60-80% of the maximum injection speed of the injection machine.

[0024] Furthermore, the degreasing process includes two parts: oxalic acid catalytic degreasing and thermal degreasing;

[0025] The degreasing temperature of the catalytic degreasing is 125-145°C, the acid feeding rate is 2-5g / min, the degreasing time is 8-14h, and the nitrogen flow rate is 30-60L / min;

[0026] The degreasing temperature of the thermal degreasing is 400-600° C., the heating rate is 1-3° C. / min, and the degreasing time is 1-2 hours.

[0027] Furthermore, the sintering process is carried out in two steps. The first step is a sintering temperature of 1320-1400°C, a heating rate of 5-10°C / min, and a holding time of 0-1h; the second step is a sintering temperature of 1200-1280°C, a cooling rate of 5-10°C / min, and a holding time of 4-10h.

[0028] Preferably, the sintering process is carried out under vacuum conditions with a vacuum degree of 10 -2 ~10 -4 Pa.

[0029] Furthermore, a pre-sintering treatment is further included after the degreasing treatment, with the pre-sintering temperature being 900-1100° C., the time being 1-2 hours, and the heating rate being 5-10° C. / min.

[0030] In order to achieve the above object, according to a second aspect of the present invention, a fine-grained and high-density TiAl alloy part is provided.

[0031] The fine-grained, high-density TiAl alloy product is prepared by the above-mentioned preparation method; wherein,

[0032] The microstructure of the TiAl alloy product is an α2 / γ full lamellar structure; both the α2 and γ phases in the α2 / γ full lamellar structure are lamellar structures, and the grain size is ≤40 μm.

[0033] Furthermore, the density of the TiAl alloy parts is greater than 98%, the tensile strength is 520-560 MPa, and the elongation is 0.9-1.5%;

[0034] Preferably, the TiAl alloy part is a TiAl alloy blade.

[0035] The preparation method of the present invention is based on powder injection molding technology. On the one hand, by introducing a SnAl sintering aid system, the pilot diffusion effect of Al between the TiAl solid phase powder and the SnAl liquid phase melt is utilized to form more diffusion channels between the solid and liquid phases, so that more liquid phase is generated during the sintering process, the formation of sintering necks is accelerated, the sintering temperature is reduced, and thus the sintering densification is accelerated. On the other hand, in order to obtain uniformly dispersed TiAl / SnAl composite powder, a high-speed airflow impact particle composite shaping system (PCS) is introduced. The "mechanical chemical effect" generated by the strong impact grinding action is used to controllably physically combine the two raw material powders of different particle sizes, thereby preparing a composite raw material powder in which the SnAl powder uniformly covers the TiAl powder. In addition, to prevent the deterioration of the mechanical properties of the alloy due to coarse grains, an optimized densification sintering technology is introduced. The active grain boundary diffusion behavior during the medium-temperature sintering stage is utilized to achieve densification of the TiAl alloy at a lower temperature, obtaining a fine and uniform grain structure. This not only further improves the mechanical properties of the alloy, but also reduces energy and resource consumption, thereby achieving low-cost manufacturing of high-performance TiAl alloy parts.

[0036] The large difference in interdiffusion coefficients between the main elements Ti and Al in TiAl alloys makes solid-phase sintering and densification of TiAl powders, which is diffusion-dominated, very difficult, resulting in poor mechanical properties of TiAl alloys prepared by pressureless sintering. To address this issue, the present invention introduces a SnAl sintering aid into the TiAl alloy powder to form a transient liquid-phase sintering system. This utilizes the pilot diffusion of Al between the solid-phase TiAl alloy powder and the liquid SnAl melt during the sintering process to increase the diffusion channels for substances in the two phases, thereby accelerating the formation of a sintering neck and promoting the sintering and densification process of the TiAl alloy powder.

[0037] The addition amount of the SnAl sintering aid of the present invention is 0.5-1.5%. If the content is too low, it is difficult to form a transient liquid phase sintering system and the sintering densification cannot be effectively promoted; if the content is too high, the thin-walled blade parts are prone to defects such as bending, cracking, collapse and deformation during the sintering process, making it difficult to control the dimensional accuracy of the final parts.

