CN111266571A - Binder, injection molding preparation method and product of TiAl alloy turbine - Google Patents

Abstract

The invention provides a binder, an injection molding preparation method of a TiAl alloy turbine and a product. The adhesive comprises the following components in percentage by volume: 50-70% of paraffin, 3-15% of high-density polyethylene, 5-10% of polypropylene, 5-10% of stearic acid and 5-17% of silicone resin. The adhesive of the invention is improved by adding the skeleton agent component silicone resin with low melting point and high decomposition temperature into the traditional wax-based adhesive system, and endows the turbine blank with strong shape-preserving capabilityWhen the silicone resin is decomposed at high temperature, the silicone resin can react with TiAl matrix in situ to generate Ti with fine dispersion distribution₂AlC and Ti₅Si₃Reinforcing phase, and further effectively improving the mechanical property of the TiAl alloy turbine.

Description

Binder, injection molding preparation method and product of TiAl alloy turbine

technical field

The invention relates to the technical field of powder metallurgy, in particular to a binder, a preparation method for injection molding of a TiAl alloy turbine, and a product thereof.

Background technique

Turbocharging technology is one of the most effective means to achieve energy saving and emission reduction in the automotive industry. The technology uses the inertial impulse of exhaust gas discharged from the engine to push the turbine in the turbine chamber, and the turbine drives the coaxial impeller. When the engine speed increases, the exhaust gas discharge speed and the turbine speed also increase synchronously, the impeller compresses more air into the cylinder, the pressure and density of the air increase, which can burn more fuel, correspondingly increase the amount of fuel and adjust the speed of the engine, Thereby increasing the output power of the engine. The supercharger turbine is the core component, and its performance directly determines the energy saving and emission reduction effect of the engine. For a long time, the precision casting method has been the main forming method of turbocharger turbines, but defects such as inclusions, porosity, coarse grains and composition segregation are easily generated during the casting process, which seriously limits the improvement of turbine life. In recent years, many developed countries have used metal powder injection molding to prepare turbocharger turbines. This technology can overcome the casting defects in the precision casting process, and realize the batch and near-net shape preparation of complex-shaped parts, and the size of the prepared samples High precision, uniform organization and excellent performance.

Turbine materials are constantly updated with the rapid development of supercharger technology. Initially, 20Cr3MoWV(A) was generally used in turbocharger turbines for diesel engines. Later, with the development of lightweight, miniaturized, and high-speed turbochargers, this material was gradually replaced by Inconel713 nickel-based superalloys. However, this material also has great limitations. For example, due to the large mass of the turbine, the response is poor, the inertia of the impeller is slow to respond to sudden changes in the throttle, and the turbine has problems such as "lag response". Therefore, the lightweight of supercharged turbine materials has become one of the important ways to improve engine performance. The TiAl-based alloy has the characteristics of light weight, high strength and heat resistance, and the service temperature can reach more than 700 ℃. Compared with the nickel-based superalloy, the TiAl-based alloy can achieve a weight reduction of 40-50% when used in the preparation of the supercharged turbine, which significantly improves the performance of the supercharged turbine engine. Accelerating responsiveness and reducing emission pollution during engine starting and shifting have shown great potential to replace traditional nickel-based superalloys in a new generation of high-temperature structural materials used in engines.

However, the preparation method of TiAl alloy powder injection molding for engine supercharger also has some problems. Paraffin-based binder is a binder system with the longest research time and the most mature technology. When it is used for the preparation of injection molding TiAl alloy supercharger turbine, due to the large size of the supercharger turbine, especially the turbine. The thickness of the central part and the blade part is very uneven. In the second stage of thermal degreasing of degreasing, when the binder component bearing the skeleton agent is completely removed, the sintering is formed due to the temperature at the end of the thermal degreasing stage and the pre-sintering of the degreasing blank. The temperature difference of the neck is too large, and the weak van der Waals force between the powder particles will cause the degreasing blank to keep its shape until the sintered neck is formed, causing the turbine degreasing blank to collapse during the thermal degreasing process. Therefore, this is the current TiAl alloy for engine superchargers. An urgent problem to be solved in the preparation process of powder injection molding.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a binder, a preparation method for injection molding of TiAl alloy turbine and products, the binder used for the injection molding of TiAl-based alloy powder is a low melting point, high decomposition temperature skeleton agent component silicone The resin is improved by adding the traditional wax-based binder system to give the turbine body strong shape retention ability. At the same time, the silicone resin will react with the TiAl matrix in-situ during the high temperature decomposition process, resulting in finely dispersed Ti ₂ AlC and Ti ₅ . Si ₃ enhances the phase, thereby effectively improving the mechanical properties of the TiAl alloy turbine, so as to solve the technical problem of the collapse of the turbine degreasing blank during thermal degreasing caused by the use of traditional binders in the prior art.

