Powder metallurgy preparation method for silicon carbide aluminum-based material capable of regulating and controlling anisotropy

Abstract

The invention relates to the technical field of powder metallurgy preparation, and discloses a silicon carbide aluminum-based material powder metallurgy preparation method capable of regulating and controlling anisotropy, which comprises the following steps: a precursor slurry preparation step: preparing Bingham fluid slurry with specific rheological parameters; a yield stress gating centrifugation step: utilizing a cascade centrifugation procedure, firstly maintaining a solid-like state of the slurry through low centrifugal force to inhibit sedimentation, and then triggering shear thinning through high centrifugal force to drive the flaky silicon carbide to be directionally arranged; according to the preparation method, a yield stress gating mechanism is constructed, and the contradiction between slurry suspension stability and particle orientation kinetics is solved in a single working procedure.

Description

Technical Field

[0001] This invention relates to a powder metallurgy preparation method for silicon carbide aluminum-based materials with controlled anisotropy, belonging to the field of powder metallurgy preparation technology. Background Technology

[0002] Currently, silicon carbide particle-reinforced aluminum matrix composites possess high specific strength, high wear resistance, and controllable thermophysical properties, making them a key basic material for high-power electronic packaging and thermal management systems. In powder metallurgy preparation processes, to avoid the thermal conductivity and modulus performance problems of traditional spherical particle-reinforced systems, the introduction of lamellar silicon carbide reinforcing phases and the induction of directional alignment to construct anisotropic structures have become the mainstream technical path for improving the vector transport performance of materials. Under the existing powder metallurgy and slurry forming technology system, constructing an ordered array of high volume fraction lamellar reinforcing phases faces physical constraints. Due to the density difference between silicon carbide and the aluminum matrix, the two phases mixed to form a suspension system are subject to the inherent contradiction between Stokes sedimentation law and fluid dynamic orientation mechanism under the action of force field.

[0003] Conventional preparation processes struggle to balance molding density and microstructural order in high-volume systems. For instance, Chinese invention patent CN103602869A discloses a powder metallurgy method for preparing high-volume silicon carbide aluminum-based composite materials. This method addresses the agglomeration problem of high-volume powder by introducing a self-made binder composed of plant protein and shellac. However, this approach is limited by the isotropic nature of static molding processes. The cold pressing process lacks a driving force for the rheological shear field that causes the flaky particles to deflect. As a result, the reinforcing phase is randomly and disordered in the matrix, making it difficult to construct directional and efficient heat conduction channels. Furthermore, conventional atmospheric segmented sintering processes cannot provide a chemical pinning mechanism to suppress the flow of the high-temperature liquid phase. The melting and flow of the matrix destroys the weak structural advantages of the green body, making it difficult to achieve both sintering densification and structural order.

[0004] Therefore, how to solve the contradiction between component segregation caused by density difference and directional alignment resistance caused by viscosity in the fluid forming process of heterogeneous powder systems, and how to achieve non-destructive locking and densification of micro-oriented structures under low temperature and low pressure conditions, has become the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for preparing silicon carbide aluminum-based materials with controlled anisotropy using powder metallurgy, comprising the following steps:

[0006] The precursor slurry preparation step involves preparing sheet-like materials with an aspect ratio of 8:1 to 15:1. Silicon carbide powder, spherical aluminum-based powder, titanium hydride powder, and a rheology modifier are dispersed in a liquid medium, and the solid content is adjusted to 75 wt% to 82 wt% to prepare a precursor slurry with Bingham fluid characteristics. The static yield stress of the precursor slurry is measured and controlled within the range of 10 Pa to 25 Pa, and at a shear rate of 100... The apparent viscosity at that time was less than 2 Pa·s;

[0007] The yield stress-gated centrifugation process involves injecting the precursor slurry into a mold and placing it in a centrifugal force field to execute a stepped procedure. In the first stage, a centrifugal acceleration of 20g to 40g is applied, maintaining the maximum shear stress generated within the precursor slurry below the static yield stress, using the yield skeleton to support the suspension of solid particles. In the second stage, the centrifugal acceleration is linearly increased to 400g to 800g, causing the internal shear stress to exceed the static yield stress, triggering thixotropic liquefaction and driving the sheet-like... - Silicon carbide powder is oriented perpendicular to the direction of centrifugal force; in the third stage, after the particles are packed and compacted, the machine is stopped, and the precursor slurry physically locks the orientation structure inside the green body through its thixotropic recovery properties.

[0008] In the in-situ reaction sintering step, the green body is degreased by vacuum heating, and the surface of the aluminum-based powder is reduced by hydrogen gas decomposed from titanium hydride powder. The temperature is raised to the solid-liquid two-phase region, where the transient liquid phase generated by the aluminum-titanium reaction wets and chemically pins the sheet-like structure. -The directional arrangement of silicon carbide powder, cooled, yields anisotropic silicon carbide aluminum-based materials.