[0038] The loading amount and uniformity of the feed are the most important factors affecting the dimensional accuracy of the final injection molded parts. The feed is made by mixing raw material powder and a binder, and the binder is a short-lived carrier that can be completely removed after the catalytic degreasing and thermal degreasing stages. In other words, uniform feeding depends on uniform raw material powder. Therefore, achieving uniform mixing of TiAl pre-alloyed powder and SnAl pre-alloyed powder is the basis for preparing high-precision blade parts. To this end, the present invention introduces a high-speed airflow impact particle composite shaping system (PCS), which utilizes the "mechanical chemical effect" produced on the surface of TiAl powder particles under strong impact grinding under the protection of high-purity argon gas, so that the soft SnAl pre-alloyed powder particles can be evenly coated on the surface of the hard TiAl alloy powder masterbatch, and achieves the homogenized composite preparation of TiAl powder and SnAl pre-alloyed powder without changing the basic properties of the material.

[0039] On the other hand, during the PCS treatment, the irregular SnAl pre-alloyed powder can be sphericalized under the high-speed impact of the rotor without changing the properties of SnAl itself. Therefore, the tap density of the TiAl / SnAl composite powder after PCS treatment is increased, the angle of repose is reduced, and the fluidity is improved, which allows the feeding to evenly fill the blade cavity with a higher loading amount, which is beneficial to improving the dimensional accuracy of thin-walled blade parts.

[0040] In addition, the PCS process of the present invention has an optimal rotation speed of 2500-3200 r / min and a time of 10-50 min. If the rotation speed is too high or the time is too long, the powder will be excessively compounded, resulting in the crushing of the raw material powder and the reduction of the fluidity of the feed, thereby resulting in low loading capacity and dimensional accuracy control; if the rotation speed is too low or the time is too short, the particle compounding process will be insufficient, and TiAl / SnAl composite powder with good dispersion cannot be prepared, and it is difficult to control the dimensional accuracy of the final product.

[0041] Generally, the higher the sintering temperature, the more significant the grain growth under high energy. According to the Hall-Page equation, the larger the grain size, the lower the yield strength of the material. However, as an intermetallic compound, TiAl alloy has a large intrinsic brittleness. The large grain size often causes the alloy to fail prematurely during service. To this end, the present invention adopts an optimized two-step sintering process. First, the temperature is raised to the first sintering temperature of 1300-1400°C at a relatively fast rate and kept warm for a short time. This not only achieves the basic densification of the alloy (density of 85-90%), but also controls the grain growth under the influence of the pore pinning grain boundary effect. Subsequently, the temperature is lowered to the medium temperature stage of 1200-1280°C. Under the action of active grain boundary diffusion, the residual pores are annihilated, and finally the sintered body is highly densified.

[0042] The TiAl alloy blades for aircraft engines prepared by the present invention have a more uniform and fine structure and excellent mechanical properties. They avoid the hot isostatic pressing and homogenization heat treatment required to eliminate casting defects and component segregation of the TiAl alloy ingot, and also avoid the repeated blanking and forging required to refine the grain structure. This solves the problem of difficult-to-process deformation of brittle TiAl alloys. The preparation process is simple, and the manufacturing cost is greatly reduced.

[0043] Beneficial effects of the present invention:

[0044] (1) The powder injection molding technology is used to achieve the near-net-shape preparation of TiAl alloy blades for aircraft engines. Compared with the existing precision casting technology, the process is simpler, the material utilization rate is higher, the cost is greatly reduced, and it is easy to achieve batch production of blade parts.

[0045] (2) The designed TiAl / SnAl transient liquid phase sintering system effectively promotes the formation of sintering necks, which not only reduces the sintering temperature but also accelerates the sintering process and improves the densification behavior of TiAl powder during pressureless sintering.