In order to achieve the above object, according to the first aspect of the present invention, an adhesive is provided.

The binder includes the composition in volume percentage: 50-70% of paraffin, 3-15% of high-density polyethylene, 5-10% of polypropylene, 5-10% of stearic acid, and 5-17% of silicone resin .

In order to achieve the above object, according to the second aspect of the present invention, a method for preparing a TiAl alloy turbine by injection molding is provided.

The injection molding preparation method of the TiAl alloy turbine comprises the following steps:

S1, preparation of feed: the TiAl-based pre-alloy powder and the binder according to claim 1 are mixed according to a certain ratio, and then crushed to form a granular feed;

S2, injection molding: injection molding the feed material on an injection machine to obtain a turbine blank;

S3, degreasing and pre-sintering: degreasing and pre-sintering the turbine blank;

S4, sintering: the turbine body after degreasing and pre-sintering in step S3 is sintered, and the turbine part is obtained after cooling in the furnace.

Further, in step S1, the content of the binder is 60-65 vol.%; the composition of the TiAl-based pre-alloyed powder is calculated in atomic percentage: the Al content is 43-49 at.%, and the Cr content is 0-5 at.% .%, the Nb content is 1-8 at.%, and the balance is Ti.

Further, in step S1, the mixing temperature is 150-190° C., the rotating speed is 10-30 r/min, and the time is 1-2 h; after the mixing is completed, it is cut into pellets by a crusher.

Further, in step S2, the feed is heated to 120-175°C, the injection pressure is 40-80MPa, the holding pressure is 40-100MPa, the holding time is 5-25s, the mold temperature is 50-100°C, and the injection speed is It is 50-80% of the maximum injection speed of the injection machine.

Further, in step S3, the degreasing process includes a solvent degreasing process and a thermal degreasing process, and the thermal degreasing process is performed under the protection of an inert gas; the pre-sintering process is heated to 800-1200 °C at 2-10 °C/min. ℃, keep warm for 0.5～1.5h.

Further, in the solvent degreasing process, the degreasing solvent is n-heptane or trichloroethylene, the degreasing temperature is 40-55 °C, and the degreasing time is 18-48 h; Drying time is 4-12h.

Further, in the thermal degreasing process, the temperature is raised from room temperature to 150-200°C at 0.5-2°C/min, and the temperature is maintained for 0.5-1.5h to carry out the first-stage thermal degreasing; Incubate for 0.5-1.5h to carry out the second stage thermal degreasing; raise the temperature at 0.5-2°C/min to 450-600°C, hold for 0.5-1.5h to carry out the third-stage thermal degreasing; raise the temperature at 0.5-2°C/min to 600-800°C, Heat preservation for 0.5-1.5h for the fourth stage thermal degreasing.

Further, in step S4, the sintering treatment is carried out under the protection of an inert gas or under a vacuum condition, wherein the vacuum degree is 10 ^-2 to 10 ^-4 Pa; 1200°C, hold for 0.5-2h, and carry out the first-stage sintering; then raise the temperature at 1-3°C/min to 1400-1550°C, hold the temperature for 1-4h, and carry out the second-stage sintering.

In order to achieve the above object, according to the third aspect of the present invention, an article is provided.

The product prepared according to the above-mentioned injection molding preparation method of TiAl alloy turbine is characterized in that, the product is a TiAl alloy turbine, and the TiAl alloy turbine has α ₂ /γ full sheet reinforced by Ti ₂ AlC and Ti ₅ Si ₃ layer structure; wherein, the particle sizes of the Ti ₂ AlC and Ti ₅ Si ₃ are both 1-3 μm; the α ₂ phase and the γ phase in the α ₂ /γ full-sheet structure are both lath-like structures; The mass percentage of the α ₂ phase is 10-20%, and the mass percentage of the γ phase is 80-90%.

