Properties Of Silicon Nitride Ceramics Research Articles

Role of β-Si3N4 seeds in microstructure development and properties of silicon nitride ceramics: a comprehensive review

Role of β-Si3N4 seeds in microstructure development and properties of silicon nitride ceramics: a comprehensive review

Effects of the amount of magnesia on mechanical, thermal, and electrical properties of silicon nitride ceramics

Silicon nitride (Si3N4) ceramics were prepared using various amounts of magnesia (MgO) and a fixed amount of yttria as sintering additives, and their effects on the microstructures and four essential properties were evaluated: bending strength, fracture toughness, thermal conductivity, and dielectric breakdown strength (DBS). The microstructure varied with the MgO content; a smaller amount promoted grain growth, while an excess amount formed pores. The properties varied along with these structural changes. It was revealed that the four properties coexist at a high level in the range of 4–7 mol% of MgO. In addition, the large amount of MgO enhanced the electric conductivity of grain boundary and decreased the DBS. It is speculated that tips of multigrain junctions composed of a sufficiently large amount of glass modifier might work as the severe defects for the dielectric breakdown.

The influence of magnesium compounds on the properties of silicon nitride ceramics

AbstractSilicon nitride (Si3N4) ceramics using four compound sintering aids Er2O3–MgO, Er2O3–MgF3, Er2O3–Mg2Si, and Er2O3–Mg3N2. The effects of binary sintering aid types and temperatures on the microstructure, mechanical properties, and thermal conductivity of Si3N4 ceramics were investigated. The depolymerization effect of fluorine atoms introduced by MgF2 sintering additives on the silicate melt structure reduced the viscosity of the liquid phase. However, the existence of volatile phase leads to low density of Si3N4 ceramics. While the additional Si and N atoms increase the concentration of solute atoms, which was conducive to sintering densification of Si3N4 ceramics. Although Mg2Si and Mg3N2 sintering aids produced higher viscosity liquid phase compared with MgF2, denser Si3N4 ceramics were obtained at 1900°C. The Si3N4 ceramics doped with 5 mol% Er2O3 and 2 mol% Mg3N2 at 1900°C showed the excellent properties: including the highest Vickers hardness (16.8 GPa), flexural strength (912 MPa), and fracture toughness (8.1 MPa m1/2), as well as the desirable thermal conductivity (83 W/(m K)).

Microstructure and properties of silicon nitride ceramics fabricated by vat photopolymerization in combination with pressureless sintering

Silicon nitride (Si3N4) ceramics have been successfully manufactured using vat photopolymerization (VPP) technology. The formulated photocurable paste achieved a high solid loading (48 vol%) while maintaining low viscosity (3.2 Pa s at a shear rate of 30 s−1). Si3N4 ceramics doped with Al2O3–Y2O3 sintering aids were prepared using pressureless sintering at different temperatures (1650 °C, 1700 °C and 1750 °C) for 2 h. The resultant material exhibited a flexural strength of 613.3 ± 53.1 MPa, Vickers hardness of 12.6 ± 0.4 GPa, and a fracture toughness of 7.5 ± 0.3 MPa m1/2. X-ray diffraction (XRD) analysis has demonstrated a complete transformation from α-Si3N4 to β-Si3N4 at a sintering temperature of 1750 °C, where the resultant ceramic exhibited distinctive grain growth anisotropy. By investigating the shrinkage at different sintering temperatures, the sample at 1750 °C has a larger shrinkage in the Z-direction, which is also related to its anisotropic grain growth. Scanning electron microscopy (SEM) images have revealed the presence of elongated grains at a sintering temperature of 1750 °C. The combined effect of elongated grains and growth anisotropy serves to significantly enhance the overall mechanical properties of the material. This study advances current research on the preparation of high-performance Si3N4 ceramics by combining VPP technology with pressureless sintering.