[0009] Preferably, in the yield stress-gated centrifugation step, the centrifugation acceleration settings for the first and second stages follow the following inequality relationship between shear stress and yield strength: ,in, The static yield stress of the precursor slurry. This represents the maximum shear stress generated within the precursor slurry by the centrifugal acceleration during the first stage. This represents the minimum shear stress generated within the precursor slurry by the centrifugal acceleration during the second stage.

[0010] Preferably, the rheology modifier is composed of polyvinyl alcohol, polyethylene glycol, and ammonium stearate; in the precursor slurry preparation step, by adjusting the degree of polymerization of polyvinyl alcohol to 1700 to 1800 and controlling the amount of ammonium stearate added, the thixotropic ring area of ​​the precursor slurry is controlled within a preset range, so that the viscosity of the precursor slurry recovers to above 50 Pa·s within 2 to 5 seconds after the centrifugal force field is removed.

[0011] Preferably, in the precursor slurry preparation step, the average particle size of the titanium hydride powder is 2 to 3 micrometers, and the amount added is 0.5% to 2.0% of the total solid mass in the precursor slurry; in the in-situ reaction sintering step, heating to the solid-liquid two-phase region includes controlling the temperature at 580 degrees Celsius to 620 degrees Celsius, where the titanium hydride powder decomposes the residual titanium component and undergoes a eutectic reaction with the surrounding aluminum-based powder, generating titanium-rich liquid phase microregions in situ at a temperature lower than the melting point of the aluminum-based powder.

[0012] Preferably, in the yield stress-gated centrifugation step, the duration of the first stage is set to 30 to 60 seconds, and the duration of the second stage is set to 60 to 120 seconds; the transition from the first stage to the second stage adopts a linear acceleration mode, and the acceleration slope is controlled at 50g to 100g per second.

[0013] Preferred, sheet-like - The average particle size D50 of silicon carbide powder is 30 to 50 micrometers, and the average particle size D50 of spherical aluminum-based powder is 5 to 10 micrometers; in the precursor slurry preparation step, the spherical aluminum-based powder is filled into the sheet-like... - The interlayer voids of silicon carbide powder form microstructural units with dense packing characteristics.

[0014] Preferably, the heating degreasing process in the in-situ reaction sintering step includes: heating to the range of 300 to 450 degrees Celsius at a rate of 2 to 5 degrees Celsius per minute and holding at that temperature in a vacuum environment of less than 10 Pa, and using the pyrolysis properties of the rheology modifier to construct microporous channels for hydrogen to escape.

[0015] Preferably, in the in-situ reaction sintering step, the transient liquid phase is in the sheet-like... - A titanium carbide and titanium aluminide composite interface layer with a thickness of 10 nanometers to 50 nanometers is formed on the surface of silicon carbide powder. This composite interface layer connects the aluminum-based powder and the sheet-like... -Silicon carbide powder.

[0016] Preferably, the yield stress-gated centrifugation step is performed in a vacuum centrifugal casting machine with constant temperature control; throughout the execution of the step procedure, the air pressure in the mold cavity is kept below 500 Pa, and the temperature of the precursor slurry is maintained at 20 to 30 degrees Celsius.

[0017] Preferably, the precursor slurry preparation step further includes: preparing the flake-shaped slurry before dispersion. - Silicon carbide powder undergoes surface pretreatment, and silane coupling agents are used in sheet-like formations. - Organic functional groups are grafted onto the surface of silicon carbide powder.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. In anisotropic silicon carbide aluminum-based materials, a rheological control mechanism for yield stress threshold is constructed in conjunction with a stepped centrifugal loading procedure to resolve the contradiction between the easy sedimentation and stratification of the lamellar reinforcing phase and the difficulty in rotational orientation in the liquid medium. Utilizing the Bingham fluid properties of the slurry, the solid particles are supported by the static yield stress of the matrix medium during the low-speed degassing and static stage, forming a rigid skeleton that resists gravity and low centrifugal force, and suppressing Stokes sedimentation and component segregation caused by density difference. In the high-speed forming stage, the shear field of the super-yield point is used to stimulate the shear thinning behavior of the slurry, reduce fluid resistance and orient the lamellar particles under the action of hydrodynamic torque. The stress gating mechanism ensures that the green body obtains a highly anisotropic microstructure while maintaining the uniformity of component distribution along the thickness direction.

[0020] 2. By utilizing the relay effect of rheological properties and in-situ chemical reactions, the orientation structure is inherited from the green state to the sintered finished product. At the moment the centrifugal molding ends, the slurry rapidly returns to a high viscosity state due to thixotropy, forming a physical lock on the already oriented sheet particles, preventing structural relaxation during green demolding and transfer. In the subsequent sintering process, the decomposition products of titanium hydride react with the aluminum matrix to generate a titanium-rich transient liquid phase. Before the aluminum matrix fully melts and flows, it preferentially wets the surface of the sheet particles and contact nodes to form chemical pinning, avoiding the disintegration of the orientation structure caused by large-scale matrix flow in traditional liquid phase sintering, and ensuring that the pre-designed anisotropic heat conduction channels are retained in the final product.

