A tantalum carbide-based composite coating for high-temperature crystal growth and a preparation method and application thereof

Abstract

This invention relates to a tantalum carbide-based composite coating for high-temperature crystal growth, its preparation method, and its application. The tantalum carbide-based composite coating includes: a high-temperature resistant substrate; a Ta2C buffer layer formed on the surface of the substrate; a gradient transition layer formed on the Ta2C buffer layer, the chemical composition of which gradually changes from Ta2C phase to TaC phase from bottom to top, with the C / Ta atomic ratio increasing in a gradient distribution within the layer; and a TaC main functional layer formed on the gradient transition layer. Compared with the prior art, this invention maintains the performance of the high-purity TaC main functional layer on the surface, eliminates stress failure caused by CTE mismatch, and also takes into account the interface requirements of different crystals (AlN / SiC).

Description

Technical Field

[0001] This invention relates to the field of semiconductor crystal growth technology, and in particular to a tantalum carbide-based composite coating for high-temperature crystal growth, its preparation method, and its application. Background Technology

[0002] Wide-bandgap semiconductor materials, such as aluminum nitride (AlN) and silicon carbide (SiC), have become ideal substrate materials for fabricating deep ultraviolet light-emitting diodes (LEDs), lasers, and high-power radio frequency devices due to their excellent properties such as wide bandgap and high thermal conductivity. Currently, high-quality AlN and SiC single crystals are mainly grown using the physical vapor transport (PVT) method at extremely high temperatures (e.g., approximately 2200°C). However, in this harsh growth environment, core thermal field components face severe challenges, specifically involving the material's high-temperature resistance, corrosion resistance, and thermal matching performance.

[0003] In terms of high-temperature resistance and corrosion resistance, commonly used materials such as graphite easily release carbon impurities at high temperatures, contaminating the crystals and being corroded by growth vapors. Tungsten (W) is a preferred substrate material due to its high melting point (approximately 3410°C) and low vapor pressure; however, pure tungsten still reacts slowly with growth vapors at high temperatures, and there is a risk of grain boundary impurity diffusion. To protect the tungsten substrate, the industry typically deposits a tantalum carbide (TaC) coating on its surface. However, the coefficient of thermal expansion (CTE) of tungsten is approximately 4.5 × 10⁻⁶. -6 / K, while the CTE of the TaC coating is approximately 6.5–7.5 × 10⁻⁶. -6 / K, and there is a significant difference between the two. During the cooling process from the deposition temperature or growth temperature (above 2000℃) to room temperature, the huge difference in CTE can cause extremely high tensile stress within the coating, leading to coating cracking, peeling, and even seed crystal detachment, severely restricting device reliability and performance. Therefore, the material compatibility and durability issues of thermal field components under high-temperature growth environments urgently need to be addressed in existing technologies.

[0004] Patent publication number CN120555943A discloses a tantalum-tungsten alloy material with a tantalum carbide infiltration layer and its preparation method. The tantalum-tungsten alloy material with the tantalum carbide infiltration layer includes a tantalum-tungsten alloy substrate and a tantalum carbide infiltration layer. The tantalum carbide infiltration layer is bonded to the surface of the tantalum-tungsten alloy substrate and includes a TaC phase and a Ta2C phase. The surface of the tantalum-tungsten alloy substrate has two infiltration layers, one dominated by Ta2C and the other by TaC and Ta2C. However, the disclosed technology is an in-situ carburizing modification technique. The coating formation depends on the natural diffusion of carbon atoms into the tantalum-tungsten alloy substrate and consumes tantalum elements within the substrate to generate tantalum carbide in situ. This results in the coating being severely constrained by the substrate composition and forming an uncontrollable TaC / Ta2C mixed phase. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art by providing a tantalum carbide-based composite coating for high-temperature crystal growth, its preparation method and application, which maintains the performance of the high-purity TaC main functional layer on the surface, eliminates stress failure caused by CTE mismatch, and takes into account the interface requirements of different crystals (AlN / SiC).

[0006] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a tantalum carbide-based composite coating for high-temperature crystal growth, comprising: High-temperature resistant substrate; A tantalum carbide (Ta2C) buffer layer formed on the surface of the substrate; The gradient transition layer formed on the Ta2C buffer layer has a chemical composition that gradually changes from Ta2C phase to TaC phase from bottom to top, and the carbon / tantalum (C / Ta) atomic ratio in the layer increases in a gradient. And the TaC main functional layer formed on the gradient transition layer.

[0007] Furthermore, the thickness of the substrate is less than 5 mm, the thickness of the Ta2C buffer layer is less than 30 μm, the thickness of the gradient transition layer is less than 50 μm, and the thickness of the TaC main functional layer is less than 100 μm.

[0008] Furthermore, the CTE of the gradient transition layer varies with a gradient along its thickness direction; The CTE transition from the Ta2C buffer layer to the gradient transition layer to the TaC main functional layer is continuous and smooth.

[0009] Furthermore, the phase structure of the gradient transition layer sequentially includes: a phase region dominated by Ta2C, a two-phase region where Ta2C and TaC coexist, and a phase region dominated by TaC.

[0010] Furthermore, the substrate is made of tungsten (W), W alloy, molybdenum (Mo), Mo alloy, graphite, or C / C composite material.

[0011] Furthermore, the coefficient of thermal expansion of the tungsten substrate is 4.5 × 10⁻⁶. -6 / K; The coefficient of thermal expansion of tungsten / molybdenum alloy substrates is typically between 4.0 and 6.0 × 10⁻⁶. -6 / K.

[0012] Furthermore, the coefficient of thermal expansion of the Ta2C buffer layer is 4.5–5.5 × 10⁻⁶. -6 The thermal expansion coefficient of the TaC main functional layer is 6.5–7.5 × 10⁻⁶ K. -6 / K.

[0013] Furthermore, the substrate includes a planar substrate or a complex curved surface substrate.

[0014] Furthermore, the tantalum carbide-based composite coating also includes a surface modification layer formed on the TaC main functional layer, wherein the surface modification layer is at least one of an Al-containing tantalum carbide solid solution layer, an Al-Ta-CN compound layer, a highly dense TaC layer, or a TaC layer with a specific crystal orientation.

[0015] The second technical solution of the present invention provides a method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, which employs a chemical vapor deposition (CVD) process and includes the following steps: S1. Deposition of Ta2C buffer layer: The substrate is placed in the CVD reaction chamber, vacuumed and heated to the deposition temperature, and C source gas, Ta source gas and reducing gas are introduced into the CVD reaction chamber. A Ta2C buffer layer is deposited on the substrate cladding surface. At this time, the C / Ta atom ratio in the reaction atmosphere is the first value. S2. Gradient transition layer deposition: The flow rate of the C source gas is dynamically adjusted so that the C / Ta atomic ratio in the reaction atmosphere increases gradually from the first ratio to the second ratio, thereby depositing a gradient transition layer on the surface of the Ta2C buffer layer, in which the chemical composition gradually changes from Ta2C phase to TaC phase from bottom to top. S3. Deposition of TaC main functional layer: Adjust the flow rate of the C source gas so that the C / Ta atomic ratio in the reaction atmosphere is maintained at the second ratio value, and deposit TaC main functional layer on the surface of the gradient transition layer.

