Spark plasma sintering preparation method of high-density fine-grain pure tantalum

Abstract

The invention discloses a spark plasma sintering preparation method of high-density fine-grain pure tantalum, and belongs to the technical field of preparation of refractory metal materials. According to the method, high-purity tantalum powder is sintered in SPS equipment under the technological conditions of 1350-1450 DEG C, 30-50 MPa and 2-15 min, temperature, pressure and time parameters are optimized through a system, and the pure tantalum material which is high in relative density (98.7% at most), controllable in grain size (4-29 micrometers), low in oxygen content (smaller than or equal to 0.22 wt.%) and excellent in mechanical property (the hardness is 268-339 HV, and the bending strength is 340-774 MPa) is prepared. The process is simple, parameters are easy to control, sintering time is short, energy is saved, environment friendliness is achieved, and the prepared pure tantalum material is excellent in comprehensive performance and especially suitable for manufacturing of high-performance sputtering targets and capacitors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refractory metal material preparation, and particularly relates to a high-density fine-grain pure tantalum preparation method by spark plasma sintering. BACKGROUND

[0002] Tantalum (Ta) as an important refractory metal, with its extremely high melting point (3017 ℃), excellent corrosion resistance, good biocompatibility and dielectric strength, plays an indispensable strategic role in the field of modern high-tech industry, especially solid electrolytic capacitor and semiconductor sputtering target.

[0003] The traditional preparation method of pure tantalum mainly includes electron beam melting (EBM) and traditional powder metallurgy (PM). Electron beam melting can obtain high-purity tantalum ingot, but the grain is usually coarse and there is chemical composition segregation, and subsequent hot mechanical processing such as forging and rolling is needed to refine the organization, resulting in increased energy consumption and production cost. Although traditional powder metallurgy can realize near-net-shape forming, it usually needs high sintering temperature and long holding time, which easily leads to excessive grain growth and damages the mechanical properties. In addition, tantalum has a strong affinity for interstitial elements such as oxygen (O) and nitrogen (N), and its mechanical properties (especially plasticity) are extremely sensitive to trace contamination during high-temperature processing. Therefore, it is crucial to develop a new preparation technology that can realize sufficient densification, effectively inhibit grain coarsening and control the content of impurity elements, for promoting the application of pure tantalum.

[0004] Spark Plasma Sintering (SPS) technology can realize the densification of powder materials at relatively low temperature and short time, effectively inhibit grain growth, and is very suitable for preparing fine-grained or even nanostructured refractory metals due to its characteristics of rapid heating, external field pressure and pulse current. The patent "CN120647372 A Yttrium Tantalate Ceramic Ferroelectric Domain Width Control Method Based on SPS" controls the ferroelectric domain width through a single temperature parameter control method, which can be used to optimize the microstructure of YTaO4 ceramic material. The preparation steps include ball milling high-purity Y2O3 and Ta2O5, and then loading the obtained powder into a graphite mold for spark plasma sintering. However, the compound material containing tantalum element is used in the preparation process, and single pure tantalum is not used as raw material. The patent "CN 114540689 B An Ultra-low Elastic Modulus Antibacterial Medical Tantalum Alloy and Its Preparation Method" discloses an ultra-low elastic modulus antibacterial medical tantalum alloy, which is prepared by mechanical alloying (MA) and spark plasma sintering (SPS). However, the prepared is a tantalum alloy, and the mass percentage content of tantalum powder used is 75-96%, and single pure tantalum is not used as raw material. It can be seen that existing researches are mostly focused on the SPS process of materials containing tantalum element or tantalum alloy, and there is a lack of systematic research on the SPS sintering process of pure tantalum. The paper "SPS Preparation of Refractory Molybdenum and Molybdenum Tantalum Sputtering Target Material" (doi: 10.3969 / j.issn.1003-7292.2022.01.002) uses spark plasma sintering (SPS) technology to prepare pure molybdenum and two different compositions (Mo-3%Ta, Mo-5%Ta) of molybdenum tantalum alloy target material. As can be seen from the results, there are great differences in phase, micro-morphology, density, hardness and thermal conductivity between pure molybdenum and molybdenum tantalum alloy. That is, the relevant properties of single raw material cannot be inferred from the experimental information results of the alloy. Therefore, although existing technologies exist for the SPS process of compound materials containing tantalum element or tantalum alloy, the influence of sintering parameters (temperature, pressure, time) of pure tantalum in SPS on its densification behavior, microstructure evolution (grain size, porosity, oxygen content) and final mechanical properties (hardness, bending strength) is still unclear. At the same time, it is difficult to directly prepare pure tantalum with a density of >95% by traditional sintering method, and usually requires subsequent rolling process to further improve the density; the grain size of pure tantalum prepared by conventional sintering method or melting method is usually 50 microns or even hundreds of microns, and the particle is relatively coarse; therefore, how to directly prepare pure tantalum with higher density and finer particle size is a problem to be solved at present. SUMMARY

