Large SiC Particles Research Articles

High conversion of H2S to H2 and S via a robust microwave-induced discharge plasma

Direct conversion of H2S could achieve the co-production of hydrogen and sulfur, avoiding hydrogen waste in the traditional Claus process. Herein, we propose a robust SiC-mediated microwave-induced discharge plasma, achieving H2S conversion of 98.8% to H2 and S with the inlet H2S of 2% (volume concentration) at 600 W. We realize efficient excitation and stable maintenance of microwave plasma in the multimode cavity via optimizing large SiC particles at the waveguide port. In addition, the introduction of tungsten sheets enhances discharge plasma. The H2S conversion of 52.8% was realized for the high inlet H2S concentration (30%) at 600 W. In-situ optical emission spectroscopy reveals that atomic S and H are the key reactive intermediates in the overall H2S decomposition. Direct electron-H2S collision coupling excited Ar atom-H2S collision contributes to H2S direct conversion. This work paves a path to hydrogen production toward sustainable energy applications from the direct conversion and utilization of H2S.

Mechanical properties and microstructure of Cf/ZrC-SiC and Cf/SiC composites produced by precursor infiltration and pyrolysis combined with gaseous silicon infiltration

Cf/SiC and Cf/ZrC-SiC composites were fabricated via a novel combined process, which achieved a lower open porosity below 8% compared with the single PIP process. Nevertheless, Cf/SiC and Cf/ZrC-SiC composites did not possess the superior mechanical properties, but the poorer ones. Meanwhile, the veiled factors affecting the mechanical properties have been clarified. The large SiC particles (as large as ~40 µm) degraded the strength of matrix, thereby deteriorating mechanical properties of Cf/ZrC-SiC and Cf/SiC composites. Moreover, higher processing temperature (1700 °C) of the combined process and large CTE differences resulted in larger thermal residual stress in the composites compared with single PIP process with lower processing temperature (1200 °C), which also restrained the improvements of mechanical properties.

Microstructure, mechanical properties and wear behaviour of the AZ91–Mg2Si–SiC hybrid composites

The present study investigates the effect of different amounts of SiC particles on the microstructure, mechanical properties and wear behaviour of the cast and extruded AZ91–Mg2Si composite. The microstructural analysis of the cast samples showed the primary α-Mg, semicontinuous networks of the Mg17Al12 intermetallics and scattered Mg2Si and SiC particles. The hot extrusion resulted in a refined grain structure and homogenously distributed particles. More SiC particles had a positive influence on the microstructural refinement and decrement of the grain size. Increasing the SiC particles improved the hardness and compressive strength and decreased compressive elongation. Furthermore, the wear tests exhibited that more SiC particles enhanced the wear properties. However, at the highest loads, the extruded composite with large SiC particles displayed weak wear resistance.

Microstructure and resistance to thermal shock of SiC coatings that are prepared on C/C-composite pyrocarbon matrices of various textures

SiC coatings were prepared on rough laminar (RL) pyrocarbon and smooth laminar (SL) pyrocarbon matrices of carbon/carbon composites with pack cementation via the same process. The influence of the pyrocarbon texture on the thermal shock properties and, where relevant, the microstructures of the coatings were explored. The results demonstrated that the RL-SiC (RLS) coating consisted of large SiC particles compared with the SL-SiC (SLS) coating. The thicknesses of the RLS coating and SLS coating were 288 μm and 121 μm, respectively. At 1500 °C, the RLS coating had a mass loss of 0.29% after 30 cycles, while the mass loss of the SLS coating was 2.01%. The original cracks, which had widths of approximately 3.0 μm, on the RLS coating and the SLS coating could seal quickly and had no catastrophic consequences on the coating thermal shock property. The thermal shock RLS-coated specimen performed well since the rough laminar pyrocarbon had a similar coefficient of thermal expansion to SiC, which was crucial for decreasing the microcrack production. Moreover, the rough laminar pyrocarbon easily reacted with silicon, which was advantageous for the formation of thick coatings and provided durability under thermal shock conditions.