[0016] Further, in steps S1 to S3, the first ratio is 4 to 5, the second ratio is 6 to 8, and the second ratio is preferably 6.8 to 7.6; In step S2, the C / Ta atomic ratio in the reaction atmosphere increases linearly or non-linearly from a first ratio to a second ratio.

[0017] Furthermore, the rate of linear increase in the C / Ta atomic ratio in the reaction atmosphere is 0.1–5 h⁻¹. -1 Preferably 0.5~2 h -1 .

[0018] Furthermore, when the C / Ta atomic ratio in the reaction atmosphere is nonlinear, the nonlinearity increases in a manner including power function, exponential function, or logarithmic function.

[0019] Furthermore, when using a power function, the relationship conforms to C(t) = A + B × (t / T0). nWhere C(t) is the volume concentration of the carbon source gas at time t; t is the real-time time of gradient layer deposition, ranging from 0 ≤ t ≤ T0; A is the initial concentration, corresponding to the growth environment of the Ta2C enriched phase, preferably ranging from 1.0% to 1.3%; B is the total increase in concentration, preferably ranging from 0.4% to 0.8%; T0 is the total deposition time of the gradient transition layer, preferably ranging from 60 to 240 minutes; n is the power exponent, and the value of n can be set from 1.5 ≤ n ≤ 4.0. When n = 2, it is parabolic.

[0020] Furthermore, if it is necessary to further extend the thickness of the low-stress Ta2C enrichment zone near the substrate, an exponential function-type increasing method can be used, with the governing equation being: C(t) = A + B × The definitions and value ranges of A, B, t, and T0 are the same as those of the power function type mentioned above, and k is a shape factor characterizing the curvature of the curve, with a value range of 1≤k≤5. In this form, the concentration increases slowly in the early stages of deposition and rapidly increases in the late stages.

[0021] Furthermore, if it is necessary to transition the coating to the TaC functional layer earlier to increase the thickness of the surface corrosion-resistant layer, a logarithmic function-based increasing method can be adopted. The governing equation is: C(t) = A + B × (t / T0)¹ / m, where the definitions and ranges of A, B, t, and T0 are the same as those of the power function-based method described above, and m is preferably 2 ≤ m ≤ 3. This method results in a rapid increase in concentration during the initial deposition phase, followed by a stabilization phase.

[0022] Further, in steps S1 to S3, the C source gas is one or more of methane (CH4), ethylene (C2H4), and ethane (C2H6), preferably C2H4; The Ta source gas is tantalum pentachloride (TaCl5) and / or tantalum pentafluoride (TaF5) gas; The reducing gas is hydrogen (H2); The deposition temperature is 900–1100℃, preferably 900–1000℃; the deposition pressure is 50–100 mbar, preferably 60–80 mbar.

[0023] Furthermore, the process of introducing the Ta source gas is as follows: heating the Ta source powder to sublimate it into vapor, and then carrying it into the CVD reaction chamber through a carrier gas.

[0024] Furthermore, the heating temperature is 100–150°C, preferably 120–140°C. At this temperature, the Ta source powder undergoes controlled sublimation to generate stable precursor vapor, which ensures a sufficient deposition rate and avoids flow fluctuations caused by powder melting. The carrier gas is argon.

[0025] Furthermore, the composition of the reaction gas in the CVD reaction chamber, by volume percentage concentration, is: 0.4%–0.6% Ta source gas, 1.0%–1.4% C source gas, 20%–30% carrier gas, and the remainder is reducing gas.

[0026] Furthermore, in steps S1 to S3, hydrogen chloride (HCl) gas is introduced into the CVD reaction chamber at a volume percentage concentration of 1.0% to 1.5%. The introduction of HCl gas can suppress the generation of powdery byproducts in the gas phase, thereby obtaining a dense TaC main functional layer with few defects.

[0027] Furthermore, it also includes step S4, surface modification layer deposition: Stop the flow of C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, and perform in-situ aluminization modification on the TaC main functional layer to obtain an Al-containing tantalum carbide solid solution layer. Alternatively, stop the introduction of the C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, and perform in-situ aluminization modification on the TaC main functional layer to obtain an Al-containing tantalum carbide solid solution layer. Then, introduce N source gas to transform the Al-containing tantalum carbide solid solution layer into an Al-Ta-CN compound layer, a highly compacted TaC layer, or a TaC layer with a specific crystal orientation. The reaction temperature is 1000~1200℃, and the reaction time is 10~60min; the volume percentage concentration of the Al source is 0.5%~1.0%, and the Al source gas includes one or more of aluminum chloride (AlCl3) gas, trimethylaluminum (TMA) gas, or aluminum vapor; The volume percentage concentration of the N source gas is 5.0% to 12.0%, and the N source gas includes NH3 and / or N2; Further, in step S1, the substrate is pretreated. The pretreatment process is as follows: the substrate is cut and its surface is polished, then cleaned with a cleaning solution, and then dried for later use.

[0028] Furthermore, the cleaning solution is acetone and / or anhydrous ethanol.

[0029] The third technical solution of the present invention is to provide an application of a tantalum carbide-based composite coating for high-temperature crystal growth, wherein the tantalum carbide-based composite coating is used as a core thermal field component in the field of high-temperature crystal growth.

[0030] Furthermore, the core thermal field component includes one or more of the following: a growth crucible, a crucible cover, a seed crystal holder, a flow guide tube, or a heater.

[0031] Furthermore, high-temperature crystal growth includes the growth of AlN, SiC, GaN, diamond, or BN crystals.

[0032] Compared with the prior art, the present invention has the following advantages: (1) Based on traditional CVD technology, this invention creatively constructs a gradient transition layer with continuous and gradual changes in chemical composition and phase structure between the Ta2C buffer layer and the TaC main functional layer by precisely and dynamically controlling the C / Ta atomic ratio in the reaction gas. This achieves a smooth transition of the material's CTE from the substrate to the surface, thereby significantly reducing the thermal stress accumulated at the interface due to CTE mismatch and fundamentally improving the coating's resistance to cracking and peeling under thermal cycling.

[0033] (2) Through subsequent in-situ surface aluminization (and optional nitriding) modification processes, this invention further enhances the density, hardness, and chemical stability of the coating surface while ensuring the excellent intrinsic properties of the TaC main functional layer. This results in a composite coating that possesses excellent interfacial bonding strength, outstanding thermal shock resistance, and high compatibility and adaptability to high-temperature crystal growth environments (such as the high-temperature and corrosive atmosphere required for AlN and SiC growth).

