Cutting performance of multilayer diamond coated silicon nitride inserts in machining aluminum-silicon alloy

Aluminum-silicon （Al-Si） alloy is very difficult to machine and diamond tools are considered by far the best choice for the machining of these materials. Experimental results in the machining of the Al-Si alloy with diamond coated inserts are presented. Considering the fact that high adhesive strength and fine surface morphology play an importance role in the applications of chemical vapor deposition （CVD） diamond films, multilayer technique combining the hot filament CVD （HFCVD） method is proposed, by which multilayer diamond-coating on silicon nitride inserts is obtained, microcrystalline diamond （MCD）/ nanocrystalline diamond （NCD） film. Also, the conventional monolayer NCD and MCD coated inserts are produced for comparison. The as-deposited diamond films are characterized by field emission scanning electron microscopy （FE-SEM） and Raman spectrum. All the CVD diamond coated inserts and uncoated insert endure the aluminum-silicon alloy turning to estimate their cutting performances. Among all the tested inserts, the MCD/NCD coated insert exhibits the perfect behavior as tool wear due to its very low flank wear and no diamond peeling.

Research on Abrasives in the Chemical Mechanical Polishing Process for Silicon Nitride Balls

Silicon nitride (Si 3N 4) has been the main material for balls in ceramic ball bearings, for its lower density, high strength, high hardness, fine thermal stability and anticorrosive, and is widely used in various fields, such as high speed and high temperature areojet engines, precision machine tools and chemical engineer machines. Silicon nitride ceramics is a kind of brittle and hard material that is difficult to machining. In the traditional finishing process of silicon nitride balls, balls are lapped by expensive diamond abrasive. The machining is inefficiency and the cost is high, but also lots of pits, scratch subsurface micro crazes and dislocations will be caused on the surface of the balls, the performance of the ball bearings would be declined seriously. In these year, a kind of new technology known as chemical mechanical polishing is introduced in the ultraprecision machining process of ceramic balls. In this technology, abrasives such as ZrO 2, CeO 2 whose hardness is close to or lower than the work material (Si 3N 4) are used to polishing the balls. In special slurry, these abrasives can chemo-mechanically react with the work material and environment (air or water) to generate softer material (SiO 2). And the resultants will be removed easily at 0.1 nm level. So the surface defects can be minimized, very smooth surface (Ra=4 nm) and fine sphericity (0.15～0.25 μm ) can be obtained, and the machining efficiency is also improved. The action mechanism of the abrasives in the chemical mechanical polishing process in finishing of silicon nitride ball will be introduced in this paper.

Study on the Performance of PECVD Silicon Nitride Thin Films

Mechanical properties and corrosion resistance of Si3N4 films are studied by using different experiment parameters, such as plasma enhanced chemical vapor deposition(PECVD) RF power, ratio of reaction gas, reaction pressure and working temperature. The etching process of Si3N4 is studied by inductively coupled plasma (ICP) with a gas mixture of SF6 and O2. The influence of the technique parameters, such as ICP power, DC bias, gas composition, total flow rate, on the etching selectivity of Si3N4/EPG533 which is used as a mask layer and the etching rate of Si3N4 is studied, in order to get a better etching selectivity of Si3N4/EPG533 with a faster etching rate of Si3N4. The optimized process parameters of etching Si3N4 by ICP are obtained after a series of experiments and analysis. Under the conditions of total ICP power of 250 W, DC bias of 50W, total flow rate of 40 sccm and O2 composition of 30%, the etching selectivity of 2.05 can be reached when Si3N4 etching rate is 336 nm/min.

Fabrication of Fine-Grained Si_3N_4-Si_2N_2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .

Effect of Additives on the Sintering of Amorphous Nano-sized Silicon Nitride Powders

Amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering. The influences of the additives of Y2O3 and Al2O3 prepared by two different ways, the polyacrylamide gel method and the precipitation method, were investigated. The grain sizes of the additives prepared by the first method were finer than those of prepared by the latter method. When sintered at the same temperature, 1700 ℃, the average grain size of the silicon nitride is 0.3 um for the sample with the former additives, which is much finer than the one with the latter additives. The density of additives prepared by precipitation method is clearly lower than those of prepared by polyacrylamide gel method.

