SiC Specimens Research Articles

Effect of Heat Treatment Process on the Hardness of Aluminium356/Silicon Carbide Particulate Composites

This research is aimed to study effect of holding time and temperature in solution treatment and ageing on the hardness of the Aluminum A356 reinforced with silicon carbide particles. Alumimium matrix coposite was particulated with 15 microns-SiC with the content of 15 percent by weight. A356/SiC composites was prepared by the stirr casting. The stirrer was continuously stired at a speed of 300 rpm during acooling temperature to semi-solid state of 610 °C. During stirring the SiC powder was slowly added into the melt and continuously stirred for another 10 min. Then poured into the mold at the pouring temperature of 680°C. A356/SiC composites then subjected to a solid solution treatment with temperature of 540 °C for 1 hr. quenched with water and age hardening temperature of 120 and 135 °C for 3, 6, 12 and 18 hr. The result showed that, in as cast conditions, the composite with 15 microns silicon carbide, the 15 wt%SiC specimen exhibited the average hardness of 64.33 HB. After solution treated, the hardness of samples decreased. the specimen exhibited the average hardness of 53.83 HB. After ageing, the hardness of samples increased. the specimen ageing 120 °C 6 hr. exhibited the lowest average hardness of 51.45 HB while the specimen ageing 135 °C 18 hr. exhibited the highest average hardness of 73.54 HB.

Comparison of hydrothermal corrosion behavior of SiC with Al2O3 and Al2O3 + Y2O3 sintering additives

AbstractFully dense SiC bulks with Al2O3 and Al2O3 + Y2O3 sintering additives were prepared by spark plasma sintering and the effect of sintering additives on the hydrothermal corrosion behavior of SiC bulks was investigated in the static autoclave at 400°C/10.3 MPa. The SiC specimen with Al2O3 sintering additive exhibited a higher weight loss and followed a linear law. However, the SiC specimen with Al2O3 + Y2O3 additive exhibited a lower weight loss and followed a parabolic law, indicating that the corrosion kinetic and mechanism were different for these two SiC bulks. Further examination revealed that, a deposited layer was formed on the surface of SiC specimen with Al2O3 + Y2O3 sintering additive after corrosion, which can effectively protect the SiC specimen from further corrosion, and thereby improved the corrosion resistance of the SiC specimen with Al2O3 + Y2O3 sintering additive.

Numerical and experimental benchmarking of the dynamic response of SiC and TZM specimens in the MultiMat experiment

The MultiMat experiment was successfully conducted at CERN's HiRadMat facility, aiming to test novel high-performance materials for use in beam intercepting devices, allowing the derivation and validation of material constitutive models. This article provides an analysis of results for two materials tested in the experiment, namely Silicon Carbide and Titanium Zirconium Molybdenum, with the aim of benchmarking the material constitutive models currently available in literature with experimental results. The material models were implemented in numerical simulations, successfully modelling dynamic longitudinal and flexural phenomena. The article further studies the modelling of the complex boundary conditions present in the experiment, the internal damping characteristics of the materials, and the failure of certain specimens. The strength and failure models proved adequate to model a number of experimental scenarios tested, but require further study to describe the material behaviour at the high strain rates and temperatures induced by accidental particle beam impacts. A post-irradiation examination of the tested specimens was also performed to study the nature of failure in the specimens, and is to be coupled with quasi-static and high strain rate tests for both materials, allowing for the validation of the currently available models and the description of material behaviour across a wide range of strain rates and temperatures.