[0034] (3) The crystal growth environment is usually above 2000℃~2200℃. The thermal expansion coefficient of tungsten, molybdenum or graphite substrates differs greatly from that of the pure TaC functional layer on the surface. In extreme high-temperature environments, this mismatch in thermal expansion coefficients will generate huge thermal stress at the interface between the coating and the substrate, eventually leading to coating cracking or even large-area peeling. The thermal expansion coefficient of Ta2C is between that of the substrate and TaC. Depositing pure Ta2C as the first layer on the substrate can play a stress buffering role. By continuously adjusting the flow ratio of carbon source and tantalum source gas over time during the CVD process (C / Ta ratio increases from small to large), a continuous solid solution / mixed phase gradient layer is deposited, with Ta2C gradually decreasing and TaC gradually increasing. This makes the thermal expansion coefficient inside the coating present a smooth upward curve, eliminating the thermal stress concentration points caused by abrupt changes in the physical interface. This solves the problem of coating cracking and peeling.

[0035] (4) The TaC coating surface is relatively smooth and chemically inert, making it difficult for seed crystals to form strong chemical bonds on the coating. Seed crystals are easily detached due to gravity or airflow disturbances. This invention introduces Al source gas (or further introduces N source gas) at high temperature, causing aluminum atoms to diffuse into the TaC surface lattice, forming an extremely thin aluminum-rich bonding layer or further forming an Al-Ta-N transition thin layer. Microscopically, this increases the surface's chemical activity and roughness, enabling the seed crystals to form strong chemical covalent bonds with the modified layer, thus ensuring that the seed crystals do not detach under high temperature and the scouring of growth steam.

[0036] (5) This invention forces the deposition of a coating with a gradually changing composition by adjusting the C / Ta ratio, which can be used on different substrates. The tantalum source in this invention is entirely derived from an external mixed gas; the tungsten alloy substrate itself does not participate in any chemical reaction, only providing a surface for gas crystallization. This invention employs chemical vapor deposition, the principle of which is the stacking and crystallization after a chemical vapor reaction. Both carbon and tantalum elements originate entirely from the external reactant gas; the substrate does not participate in the reaction. This makes the coating composition completely independent of the substrate composition. The coating dynamically changes by adjusting the C / Ta atomic ratio, directly depositing a composite coating with continuously varying composition and a designable structure. It can be dynamically adjusted according to the thermal expansion coefficient of different substrates, achieving customized coating performance and broad applicability. Attached Figure Description

[0037] Figure 1 The diagram shown is a schematic diagram of the hierarchical structure of the tantalum carbide-based composite coating shown in Embodiment 1 of the present invention (not drawn to scale). Figure 2 This is a simulation diagram of the cross-sectional thermal stress distribution of the tantalum carbide-based composite coating in Embodiment 1 of the present invention; Figure 3 The diagram shown is a schematic diagram of the tantalum carbide-based composite coating layer structure shown in Embodiment 2 of the present invention (not drawn to scale). Figure 4 This is a simulation diagram of the cross-sectional thermal stress distribution of the tantalum carbide-based composite coating in Example 3 of the present invention; Figure 5 The simulation diagram shows the cross-sectional thermal stress distribution of the tantalum carbide-based composite coating in Comparative Example 1. Figure 6 The image shows a simulation of the cross-sectional thermal stress distribution of the tantalum carbide-based composite coating in Comparative Example 2.

[0038] Explanation of markings in the diagram: 1-Substrate, 2-Ta2C buffer layer, 3-Gradient transition layer, 4-TaC main functional layer, 5-Surface modification layer. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0040] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0041] A tantalum carbide-based composite coating for high-temperature crystal growth, comprising: High-temperature resistant substrate 1; A tantalum carbide (Ta2C) buffer layer 2 is formed on the surface of the substrate; The gradient transition layer 3 formed on the Ta2C buffer layer 2 has a chemical composition that gradually changes from Ta2C phase to TaC phase from bottom to top, and the carbon / tantalum (C / Ta) atomic ratio in the layer increases in a gradient. And the TaC main functional layer 4 formed on the gradient transition layer 3.

[0042] In some specific embodiments, the thickness of the substrate 1 is less than 5 mm, the thickness of the Ta2C buffer layer 2 is less than 30 μm, the thickness of the gradient transition layer 3 is less than 50 μm, and the thickness of the TaC main functional layer 4 is less than 100 μm.

[0043] In some specific embodiments, the CTE of the gradient transition layer 3 varies with a gradient along its thickness direction; The CTE transition from the Ta2C buffer layer 2 to the gradient transition layer 3 to the TaC main functional layer 4 is continuous and smooth.

[0044] In some specific embodiments, the phase structure of the gradient transition layer 3 sequentially includes: a phase region dominated by Ta2C, a two-phase region where Ta2C and TaC coexist, and a phase region dominated by TaC.

[0045] In some specific embodiments, the substrate 1 is made of tungsten (W), W alloy, molybdenum (Mo), Mo alloy, graphite, or C / C composite material.

[0046] In some specific embodiments, the coefficient of thermal expansion of the tungsten substrate 1 is 4.5 × 10⁻⁶. -6 / K; The coefficient of thermal expansion of tungsten alloy / molybdenum alloy substrates (such as W-Mo, W-Re, TZM molybdenum alloys, etc.) is typically between 4.5 and 6.0 × 10⁻⁶. -6 / K; The coefficient of thermal expansion of high-purity graphite isostatically pressed graphite substrate is typically between 4.0 and 6.0 × 10⁻⁶. -6 / K.

[0047] The coefficient of thermal expansion of the Ta2C buffer layer 2 is 4.5–5.5 × 10⁻⁶. -6 The thermal expansion coefficient of the TaC main functional layer 4 and the Ta2C buffer layer 2 is 4.5~5.5×10. -6 / K, the thermal expansion coefficient of the TaC main functional layer 4 is 6.5~7.5×10. -6 / K.

[0048] The coefficient of thermal expansion of the Ta2C buffer layer 2 is 4.5–5.5 × 10⁻⁶. -6 / K,TaC main functional layer 4 thermal The substrate 1 includes a planar substrate or a complex curved surface substrate.

[0049] The coefficient of thermal expansion of the Ta2C buffer layer 2 is 4.5–5.5 × 10⁻⁶. -6 / K, The tantalum carbide-based composite coating of the TaC main functional layer 4 further includes a surface modification layer 5 formed on the TaC main functional layer 4. The surface modification layer 5 is at least one of the following: an Al-containing tantalum carbide solid solution layer, an Al-Ta-CN compound layer, a highly dense TaC layer, or a TaC layer with a specific crystal orientation.