[0005] Aiming at the prior art, the present application aims to provide a high-density fine-grain pure tantalum discharge plasma sintering preparation method. Currently, there is no clear numerical standard for the definition of high density and fine grain in the industry. The density of pure tantalum obtained by traditional sintering method is usually less than 95%, and the 98.7% density of pure tantalum in the present application reaches the level of high density beyond the prior art. The grain size of pure tantalum prepared by conventional sintering method or smelting method is usually above 50 microns, and the grain size of pure tantalum in the present application is finer, reaching 4-29 microns, which can be called fine grain (fine grain). The present application uses discharge plasma sintering (SPS) technology to prepare high-density fine-grain pure tantalum material. By optimizing and controlling the sintering process parameters (temperature, pressure, time), pure tantalum products with high density, fine grain structure and excellent mechanical properties are obtained to solve the problems of coarse grain, low density and poor mechanical properties in the preparation process of pure tantalum material in the prior art, which is suitable for the manufacture of high-end sputtering target material and capacitor.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: In a first aspect of the present application, a high-density fine-grain pure tantalum discharge plasma sintering preparation method is provided, comprising the following steps: The tantalum powder is loaded into a graphite mold, and the graphite mold is sintered in a discharge plasma sintering device under vacuum or protective atmosphere; after sintering is completed, it is cooled to room temperature to obtain high-density fine-grain pure tantalum; The purity of the tantalum powder is 99.9 wt.% and above, and the average particle size is 1-100 microns; The sintering process parameters are as follows: sintering temperature 1300-1500 ℃, axial pressure 20-60 MPa, holding time 2-15 min, and heating rate 50-150 ℃ / min.

[0007] In the present application, the purity and particle size of the tantalum powder are limited in the above range, which is beneficial to ensure that the final obtained pure tantalum material has high density and good mechanical properties, and at the same time, it is beneficial to control the cost and suitable for industrial mass production.

[0008] In the present application, the loading process is carried out in a glove box or dry environment to avoid powder adsorption of water and oxygen. After the tantalum powder is loaded into the graphite mold, carbon paper or tantalum foil is placed on the upper and lower ends of the powder to facilitate subsequent demolding and reduce the pollution of the mold to the sample.

[0009] Further, the sintering process parameters are as follows: sintering temperature 1350-1450 ℃, axial pressure 20-40 MPa, holding time 2-10 min, and heating rate 100 ℃ / min.

[0010] Further, the tantalum powder is dried before use.

[0011] In a second aspect, the application provides high-density fine-grained pure tantalum prepared by the method of spark plasma sintering, characterized in that the high-density fine-grained pure tantalum has the following technical indexes: relative density not less than 94.2%, average grain size 4-29 μm, Vickers hardness 268-339 HV, and three-point bending strength 340-774 MPa.

[0012] Further, the high-density fine-grained pure tantalum has oxygen content not higher than 0.22 wt.%.

[0013] In a third aspect, the application provides use of the high-density fine-grained pure tantalum material in preparation of a sputtering target or a high-performance capacitor electrode.

