Multiphase Ceramics Research Articles

Top-down material design of multi-phase ceramics

A methodology for the top-down design of ceramic materials composed of two or more phases has been developed. It is demonstrated on the example of the well-known alumina/zirconia (AZ) material system. Core of the method is an automated simulation chain based on representative volume elements for generating a database of microstructure-property relations. The database emanating from this simulation chain was used to train machine learning models for enabling fast predictions of material microstructure according to preset material properties. A gradient boosting algorithm provided reliable and fast calculations for the exemplary chosen thermal and mechanical properties of the AZ material system. This enables reverse identification of selected microstructural parameters needed to obtain a specific value of a material property of interest, or briefly: top-down ceramic material design. • An automatized microstructure-property simulation chain for ceramics was developed. • The simulation concept can handle complex phenomena like internal thermal stresses. • A machine learning model (gradient boosting) was trained on calculated properties. • The ML model enables fast reverse identification of microstructural parameters.

Dielectric and microwave absorption properties of polymer‐derived TiC/SiC/SiOC multiphase ceramics in X band

AbstractPolymer‐derived TiC/SiC/SiOC ceramics were prepared using tetrabutyl titanate (TBT)‐modified polysiloxane (PSO) as precursor. The effects of heat treatment temperature and TBT content in precursor on the microstructure, phase composition, and microwave absorbing properties of TiC/SiC/SiOC ceramics were investigated. The crystallinity of the ceramics increases with the increase of heat treatment temperature. With the increase of TBT content, the TiC content of the ceramics increases and the SiC content decreases. When the TBT content ranges from 1 to 5 wt.%, the increase of TBT content has little effect on the real part of the dielectric constant of TiC/SiC/SiOC ceramics. When the TBT content is 7 wt.%, the imaginary part of the dielectric constant of the ceramics changes. For TiC/SiC/SiOC ceramic obtained from the pyrolysis of PSO‐TBT precursor with 7 wt.% TBT, the dielectric constant is within the target electromagnetic parameters. Therefore, it has an effective absorption bandwidth of 4.2 GHz, covering the entire X band, showing an excellent microwave absorbing performance.

Study of phase transformation dynamics, structural and optical properties of ferroelectric SrTiO3 ceramics

In this work, ferroelectrics of the SrTiO3 type were obtained using solid-phase synthesis method and subsequent thermal annealing. Using the X-ray diffraction method, the dynamics of phase transformations of the TiO2/Sr2Ti6O13/Sr3Ti2O7 → TiO2/Sr2Ti6O13/Sr3Ti2O7/SrTiO3 → SrTiO3/Ti3O5 type was established. According to the data obtained, it was found that thermal annealing in the range of 200–1100 °C allows obtaining both complex multiphase ceramics and SrTiO3 ceramics with a perovskite structure. As a result of determination of the optical properties, it was found that an increase in the structural ordering degree and the formation of a stable SrTiO3 phase, a broad induced absorption band appears in the region of 3.0–3.3 eV, with a maximum of 3.14 eV. During the determination of ferroelectric characteristics, it was found that the formation of a stable SrTiO3 phase in ceramics structure leads to a sharp increase in dielectric constant and a decrease in Curie-Weiss temperature from 125-130 °C to 105–110 °C.

Microstructure and wear properties of TiN–Al2O3–Cr2B multiphase ceramics in-situ reinforced CoCrFeMnNi high-entropy alloy coating

In order to improve the hardness and wear resistance of high entropy alloy (HEA) coating, the TiN–Al 2 O 3 –Cr 2 B multiphase ceramics reinforced CoCrFeMnNi high-entropy alloy coating was prepared by the plasma cladding. The composite coating was composed of face-centered-cubic (FCC) structure alloy phase and the in-situ synthesized TiN–Al 2 O 3 –Cr 2 B multiphase ceramics, and exhibited the good bonding in interface. Compared with the pure CoCrFeMnNi coating, the hardness of the composite coating (320 HV 0.3 ) increased by 71.90%, owing to the dispersion distribution of TiN–Al 2 O 3 –Cr 2 B multiphase ceramics and the solid solution of Al/Ti in the HEA matrix. The wear rate of reinforced HEA composite coating were 0.51 × 10 −5 , 0.98 × 10 −5 , 0.30 × 10 −5 and 0.25 × 10 −5 mm 3 N −1 m −1 , which were 20.48% (25 °C), 34.75% (200 °C), 16.13% (400 °C) and 10.12% (600 °C) of pure HEA coating, respectively. The wear mechanisms of the cladded coatings were adhesive wear, abrasive wear, oxidation wear. The strengthening of TiN–Al 2 O 3 –Cr 2 B multiphase ceramics acted as a disincentive to the adhesive wear of the composite coating during high temperature sliding progress. Besides, the multiphase ceramics played the load-bearing and load transfer role to improve the wear resistance of the composite coating. • The TiN–Al 2 O 3 –Cr 2 B multiphase ceramics reinforced CoCrFeMnNi high-entropy alloy coating was prepared by plasma cladding. • The TiN–Al 2 O 3 –Cr 2 B multiphase ceramics were in-stiu synthesized in HEA matrix. • The strengthening mechanisms were dispersion distribution of multiphase ceramics and the solution of Al/Ti in HEA matrix. • The ceramics in the composite coating played the load-bearing and load transfer role to improve the wear resistance.

