Rare earth metal ceramic and preparation method thereof

Abstract

The invention discloses a rare earth metal ceramic and a preparation method thereof, and belongs to the technical field of metal ceramic preparation, the rare earth metal ceramic comprises, by mass, 45-65% of a ceramic phase, 30-50% of a metal binding phase and 3-8% of a rare earth additive, the ceramic phase is composed of one of TiC and WC and one of Al2O3 and ZrO2, the metal binding phase is composed of a Ni-Co alloy and Mo or Cr, and the rare earth additive is composed of one of Al2O3 and ZrO2. The rare earth additive is composed of mixed rare earth oxide and nano rare earth fluoride. The invention further provides a preparation method of the rare earth additive. Through the synergistic effect of oxide grain boundary purification and fluoride liquid phase sintering in a two-phase rare earth system, the problem that traditional single rare earth is difficult to add and disperse is solved, through staged hot pressing sintering, dual optimization of grain refinement and density improvement is achieved, and the high-temperature oxidation resistance and interface bonding strength of metal ceramic are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of metal ceramic preparation, in particular to a rare earth metal ceramic and a preparation method thereof. Background Art

[0002] As a type of high-performance composite material that combines the good toughness of the metal phase with the high hardness and high temperature resistance of the ceramic phase, metal ceramics have wide and critical applications in many fields such as mechanical processing, aerospace, energy and chemical industry.

[0003] However, common metal ceramics currently on the market, such as TiC-Ni and WC-Co systems, have exposed many problems that need to be solved in practical applications. In terms of performance, their high-temperature oxidation resistance is insufficient. When they serve for a long time in a high-temperature environment, they are prone to generate loose oxide layers (such as TiO2 and WO3). This not only leads to a decrease in the hardness of the material, but also greatly reduces the mechanical properties of the material, seriously affecting its service life and reliability. In terms of the combination of ceramic phase and metal phase, the interface bonding force between the two is weak. Due to the difference in physical and chemical properties, when subjected to external forces or temperature changes, stress concentration is easily generated at the interface, which in turn causes cracks, leading to failure phenomena such as cracking and breakage of the material. In terms of preparation technology, traditional preparation methods easily lead to coarse grains of the material, with many pores inside, and it is difficult to achieve the ideal density, which makes it impossible to fully exert the wear resistance and corrosion resistance of the material, limiting the further application of metal ceramics in fields with higher performance requirements.

[0004] Although some studies have attempted to improve the performance of metal ceramics by adding rare earth elements, most of them only use a single rare earth oxide. The single rare earth phase has the problem of uneven dispersion in the material, which cannot fully exert the advantages of the rare earth elements. In addition, there is a lack of systematic optimization of the amount of rare earth elements added, making it difficult to maximize the improvement of material performance. Therefore, there is an urgent need to develop a new rare earth metal ceramic and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a rare earth metal ceramic and a preparation method thereof to solve the problems in the background technology.

[0006] To achieve the above-mentioned object, the present invention provides a rare earth metal ceramic, which comprises, by mass percentage, 45-65% of a ceramic phase, 30-50% of a metal bonding phase, and 3-8% of a rare earth additive, wherein the ceramic phase is composed of one of TiC and WC and one of Al2O3 and ZrO2, the metal bonding phase is composed of a Ni-Co alloy and Mo or Cr, and the rare earth additive is composed of a mixed rare earth oxide and a nano rare earth fluoride, and the mass ratio of the mixed rare earth oxide to the rare earth fluoride is (8-9):(1-2).

[0007] Preferably, in the Ni-Co alloy, the molar ratio of Ni to Co is 3:1 to 5:1, the mixed rare earth oxide is composed of Y2O3, CeO2, and La2O3 in a molar ratio of 1:1:1, and the rare earth fluoride is one or a mixture of YF3 and LaF3.

