Si3N4 Composites Research Articles

Low-temperature oxidation of MoSi2–Si3N4 composites

Composites in the MoSi2 + Si3N4 system containing 1.0, 2.5, and 5.0 wt % Si3N4 were synthesized by hot pressing at the temperature of 1650°C and the pressure of 30 MPa. Silicon nitride powders of two types of were used as reinforcing additives: one with isometric equiaxed crystals and one with fibrous structure. The samples were characterized by microstructural and phase analyses; the relative density and the flexural strength were determined. Composites with the flexural strength of up to 410 MPa were synthesized. The resistance to low-temperature oxidation of MoSi2 + Si3N4 composites in air at the temperature of 750°C was studied. The increase in the resistance to oxidation of composites with silicon nitride in air compared to pure molybdenum disilicide for both types of silicon nitride powders was established. For all the composites obtained, the parabolic oxidation rate constants were calculated.

Influence of Sintering Aids on the Sintering and Conductivity Properties of Si<sub>3</sub>N<sub>4</sub> Composites

Silicon nitride (Si3N4) is one of the most important engineering materials. The developing trend of Si3N4 ceramic should be its composite with reinforce phase. However, due to its low self-diffusion coefficient at high temperature, the Si3N4 is very hard to be densified without sintering aids. In the present work, the Y2O3 and light rare-earth oxides of La series (La2O3, CeO2, Pr2O3, Sm2O3) and AlN, Al2O3, MgO, CaCO3 were chosen to be sintering aids. Their effect on the sintering of Si3N4 composite was studied. The results showed that the Y2O3 was the best sintering aid in all members, and the Y2O3-La2O3-AlN ternary composition was the best formula.

Preparation of Sialon/Si<sub>3</sub>N<sub>4</sub>-SiC Composite Refractories Using Kyanite Tailings

Sialon-SiC composite powders were synthesized from kyanite tailings through the carbothermal reduction nitridation (CRN) technique. Using Sialon-SiC composites to substitute Si3N4 composites via the CRN technique synthesize Sialon/Si3N4-SiC composite refractories. The phase composition, cross section morphology, and the substituent amount of Sialon-SiC composites impact on refractories mechanical properties were investigated, respectively. The optimized synthesis temperature for the CRN reaction was found to be 1550 °C for 4 h with the excess carbon 20%. The substituent amount of Sialon-SiC was 25%, the mechanical properties of Sialon/Si3N4-SiC composite refractories reached optimal performance, which bending strength value was 41.8 MPa and compression strength value was 61.6 MPa.

Thermal shock resistance and oxidation behavior of in-situ synthesized MgAl2O4–Si3N4 composites used for solar heat absorber

MgAl2O4–Si3N4 ceramics were fabricated via pressureless sintering by using α-Si3N4, α-Al2O3 and MgO as starting materials. MgAl2O4 was in-situ synthesized in the composite ceramics to improve the sintering process and high-temperature performance of Si3N4. Results show that the composite with approximately 30wt% MgAl2O4 sintered at 1620°C exhibits the best physical properties, excellent thermal shock resistance, oxidation resistance and solar absorptance. No cracks were found after 30 thermal shock cycles (1100–25°C, wind cooling). At the same time, the bending strength has experienced an improvement of 24.5%, which increases to 248MPa. A dense oxide film is formed on the surface of the sample during oxidation at 1300°C, which protects it from further oxidation. The oxidation kinetics of MgAl2O4–Si3N4 ceramic transforms from passivation oxidation into activation oxidation with increasing MgAl2O4 content. Only moderate amount of MgAl2O4 (10–30wt%) can provide the excellent oxidation resistance. These in-situ MgAl2O4–Si3N4 composites could be a promising candidate for solar heat absorbing material.

