Method for producing composite zirconium ceramics with silicon additives, having increased compressive strength and transformation-induced plasticity

Abstract

FIELD: composite ceramic.SUBSTANCE: invention relates to methods for producing high-strength materials, namely composite ceramics based on zirconium dioxide stabilized in the tetragonal phase, capable of transformation-induced plasticity at room temperature. The invention can be used in the production of durable and wear-resistant parts for structural and medical purposes, including those operating under conditions of high temperatures and high humidity or aggressive environments (dies, bearings, grinding balls, cutting tools, implants, etc.). To obtain high-strength composite zirconium ceramics, fine powders of zirconium dioxide 90.625 wt.%, calcium oxide 2.9 wt.%, aluminium oxide 4.975 wt.% and silicon 0.5 wt.% are mixed mechanically. The resulting powder mixture is dispersed and homogenized in distilled water, ground in a planetary mill, and the mixture is dried in a dry-heat oven at a temperature of 80 °C and separation from grinding balls. The samples are formed by uniaxial pressing at a pressure of 500 MPa for 20 minutes. Sintering is carried out in two stages: first at a temperature of 1300 °C for 5 minutes, then at a temperature of 1200 °C for 4 hours.EFFECT: production of composite ceramics based on zirconium dioxide with increased compressive strength and the ability to undergo transformation-induced plasticity at room temperature.1 cl, 1 dwg, 1 tbl, 1 ex

Description

[0001] The invention relates to methods for producing high-strength composite ceramics based on tetragonal-stabilized zirconia capable of transformation-induced plasticity at room temperature. Zirconia ceramics (stabilized in the tetragonal phase) strengthened with aluminum oxide, or ATZ ceramics (Alumina Toughened Zirconia), possess a unique combination of outstanding mechanical properties with chemical, thermal, and radiation resistance, as well as bioinertness, providing it with a wide range of practical applications in industry and medicine.

[0002] Two main drawbacks of ATZ ceramics are known: 1) low-temperature degradation (LTD), which is most pronounced when using Y2O3 as a stabilizer for the tetragonal phase of t-ZrO2; 2) brittleness at room temperatures. However, methods for suppressing LTD and special additives to ATZ ceramics that provide them with transformation-induced plasticity are known. For example:

[0003] Composite ceramics based on zirconium dioxide (reinforced with aluminum oxide) are known, which use stabilizers of the tetragonal phase of zirconium dioxide that are alternative to yttrium oxide: СеО2 [Patent RU 2710648 C1, published 12 / 30 / 2019 Bulletin No. 1] and CaO [Dmitrievskii A.A., Zhigacheva DG, Efremova NY, Umrikhin AV, Phase composition stability of nanostractured composite ceramics based on CaO-ZrO2 under hydrothermal impact / / Nanotechnologies in Russia. 2019. V. 14. No. 3-4, pp. 125-131. DOI: 10.1134 / S1995078019020058]. Such ceramics are less susceptible to LTD.

[0004] The disadvantage of these materials is their lower microhardness and flexural strength (compared to ATZ ceramics stabilized with Y2O3), as well as their brittleness at room temperature.

[0005] ATZ ceramics stabilized with CeO2 and SrAl additives are known 12 O 19(8 об. %) [Chevalier J., Liens A., Reveron Н., Zhang F., Reynaud P., Douillard Th., Preiss L., Sergo V., Lughi V., Swain M., Courtois N., Zirconia-based composites with a metal-like mechanical behavior / / J. Am. Ceram. Soc. 2020. V. 103. P. 1482–1513. DOI: 10.1111 / jace. 16903], Neither Ca(NO3)2, nor Sr(NO3)2[M. Li, B. Tunca, B. Van Meerbeek, et al. al., Tough and damage-tolerant monolithic zirconia ceramics with transformation-induced plasticity by grain-boundary segregation, J. Eur. Ceram. Soc. 43 (2023) 2078–2 https: / / doi.org / 10.1016 / j.jeurceramsoc.2022.11.069], and the amount of CaO catalyst, in the presence of SiO2(2-5 min. %); [Dmitrievskiy AA, Efremova N.Yu., Zhigacheva DG, Ovchinnikov PN, Vasyukov VV, Kobzev VV, Rabotyagova DI, Room-temperature plasticity of alumina-toughened zirconia with silica addition, International Journal of Refractory Metals and Hard Materials, 2024. V. 119. p. 106527. DOI: 10.1016 / j.ijrmhm.2023.106527; Patent RU 2701765 C1, published 01.10.2019 Bulletin No. 28], which are characterized by deviation from elastic deformation during four-point bending, or uniaxial compression at room temperature.