[0046] (3) The optimized two-step sintering process of TiAl / SnAl composite powder can effectively inhibit the grain growth process. The prepared TiAl alloy can obtain a uniform and fine microstructure and excellent mechanical properties while achieving high densification. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0048] Figure 1 This is a scanning electron microscope image of the Ti-48Al-2Cr-2Nb powder in Example 1 provided by the present invention;

[0049] Figure 2 This is a scanning electron microscope image of the microstructure of the part prepared in Example 1 provided by the present invention. DETAILED DESCRIPTION

[0050] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0051] When TiAl alloy blades are produced using traditional casting processes, defects such as component segregation, porosity, and shrinkage cavities are inevitably generated, which seriously deteriorate the mechanical properties of the parts. In addition, TiAl alloy itself has poor plasticity, is difficult to form, and has poor machinability. To this end, the present invention uses powder injection molding technology to produce thin-walled TiAl alloy blades for aircraft engines. This not only achieves nearly 100% utilization of the raw materials, but also achieves near-net-net shaping of the blades, avoids or minimizes the machining process to the greatest extent, reduces production costs, and improves manufacturing efficiency, providing a new approach for the efficient manufacture of complex-shaped TiAl alloy parts.

[0052] According to a specific embodiment of the present invention, a method for preparing a fine-grained and high-density TiAl alloy part is provided, wherein the TiAl alloy part may be a TiAl alloy blade.

[0053] The microstructure of the TiAl alloy product of the present invention is an α2 / γ full lamellar structure, in which both α2 and γ phases are lamellar structures, and the grain size is ≤40 μm.

[0054] The TiAl alloy products of the present invention have a density greater than 98%, a tensile strength of 520-560 MPa, and an elongation of 0.9-1.5%.

[0055] The method for preparing a fine-grained, high-density TiAl alloy part of the present invention comprises the following steps:

[0056] 1) Using TiAl pre-alloyed powder and SnAl pre-alloyed powder as raw materials, TiAl / SnAl composite powder is prepared. The preparation process includes:

[0057] 1-1) Premixing TiAl pre-alloyed powder and SnAl pre-alloyed powder to obtain premixed powder;

[0058] 1-2) The premixed powder is subjected to composite treatment using PCS to obtain TiAl / SnAl composite powder.

[0059] Among them, SnAl pre-alloyed powder can be evenly coated on the surface of hard TiAl alloy powder, and the homogenized composite preparation of TiAl powder and SnAl pre-alloyed powder is achieved without changing the basic properties of the material.

[0060] In an embodiment of the present invention, the rotation speed of the PCS powder treatment is 2500-3200 r / min, the time is 10-50 min, and the protective atmosphere is high-purity argon.

[0061] In an embodiment of the present invention, the premixing treatment is carried out on a roller mill at a rotation speed of 100 to 200 r / min, a time of 6 to 10 hours, a ball-to-material ratio of 1 to 5:1, and a protective atmosphere of high-purity argon.

[0062] In an embodiment of the present invention, the content of SnAl pre-alloyed powder in the TiAl / SnAl composite powder is 0.5-1.5% by atomic percentage.

[0063] In an embodiment of the present invention, the TiAl pre-alloyed powder comprises, in atomic percentage, 45-50% Al, 1-5% Cr, 1-8% Nb, and the balance Ti.

[0064] As an embodiment of the present invention, the particle size of the TiAl pre-alloyed powder ranges from 0 to 20 μm.

[0065] In an embodiment of the present invention, the SnAl pre-alloyed powder comprises, by mass percentage, 85-95% Sn and 5-15% Al.

[0066] As an embodiment of the present invention, the particle size of the SnAl pre-alloyed powder ranges from 0 to 10 μm.

[0067] 2) TiAl / SnAl composite powder and binder are used as raw materials, which are mixed and crushed into granular feed.

[0068] As an embodiment of the present invention, the volume percentage of the TiAl / SnAl composite powder in the particle size feed is 60-65%.

[0069] In an embodiment of the present invention, the binder comprises, by mass percentage, 75-85% polyoxymethylene, 2-10% high-density polyethylene, 2-8% ethylene-vinyl acetate copolymer, and 5-10% stearic acid.

[0070] In the embodiment of the present invention, the mixing temperature is 170-200° C., the mixing time is 1-2 hours, and the mixing speed is 10-30 r / min.

[0071] 3) The granular feed is injection molded to obtain an injection blank.