Fabrication and contact resistivity of W–Si3N4/TiB2–Si3N4/p–SiGe thermoelectric joints

The design and fabrication of silicon germanium (SiGe) thermoelectric elements, typically including the selection of electrode and intermediate materials, the process of joining electrode and intermediate layer onto thermoelectric materials, are the major challenge for SiGe thermoelectric device technology. In this study, W–Si3N4 and TiB2–Si3N4 composites are designed as the electrode and intermediate layer, respectively, and the W–i3N4/TiB2–Si3N4/p–Si80Ge20B0.6 joints are fabricated by a one-step spark plasma sintering process. The influences of the composition of TiB2–Si3N4 intermediate layer on the interfacial structure, contact resistivity and interfacial thermal stability are investigated. The interfacial thermal stability is improved with increasing Si3N4 content in TiB2–Si3N4 intermediate layer due to the reduced mismatch of coefficients of thermal expansion between the intermediate layer and SiGe. On the other hand, the contact resistivity increases with the rising of Si3N4 content due to the weakened TiB2/SiGe ohmic contact, which degrades the device efficiency. As the balanced point, the intermediate layer with the composition of 80vol% TiB2+20vol% Si3N4 provides good interfacial thermal stability and moderately small contact resistivity (~75μΩcm2 after aging at 1000°C for 120h) simultaneously, which is an optimized intermediate layer composition for W–Si3N4/TiB2–Si3N4/p–Si80Ge20B0.6 thermoelectric element. The TiB2–Si3N4 intermediate layer has excellent chemical stability to both W–Si3N4 electrode and SiGe thermoelectric material at high temperatures, which contributes to the sharp interface of the joint and effectively prevents the inter-diffusion between the electrode and the SiGe.

Mechanical and Tribological Performance of Graphite/Silicon Nitride Composites: A Comparison between Pressureless and Spark Plasma Sinter Processing

Graphite particle (GP)-reinforced silicon nitride (Si3N4) composites were fabricated using pressureless sintering (PLS) and spark plasma sintering (SPS) in the presence of Y2O3-AlN-SiO2 ternary system. Different densification behaviors of the specimens fabricated by PLS and SPS were observed. While increasing GP content drastically reduced matrix densification during PLS at 2023 K (1750 °C) with 2 hours dwell, SPS at 1923 K (1650 °C) for only 10 minute under 50 MPa pressure resulted in much dense composites even up to 3.5 wt pct GP loading. Mechanical and tribological characterizations revealed that SPS-ed composites can offer improved performance compared to pure Si3N4. SPS-ed 1.5 wt pct GP/Si3N4 composite offered the highest resistance to wear up to 20 N normal load. Wear rate (W R) of that composite reduced by ~24 pct than that obtained for pure Si3N4 (W R ≈ 1.14 × 10−3 mm3/N m). Furthermore, W R of SPS-ed 2.5 wt pct GP/Si3N4 composite at F N = 10 to 20 N was found to be only ~1/8th of W R values of PLS-ed 2.5 wt pct GP/Si3N4 composite (10N W R ≈ 6.61 × 10−3 mm3/Nm; 20N W R ≈ 9.45 × 10−3 mm3/Nm). Present study indicated promising opportunity of SPS for fabricating improved Si3N4 composites through GP addition. The reinforcing particles not only rendered its self-lubrication effect to SPS consolidated composites but also significantly promoted the rate of matrix densification during SPS cycle by the virtue of its high thermal and electrical conducting nature.

An investigation of mechanical properties and corrosion resistance of Al2618 alloy reinforced with Si3N4, AlN and ZrB2 composites

Aluminum 2618 matrix composites (AMCs) reinforced by AlN, Si3N4 & ZrB2 particles were fabricated from Al2618- x wt% AlN, Si3N4, ZrB2 (x = 0, 2, 4, 6, 8) by stir casting. In ZrB2 particles were fabricated by in-situ reaction from mixtures of K2ZrF6 & KBF4. The mechanical properties of the composites were increased with respect to the percentage of weight. The corrosion behavior of metal matrix composites (MMCs) is strictly linked with the presence of heterogeneities such as reinforcement phase, micro crevices, porosity, secondary phase precipitates, and interaction products. The present work is investigated relating to the corrosion resistance of Aluminum (2618) metal matrix composites (AMCs) reinforced with AlN, Si3N4 & ZrB2 was investigated by electro chemical studies such as polarization study and AC impedance spectra. The above materials are immersed in an aquaise 3.5% Sodium Chloride (Nacl) solution corrosion parameters such as corrosion potential (Ecorr), corrosion current (Icorr), Linear Polarization Resistance (LPR), charge transfer resistance (Rt), Double layer capacitance (Cdl) will be evaluated from this and the most corrosion resistance material is determined. Finally the results are obtained by the polarization studies and AC impedance spectra which leads to the conclusion that the corrosion resistance of 0% of Al2618 alloy has a low corrosion resistance and the composites have a high corrosion resistance. The corrosion resistance is gradually increased with respect to the Wt% of composites (2%, 4%, 6%, 8%).