[0006] The disadvantage of the listed composite ceramics is that oxygen-containing compounds (SrAl 12 O 19 , Ca(NO3)2, Sr(NO3)2, or SiO2). The dissociation of these compounds during the sintering process of ceramics can cause an excess of oxygen in the structure of tetragonal zirconium dioxide, which prevents the strengthening of the ceramics.

[0007] The closest analogue of the invention in terms of composition and technological modes for the production of high-strength composite ceramics is a method for producing nanostructured composite ceramics based on zirconium, aluminum, and silicon oxides [RU 2701765 C1, published 01.10.2019 Bulletin No. 28]. In this invention, by introducing silicon dioxide additives into ATZ ceramics (in which CaO was used as a stabilizer for the tetragonal phase of zirconium dioxide t-ZrO2), a high-density composite ceramics with increased values ​​​​of compressive strength and fracture toughness was obtained. It is important to note that the composite ceramics developed and described in this invention have the ability to inelastic deformation (transformation-induced plasticity).

[0008] The disadvantage of this method for producing composite ceramics is the excessive saturation of zirconium dioxide grains with oxygen as a result of the dissociation of SiO2 during the sintering of silicon-containing ATZ+SO2 ceramics, which prevents the achievement of the highest possible strength properties and ultimate deformations.

[0009] The objective of the invention is to obtain composite ceramics based on zirconium dioxide (stabilized in the tetragonal phase by calcium oxide), reinforced with aluminum oxide, with the addition of crystalline silicon, characterized by increased compressive strength and transformation-induced plasticity.

[0010] The stated problem is solved by the fact that the claimed method for producing composite ceramics achieves increased strength and transformation-induced plasticity during uniaxial compression at room temperature by introducing a special crystalline silicon additive into the ATZ ceramic. Furthermore, the use of calcium oxide as a stabilizer for the tetragonal phase t-ZrO2 in the production of the claimed ceramics increases the ceramics' resistance to low-temperature degradation and reduces its sintering temperature to 1300°C. The latter, firstly, helps reduce thermally stimulated grain growth and secondly, reduces equipment costs (high-temperature furnaces) and energy consumption.

[0011] It is known from the prior art that the formation of thin silicon-containing layers at the grain boundaries of ZrO2 causes a decrease in the height of the energy barrier for tetragonal-monoclinic transformations of zirconium dioxide, an associated increase in mechanically induced t-ZrO2→m-ZrO2 transformability and, as a consequence, provides transformation-induced plasticity and an increase in strength. [Dmitrievskiy A.A., Efremova N.Yu., Ovchinnikov P.N., Vasyukov V.V., Reversible transformation-induced plasticity of alumina toughened zirconia (ATZ) with SiO2additive / / ​​Ceramics International. 2025. V. 51. P. 15250-15255 DOI: 10.1016 / j.ceramint.2025.01.361]. However, the introduction of silicon dioxide into ATZ ceramics to form thin silicon-containing layers at the ZrO2 grain boundaries is associated with the formation of excess oxygen in the zirconia lattice. This negatively affects the strength properties of the resulting composite zirconia ceramics.

[0012] Thus, the proposed method for producing high-strength composite zirconium ceramics with transformation-induced plasticity (containing crystalline silicon as a special additive) ensures the formation of thin silicon-containing layers at the grain boundaries of ZrO2 and does not cause excess oxygen content in the zirconium dioxide lattice.

[0013] A distinctive feature of the proposed method is the use of crystalline (oxygen-free) silicon as a special additive to composite zirconia ceramics (stabilized in the tetragonal phase by calcium oxide) reinforced with aluminum oxide. This ensures increased compressive strength and transformation-induced plasticity at room temperature.