[0008] The present invention also provides a method for preparing the rare earth metal ceramic, comprising the following steps:

[0009] S1. Raw material preparation: TiC powder or WC powder and Al2O3 powder or ZrO2 powder are placed in a ball mill and ball-milled under inert gas to obtain a ceramic phase premixed powder; Ni-Co alloy powder is mixed with Mo powder or Cr powder and then vacuum-dried to obtain a metal binder phase powder; mixed rare earth oxides and rare earth fluorides are added to anhydrous ethanol and ultrasonically dispersed to obtain a uniform slurry;

[0010] S2, mixing the ceramic phase premixed powder and the metal binder phase powder, adding the mixture to the slurry in multiple batches, and simultaneously performing vacuum stirring. After completion, the mixture is spray-dried to obtain a composite powder coated with a rare earth layer;

[0011] S3. The composite powder is loaded into a graphite mold and placed in a vacuum hot pressing furnace for two-stage sintering. The temperature of the first stage is 850-950°C, a pressure of 20-30 MPa is applied, and the temperature is kept for 1 hour. The rare earth fluoride softens to form a liquid phase, promoting diffusion and the formation of an interface transition layer. The temperature of the second stage is 1350-1450°C, a pressure of 40-60 MPa is applied, and the temperature is kept for 2 hours. The oxide inhibits grain coarsening, and the fluoride liquid phase fills the pores, achieving dual optimization.

[0012] After sintering, the material is cooled to room temperature at a cooling rate of 5 to 10°C / min to obtain rare earth metal ceramics.

[0013] Preferably, in S1, the mass ratio of TiC powder or WC powder to Al2O3 powder or ZrO2 powder is (6-10):(1-3); the mass ratio of Ni-Co alloy powder to Mo powder or Cr powder is (5-8):(1-2).

[0014] Preferably, in said S1, the ball milling time is 4 to 6 hours, the ball-to-material ratio is 8 to 12:1, and the ball milling medium is zirconia balls; during the vacuum drying process, the vacuum degree is ≤10 -3 Pa, temperature is 120℃, vacuum time is 1.5~2h; ultrasonic time is 1~3h.

[0015] Preferably, in S1, the particle size of the rare earth fluoride is 50 to 100 nm.

[0016] Preferably, in said S2, during the vacuum stirring process, the vacuum degree is ≤10-2 Pa; during the spray drying process, the inlet air temperature is 160-190°C and the atomization pressure is 0.3 MPa.

[0017] Preferably, in S3, the heating rate of the first stage sintering is 5-15°C / min, and the heating rate of the second stage sintering is 10-20°C / min.

[0018] Therefore, the rare earth metal ceramic and the preparation method thereof of the present invention have the following beneficial effects:

[0019] (1) TiC or WC in the ceramic phase of the present invention imparts high hardness to the material, and Al2O3 or ZrO2 can effectively inhibit abnormal grain growth, optimize the microstructure of the material, and improve the stability of the material; the Ni-Co alloy and Mo or Cr in the metal bonding phase cooperate with each other, and the Ni-Co alloy improves the wettability of the ceramic phase and the metal phase and enhances the interface bonding, while Mo or Cr forms a strengthening phase, further improving the strength and hardness of the material, and rare earth oxides and rare earth fluorides form a two-phase rare earth system, the former purifies the grain boundary, and the latter generates a low-melting-point liquid phase during sintering, promoting densification. Through the synergistic effect of the two, the high-temperature oxidation resistance of the material is greatly enhanced.

[0020] (2) The preparation method of the present invention adopts a staged sintering process. In the low-temperature diffusion stage, the rare earth coating layer begins to soften and initially contacts the metal bonding phase. The rare earth elements (especially fluorides) diffuse into the metal phase to form an interface transition layer; in the high-temperature densification stage, the ceramic phase particles and the metal bonding phase are fully integrated, and the rare earth fluoride liquid phase fills the pores. At the same time, the oxides inhibit the coarsening of the ceramic phase. Mo / Cr, as an alloying element in the metal bonding phase, forms a stable compound with the rare earth to further fix the rare earth elements at the interface; the above process avoids the abnormal growth of ceramic phase grains at high temperatures and achieves grain refinement. At the same time, the high-pressure and high-temperature stage enables the material to reach a near-theoretical density (≥99%), effectively reducing internal pores, improving the density and uniformity of the material, and thereby improving the wear resistance and corrosion resistance of the material.

[0021] (3) The present invention utilizes a method of coating the powder with rare earth slurry, so that the rare earth elements are preferentially enriched at the ceramic / metal interface during the sintering process, forming a stable (Y, Ce)Ox transition layer. This transition layer can effectively reduce the interfacial energy, enhance the bonding force between the ceramic phase and the metal phase, inhibit the expansion of cracks at the interface, and improve the overall strength and reliability of the material, so that it can still maintain good performance under complex working conditions.