Effect of SiC particle size on densification behavior and mechanical properties of SiCp/AlSi10Mg composites fabricated by laser powder bed fusion

The effect of SiC particle size (300, 600 and 1200 mesh) on the properties of 15 wt% SiC particles reinforced AlSi10Mg matrix composites fabricated by laser powder bed fusion (LPBF) was investigated. The results showed that the laser absorptivity of blended powder increased as the SiC particle size decreased, which was useful to improve the densification of the LPBFed composites. The highest relative density of 98.9% was obtained at 1200 mesh of SiC particle. The amount of the interfacial reaction products, including Al4SiC4 and Si, was increased by reducing the SiC particle size. For all types of composites, SiC particles had a good wettability with the aluminum matrix owing to the high temperature and the interfacial reaction during the LPBF process. The mechanical properties were significantly improved by decreasing the SiC particles size. The microhardness of 316.1 HV0.2 and the ultimate compressive strength of 764.1 MPa were achieved using SiC particle having 1200 mesh size. The existence of the pores in the aluminum matrix and the SiC particle’s cracking were the primary reasons for the failure of the composites. Furthermore, large SiC particles were more easily cracked. When the SiC particle size decreased from 300 mesh to 1200 mesh, the average coefficient of friction (COF) distinctly reduced from 0.45 to 0.18 and wear rate decreased from 9.09 to 2.02 × 10−4 mm3N−1m−1, respectively. The abrasive and adhesive wear were the dominant wear mechanism of the LPBFed composites with 300 mesh of SiC particle. However, as the SiC particle decreased to 1200 mesh, the main wear mechanism was transferred to the delamination and abrasive mechanism. These results have contributed to understanding the characteristics of LPBFed SiCp/AlSi10Mg composites.

The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites

In the present work, the effect of aging temperature and particle size ratio of SiC particles on the mechanical and tribological properties of A357 composites reinforced with dual particle size SiC were investigated. The composites were prepared by melt-stirring assisted permanent mold casting technique with different weight fractions (3% coarse +3% fine, 4% coarse +2% fine, and 2% coarse +4% fine) of large and small size SiC particles. These three prepared composites are referred as DPS1, DPS2 and DPS3 composites. The solutionizing temperature was maintained constant at 540°C for 9h while the aging was done at 160°C, 180°C and 200°C (T6 treatment) for 6h. Optical and scanning electron microscopy studies showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. High-resolution transmission electron microscopy images showed formation of uniformly dispersed needle-like β″ phase and spherical shaped β-Mg2Si precipitates under peak aging conditions. Compared to T6 treated A357 alloy, the T6 treated DPS A357 composites showed improved yield strength, tensile strength, hardness and wear resistance. Among the three composites, hardness and wear resistance of T6 treated DPS2 composite was found to be significantly higher when compared to the other two composites (DPS1 and DPS3). Ratio of large particles to small particles also seems to effect the mechanical and tribological properties. Presence of more small particles was found to be good for strength and ductility whereas more large particles were found to be good for hardness and wear resistance.

Ablation behavior of SiCp/AA2024 composites irradiated by a single-pulse nanosecond laser

In this study, homogenous Al alloy and SiC materials and SiCp/AA2024 composites with mean particle diameters of 5 μm and 30 μm were irradiated by a single-pulse nanosecond fiber laser with a 200 ns pulse width and 1064 nm wavelength. Using a laser pulse, regular circular heat-affected zones (HAZ) were formed in the homogenous materials. For the composites, an Al allloy matrix was melted and sputtered, and the SiC particles bulged when irradiated by the laser pulse. According to the measured results, the HAZ increased with the pulse energy density in a logarithmic pattern. Nonlinear fitting results demonstrated that the damage thresholds of the composites and SiC homogenous materials were the lowest and highest, respectively. SiCp/AA2024 composites with different mean particle diameters exhibited similar damage thresholds. The measured etching depths of the SiC particles and Al alloy matrix were smaller than the respective values of the homogenous materials. Thermal simulation results revealed that thermal-mechanical coupling occurred between the SiC particles and Al alloy matrix. The SiC particles in the composite heated more rapidly under a nanosecond laser, and the heat was then transferred to the matrix. Large SiC particles constrained the matrix’s molten pool, which accelerated its gasification but hindered further etching.

Tribological behavior of composites fabricated by reactive SPS sintering in Ti‐Si‐C system

AbstractIn this study, wear and friction behavior of two based‐composites from the Ti‐Si‐C system, (40 wt% TiC; 28 wt% Ti5Si3; 17 wt% Ti3SiC2) and (18 wt% TiC; 26 wt% Ti5Si3; 41 wt% Ti3SiC2) reinforced by 15 wt% of large size SiC (100‐150 µm) particles were investigated. The four‐phase composites exhibited approximatively the same friction coefficient (µ ~ 0.9) under high loads (10 N and 7 N). The composite with high Ti3SiC2 showed higher wear rate values by one order of magnitude. However, under 1 N, the composite with high TiC content showed a higher running‐in period and a lower steady state µ value (0.37 after 1000 m sliding distance). Scanning electron microscopy, Energy Dispersive X‐Ray and Raman spectroscopy analysis of the worn surfaces of the two composites revealed that oxidation was the dominant wear mechanism. The oxidation process and the removal kinetics of the oxides during sliding controlled the tribological behavior of the composites. The influence of processing variables on microstructures development and wear mechanisms of the composites is discussed.