Microscopic mechanical properties of silicon nitride ceramics corroded in sulfuric acid solution

The microscopic mechanical properties including the bending strength and Young’s modulus for Si3N4 ceramics doped with Y2O3 and Al2O3 which was immersed in 5 wt% sulfuric acid solution using microcantilever beam specimens was investigated in comparison with the macroscopic results obtained in conventional three-point bending tests. Both the properties sharply dropped in very short periods of the corrosion in the microcantilever tests, resulting from the dissolutions of yttrium and aluminum ions of grain boundary glass networks, followed by the hydration. After the drops at the beginning of the corrosion, they showed little degradation afterwards. The degradation behaviors of the mechanical properties are basically the same as those in conventional macroscopic approaches; however, they changes appear in very short periods of the corrosion in the microcantilever bending tests. This study also verified that a small difference of a ratio of sintering additives results in different grain boundary strengths of Si3N4 ceramics.

Progress in Preparation and Properties of Porous Silicon Nitride Ceramics

Porous silicon nitride ceramics is a promising functional ceramic material. In recent years, the research on the preparation of porous silicon nitride ceramics within different methods has been widely investigated. First, this work reviews the main synthesis methods of Si3N4 porous ceramics in detail, and compares the differences between strength and porosity caused by each method. The characteristics and advantages of different technologies under the current conditions were evaluated. Second, the dielectric properties, sound absorption properties and permeability properties of silicon nitride ceramics were compared and summarized based on the experimental results. Third, the applications fields of porous silicon nitride ceramics, such as smelting industry, catalyst carrier, sound absorption, wave-transparent, and biomedical fields were explored. Finally, the assessment of different silicon nitride ceramics preparation technologies was elaborated. This review gives an outlook on the porous silicon nitride ceramics, which shows great potential for further research in this field.

The effect of tungsten introduction on the tribological properties of Si3N4 ceramics paired with GCr15 steel under nonlubricated conditions

Silicon nitride ceramics were fabricated by gas pressure sintering using Y2O3 and Al2O3 as sintering aids, and 5 vol% tungsten particles were introduced to improve their wear resistance. The tribological properties of silicon nitride ceramics were tested as well as the relative density, hardness, flexural strength, and fracture toughness. During the wear process, the introduction of tungsten particles changes the morphology of the worn area and has a positive effect on wear reduction and lubrication. As a result, the friction coefficient of the system decreases, and the wear rate of silicon nitride ceramics is reduced to approximately half of the original. Tungsten particles were found to be a new lubricating phase for silicon nitride ceramics.

Synergistic effect of binary fluoride sintering additives on the properties of silicon nitride ceramics

A variety of combinations of YF3 and MgF2 were used as sintering aids in the fabrication of Si3N4 ceramics via gas pressure sintering (GPS). The synergistic effects of YF3 and MgF2 on the liquid viscosity, mechanical properties, thermal conductivities, and grain growth kinetics of the Si3N4 ceramics were investigated. The results showed that appropriately adjusting the YF3/MgF2 ratio could decrease liquid viscosity, reducing the diffusion energy barrier of the solute atom and promoting mass transfer. Meanwhile, the chemical bonding strength in the grain boundary complexions formed by the metal cations also influenced grain boundary migration. Samples doped with 4 mol% YF3 and 2 mol% MgF2 achieved the lowest grain growth exponent (n = 2.9) and growth activation energy (Q = 616.7 ± 16.5 kJ mol−1) as well as the highest thermal conductivity (83 W m−1 K−1) and fracture toughness (8.82 ± 0.13 MPa m1/2).

Some New Aspects of Microstructural Design of β-Si3N4Ceramics

AbstractA new possibility in tailoring microstructures and properties of silicon nitride ceramics is demonstrated by the use of fine b-Si3N4powders. Fine powders were produced by a plasmachemical synthesis and by crystallisation of amorphous Si3N4in the presence of an oxide nitride liquid. A wide range of microstructures can be obtained depending on sintering and powder characteristics. At low sintering temperatures microstructures consisting of nanosized, equiaxed grains were obtained, whereas at high temperatures or long sintering times microstructures consisting of fine needle like grains were formed. Microstructural analysis revealed a high anisotropic grain growth of the b grains in the fine grained materials.