[0050] A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a chemical vapor deposition (CVD) process, includes the following steps: S1, Ta2C buffer layer 2 deposition: The substrate 1 is placed in the CVD reaction chamber, vacuumed and heated to the deposition temperature, and C source gas, Ta source gas and reducing gas are introduced into the CVD reaction chamber. A Ta2C buffer layer 2 is deposited on the cladding surface of the substrate 1. At this time, the C / Ta atom ratio in the reaction atmosphere is the first value. S2, Gradient transition layer 3 deposition: The flow rate of the C source gas is dynamically adjusted so that the C / Ta atomic ratio in the reaction atmosphere increases gradually from the first ratio to the second ratio, thereby depositing a gradient transition layer 3 on the surface of the Ta2C buffer layer 2, in which the chemical composition gradually changes from Ta2C phase to TaC phase from bottom to top. S3, TaC main functional layer 4 deposition: Adjust the flow rate of the C source gas so that the C / Ta atomic ratio in the reaction atmosphere is maintained at the second ratio value, and deposit the TaC main functional layer 3 on the surface of the gradient transition layer 3.

[0051] In some specific embodiments, in steps S1 to S3, the first ratio is 4 to 5, the second ratio is 6 to 8, and the second ratio is preferably 6.8 to 7.6; In step S2, the C / Ta atomic ratio in the reaction atmosphere increases linearly or non-linearly from a first ratio to a second ratio.

[0052] In some specific embodiments, the rate of linear growth of the C / Ta atomic ratio in the reaction atmosphere is 0.1~5 h. -1 Preferably 0.5~2 h -1 .

[0053] In some specific embodiments, when the C / Ta atomic ratio in the reaction atmosphere is nonlinear, the nonlinearity increases in a manner including power function, exponential function, or logarithmic function.

[0054] In some specific embodiments, when a power function is used, the relationship conforms to C(t) = A + B × (t / T0).n Where C(t) is the volume concentration of the carbon source gas at time t; t is the real-time time of gradient layer deposition, ranging from 0 ≤ t ≤ T0; A is the initial concentration, corresponding to the growth environment of the Ta2C enriched phase, preferably ranging from 1.0% to 1.3%; B is the total increase in concentration, preferably ranging from 0.4% to 0.8%; T0 is the total deposition time of the gradient transition layer, preferably ranging from 60 to 240 minutes; n is the power exponent, and the value of n can be set from 1.5 ≤ n ≤ 4.0. When n = 2, it is parabolic.

[0055] In some specific embodiments, if it is necessary to further extend the thickness of the low-stress Ta2C enrichment region near the substrate, an exponential function-type increment can be used, with the governing equation being: C(t) = A + B × The definitions and value ranges of A, B, t, and T0 are the same as those of the power function type mentioned above, and k is a shape factor characterizing the curvature of the curve, with a value range of 1≤k≤5. In this form, the concentration increases slowly in the early stages of deposition and rapidly increases in the late stages.

[0056] In some specific embodiments, if it is necessary to transition the coating to the TaC functional layer earlier to increase the thickness of the surface corrosion-resistant layer, a logarithmic function-type incremental approach can be adopted, with the governing equation being: C(t) = A + B × (t / T0)¹ / m, where the definitions and value ranges of A, B, t, and T0 are the same as those of the power function type described above, and m is preferably 2 ≤ m ≤ 3. This form results in a rapid increase in concentration during the initial deposition phase, followed by a stabilization phase.

[0057] In some specific embodiments, in steps S1 to S3, the C source gas is one or more of methane (CH4), ethylene (C2H4), and ethane (C2H6), preferably C2H4; The Ta source gas is tantalum pentachloride (TaCl5) and / or tantalum pentafluoride (TaF5) gas; The reducing gas is hydrogen (H2); The deposition temperature is 900–1100℃, preferably 900–1000℃; the deposition pressure is 50–100 mbar, preferably 60–80 mbar.

[0058] In some specific embodiments, the process of introducing the Ta source gas is as follows: heating the Ta source powder to sublimate it into vapor, and then carrying it into the CVD reaction chamber through a carrier gas.

[0059] In some specific embodiments, the heating temperature is 100-150°C, preferably 120-140°C. At this temperature, the Ta source powder undergoes controlled sublimation to generate stable precursor vapor, which ensures a sufficient deposition rate and avoids flow fluctuations caused by powder melting. The carrier gas is argon.

[0060] In some specific embodiments, the composition of the reaction gas in the CVD reaction chamber, by volume percentage concentration, is: 0.4%–0.6% Ta source gas, 1.0%–1.4% C source gas, 20%–30% carrier gas, and the balance is reducing gas.

[0061] In some specific embodiments, in steps S1 to S3, hydrogen chloride (HCl) gas is also introduced into the CVD reaction chamber, with a volume percentage concentration of 1.0% to 1.5%. The introduction of HCl gas can suppress the generation of powdery byproducts in the gas phase, thereby obtaining a dense TaC main functional layer 4 with few defects.

[0062] In some specific embodiments, step S4, deposition of surface modification layer 5, is also included: Stop the flow of C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, and perform in-situ aluminization modification on the TaC main functional layer 4 to obtain an Al-containing tantalum carbide solid solution layer. Alternatively, stop the introduction of the C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, and perform in-situ aluminization modification on the TaC main functional layer 4 to obtain an Al-containing tantalum carbide solid solution layer. Then, introduce N source gas to transform the Al-containing tantalum carbide solid solution layer into an Al-Ta-CN compound layer, a highly dense TaC layer, or a TaC layer with a specific crystal orientation. The reaction temperature is 1000~1200℃, and the reaction time is 10~60min; the volume percentage concentration of the Al source is 0.5%~1.0%, and the Al source gas includes one or more of aluminum chloride (AlCl3) gas, trimethylaluminum (TMA) gas, or aluminum vapor; The volume percentage concentration of the N source gas is 5.0% to 12.0%, and the N source gas includes NH3 and / or N2; In some specific embodiments, in step S1, the substrate 1 is pretreated. The pretreatment process is as follows: the substrate 1 is cut and its surface is polished, then cleaned with a cleaning solution, and then dried for later use.

[0063] In some specific embodiments, the cleaning solution is acetone and / or anhydrous ethanol. Thirdly, it provides an application of a tantalum carbide-based composite coating for high-temperature crystal growth, wherein the tantalum carbide-based composite coating is used as a core thermal field component in the field of high-temperature crystal growth.

[0064] In some specific embodiments, the core thermal field component includes one or more of the following: a growth crucible, a crucible cover, a seed crystal holder, a flow guide tube, or a heater.

[0065] In some specific embodiments, high-temperature crystal growth includes the growth of AlN, SiC, GaN, diamond, or BN crystals.

[0066] Each of the above embodiments can be implemented individually or in any combination of two or more.

[0067] The following description uses specific examples to illustrate the point.