An investigation of mechanical properties and material removal rate, tool wear rate in EDM machining process of AL2618 alloy reinforced with Si3N4, AlN and ZrB2 composites

It is submitted that new approach is tried to find out what would be the outcome if Aluminum 2618 reinforced by AlN (Aluminum Nitride), Si3N4 (Silicon Nitride) & ZrB2(Zirconium Boride) particles were fabricated in Wt % (x = 0,2,4,6,8) by stir casting method. If the wt% is increased, the mechanical properties of the composite will proportionally increase. There will be no other promising technique than Electrical Discharge Machining (EDM) for machining metal matrix composites when they were conducted on the Aluminum 2618 composite work piece using a copper electrode in an EDM machining. It becomes very vital in the field machines and mechanism to find out Current(I), Pulse on time(TON), Pulse off time (TOFF) on Metal Removal Rate (MRR),Tool Wear Rate(TWR) on the machining of hybrid Al2618 metal matrix composites. Taghuchi's design of experiment was used to analyse the machining characteristics of hybrid composites. To effect the parameters like current (I), Pulse on time(TON), Pulse off time (TOFF) has been chosen as the input parameters of this work. Machining results go to show that Al2618 composites have improved mechanical properties and as a result of Material Removal Rate (MRR) and Tool Wear Rate (TWR) are reduced. Hence ANOVA (Analysis of Variance) and signal to Noise ratio are used to determine the influence of input parameters on the Material Removal Rate and Tool Wear Rate (TWR).

Absorption properties of twinned SiC nanowires reinforced Si3N4 composites fabricated by 3d-prining

Near net- and complex shaped porous silicon nitride (Si3N4) composites reinforced with in-situ formed twinned silicon carbide (SiC) nanowires (NWs) were successfully fabricated by 3d-printing (3DP) followed by polymer precursor infiltration and pyrolysis (PIP) up to 1400°C. An increase of the PIP cycle number of the printed bodies resulted in a homogeneous distribution of SiC NWs in the fabricated composites. An increase of SiC NW content in the fabricated composites led to the growth of both the real and the imaginary parts of permittivity. The formation of twinned SiC NWs with high electrical conductivity led to a minimal electromagnetic wave RC of −57dB, demonstrating that Si3N4–SiC ceramics with the in-situ formed SiC NWs have a superior microwave absorbing ability.

Fabrication and characterization of Si3N4 reinforced Al2O3-based ceramic tool materials

Al2O3–Si3N4 composites ceramic tool materials with Y2O3 as sintering additive were fabricated by the hot pressing process at 1450°C for 30min under 32MPa in vacuum. Different mass fractions of Si3N4 as reinforcements were employed. The mechanical properties, microstructure, strengthening and toughening mechanisms of the composites were investigated. The content of Si3N4 had significant effect on the mechanical properties and microstructure of the composites. Al2O3-25wt% Si3N4-1wt% Y2O3 had the optimum comprehensive mechanical properties with flexural strength, fracture toughness, Vickers hardness and relative density of 768.7±63.9MPa, 6.8±0.4MPam1/2, 19.6±0.4GPa and 99.6±0.2% respectively. A core–shell structure with Si3N4 as core and Al2O3 as shell was firstly formed in the composite. The core–shell structure was generated through a rapid dissolution–transport–precipitation process. Elongated β-Si3N4 grains with a diameter of 0.3–0.5µm and aspect ratio of 5 were in-situ synthesized. The improved mechanical properties were attributed to the strengthening and toughening mechanisms including the mixed fracture mode of intergranular and transgranular fracture, the crack deflection, the high grain boundary strength, the pinning and bridging effects of the core–shell structure and the elongated grains.

Graphene nanoribbon ceramic composites

By unzipping multi-walled carbon nanotubes (MWCNTs) it is possible to obtain graphene nanoribbons (GNRs) that could then be used as fillers in ceramic composites. Here we report the fabrication of silicon nitride (Si3N4) ceramics with different contents of GNRs by spark plasma sintering. The GNR fillers confer electrical conductivity to the Si3N4 composites, following a semiconducting-like behavior at relatively low volume filler concentrations (0.04). In addition, a toughening effect, produced by GNRs bridging the cracks was observed. GNRs appear to be an efficient alternative to graphene-based composites, useful in the fabrication of novel multifunctional ceramic composites.