The one-step pyrolysis process of rattan-based silicon carbide multiphase ceramics prepared by sol\u2013gel method

The sol–gel method was used to prepare rattan-based silicon carbide (R–SiC) composite ceramics under different pyrolysis parameters through adjustment of the temperature and retention time of the one-step pyrolysis process. The crystalline phases, microscopic morphology, element distribution and specific surface area of the silicon carbide (SiC) were characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), X-ray fluorescence spectrometer (XRF), field-emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and N2 physisorption. The results showed that the R–SiC prepared at different pyrolysis parameters was able to retain the porous structure of pristine rattan stem. The R–SiC prepared at 1500 ℃ for 120 min possessed the lowest density (0.25 g/cm3), the largest specific surface area (43.38 m2/g) and the highest SiC yield (44.24%). The SiC whisker was the major SiC morphology on the cross section of the R–SiC. Furthermore, the pyrolysis parameters were optimized with the SiC preparation process reaction mechanism, and material transformation methods were also discussed. This one-step pyrolysis process simplified the preparation of biogenic SiC ceramics and thus provided a potential route for the value-added utilization of rattan.

Study on low temperature sintering behavior and dielectric properties of BaTi4O9/La2O3-B2O3-CaO microwave dielectric ceramic

In this paper, La2O3-B2O3-CaO (LBC) glass ceramics were sintered at low temperature to density BaTi4O9 (BT4) microwave dielectric ceramics. The effects of composition ratio and sintering temperature on the micromorphology, phase composition and microwave dielectric properties of LBC/BT4 multiphase ceramics were investigated. Experimental results showed that LBC microcrystalline glass and BT4 happened between the ceramic interface reaction obviously, and with the increase of microcrystalline glass content and sintering temperature increases, density, dielectric constant epsilon εr value and the quality factor Qf value were increased after the first decrease. And the resonant frequency temperature coefficient of τf value with the increase of LBC content decreases, and with the increase of sintering temperature, it goes up and then it goes down. When the content of LBC glass ceramics is 50 wt%, LBC/BT4 multiphase ceramics sintered at 875 °C for 2 h have good microwave dielectric properties εr = 26, Qf = 8000 GHz, τf; = +150 ppm/°C.

Ultrafast preparation of Al2O3–ZrO2 multiphase ceramics with eutectic morphology via flash sintering

Herein, Al 2 O 3 –ZrO 2 multiphase ceramics with a eutectic molar ratio were prepared using the flash sintering technique at 1200 °C in 2 min. The samples were divided into two regions according to the microscopic morphology: multiphase ceramics zone and eutectic ceramics zone. The multiphase ceramics zone uniformly distributed irregular Al 2 O 3 and ZrO 2 phases. The eutectic zone presented typical eutectic morphology, where different morphologies of ZrO 2 was uniformly embedded in the Al 2 O 3 matrix, mainly showing fine lamellar, rod-like and irregular network morphology. Overall, flash sintering is a promising route to prepare high-performance multiphase ceramics.