[0068] Example 1 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten substrate with a diameter of 50 mm and a thickness of 3 mm and a purity of 99.9% was selected as substrate 1. The surface of the tungsten substrate 1 was ground and polished to achieve a surface roughness Ra < 0.2 mm. Subsequently, substrate 1 was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed, dried with high-purity nitrogen, and placed in a 100°C oven for later use.

[0069] (2) Deposition of Ta2C buffer layer 2 The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to its ultimate vacuum, the deposition zone was heated to 950°C, and the pressure was maintained at a stable 60 mbar. A thermostatic evaporator containing solid tantalum pentachloride (TaCl5) powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar at a flow rate of 500 sccm as the carrier gas. Simultaneously, C2H4, HCl, and H2 were introduced. During this stage, the volume percentage concentrations of each reactant gas were precisely controlled as follows: TaCl5 approximately 0.5%, C2H4 approximately 1.2%, HCl approximately 1.2%, Ar approximately 25%, with the balance being H2. At this point, the C / Ta atomic ratio was approximately 4.8. The deposition time was 2 hours, forming a dense Ta2C2 buffer layer with a thickness of approximately 15 mm on the surface of the tungsten substrate 1.

[0070] (3) Gradient transition layer 3 deposition The deposition temperature (950℃) and pressure (60 mbar) were kept constant. During the next 2 hours of deposition, the flow rates of TaCl5, HCl, Ar, and H2 were kept constant, while the flow rate of C2H4 was dynamically adjusted linearly to gradually increase its volume concentration from 1.2% to 1.7% (i.e., the C / Ta atomic ratio linearly transitioned from 4.8 to 6.8). During this process, the chemical composition of the coating gradually transitioned from Ta2C to TaC, forming a gradient transition layer 3 with a thickness of approximately 20 mm.

[0071] (4) Deposition of TaC main functional layer 4 After gradient layer deposition, the C2H4 flow rate was stabilized. At this point, the gas volume percentage concentration was approximately: TaCl5 0.5%, C2H4 1.7%, HCl 1.2%, Ar 25%, with the balance being H2. The C / Ta ratio was approximately 6.8. Deposition continued for 4 hours under these conditions, resulting in the growth of a TaC functional layer with a thickness of approximately 40 mm on the gradient layer surface.

[0072] like Figure 1 The diagram shown is a schematic representation of the layer structure of the tantalum carbide-based composite coating according to Embodiment 1 of the present invention (not drawn to scale). The tantalum carbide-based composite coating includes: a high-temperature resistant substrate 1; a tantalum carbide (Ta2C) buffer layer 2 formed on the surface of the substrate; a gradient transition layer 3 formed on the Ta2C buffer layer 2, the chemical composition of which gradually changes from Ta2C phase to TaC phase from bottom to top, and the carbon / tantalum (C / Ta) atomic ratio in the layer increases in a gradient; and a TaC main functional layer 4 formed on the gradient transition layer 3.

[0073] Figure 2 The image shows a simulation of the cross-sectional thermal stress distribution of the tantalum carbide-based composite coating in Example 1 after preparation and cooling to room temperature. Due to the composition and structural gradient design formed by dynamically adjusting the C / Ta atomic ratio, the thermal stress in the coating cross-section (especially at the interfaces of each layer) exhibits a smooth and continuous distribution characteristic with no obvious stress abrupt peaks. This confirms that the gradient structure can effectively alleviate the stress concentration at the interface, thereby ensuring the overall bonding reliability of the coating and significantly reducing the risk of interface cracking.

[0074] The tantalum carbide-based composite coating obtained in Example 1 was used as a seed crystal holder in the field of high-temperature crystal growth. Before growing AlN high-temperature crystals, the seed crystal needs to be fixed on the seed crystal holder prepared in Example 1. The specific bonding steps are as follows: (1) Cleaning and drying: The seed crystal holder and the seed crystal are placed in anhydrous ethanol and deionized water respectively for ultrasonic cleaning for 15 minutes each to remove surface oil and particles, and then dried in a vacuum oven at 120℃ for later use. (2) Apply adhesive: Apply a layer of high-temperature adhesive (such as phenolic resin) evenly to the coating of the seed crystal holder. (3) Adhesion and compaction: Adhere the non-growth surface of the seed crystal to the surface of the seed crystal holder coated with adhesive, gently rotate and press to remove air bubbles at the interface, and ensure that the seed crystal and the coating surface are completely adhered without macroscopic gaps; (4) Curing and high-temperature carbonization: Place the bonded seed crystal holder assembly in a vacuum curing oven and keep it at 150~200℃ for 2 hours to allow the resin to crosslink and cure; then gradually raise the temperature to 800~1000℃ under the protection of inert gas (such as argon or nitrogen) for treatment.

[0075] (5) Crucible assembly: Place the seed crystal holder with the seed crystal attached above on the top of the crystal growth crucible (such as a high-purity graphite crucible or a tungsten crucible), so that the growth surface of the seed crystal is facing down and suspended directly opposite the high-purity powder raw material area at the bottom of the crucible.

[0076] The tantalum carbide-based composite coating prepared in this invention is used as a seed crystal holder in the high-temperature physical vapor transport (PVT) growth of wide-bandgap semiconductors. After undergoing long-term vapor sublimation growth at extremely high temperatures (typically above 2000°C) and subsequent cooling thermal shock cycles, this invention demonstrates significantly superior practical application performance compared to existing technologies, specifically in the following two core aspects: First, in existing technologies, seed crystal holders with conventional single-layer coatings are prone to interfacial stress concentration during drastic temperature rises and falls due to the large mismatch in the coefficient of thermal expansion (CTE) between the coating and the substrate. This leads to large-area cracking of the coating or peeling off from the substrate. This directly causes severe warping of the seed crystals bonded to them, or even causes them to fall to the bottom of the crucible, resulting in direct scrapping of the crystal growth process. In contrast, the seed crystal holder of this invention benefits from the excellent thermal stress buffering effect of its internal Ta2C-TaC gradient transition layer 3, ensuring that the seed crystal remains firmly attached to the substrate throughout the crystal growth cycle, greatly improving the success rate and yield of the high-temperature crystal growth process.

[0077] Secondly, in existing technologies, due to the intense thermal corrosion under high-temperature thermal fields, the surface of conventional seed crystal holders is easily damaged and cannot effectively block the diffusion of elements from the substrate (such as metallic tungsten impurities, free carbon, etc.) into the high-temperature growth region, resulting in severe impurity contamination inside the crystal, which in turn leads to high-density lattice dislocations and microcracks. The outermost high-purity dense TaC functional layer 4 of this invention can effectively resist the erosion of high-temperature active gas flow and also cut off the channels for substrate impurities to diffuse outward.