[0072] In an embodiment of the present invention, the injection temperature is 170-200°C, the injection pressure is 110-130 MPa, the holding pressure is 100-120 MPa, the holding time is 3-10s, the mold temperature is 100-120°C, and the injection speed is 60-80% of the maximum injection speed of the injection machine.

[0073] 4) Degreasing the injection molded product.

[0074] In the embodiment of the present invention, the degreasing process includes two parts: oxalic acid catalytic degreasing and thermal degreasing; wherein,

[0075] The degreasing temperature of catalytic degreasing is 125-145℃, the acid feeding rate is 2-5g / min, the degreasing time is 8-14h, and the nitrogen flow rate is 30-60L / min;

[0076] The degreasing temperature of thermal degreasing is 400-600℃, the heating rate is 1-3℃ / min, and the degreasing time is 1-2h.

[0077] It is worth mentioning that the degreasing process can be carried out under vacuum conditions with a vacuum degree of 10 to 60 Pa.

[0078] 5) After thermal degreasing, the injection molded product is pre-sintered.

[0079] In an embodiment of the present invention, the pre-sintering temperature is 900-1100° C., the time is 1-2 hours, and the heating rate is 5-10° C. / min.

[0080] 6) Sintering treatment to obtain TiAl alloy parts.

[0081] In an embodiment of the present invention, the sintering process is carried out in two steps. The first step is a sintering temperature of 1320-1400°C, a heating rate of 5-10°C / min, and a holding time of 0-1h; the second step is a sintering temperature of 1200-1280°C, a cooling rate of 5-10°C / min, and a holding time of 4-10h.

[0082] It is worth mentioning that the sintering process is carried out under vacuum conditions with a vacuum degree of 10 -2 ~10-4 Pa.

[0083] The injection molding preparation method of the fine-grained and high-density TiAl alloy blade component of the present invention will be described in detail below through specific examples.

[0084] Example 1:

[0085] Using 0-20 μm Ti-48Al-2Cr-2Nb pre-alloyed powder and 0-10 μm Sn-10Al pre-alloyed powder as raw materials, with the Sn-10Al pre-alloyed powder content being 1% by atomic percentage; placing the two raw material powders in a ball mill under the protection of high-purity argon gas, and then pre-mixing them on a roller mill at a speed of 150 r / min for 10 hours, with a ball-to-material ratio of 4:1; after the pre-mixing is completed, the mixed powder is compounded in a PCS device at a speed of 2800 r / min for 30 minutes, and the composite powder is vacuum-packaged for later use;

[0086] The composite powder was used as the raw material, with a solid powder loading of 62%. Binders were then weighed in percentages of 82% polyoxymethylene, 4% high-density polyethylene, 7% ethylene-vinyl acetate copolymer, and 7% stearic acid. The composite powder and binders were then uniformly mixed in an argon-filled internal mixer at 180°C, 25 rpm, and 2 hours. After mixing, the feedstock was removed and passed through a crusher to obtain granular feedstock.

[0087] The granular feed is placed in an injection machine and heated to 185°C before injection. The injection pressure is 120 MPa, the holding pressure is 110 MPa, the holding time is 5 s, the mold temperature is 110°C, and the injection speed is 65% of the maximum injection speed of the injection machine to obtain a blade injection green body.

[0088] The blade injection green body was placed in a degreasing furnace for oxalic acid catalytic degreasing treatment. The degreasing temperature was 135°C, the acid feed rate was 3g / min, the nitrogen flow rate was 35L / min, and the degreasing time was 12h.

[0089] The debinded blank was placed in a vacuum furnace for thermal debinding and pre-sintering treatment. The debinding atmosphere was high-purity argon, the debinding temperature was 450°C, the heating rate was 1°C / min, and the debinding time was 1 hour. After the thermal debinding was completed, the temperature was increased to 1000°C at a rate of 6°C / min, kept at this temperature for 1 hour, and then pre-sintering was carried out.

[0090] Finally, the pre-sintered blank is sintered. The sintering process is carried out under vacuum conditions with a vacuum degree of 10 -3The specific sintering process is as follows: heating from room temperature to 1320°C at 6°C / min and keeping warm for 0.4h; then cooling to 1280°C at 5°C / min and keeping warm for 4h; then cooling to room temperature with the furnace to obtain TiAl alloy blade parts.