[0014] A silicon-doped zirconia ceramic composite with enhanced compressive strength and transformation-induced plasticity was prepared as follows. A powder mixture was prepared with the following weight ratios: ZrO2:CaO:Al2O3:Si 90.625:2.9:4.975:0.5. The resulting powder mixture was dispersed in distilled water (mixture:water weight ratio 1:3) and homogenized in an ultrasonic bath. The mixture was ground in a planetary mill with zirconium dioxide balls for 5 hours. The grinding mode was selected such that the kinetic energy of the balls before collision corresponded to 2×10 -5J. The suspensions are then dried in a dry-heat oven (in an air atmosphere) at a temperature of T0 = 80°C for 24 hours, and the resulting powder mixture is separated from the grinding balls. The prepared powder mixture is poured into a press mold. Ceramics are formed by uniaxial pressing at a pressure of 500 MPa for 20 minutes. Composite ceramics are sintered in an air atmosphere using a two-stage mode: first, they are heated to a temperature of T1 = 1300°C at a constant rate (5°C / min) and held for 5 minutes, then the temperature is reduced to T2 = 1200°C and held for 4 hours. Cooling to room temperature is carried out at a rate not exceeding 5°C / min.

[0015] Example.

[0016] The initial powder mixture was prepared using zirconium dioxide (Sigma-Aldrich, USA), aluminum oxide (Hongwu international group LTD, Hong Kong), calcium oxide (Reachem, Russia), and silicon (ELMA, Russia) in the specified ratios. The powder mixture was mixed, ground, and nanostructured in a Pulverisetter 7 Premium Line planetary mill (Fritsch, Germany) using magnesium oxide-stabilized zirconium dioxide balls (1.5 mm in diameter).

[0017] After grinding, the contents of the bowls (the resulting suspension along with the grinding balls) were placed in a dry-heat oven and dried for 24 hours at 80°C. Next, separation was performed: the powder mixture was separated from the grinding balls using an Analysette 3 Spartan vibration analyzer (Fritsch, Germany) and a sieve with a mesh size of 1 mm.

[0018] The specimens were formed in a cylindrical mold and subsequently sintered under the conditions described above. A SNOL 4 / 1300 muffle furnace (Umega, Lithuania) was used for sintering. To study the mechanical properties by uniaxial compression (registering load-deformation diagrams), parallelepipeds with a cross-section of 2 × 2 mm were cut from the cylindrical specimens. Cutting was performed using a diamond disk. Surface preparation for microhardness and elastic modulus analysis by indentation was performed using a BETA-VECTOR, SIMPLIMET 1000, and ISOMET 4000 sample preparation system (Buehler, USA). To relieve stresses arising from cutting, grinding, and polishing, the specimens were annealed. Annealing was performed in a single-stage mode: samples were heated to 1200°C and held for 1 hour, then cooled to 900°C. The temperature change rate did not exceed 5°C / min.Cooling from temperature T = 900°C to room temperature was uncontrolled (in a closed furnace).

[0019] To compare the strength properties of composite zirconia ceramics reinforced with aluminum oxide with the addition of silicon (ATZ+Si) and ATZ ceramics with the addition of silicon dioxide (ATZ+SiO2), as well as silicon-free ATZ ceramics, samples of the latter two types were also produced using the technology described above. In this case, the ratios of the component concentrations were maintained as follows: for composite ceramics with the addition of silicon dioxide ZrO2:CaO:Al2O3:SiO2 - 91.17:2.89:4.95:0.99; for silicon-free ceramics - ZrO2:CaO:Al2O3- 91.67:2.9:5. Note that the concentration of silicon dioxide in ATZ+SiO2 ceramics was chosen in such a way that two conditions would be met. Firstly, the concentration of SiO2 should correspond (according to the data of [Dmitrievskiy AA, Efremova N.Yu., Zhigacheva DG, Ovchirmikov PN, Vasyukov VV, Kobzev VV, Rabotyagova DI, Room-temperature plasticity of alumina-toughened zirconia with silica addition, International Journal of Refractory Metals and Hard Materials, 2024. V. 119. P.106527. DOI: 10.1016 / j.ijrmhm.2023.106527]) the maximum dependence of the compressive strength of ATZ+SiO2 ceramics on the SiO2 concentration in them. Secondly, the atomic content of Si in ATZ+Si and ATZ+SiO2 ceramics should be the same.