Effect of LiYO2 addition on sintering behavior and indentation properties of silicon nitride ceramics

Abstract The influence of the sintering additive LiYO2 (5– 15 wt.%) on sintering behavior, microstructure and mechanical properties of Si3N4 ceramics was investigated. Since LiYO2 enables densification of Si3N4 at extraordinarily low temperatures, sintering was carried out in the range from 1200– 1700 °C. Densification was found to be enhanced with increasing additive content due to an increasing volume fraction of the liquid. The phase transformation and grain growth occurred through a solution-reprecipitation mechanism, where the precipitation took place preferentially on pre-existing β-Si3N4 nuclei (of which the starting powder already contained 20 wt.%). The indentation fracture toughness increased with both sintering time and additive content as a result of the growth of elongated grains.

A study on fabrication of silicon nitride-based advanced ceramic composite materials via spark plasma sintering

The present study provides an overview of the fabrication of silicon nitride (Si3N4)-based advanced ceramic materials using spark plasma sintering. Being an excellent engineering ceramic material, silicon nitride is extensively being used in tribological components, aerospace, and automotive industries due to its unique blend of thermo-mechanical, tribological, and chemical properties. The selection of the sintering process, as well as sintering aids, strongly affects the properties of silicon nitride ceramics. Several conventional sintering techniques have been utilized in the past to optimize the structure and properties of silicon nitride ceramics such as hot pressing. However, spark plasma sintering, a relatively new, non-conventional, powder consolidating technique has recently gained significant attention to fabricate silicon nitride ceramic due to high heating rates, extremely short sintering time, and relatively low sintering temperatures which renders it an ideal technique for mass production. Both the composition and concentration of sintering additives during processing play a vital part in achieving the final desired properties of the bulk silicon nitride ceramic materials. In this review, the critical aspects like the effects of additive composition, additive concentration, and sintering parameters on microstructure and bulk properties of silicon nitride ceramics fabricated via spark plasma sintering are presented. The review may come in handy for scientists and engineers concerned with fabricating future silicon nitride composites with desired properties and performance for different engineering applications.

Grain boundary character distributions in Si<sub>3</sub>N<sub>4</sub> ceramics

The structure of grain boundary has an essential influence on the physical and mechanical properties, especially the high-temperature mechanical properties of silicon nitride ceramics. In the present work, the five-parameter analysis method which is established based on electron backscatter diffraction (EBSD), and stereology and statistics are used to study the grain boundary character distributions in the two commercial silicon nitride ceramic ball samples. These two samples are both fabricated by hot isostatic pressing but made in China and abroad, respectively. The results indicate that the misorientation distributions of the two samples radically deviate from the random distribution at a rotation angle of 180°, showing that the frequency of the relevant grain boundaries is dramatically higher than that of the randomly distributed ones. These grain boundaries are mainly those possessing the misorientations of [0 1 –1 0]/180° and [–1 2 –1 0]/180°, corresponding to <i>Σ</i>2 and <i>Σ</i>3 boundaries, respectively. The grain boundary inter-connections (GBICs) of the <i>Σ</i>2 boundaries are basically the same in the two samples, and they are dominated mainly by the {0 0 0 1}/{0 0 0 1} basal-to-basal inter-connection. However, the GBICs of <i>Σ</i>3 boundaries are quite different in the two samples. they primarily the {–1 2 –1 0}/{–1 2 –1 0} prismatic-to-prismatic inter-connection for the <i>Σ</i>3 boundaries in the sample made in China, but it is mainly the {1 0 –1 0}/{1 0 –1 0} prismatic-to-prismatic inter-connection for the <i>Σ</i>3 boundary in the sample made abroad. Crystallographic analysis shows that the planar coincidence site density (PCSD) for the {–1 2 –1 0}/{–1 2 –1 0}, {0 0 0 1}/{0 0 0 1} and {1 0 –1 0}/{1 0 –1 0} GBIC are 2.45 /nm<sup>2</sup>, 7.95 /nm<sup>2</sup> and 9.10 /nm<sup>2</sup>, respectively, implying that the degree of the structural ordering increases in turn. Further discussion emphasizes that the grain boundaries possessing {1 0 –1 0}/{1 0 –1 0} GBIC and {0 0 0 1}/{0 0 0 1} GBIC should be one type of special boundaries due to their high degrees of structural ordering.