[0021] 3. Utilizing titanium hydride as a multifunctional in-situ reaction source, the interface bonding state between silicon carbide and aluminum matrix is ​​improved without the assistance of external reducing atmosphere and high-pressure sintering equipment. During the heating process, titanium hydride decomposes and releases active hydrogen atoms to reduce the oxide film on the surface of aluminum powder in situ, exposing a fresh metal surface. The residual titanium component reduces the contact angle of aluminum melt on the silicon carbide surface, promotes capillary flow and filling of liquid phase in the interparticle gaps, and the in-situ activation mechanism reduces the sintering temperature required for material densification, inhibits the formation of harmful interfacial reactants at high temperatures, improves interfacial heat conduction efficiency, and improves the mechanical processing properties of the material. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of silicon carbide aluminum-based materials based on the yield stress gating mechanism of this invention.

[0023] Figure 2 This is a graph showing the trend of the effect of the amount of titanium hydride added on the key performance indicators of the material in this invention.

[0024] Figure 3 This is a logic diagram of the entire process operation and key control parameters of this invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a powder metallurgy method for preparing anisotropic silicon carbide aluminum-based materials. Through three core stages—rheological modulation of the precursor slurry, yield stress-gated centrifugal orientation molding, and in-situ reactive liquid-phase sintering—a structural genetic mechanism is established in the material preparation process. In the precursor stage, a Bingham fluid system with a specific yield stress threshold is constructed. In the molding stage, a stepped centrifugal force field triggers a binary transition in the slurry's rheological state, constructing a directional and uniformly composed layered structure in the green body. In the sintering stage, a transient liquid phase generated by an in-situ chemical reaction locks in this physical structure. In the powder metallurgy process for preparing high-volume-fraction plate-like particle-reinforced metal matrix composites, the slurry system needs to address the physical constraint between rheological stability and kinetic orientation. Low-viscosity media reduce the resistance to rotational orientation of plate-like particles in the flow field, but cause the denser silicon carbide particles to undergo Stokes sedimentation under gravity, leading to component segregation. This invention configures a thixotropic slurry system with specific yield stress-gated characteristics; a diameter-to-thickness ratio of [missing information] is selected. to flakes -Silicon carbide powder, average particle size for to Spherical aluminum-based powder and average particle size for to Titanium hydride powder was used as the solid-phase raw material. The spherical aluminum-based powder, with a particle size smaller than that of the sheet-like silicon carbide, filled the interlayer voids of the sheet-like particles, forming a dense packing structure. The solid-phase powder was dispersed in an aqueous medium containing a rheology modifier, the rheology modifier being composed of a polymer with a degree of polymerization of [insert value here]. to It is composed of polyvinyl alcohol, polyethylene glycol, and ammonium stearate. During the preparation process, the solid content is controlled at... to The range of parameters is determined, and the amount of ammonium stearate dispersant is adjusted to prepare the slurry into a Bingham-type fluid. The core of process parameter control lies in the calibration of the slurry's yield stress. The rheological curve of the slurry is measured using a rotational rheometer to control its static yield stress. In to Range, and at a shear rate of The apparent viscosity at that time is lower than .

[0027] To achieve venting, anti-settling, and directional alignment of the slurry in a single process, this invention employs a stepped centrifugal molding process with a yield stress gating mechanism. The precursor slurry is injected into a mold cavity and placed in a planetary centrifugal casting machine with vacuum and constant temperature control functions. During the molding process, the air pressure in the mold cavity is lower than... And the slurry temperature is maintained at to The experiment was conducted under specific conditions. The acceleration threshold was calibrated using a coupled model of fluid statics and centrifugal force field, and the slurry filling height within the mold cavity was measured. and slurry density Construct a function to calculate the maximum shear stress at the bottom. Calculate the upper limit of acceleration in the first stage. (Setting a safety factor) ), ensuring the global stress field To maintain the Bingham skeleton; calculate the lower limit of the second-stage acceleration. (Set overdrive coefficient) ), ensuring the global stress field To induce deep shear thinning; the first stage is a sub-yield steady-state degassing, applied... to The centrifugal acceleration and duration are set to to At this stage, the maximum shear stress generated by centrifugal force within the slurry... Controlled to be less than the static yield stress Within a certain range, the slurry maintains a near-solid suspension structure, using a structural framework to lock the spatial position of solid particles, expel air bubbles, and block relative sedimentation between particles, ensuring the uniform distribution of green components; the second stage is super-yield transient orientation, with the centrifuge operating at a speed of [missing information - likely a speed or value] per second. to The slope of the linear acceleration increases the centrifugal acceleration to... to and maintain to Under this high gravitational field, the minimum shear stress generated inside the slurry Breakthrough static yield stress The slurry undergoes thixotropic shear thinning, resulting in a decrease in apparent viscosity. The flake-like silicon carbide powder, within the liquefied matrix, is subjected to hydrodynamic torque, driving its planar normal direction to align parallel to the centrifugal force, thus causing it to settle and accumulate. The third stage is viscosity recovery locking. After the particles have completed dense packing, the process is rapidly stopped, utilizing the thixotropic recovery characteristics of the slurry to achieve viscosity recovery after the shear field disappears. to Internal recovery to viscosity greater than The high yield stress state prevents the green body from becoming structurally loose due to vibration or its own weight during subsequent demolding and transfer, thus retaining the orientation structure induced by the centrifugal field in the green body.