Preparation and Properties of Macroporous Silicon Nitride Ceramics by Gelcasting and Carbonthermal Reaction

Macroporous silicon nitride （Si3N4） ceramics with high strength, uniform structure and relatively high porosity were obtained by gelcasting and carbonthermal reaction in a two-step sintering technique. Microstructure and composition were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）. Open porosity, pore size distribution and basic mechanical performance were measured by Archimedes method, mercury intrusion porosimetry and three-point bending methods, respectively. SEM and TEM results revealed that pores were formed by elongated β-Si3N4. SADP measurement proved the formation of SiC particles. The SiC granules were beneficial for the formation of high ratio elongated β-Si3N4, and at proper amount, they also acted as reinforcement phase. Thermodynamic analysis indicated that the mechanisms of the reactions were mainly associated with liquid-solid reaction and gas-liquid reaction.

Effect of Particle Size on Silicon Nitride Ceramic Slurry by Stereolithography

The effects of particle size,gradation and solid loading of silicon nitride (Si_(3)N_(4)) on the rheological behavior and curing properties of ceramic slurry are studied by stereolithography (SLA).The results show that the particle size of Si_(3)N_(4) powder has a signif icant influence on the rheological properties and stability of the slurry.When m_(D50=1.3μm):m_(D50=2.3μm)=3:7,the slurry viscosity is low and the sedimentation is slow.The most important thing is that with the increase of the solid loading of the slurry,the viscosity of the slurry increases,the stability becomes higher,and the curing thickness decreases.The curing thickness of Si_(3)N_(4) ceramic slurry with solid loading of 50 vol% can reach nearly 50μm.The above results finally show that the process optimizes the formulation of the slurry in rheological and curing properties.

Synthesis and characterization of high strength polyimide/silicon nitride nanocomposites with enhanced thermal and hydrophobic properties

Polyimide(PI)composite films were synthesized incorporating amino modified silicon nitride(Si_(3)N_(4))nanoparticles into PI matrix via in situ polymerization technique.The mechanical and thermal performances as well as the hydrophobic properties of the as prepared composite films were investigated with respect to the dosage of the filler in the PI matrix.According to Thermogravimetric(TGA)analysis,meaningful improvements were achieved in T5(5%weight loss temperature)and T10(10%weight loss temperature)up to 54.1℃ and 52.4℃,respectively when amino functionalized nano Si_(3)N_(4) particles were introduced into the PI matrix.The differential scanning calorimetry(DSC)results revealed that the glass transition temperature(Tg)of the composites was considerably enhanced up to 49.7℃ when amino functionalized Si_(3)N_(4) nanoparticles were incorporated in the PI matrix.Compared to the neat PI,the PI/Si_(3)N_(4) nanocomposites exhibited very high improvement in the tensile strength as well as Young’s modulus up to 105.4%and 138.3%,respectively.Compared to the neat PI,the composites demonstrated highly decreased water absorption behavior which showed about 68.1%enhancement as the content of the nanoparticles was increased to 10 wt%.The SEM(Scanning electron microscope)images confirmed that the enhanced thermal,mechanical and water proof properties are essentially attributed to the improved compatibility of the filler with the matrix and hence,enhanced distribution inside the matrix because of the amino groups on the surface of Si_(3)N_(4) nanoparticles obtained from surface functionalization.

The Role of Nanodispersed Nitrides in the Sintering of Silicon Nitride Ceramics

The synthesis of ceramics based on silicon nitride using nanopowders of TiN and Si3N4 as additives was studied. The ceramic compositions were pressurelessly sintered under ni- trogen atmosphere at different temperatures （1550℃, 1650℃ and 1750℃） with a heating rate of 10℃/min and a holding time of 2 h. The nanodispersed nitrides （NDN） were produced by electric-arc plasma synthesis and characterized. The ceramic composites obtained with nanoparticles of 1wt% to 5wt% TiN and 20wt% Si3N4 were characterized by scanning electron microscopy （SEM）, atom force microscopy （AFM） and energy-dispersive spectrometry （EDX）. The effect of the addition of nanodispersed powders on the mechanical properties and microstructure of Si3N4 ceramics was investigated.

