Damping performance of SiC nanoparticles reinforced magnesium matrix composites processed by cyclic extrusion and compression

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))

Surface Modification of SiC Nanoparticles with PMMA by Low Temperature Plasma

An investigation into Poly （methyl methacrylate） （PMMA） grafted onto nano-SiC particles is reported in this study. In our experiment, the grafting polymerization reaction is induced by radio frequency （RF） discharge of N2 plasma treatment of the nanosized powder. FTIR （Fourier transform infrared spectrum）, XPS （X-ray photoelectron spectroscopy） and TGA （Thermogravimetric analysis） results reveal that PMMA is grafted onto the surface of silicon carbide powder, and the crystal structure of the silicon carbide powder observed with XRD （X- ray diffraction） spectra is unchanged before and after the plasma graft polymerization.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Structural characterization of SiC nanoparticles

The structure and size of SiC nanoparticles were studied by different characterization methods including small angle X-ray scattering（SAXS）,transmission electron microscope（TEM）,and X-ray diffraction（XRD）.The results showed that particle size distributions determined respectively from SAXS and TEM are comparable and follow the log-normal function.The size distribution of the particles is between 10 to 100nm with most of them being in the range of 20-50nm.The average particle size is around 42nm.XRD identifies the phase of the SiC nanoparticles and suggests the average size of the single crystalline domain to be around 21nm.The combined results from XRD and SAXS suggest the existence of many polycrystals,which is confirmed by the HRTEM observation of particles with twins and stacking faults.The material synthesis methods leading to various particle sizes are also discussed.

Effects of Trace Amount Modified SiC Nanoparticles and Electromagnetic Stirring (EMS) on Microstructure and Mechanical Properties of 7055 Aluminum Alloy

The effects of trace amount modified SiC nanoparticles and electromagnetic stirring(EMS)on mierostructures and mechanical properties of 7055 aluminum alloy are investigated experimentally.The result shows that the original developed coarse dendrite and columnar with obvious orientation microstructure turns into homogeneous equiaxed microstructure with the application of trace amount modified SiC nanoparticles and EMS.A minimum grain size is 96 μm and has been observed when the addition of modified SiC nanoparticles is 0.05%and the current of EMS is 100A.The ultimate tensile strength is increased by 15.8%and the elongation is improved by 50%compared to those without modified SiC nanoparticles and EMS.Moreover,the compound effects of trace amount modified SiC nanoparticles and EMS is discussed to explain the mechanisms of grain refinement and mechanical properties on 7055 aluminum alloy.

Fabrication, Characterization and Thermophysical Property Evaluation of SiC Nanofluids for Heat Transfer Applications

Nanofluids(NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles(NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional heat transfer fluids. In this study we report in detail on fabrication, characterization and thermo-physical property evaluation of SiC NFs, prepared using SiC NPs with different crystal structures,for heat transfer applications. For this purpose, a series of SiC NFs containing SiC NPs with different crystal structure(α-SiC and β-SiC) were fabricated in a water(W)/ethylene glycol(EG) mixture(50/50 wt%ratio). Physicochemical properties of NPs/NFs were characterized by using various techniques, such as powder X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM),Fouriertransform infrared spectroscopy(FTIR), dynamic light scattering(DLS) and Zeta potential analysis.Thermo-physical properties including thermal conductivity(TC) and viscosity for NFs containing SiC particles(α- and β- phase) weremeasured. The results show among all suspensions NFs fabricated with α-SiC particles have more favorable thermo-physical properties compared to the NFs fabricated with β-SiC.The observed difference is attributed to combination of several factors, including crystal structure(β- vs. α-), sample purity,and residual chemicals exhibited on SiC NFs. A TC enhancement of ～20% while 14% increased viscosity were obtained for NFs containing 9 wt% of particular type of α-SiC NPs indicating promising capability of this kind of NFs for further heat transfer characteristics investigation.

(Bi,Sb)_(2)Te_(3)/SiC nanocomposites with enhanced thermoelectric performance:Effect of SiC nanoparticle size and compositional modulation

Fabrication of nanoparticle-dispersed composites is an effective strategy for enhancing the performance of thermoelectric materials,and in particular SiC nanoparticles have been often used to create composites with Bi_(2)Te_(3)-based applied thermoelectric materials.However,the effect of particle size on the thermoelectric performance is unclear.This work systematically investigated the electrical and thermal properties of a series of(Bi,Sb)_(2)Te_(3)-based nanocomposites containing dispersed SiC nanoparticles of different sizes.It was found that particle size has a significant impact on the electrical properties with smaller SiC nanoparticles giving rise to higher electrical conductivity.Even though the dispersed SiC nanoparticles enhanced the Seebeck coefficient,no apparent dependence of the enhancement on the particle size was observed.It was also found that smaller SiC nanoparticles scatter phonons to some extent while the larger nanoparticles contribute to increased thermal conductivity.Eventually,the highest ZT value of 1.12 was obtained in 30 nm-SiC dispersed sample,corresponding to an increase by 18%from 0.95 for the matrix made from commercial scraps,and then the ZT was further boosted to 1.33 by optimizing the matrix composition and expelling excess Te during the optimized spark plasma sintering process.This work proves that the dispersion of smaller SiC nanoparticles in p-type(Bi,Sb)_(2)Te_(3) materials is more effective than the dispersion of larger nanoparticles.In addition,it is revealed that additional compositional and/or processing optimization is vital and effective for obtaining further performance enhancement for nanocomposites of SiC nanoparticles dispersed in(Bi,Sb)_(2)Te_(3).