[0028] Vacuum heating and degreasing of the green body, in In the following vacuum environment, at a rate of... to The rate of heating up to to The temperature is maintained within a certain range, and microporous channels for gas escape are constructed using the pyrolysis properties of the rheology modifier. The temperature is then increased to the decomposition temperature range of titanium hydride. The highly reactive hydrogen released during decomposition is used to reduce the oxide film on the surface of the aluminum-based powder in situ, exposing a fresh metal surface. This process does not introduce an external reducing atmosphere and executes the titanium hydride thermal decomposition range. The gas pressure-heating rate closed-loop control procedure is used to set the critical threshold of furnace gas pressure. Real-time monitoring of vacuum level inside the furnace ,when At this time, the temperature control system is instructed to pause heating and maintain an isothermal state, while the vacuum pump unit's pumping section is adjusted to control the pressure rise rate. ,treat Falling back to The heating process will then resume; the key to sintering lies in the formation and pinning of the transient liquid phase, raising the temperature to... to In the solid-liquid two-phase region of aluminum, the micro- and nano-sized titanium components remaining from the decomposition of titanium hydride undergo a eutectic reaction with the surrounding aluminum-based powder, generating a titanium-rich transient liquid phase microregion in situ at a temperature below the melting point of pure aluminum. Due to the exposure of the fresh aluminum surface and the interfacial activity of titanium, this liquid phase wets the sheet-like... -Silicon carbide powder surface, reacting at the interface to form a thickness of to A composite interface layer of titanium carbide and titanium aluminide is prepared. Before the aluminum matrix undergoes large-scale flow, the composite interface layer preferentially chemically pins the oriented silicon carbide particles at the contact nodes. After cooling, the microstructure locked by the in-situ reaction is retained, thus preparing a silicon carbide aluminum matrix composite material with anisotropic thermophysical properties. This material establishes continuous high thermal conductivity channels in the direction parallel to the lamellar direction, while retaining the flexible buffering properties of the aluminum matrix in the vertical direction.

[0029] Example 1: In the industrial scenario of high-power IGBT module packaging, the thermal management system faces extremely stringent requirements for directional heat dissipation and the challenge of matching thermal expansion coefficients. This application requires the material to have extremely high thermal conductivity in the direction perpendicular to the substrate thickness (Z-axis) to achieve rapid heat dissipation. Simultaneously, the thermal expansion coefficient in the direction parallel to the substrate plane (XY plane) must be strictly matched with the ceramic substrate or chip to prevent interfacial delamination during thermal cycling. Traditional powder metallurgy processes, due to the difficulty in avoiding gravity sedimentation caused by the solid-liquid density difference, often lead to component delamination along the thickness direction when pursuing high orientation, resulting in silicon carbide enrichment at the bottom and aluminum enrichment at the top. This fails to meet the requirements of high-power devices for homogeneous thermal properties. When the preparation system of this invention faces the above conditions, it addresses the static sedimentation challenge by modulating a high-solids-content Bingham fluid slurry, selecting a diameter-to-thickness ratio of... flakes -Silicon carbide powder and average particle size Spherical aluminum-based powder was dispersed in an aqueous medium containing PVA-1788 and ammonium stearate, and the solid content was adjusted to... The static yield stress of the slurry was precisely calibrated using a rotational rheometer. Stable at This specific rheological parameter setting allows the slurry to resist the effects of silicon carbide particles during subsequent mold filling and low-speed venting stages, thanks to the yield skeleton formed internally. Gravitational settlement stress caused by density difference.