[0020] Indentation (to determine microhardness H) was performed using a Vickers pyramid on an automatic hardness tester Duramin-A300 (EmcoTest, Austria).

[0021] A floor-mounted, dual-column servohydraulic testing machine MTS 870 (Landmark, USA) was used to record the stress-strain curve (σ-ε diagram). The piston displacement velocity was kept constant (1 μm / s). The modulus of elasticity E (as the slope of the stress-strain curve at the elastic deformation stage) and the compressive strength σ were determined from the stress-strain curve. C and the ultimate relative deformation ε C .

[0022] The values ​​of the main measured characteristics of composite zirconia ceramics with the addition of silicon (ATZ+Si), as well as ATZ+SiO2 and ATZ ceramics are presented in Table 1.

[0023] Table 1. Mechanical properties of composite zirconia ceramics with the addition of silicon (ATZ+Si) and silicon dioxide (ATZ+SiO2), as well as silicon-free ATZ ceramics.

[0024]

[0025] As an example demonstrating the transformation-induced plasticity of silicon-containing composite zirconia ceramics, Fig. 1 shows the typical stress-strain curves recorded during uniaxial compression (at room temperature) of ATZ+Si, ATZ+SiO2, and ATZ ceramics samples. It is evident that, unlike ATZ ceramics, which are elastically deformed to failure, ATZ+Si and ATZ+SiO2 ceramics exhibit deviation from elastic deformation, that is, according to [Dmitrievskiy A.A., Efremova N.Yu., Zhigacheva DG, Ovcmnnikov PN, Vasyukov VV, Kobzev VV, Rabotyagova DI, Room-temperature plasticity of alumina-toughened zirconia with silica addition / / International Journal of Refractory Metals and Hard Materials, 2024. V. 119. P. 106527. DOI: 10.1016 / j.ijrmhm.2023.106527], transformation-induced plasticity. The ultimate residual deformation in ATZ+Si ceramics can reach values ​​of ε = 0.25% (Fig. 1).

[0026] It is important to note that the use of silicon as an additive to ATZ ceramics provides an increase in compressive strength by 30.8% (relative to silicon-free ATZ ceramics) and by 4.9% (relative to ATZ+SiO2 ceramics, i.e., ceramics with the addition of silicon dioxide). Furthermore, the use of silicon as a special additive to ATZ ceramics (at a concentration of 0.5 wt%) causes a much smaller change in elastic modulus compared to changes caused by the introduction of SiO2 additive (in concentrations equivalent to the amount of silicon).

[0027] Thus, increasing the compressive strength (σ с= 2.8±0.1 GPa) and the appearance of transformation-induced plasticity (maximum residual strain determined from the stress-strain curve ε = 0.25±0.03%) in composite zirconium ceramics (stabilized in the tetragonal phase by calcium oxide), reinforced with aluminum oxide, is achieved by introducing into its composition an additive of Si (at a concentration of 0.5 wt.%).

[0028] Fig. 1 shows typical stress-strain curves recorded during uniaxial compression at room temperature of ATZ+Si (curve 1), ATZ+SiO2 (curve 2), and ATZ ceramics (curve 3) samples.

Claims

A method for producing high-strength composite ceramics capable of transformation-induced plasticity, including preparing a mixture of zirconium dioxide, aluminum oxide, calcium oxide and additive powders, wet grinding the mixture in a planetary mill at a mass ratio of the mixture to distilled water of 1:3 for grinding and nanostructuring the mixture, drying in a dry-heat oven in an air atmosphere at a temperature of 80 ° C for 24 hours, molding samples by uniaxial dry pressing at a pressure of 500 MPa, sintering in air in a two-stage mode, in which at the first stage the samples are heated to a temperature of T1 = 1300 ° C, then the temperature is reduced to T2 = 1200 ° C with a holding time of 4 hours, characterized in that crystalline silicon is used as an additive at a weight ratio of powders: zirconium dioxide 90.625%, aluminum oxide 4.975%, calcium oxide 2.9% and silicon 0.5%, and also the fact that uniaxial pressing is carried out for 20 minutes,and during sintering, a 5-minute hold is carried out at a temperature of T1=1300°C.

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