CN118530028A - A medium-entropy nitride ceramic material and preparation method thereof - Google Patents

Abstract

The present invention relates to a medium-entropy nitride ceramic material and a preparation method thereof. The raw materials are TiN powder, TaN powder and NbN powder, anhydrous ethanol is added after mixing, and the mixed powder is ground in an inert atmosphere to obtain a mixed powder; the mixed powder is then pressed into shape and then spark plasma sintered, and naturally cooled to room temperature to obtain a medium-entropy nitride ceramic Ti _1‑x (Ta _1/2 Nb _1/2 ) _x N (0<x<1). The present invention successfully synthesizes bulk nitride ceramics by adjusting the content of Ti and the preparation process. It not only expands the nitride system, but also has potential application prospects in extremely harsh working conditions such as high temperature and high load.

Description

A medium-entropy nitride ceramic material and preparation method thereof

Technical Field

The present invention belongs to the technical field of medium/high entropy compound preparation, and relates to a method for preparing a medium entropy nitride and a bulk ceramic thereof, and in particular to a method for preparing a medium entropy nitride Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) with different Ti contents, so as to improve the relevant properties of the nitride, thereby expanding the application of the nitride.

Background Art

Transition metal nitrides (TMNs) have the characteristics of high melting point, high thermal stability, strong chemical inertness and high hardness. They can be used as protective films for surface protection of high-end equipment structural components and moving parts. However, with the rapid development of modern industry, the integration of mechanical equipment is increasing, and the service conditions of related components are becoming more and more harsh. Therefore, it is urgent to further optimize the mechanical properties and wear resistance of TMNs protective films to improve their service durability and reliability. Medium/high entropy nitrides (MENs/HENs, ≥3/4 metal cations) significantly broaden the composition design space through the random combination of multiple principal elements, giving them special properties that traditional single nitrides cannot achieve. Reference "Super-hard (MoSiTiVZr)N _x high-entropynitride coatings[J]. Journal ofAlloys and Compounds, 2022, 926: 166807." Coatings of (MoSiTiVZr)N _x with different nitrogen contents were prepared. The results showed that the increase in N content caused the structure of the (MoSiTiVZr)N _x high-entropy nitride coating to change from amorphous to single FCC, and the grain size, hardness, damage resistance and wear resistance were significantly improved. Reference "Nitrogen vacancies regulate lattice distortion to strengthen the mechanical properties and wear resistance of (NbMoTaW)N _x films. Journal of Inorganic Materials, 2024, (06): 715-725" By adjusting nitrogen vacancies, the study achieved the coordinated regulation of the sublattice distortion of nitrogen atoms and metal atoms, which provides a new idea for regulating and optimizing the performance of nitride films and better coping with the mechanical damage problem of protective films under complex service environments. In the early days, people focused on the doping of single metal elements in TiN. Recently, with the rise of research on high-entropy materials, in order to maximize the configurational entropy, current research is mostly focused on high-entropy systems with four or more metal components, while there is less research on medium-entropy nitrides with three metal components. So far, there has been no report on the Ti-Nb-Ta medium-entropy nitride system.

Summary of the invention

The present invention discloses a medium entropy ceramic material Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) and a preparation method thereof, wherein the material comprises three metal elements, namely Ti, Nb and Ta, and the content of Ti in the system is adjustable. Through component adjustment and preparation process, a bulk nitride ceramic material with excellent mechanical properties, high temperature resistance and high wear resistance is obtained, which meets the safe and reliable service requirements of mechanical parts under harsh working conditions such as high temperature and high load.

The medium entropy nitride ceramic is a single-component ceramic, and its molecular formula is expressed as Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1), wherein the metal elements have non-equimolar ratios and the components of the Ti content can be adjusted, and the total amount of the metal elements is 1. TaN, NbN and TiN have similar lattice parameters and the same crystal structure (face-centered cubic structure), which enables them to form a uniform solid solution at high temperature. At the same time, Ti is relatively light and has good ductility and toughness. Combining with Ta and Nb can improve the toughness and fracture resistance of the material while maintaining high hardness, and the carbides of Ta, Nb and Ti have good stability in high temperature environments and are not prone to phase change or decomposition, which makes them exhibit excellent performance in high temperature environments. Therefore, the medium entropy ceramic material obtained by this combination can maintain excellent performance in a variety of extreme environments such as high temperature, high pressure, corrosion, etc., so as to be suitable for a wide range of industrial applications. The series of medium entropy nitride ceramics have the crystallization characteristics of a rock salt structure, and a schematic diagram of its crystal structure is shown in Figure 1.