[0030] The centrifugal forming module executes a stepped acceleration procedure to trigger the orientation action, and the system in Running at low centrifugal acceleration At this point, the shear stress generated inside the slurry is still lower than The yield threshold is maintained to keep the solid-like state so that bubbles can be expelled without stratification, and then the centrifuge is used... The rate is linearly accelerated to At this instant in the high gravity field, the shear stress inside the slurry exceeds the yield stress, and the viscosity drops sharply. The following is triggered by thixotropic liquefaction, where the sheet-like silicon carbide particles, driven by hydrodynamic torque, move within this low-viscosity fluid. The particles rapidly rotate until their planar normal is parallel to the direction of centrifugal force and then compactly accumulate. After centrifugation... Within, the slurry viscosity rapidly recovers to [a certain value] through a thixotropic recovery mechanism. The above describes the physical locking of the formed orientation structure; finally, the in-situ reaction sintering stage achieves permanent solidification of the structure through a chemical mechanism. After the green body is degreased in a vacuum environment, the doped structure is then... Titanium hydride powder in The highly reactive hydrogen gas released during decomposition reduces the oxide film on the surface of the aluminum powder in situ. When the temperature further rises... In the solid-liquid two-phase region, the titanium hydride decomposes the residual titanium component and reacts with the surrounding aluminum matrix to generate a titanium-rich transient liquid phase. This high surface energy liquid phase preferentially wets and coats the oriented silicon carbide layers, forming at the interface. The thick TiC / Al3Ti composite layer, with its in-situ generated chemical pinning points, firmly locks the orientation of silicon carbide particles before the aluminum matrix undergoes large-scale melting and flow. This effectively avoids the risk of orientation structure disintegration caused by matrix flow during conventional liquid-phase sintering. The resulting composite material achieves the designed thermal conductivity in the Z-axis direction, and the silicon carbide volume fraction fluctuation along the thickness direction is controlled within a certain range. Within.

[0031] Example 2: This example constructs a multi-dimensional control experimental system. The experimental platform uses a customized vacuum hot-pressing centrifugal casting machine, which integrates a precisely temperature-controlled induction heating module and a maximum rotation speed of [missing information]. To simulate environmental disturbances that may occur in real industrial production, a planetary centrifugal disc was used in the experiment. During the experiment, a frequency of [frequency value missing] was actively introduced at the centrifuge's shaft. Amplitude is The mechanical vibration is superimposed on the heating power supply, resulting in a signal-to-noise ratio of... Electromagnetic noise interference; the experimental group design follows the principle of multi-dimensional comparison, as follows: the sample group of this invention adopts the process parameters that fully comply with the aforementioned process parameters, namely the static yield stress of the slurry. for The centrifugation process includes Exhaust and Orientation gradient specification; compared with sample group 1 (low yield stress group), the static yield stress of the slurry was adjusted to With all other conditions unchanged, the aim was to verify the necessity of the yield stress gating mechanism to combat settlement; in contrast, the low-speed exhaust stage was omitted in control sample group 2 (constant high centrifugation group), and stress was directly applied. Centrifugal force was used to verify the effect of stepped centrifugation on porosity and structural uniformity; the acceleration during the centrifugation orientation stage was set to [value missing] in the out-of-range control group 1. The aim was to investigate the potential negative impact of excessive centrifugal force on component stratification.

[0032] During the experiment, the rheological state of the slurry was indirectly characterized by real-time monitoring of the centrifuge shaft torque. Data from the sample group of this invention showed that the torque remained stable and low during the low-speed exhaust stage, indicating that the slurry was in a stable solid-like suspension. When the rotation speed was linearly increased to the high-speed orientation stage, the torque showed a characteristic transient decrease and then tended to stabilize. This phenomenon was highly consistent with the shear thinning behavior of Bingham fluid. In contrast, the control sample group 1 showed obvious torque fluctuations during the static stage, indicating that the particles had settled. After preparation, the density of each sample group was determined by Archimedes' displacement method, and the orientation degree of silicon carbide particles and the volume distribution along the thickness direction were statistically analyzed by scanning electron microscopy (SEM) combined with image analysis software. The key experimental data are shown in Table 1.

[0033] Table 1: Comparison of Key Performance Indicators for Each Experimental Group

[0034]

[0035] The data from the comparative sample group 1 show that when the yield stress is below the lower limit of the range defined in this invention, the top / bottom SiC volume fraction ratio deviates significantly from 1, indicating that the low viscosity medium cannot suppress Stokes sedimentation caused by density difference. Although the orientation is still acceptable, the unevenness of the components damages the Z-axis thermal conductivity. Although the comparative sample group 2 maintains the uniformity of the components, the density is reduced, confirming the indispensability of the low-speed degassing stage for eliminating air bubbles in high viscosity slurry. The results of the out-of-range control group 1 show that although the higher centrifugal force slightly improves the orientation, the uniformity of component distribution deteriorates (the ratio drops to 0.72), indicating that excessive centrifugal force will break through the support limit of the yield skeleton and cause secondary delamination.