Microstructure and Mechanical Properties of BN Nanotubes Reinforced Si<sub>3</sub>N<sub>4</sub> Porous Composites

The high dielectric constant of Si3N4 ceramic limited its application as wave-transparent materials, thus Si3N4 ceramics always been prepared as porous ceramics to enhance the properties of wave transparent. While the mechanical properties would be declined in this way, so the BNNTs were used to improve the properties of the composites in this paper. The porous BNNTs/ Si3N4 composites were prepared by normal pressure sintering in nitrogen atmosphere. Then the effects of sintering temperature and contents of BNNTs to Si3N4 porous ceramics and composites were investigated. The results show that the Si3N4 phase was transformed to β-Si3N4 completely when the sintering temperature was raised to 1750°C. The BNNTs and rod-like β-Si3N4 guaranteed the considerable mechanical properties of the composites, and the mechanical properties increased with the increase of the sintering temperature and the addition of the BNNTs. When the sintering temperature was 1750°C and the content of BNNTs was 0.5wt.%, the porosity and density of the composite are 35% and 2.0g/cm3, respectively. While the flexural strength and the elastic modulus of the composite are 231.8MPa and 62.04GPa, respectively.

Influence of Silicon Nitride (Si<sub>3</sub>N<sub>4</sub>) Addition on Microstructure, Mechanical and Thermal Properties of Sn-0.7Cu Lead-Free Solder

This research has investigated the solder performances of Sn-0.7Cu lead-free solder reinforced with silicon nitride (Si3N4). The Sn-0.7Cu + Si3N4 composite solder were fabricated via powder metallurgy (PM) technique with five different weight percentages (0, 0.25, 0.5, 0.75 and 1.0). Results showed that distribution of Si3N4 along the grain boundaries has increased the hardness of the Sn-0.7Cu + Si3N4 composite solders compared to monolithic Sn-0.7Cu solder alloy. Addition of Si3N4 reinforcement had no significant effect to the melting temperature of the solder. Overall, the entire range of Sn-0.7Cu + Si3N4 composition greatly improves the microhardness of the eutectic solder.

Experimental investigation on the hardness of ultrafine-grained Si2N2O^|^ndash;Si3N4 composites developed by hot-press sintering technology

Experimental investigation on the hardness of ultrafine-grained Si2N2O^|^ndash;Si3N4 composites developed by hot-press sintering technology

WC–Si3N4 composites prepared by two-step spark plasma sintering

The WC−xwt.% Si3N4 (x=1–15) composites were prepared by two-step spark plasma sintering. The densification behavior, phase constitution, microstructure and mechanical properties of the WC–Si3N4 composite were investigated. Addition of a small amount of Si3N4 to WC can significantly facilitate sintering due to liquid sintering. After two-step sintering, the α→β-Si3N4 transformation rate and the fracture toughness increase with the Si3N4 content, and then decrease as the Si3N4 content exceeds 10wt.%. As the Si3N4 content reaches 10wt.%, the α→β-Si3N4 transition rate reaches ~100%, and the fracture toughness of the specimen reaches 10.94MPa·m1/2. The existence of Si in the starting powder helps eliminate the formation of decarburized-phase W2C. During liquid-sintering, abnormal WC-grain growth tends to happen through two-dimensional nucleation. When the Si3N4 content increases to 3wt.% and above, abnormal WC-grain growth is suppressed due to the pinning effect by Si3N4 particles. As the Si3N4 content increases from 3 to 15wt.%, the average WC-grain size increases until the Si3N4 content reaches 12wt.%, and then decrease. With the Si3N4 content increases, the hardness of the specimens monotonically decreases.

