Enhancement of the self-healing ability in oxidation induced self-healing ceramic by modifying the healing agent

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.

Flexural strength, elastic modulus, and hardness were used to characterize the mechanical properties of ZrB 2 –SiC composites that contained varying SiC particle sizes. Dense ZrB 2 –SiC composites consisting of 70 vol% ZrB 2 and 30 vol% α‐SiC were produced via hot pressing. This series of composites had maximum SiC particle sizes that ranged from 4.4 to 18 μm. The mechanical properties scaled with the maximum SiC particle size, not with ZrB 2 grain size. Flexural strength decreased as the maximum size of SiC particles increased from 1150 MPa at 4.4 μm to 245 MPa at 18 μm with an abrupt decrease in strength at ~11.5 μm. Elastic modulus remained constant at ~530 GPa for compositions containing SiC particles smaller than 11.5 μm, but exhibited a decrease with larger SiC particle sizes. Vickers and Knoop hardness were 21.4 and 17.2 GPa, respectively, for ceramics with SiC particle sizes <11.5 μm, but hardness decreased for larger SiC particle sizes. The decreases in strength, elastic modulus, and hardness with SiC particles larger than 11.5 μm were coincident with stress‐induced microcracking in the composites.

Effects of reinforcement particle size in MMCs on extrusion die wear

This paper deals with the investigation of mechanical properties by introducing micro size SiC particulates and Graphite particulates into Al-4.5%Cu alloy matrix. SiC and Graphite particle reinforced Al alloy metal matrix composites were prepared by stir casting method. Al-Cu alloy was taken as the base matrix to which SiC and Graphite particulates were used as reinforcements. 6 wt. % of SiC and Graphite particulates were added to the base matrix to fabricate Al-4.5Cu – 6 wt. % SiC and Al-4.5%Cu – 6 wt. % Graphite composites. For each composite, the reinforcement particles were pre-heated to a temperature of 600oC and then dispersed in steps of two into the vortex of molten Al-Cu alloy to improve wettability and distribution. The Micostructural study was done by using optical microscope, which revealed the uniform distribution of SiC and Graphite particles in matrix alloy. Mechanical properties like hardness, tensile and impact strength were evaluated as per ASTM standards. Hardness and tensile strength increased with addition of 6 wt. % of SiC particulates in the base matrix Al-Cu alloy compared to Al-Cu-6wt. % Graphite composites.

Charge accumulation phenomenon on gas–solid interface greatly restricts the development of HVDC energy transmission system. In this study, the surface charge transport behavior and flashover performance on alumina/epoxy spacer coated by SiC/epoxy composites are experimentally investigated under DC stress. SiC/epoxy composites with varied SiC particle size are fabricated and deposited on spacer surface. Nearly a charge free surface is achieved especially at smaller SiC particle size, even when metallic wires are adhered on spacer surface and connected to high voltage electrode. The DC flashover voltage increases with the decrease of SiC particle size. On the one hand, smaller SiC particle size exhibits more outstanding nonlinear conductivity characteristics, contributing to accelerating charge dissipation, whereas on the other hand, it would introduce plenty of shallow traps due to the increased interfacial regions between SiC particle and epoxy matrix, resulting in aggravating charge accumulation. A theoretical model is proposed to reveal the control mechanism of SiC/epoxy coating with different SiC particle size on flashover performance. The validity of this model can be confirmed based on the surface trap distribution, carrier mobility and our previous investigations on gas–solid interface flashover development process.