Effect of Nitriding Process on Phase and Microstructure of Silicon Nitride Fibers Prepared by Direct Nitriding Method

In this paper,Si3N4 fiber materials were fabricated by nitridation of porous Si green bodies,which were prepared by the foaming method combined with gel-casting.The effect of the nitriding process(the heating rate and the nitrogen flow rate)on the phase and the microstructure was studied.The results show that decreasing the heating rate and the nitrogen flow rate is both beneficial to the growth of Si3N4 nanofibers and promoting the disintegration of the pore wall structure of the porous green bodies.The optimized nitrogen flow rate and the heating rate for the growth of silicon nitride fibers are 150 mL/min and 0.5℃/min,respectively.

Influence of Yb_2O_3-MgO on Mechanical Properties and Thermal Conductivity of Silicon Nitride Ceramics via Gas Pressure Sintering

In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering（ 0. 6 MPa N2atmosphere） to investigate how the amounts of Yb2O3- Mg O influence the mechanical properties and thermal conductivity of silicon nitride ceramics. The total contents of Yb2O3- Mg O added were 1 mol%,2 mol%,4 mol%,6 mol%,8 mol%,10 mol%,12 mol%,14 mol%,keeping the Yb2O3-Mg O molar ratio of 1 ∶ 1 steadily. Curves of the relative density,thermal conductivity and bending strength plotted against the aids content present a ‘mountain＇shape with a maximum at nearly 10 mol% aids. The fracture toughness increased with the amounts of additives up to10 mol% and decreased slightly thereafter. The mechanical properties and thermal conductivity were almost proportional to the amount of the additives before10 mol%. When the content of aids exceeded 10 mol%,it would weaken the mechanical properties and thermal conductivity of the ceramics. The optimum content of Yb2O3- Mg O was 10 mol% by gas pressure sintering（ 0. 6MPa） at 1 850 ℃ for 4 h,which led to a relative density of 98. 9%,a flexural strength of（ 966 ± 38）MPa as well as a fracture toughness of（ 6. 29 ± 0. 29）MPa·m1 /2and thermal conductivity of 82 W /（ m·K）.

Synthesis,Characterizations and in Vitro Assessment of the Cytotoxicity and Genotoxicity of Novel Silicon Nitride-Based Porous Ceramics

Porous Si3N4-SiO2-based ceramics with different porosity were prepared via free sintering of Si3N4 on air with an addition of semolina (5, 10 and 20 wt%) as a pore-forming agent. The semolina content in the starting powder controlled the volume fraction of pores in the sintered body. Small pores (5 μm) formed a continuous network in the whole volume of the ceramic material, while the large pores (~100 μm), formed from the added semolina were mostly isolated in the ceramic matrix. Mercury porosimetry and strength measurements have shown that specific surface area, volume density and compressive strength decreased with the amount of semolina in the samples. Mechanical properties similar to bone were obtained for the sample with 20 wt% semolina pore forming agent (compressive strength 350 MPa, density 2.17 g.cm-3). The prepared Si3N4-SiO2-based ceramics were evaluated for cytotoxic and genotoxic potential on human fibroblast VH10 and B-HNF-1 cells. Biological tests have shown that both these human fibroblast cell lines were sensitive to the samples with lower porosity and cell growth inhibition was observed in the range 14.9% - 21.3%. The cytotoxicity of the sample with the highest porosity (~40%) was not significant (10%). The microscopic observations have shown that VH10 and B-HNF-1 cells growing around the silicon nitride ceramic discs were homogeneously distributed on the cultivation surface. No significant morphologic changes were found in treated cells, their morphology was very similar to that of the control cells. None of the tested Si3N4-based ceramic samples induced necrotic/apoptotic death of human fibroblasts. Sample S-20 had similar properties to bones and was characterized by very good biocompatibility, slight cytotoxicity and none genotoxicity. Therefore, Si3N4-SiO2-based ceramics prepared by free sintering on air are potential biomaterials for medical applications.