[0014] The application has the following advantages: The application successfully directly prepares high-density fine-grained pure tantalum material by optimizing the process parameters of spark plasma sintering. The highest-density pure tantalum prepared in the application has a density of 98.7%, which is higher than the density of the prior art. The grain size of the pure tantalum is also finer, i.e. 4-29 μm. The application can inhibit excessive grain growth while achieving full densification of the material by precisely controlling the key parameters such as sintering temperature, pressure and time. The application also has a low oxygen content. If the sintering temperature is too high or the holding time is too long, the density can be further increased, but the grain size will be significantly coarsened, which will damage the bending strength and plasticity of the material. If the pressure is too high, the requirement for the equipment will be more stringent. The method of the application is simple, the parameters are easy to control, the product quality is stable, and the method has the characteristics of strong operability and batch production. The high-density fine-grained pure tantalum material prepared by the application has excellent mechanical properties and a low oxygen content, and is particularly suitable for use in a sputtering target or a high-performance capacitor electrode. DETAILED DESCRIPTION

[0015] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0016] The high-density fine-grained pure tantalum material prepared by the application has excellent mechanical properties and a low oxygen content, and is particularly suitable for use in a sputtering target or a high-performance capacitor electrode.

[0017] Sputtering is one of the main techniques for preparing thin film materials. It uses ions generated by an ion source to form a high-speed ion beam in a vacuum through acceleration and aggregation, which bombards the solid surface. The kinetic energy exchange between the ions and the atoms on the solid surface causes the atoms on the solid surface to leave the solid and deposit on the substrate surface. The bombarded solid is the raw material for preparing sputtering deposition thin films, which is called sputtering target material. The technical index requirements of the sputtering target material are as follows: 1. high density / low porosity; 2. fine grain and uniformity of organization; 3. high purity / low oxygen content; 4. excellent mechanical properties.

[0018] The electrode is the main component of the capacitor, and the technical index requirements of the high-performance capacitor electrode are as follows: 1. high purity; 2. fine grain structure; 3. high density.

[0019] The sputtering target material or high-performance capacitor electrode prepared by the prior art is difficult to meet the requirements, mainly due to the following reasons: 1. The main problem of electron beam melting (EBM) technology is coarse grains and composition segregation.

[0020] The reasons for not meeting the requirements: the tantalum ingot obtained by EBM has coarse grains and uneven organization, which will lead to: for target material: uneven rate during sputtering, poor quality of thin film formed, and coarse grains affecting the mechanical properties of the target material. For capacitor: the anode oxide layer formed by coarse grains is not dense and uniform enough, and defects are easy to occur, which leads to increased leakage current of the capacitor and decreased reliability. Although the purity of EBM is high, in order to refine the grains, subsequent hot mechanical processing such as forging and rolling must be carried out, which increases the complexity and cost of the production process.

[0021] 2. The main problem of traditional powder metallurgy (PM) technology is low density and easy grain coarsening. The reasons for not meeting the requirements: traditional PM process needs high sintering temperature and long holding time to realize densification, but this inevitably leads to excessive grain growth. For target material and capacitor: insufficient density (lower than the minimum standard of 94.2% of the present application) means that there are many pores in the material. For the target material, the pores will cause the sputtering process to be unstable; for the capacitor, the pores will become a breakdown weak point. Grain coarsening will cause similar problems as EBM, which will damage the performance of the final product. In addition, long-term high-temperature sintering increases the risk of contamination of tantalum powder (especially the increase of oxygen content), which is not conducive to obtaining high-purity final products. In summary, the prior art (EBM and traditional PM) has a common contradiction: it is difficult to simultaneously achieve the three key indicators of "high density", "fine grain size" and "high purity / low contamination". Either sacrifice the grain size for purity and high density (such as EBM), or cause grain coarsening and contamination in the pursuit of densification (such as traditional PM). The core advantage of the present application is to use spark plasma sintering (SPS) technology, to achieve rapid densification of the powder at a lower temperature and in a very short time by precisely controlling the temperature, pressure and time parameters, to successfully inhibit grain growth and control oxygen content, thereby preparing pure tantalum materials with excellent comprehensive performance that can simultaneously meet the stringent requirements of high-end sputtering targets and high-performance capacitor electrodes.