In the traditional paraffin-based binder system, the decomposition temperature of high-density polyethylene, which is a polymer framework agent, is 450-550 °C, while the sintering neck formation temperature of TiAl alloy powder is 800-1200 °C. In the process of thermal degreasing, if the high-density polyethylene acting as a skeleton agent is completely removed, the weak van der Waals force between the powder particles is difficult to maintain the shape of the green body to the pre-sintering temperature due to the large difference between the degreasing temperature in the third stage and the pre-sintering temperature. The sintered state causes the TiAl turbine to collapse. The main chain is inorganic bonding, the side chain is organic bonding silicone resin has high temperature decomposition temperature unmatched by other organic polymer materials. Therefore, the introduction of a silicone resin skeleton agent with low melting and high decomposition temperature can not only satisfy the uniform mixing of each binder component during the mixing process, but also fill the stage of the third stage of degreasing to the sintering neck formation stage in the thermal degreasing process. The blank, continue to play the role of skeleton agent to maintain the shape of the green body, effectively improve the stability of the TiAl alloy turbine green body during the thermal degreasing process, and ensure the injection molding process preparation of the highly complex shape TiAl turbine. In addition, the melting temperature of the silicone resin is 150-200 °C, and the decomposition temperature is 500-750 °C. During the high-temperature decomposition of the silicone resin, C and Si will be generated, and in situ with the TiAl matrix, the dispersed Ti ₂ AlC and Ti will be formed. The ₅ Si ₃ ceramic particle reinforcement phase significantly improves the mechanical properties of the material. The addition amount of the silicone resin of the present invention is 5-17%. If the addition amount is too low, it will be difficult to effectively function as a skeleton agent to maintain the shape of the green body. If the addition amount is too high, Ti ₂ AlC and Ti ₅ Si will be formed. _3. Too much reinforcing phase will cause agglomeration and deteriorate the performance of the material. Experiments have confirmed that this process can obtain turbocharger turbine components with high dimensional accuracy, uniform interior and excellent mechanical properties.

The present invention designs and prepares a TiAl alloy turbine with α ₂ /γ full-sheet structure reinforced by Ti ₂ AlC and Ti ₅ Si ₃ . Higher requirements. For TiAl alloys, Ti ₂ AlC particles are known to be one of the more effective reinforcing phase particles. The Ti ₅ Si ₃ phase is also a reinforcing phase that has been reported to significantly improve the high temperature properties of TiAl alloys. Therefore, the generation of Ti ₂ AlC and Ti ₅ Si ₃ enhanced phases can effectively improve the mechanical properties of TiAl alloy turbines. In addition, among the four typical structures of TiAl alloys, the uniform and fine α ₂ /γ full-sheet structure not only has good room temperature properties, but also has excellent high temperature properties. In the present invention, the Al content in the raw material powder is controlled to control the respective proportions of the _α2 and γ phases in the lamellar structure, and the percentage of the _α2 phase is determined to be 10-20%. If the proportion of the _α2 phase is too low, It will seriously reduce its fracture toughness and creep resistance. If the proportion of _α2 phase is too high, the room temperature mechanical properties will be poor, such as tensile strength and plasticity will be greatly reduced, and it is difficult to obtain better comprehensive mechanical properties. Experiments have confirmed that this process can obtain turbocharger turbine components with uniform distribution of reinforced phases, fine grains, full lamellar structure and excellent comprehensive performance.

Beneficial effects of the present invention:

(1) The powder injection molding technology is used to realize the near-net-shape preparation of TiAl alloy supercharger turbines for engines with complex shapes. Compared with the existing machining technology, the process is simpler, the equipment requirements are lower, the material utilization rate is high, and the cost is greatly reduced. It is easy to realize batch production of supercharger turbines.

(2) A new paraffin-based binder system suitable for the preparation of TiAl alloy turbine was designed, which improved the shape retention of the billet and the dimensional accuracy of the final product.

(3) A TiAl alloy turbocharger turbine with α ₂ /γ full lamella structure reinforced by specific Ti ₂ AlC and Ti ₅ Si ₃ was designed, which has excellent mechanical properties at room temperature and high temperature.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating preferred embodiments only and are not to be considered limiting of the invention. Also, the same components are denoted by the same reference numerals throughout the drawings. In the attached image:

FIG. 1 is a scanning electron microscope topography diagram of the TiAl-based alloy raw material powder in Example 1 of the present invention.

Detailed ways

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be more thoroughly understood, and will fully convey the scope of the present disclosure to those skilled in the art.

The invention discloses an improved wax-based binder for injection molding of TiAl alloy powder. The binder comprises the following components in volume percentage: 50-70% of paraffin, 3-15% of high-density polyethylene, Polypropylene 5-10%, stearic acid 5-10%, silicone resin 5-17%.

In the above embodiment, the binder is mainly composed of 50-70% paraffin, 3-15% high-density polyethylene, 5-10% polypropylene, 5-10% stearic acid and 5-17% silicone by volume percentage. Resin composition, in which low melting point, high decomposition temperature skeleton agent component silicone resin is added to the traditional wax-based binder system for improvement, giving the turbine blank strong shape retention ability and solving the problem of easy collapse during thermal degreasing. At the same time, the silicone resin will react with the TiAl matrix in-situ during the high temperature decomposition process to generate finely dispersed Ti ₂ AlC and Ti ₅ Si ₃ reinforced phases, thereby effectively improving the mechanical properties of the TiAl alloy turbine. The addition amount of silicone resin is in the range of 5-17%. If the addition amount is too low, it will be difficult to effectively play the role of a skeleton agent and maintain the shape of the green body; if the addition amount is too high, the generated Ti ₂ AlC and Ti ₅ Too much Si ₃ reinforced phase leads to agglomeration, which deteriorates the properties of the material.