1. To realize the above-mentioned medium entropy nitride ceramics, the present invention adopts the following preparation scheme:

1) TiN powder, TaN powder and NbN powder are weighed according to the stoichiometric ratio of each element in the above molecular formula, mixed, added with 5%-10% anhydrous ethanol, and ground in an inert atmosphere to obtain a mixed powder; the purity of the raw material TiN powder, TaN powder and NbN powder is ≥99%, and the particle size is ≤45 μm.

Grinding is to place the raw materials in the ball mill of the ball mill, and add tungsten carbide grinding balls to grind into mixed powder; during grinding, the mass ratio of grinding balls to mixed materials is 5:1~20:1; the speed of the ball mill is 200~600 r/min; the ball milling time is 8~15 h;

The purpose of ball milling is to make the powder and the grinding balls in the jar collide and rub against each other at high speed, so as to crush, grind, mix and disperse the samples.

2) The mixed powder obtained in step 1) is placed in a vacuum drying oven and dried at 50-80° C. for 1-3 hours to obtain the desired target mixed powder.

3) The target mixed powder obtained in step 2) is pressed into a green body by a hydraulic press at 30 MPa, and then the green body is subjected to spark plasma sintering. After sintering, the green body is cooled to obtain the target product Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) bulk ceramic.

The sintering process has a great influence on the structure and properties of the synthesized non-isotropic medium entropy nitride ceramics. If the sintering temperature is too low, the sintering will not be dense and a single phase cannot be synthesized. If the temperature is too high, melting and metal liquid will flow out. If the holding time is too long and the pressure is too high, the grains will grow larger, resulting in poor performance. Therefore, the process of spark plasma sintering in the present invention is: the heating rate is 20~300℃/min, the sintering temperature is 1800~2100℃, the holding time is 0.1~1h, the pressure is 1.5~30MPa, and the vacuum degree is < ^101Pa .

The synthesis mechanism of the present invention is as follows: using transition metal nitride TM (TiN, TaN, NbN) powder as raw material, based on the TM(s)→HEN-Ti _x (s) reaction idea, by controlling the Ti content, mechanical grinding and hot pressing sintering technology are used to in-situ induce the synthesis of a series of medium-entropy nitride ceramic materials with uniform tissue distribution.

2. Structure and properties of intermediate entropy ceramic material Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1)

The present invention ingeniously adjusts the content of Ti and successfully designs and prepares a medium entropy ceramic material by using a spark plasma sintering method. The molecular formula is Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1), and the crystal structure belongs to a face-centered cubic structure. When x = 0.2, 0.4, 0.6, and 0.8, the unit cell parameters are: Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N ( a = 4.2761 Å), Ti _0.6 (Ta _{1/ 2} Nb _1/2 ) _0.4 N ( a = 4.3065 Å), Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N ( a = 4.3280 Å) and Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N ( a = 4.3504 Å).

1. Structural characterization

FIG2 is an XRD spectrum of the medium-entropy nitride ceramic material synthesized by the present invention. As can be seen from FIG2 , the prepared Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramic is a pure cubic phase, does not contain other impurity phases, and with the change of Ti content, the diffraction peak shows a regular shift.

Figure 3 is a SEM image of the intermediate entropy nitride ceramic material synthesized by the present invention, and Figure 4 is an EDS energy spectrum element distribution diagram of the non-equiratio intermediate entropy nitride ceramic material synthesized by the present invention; from the microscopic morphology of Figure 3, it can be seen that the Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics synthesized by the present invention are denser and have fewer defects; from Figure 4, it can be seen that the three transition metal constituent elements of the Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics synthesized by the present invention are uniformly distributed, and the element ratio is consistent with the proportion of the raw materials.