Enhanced ablation resistance of HfB2-HfC/SiBCN ceramics under an oxyacetylene torch environment

• Hot-pressed HfB 2 -HfC/SiBCN ceramics were first successfully fabricated. • The mass and linear ablation rates of the HfB 2 -HfC/SiBCN were 0.0025 mg/s and 0.0004 mm/s. • The ablation mechanisms of HfB 2 -HfC/SiBCN ceramics have been proposed. To further improve the ablation resistance of SiBCN ceramics, nanosized HfB 2 was introduced by mechanical alloying and subsequent reactive hot-pressing techniques to fabricate HfB 2 -HfC/SiBCN multiphase ceramics. The mass and linear ablation rates of the 30 vol% HfB 2 -HfC containing SiBCN ceramics under an oxyacetylene flame for 10 s were lower than those of ZrB 2 -ZrN/SiBCN and SiBCN, reaching to 0.0025 mg/s and 0.0004 mm/s respectively. Even ablated for 60 s, no trace of cracks appeared on the ablation surface. Oxidation of ceramic matrix, denudation of oxides, erosion by the combustion flow and the re-oxidation of the exposed matrix governed the ablation process.

Columbite-rich multiphase TiO2 nanoceramic with superior mechanical and dielectric properties

Columbite-rich multiphase TiO2 nanoceramics with outstanding mechanical and dielectric properties were successfully prepared through high-pressure sintering by using anatase-type TiO2 as precursor. High-pressure sintering combined with phase transformation assisted consolidation can effectively refine the grain size of the recovered samples. This process is conducive to obtain nanocrystalline columbite-rich TiO2 ceramics with excellent performance. The highest hardness is approximately 12.76 GPa, which is 2.5 times higher than that of ordinary coarse-grained ceramics. The effect of columbite phase on the hardness of multiphase ceramics is discussed. The columbite-rich TiO2 ceramic shows a colossal permittivity (∼8 × 103) and low loss (∼0.2) at 1 kHz and room temperature, which are superior to that of undoped rutile polycrystalline ceramics. This ceramic shows a steadier frequency-dependent dielectric permittivity and loss than rutile TiO2 crystal. These results enrich the fundamental knowledge of columbite-rich TiO2, thereby enabling the exploitation of new applications.

Effect of Ti and its compounds on the mechanical properties and microstructure of B4C ceramics fabricated via pressureless sintering

The addition of Ti and its compounds particles has the potential to effectively enhance the fracture toughness of B 4 C ceramics. However, the influence of different Ti-based compounds on B 4 C ceramics has not been extensively studied. In this work, B 4 C–TiB 2 multiphase ceramics were prepared by adding 5% Ti or its compounds (TiO 2 , TiB 2 or TiC) in B 4 C and the effects of the additives on the B 4 C ceramics were studied. For this purpose, we adopted a sintering process carried out in situ in the absence of pressure at a temperature of 2250 °C for 1 h. It was evident from the results that the additives are capable of enhancing the sintering densification characteristics and the properties exhibited by B 4 C, as opposed to single-phase B 4 C ceramics. Additionally, different additives have varied effects on the microstructures and mechanical properties of B 4 C–TiB 2 multiphase ceramics. The results of the study indicate that the TiC-added sample exhibits the most optimal mechanical properties, with 4.52 MPa m 1/2 fracture toughness, 344.0 MPa flexural strength, 26.2 GPa hardness, and 516.0 GPa elastic modulus.

Fracture and damage model of composite ceramics

It is of great significance to study the damage and fracture mechanism of trigonometrically symmetric eutectic multiphase ceramics with excellent mechanical properties at room temperature and high temperature. According to the microstructure characteristics of inner triangular symmetric eutectic in multiphase ceramics, a two-scale cell model containing triangular symmetric eutectic was established. The fracture stress of cohesive bond in eutectic was calculated by considering the conditions of cohesive bond fracture at interface phase and fiber junction. The damage variable was introduced and combined with cohesive bond fracture stress to establish the microcosmic damage fracture stress model of eutectic Based on the Dugdale Barenblatt model, the damage localization band model is established by introducing the micro damage fracture stress as the residual strength. It is found that with the increase of fiber volume fraction, the strong confinement of interface phase is destroyed, the residual strength decreases and the length of damage localization band increases with the increase of fiber volume fraction. Reducing the damage degree and selecting the appropriate fiber volume content can increase the fracture stress of eutectic, and then reduce the length of damage localization band, increase the threshold value of crack instability propagation, and enhance the material strength.