[0022] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific embodiments.

[0023] The test materials not specifically described in the embodiments of the present application are all conventional test materials in the art and can be purchased through commercial channels. The spark plasma sintering furnace used in the present application is a LABOX-350 spark plasma sintering furnace produced by Japan SinterLand Inc. The purity of the tantalum powder used in the experiment is ≥99.9 wt.%, the average particle size is 5 microns, and it is prepared by hydrogen reduction method and provided by Ningxia Dongfang Tantalum Industry Co., Ltd.

[0024] Example 1: Preparation of cylindrical pure tantalum sintered body The pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, and the current type of the spark plasma sintering furnace was set to direct current pulse current, and the pulse sequence was 40:7. After vacuumizing, it was heated to 1450 °C at an axial pressure of 40 MPa and a heating rate of 100 °C / min, and held for 10 min, then cooled to room temperature with the furnace, and the sample was taken out, obtaining a cylindrical pure tantalum sintered body with a diameter of 20 mm.

[0025] Example 2: Preparation of cylindrical pure tantalum sintered body The pure tantalum sintered body was prepared according to the method of Example 1, except that the sintering temperature was 1400 °C and the other parameters remained unchanged. Specifically as follows: The pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, the current type of the spark plasma sintering furnace was set to direct current pulse current, and the pulse sequence was 40:7. After vacuumizing, the sample was heated to 1450 °C at a heating rate of 100 °C / min under an axial pressure of 30 MPa, and then cooled to room temperature with the furnace, and a cylindrical pure tantalum sintered body with a diameter of 20 mm was obtained.

[0026] Example 3: Preparation of a cylindrical pure tantalum sintered body The pure tantalum sintered body was prepared according to the method of Example 1, except that the sintering temperature was 1350 °C, and other parameters remained unchanged. Specifically as follows: The pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, the current type of the spark plasma sintering furnace was set to direct current pulse current, and the pulse sequence was 40:7. After vacuumizing, the sample was heated to 1350 °C at a heating rate of 100 °C / min under an axial pressure of 40 MPa, and then cooled to room temperature with the furnace, and a cylindrical pure tantalum sintered body with a diameter of 20 mm was obtained.

[0027] Example 4: Preparation of a cylindrical pure tantalum sintered body The pure tantalum sintered body was prepared according to the method of Example 1, except that the sintering pressure was 20 MPa, and other parameters remained unchanged. Specifically as follows: The pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, the current type of the spark plasma sintering furnace was set to direct current pulse current, and the pulse sequence was 40:7. After vacuumizing, the sample was heated to 1450 °C at a heating rate of 100 °C / min under an axial pressure of 20 MPa, and then cooled to room temperature with the furnace, and a cylindrical pure tantalum sintered body with a diameter of 20 mm was obtained.

[0028] Example 5: Preparation of a cylindrical pure tantalum sintered body The pure tantalum sintered body was prepared according to the method of Example 1, except that the sintering pressure was 30 MPa, and other parameters remained unchanged. Specifically as follows: Pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, and the current type of the spark plasma sintering furnace was set to direct current pulse current with a pulse sequence of 40:7. After vacuumizing, the sample was heated to 1450 °C at a heating rate of 100 °C / min under an axial pressure of 30 MPa, and then cooled to room temperature with the furnace, and then the sample was taken out, to obtain a cylindrical pure tantalum sintered body with a diameter of 20 mm.

[0029] Example 6: Preparation of a cylindrical pure tantalum sintered body A pure tantalum sintered body was prepared according to the method of Example 1, except that the holding time was 5 min, and other parameters remained unchanged. Specifically as follows: Pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, and the current type of the spark plasma sintering furnace was set to direct current pulse current with a pulse sequence of 40:7. After vacuumizing, the sample was heated to 1450 °C at a heating rate of 100 °C / min under an axial pressure of 40 MPa, and then cooled to room temperature with the furnace, and then the sample was taken out, to obtain a cylindrical pure tantalum sintered body with a diameter of 20 mm.