[0091] Examples 2-6 were prepared using the same method as Example 1, differing in the raw material powder parameters, process parameters used in preparing the composite powder, binder composition, and various parameters of the powder injection molding and sintering processes. The raw material powder parameters, composite powder preparation methods, binder composition, injection molding process, and sintering process parameters for Examples 1-6 are summarized in Tables 1-5.

[0092] Table 1 Parameters of TiAl / SnAl composite powders in Examples 1 to 6

[0093]

[0094] Table 2 Preparation process parameters of TiAl / SnAl composite powder in Examples 1 to 6

[0095]

[0096] Table 3 Preparation process parameters of the binder in Examples 1 to 6

[0097] category Polyoxymethylene (%) High-density polyethylene (%) Ethylene-vinyl acetate copolymer (%) Stearic acid (%) Example 1 82 4 7 7 Example 2 85 3 4 8 Example 3 76 7 8 9 Example 4 78 8 8 6 Example 5 81 6 7 6 Example 6 83 4 8 5

[0098] Table 4 Summary of mixing and injection molding process parameters in Examples 1 to 6

[0099]

[0100] Table 5 Summary of degreasing and sintering process parameters in Examples 1 to 6

[0101]

[0102]

[0103] The following is a performance comparison experiment on the TiAl alloy blade parts prepared in Examples 1 to 6 and the TiAl alloy blade parts prepared in Comparative Examples 1 to 12.

[0104] 1. Experimental Subjects

[0105] The TiAl alloy blade parts prepared in Examples 1 to 6 and the TiAl alloy blade parts prepared in Comparative Examples 1 to 12, wherein:

[0106] Comparative Example 1:

[0107] The TiAl alloy product was prepared by the same preparation process as in Example 1, with the only difference being the composition of the feed: the powder raw material was a single Ti-48Al-2Cr-2Nb pre-alloyed powder with a particle size range of 0 to 20 μm.

[0108] Comparative Example 2:

[0109] TiAl alloy parts were prepared using the same preparation process as in Example 1, with the only difference being the feed composition: the powder raw material was a mixture of Ti-48Al-2Cr-2Nb pre-alloyed powder with a particle size range of 0 to 20 μm and 0.1% Sn-10Al pre-alloyed powder in an atomic percentage.

[0110] Comparative Example 3:

[0111] TiAl alloy parts were prepared using the same preparation process as in Example 1, with the only difference being the feed composition: the powder raw material was a mixture of Ti-48Al-2Cr-2Nb pre-alloyed powder with a particle size range of 0 to 20 μm and 2% Sn-10Al pre-alloyed powder in an atomic percentage.

[0112] Comparative Example 4:

[0113] The TiAl alloy parts were prepared by the same preparation process as in Example 3, with the only difference being the processing of the raw powder: the powder raw materials were mixed with a binder in a roller mill and then prepared into injection feed.

[0114] Comparative Example 5:

[0115] The TiAl alloy parts were prepared by the same preparation process as in Example 3, with the only difference being the processing process of the raw material powder: after premixing, the mixed powder was compounded in a PCS device at a speed of 3400 r / min for 10 min.

[0116] Comparative Example 6:

[0117] The TiAl alloy parts were prepared by the same preparation process as in Example 3, with the only difference being the processing process of the raw material powder: after premixing, the mixed powder was compounded in a PCS device at a speed of 2400 r / min for 60 min.

[0118] Comparative Example 7:

[0119] The TiAl alloy parts were prepared by the same preparation process as in Example 3, with the only difference being the processing process of the raw material powder: after premixing, the mixed powder was compounded in a PCS device at a speed of 2800 r / min for 60 min.

[0120] Comparative Example 8:

[0121] The TiAl alloy product was prepared by the same preparation process as in Example 5, except that the two-step sintering method was not used: heating from room temperature to 1450° C. at a rate of 5° C. / min and holding for 2 h.

[0122] Comparative Example 9:

[0123] The TiAl alloy product was prepared by the same preparation process as in Example 5, with the only difference being the temperatures of the two sintering steps: the first step sintering temperature was 1460°C, and the second step sintering temperature was 1250°C.