[0022] The technical solution of the present invention is further described in detail below through examples. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further illustrated by the following examples.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0025] Example 1

[0026] Preparation of TiC-based high-temperature wear-resistant cermets, the raw materials are as follows:

[0027] Ceramic phase (55%): TiC (45%, purity ≥99%, particle size 1-3 μm), Al2O3 (10%, purity ≥99.5%, particle size 0.5-2 μm);

[0028] Metal binder phase (40%): Ni-30Co alloy (35%, atomized powder, particle size ≤45μm), Mo (5%, purity ≥99.9%, particle size ≤50μm);

[0029] Rare earth additive (5%): mixed oxide of Y2O3, CeO2, La2O3 in a molar ratio of 1:1:1 (4.5%, purity ≥99.95%, particle size 50-80nm), YF3 (0.5%, nanometer grade, particle size ≤100nm, purity ≥99.9%);

[0030] The specific preparation steps are as follows:

[0031] S1. Process the raw materials as follows:

[0032] 1) Ceramic Phase Premixing: Place 450g TiC powder and 100g Al2O3 powder in a planetary ball mill. Add 3mm diameter zirconia balls at a ball-to-powder ratio of 12:1. Maintain positive pressure with argon (99.99% purity) and mill at 400 rpm for 5 hours. Stop the mill every hour for 10 minutes to cool the mixture to prevent local overheating.

[0033] 2) Metal phase dehydration: 350g Ni-30Co alloy powder and 50g Mo powder were mixed and placed in a vacuum drying oven at a vacuum degree of ≤10 -3 Dry at 120℃ for 2 hours, and pass through 100 mesh sieve for later use.

[0034] 3) Preparation of rare earth slurry: 4.5 g of Y2O3, CeO2, La2O3 and 0.5 g of YF3 were added to 500 mL of anhydrous ethanol, placed in an ultrasonic cleaning machine, and dispersed at a frequency of 40 kHz and a power of 500 W for 2 hours to form a uniform slurry with a solid content of 10%.

[0035] S2, 550g of ball-milled ceramic phase premixed powder was mixed with 400g of dehydrated metal binder phase powder, and rare earth slurry was added in three batches, each with an interval of 15 minutes, while vacuum stirring was started at a speed of 300rpm and a vacuum degree of ≤10 -2 Pa, total stirring time 2 hours;

[0036] After the mixing is completed, a spray dryer is used to control the air inlet temperature to 180°C, the atomization pressure to 0.3 MPa, and the feed rate to 20 mL / min for spray drying to obtain particles with a diameter of 5 to 20 μm and a bulk density of 2.0 g / cm 3 Spherical composite powder with a rare earth layer coated on its surface.

[0037] S3, fill the composite powder into a graphite mold with a diameter of 50mm and an inner wall coated with BN release agent, put it into a vacuum hot press furnace, and evacuate to ≤10 -4 After Pa, sintering is carried out in stages;

[0038] During the first stage of sintering, the temperature was raised to 900°C at 10°C / min, a pressure of 20 MPa was applied (precisely controlled by the hydraulic system), and the temperature was kept for 1 hour, during which the vacuum degree was maintained ≤10 -3 Pa promotes the initial diffusion of Ni-Co alloy and Mo.

[0039] In the second stage, the temperature was raised to 1400°C at a rate of 15°C / min, the pressure was increased to 50 MPa, and the temperature was kept at this temperature for 2 hours. The temperature in the furnace was monitored in real time by an infrared thermometer (with a deviation of ±5°C).

[0040] After sintering, the heating power was turned off, and the sample was cooled to room temperature at a rate of 8°C / min, and the metal ceramic sample was taken out.

[0041] The prepared samples were tested for performance. The hardness was measured by a Vickers hardness tester (HV-1000) to be 92.5 HRA. The flexural strength was measured by a three-point bending test (span 30 mm) to be 1250 MPa. The density was measured by the Archimedes drainage method to be 99.2%. After being heated at 1000°C in a muffle furnace for 100 hours, the weight increased by 0.8 mg / cm 2 The interfacial binding energy measured by TI950 nanoindenter is 0.68 j / m 2 .