The invention discloses a preparation method for injection molding of a TiAl alloy turbine. The method specifically includes the following steps:

S1, preparation of feed: the TiAl-based pre-alloy powder and the above-mentioned binder are mixed, and then crushed to form a granular feed.

In this step, the TiAl-based pre-alloyed powder and the above-mentioned binder are selected as raw materials, and the ratio of the TiAl-based pre-alloyed powder and the binder is determined, wherein the content of the binder is 60-65 vol.%; The composition of the base pre-alloyed powder is calculated in atomic percentage: the Al content is 43-49 at.%, the Cr content is 0-5 at.%, the Nb content is 1-8 at.%, and the balance is Ti; its SEM morphology is shown in the following figure. Figure 1. The above-mentioned TiAl-based pre-alloy powder and binder are put into an internal mixer for uniform mixing, and then crushed by a crusher to make granular feed; wherein, the mixing temperature is 150-190 ° C, and the rotating speed is 10-30 r/ min, the time is 1～2h.

S2, injection molding: injection molding the feed material on an injection machine to obtain a turbine blank.

In this step, the feed is heated to 120-175°C, the injection pressure is 40-80MPa, the holding pressure is 40-100MPa, the pressure-holding time is 5-25s, the mold temperature is 50-100°C, and the injection speed is the maximum of the injection machine. 50-80% of the injection speed.

S3, Degreasing and Pre-sintering: The turbine blank is de-greasing and pre-sintering.

In this step, the degreasing treatment includes a solvent degreasing process and a thermal degreasing process, wherein the degreasing solvent in the solvent degreasing process is n-heptane or trichloroethylene, the degreasing temperature is 40-55 °C, and the degreasing time is 18-48 h; After completion, the drying treatment is carried out at a temperature of 45 to 55 °C, and the drying time is 4 to 12 hours. Then, the thermal degreasing process is carried out under the protection of inert gas, wherein the inert gas is high-purity argon gas; the thermal degreasing process is carried out by heating the temperature from room temperature to 150-200 ℃ at 0.5-2 ℃/min, and keeping the temperature for 0.5-1.5 h to carry out the first stage Thermal degreasing; heating at 0.5-1.5°C/min to 300-400°C, holding for 0.5-1.5h for the second stage thermal degreasing; heating at 0.5-2°C/min to 450-600°C, holding for 0.5-1.5h for the third stage Thermal degreasing; heating at 0.5-2°C/min to 600-800°C, holding for 0.5-1.5h for the fourth stage of thermal degreasing; finally, heating at 2-10°C/min to 800-1200°C, holding for 0.5-1.5h for pre-heating sintering.

S4, sintering: the turbine body after degreasing and pre-sintering in step S3 is sintered, and the turbine part is obtained after cooling in the furnace.

In this step, the sintering treatment is carried out under the protection of inert gas or under vacuum conditions, wherein the degree of vacuum is 10 ^-2 to 10 ^-4 Pa; ～1200°C, hold the temperature for 0.5～2h, and carry out the first stage sintering; then raise the temperature at 1～3°C/min to 1400～1550°C, hold the temperature for 1～4h, and carry out the second stage sintering.

The injection molding preparation method of the TiAl alloy turbine will be described in detail below through specific examples.

Example 1:

S1, preparation of feedstock: First select TiAl-based pre-alloy powder and binder, wherein: TiAl-based pre-alloy powder is composed of 48at.%Al, 2at.%Cr, 2at.%Nb, and the balance is Ti; then Selected 65% solid powder loading, respectively weighed 65% paraffin wax, 6% high density polyethylene, 9% polypropylene, 15% silicone resin, 5% stearic acid by volume to form binder system;

Then, the TiAl-based pre-alloyed powder and the binder are mixed at a temperature of 160° C., a rotational speed of 20 r/min, and a time of 2 h. After the mixing is completed and cooled to room temperature, the feed is taken out, and then the granular feed is obtained by a crusher.

S2, injection molding:

Put the feed material into the injection machine and heat it to 165℃ for injection. The injection pressure is 60MPa, the holding pressure is 70MPa, the pressure holding time is 10s, the mold temperature is 60℃, and the injection speed is 50% of the maximum injection speed of the injection machine. , to prepare a TiAl alloy turbine blank for an engine supercharger.