[0078] Example 2 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten sheet with a diameter of 50 mm and a thickness of 3 mm was selected as substrate 1. The surface of the tungsten substrate 1 was ground and polished to achieve a surface roughness Ra < 0.2 mm. Subsequently, substrate 1 was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed, dried with high-purity nitrogen, and placed in a 100°C oven for drying.

[0079] (2) Deposition of Ta2C buffer layer 2 The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to the ultimate vacuum level, the deposition zone was heated to 950°C and the pressure was kept stable at 60 mbar. A constant-temperature evaporator containing solid TaCl5 powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar with a flow rate of 500 sccm as the carrier gas. C2H4, HCl and H2 were introduced at the same time. During this stage, the volume percentage concentration of each reaction gas was precisely controlled as follows: TaCl5 about 0.5%, C2H4 about 1.2%, HCl about 1.2%, Ar about 25%, and the balance was H2. At this time, the C / Ta atomic ratio was about 4.8. The deposition time was 2 hours, and a dense Ta2C2 buffer layer with a thickness of about 15 mm was formed on the surface of the tungsten substrate (1).

[0080] (3) Gradient transition layer 3 deposition The deposition temperature (950℃) and pressure (60 mbar) were kept constant. During the next 2 hours of deposition, the flow rates of TaCl5, HCl, Ar, and H2 were kept constant, while the flow rate of C2H4 was dynamically adjusted linearly to gradually increase its volume concentration from 1.2% to 1.7% (i.e., the C / Ta atomic ratio linearly transitioned from 4.8 to 6.8). During this process, the chemical composition of the coating gradually transitioned from Ta2C to TaC, forming a gradient transition layer 3 with a thickness of approximately 20 mm.

[0081] (4) Deposition of TaC main functional layer 4 After gradient layer deposition, the C2H4 flow rate was stabilized. At this point, the gas volume percentage concentration was approximately: TaCl5 0.5%, C2H4 1.7%, HCl 1.2%, Ar 25%, with the balance being H2. The C / Ta ratio was approximately 6.8. Deposition continued for 4 hours under these conditions, resulting in the growth of a TaC functional layer with a thickness of approximately 40 mm on the gradient layer surface.

[0082] (5) Surface modification layer 5 deposition The supply of TaCl5 and C2H4 was cut off, while maintaining an H2 and Ar atmosphere. The reaction chamber temperature was raised to 1100℃. Gaseous AlCl3 was introduced to perform in-situ aluminization modification treatment on the TaC surface for 30 minutes. After the treatment, the furnace was slowly cooled to room temperature to obtain surface modification layer 5, which is an Al-containing tantalum carbide solid solution layer.

[0083] like Figure 3The diagram shown is a schematic representation of the layer structure of the tantalum carbide-based composite coating according to Embodiment 2 of the present invention (not drawn to scale). The tantalum carbide-based composite coating includes: a high-temperature resistant substrate 1; a tantalum carbide (Ta2C) buffer layer 2 formed on the surface of the substrate; a gradient transition layer 3 formed on the Ta2C buffer layer 2, the chemical composition of which gradually changes from Ta2C phase to TaC phase from bottom to top, and the carbon / tantalum (C / Ta) atomic ratio in the layer increases in a gradient; a TaC main functional layer 4 formed on the gradient transition layer 3; and a surface modification layer 5 formed on the TaC main functional layer 4, wherein the surface modification layer 5 is an Al-containing tantalum carbide solid solution layer.

[0084] The tantalum carbide-based composite coating prepared in Example 2 of this invention, through the structural design of the Ta2C buffer layer 2 and the continuous gradient transition layer 3, constructs a continuous gradient of thermal expansion coefficients from the substrate to the surface within the coating system, achieving stepwise matching of thermal expansion performance. This effectively buffers and dissipates interfacial thermal stress, significantly improving the coating's resistance to cracking and peeling during high-temperature deposition and thermal cycling, ensuring the reliability of components under extreme thermal shock conditions. Furthermore, the continuous deposition of composition and phases achieved by dynamically adjusting the C / Ta atomic ratio enables atomic-scale diffusion bonding and strong chemical bonding between layers, fundamentally endowing the coating system with excellent interfacial bonding strength and overall structural integrity. In addition, the aluminization modification layer 5 on the surface introduces aluminum elements into the TaC lattice through high-temperature diffusion, forming a metallurgically bonded reinforced surface. This surface not only further improves the coating's density and chemical stability but also provides optimized interfacial conditions for the subsequent epitaxial growth of AlN, SiC, and other crystals, promoting uniform formation and adhesion of crystal nuclei. This effectively ensures the stability of seed crystal fixation during high-temperature crystal growth, preventing its displacement or detachment.

[0085] Example 3 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten sheet with a diameter of 50 mm and a thickness of 3 mm was selected as substrate 1. The surface of the tungsten substrate 1 was ground and polished to achieve a surface roughness Ra < 0.2 mm. Subsequently, substrate 1 was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed, dried with high-purity nitrogen, and placed in a 100°C oven for drying.

[0086] (2) Deposition of Ta2C buffer layer 2 The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to the ultimate vacuum level, the deposition zone was heated to 1000°C and the pressure was kept stable at 80 mbar. A constant-temperature evaporator containing solid TaCl5 powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar with a flow rate of 500 sccm as the carrier gas. C2H4, HCl and H2 were introduced at the same time. During this stage, the volume percentage concentration of each reaction gas was precisely controlled as follows: TaCl5 about 0.5%, C2H4 about 1.15%, HCl about 1.2%, Ar about 25%, and the balance was H2. At this time, the C / Ta atomic ratio was about 4.6. The deposition time was 2 hours, and a dense Ta2C buffer layer 2 with a thickness of about 15 mm was formed on the surface of the tungsten substrate (1).

[0087] (3) Gradient transition layer 3 deposition The deposition temperature (1000℃) and pressure (80 mbar) were kept constant. During the next 2 hours of deposition, the flow rates of TaCl5, HCl, Ar, and H2 were kept constant, while the flow rate of C2H4 was dynamically adjusted in a non-linear (parabolic) manner, causing its volume percentage concentration C(t)s to gradually increase from 1.15% to 1.7% over time t (minutes) according to a functional relationship (i.e., the C / Ta atomic ratio non-linearly transitioned from 4.6 to 6.8). During this process, the chemical composition of the coating gradually transitioned from Ta2C to TaC, forming a gradient transition layer 3 with a thickness of approximately 20 mm.

[0088] (4) Deposition of TaC main functional layer 4 After gradient layer deposition, the C2H4 flow rate was stabilized. At this point, the gas volume percentage concentrations were: TaCl5 approximately 0.5%, C2H4 approximately 1.7%, HCl approximately 1.2%, Ar approximately 25%, with the balance being H2. The C / Ta ratio was approximately 7.0. Deposition continued for 4 hours under these conditions, resulting in the growth of a TaC functional layer with a thickness of approximately 40 mm on the gradient layer surface.