[0030] Example 7: Preparation of a cylindrical pure tantalum sintered body A pure tantalum sintered body was prepared according to the method of Example 1, except that the holding time was 2 min, and other parameters remained unchanged. Specifically as follows: Pure tantalum powder was loaded into a graphite mold with an inner diameter of Φ20 mm, and tantalum foils were placed on both ends of the powder to facilitate demolding. The mold was placed in a spark plasma sintering furnace, and the current type of the spark plasma sintering furnace was set to direct current pulse current with a pulse sequence of 40:7. After vacuumizing, the sample was heated to 1450 °C at a heating rate of 100 °C / min under an axial pressure of 40 MPa, and then cooled to room temperature with the furnace, and then the sample was taken out, to obtain a cylindrical pure tantalum sintered body with a diameter of 20 mm.

[0031] Test Example 1: The properties of the cylindrical pure tantalum sintered body materials prepared in Examples 1-7 were tested. The test methods are as follows: The sample density was measured by the Archimedes drainage method, and the relative density was calculated based on the theoretical density; the hardness was measured by a Vickers hardness tester (load 1 kgf); the bending strength was evaluated by three-point bending test using a universal testing machine; the average grain size was obtained by analyzing the SEM photos of the fracture using the "nano measure" software. The oxygen content was measured by GDMS. The results are shown in Table 1.

[0032] Table 1. Performance test of cylindrical pure tantalum sintered body materials As can be seen from Table 1, by adjusting the temperature, pressure and holding time of the spark plasma sintering, pure tantalum materials with different microstructures and mechanical properties can be obtained. After comprehensive comparison, Example 7 (1450 °C / 40 MPa / 2 min) has the optimal comprehensive mechanical properties while maintaining a high density (95.1%) and the smallest grain size (5.56 μm) and the highest bending strength (773.8 MPa). Example 1 (1450 °C / 40 MPa / 10 min) obtains the highest density (98.7%) and hardness (338.5 HV). This shows that by optimizing the SPS process parameters, high-performance pure tantalum materials can be customized for different application requirements (such as focusing on strength or hardness).

[0033] The preferred embodiments of the present application have been described above with the aid of drawings and are not intended to limit the application, which can be modified and changed by various skilled persons in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing high-density, fine-grained pure tantalum by spark plasma sintering, characterized in that, Includes the following steps: Tantalum powder is loaded into a graphite mold, and the graphite mold is sintered in a discharge plasma sintering apparatus under vacuum or a protective atmosphere. After sintering, the mold is cooled to room temperature to obtain high-density fine-grained pure tantalum. The pulse current sequence used in spark plasma sintering is 40:(2-10); The tantalum powder has a purity of 99.9 wt.% or higher and an average particle size of 1-100 μm; The sintering process parameters are as follows: sintering temperature 1300~1500 ℃, axial pressure 20~60 MPa, holding time 2~15 min, heating rate 50~150℃ / min.

2. The method for preparing high-density fine-grained pure tantalum by spark plasma sintering according to claim 1, characterized in that, The pulse current sequence used in spark plasma sintering is 40:7; The sintering process parameters are as follows: sintering temperature 1350~1450 ℃, axial pressure 20~40 MPa, holding time 2~10 min, heating rate 100 ℃ / min.

3. The method for preparing high-density fine-grained pure tantalum by spark plasma sintering according to claim 1 or 2, characterized in that, The tantalum powder is dried before use.

4. The high-density, fine-grained pure tantalum obtained by the spark plasma sintering method according to any one of claims 1-3, characterized in that, The technical specifications of high-density fine-grained pure tantalum are as follows: relative density not less than 94.2%, average grain size of 4-29 μm, Vickers hardness of 268-339 HV, and three-point bending strength of 340-774 MPa.

5. The high-density fine-grained pure tantalum according to claim 4, characterized in that, The oxygen content of high-density fine-grained pure tantalum is no higher than 0.22 wt.%.

6. The application of the high-density fine-grained pure tantalum material as described in claim 4 or 5 in the preparation of sputtering targets or high-performance capacitor electrodes.

Images