Oxidation Resistance, Compressive Strength and Thermal Shock Resistance of SiC Ceramics Prepared by Two Processing Routes

In the present paper, direct foaming technique and sacrificial template method were used to prepare porous alumino-silicate bonded SiC ceramics from mixtures of silicon carbide, kaolin and calcined alumina. The direct foaming process depends on generating bubbles inside the slurry of SiC mixtures through a reaction between CaC2 and Al powder in presence of H2O to form C2H2 and H2 gases in two steps of the reaction. In the sacrificial template method, the pores were created in the prepared SiC specimens after burning out the used sacrificial template, corn and potato starch. Some fired specimens were selected to study the effect of their composition and preparation conditions on their oxidation resistivity, compressive strength and thermal shock resistivity. Based on purity and homogenous microstructure, the present study offers SiC specimens with good oxidation resistance where they exhibit (0.1 to 2 mg/cm2) increase in mass after oxidation in air at a temperature of 1100 C for 65 h, despite their high open porosity values. The present SiC specimens have high thermal shock resistivity. However, the foamed specimens showed better resistivity than those prepared by the sacrificial template method. Using the extruder for shaping the latter specimens improves their resistivity to thermal shock. The compressive strength of both groups of specimens is affected by their composition and preparation conditions.

Thermal shock and chemical corrosion resistance of oxide bonded porous SiC ceramics prepared by infiltration technique

Using the water- and air-quenching technique, the thermal shock resistance to cooling was evaluated as a function of quenching temperatures and quenching cycles for oxide bonded porous SiC ceramics prepared by infiltration technique. It was observed that the residual strength of the quenched samples decreases with increase in the quenching temperature. However residual strength becomes independent of quenching cycles after certain cycles since the thermal shock produced by repeated cycles remained almost constant. The hot corrosions of SiC samples exposed to Na2SO4 salt were performed at 1000 °C. The weight loss, strength reduction and morphology evolution of the SiC specimens during corrosion were revealed and explained. The chemical and thermal shock resistance results suggest a potential advantage of porous SiC ceramics prepared by infiltration technique for several industrial applications.

Effect of different heat treatments on oxidation-bonded SiC membrane for water filtration

The porous SiC-based membrane has proved its validity in microfiltration membrane fabrication, but application is limited due to its high fabrication cost. In this study, the oxidation-bonding technique was used to fabricate a SiC microfiltration membrane. The oxidation behaviour exhibited during different thermal treatments was related to pore morphology, and ultimately membrane permeance. Corrosion properties of the oxidation-bonded SiC specimens were also studied. We have found that a membrane made by coating an oxidation-bonded SiC layer over a clay-bonded SiC support and sintered at 1000 °C for 3 h could make a defect-free, corrosion resistant microfiltration membrane with pure water membrane permeance above 700 LMH per bar over the 1 h operation time. The membrane has a narrow pore size distribution, with an average pore size of 78 nm.

Characterization of Porous Alumino-Silicate Bonded SiC-Ceramics Prepared by Hand-Pressing and Extrusion Methods

Silicon carbide was mixed with alumina and kaolin to obtain porous alumino-silicate bonded SiC ceramics. Starch was added as sacrificial template. The mixtures were processed by hand-pressing and extrusion method. The effect of firing temperature (1450 ∘C) and the addition of starch on the composition and characteristics of fired specimens were studied. The changes in phase composition and microstructure of fired SiC specimens were followed through x-ray diffraction analysis and scanning electron microscopy, respectively. The sintering parameters and thermal oxidation in air of such specimens were determined. The results indicated that silicon carbide is oxidized during firing into silica which reacted with silica-alumina mixture forming alumino-silicate bonding. Meanwhile, starch burnt out leaving pores inside the specimens. Porous SiC specimens of 1.72 to 1.79 g.cm−2 bulk density, 40 to 45% open porosity and 250 to 350 N.cm−2 compressive strength could be obtained by using a mixture of 80 mass% SiC and 20 mass% alumina and kaolin as starting materials. The properties of porous SiC specimens depend on the type and amount of used starch. The extrusion method is favorable for preparing porous SiC articles of homogeneous microstructure and good properties.

Fabrication of complicated silicon carbide ceramic components using combined 3D printing with gelcasting

The possibility of obtaining complex structure SiC ceramic components by 3D printing and gelcasting was demonstrated. PEG was used to improve the surface quality of SiC specimen and sucrose was used as the carbon source. Effects of PEG and sucrose on the stability and rheological properties of SiC slurry were studied. The mechanism of inhibiting SiC surface exfoliation by PEG and the effect of different sucrose content on the properties and microstructure of SiC ceramic were investigated. The results showed that the addition with 1.0wt% PEG and 4.0wt% sucrose can improve the surface quality and sintered body properties of SiC ceramics. Therefore, a complex structure SiC impeller, which had good surface quality and properties, was successfully fabricated.