[0124] Comparative Example 10:

[0125] The TiAl alloy product was prepared by the same preparation process as in Example 5, with the only difference being the temperatures of the two sintering steps: the first step sintering temperature was 1280°C, and the second step sintering temperature was 1250°C.

[0126] Comparative Example 11:

[0127] The TiAl alloy product was prepared by the same preparation process as in Example 5, with the only difference being the temperatures of the two sintering steps: the first step sintering temperature was 1380°C, and the second step sintering temperature was 1300°C.

[0128] Comparative Example 12:

[0129] The TiAl alloy product was prepared by the same preparation process as in Example 5, with the only difference being the temperatures of the two sintering steps: the first step sintering temperature was 1360°C, and the second step sintering temperature was 1150°C.

[0130] 2. Experimental Methods

[0131] The performance of the TiAl alloy blade components prepared in Examples 1 to 6 and Comparative Examples 1 to 12 was measured using conventional testing methods in the prior art.

[0132] Performance testing:

[0133] (1) Relative density test: The relative density of the products prepared in Examples 1 to 6 and Comparative Examples 1 to 12 was measured respectively.

[0134] (2) Mechanical property test: The tensile strength and elongation of the parts prepared in Examples 1 to 6 and Comparative Examples 1 to 12 were measured at room temperature.

[0135] 3. Experimental Results

[0136] The experimental results of Examples 1 to 6 and Comparative Examples 1 to 12 are summarized in Table 6.

[0137] Table 6 Comparison of properties of injection molded parts prepared in Examples 1 to 6 and Comparative Examples 1 to 12

[0138]

[0139]

[0140] After testing, the TiAl alloy parts prepared in Examples 1 to 6 have a high density of more than 98%, uniform structure, fine grains, and a grain size of ≤40μm. They have excellent mechanical properties, a room temperature tensile strength of 520-560MPa, and an elongation of 0.9-1.5%.

[0141] Through data comparison, the TiAl alloy parts prepared in Comparative Examples 1 to 3 have poor density, and the presence of more pores causes the parts to break and fail prematurely during the test process; while in Examples 1 to 6 of the present invention, by introducing SnAl sintering aids into the TiAl alloy powder, a transient liquid-phase sintering system is formed. The SnAl liquid-phase melt formed during the sintering densification process can exert a capillary force on the TiAl powder particles. This capillary force is equivalent to an external pressure. Combined with the multiple diffusion channels formed between the solid-phase TiAl powder and the liquid-phase SnAl melt under the action of the concentration gradient, the diffusion migration of the material is accelerated, the formation of the sintering neck is promoted, and the densification sintering process of the part is promoted.

[0142] In Comparative Examples 5 to 8, if the premixed powder is not PCS treated or the rotation speed is too high or the time is too long during PCS treatment, the powder compounding will be uneven, the uniformity and fluidity of the TiAl / SnAl composite powder produced will deteriorate, the feed loading amount will be reduced, and the final product will have low density, uneven structure, and deteriorated mechanical properties.

[0143] In addition, in Comparative Examples 8, 9, and 11, the grains of the TiAl alloy parts produced were significantly coarsened, the density decreased, and the mechanical properties deteriorated under the traditional sintering system or the excessively high two-step sintering temperature. In Comparative Examples 10 and 12, the grain size of the TiAl alloy produced was reduced compared to Comparative Examples 9 and 11. However, due to the inactive grain boundary diffusion at low temperatures, there were many residual pores, the density of the parts was poor, and severe brittle fracture occurred during the test, making them worthless. It can also be seen from this that changes in the content of any component of the composite powder of the present invention or the preparation process will directly affect the microstructure of the injection molded parts; and the absence or change of any parameter in the sintering system of the present invention will not successfully produce fine-grained, high-density injection molded TiAl alloy parts.