S3, degreasing and pre-sintering:

Put the above blanks into trichloroethylene solution for solvent degreasing, the degreasing temperature is 45 °C, and the time is 48 h. After the solvent degreasing is completed, it is dried in a blast drying oven at 45 °C, and the drying time is 8 h; Thermal degreasing was carried out under the protection of high-purity argon gas. The thermal degreasing conditions were as follows: the temperature was raised from room temperature to 180 °C at 1 °C/min, and the temperature was maintained for 1 h for the first stage of thermal degreasing; then the temperature was increased at 0.5 °C/min to 350 °C, and the temperature was kept for 1 h for the first stage of thermal degreasing. Two-stage thermal degreasing; followed by heating at 1°C/min to 500°C, and holding for 1 h for the third-stage thermal degreasing; then heating at 1°C/min to 750°C and holding for 0.5h for the fourth-stage thermal degreasing; finally, at 5°C/min The temperature was raised to 1100 °C, and the temperature was kept for 1 h for pre-sintering.

S4, Sintering:

The degreasing blanks are put into a vacuum furnace for sintering, and the vacuum degree is 10 ^-3 Pa. The sintering process is as follows: firstly, the temperature is raised to 1100°C at 5°C/min, and kept for 1 hour; then, the temperature is raised to 1480°C at 2°C/min, and the temperature is kept for 2 hours, and then cooled to room temperature with the furnace to obtain turbine parts.

Example 2:

S1, preparation of feed: First select TiAl-based pre-alloy powder and binder, wherein: TiAl-based pre-alloy powder is composed of 46at.%Al, 1at.%Cr, 3at.%Nb, and the balance is Ti; then Selected 67% solid powder loading, respectively weighed 65% paraffin, 9% high-density polyethylene, 9.5% polypropylene, 9% silicone resin, 7.5% stearic acid by volume to form binder system;

Then, the TiAl-based pre-alloyed powder and the binder are mixed at a temperature of 165° C., a rotational speed of 25 r/min, and a time of 2 h. After the mixing is completed and cooled to room temperature, the feed is taken out, and then the granular feed is obtained by a crusher.

S2, injection molding: put the feed material into the injection machine and heat it to 167°C for injection. The injection pressure is 60MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 70°C, and the injection speed is the maximum of the injection machine. 60% of the injection speed to prepare a TiAl alloy turbine blank for an engine supercharger.

S3, degreasing and pre-sintering: put the blanks into trichloroethylene solution for solvent degreasing, the degreasing temperature is 48 ℃, and the time is 40 h; The time is 6h; then thermal degreasing is carried out under the protection of high-purity argon gas. The thermal degreasing conditions are: from room temperature to 160°C at 1°C/min, holding for 1h; then heating at 0.5°C/min to 380°C and holding for 1h; Heat up to 500°C at 1°C/min and hold for 1h; then heat up to 780°C at 1°C/min and hold for 0.5h; finally, heat up to 1100°C at 6°C/min and hold for 1h for pre-sintering.

S4, sintering: put the degreasing blank into a vacuum furnace for sintering, and the vacuum degree is 10 ^-3 Pa. The sintering process is as follows: firstly, the temperature is raised to 1200°C at 6°C/min, and kept for 1 hour; then, the temperature is raised to 1490°C at 2°C/min, and the temperature is kept for 2 hours, and then cooled to room temperature with the furnace to obtain turbine parts.

Example 3:

S1, preparation of feed: First select TiAl-based pre-alloy powder and binder, wherein: TiAl-based pre-alloy powder is composed of 46at.%Al, 1at.%Cr, 3at.%Nb, and the balance is Ti; then Selected 67% solid powder loading, respectively weighed 65% paraffin wax, 13% high density polyethylene, 9.5% polypropylene, 5% silicone resin, 7.5% stearic acid by volume to form binder system;

The TiAl-based pre-alloyed powder is mixed with the binder at a temperature of 170° C., a rotational speed of 30 r/min, and a time of 2 h. After the mixing is completed and cooled to room temperature, the feed is taken out, and then the granular feed is obtained by a crusher.

S2, injection molding: put the feed material into the injection machine and heat it to 170°C for injection, the injection pressure is 70MPa, the pressure holding pressure is 90MPa, the pressure holding time is 20s, the mold temperature is 80°C, and the injection speed is the maximum of the injection machine. 55% of the injection speed to prepare a TiAl alloy turbine blank for an engine supercharger.

S3, degreasing and pre-sintering: put the blank into n-heptane solution for solvent degreasing, the degreasing temperature is 50℃, and the time is 36h; The time is 5h; then thermal degreasing is carried out under the protection of high-purity argon gas. The thermal degreasing conditions are as follows: from room temperature to 150°C at 0.5°C/min, holding for 1h; then heating at 0.5°C/min to 350°C and holding for 1h; The temperature was heated to 550°C at 1°C/min and held for 1 h; then, the temperature was raised to 800°C at 1°C/min and held for 0.5h; finally, the temperature was raised to 1000°C at 5°C/min and held for 1 h for pre-sintering.