2. Performance evaluation

2.1 Mechanical properties

The hardness of Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) was tested using a Vickers microhardness tester. The test conditions were: load 500 gf, loading duration 10 s, and each sample was tested 10 times at a randomly selected point to obtain the average value; the test results are shown in Table 1.

Table 1 Hardness of the entropy ceramic material of the present invention at room temperature

2.2 High temperature tribological properties

The high temperature tribological properties were tested using a high temperature reciprocating friction and wear tester, the test temperature was RT~1000℃, Al ₂ O ₃ ball was used as the friction pair, the load was 10N, the reciprocating length was 5mm, and the test time was 30min. Figure 5 shows the friction coefficient curve of the prepared Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics at RT~1000℃. The experimental results show that the prepared Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics have excellent tribological properties at room temperature to high temperature, and the friction coefficient at 600℃ is lower than that of the reported [Design and Mechanical and Tribological Properties of Nitride-based Smart Nanostructured Composite Films. Jiangsu University of Science and Technology, 2016] TiN film at 600℃ (>0.73), and Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N and Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N have the lowest friction coefficient of 0.4~0.5 at 1000℃, while Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N and Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N has the lowest friction coefficient of 0.4~0.5 at 800℃, which indicates that the friction properties of nitride ceramics are improved by adjusting the Ti content.

3. Application of medium entropy ceramic materials

The non-isotropic Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics synthesized by adjusting the Ti content in the present invention have not been reported so far. Titanium nitride (TiN) is a new type of multifunctional metal ceramic material with excellent properties such as high melting point, high hardness, wear resistance, good chemical stability, good electrical and thermal conductivity and optical properties. Its melting point is 2930~2950℃, it is a good conductor of heat and electricity, and it has superconductivity at low temperatures, and is a material for manufacturing jet engines. The Vickers hardness of the synthesized series of Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramics increases with the decrease of Ti content. At present, nitrides are mostly used to prepare thin films and coatings, while there are relatively few reports on preparing them into bulk materials, and no one has reported preparing them into non-isotropic bulk mesoentropy nitride ceramics by adjusting the Ti content. Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) has excellent tribological properties at high temperatures and is expected to be used as high-temperature thermal protection materials and high-temperature structural parts such as refractory and wear-resistant materials. It has great application potential in structural components serving in extreme working conditions of aerospace and marine engines.

In summary, the initial materials used in the method of the present invention are relatively economical and cost-saving. The raw materials used are simple and common, available on the market, easy to obtain and cheap, and convenient for the implementation of the process. Compared with the existing medium/high entropy equiatomic ratio nitrides, the Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0<x<1) ceramic block material prepared by the present invention contains different contents of Ti elements, so that it exhibits more excellent mechanical properties and tribological properties. In addition, the method of the present invention also has the advantages of simple preparation process, strong controllability, and easy scale-up.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the crystal structure of Ti _1-x (TaNb) _x N (0<x<1) ceramics prepared in an embodiment of the present invention.

FIG. 2 is an XRD spectrum of the Ti _1-x (TaNb) _x N (0<x<1) ceramic prepared in an embodiment of the present invention.

FIG3 is a SEM image of the Ti _1-x (TaNb) _x N (0<x<1) ceramic prepared in an embodiment of the present invention.

FIG. 4 is an EDS spectrum element distribution diagram of the Ti _1-x (TaNb) _x N (0<x<1) ceramic prepared in an embodiment of the present invention.

5 is a friction curve diagram of the Ti _1-x (TaNb) _x N (0<x<1) ceramic prepared in an embodiment of the present invention, wherein a: x=0.2; b: x=0.4; c: x=0.6; d: x=0.8.

DETAILED DESCRIPTION

The synthesis method of the Ti _1-x (TaNb) _x N (0<x<1) ceramic bulk material of the present invention is specifically described below through examples.

Example 1 Preparation of High Entropy Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N Ceramics

(1) TiN powder, TaN powder and NbN powder were used as raw materials and weighed according to the molar ratio of Ti, Ta, Nb and N of 2:4:4:10. The total weight of the original ingredients was about 30 g. The original ingredients were placed in a ball mill (tungsten carbide grinding balls: mixed materials = 5:1). Anhydrous ethanol (5% by weight of the total weight of the ingredients) was added as a ball milling medium, and the ball mill was placed in a planetary ball mill. The mixed powder was obtained after ball milling at 300 r/min for 8 h under inert gas protection.