SiCnw/PyC core-shell networks to improve the bonding strength and oxyacetylene ablation resistance of ZrB2–ZrC coating for C/C–ZrB2–ZrC–SiC composites

To enhance the bonding strength and oxyacetylene ablation resistance of the ZrB2–ZrC coated C/C–ZrB2–ZrC–SiC composites obtained by the combination of supersonic atmosphere plasma spray (SAPS) and precursor infiltration and pyrolysis (PIP), novel SiC nanowire (SiCnw)/pyrolytic carbon (PyC) core-shell structures are designed and introduced into the coating. Compared to SiC nanowires which are widely added into ceramics, metals and so on, SiCnw/PyC core-shell structures have a better cohesion. Additionally, the bonding strength of coating can be largely improved through the toughening mechanism of SiCnw/PyC structures. After being exposed to oxyacetylene ablation torch, the best ZrB2–ZrC coated C/C–ZrB2–ZrC–SiC specimens with SiCnw/PyC networks possess a linear ablation rate of −0.9 ± 0.5 μm/s and a mass ablation rate of −0.3 ± 0.6 mg/s, while the linear and mass ablation rates of the C/C–ZrB2–ZrC–SiC specimens for comparison are up to 4.2 ± 1.0 μm/s and 1.2 ± 0.8 mg/s, respectively. The significant improvement of oxyacetylene ablation resistance is attributed to a lower surface temperature during ablation, a lower thermal stress in the coating, and a better bonding strength of the coating/substrate interface owing to the introduction of SiCnw/PyC core-shell structures.

Effect of Volume Fraction of Reinforcement and Milling Time on Physical and Mechanical Properties of Al7075–SiC Composites Fabricated by Powder Metallurgy Method

The volume fraction of reinforcement and milling time are two important factors in fabricating aluminum metal matrix composites via powder metallurgy (P/M) techniques. In the present work, the effects of volume fraction of reinforcement and milling time on the microstructure, relative density, hardness, and compressive strength were studied. The Al7075 and SiC powders were mixed by a planetary ball mill for about 4 and 8 h, and Al7075–x vol.% SiC specimens (x = 4, 6, 8) were fabricated by a uniaxial cold press and sintered at 873 K (600°C) for 1 h. The crystallite size and morphology of the powder particles were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that with increasing milling time and volume fraction of the reinforcement phase, the hardness and compressive strength increased. The SEM illustrates that the number of voids increases as SiC content increases, but their size decreases.

Effect of cryogenic thermal cycling on SiC-modified C/C composites

The bonding strength, mechanical properties and high-temperature thermal shock resistance of C/C–SiC composites after undergoing simulated low earth orbit environment including cryogenic thermal cycles (CTCs) between 153 and 393 K for 200 times with high-vacuum state of 1.3 × 10−3 Pa were investigated. Results of the tests showed that, the bonding strength at coating/substrate interface monotonically decreased as the CTCs increased. After 100 CTCs, the flexural strength of C/C–SiC composites enhanced and the percentage of remaining strength was 102.60%, while, the mass loss of specimens decreased from 2.08 to 0.89% after thermal shock resistance test between 1773 K and room temperature for 15 times. Once CTCs exceed 100 times, the mass loss increased, the flexural strength reduced and remained only 87.40% of initial strength after 200 CTCs. The fractural behaviour of CTCs-treated modified composites exhibited typical brittle mode. A model based on the evolution of the residual thermal stress after CTCs treatment was proposed to explain the oxidation failure mechanism of C/C–SiC specimens.