[0042] Example 2

[0043] Preparation of WC-based corrosion-resistant cermets, the raw materials are as follows:

[0044] Ceramic phase (50%): WC (40%, purity ≥99.5%, particle size 2-4 μm), ZrO2 (10%, yttrium-stabilized <3 mol% Y2O3>, particle size 0.8-3 μm);

[0045] Metal binder phase (45%): Ni-40Co alloy (40%, atomized powder, particle size ≤45μm), Cr (5%, purity ≥99.9%, particle size ≤50μm);

[0046] Rare earth additive (5%): mixed oxide of Y2O3, CeO2, La2O3 in a molar ratio of 1:1:1 (4.25%, purity ≥99.95%, particle size 30-70nm), YF3 (0.75%, nanometer grade, particle size ≤80nm);

[0047] The specific preparation steps are the same as those in Example 1, the ceramic phase is WC and ZrO2, the metal bonding phase is Ni-40Co alloy and Cr, and the rare earth fluoride is LaF3;

[0048] The ceramic phase premixing process in S1 was modified as follows: WC and ZrO2 were ball-milled for 6 h, with a ball-to-material ratio of 10:1, using zirconia balls with a diameter of 5 mm, and an argon flow rate of 20 L / h to maintain the atmosphere;

[0049] The rare earth slurry preparation process in S1 was modified as follows: ultrasonic dispersion frequency 60 kHz, power 600 W, dispersion time 3 h, and ethanol dosage 600 mL;

[0050] The first stage sintering in S3 was modified as follows: heating to 950°C at 8°C / min and applying a pressure of 25 MPa; the second stage was modified as follows: heating to 1350°C at 12°C / min and applying a pressure of 55 MPa.

[0051] The performance test of the prepared product showed that its hardness was 93.0HRA and its fracture toughness was 13.2MPa·m 1 / 2 The corrosion rate of 3.5% NaCl is 0.015mm / a; the grain boundary energy is 0.38J / m 2 .

[0052] Comparative Example 1

[0053] In this comparative example, all rare earth additives were removed, and the remaining components were the same as in Example 1, with the mass percentages modified to 55% ceramic phase and 45% metal binder phase. The specific preparation steps were as follows:

[0054] S1. Process the raw materials as follows:

[0055] 1) Ceramic Phase Premixing: Place 450g TiC powder and 100g Al2O3 powder in a planetary ball mill. Add 3mm diameter zirconia balls at a ball-to-powder ratio of 12:1. Maintain positive pressure with argon (99.99% purity) and mill at 400 rpm for 5 hours. Stop the mill every hour for 10 minutes to cool the mixture to prevent local overheating.

[0056] 2) Metal phase dehydration: 350g Ni-30Co alloy powder and 50g Mo powder were mixed and placed in a vacuum drying oven at a vacuum degree of ≤10 -3 Dry at 120℃ for 2 hours, and pass through 100 mesh sieve for later use.

[0057] S2. 550 g of the ball-milled ceramic phase premixed powder and 400 g of the dehydrated metal binder phase powder were placed in a ball mill and mixed for 3 h to obtain a composite powder.

[0058] S3, fill the composite powder into a graphite mold with a diameter of 50mm and an inner wall coated with BN release agent, put it into a vacuum hot press furnace, and evacuate to ≤10 -4 After Pa, single-stage sintering was carried out at a temperature of 1400°C, a pressure of 30 MPa, and the temperature was kept for 3 hours.

[0059] The performance test of the product in Comparative Example 1 showed that the hardness of Comparative Example 1 was 88.2HRA, which was lower than that of Example 1 by 4.6%. The bending strength of Comparative Example 1 was only 980MPa, which was 21.6% lower than that of Example 1. The density of Comparative Example 1 was 96.5%, which was 2.7% lower than that of Example 1. The high temperature oxidation weight gain of Comparative Example 1 reached 3.2mg / cm 2 This value is three times that of Example 1, that is, it increases by 300% compared with Example 1, indicating that the initial combination of the ceramic phase and the metal bonding phase in this comparative example is insufficient, and the interface defects increase.

[0060] Comparative Example 2

[0061] In this comparative example, the rare earth additive was changed to Y2O3 (without fluoride), and the rest was the same as in Example 1. The specific preparation steps were the same as in Example 1, except that the rare earth slurry in S1 was changed to contain only Y2O3, and ultrasonic dispersion was performed for 1 hour; the sintering pressure in step S3 was all changed to 30 MPa.