Synergistic Effect of Binary Fluoride Sintering Additives on the Properties of Silicon Nitride Ceramics

Synergistic Effect of Binary Fluoride Sintering Additives on the Properties of Silicon Nitride Ceramics

Influence of MXene (Ti3C2) Phase Addition on the Microstructure and Mechanical Properties of Silicon Nitride Ceramics.

This paper discusses the influence of Ti3C2 (MXene) addition on silicon nitride and its impact on the microstructure and mechanical properties of the latter. Composites were prepared through powder processing and sintered using the spark plasma sintering (SPS) technic. Relative density, hardness and fracture toughness, were analyzed. The highest fracture toughness at 5.3 MPa·m1/2 and the highest hardness at HV5 2217 were achieved for 0.7 and 2 wt.% Ti3C2, respectively. Moreover, the formation of the Si2N2O phase was observed as a result of both the MXene addition and the preservation of the α-Si3N4→β-Si3N4 phase transformation during the sintering process.

Elimination of grain boundaries and its effect on the properties of silicon nitride ceramics

To eliminate the excess grain boundary phase in silicon nitride ceramics prepared through hot pressing and a post-sintering heat treatment, carbon was introduced into the sintered ceramics. This was accomplished in two ways: first, a small amount of carbon was used as a sintering additive; however, this creates large pores in the ceramics, resulting in a decrease in the thermal conductivity and mechanical properties of the samples. Alternatively, the C/Si3N4 power bed could be used instead of the BN/Si3N4 power bed, which obviously eliminates the grain boundary phase. Further, the C/Si3N4 power bed possess excellent mechanical properties while increasing the thermal conductivity of the samples. Therefore, the silicon nitride ceramics with 123 W m−1 K−1 thermal conductivity and 986 MPa bending strength of can be obtained using the C/Si3N4 powder bed during the post-sintering heat treatment.

Preparation of Si3N4 ceramics by aqueous gelcasting using non-toxic agar powder as gelling agent without cooling crosslink process

Abstract A non-toxic and low-cost gelcasting system was successfully developed using agar as gelling agent to fabricate silicon nitride ceramic green bodies without cooling crosslink process, and silicon nitride ceramic was obtained by pressureless sintering. The effects of agar contents on rheological behavior of silicon nitride suspension, microstructure and mechanical properties of silicon nitride ceramics were investigated. The silicon nitride ceramic suspension with 45 vol% solid loading using 1.2 wt% ammonium polyacrylate (PAA-NH4) as dispersant was successfully prepared for gelcasting. After removing binder at 800 °C for 2 h and pressureless sintering at 1800 °C for 2 h, the silicon nitride ceramics exhibited homogeneous and interlocking microstructure composed of elongated β-Si3N4 phase, which contributes to its mechanical properties. With the increase of agar powder content from 0.25 wt% to 1.5 wt%, the shrinkage and flexural strength of the silicon nitride ceramics increased firstly and then decreased. When the agar powder content was 0.5 wt%, the silicon nitride ceramics had the optimized flexural strength (218 ± 25 MPa) with relative density of 92.85 ± 2.19% and the shrinkage of 16.03 ± 0.15%. Using agar as gelling agent to prepare silicon nitride ceramics by gelcasting is believed to be a novel and low-cost method, which could be used to prepare other high performance ceramics in the future.

New method of free silicon determination in pressureless sintered silicon nitride by Raman spectroscopy and XRD

Abstract Formation of silicon affects different physical properties of silicon nitride ceramics. Decomposition of Si3N4 and formation of free Si are highly important processes and depend on many factors. The proposed method of combined nano-Raman spectroscopy and X-ray diffraction (XRD) allows quantitative analysis of Si in silicon nitride. Raman spectroscopy enables the determination of atomic bonds and rapid and easy identification of free silicon. Further analysis of the crystalline phases by XRD enables the calculation of the amount of free silicon. The proposed complex method allows the characterization of such complicated processes as silicon nitride decomposition, microstructure formation and, in particular, the formation of the nanoscale grain boundary phase because Si nanosized precipitates are the nucleants of secondary phases during crystallization. Strong 522.8 cm−1 mode and 943.1–984.3 cm−1 transverse optical modes of free Si were clearly observed in the investigated silicon nitride that was subjected to pressureless sintering at 1800 °C. Reported ceramics demonstrated typical microstructures with elongated grains and relatively high microhardness and Young's modulus. It was shown that the aspect ratio depended linearly on the microhardness and Young's modulus. High values of the Young's modulus (more than 290 GPa) and microhardness (more than 1800 HV) were shown for reported silicon nitride produced by hot pressing and pressureless sintering via cold isostatic pressing with a higher quantity of sintering agent. The features of molecular structure of the reported Si3N4 ceramics were clearly described and discussed in detail and were found to be in good agreement with the microstructure and phase composition of these ceramics.