Highly resistive SiC ceramics sintered with Al2O3-AlN-Y2O3 additions

A polycrystalline SiC ceramic prepared by pressureless sintering of α-SiC powders with 3vol% Al2O3-AlN-Y2O3 additives in an argon atmosphere exhibited a high electrical resistivity of ~1013Ωcm at room temperature. X-ray diffraction revealed that the SiC ceramics consisted mainly of 6H- and 4H-SiC polytypes. Scanning electron microscopy and high resolution transmission electron microscopy investigations showed that the SiC specimen contained micron-sized grains surrounded by an amorphous Al-Y-Si-O-C-N film with a thickness of ~4.85nm. The thick boundary film between the grains contributed to the high resistivity of the SiC ceramic.

The feasibility and application of gray scale adjustment method in high temperature digital image correlation

In this paper, the basic principle and application of linear gray scale adjustment method are investigated in high temperature digital image correlation (DIC) technology. First, the simple linear gray scale adjustment method is proposed, which can adjust the gray scale value of the saturated pixels and diminish the correlation error caused by the saturated pixels. Then, both the simulated high temperature images and DIC correlation results before and after the gray scale adjustment are provided and analyzed to verify its effectiveness, in which the displacement error decreased from 0.1 pixels to 0.04 pixels after the linear gray scale adjustment for high temperature images. Finally, the linear gray scale adjustment method is used to extract the displacement with high accuracy in high temperature experiment of SiC specimen, and the displacement error decreased from 0.5 pixels to 0.1 pixels after the linear gray scale adjustment.

Hot-spots generation, exaggerated grain growth and mechanical performance of silicon carbide bulks consolidated by flash spark plasma sintering

Flash Spark Plasma Sintering (FSPS) that combines flash sintering and electric field assisted sintering was used to densify SiC ceramics. FSPS was compared with ‘conventional’ SPS which used a moderate 100 °C·min−1 heating rates. Dense SiC specimens were obtained despite being at temperature of 1850–2050 °C for few seconds. FSPS lead to generation of hot-spots and thus caused localized exaggerated grain-growth. This allows producing silicon carbide ceramics with bimodal grain size distribution. Analysis of microstructure and strength of silicon carbide ceramics consolidated using flash heating allowed proposing several optimization routes of the FSPS process.

Conductive SiC ceramics fabricated by spark plasma sintering

Bulk SiC ceramics were fabricated by spark plasma sintering, and the effects of Y2O3 addition on the structural and electrical properties were investigated. Raman spectroscopy revealed that SiC specimens with low Y2O3 content (0.01 and 0.05wt%) contained a graphitic phase (1580 and 2710cm−1) which was insignificant for high Y2O3 content (1.0 and 5.0wt%). Carbon-rich SiC specimens exhibited p-type conduction character, while others exhibited n-type character. The p- and n-type SiC specimens had electrical resistivities around 10−2Ωcm but exhibited photoluminescence spectra quite different from each other. The p-type character is primarily attributable to silicon vacancies (VSi), while the n-type character is ascribed to nitrogen substitution in carbon sites (NC) of the zincblende lattice. The change in conduction type with yttria addition in the SiC specimen can be understood in terms of a competition between the densities of VSi and NC.

The relationship between microstructure and flexural strength of pressureless liquid phase sintered SiC ceramics oxidized at elevated temperatures

The oxidation behavior of pressureless liquid phase sintered SiC ceramics with Al2O3 and Y2O3 as sintering additives was investigated in the temperature range from 1000°C to 1600°C at the interval of 100°C for 5h. The relationship between residual flexural strength and microstructure was analyzed in detail. It was found that the SiC specimens suffered from mild oxidation below 1300°C. The flexural strength of SiC specimens after oxidation at 1100°C was the highest (90% of the original strength) due to the formation of dendritic grains, which filled pores and healed cracks. And the flexural strength was almost above 80% of the original flexural strength when the oxidation temperature was below 1300°C. Meanwhile, the weight of specimens underwent steady increase. However, when the oxidation temperature was elevated to above 1400°C, the specimens began to suffer from severe oxidation, which resulted in a lot of through pores and cracks on the surface, bringing about the sharp decrease of flexural strength to 30% of original strength when the oxidation temperature of 1600°C was reached. And the weight of the specimens after huge increase began to show downtrend when the oxidation temperature was elevated to 1600°C due to the spalling of oxidation products.