[0036] Example 3: This example combines Figures 1 to 3 A method for preparing anisotropic silicon carbide aluminum-based materials using powder metallurgy is described, such as... Figure 1 As shown, the process begins at the raw material input module, where sheet materials are introduced. - Silicon carbide, spherical aluminum-based powder, titanium hydride powder, and rheology modifiers are used in the process. The process then enters the first stage: the precursor slurry preparation step to prepare Bingham fluid slurry. The slurry is injected into the mold and enters the second stage: the yield stress-gated centrifugal core forming step. This process sequentially executes the sub-yield steady-state degassing stage that uses low centrifugal force to maintain a solid-like skeleton, the super-yield transient orientation stage that uses high centrifugal force to trigger shear thinning through stepwise acceleration, and the viscosity recovery and locking stage after rapid shutdown. After the green body is transferred, it enters the third stage: the in-situ reaction sintering step to solidify the structure. This includes three key sub-steps: vacuum degreasing and surface reduction, heating to the solid-liquid two-phase region, and transient liquid-phase chemical pinning. Finally, the finished product is output after cooling and demolding, obtaining anisotropic silicon carbide aluminum-based material.

[0037] like Figure 2 As shown, the horizontal axis represents the amount of titanium hydride added, in wt%. The left main vertical axis represents the density, in %. The right first vertical axis represents the thermal conductivity along the Z-axis, in %. The second vertical axis on the right represents fracture toughness, in units of... The three data curves clearly show that as the amount of titanium hydride added increases from 0 to 3 wt%, the material's density and Z-axis thermal conductivity first increase and then decrease, reaching a peak near 1 wt%, while the fracture toughness shows a monotonically decreasing trend with increasing addition amount; for example... Figure 3 As shown, the slurry preparation use case specifically covers the operational details of powder surface pretreatment grafting with organic functional groups, adjusting the rheological shear thinning properties of Bingham fluid, and measuring / controlling the static yield stress of 10Pa-25Pa. The centrifugal molding use case is subdivided into three sub-stages: the first stage: sub-yield venting to maintain a solid-like framework, the second stage: super-yield orientation-triggered thixotropic liquefaction, and the third stage: viscosity recovery to lock the physical structure freezing. The in-situ reaction sintering use case includes the key actions of constructing venting channels through vacuum heating debinding and generating a transient liquid phase to pin the TiC / Al3Ti interface layer.

[0038] Example 4: This example provides a targeted explanation and verification of the scientific rationality of the in-situ reaction mechanism and key component ratio of titanium hydride powder in the preparation scheme, eliminating potential technical black boxes regarding the transient liquid phase formation mechanism and the setting of the addition amount. Addressing the challenge of interfacial reaction control in the preparation of silicon carbide aluminum-based composite materials, this invention proposes using titanium hydride powder as an in-situ reaction source. During sintering, the decomposition and reaction of titanium hydride is not a single chemical process but involves a multi-stage physicochemical evolution. When the temperature rises to... to During the interval, titanium hydride undergoes a decomposition reaction, releasing highly reactive atomic hydrogen that rapidly diffuses to the surrounding aluminum powder surface. This process follows Fick's diffusion law for gases in porous media. The reactive hydrogen can effectively reduce the alumina film on the aluminum powder surface, exposing a fresh metallic aluminum surface, thereby lowering the energy barrier for subsequent liquid phase wetting. No liquid phase is generated during this stage; instead, a clean solid surface is prepared for the spread of the liquid phase.

[0039] When the temperature rises to to The residual titanium component undergoes a eutectic reaction with the surrounding aluminum matrix. According to the Al-Ti binary phase diagram, within this temperature range, titanium and aluminum can react to generate titanium-rich liquid phase microregions. This transient liquid phase has a low melting point and high surface energy, and under the drive of capillary force, it can rapidly fill the interlayer voids and contact nodes of the lamellar silicon carbide particles. More importantly, titanium, as an active metal, can reduce the wetting angle of the aluminum liquid on the silicon carbide surface, promoting the spreading of the liquid phase on the silicon carbide surface. In this process, titanium reacts with silicon carbide and aluminum. In-situ reaction generates a nanoscale titanium carbide (TiC) and titanium aluminide (Al3Ti) composite interface layer. This interface layer not only chemically pins the silicon carbide particles, preventing displacement and disintegration during molten aluminum flow, but also effectively blocks direct contact between the molten aluminum and silicon carbide, inhibiting the excessive formation of the brittle aluminum carbide (Al4C3) phase. The setting of the titanium hydride addition amount is not based on arbitrary empirical values, but on a deep understanding of the constraint relationship between the degree of interface reaction and material properties. If the titanium hydride addition amount is lower than... The active hydrogen produced by decomposition is insufficient to completely reduce the oxide film on the surface of aluminum powder, and the amount of transient liquid phase generated is too small to form a continuous wetting network. This results in weak bonding between silicon carbide particles, and the density and thermal conductivity cannot meet expectations. If the amount added is higher than... Although wettability is improved, excessive titanium reacts with aluminum to form a large amount of brittle intermetallic compounds such as Al3Ti. These brittle phases accumulate at grain boundaries, reducing the mechanical properties of the material, especially fracture toughness. In addition, excessive hydrogen release may form pores that are difficult to expel within the sintered body, further impairing density. Therefore, the amount of titanium hydride added is strictly controlled. to Within the range.