Effective properties and elastic stress field of two-scale composite ceramics

Analysis of the effective properties and elastic stress field in two-scale composite ceramics as mechanical properties analyzer can be a daunting task to handle. Here, we address the most prominent hurdles, namely, the complex structure characteristics of dual-scale multiphase ceramics. We propose two-scale matrix-inclusion model and conducts the mechanical properties analysis of two types of scale interfaces to improve calculation accuracy. Our model estimates the different field at the nano-interface under different applied loadings, along with the considering on continuous condition of stress and displacement at nano-interface and the condition of far-field stress-strain. We show how to solve the problem of solving the elastic field of a thin interface layer into a problem of solving the incompletely combined interface elastic field under different conditions, analyzing the slip stress field of the meso-contact interface under longitudinal and transverse shear. • Proposed the analysis model of the effective properties and elastic stress field in two-scale composite ceramics. • The nano perfect interface model was established regarding on the nano structure characteristics of multiphase ceramics. • The microscopic contact interface model was established based on the weak connection characteristics of micro-interface.

Thermoelectric Multiphase Ceramics Based on Layered Calcium Cobaltite, as Synthesized Using Two-Stage Sintering

Multiphase ceramics are synthesized based on layered calcium cobaltite with a different cobalt oxide content by solid state synthesis followed by two-stage sintering. The phase composition is established, and the microstructure, electrical conductivity, and thermal electromotive force are investigated. The effect that the cation and phase compositions of ceramics have on its carrier transport properties and thermoelectric properties is established. The highest value for the power factor P is observed for multiphase ceramics with the composition Ca3Co3.4O9 + δ (0.7Ca3Co4O9 + δ + 0.3Ca3Co2O6), which is 265 μW/(m K2) at a temperature of 1100 K. This value is 20% higher than that for the Ca3Co4O9 + δ sample (P1100 = 218 μW/(m K2)) and exceeds the power factor value for low-density Ca3Co4O9 + δ ceramics prepared by the conventional solid state synthesis by a factor of 2.65.

Constitutive model of multiphase ceramics based on microcrack damage evolution

abstract The damage evolution of microcracks that dispersed in eutectic composite ceramics is an important factor leading to fracture failure. We propose a meso damage model (CMMC), which uses our proposed two-scale cellular model with microcracks, and fully considers the characteristics of the microstructure on the eutectic composite ceramics, thus providing a more objective structural modeling. In addition, there are two significant features existing in CMMC: One is to use the interaction direct derivative (IDD) estimate method to calculate the additional flexibility increment caused by a single open elliptical microcrack, which considers the spatial orientation of the microcrack. The other is that the additional flexibility tensor from the microcrack system is obtained by introducing probability density function and selecting appropriate microcrack growth criteria. Experiments on the related datasets show that CMMC achieves the consistent results compared with the experimental data. Furthermore, the effects of microcrack aspect ratio and microstructure parameters on the effective properties of multiphase ceramics were analyzed by using numerical method. • Damage evolution of microcracks in composite ceramics leading to fracture failure. • A meso damage model based on microcrack damage evolution is proposed. • Microcrack aspect ratio affects effective properties of multiphase ceramics. • Microstructure parameters influences effective properties of multiphase ceramics. • The additional flexibility tensor from the microcrack system is obtained.

Improving hydration resistance of MgO–CaO ceramics by in situ synthesized CaZrO3 coatings prepared using a non-hydrolytic sol

Abstract As refractories, MgO–CaO materials exhibit excellent properties such as high refractoriness and good thermal shock resistance; however, their poor hydration resistance limits their practical applications. In this study, calcium zirconate (CaZrO3) coatings were deposited on CaO and MgO–CaO ceramics by dipping the ceramics in a non-hydrolytic sol. The optimised coating on the MgO–CaO ceramics was prepared by dipping the ceramics once in a 0.6 mol/L zirconia sol. The CaZrO3 coating was in situ synthesized after calcination. The multiphase ceramics with different CaO contents were characterised using scanning electron microscopy to determine the grain sizes of MgO and CaO and to analyse the distribution of CaO in the MgO matrix and the surface porosity of the samples. The microstructure and phase analysis results showed that most of the CaO on the surface transformed into CaZrO3 and was located at the grain boundaries. The MgO–CaO ceramics with the CaZrO3 coatings, especially the ceramics with 20 wt% CaO, showed significantly improved hydration resistance as compared to the untreated ceramics.