[0089] (5) Surface modification layer 5 deposition The supply of TaCl5 and C2H4 was cut off, while maintaining an H2 and Ar atmosphere. The reaction chamber temperature was raised to 1100℃. Gaseous AlCl3 was introduced to perform in-situ aluminization modification treatment on the TaC surface for 30 minutes. After the treatment, the furnace was slowly cooled to room temperature to obtain surface modification layer 5, which is an Al-containing tantalum carbide solid solution layer.

[0090] This invention aims to further optimize the thermal stress distribution within the gradient transition layer by fine-tuning the deposition parameters and introducing nonlinear gradient variations. The coating prepared at 1000℃ and 80mbar is expected to maintain a dense microstructure comparable to that of Example 1, and possess excellent thermal shock resistance and interfacial adhesion, thus demonstrating that the gradient construction method proposed in this invention has good repeatability and universality within a reasonable process window.

[0091] Figure 4 The figure shows a simulation of the cross-sectional thermal stress distribution of the tantalum carbide composite coating in Example 3 (deposition using nonlinear parameters) after preparation and cooling to room temperature. As shown, due to the introduction of nonlinear dynamic adjustment of the C / Ta atomic ratio during vapor deposition, a nonlinear transition in composition and thermal expansion coefficient is formed within the coating. Compared to the linear stress ramp-up characteristic of Example 1, the thermal stress curve of Example 3 exhibits a smooth nonlinear arc transition within the gradient transition layer. Especially in the first half of the transition from the buffer layer to the gradient layer (Ta2C-rich side), the stress remains at a low level, and the stress accumulation rate slows down significantly. This confirms that the nonlinear gradient design further optimizes the spatial distribution of interlayer residual stress, making its overall stress release more gentle. This design further reduces the risk of stress concentration at the core interface.

[0092] Comparative Example 1 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten sheet with a diameter of 50 mm and a thickness of 3 mm was selected as substrate 1. The surface of the tungsten substrate 1 was ground and polished to achieve a surface roughness Ra < 0.2 mm. Subsequently, substrate 1 was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed, dried with high-purity nitrogen, and placed in a 100°C oven for drying.

[0093] (2) Deposition of TaC main functional layer 4 The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to its ultimate vacuum, the deposition zone was heated to 950°C, and the pressure was maintained at a stable 60 mbar. A constant-temperature evaporator containing solid TaCl5 powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar at a flow rate of 500 sccm as the carrier gas. Simultaneously, C2H4, HCl, and H2 were introduced. During this stage, the volume percentage concentrations of each reactant gas were precisely controlled as follows: TaCl5 approximately 0.5%, C2H4 approximately 1.8%, HCl approximately 1.2%, Ar approximately 25%, with the balance being H2. At this point, the C / Ta atomic ratio was approximately 7.2. The deposition time was 4 hours, forming a TaC functional layer with a thickness of approximately 40 mm on the surface of the tungsten substrate 1.

[0094] Figure 5 The figure shows a simulated cross-sectional thermal stress distribution after directly depositing the TaC main functional layer 4 on a tungsten substrate 1 under the condition of no gradient transition layer design, as shown in Comparative Example 1. As shown, at the interface between the tungsten substrate and the TaC coating (approximately 0.003 m on the horizontal axis), the thermal stress curve shows a significant and sharp increase, forming a sharp stress peak. This result indicates that due to the lack of a gradient buffer between composition and properties, there is a large thermal mismatch stress concentration at the interface, which can easily induce cracking or peeling of the coating from the substrate 1 during thermal cycling.

[0095] Because this comparative example lacks the Ta2C buffer layer 2 and gradient transition layer 3, a drastic abrupt change in the coefficient of thermal expansion occurs between the tungsten substrate 1 and the TaC main functional layer 4. Theoretically, during the cooling process from the deposition temperature of 950℃ to room temperature, a huge residual tensile stress far exceeding the material bonding strength will be generated at the interface. Therefore, it is expected that this single-layer coating will be highly susceptible to developing network microcracks or even macroscopic peeling due to stress release after preparation. If this inherently defective component is applied to a high-temperature crystal growth environment of 2200℃, the aforementioned cracks will become rapid corrosion channels for the high-temperature growth vapor, highly likely leading to complete coating failure and erosion damage to the tungsten substrate 1, thus completely failing to meet the requirements of long-cycle, high-stability crystal growth processes.

[0096] Comparative Example 2 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten sheet with a diameter of 50 mm and a thickness of 3 mm was selected as the substrate (1). The surface of the tungsten substrate (1) was ground and polished to make its surface roughness Ra < 0.2 mm. Subsequently, the substrate (1) was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed and dried with high-purity nitrogen gas, and placed in a 100°C oven for drying.

[0097] Gradient transition layer 3 deposition The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to its ultimate vacuum, the deposition zone was heated to 950°C, while maintaining a stable pressure of 60 mbar. A thermostatic evaporator containing solid TaCl5 powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar at a flow rate of 500 sccm as the carrier gas. Simultaneously, C2H4, HCl, and H2 were introduced. At this stage, the volume percentage concentrations of each reactant gas were precisely controlled as follows: TaCl5 approximately 0.5%, C2H4 approximately 1.2%, HCl approximately 1.2%, Ar approximately 25%, with the balance being H2. At this point, the C / Ta atomic ratio was approximately 4.8. The deposition temperature (950°C) and pressure (60 mbar) were kept constant. During the subsequent 2-hour deposition process, the flow rates of TaCl5, HCl, Ar, and H2 were kept constant, while the flow rate of C2H4 was dynamically adjusted in a linear manner, gradually increasing its volume concentration from 1.2% to 1.7% (i.e., the C / Ta atomic ratio linearly transitioned from 4.8 to 6.8). During this process, the chemical composition of the coating gradually transitioned from Ta2C to TaC, forming a gradient transition layer 3 with a thickness of approximately 20 mm.

[0098] Figure 6 The figure shows a simulation of the cross-sectional thermal stress distribution after directly depositing the gradient transition layer 3 on the tungsten substrate 1 in Comparative Example 2. As shown, after the pure Ta2C buffer layer was peeled off, although there was a compositional gradient within the coating, an extremely sharp residual stress abrupt peak still appeared at the interface between the substrate and the coating. This extreme stress concentration phenomenon indicates that without a pure Ta2C buffer layer with a low coefficient of thermal expansion as a stress-relieving base, the stress state at the interface will be severely deteriorated, and large-area peeling of the coating from the substrate surface is very likely to occur during actual high-temperature thermal shock cycling. The internal thermal stress of the coating in Comparative Example 2 is much higher than that of the coating in Example 2.