[0144] The foregoing description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed herein are intended to be encompassed within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for preparing a fine-grained, high-density TiAl alloy part, characterized in that: The TiAl alloy product has a grain size of ≤40 μm and a density of >98%. The preparation method comprises the following steps: TiAl pre-alloyed powder and SnAl pre-alloyed powder are pre-mixed as raw materials to obtain a pre-mixed powder; the pre-mixed powder is composite-treated by a high-speed airflow impact particle composite shaping system to prepare a TiAl / SnAl composite powder in which the SnAl pre-alloyed powder uniformly coats the TiAl pre-alloyed powder; wherein the content of the SnAl pre-alloyed powder in the TiAl / SnAl composite powder is 0.5-1.5% by atomic percentage; the high-speed airflow impact particle composite shaping system is used at a rotation speed of 2500-3200 r / min for a processing time of 10-50 min, and the protective atmosphere is high-purity argon gas; TiAl / SnAl composite powder and a binder are used as raw materials, which are mixed and then crushed into granular feed; the binder is composed of 75-85% polyoxymethylene, 2-10% high-density polyethylene, 2-8% ethylene-vinyl acetate copolymer, and 5-10% stearic acid in percentage by mass; The granular feed is then sequentially subjected to injection molding, degreasing and sintering treatments to produce a TiAl alloy part. The sintering treatment is carried out in two steps. In the first step, the sintering temperature is 1320-1400°C, the heating rate is 5-10°C / min, and the holding time is 0-1h. In the second step, the sintering temperature is 1200-1280°C, the cooling rate is 5-10°C / min, and the holding time is 4-10h.

2. The preparation method according to claim 1, wherein The rotation speed of the premixing treatment is 100-200 r / min, the time is 6-10 h, the ball-to-material ratio is 1-5:1, and the protective atmosphere is high-purity argon.

3. The preparation method according to claim 1, wherein The TiAl pre-alloyed powder is composed of 45-50% Al, 1-5% Cr, 1-8% Nb, and the balance Ti in atomic percentage. The SnAl pre-alloyed powder comprises, by mass percentage, 85-95% Sn and 5-15% Al.

4. The preparation method according to claim 1, wherein The particle size of the TiAl pre-alloyed powder ranges from 0 to 20 μm and is not 0.

5. The preparation method according to claim 1, wherein The particle size of the SnAl pre-alloyed powder is in the range of 0 to 10 μm and is not 0.

6. The preparation method according to claim 1, wherein The volume percentage of the TiAl / SnAl composite powder in the granular feed is 60-65%.

7. The preparation method according to claim 1, wherein The mixing temperature is 170-200° C., the mixing time is 1-2 hours, and the mixing speed is 10-30 r / min.

8. The preparation method according to claim 1, wherein The injection molding process has an injection temperature of 170-200°C, an injection pressure of 110-130 MPa, a holding pressure of 100-120 MPa, a holding time of 3-10 seconds, a mold temperature of 100-120°C, and an injection speed of 60-80% of the maximum injection speed of the injection machine.

9. The preparation method according to claim 1, wherein The degreasing process includes two parts: oxalic acid catalytic degreasing and thermal degreasing; The degreasing temperature of the catalytic degreasing is 125-145°C, the acid feeding rate is 2-5g / min, the degreasing time is 8-14h, and the nitrogen flow rate is 30-60L / min; The degreasing temperature of the thermal degreasing is 400-600° C., the heating rate is 1-3° C. / min, and the degreasing time is 1-2 hours.

10. The preparation method according to claim 1, wherein The sintering process is carried out under vacuum conditions with a vacuum degree of 10 -2 ~10 -4 Pa.

11. The preparation method according to claim 1, wherein The method further includes a pre-sintering process after the degreasing process, wherein the pre-sintering temperature is 900-1100° C., the time is 1-2 hours, and the heating rate is 5-10° C. / min.

12. A fine-grained, high-density TiAl alloy part, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 11; wherein, The microstructure of the TiAl alloy product is an α2 / γ full lamellar structure; both the α2 and γ phases in the α2 / γ full lamellar structure are lamellar structures.

13. The fine-grained, high-density TiAl alloy part according to claim 12, wherein: The tensile strength of the TiAl alloy part is 520-560 MPa, and the elongation is 0.9-1.5%.

14. The fine-grained, high-density TiAl alloy part according to claim 12, wherein: The TiAl alloy part is a TiAl alloy blade.

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