Effects of different types of rare earth oxide additives on the properties of silicon nitride ceramic substrates

Abstract 5 wt% of different types of rare earth oxides (Re2O3, Re = Lu, La, Yb, Y, Nd, Er, Sm, Ce, Dy, Eu, Gd) and 2 wt% MgO as additives were selected in this study based on previous studies on rare earth oxide additive concentrations. The effects of rare earth oxide type on the microstructure, phase composition, thermal conductivity, mechanical properties, and dielectric properties of silicon nitride ceramics were systematically investigated. Samples doped with rare earth oxides with smaller ionic radii (such as Yb2O3, Lu2O3, Er2O3, and Dy2O3) showed higher thermal conductivity. Samples doped with Eu2O3 and Yb2O3 showed fine-grained microstructures due to inhibition of dissolution, diffusion, and re-precipitation of silicon nitride. Silicon nitride ceramics doped with Eu2O3 showed the lowest thermal conductivity and dielectric constant (

High α-β phase transition and properties of YbF3-added porous Si3N4 ceramics obtained by low temperature pressureless sintering

In this paper, we used YbF3 as a sintering additive to get a high α-β phase transition in porous Si3N4 ceramics. The mechanism of YbF3 as sintering additives as well as the relationship between microstructure and mechanical properties have been investigated in detail. In addition, we used pressureless sintering to lower the temperature to 1550 °C. YbF3 makes α-Si3N4 completely transform to β-Si3N4, whereas only 41.1% β-Si3N4 could be obtained with Yb2O3. This process yielded ceramics with more flexural strength and increased fracture toughness using less energy. In addition, using YbF3 substituted for part Yb2O3 could promote sintering behaviors of Si3N4 ceramics at low temperature to increase α-β phase transition rate and improve the properties of silicon nitride ceramics significantly. In particular, when we used YbF3-Yb2O3 as additives, we obtained a flexural strength of 269.87 MPa and a fracture toughness of 4.59 MPa·m1/2.

Investigation on mechanical properties and microstructure of silicon nitride ceramics fabricated by spark plasma sintering

In order to prepare high-performance and stable performance silicon nitride-based ceramic cutting tools, orthogonal experiment was carried out firstly to study the influence of sintering temperature and sintering aids (MgSiN2, Y2O3 and CeO2) on the densification and mechanical properties of the Si3N4 materials by spark plasma sintering. The results showed that Si3N4 ceramics with 5 wt%MgSiN2, 3 wt%Y2O3 and 1 wt%CeO2 sintering aids had the best relative density and mechanical properties at 1650 ℃. Secondly, the effects of sintering temperature on the densification, microstructure and mechanical properties of Si3N4 ceramics with 5 wt%MgSiN2, 3 wt%Y2O3 and 1 wt%CeO2 sintering aids were studied in detail. The results showed that the relative density of Si3N4 ceramics reached the maximum of 99.40 ± 0.14% at 1650 ℃, the Vickers hardness and fracture toughness were 16.53 ± 0.12 GPa and 6.89 ± 0.20 MPa m1/2, respectively. The grain shapes were composed of equiaxed α-Si3N4 and long columnar β-Si3N4, and the transformation rate of α-Si3N4 to β-Si3N4 was 42.5%. Finally, the statistical distribution of the relative density, phase transformation rate and mechanical properties of Si3N4 ceramics with 5 wt%MgSiN2, 3 wt%Y2O3 and 1 wt%CeO2 sintering aids at 1650 ℃ was investigated. It was found that the mechanical properties of silicon nitride ceramics sintered by spark plasma sintering were less dispersive, and the hardness and fracture toughness obeyed the two parameters Weibull distribution well.