(2) The mixed powder obtained in step (1) is dried and pre-pressed with a hydraulic press at 30 MPa to obtain a green body, which is then subjected to spark plasma sintering. Spark plasma sintering process conditions: the atmosphere furnace is evacuated to a vacuum reading of <10 ¹ Pa, and then the furnace temperature is raised from room temperature to 1800°C at a heating rate of 90°C/min and kept at this temperature for 10 min; then the power is turned off and the mixture is naturally cooled to room temperature to obtain Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N ceramics. The XRD spectrum (Figure 2) shows that the prepared Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N ceramics are pure phases and do not contain other impurities; the SEM image and element distribution diagram (Figures 3 and 4) show that the element ratio of the synthesized Ti _0.8 (Ta _1/2 Nb _1/2 ) _0.2 N ceramics is consistent with the raw material ratio, and the three transition metal constituent elements are evenly distributed.

The prepared Ti _0.8 (TaNb) _0.2 N ceramic has a unit cell parameter of 4.2761 Å and a Vickers hardness of 12.375±0.42 GPa, and exhibits excellent tribological properties from room temperature to high temperature.

Example 2 Preparation of High Entropy Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N Ceramics

(1) TiN powder, TaN powder and NbN powder were used as raw materials and weighed according to the molar ratio of Ti, Ta, Nb and N of 6:2:2:10. The total weight of the original ingredients was about 30 g. The original ingredients were placed in a ball mill (tungsten carbide grinding balls: mixed materials = 5:1). Anhydrous ethanol (6% of the total weight of the ingredients) was added as a ball milling medium, and the ball mill was placed in a planetary ball mill. The mixed powder was obtained after ball milling at 400 r/min for 9 h under inert gas protection.

(2) The mixed powder obtained in step (1) is dried and pre-pressed with a hydraulic press at 30 MPa to obtain a green body, which is then subjected to spark plasma sintering. Spark plasma sintering process conditions: the atmosphere furnace is evacuated to a vacuum reading of <10 ¹ Pa, and then the furnace temperature is raised from room temperature to 1900°C at a heating rate of 100°C/min and kept at this temperature for 10 minutes; then the power is turned off and the mixture is naturally cooled to room temperature to obtain Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N ceramics. The XRD spectrum (Figure 2) shows that the prepared Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N ceramics are pure phases and do not contain other impurities; the SEM image and element distribution diagram (Figures 3 and 4) show that the element ratio of the synthesized Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N ceramics is consistent with the raw material ratio, and the three transition metal constituent elements are evenly distributed.

The prepared Ti _0.6 (Ta _1/2 Nb _1/2 ) _0.4 N ceramic has a unit cell parameter of 4.3065 Å and a Vickers hardness of 12.855±0.26 GPa, and has excellent tribological properties from room temperature to high temperature.

Example 3 Preparation of High Entropy Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N Ceramics

(1) TiN powder, TaN powder and NbN powder were used as raw materials and weighed according to the molar ratio of Ti, Ta, Nb and N of 4:3:3:10. The total weight of the original ingredients was about 30 g. The original ingredients were placed in a ball mill (tungsten carbide grinding balls: mixed materials = 5:1). Anhydrous ethanol (7% of the total weight of the ingredients) was added as a ball milling medium, and the ball mill was placed in a planetary ball mill. The mixed powder was obtained after ball milling at 500 r/min for 10 h under inert gas protection.

(2) The mixed powder obtained in step (1) is dried and pre-pressed with a hydraulic press at 30 MPa to obtain a green body, which is then subjected to spark plasma sintering. Spark plasma sintering process conditions: the atmosphere furnace is evacuated to a vacuum reading of <10 ¹ Pa, and then the furnace temperature is raised from room temperature to 2000°C at a heating rate of 110°C/min and kept at this temperature for 10 minutes; then the power is turned off and the mixture is naturally cooled to room temperature to obtain Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N ceramics. The XRD spectrum (Figure 2) shows that the prepared Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N ceramics are pure phases and do not contain other impurities; the SEM image and element distribution diagram (Figures 3 and 4) show that the element ratio of the synthesized Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N ceramics is consistent with the raw material ratio, and the three transition metal constituent elements are evenly distributed.