[0062] The product was tested for performance, and its density was 97.8%, which was 1.4% lower than that of Example 1. The weight gain after oxidation at 1000°C was 1.5 mg / cm 2 , which is more than that in comparative example 1. SEM detection shows that the rare earth agglomeration rate is 18%. The above results show that this comparative example lacks the interfacial wettability regulating effect of nano-fluoride and the rare earth is insufficiently enriched at the interface.

[0063] Therefore, the present invention provides a rare earth metal ceramic and a preparation method thereof, which solves the problem of difficult dispersion of traditional single rare earth additions through the synergistic effect of oxide grain boundary purification and fluoride liquid phase sintering in a dual-phase rare earth system. Through staged hot pressing sintering, dual optimization of grain refinement and density improvement is achieved, thereby enhancing the high-temperature oxidation resistance and interface bonding strength of the metal ceramic.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A rare earth metal ceramic, characterized in that: Calculated by mass percentage, it includes 45-65% ceramic phase, 30-50% metal bonding phase, and 3-8% rare earth additive, wherein the ceramic phase is composed of one of TiC and WC and one of Al2O3 and ZrO2, the metal bonding phase is composed of Ni-Co alloy and Mo or Cr, and the rare earth additive is composed of mixed rare earth oxide and nano rare earth fluoride, and the mass ratio of mixed rare earth oxide to rare earth fluoride is (8-9):(1-2).

2. The rare earth metal ceramic according to claim 1, characterized in that: In the Ni-Co alloy, the molar ratio of Ni to Co is 3:1 to 5:1, the mixed rare earth oxide is composed of Y2O3, CeO2, and La2O3 in a molar ratio of 1:1:1, and the rare earth fluoride is one or a mixture of YF3 and LaF3.

3. A method for preparing the rare earth metal ceramic according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Raw material preparation: TiC powder or WC powder and Al2O3 powder or ZrO2 powder are placed in a ball mill and ball-milled under inert gas to obtain a ceramic phase premixed powder; Ni-Co alloy powder is mixed with Mo powder or Cr powder and then vacuum-dried to obtain a metal binder phase powder; mixed rare earth oxides and rare earth fluorides are added to anhydrous ethanol and ultrasonically dispersed to obtain a uniform slurry; S2, mixing the ceramic phase premixed powder and the metal binder phase powder, adding the slurry in multiple times, and simultaneously performing vacuum stirring. After the mixing is completed, the mixture is spray-dried to obtain a composite powder coated with a rare earth layer; S3. The composite powder is loaded into a graphite mold and placed in a vacuum hot press furnace for two-stage sintering. The first stage is sintered at a temperature of 850-950°C, a pressure of 20-30 MPa, and a holding temperature of 1 hour. The second stage is sintered at a temperature of 1350-1450°C, a pressure of 40-60 MPa, and a holding temperature of 2 hours. After sintering, the material is cooled to room temperature at a cooling rate of 5 to 10°C / min to obtain rare earth metal ceramics.

4. The method for preparing a rare earth metal ceramic according to claim 3, wherein: In the S1, the mass ratio of TiC powder or WC powder to Al2O3 powder or ZrO2 powder is (6-10):(1-3); the mass ratio of Ni-Co alloy powder to Mo powder or Cr powder is (5-8):(1-2).

5. The method for preparing a rare earth metal ceramic according to claim 3, wherein: In the S1, the ball milling time is 4 to 6 hours, the ball-to-material ratio is (8 to 12):1, and the ball milling medium is zirconia ball; during the vacuum drying process, the vacuum degree is ≤10 - 3 Pa, temperature is 120℃, vacuum time is 1.5~2h; ultrasonic time is 1~3h.

6. The method for preparing a rare earth metal ceramic according to claim 3, wherein: In the above-mentioned S1, the particle size of the rare earth fluoride is 50 to 100 nm.

7. The method for preparing a rare earth metal ceramic according to claim 3, wherein: In the S2, during the vacuum stirring process, the vacuum degree is ≤10 -2 Pa; during the spray drying process, the inlet air temperature is 160-190°C and the atomization pressure is 0.3 MPa.

8. The method for preparing a rare earth metal ceramic according to claim 3, wherein: In the above-mentioned S3, the heating rate of the first stage sintering is 5-15°C / min, and the heating rate of the second stage sintering is 10-20°C / min.