S4, sintering: put the degreasing blank into a vacuum furnace for sintering, and the vacuum degree is 10 ^-2 Pa. The sintering process is as follows: firstly, the temperature is raised to 1200°C at 8°C/min, and kept for 1 hour; then, the temperature is raised to 1460°C at 2°C/min, and the temperature is kept for 2 hours, and then cooled to room temperature with the furnace to obtain turbine parts.

Example 4:

S1, preparation of feed: firstly select TiAl-based pre-alloy powder and binder, wherein: TiAl-based pre-alloy powder is composed of 45at.%Al, 2at.%Cr, 8at.%Nb, and the balance is Ti; then Selected 65% solid powder loading, respectively weighed 65% paraffin, 6% high-density polyethylene, 8% polypropylene, 15% silicone resin, 6% stearic acid by volume to form binder system;

The TiAl-based pre-alloyed powder is mixed with the binder at a temperature of 170° C., a rotational speed of 30 r/min, and a time of 3 hours. After the mixing is completed and cooled to room temperature, the feed is taken out, and then the granular feed is obtained by a crusher.

S2, injection molding: put the feed material into the injection machine and heat it to 175°C for injection. The injection pressure is 80MPa, the holding pressure is 100MPa, the pressure holding time is 25s, the mold temperature is 100°C, and the injection speed is the maximum of the injection machine. 65% of the injection speed to prepare a TiAl alloy turbine blank for an engine supercharger.

S3, degreasing and pre-sintering: put the blank into n-heptane solution for solvent degreasing, the degreasing temperature is 50 °C, and the time is 40 h; The time is 5h; then thermal degreasing is carried out under the protection of high-purity argon gas, and the thermal degreasing conditions are: from room temperature to 160°C at 0.5°C/min, holding for 1h; then heating to 360°C at 0.5°C/min, holding for 1h; The temperature was increased to 550°C at 0.5°C/min and held for 1 hour; then, the temperature was increased to 750°C at 0.5°C/min and held for 1 hour; finally, the temperature was raised to 1200°C at 8°C/min and held for 1 hour for pre-sintering.

S4, sintering: put the degreasing blank into a vacuum furnace for sintering, and the vacuum degree is 10 ^-4 Pa. The sintering process is as follows: firstly, the temperature is raised to 1200°C at 8°C/min, and kept for 1 h; then, the temperature is raised to 1480°C at 2°C/min, kept for 2 h, and then cooled to room temperature with the furnace to obtain turbine parts.

Example 5:

S1, preparation of feed: firstly select TiAl-based pre-alloy powder and binder, wherein: TiAl-based pre-alloy powder is composed of 43at.%Al, 2at.%Cr, 1at.%Nb, and the balance is Ti; then Selected 65% solid powder loading, respectively weighed 65% paraffin, 6% high-density polyethylene, 8% polypropylene, 15% silicone resin, 6% stearic acid by volume to form binder system;

The TiAl-based pre-alloyed powder is mixed with the binder at a temperature of 170° C., a rotational speed of 30 r/min, and a time of 3 hours. After the mixing is completed and cooled to room temperature, the feed is taken out, and then the granular feed is obtained by a crusher.

S2, injection molding: put the feed material into the injection machine and heat it to 175°C for injection. The injection pressure is 80MPa, the holding pressure is 100MPa, the pressure holding time is 25s, the mold temperature is 100°C, and the injection speed is the maximum of the injection machine. 65% of the injection speed to prepare a TiAl alloy turbine blank for an engine supercharger.

S3, degreasing and pre-sintering: put the blank into n-heptane solution for solvent degreasing, the degreasing temperature is 50 °C, and the time is 40 h; The time is 5h; then thermal degreasing is carried out under the protection of high-purity argon gas, and the thermal degreasing conditions are: from room temperature to 160°C at 0.5°C/min, holding for 1h; then heating to 360°C at 0.5°C/min, holding for 1h; The temperature was increased to 550°C at 0.5°C/min and held for 1 hour; then, the temperature was increased to 750°C at 0.5°C/min and held for 1 hour; finally, the temperature was raised to 1200°C at 8°C/min and held for 1 hour for pre-sintering.

S4, sintering: put the degreasing blank into a vacuum furnace for sintering, and the vacuum degree is 10 ^-4 Pa. The sintering process is as follows: firstly, the temperature is raised to 1200°C at 8°C/min, and kept for 1 h; then, the temperature is raised to 1480°C at 2°C/min, kept for 2 h, and then cooled to room temperature with the furnace to obtain turbine parts.

In the following, a performance comparison experiment will be conducted between the turbine parts prepared by the preparation methods in Examples 1 to 5 and the turbine parts prepared by the traditional preparation process.