A novel silica aerogel/porous Si3N4 composite prepared by freeze casting and sol-gel impregnation with high-performance thermal insulation and wave-transparent

A novel silica aerogel/porous Si3N4 composite with high-performance thermal insulation and wave-transparent has been prepared by freeze casting and sol-gel impregnation. The morphology, microstructure and properties of the composite were investigated. After impregnating of silica aerogel, the composite has nanometer porous structures. The results of performance test show that the room-temperature thermal conductivity remarkably decreased and the compressive strength increased while impregnating porous Si3N4 with silica aerogel. The composite exhibits low thermal conductivity (0.043 Wm−1K−1), low dielectric constant (~1.6) and loss tangent (~0.0018). The silica aerogel/porous Si3N4 composite can be suitable for use in thermal insulation and wave-transparent functional integration material.

The influence of sintering on the dispersion of carbon nanotubes in ceramic matrix composites

Optimizing the dispersion of carbon nanostructures in ceramic matrix composites is a fundamental technological challenge. So far most efforts have been focused on improving the dispersion of nanostructures during the powder phase processing, due to the limited information and control on their possible redistribution during the sintering. Here, we address this issue by comparing multi-walled carbon nanotubes reinforced Si3N4 composites prepared from the same starting powder dispersion but sintered using two different techniques. We employ ultra-small angle neutron scattering measurements to gain reliable information on the dispersion of nanostructures allowing a direct comparison of their redistribution during the sintering.

Protective Engobes for Si3N4 Ceramics Sintered in Air-Atmosphere Furnace

Silicon nitride ceramics were sintered at 1640°C in an air-atmosphere furnace using an alumina crucible, alumina packing powder, and protective Al2O3 engobes as well as glass ceramic engobes obtained from the system SiO2-ZnO-Al2O3 The Si3N4 composite was prepared from β-Si3N4 powder with addition of MgO and Al2O3 as sintering aids. It was found that the densest silicon nitride ceramic with only partial oxidation was the sample covered with the Al2O3 engobe. Three phases were identified by XRD analysis: β-Si3N4, α-Si3N4, and Si2N2O. The obtained results are promising and encourage continuous research in this field to ensure protection from and prevention of intensive oxidation.

Effect of Si3N4 Addition on Compressive Creep Behavior of Hot‐Pressed ZrB2–SiC Composites

Compressive creep studies have been carried out on hot‐pressed ZrB2–SiC (ZS) and ZrB2–SiC–Si3N4 (ZSS) composites in air under stress and temperature ranges of 93–140 MPa and 1300°C–1425°C, respectively for time durations of ≈20–40 h. The results of these studies have shown the creep resistance of ZS composite to be greater than that of ZSS. As the temperature is increased from 1300°C to 1425°C, the stress exponent of ZS decreases from 1.7 to 1.1, whereas that of ZSS drops from 1.6 to 0.6. The activation energies for these composites have been found as ≈95 ± 32 kJ/mol at temperatures ≤1350°C, and as ≈470 ± 20 kJ/mol in the range of 1350°C–1425°C. Studies of the postcreep microstructures using scanning and transmission electron microscopy have shown the presence of glassy film with cracks at both ZrB2 grain boundaries and ZrB2–SiC interfaces. These results along with calculated values of activation volumes suggest grain‐boundary sliding as the major damage mechanism, which is controlled by O2− diffusion through SiO2 at ≤1350°C, and by viscoplastic flow of the glassy interfacial film at temperatures ≥1350°C. Studies by transmission electron microscopy have shown formation of crystalline precipitates of Si2N2O near ZrB2–SiC interfaces in ZSS tested at ≥1400°C, which along with stress exponent values <1 suggests that grain‐boundary sliding involving solution‐precipitation‐type mechanism is operative at these temperatures.

Elastic–plastic analysis of ultrafine-grained Si2N2O–Si3N4 composites by nanoindentation and finite element simulation

Ultrafine-grained Si2N2O–Si3N4 composites are fabricated by hot-press sintering of amorphous nano-sized silicon nitride powders at 1600, 1650, and 1700°C with nano-sized Al2O3 and Y2O3 as additives. Sintered materials of increasing average grain sizes of 280, 360, and 480nm were obtained with increasing sintering temperature. Hardness and elastic modulus are tested by nanoindentation. Finite element simulations of the nanoindentation are performed to study the elastic and plastic mechanical properties based on the elastic modulus and P–h curve that were obtained through the nanoindentation tests. A theoretical method is proposed for calculating the stress–strain relationship of brittle ceramic materials based on the experimental nanoindentation data. Several relevant coefficients in the theoretical calculation formula are determined by comparing the calculation and simulation results.