Atomic-resolution Observations of Grain Boundary Segregation in Multiphase Ceramics by Aberration-corrected STEM

Atomic-resolution Observations of Grain Boundary Segregation in Multiphase Ceramics by Aberration-corrected STEM

The effect of transition metal carbides MeC (Me = Ti, Zr, Nb, Ta, and W) on mechanical properties of B4C ceramics fabricated via pressureless sintering

In this study, boron carbide-metallic boride (B 4 C-MeB x , Me = Ti, Zr, Nb, Ta, or W) multiphase ceramics were fabricated via in situ pressureless sintering at 2250 °C for 1 h. The effects of transition metal carbides, namely, TiC, ZrC, NbC, TaC, and WC, on the phase composition, microstructure, and mechanical properties of the ceramics were investigated. The results showed that MeC could facilitate the sintering densification of B 4 C by distributing second-phase particles uniformly throughout the B 4 C. Additionally, the main phases observed were B 4 C and (Me, W)B x (Me = Ti, Zr, Nb, or Ta) due to the doping of a small amount of WC during the ball milling process. As a result, the mechanical properties of B 4 C-MeB x showed significant improvements when compared with those of single-phase B 4 C ceramics. B 4 C–NbB 2 ceramics were found to exhibit the best mechanical properties, with an elastic modulus of 393.0 GPa, a hardness of 28.7 GPa, a flexural strength of 368.0 MPa, and a fracture toughness of 6.94 MPa m 1/2 .

Synthesis and pyrolysis of non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics

Abstract Multiphase ceramics like ZrC/SiC are promising candidates as ultra-high temperature ceramics for applications in extreme environments. In this work, non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics were synthesized by a one-pot reaction of three components – metal source, silicon source, and activating reagent. Molecular structures of the precursors were identified by 1H NMR and FTIR. Transformation process of the precursors to the ZrC/SiC ceramics was investigated via XRD and SEM. After heat-treatment at 1600 °C under argon, the obtained ZrC/SiC and HfC/SiC ceramics features a particle size of 100–200 nm and high metal content without excess carbon. The elemental composition of pyrolyzed ceramics can be tuned by varying the ratio of the reagents in the synthesis of precursors. This strategy also inspires a facile fabrication of composite ceramics with other elemental compositions.

Microstructure and wear behaviour of in-situ TiN-Al2O3 reinforced CoCrFeNiMn high-entropy alloys composite coatings fabricated by plasma cladding

• The in-situ TiN-Al 2 O 3 multiphase ceramic particles reinforced CoCrFeNiMn HEAs coating was prepared via plasma cladding. • The nano Al 2 O 3 were mainly wrapped by the micron TiN to form a multiphase ceramic structure. • The TiN-Al 2 O 3 particles are beneficial to enhance the hardness and wear resistance of the CoCrFeNiMn coatings. • The TiN-Al 2 O 3 particles promoted the abrasive wear and eliminated the adhesive wear during sliding process. The micro-nano TiN-Al 2 O 3 multiphase ceramics were in-situ synthesized in CoCrFeNiMn high-entropy alloys (HEAs) coating by plasma cladding. The as-prepared coating has a FCC single-phase. The hardness of TiN-Al 2 O 3 /CoCrFeNiMn HEAs composite coating was 17.6% higher than that of pure HEAs coating. The wear volume of the composite coating was 11.07 × 10 -3 mm 3 , which was 12.5% lower than that of pure HEAs coating. Furthermore, the TiN-Al 2 O 3 ceramic particles have significant effect to restrain the adhesive wear and promote the steady-state friction of the HEAs coating during sliding process.

Fabrication, microstructure, and properties of SiC/Al4SiC4 multiphase ceramics via an in-situ formed liquid phase sintering

The SiC/Al4SiC4 composites with the improved mechanical properties and thermal conductivity were fabricated by the in-situ reaction of polycarbosilane (PCS) and Al powders using spark plasma sintering. The addition of 5 wt% yttrium (Y) sintering additive was useful to obtain fully dense samples after sintering at a relatively low temperature of 1650 °C, due to the formation of a liquid phase during sintering. The average particle size of the in-situ formed SiC was ~300 nm. The fracture toughness (4.9 MP·m1/2), Vickers hardness (16.3 GPa), and thermal conductivity (15.8 W/(m·K)) of the SiC/Al4SiC4 composite sintered at 1650 °C were significantly higher than the hardness (13.2 GPa), fracture toughness (2.16 MPa·m1/2), and thermal conductivity (7.8 W/(m·K)) of the monolithic Al4SiC4 ceramics. The improved mechanical and thermal properties of the composites were attributed to the high density, fine grain size, as well as the optimized grain boundary structure of the SiC/Al4SiC4 composites.