1. Experimental object

The turbine parts prepared in Examples 1-5 and the turbine parts prepared in Comparative Examples 1-5, wherein:

Comparative Example 1:

The TiAl-based pre-alloyed powder with the same composition as in Example 1 was used, and then 65% of the solid powder loading was selected, and 65% of paraffin, 15% of high-density polyethylene, and 15% of polypropylene were weighed by volume. 5% stearic acid constitutes the binder system.

Then, the preparation of feed, injection molding, degreasing, pre-sintering and sintering are carried out in sequence. The thermal degreasing conditions are as follows: from room temperature to 180 °C at 1 °C/min, and holding for 1 h for the first stage of thermal degreasing; and then at 0.5 °C/min. The temperature was increased to 350°C and held for 1 hour for the second stage of thermal degreasing; then, the temperature was increased to 500°C at 1°C/min and held for 1 hour for the third stage of thermal degreasing;

After testing, in Comparative Example 1, from the third stage of thermal degreasing to the pre-sintering stage, the degreased green blade was greatly collapsed and deformed, and its shape could not be maintained.

Comparative Example 2:

The turbine parts were prepared by the same preparation process as in Example 1, except that the content of each component in the binder system was different, especially the content of silicone resin was relatively low, specifically weighing 65% by volume respectively Paraffin wax, 17% high density polyethylene, 10% polypropylene, 3% silicone resin, 5% stearic acid make up the binder system.

After testing, in Comparative Example 2, from the fourth stage of thermal degreasing to the pre-sintering stage, the degreasing green blade was seriously deformed, and there were a large number of cracks, which did not meet the requirements for use.

Comparative Example 3:

The turbine part was prepared by the same preparation process as in Example 1, except that the content of each component in the binder system was different, especially the content of silicone resin was relatively high. Paraffin wax, 5% high density polyethylene, 6% polypropylene, 19% silicone resin, 5% stearic acid, constitute the binder system.

Comparative Example 4:

The turbine parts are prepared by the same preparation process as in Example 1, except that the composition content of the TiAl-based pre-alloyed powder is different. The composition of the TiAl-based pre-alloyed powder is 49at.%Al, 2at.%Cr, 8.5at .%Nb, the balance is Ti.

Comparative Example 5:

The turbine parts were prepared by the same preparation process as in Example 1, except that the composition content of the TiAl-based pre-alloyed powder was different. The composition of the TiAl-based pre-alloyed powder was 42 at.% Al, 2 at.% Cr, 1 at. %Nb, the balance is Ti.

2. Experimental method

The performance of the turbine parts prepared in Examples 1 to 5 and Comparative Examples 1 to 5 was measured by using conventional inspection methods in the prior art.

Performance check:

(1) Relative density test: The relative density of the turbine parts prepared in Examples 1 to 5 and Comparative Examples 1 to 5 was measured respectively.

(2) Mechanical property test: The room temperature tensile strength and elongation were measured for the turbine parts prepared in Examples 1 to 5 and Comparative Examples 1 to 5, respectively.

3. Experimental results

After testing, the TiAl alloy turbines prepared by the preparation methods in Examples 1 to 5 have fine grains, uniform structure, and have a α ₂ /γ full lamellar structure enhanced by Ti ₂ AlC and Ti ₅ Si ₃ ; ₂ The particle size of AlC and Ti ₅ Si ₃ is 1-3 μm; the α ₂ phase and the γ phase in the α ₂ /γ full-sheet structure are both lath-like structures; the mass percentage of the α ₂ phase is 10-20% , the mass percentage of the γ phase is 80-90%.

The experimental results of Examples 1 to 5 and Comparative Examples 1 to 5 are summarized below, as shown in Table 1.

Table 1 Performance comparison of turbine parts prepared from Examples 1 to 5 and Comparative Examples 1 to 5

Through data comparison, in Comparative Example 1, from the third stage of thermal degreasing to the pre-sintering stage, the degreased green blade was greatly collapsed and deformed, and its shape could not be maintained; while in Examples 1 to 5 of the present invention, by introducing low Melting and high decomposition temperature silicone resin skeleton agent effectively improves the stability of TiAl alloy turbine green body during thermal degreasing process, and ensures the preparation of highly complex shape TiAl turbine by injection molding process. At the same time, the designed and prepared Ti ₂ AlC and Ti ₅ Si ₃ enhanced α ₂ /γ full lamellar microstructure enables the TiAl alloy turbocharger turbine to have excellent comprehensive mechanical properties. In addition, the TiAl turbine for a turbocharger prepared in Comparative Example 4, although the grains are fine and the structure is uniform, the matrix structure is near γ structure, mainly composed of γ equiaxed crystals, Ti ₂ AlC and Ti ₅ Si ₃ reinforced phases The particle size is about 1 μm, and the density, room temperature tensile strength and elongation are relatively low; it can also be seen from this that the change of the content of any one of the components in the TiAl-based pre-alloyed powder of the present invention will directly affect the increase. The structure of the TiAl turbine used in the press; and the absence or change of any component in the binder of the present invention, or the change of the ratio between the components, can not give the turbine body strong shape-retaining ability, so as to solve its problem in thermal degreasing. The process is prone to collapse.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (10)

1. An adhesive is characterized by comprising the following components in percentage by volume: 50-70% of paraffin, 3-15% of high-density polyethylene, 5-10% of polypropylene, 5-10% of stearic acid and 5-17% of silicone resin.