Study on characteristics in high-speed milling SiCp/Al composites with small particles and high volume fraction by adopting PCD cutters with different grain sizes

Silicon carbide particle–reinforced aluminum matrix (SiCp/Al) composites were milled at a high speed by adopting polycrystalline diamond (PCD) tools, which the diamond grain sizes were 5, 10, 25, and 32 μm. The machined materials were SiCp/Al composites which the volume fraction was 45% and grain size of SiC particles was 5 μm. The tool wear resistance and wear morphology of polycrystalline diamond cutters were investigated. And it centered on the effects of diamond grain sizes on the cutting forces as well as the machined surface roughness. The obtained results indicated the difference of corresponding tool wear resistance between larger SiC particles and smaller SiC particles during high-speed milling SiCp/Al composites with higher volume fraction. When the grain size and volume fraction of SiC granules are 5 μm and 45%, the tool wear resistances of four diamond grain sizes were all far higher than those of tools in machining composites with higher volume fraction (56%) and larger 60-μm SiC particles. And the PCD tools of larger diamond grain size acted on better wear resistance. Both the corresponding cutting forces and surface roughness were also smaller. As cutting distance increased, the variation law of cutting forces had a good correspondence with the tool wear of PCD cutters of different diamond grain sizes. The machined surface roughness had a decreasing trend in general, but the fluctuation range was tiny. The main wear morphology was flank wear and slight wear groove marks. And there was no chipping of cutting edge and coarse wear groove marks. A large amount of the machined materials was adhered on flake face in the cutting process, but built-up edge was not formed.

Microstructure, mechanical and wear properties of the A357 composites reinforced with dual sized SiC particles

Current work reports on the development of A357 alloy composite which is reinforced with dual size SiC particles by stir casting route. Influence of different weight fractions (3% coarse+ 3% fine, 4% coarse + 2% fine, and 2% coarse + 4% fine) of dual size SiC particles on mechanical properties and wear resistance of A357 composites is the focus of this work. Hardness and tensile properties were studied for dual size composites and then were compared with A357 alloy. Microstructural study, fractured surface and worn surface investigation were carried out using optical and scanning electron microscopes respectively. Microstructural analysis showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. Compared to A357 alloy, the composites showed improvement in hardness, yield, and tensile strength. In particular, composite with 4 wt. % of fine and 2 wt. % of large SiC particles displayed the highest tensile strength while composite with 4 wt. % of large and 2 wt. % of fine SiC particles exhibited high hardness and wear resistance among A357 alloy and dual particle size composites. The strengthening mechanisms that contributed to improvement in strength values were effective load transfer and dislocation strengthening due to thermal mismatch.

Experimental study on SiCp/Al composites with different volume fractions in high-speed milling with PCD tools

The single-tooth milling cutter with diamond grain size of 5 μm was used for high-speed milling silicon carbide particle-reinforced aluminum matrix (SiCp/Al) composites with larger SiC particles and different volume fractions. The volume fractions of SiC particles were 15, 25, 30, and 56%, respectively. The effects of volume fraction of SiC particles on tool wear morphology and wear resistance were analyzed in this paper. The effects on cutting force and machined surface roughness were also studied. The results show that it has little effect of volume fraction of SiC particles on the tool wear morphology, but it has a great effect on the variety of wear amount and wear rate. When SiCp/Al composites wit h low volume fraction are machined, the tool wear amount of polycrystalline diamond (PCD) tools is small and increase slowly. When workpiece with high volume fraction is machined, the tool wear amount increases significantly with the increase of cutting distance. The measured cutting force changes differently when SiCp/Al composites with different volume fractions are machined at high speed. In the initial cutting period, there is little influence of volume fraction on the cutting force component. However, the influence becomes significant with the increase of cutting distance. The machined surface roughness with different volume fractions is larger and has a certain fluctuation in the initial cutting stage. When the cutting distance increases to a certain extent, the surface roughness decreases and tends to be steady. All in all, the surface roughness is larger when the volume fraction of SiC particles is higher.