[0040] To verify the rationality of the above mechanism and parameter settings, a set of gradient comparison experiments was designed, and the sample group of this invention was supplemented with... Titanium hydride, added to control group A Titanium hydride, added to control group B Titanium hydride, under the same sintering process, yielded the sample group of the present invention. With its high density and excellent Z-axis thermal conductivity, the density of sample A is only [missing information]. Furthermore, obvious unbound areas were observed at the interface, confirming the problem of insufficient wetting at low addition levels. In contrast, although sample group B achieved a density of [missing information], [missing information]. However, the fracture toughness decreased compared to the sample group of this invention. Furthermore, coarse Al3Ti phase aggregates were observed in the microstructure, verifying the damage to mechanical properties caused by excessive addition.

[0041] Example 5: This example focuses on the static yield stress of the precursor slurry. To determine the required parameters, a standardized offline calibration and data filling procedure was established. Based on Stokes' law of sedimentation, the minimum shear stress threshold required for silicon carbide particles of a given size and density to remain suspended in a gravitational field was calculated. Using this theoretical value as a benchmark, a series of materials with different solid contents (gradients of 1 / 2) were prepared. Slurry samples containing rheology modifiers and their proportions were analyzed using a rotational rheometer equipped with a coaxial cylindrical measuring system. Steady-state shear scans were performed on each sample under isothermal conditions to record the changes in shear stress with shear rate. The Herschel-Bulkley model was then used for fitting to analyze the static yield stress of each sample. And consistency coefficient, these rheological parameters are correlated with the static settling stability of the corresponding samples (through... (Characteristics of the supernatant height after standing for hours) Establish a related database. In actual production, by simply measuring the density and particle size distribution of the current batch of raw materials, the optimal solid content and modifier formulation that meet the anti-sedimentation requirements and are conducive to subsequent centrifugation orientation can be quickly identified by consulting this database.

[0042] In addition to addressing the migration issues of centrifugal molding processes across different equipment, this invention establishes a pre-deployment calibration procedure for on-site deployment. Due to differences in the arm radius and motor response characteristics of different centrifuge models, directly replicating centrifugal acceleration values ​​may lead to deviations in the actual shear stress applied to the slurry from the design value. Therefore, a standardized calibration process must be performed before new equipment is put into use. This process includes: loading a mold filled with fluid of standard density, running it at a set speed, collecting actual centrifugal acceleration data in real time using built-in or external high-precision acceleration sensors, plotting a speed-acceleration calibration curve, and simultaneously measuring the pressure distribution of the fluid on the mold wall at different speeds by pre-installing pressure-sensitive films inside the mold to verify the uniformity of the shear stress field. Based on the calibration results, the speed setting value of the control system is corrected to ensure that the actual physical field parameters applied inside the slurry fall within the effective range defined by this invention at each stage of sub-yield steady-state venting and super-yield transient orientation.

[0043] Example 6: This example discloses a standardized engineering calibration procedure for the precursor slurry preparation process, addressing key process parameters and static yield stress caused by fluctuations in the characteristics of different batches of raw materials. To address the issue of unclear criteria, ensure the reproducibility of the preparation process and the consistency of product quality, especially for sheet-like products. - Before each batch of raw materials such as silicon carbide powder, spherical aluminum-based powder, and titanium hydride powder is put into production, this procedure must be followed to determine the true density of the silicon carbide particles in that batch. With average particle size Based on Stokes' sedimentation theory, the theoretical threshold of minimum shear stress required to maintain the suspension of particles of this size in a gravitational field was calculated. ,by Based on this, a series of solid contents with gradient variations are designed, for example... to Step length And slurry samples with rheology modifier ratios were analyzed using a rotational rheometer. Steady-state shear scanning was performed on each sample under isothermal conditions, and the curves of shear stress versus shear rate were recorded.

[0044] Furthermore, the Herschel-Bulkley model was used to fit the collected rheological data, and the static yield stress of each sample was analyzed. Consistency coefficient and rheological index , will each sample Value and Compare and filter to find those that meet the requirements. (set up For all formulation combinations (with a safety factor), further static settling stability tests were conducted on the selected samples, and the results were recorded. After hours, the height of the supernatant was determined. Finally, taking into account both the yield stress compliance and the actual anti-settling effect, the optimal solid content and modifier ratio of the current batch of raw materials were determined.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing anisotropic silicon carbide aluminum-based materials using powder metallurgy, characterized in that, Includes the following steps: The precursor slurry preparation step involves preparing sheet-like materials with an aspect ratio of 8:1 to 15:

1. - Silicon carbide powder, spherical aluminum-based powder, titanium hydride powder and rheology modifier are dispersed in a liquid medium, and the solid content is adjusted to 75wt% to 82wt% to prepare a precursor slurry with Bingham fluid characteristics; The static yield stress of the precursor slurry was measured and controlled within the range of 10 Pa to 25 Pa, and at a shear rate of 100... The apparent viscosity at that time was less than 2 Pa·s; In the yield stress-gated centrifugation step, the precursor slurry is injected into a mold and placed in a centrifugal force field to perform a step-by-step procedure; in the first stage, a centrifugal acceleration of 20g to 40g is applied to keep the maximum shear stress generated inside the precursor slurry less than the static yield stress, and the yield skeleton is used to support the suspension of solid particles. The second stage linearly increases the centrifugal acceleration to 400g to 800g, causing the internal shear stress to exceed the static yield stress, triggering thixotropic liquefaction and driving the sheet-like... - Silicon carbide powder is oriented perpendicular to the direction of centrifugal force; in the third stage, after the particles are packed and compacted, the machine is stopped, and the precursor slurry physically locks the orientation structure inside the green body through its thixotropic recovery properties. In the in-situ reaction sintering step, the green body is degreased by vacuum heating, and the surface of the aluminum-based powder is reduced by hydrogen gas decomposed from titanium hydride powder. The temperature is raised to the solid-liquid two-phase region, where the transient liquid phase generated by the aluminum-titanium reaction wets and chemically pins the sheet-like structure. -The directional arrangement of silicon carbide powder, cooled, yields anisotropic silicon carbide aluminum-based materials.

2. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, In the yield stress-gated centrifugation step, the centrifugation acceleration settings for the first and second stages follow the following inequality relationship between shear stress and yield strength: ,in, The static yield stress of the precursor slurry. This represents the maximum shear stress generated within the precursor slurry by the centrifugal acceleration during the first stage. This represents the minimum shear stress generated within the precursor slurry by the centrifugal acceleration during the second stage.

3. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, The rheology modifier is composed of polyvinyl alcohol, polyethylene glycol and ammonium stearate. In the precursor slurry preparation step, by adjusting the degree of polymerization of polyvinyl alcohol to 1700 to 1800 and controlling the amount of ammonium stearate added, the thixotropic ring area of ​​the precursor slurry is controlled within a preset range, so that the viscosity of the precursor slurry recovers to above 50 Pa·s within 2 to 5 seconds after the centrifugal force field is removed.

4. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, In the precursor slurry preparation step, the average particle size of the titanium hydride powder is 2 to 3 micrometers, and the amount added is 0.5% to 2.0% of the total solid mass in the precursor slurry. In the in-situ reaction sintering step, heating to the solid-liquid two-phase region includes controlling the temperature at 580 to 620 degrees Celsius. The titanium hydride powder decomposes the residual titanium component and undergoes a eutectic reaction with the surrounding aluminum-based powder, generating titanium-rich liquid phase microregions in situ at a temperature lower than the melting point of the aluminum-based powder.

5. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, In the yield stress-gated centrifugation step, the duration of the first stage is set to 30 to 60 seconds, and the duration of the second stage is set to 60 to 120 seconds; the transition from the first stage to the second stage adopts a linear acceleration mode, and the acceleration slope is controlled at 50g to 100g per second.

6. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, flakes - The average particle size D50 of silicon carbide powder is 30 to 50 micrometers, and the average particle size D50 of spherical aluminum-based powder is 5 to 10 micrometers; in the precursor slurry preparation step, the spherical aluminum-based powder is filled into the sheet-like... - The interlayer voids of silicon carbide powder form microstructural units with dense packing characteristics.

7. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, The heating and degreasing process in the in-situ reaction sintering step includes: heating to the range of 300 to 450 degrees Celsius at a rate of 2 to 5 degrees Celsius per minute in a vacuum environment below 10 Pa and holding at that temperature, and using the pyrolysis characteristics of the rheology modifier to construct microporous channels for hydrogen to escape.

8. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, In the in-situ reaction sintering step, the transient liquid phase is in the sheet-like... - A composite interface layer of titanium carbide and titanium aluminide with a thickness of 10 to 50 nanometers is formed on the surface of silicon carbide powder, connecting the aluminum-based powder and the sheet-like material. -Silicon carbide powder.

9. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, The yield stress-gated centrifugation step is performed in a vacuum centrifugal casting machine with constant temperature control; throughout the execution of the step procedure, the air pressure in the mold cavity is kept below 500 Pa, and the temperature of the precursor slurry is maintained between 20 and 30 degrees Celsius.

10. The method for preparing anisotropic silicon carbide aluminum-based materials by powder metallurgy according to claim 1, characterized in that, The precursor slurry preparation step also includes: preparing the flakes before dispersion. - Silicon carbide powder undergoes surface pretreatment, and silane coupling agents are used in sheet-like formations. - Organic functional groups are grafted onto the surface of silicon carbide powder.

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