Chemical corrosion of liquid-phase sintered SiC in NaOH aqueous solution

Corrosion behaviour of the liquid-phase sintered SiC ceramics (LPS-SiC) was studied through exploration of weight loss, strength reduction and morphology evolution of the SiC specimens etched in the room-temperature/70°C 6.12 mol/L (20 wt-%) NaOH aqueous solutions. As a comparison, corrosion of the reaction-bonded SiC ceramics (RB-SiC) was also investigated. The results show that corrosions of the SiC specimens mainly contain homogeneous dissolution of the secondary-phase oxides in the LPS-SiC and that of Si in the RB-SiC, and peel-off of the SiC particles, resulting in increase of the surface roughness, weight loss and strength reduction of the SiC ceramics. As dipped in the 70°C NaOH solution, corrosion pores and channels form in the sublayer, leading to rapid increase of weight loss and strength reduction of the LPS-SiC. No matter in the room-temperature or 70°C NaOH solution, the LPS-SiC always has a higher corrosion resistance than the RB-SiC.

Chemical Corrosion of Liquid-Phase Sintered SiC in Acidic/Alkaline Solutions Part 1. Corrosion in HNO3 Solution

The corrosion behavior of the liquid-phase sintered SiC (LPS-SiC) was studied by dipping in 3.53 mol/L HNO3 aqueous solution at room temperature and 70 °C, respectively. The weight loss, strength reduction and morphology evolution of the SiC specimens during corroding were revealed and also the chemical corrosion process and mechanism of the SiC specimens in the acidic solution were clarified. The results show that the corrosion of the LPS-SiC specimens in the HNO3 solution is selective. The SiC particles are almost free from corrosion, but the secondary phases of BaAl2Si2O8 (BAS) and Y2Si2O7 are corroded via an acid-alkali neutralization reaction. BAS has a higher corrosion rate than Y2Si2O7, resulting in the formation of the bamboo-leaf-like corrosion pits. As the SiC specimens etched in the HNO3 solution at room temperature for 75 days, about 80 μm thickness corrosion layer forms. The weight loss and bending strength reduction of the etched SiC specimens are 2.6 mg/cm2 and 52%, respectively. The corrosion of the SiC specimens is accelerated in the 70 °C HNO3 solution with a rate about five times bigger than that in the same corrosion medium at room temperature.

Dynamic deformation characteristics of zirconium diboride–silicon carbide under multi-axial confinement

Multiaxial quasi-static and dynamic compression experiments were performed on zirconium diboride-5wt% silicon carbide (ZrB2-5wt%SiC) ceramic composite processed via spark plasma sintering technique. Cylindrical ZrB2–SiC specimens were confined using thick walled metal sleeves to generate various levels of confinement pressure on the lateral surface and then subjected to axial loads under quasi-static and dynamic conditions. Postmortem analysis revealed formation of a macroscopic shear plane in the recovered specimens and slip bands within ZrB2 grains. Compressive strengths of up to 5.6 GPa and 9.8 GPa, respectively, were reached under quasi-static and dynamic strain rates. To capture the strain rate dependent and pressure dependent response the Johnson–Holmquist (JH-2) model was used and relevant parameters were determined for future high velocity impact or shock response simulations utilizing the experimental data generated from low and high strain rate confined compression tests. A comparison of JH-2 model constants for ZrB2–SiC along with other structural ceramics revealed that pressure alone plays a deterministic role in defining the constitutive response of all brittle ceramics including ZrB2–SiC.

Comparative study of the effect of swift heavy ion irradiation at 500 °C and annealing at 500 °C on implanted silicon carbide

TEM, RS and RBS were used to characterize polycrystalline SiC specimens individually implanted with 360 keV I+ or Kr+ ions at room temperature and thereafter either irradiated with 167 MeV Xe to a fluence of 5 × 1013 cm−2 at 500 °C or annealed at 500 °C under vacuum.