[0099] Comparative Example 3 A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth, employing a CVD process, includes the following steps: (1) Pretreatment of substrate 1 A high-purity tungsten sheet with a diameter of 50 mm and a thickness of 3 mm was selected as substrate 1. The surface of the tungsten substrate 1 was ground and polished to achieve a surface roughness Ra < 0.2 mm. Subsequently, substrate 1 was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, then removed, dried with high-purity nitrogen, and placed in a 100°C oven for drying.

[0100] (2) Deposition of Ta2C buffer layer 2 The pretreated tungsten substrate was placed in the central deposition zone of a hot-wall CVD reaction chamber. After evacuating the reaction chamber to its ultimate vacuum, the deposition zone was heated to 950°C, and the pressure was maintained at a stable 60 mbar. A constant-temperature evaporator containing solid TaCl5 powder was heated to 130°C, and the sublimated TaCl5 vapor was introduced into the reaction chamber using Ar at a flow rate of 500 sccm as the carrier gas. Simultaneously, C2H4, HCl, and H2 were introduced. During this stage, the volume percentage concentrations of each reactant gas were precisely controlled as follows: TaCl5 approximately 0.5%, C2H4 approximately 1.2%, HCl approximately 1.2%, Ar approximately 25%, with the balance being H2. At this point, the C / Ta atomic ratio was approximately 4.8. The deposition time was 2 hours, forming a dense Ta2C buffer layer 2 with a thickness of approximately 15 mm on the surface of the tungsten substrate 1.

[0101] When Ta2C buffer layer 2 is used as the outermost coating surface, a large number of gaseous tantalum atoms will precipitate on the Ta2C coating surface under high temperature and low pressure conditions, causing the coating to thin rapidly. The precipitated gaseous carbon atoms will drift to the seed crystal surface with the gas flow, causing uncontrollable metallic impurity contamination (such as tantalum inclusions) in the grown crystal. At the high temperature of crystal growth, secondary carbonization will inevitably occur on the surface to generate TaC, changing from a close-packed hexagonal structure to a face-centered cubic structure, producing huge lattice distortion and causing volume expansion. Ultimately, this leads to large-area cracking, warping, and peeling on the surface. Due to the instability of Ta2C, Ta2C buffer layer 2 cannot be used as the outermost coating surface. Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention are all within the scope of protection claimed by the present invention.

Claims

1. A tantalum carbide-based composite coating for high-temperature crystal growth, characterized in that, include: High-temperature resistant substrate (1); A Ta2C buffer layer (2) is formed on the surface of the substrate. The gradient transition layer (3) formed on the Ta2C buffer layer (2) has a chemical composition that gradually changes from Ta2C phase to TaC phase from bottom to top, and the C / Ta atomic ratio in the layer increases in a gradient. And the TaC main functional layer (4) formed on the gradient transition layer (3).

2. The tantalum carbide-based composite coating for high-temperature crystal growth according to claim 1, characterized in that, The thickness of the substrate (1) is less than 5 mm, the thickness of the Ta2C buffer layer (2) is less than 30 μm, the thickness of the gradient transition layer (3) is less than 50 μm, and the thickness of the TaC main functional layer (4) is less than 100 μm.

3. The tantalum carbide-based composite coating for high-temperature crystal growth according to claim 1, characterized in that, The CTE of the gradient transition layer (3) varies with gradient along its thickness direction; The CTE transition from the Ta2C buffer layer (2) to the gradient transition layer (3) to the TaC main functional layer (4) is continuous and smooth.

4. The tantalum carbide-based composite coating for high-temperature crystal growth according to claim 1, characterized in that, The substrate (1) is made of W, W alloy, Mo, Mo alloy, graphite or C / C composite material.

5. The tantalum carbide-based composite coating for high-temperature crystal growth according to claim 1, characterized in that, The tantalum carbide-based composite coating further includes a surface modification layer (5) formed on the TaC main functional layer (4), wherein the surface modification layer (5) is at least one of an Al-containing tantalum carbide solid solution layer, an Al-Ta-CN compound layer, a highly dense TaC layer, or a TaC layer with a specific crystal orientation.

6. A method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth as described in any one of claims 1 to 5, characterized in that, The CVD process includes the following steps: S1, Ta2C buffer layer (2) deposition: The substrate (1) is placed in the CVD reaction chamber, vacuumed and heated to the deposition temperature, and C source gas, Ta source gas and reducing gas are introduced into the CVD reaction chamber. A Ta2C buffer layer (2) is deposited on the substrate (1). At this time, the C / Ta atoms in the reaction atmosphere are the first ratio. S2, Gradient transition layer (3) deposition: The flow rate of the C source gas is dynamically adjusted so that the C / Ta atomic ratio in the reaction atmosphere increases from the first ratio to the second ratio, thereby depositing a gradient transition layer (3) on the surface of the Ta2C buffer layer (2) where the chemical composition gradually changes from Ta2C phase to TaC phase from bottom to top. S3, TaC main functional layer (4) deposition: Adjust the flow rate of the C source gas so that the C / Ta atomic ratio in the reaction atmosphere is maintained at the second ratio value, and deposit the TaC main functional layer (3) on the surface of the gradient transition layer (3).

7. The method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth according to claim 6, characterized in that, In steps S1 to S3, the first ratio is 4 to 5, and the second ratio is 6 to 8; In step S2, the C / Ta atomic ratio in the reaction atmosphere increases linearly or non-linearly from a first ratio to a second ratio.

8. The method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth according to claim 6, characterized in that, In steps S1 to S3, the C source gas is one or more of CH4, C2H4, and C2H6; The Ta source gas is TaCl5 and / or TaF5 gas; The reducing gas is H2; The deposition temperature is 900–1100℃, and the deposition pressure is 50–100 mbar.

9. The method for preparing a tantalum carbide-based composite coating for high-temperature crystal growth according to claim 6, characterized in that, It also includes step S4, deposition of the surface modification layer (5): Stop the flow of C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, and perform in-situ aluminization modification on the TaC main functional layer (4) to obtain an Al-containing tantalum carbide solid solution layer. Alternatively, stop the introduction of the C source gas and Ta source gas, increase the reaction temperature, introduce Al source gas, perform in-situ aluminization modification on the TaC main functional layer (4), obtain an Al-containing tantalum carbide solid solution layer, introduce N source gas, and convert the Al-containing tantalum carbide solid solution layer into an Al-Ta-CN compound layer, a highly dense TaC layer, or a TaC layer with a specific crystal orientation. The reaction temperature is 1000~1200℃, the volume percentage concentration of the Al source gas is 0.5%~1.0%, and the Al source gas includes one or more of AlCl3 gas, trimethylaluminum gas, or aluminum vapor; The volume percentage concentration of the N source gas is 5.0% to 12.0%, and the N source gas includes NH3 and / or N2.

10. The application of the tantalum carbide-based composite coating for high-temperature crystal growth as described in any one of claims 1 to 5, characterized in that, The tantalum carbide-based composite coating is used as a core thermal field component in the field of high-temperature crystal growth.

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