Dynamic investigation of the finite dissolution of silicon particles in aluminum melt with a lower dissolution limit

The finite dissolution model of silicon particles in the aluminum melt is built and calculated by the finite difference method, and the lower dissolution limit of silicon particles in the aluminum melt is proposed and verified by experiments, which could be the origin of microinhomogeneity in aluminum-silicon melts. When the effects of curvature and interface reaction on dissolution are not considered; the dissolution rate first decreases and later increases with time. When the effects of curvature and interface reaction on dissolution are considered, the dissolution rate first decreases and later increases when the interface reaction coefficient （k） is larger than 10 1, and the dissolution rate first decreases and later tends to be constant when k is smaller than 10-3. The dissolution is controlled by both diffusion and interface reaction when k is larger than 10-3, while the dissolution is controlled only by the interface reaction when k is smaller than 10-4.

Electroless copper-phosphorus coatings with the addition of silicon carbide (SiC) particles

Cu-P-silicon carbide （SiC） composite coatings were deposited by means of electroless plating.The effects of pH values,temperature,and different concentrations of sodium hypophosphite （NaH2PO2·H2O）,nickel sulfate （NiSO4·6H2O）,sodium citrate （C6H5Na3O7·2H2O） and SiC on the deposition rate and coating compositions were evaluated,and the bath formulation for Cu-P-SiC composite coatings was optimised.The coating compositions were determined using energy-dispersive X-ray analysis （EDX）.The corresponding optimal operating parameters for depositing Cu-P-SiC are as follows：pH 9;temperature,90oC;NaH2PO2·H2O concentration,125 g/L;NiSO4·6H2O concentration,3.125 g/L;SiC concentration,5 g/L;and C6H5Na3O7·2H2O concentration,50 g/L.The surface morphology of the coatings analysed by scanning electron microscopy （SEM） shows that Cu particles are uniformly distributed.The hardness and wear resistance of Cu-P composite coatings are improved with the addition of SiC particles and increase with the increase of SiC content.

Effects of Particle Size and Content of Silicon Powder on Strength and Microstructure of Coked Al_2O_3-ZrO_2-C Refractories

Effects of particle size （A：d50 = 336. 9 μm, B：d50 =123.5μm, C： d50=19.5 μm, D： dso=2.21μm） and content （1 wt% , 3 wt% , 5 wt% , 7 wt% ） of silicon powder on cold crushing strength （CCS） , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens＇ pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.

Determination of Particle Sizes and Crystalline Phases on Colloidal Silicon Nanoparticle Suspensions

Particle size and crystallinity of silicon nanoparticles were determined by analyzing the optical extinction spectra of colloidal suspensions. Experimental results from these colloids were anaiyzed using Mie theory in connection with effective medium theory, in order to determine particle sizes and their internal structure with the simple technique of optical transmission spectroscopy. By modeling an effective refractive index for the particles, the crystalline volume fraction can be extracted from extinction spectra in addition to information about the size. The crystalline volume fraction determined in this way were used to calibrate the ratio of the Raman cross sections for nanocrystalline and amorphous silicon, which was found to be σc./σa = 0.66

Evolution of silicon particle damage on fatigue crack initiation and early propagation in an aluminum alloy

Low-cycle fatigue tests under both mechanical cyclic and thermal cyclic loadings were conducted to study the behavior of fatigue crack initiation and early propagation by means of metallographic and scanning electron microscopy(SEM).The damage mode of silicon particles has significant influence on crack behavior.Cracks are induced from fractured particles in mechanical fatigue or from debonded particles in thermal fatigue.Initiation of cracks by breaking through particles happens in particles with non-equiaxial particles,while initiation of cracks from debonded interfaces happens widely in clustered particles.For cracks induced by fracture particles,the subsequent coalescence of microcracks proceeds through the alternation of brittle fracture of particles.The sequent broken of particles takes the important part in the early propagation stage of fatigue crack.

Centrifugal casting processes of manufacturing in situ functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg2Si particles and a portion of primary silicon particles in the inner layer, a little MgzSi and primary silicon particles in the outer layer, and without any Mg2Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg2Si and primary silicon particles is.

Mechanism of fracture toughness property of aging-hardening eutectic Al-Si alloys

The micro structures and fracture toughness properties of the aged Al-12.5Si-0.7Mg alloy plate were studied by transmission electron microscopy(TEM),optical microscopy(OM),tensile,and fracture toughness(the fracture toughness value,K_(IC))testing.The mechanism of fracture toughness properties of the alloys was discussed for different sizes of silicon particle and aging precipitates.The results show that the refined and rounded silicon particles will improve the fracture toughness property of the alloys.However,the silicon particles size is no longer the main factor to affect the fracture toughness property when the silicon particles are small and they have no sharp corners.The morphology and distribution of the precipitates play an important role in the fracture toughness property of the aged alloys.Their fracture toughness decreases gradually as the aging time increases.

Investigation of the 12 orientations variants of nanoscale Al precipitates in eutectic Si of Al-7Si-0.6Mg alloy

Various orientations and diffraction patterns from nanoscale Al precipitates in eutectic Si were investigated by high-resolution transmission electron microscopy combined with transition matrix and stereographic projection.It was found that the Al precipitates had 12 variants,all orientation relationships can be expressed as:(001)Al//{111}Si,[110]Al//<110>Si.Further,a new diffraction pattern model from Al precipitates was established under[111]Si zone axis,which was in good agreement with the experiment data.The microstructure,adhesion strength and electronic structure of the interface between Al precipitate and Si matrix were studied by first-principles calculation and experimental observation.The results show that the covalent bonds are formed between interfacial Al and Si atoms,which play a key role in interfacial bind strength.Based on the Griffith fracture theory,the cracks tend to form and expand in the interior of Al precipitates firstly,and the interfaces can act as a protective layer to prevent crack propagation.Therefore,the nanoscale Al precipitates will improve the toughness of eutectic Si particles by releasing part of stress through lattice distortion.In addition,the stretched nanoscale Al precipitates can act as effective heterogeneous nucleation sites for high density deformation nanotwins in eutectic Si during deformation,which significantly improved the deformability of eutectic Si.