MICROSTRUCTURAL EFFECTS ON FRACTURE MICROMECHANISMS IN LIGHTWEIGHT METAL MATRIX COMPOSITES

In this study, 35 vol.% SiC particles with different sizes reinforced 6061 aluminium alloy matrix composites were prepared by a powder metallurgy method. The Scanning Electron Microscope (SEM) images of composites were observed, the Coefficient of Thermal Expansion (CTE) and tensile strength of composites were examined, and the influences of SiC particle size on microstructures and properties of the composites were analyzed. Furthermore, the SiCp/6061Al composites with SiC particle size of 7.5 µm were selected to investigate the SiCp/Al interface microstructure and precipitated phases by the means of SEM, TEM and HRTEM. The study indicated that, with the increase of SiC particle size, the SiC particles distributed more uniformly in the matrix, the CTE of composites increased, but the tensile strength of composites decreased. The SiCp/Al interface in this experiment is clean and smooth, and the combination mechanism of SiC and Al is the formation of a half coherent interface by closely matching of atoms. Some micron-sized coarse intermetallic particles existed in the hot-pressed composites, such as random-shaped Mg2Si, long stick shaped Al15(Mn, Fe, Cu)3Si2. When the composites were solution treated at 510 °C for 2 h and then aging treated at 190 °C for 9 h, except long stick shaped Al15(Mn, Fe, Cu)3Si2, numerous nano-sized precipitated phases (Mg2Si) with diameters of 50-200 nm dispersively distributed in the matrix. After heat treatment, the tensile strength of composite with SiC particle size of 7.5 µm enhance from 298 MPa to 341 MPa.

In this work, the in situ SiC/Al composites were successfully fabricated by the method of combustion synthesis and hot press consolidation in an Al-C-Si system. The effect of alloying elements (Mn, Zn, Ti) on the phase constitution and microstructure of in situ SiC/Al composites were investigated. Results indicated that the Al[Formula: see text]Mn[Formula: see text] and Ti[Formula: see text]Si[Formula: see text] phases were formed in the SiC/Al composites with the addition of Mn and Ti, respectively. By the addition of Mn, the size of the synthesized SiC particles was obviously reduced, and consequently the amount of SiC particles was increased. Meanwhile, the percentage of the submicro SiC particles increased about from 22% to 83%. However, the addition of Zn and Ti had little effect on the size of SiC particles.

The aluminum metal matrix composites (Al MMCs) reinforced by SiC particles with different sizes (25 nm, 150 nm and 3.5 m) were fabricated by powder metallurgy technique, and the microstructure and tensile properties of the Al MMCs were investigated. When the volume fraction of SiC particles is fixed to be 5 %, the Al MMCs reinforced by nanosized and submicron particles exhibit much higher ultimate tensile strength and yield strength, and much lower ductility compared with those of the non-reinforced aluminum. However, for the MMC reinforced by 3.5 m SiC particles, almost no strengthening effect is found. The strengthening effect of the Al MMCs is analyzed in terms of dislocation mechanism. Moreover, the tensile fracture surface shows that the damage mechanism of the Al MMCs can be changed as the size of SiC particles is changed.

A microstructural study of the wear behaviour of SiC p/Al composites

Effect of preparation conditions on gas permeability parameters of porous SiC ceramics

Effect of SiC particle size and severe deformation on mechanical properties and thermal conductivity of Cu/Al/Ni/SiC composite fabricated by ARB process

ABSTRACTThree different SiC powders with average particle sizes of 0.45, 3.5 and 10 µm were used to prepare ZrC-20vol.-% SiC ceramics by hot pressing. The effects of SiC particle size on the densification, microstructure, mechanical properties and thermal properties of ZrC–SiC ceramics were studied. Ceramics prepared from SiC with finer particle sizes exert higher bending strength, hardness and lower thermal conductivity. The ZrC–SiC ceramics with a starting SiC particle size of 3.5 µm has relative high fracture toughness than others. Analysis indicates that SiC grain size and the grain boundaries control the thermal conductivity ZrC–SiC ceramics. Ceramics prepared from SiC with the particle size of 10 µm exhibits the highest thermal conductivity due to the larger grains and less grain boundaries.

Improvements on dry friction and wear properties for reaction-sintered silicon carbide by the matching size of SiC particles

Experimental data are presented for the thermal conductivity, viscosity, and turbulent flow heat transfer coefficient of nanofluids with SiC particles suspended in ethylene glycol (EG)/water (H2O) mixture with a 50/50 volume ratio. The results are compared to the analogous suspensions in water for four sizes of SiC particles (16–90 nm). It is demonstrated that the heat transfer efficiency is a function of both the average particle size and the system temperature. The results show that adding SiC nanoparticles to an EG/H2O mixture can significantly improve the cooling efficiency while water-based nanofluids are typically less efficient than the base fluids. This is one of the few times that substantial nanofluid heat transfer enhancement has been reported in the literature based on a realistic comparison basis of constant velocity or pumping power. The trends important for engineering efficient heat transfer nanofluids are summarized.