The effect of ball-milling time and annealing temperature on fracture toughness of Ni-3 wt.% SiC using small punch testing

A set of dispersion strengthened Ni-3 wt.% SiC samples have been prepared via a powder metallurgy route for an application in molten salt reactor (MSR) systems. A mixture of 97 wt.% Ni and 3 wt.% SiC powder was prepared by varying the ball-milling time (8, 24, 36 and 48 h). The ball-milling process was followed by powder consolidation using spark plasma sintering (SPS) and rapid cooling to room temperature. The samples were then annealed at different temperatures (300 °C, 700 °C and 850 °C). The fracture behaviour of the Ni-3 wt.% SiC samples was investigated using the Small Punch Test (SPT). A scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) and electron back-scatter diffraction (EBSD), as well as transmission electron microscopy (TEM) were employed to examine the microstructure of the tested Ni-3 wt.% SiC samples. The obtained results show that the SPT fracture energy is strongly dependent on the grain size of Ni matrix, which is affected by ball-milling times and annealing temperature. It has been further found that the segregation of large SiC particles at grain boundaries promotes intergranular fracture and thus significantly reduces the fracture energy. The results indicate that the distribution and size of SiC particles at grain boundary is mainly affected by the ball-milling time. Hence, the ball-milling time governs the fracture toughness of Ni-3 wt.% SiC samples.

Effect of the Interfacial Thermal Resistance on Effective Thermal Conductivity of Al/SiC Particle-Dispersed Composites

Steady state thermal conductivity measuring device was designed to measure the effective thermal conductivity of composites. Computer simulations of thermal conduction revealed that the designed device over estimates the effective thermal conductivity, and the correction coefficient was suggested. With this designed device, the effective thermal conductivities of Al/SiC particle-dispersed composites were measured by changing the size of SiC particles from 0.3 μm to 3 μm. The critical element size which could determine the optimal size of reinforcements have been suggested, and validity of the critical element size for Al/SiC composites was confirmed. The thermal conductivity of the composites including small SiC particles was degraded by the interfacial thermal resistance between the matrix and the reinforcement. On the other hand, the thermal conductivity of the composites including large SiC particles was not affected by the interfacial thermal resistance. These results suggest that consideration of the critical element size is valid.

Experimental investigation into the effect of abrasive and force conditions in magnetic field-assisted finishing

This paper presents an experimental study on the key process parameters in magnetic field-assisted finishing (MFAF), aiming to investigate the relations between the magnetic abrasives, polishing force, material removal rate (MRR) and surface roughness. The experiments were conducted using a dual magnetic roller tool combining with a 6-axis robot arm. The effect of abrasive type and size on polishing force and MRR, wear of magnetic abrasives, surface roughness and surface morphologies obtained using different types of magnetic abrasives were evaluated quantitatively. The results show that the type of SiC-based magnetic abrasives had a higher MRR but lower polishing force than that of Al2O3-based magnetic abrasives. Due to the inability of carbonyl iron powder (CIP) carrier to hold large SiC or Al2O3 particles during the rotation motion of the magnetic roller tools, large particle size abrasives have a lower MRR as well as polishing force than small particle size abrasives. The wear of magnetic abrasives was demonstrated through scanning electron microscope (SEM) observation and energy dispersive X-ray (EDX) analysis of abrasive particles before and after polishing. The surface morphologies generated by the four different experimental conditions of magnetic abrasives were different although the surface roughness achieved a similar value.

Effect of heat treatment on the microstructure and tensile strength of KD-II SiC fibers

KD-II SiC fibers, a new type of SiC fibers, were heat treated at elevated temperatures for 1h in an Ar atmosphere. The microstructure and mechanical properties of the fibers before and after annealing were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and tensile tests, et al. The results show that the as-received fibers consisted of β-SiC nano-crystals, free carbon and a small amount of amorphous intergranular SiCxOy phase. With increasing heat treatment temperature, significant growth of β-SiC grains, ordering of free carbon and decomposition of SiCxOy phase occurred and the fiber surfaces became coarser with development of new defects, such as pores and large SiC particles. It was also found that KD-II SiC fibers maintained high strength with heat treatment at temperatures up to 1500°C, exceeding which a sharp strength degradation was observed. The strength degradation and microstructural evolution of the fibers due to heat treatment were correlated, and it can be concluded that the β-SiC grains growth, residual tensile stresses as well as surface flaws were the dominating factors for the fiber strength degradation after exposure at high temperatures.