The prepared Ti _0.4 (Ta _1/2 Nb _1/2 ) _0.6 N ceramic has a unit cell parameter of 4.3280 Å and a Vickers hardness of 14.322±0.34 GPa, and has excellent tribological properties from room temperature to high temperature.

Example 4 Preparation of High Entropy Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N Ceramics

(1) TiN powder, TaN powder and NbN powder were used as raw materials and weighed according to the molar ratio of Ti, Ta, Nb and N of 2:4:4:10. The total weight of the original ingredients was about 30 g. The original ingredients were placed in a ball mill (tungsten carbide grinding balls: mixed materials = 5:1). Anhydrous ethanol (8% of the total weight of the ingredients) was added as a ball milling medium. The ball mill was placed in a planetary ball mill and ball milled at 600 r/min for 11 h under inert gas protection to obtain a mixed powder.

(2) The mixed powder obtained in step (1) is dried and pre-pressed with a hydraulic press at 30 MPa to obtain a green body, which is then subjected to spark plasma sintering. Spark plasma sintering process conditions: the atmosphere furnace is evacuated to a vacuum reading of <10 ¹ Pa, and then the furnace temperature is raised from room temperature to 2100°C at a heating rate of 120°C/min and kept at this temperature for 10 minutes; then the power is turned off and the mixture is naturally cooled to room temperature to obtain Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N ceramics. The XRD spectrum (Figure 2) shows that the prepared Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N ceramics are pure phases and do not contain other impurities; the SEM image and element distribution diagram (Figures 3 and 4) show that the element ratio of the synthesized Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N ceramics is consistent with the raw material ratio, and the three transition metal constituent elements are evenly distributed.

The prepared Ti _0.2 (Ta _1/2 Nb _1/2 ) _0.8 N ceramic has a unit cell parameter of 4.3504 Å and a Vickers hardness of 15.062±0.25 GPa, and has excellent tribological properties from room temperature to high temperature.

Claims (5)

1. A medium entropy nitride ceramic material, characterized in that the molecular formula is Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0 <x< 1), the crystal structure is a face-centered cubic structure, and the total amount of metal elements is 1. 2. A method for preparing the medium entropy nitride ceramic material according to claim 1, characterized in that it comprises the following steps: 1) TiN powder, TaN powder and NbN powder are weighed as raw materials according to the stoichiometric ratio of each element in the above molecular formula, mixed, added with 5% to 10% anhydrous ethanol, and ground in an inert gas to obtain a mixed powder; 2) drying the mixed powder obtained in step 1), pressing the mixed powder with a hydraulic press at 30 MPa to obtain a green body, and then performing spark plasma sintering on the green body. After sintering, the green body is naturally cooled to room temperature to obtain the target product, a medium entropy nitride ceramic Ti _1-x (Ta _1/2 Nb _1/2 ) _x N (0 <x<1); the process conditions of the spark plasma sintering are: a heating rate of 20-300 ℃/min, a sintering temperature of 1800-2100 ℃, a holding time of 0.1-1 h, a pressure of 1.5-30 MPa, and a vacuum degree of <10 ¹ Pa. 3. A method for preparing a medium-entropy nitride ceramic material as claimed in claim 2, characterized in that in step 1), the purity of the raw materials TiN powder, TaN powder and NbN powder are all ≥99%, and the particle size is all ≤45 μm. 4. A method for preparing a medium-entropy nitride ceramic material as claimed in claim 2, characterized in that in step 1), the grinding is to place the raw material in a tungsten carbide ball mill of a ball mill, and add tungsten carbide grinding balls to grind into a mixed powder; during grinding, the mass ratio of the grinding balls to the mixed material is 5:1~20:1; the rotation speed of the ball mill is 200~800 rpm; and the ball milling time is 7~15 hours. 5. Use of the medium-entropy nitride ceramic material as claimed in claim 1 in structural components serving under high temperature and high load conditions.