2. The injection molding preparation method of the TiAl alloy turbine is characterized by comprising the following steps of:

s1, preparation of feed: mixing TiAl-based prealloying powder and the binder of claim 1 according to a certain proportion, and crushing to form granular feed;

s2, injection molding: injecting and forming the feed material on an injection machine to obtain a turbine blank;

s3, degreasing and pre-sintering: degreasing and presintering the turbine blank;

s4, sintering: and sintering the turbine blank degreased and presintered in the step S3, and cooling along with the furnace to obtain the turbine product.

3. The injection molding production method of the TiAl alloy turbine as claimed in claim 2, wherein in the step S1, the content of the binder is 60-65 vol.%; the TiAl-based prealloyed powder comprises the following components in atomic percentage: the Al content is 43-49 at.%, the Cr content is 0-5 at.%, the Nb content is 1-8 at.%, and the balance is Ti.

4. The injection molding preparation method of the TiAl alloy turbine as claimed in claim 2, wherein in the step S1, the mixing temperature is 150-190 ℃, the rotation speed is 10-30 r/min, and the time is 1-2 h; and cutting the mixture into granules by a crusher after the mixing is finished.

5. The method for preparing the TiAl alloy turbine through injection molding according to claim 2, wherein in the step S2, the feed material is heated to 120-175 ℃, the injection pressure is 40-80 MPa, the pressure maintaining pressure is 40-100 MPa, the pressure maintaining time is 5-25S, the mold temperature is 50-100 ℃, and the injection speed is 50-80% of the maximum injection speed of the injection machine.

6. The injection molding production method of the TiAl alloy turbine according to claim 2, wherein in the step S3, the degreasing treatment includes a solvent degreasing process and a thermal degreasing process, and the thermal degreasing process is performed under an inert gas shield; the pre-sintering treatment process is carried out at the temperature of 800-1200 ℃ at the speed of 2-10 ℃/min, and the temperature is kept for 0.5-1.5 h.

7. The injection molding preparation method of the TiAl alloy turbine as claimed in claim 6, wherein the degreasing solvent in the solvent degreasing process is n-heptane or trichloroethylene, the degreasing temperature is 40-55 ℃, and the degreasing time is 18-48 h; and after degreasing, drying at the temperature of 45-55 ℃, wherein the drying time is 4-12 h.

8. The injection molding preparation method of the TiAl alloy turbine as claimed in claim 7, wherein the thermal degreasing process is a first stage thermal degreasing process which is carried out by raising the temperature from room temperature to 150-200 ℃ at a speed of 0.5-2 ℃/min and keeping the temperature for 0.5-1.5 h; raising the temperature to 300-400 ℃ at a speed of 0.5-1.5 ℃/min, and keeping the temperature for 0.5-1.5 h to carry out second-stage thermal degreasing; heating to 450-600 ℃ at a speed of 0.5-2 ℃/min, and preserving heat for 0.5-1.5 h to carry out third-stage thermal degreasing; heating to 600-800 ℃ at a speed of 0.5-2 ℃/min, and keeping the temperature for 0.5-1.5 h to perform thermal degreasing at the fourth stage.

9. The method for manufacturing a TiAl alloy turbine through injection molding according to claim 2, wherein in the step S4, the sintering process is performed under the protection of inert gas or under vacuum condition, wherein the vacuum degree is 10^-2～10^-4Pa; raising the temperature from room temperature to 1000-1200 ℃ at a speed of 2-10 ℃/min, preserving the temperature for 0.5-2 h,sintering in the first stage; and then heating to 1400-1550 ℃ at the rate of 1-3 ℃/min, and keeping the temperature for 1-4 h, and carrying out second-stage sintering.

10. The TiAl alloy turbine product prepared by the injection molding preparation method according to any one of claims 2 to 9, wherein the product is a TiAl alloy turbine having Ti₂AlC and Ti₅Si₃Enhanced α₂A/gamma full lamellar structure; wherein, the Ti₂AlC and Ti₅Si₃The particle size of the powder is 1-3 mu m, wherein α₂α in a/gamma full lamellar structure₂Both phase and gamma phase are lath structure, the α₂The phase accounts for 10-20% by mass, and the gamma phase accounts for 80-90% by mass.

Images