Preparation and characterization of hybrid A359/(SiC+Si3N4) composites synthesized by stir/squeeze casting techniques

Stir followed by squeeze casting techniques were used to produce A359 composites containing different weight percentage of (SiC+Si3N4) particles. Microstructures of the composites showed a homogeneous and even distribution of hybrid reinforcements within the matrix. Moreover, particles agglomerations, residual porosity, and other casting problems were not noticed. Interfacial reactions between the particles and the matrix were investigated using X-ray diffraction and energy dispersive X-ray analyses. The presence of particles in squeezed composites did not only increase the peak hardness of the composites, but also accelerated the aging kinetics. As compared with the A359 matrix alloy, a compression test of the hybrid composites exhibited a significant increase in the yield and the ultimate compressive strengths with a relative reduction in the failure strain. Finite element modeling of the composite compression showed that strain concentration near large SiC particles is the main reason for low ductility of the composite. The development of those lightweight hybrid composites with high mechanical properties has a high potential to be used for automotive and aerospace applications.

Manufacturing of cast A356 matrix composite reinforced with nano- to micrometer-sized SiC particles

In this study, large micron-sized SiC particles were fragmented via ball-milling process in the presence of iron and nickel powders, separately, to fabricate composite powders of Fe–SiC and Ni–SiC. Continuous fracturing of brittle SiC powders leads to the formation of multi-modal-sized SiC powders with size of from 50 nm to slightly higher than 10 µm after 36-h ball milling. The milled powders were then incorporated into the semisolid melt of A356 aluminum alloy to ease the incorporation of fine SiC particles by using iron and nickel as their carrier agents. The final as-cast composites were then extruded at 500 °C with a reduction ratio of 9:1. Lower-sized composite powders with slight agglomeration are obtained for the 36-h milled Ni–SiC mixture compared to that of Fe–SiC powders, leading to incorporation of SiC particles into the melt with a lower size and suitable distribution for the Ni–SiC mixture. It is found that lower-sized composite particles could release the fine SiC particles into the melt more easily, while large agglomerated composite particles almost remain in its initial form, resulting in sites of stress concentration and low-strength aluminum matrix composites. Ultimate tensile strength (UTS) and yield strength (YS) values of 243 and 135 MPa, respectively, are obtained for the aluminum matrix composite in which nickel acts as the carrier of fine ceramic particles.

Formation mechanism of large SiC grains on SiC fiber surfaces during heat treatment

Three low oxygen-containing SiC fibers with different surface compositions were heat-treated at high temperature in argon, and large SiC particles were observed on the surfaces of SiC fibers with oxygen-containing surface layers. The SiC particles were identified as single crystal β-SiC. The growth process, formation mechanism of these large SiC grains and their influence on fiber strength were investigated. Nano-sized SiC particles were precipitated from the decomposition of SiCxOy in the fiber surface that acted as nuclei, and these nuclei grew gradually to form large grains because of the gaseous reaction of SiO and CO. The formation of large SiC grains was related closely to the SiC fiber surface composition, which affected SiC nucleation and SiO diffusion from the core to the fiber surface. The large grains influenced the fiber strength degradation significantly and should be avoided to retain high fiber strength.

Effect of particle size on the thermal and mechanical properties of aluminum composites reinforced with SiC and diamond

The effect of particle size on thermal conductivity (TC) and bending strength was investigated in the SiC/Al and diamond/Al (Dia/Al) composites for thermal management applications. The results showed that with the particle size of SiC increasing from 7 to 250μm, the TC of the 40vol.% SiC/Al composite was improved by 50%, from 182 to 272W/mK, while the bending strength decreased by 100% from 352 to 175MPa. Comparatively, with diamond particles increasing from 30 to 200μm, the TC of the 40vol.% Dia/Al composite increased by around 52% from 313 to 475W/mK, and the bending strength declined by 32% from 327 to 223MPa. Characterization of fracture surface indicated that large SiC particles featured by an irregular shape tended to fracture prior to the Al matrix during loading, while large diamond particles with a regular shape did not have such a tendency. Moreover, diamond particles with a high intrinsic TC contributed to global TC much more than SiC ones with a relatively low TC. Thus, in order to balance thermal and mechanical properties of particulate reinforced aluminum composites, particle size of reinforcements should be well compromised according to their intrinsic properties.

Machining Characteristics in Cryogenic Grinding of SiCp/Al Composites

In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grinding force, surface morphology, and surface roughness were investigated. At the same time, the effect of cryogenic cooling was also compared with that of conventional wet grinding. The experimental results indicated that cryogenic cooling is effective in enhancing supporting function of Al matrix to the SiC particles and improving surface quality. Additionally, the brittle fracture of SiC particles was suppressed and some ductile streaks on SiC particle could be observed.