Opto-Structural Properties of Silicon Nitride Thin Films Deposited by ECR-PECVD

Amorphous hydrogenated silicon nitride thin films a-SiNx:H (abbreviated later by SiNx) were deposited by Electron Cyclotron Resonance plasma enhanced chemical vapor deposition method (ECR-PECVD). By changing ratio of gas flow (R = NH3/SiH4) in the reactor chamber different stoichiometric layers x = [N]/[Si] ([N] and [Si] atomic concentrations) are successfully deposited. Part of the obtained films has subsequently undergone rapid thermal annealing RTA (800°C/1 s) using halogen lamps. Optical and structural characterizations are then achieved by spectroscopic ellipsometry (SE), ion beam analysis and infrared absorption techniques. The SE measurements show that the tuning character of their refractive index n(λ) with stoichiometry x and their non-absorption properties in the range of 250 - 850 nm expect for Si-rich SiNx films in the ultraviolet UV range. The stoichiometry x and its depth profile are determined by Rutherford backscattering spectrometry (RBS) while the hydrogen profile (atomic concentration) is determined by Elastic Recoil Detection Analysis (ERDA). Vibrational characteristics of the Si-N, Si-H and N-H chemical bonds in the silicon nitride matrix are investigated by infrared absorption. An atomic hydrogen fraction ranging from 12% to 22% uniformly distributed as evaluated by ERDA is depending inversely on the stoichiometry x ranging from 0.34 to 1.46 as evaluated by RBS for the studied SiNx films. The hydrogen loss after RTA process and its out-diffusion depend strongly on the chemical structure of the films and less on the initial hydrogen concentration. A large hydrogen loss was noted for non-thermally stable Si-rich SiNx films. Rich nitrogen films are less sensitive to rapid thermal process.

Studies on Dielectric Properties of Silicon Nitride at High Temperature

In this paper, the dielectric properties of silicon nitride are studied using the dielectric polarization theories. According to the developed dielectric models, the temperature dependence of dielectric constant and loss of silicon nitride is mainly analyzed. In addition, the impact of Li^＋, K^＋, Ca^2＋, Al^3＋ and Mg^2＋ doping on the dielectric properties of silicon nitride are also estimated.

Bandwidth-tunable silicon nitride microring resonators

We designed a reconfigurable dual-interferometer coupled silicon nitride microring resonator.By tuning the integrated heater on interferometer's arms,the"critical coupling"bandwidth of resonant mode is continuously adjustable whose quality factor varies from 7.9×10^(4) to 1.9×10^(5) with the extinction ratio keeping higher than 25 dB.Also a variety of coupling spanning from"under-coupling"to"over-coupling"were achieved,showing the ability to tune the quality factor from 6.0×10^(3) to 2.3×10^(5).Our design can provide an adjustable filtering method on silicon nitride photonic chip and contribute to optimize the nonlinear process for quantum photonics and all-optical signal processing.

Experimental Research on Residual Stress in Surface of Silicon Nitride Ceramic Balls

The influence of the residual stress in surface of ceramic balls on the fatigue life is large, because the life of silicon nitride ball bearings is more sensitive to the load acted on the bearings than the life of all-steel ball bearings. In this paper, the influence of thermal stress produced in sintering and mechanical stress formed in lapping process on residual stress in surface of silicon nitride ceramic balls was discussed. The residual compress stress will be formed in the surface of silicon nitride ceramic balls after sintering. The residual tensile stress will be formed in surface of silicon nitride ceramic balls in lapping process, and the size of abrasive particle is smaller, such trend is stronger. In this paper the residual stress was measured by the xylometric measurement in which the material in surface was peeled with lapping. The distribution of residual stress in surface can be calculated with the variation in specific volume. The technological parameter with which the material was peeled by lapping was given, for minimizing the extra influence of the residual stress forming in peeling on the original residual stress in surface, the abrasive particle size would not be too small and the load impressed would not be too large. Some experimental researches on residual stress in surface of silicon nitride ceramic balls were made. The surface of silicon nitride ceramic balls presented residual compressive stress after sintering and the influence of the ball size on the residual stress is feeble. It is expected that the size of ball blank is same for achieving the same residual compressive stress in surface on balls after final machining. In lapping process, the surface of silicon nitride ceramic balls presented residual tensile stress, the larger the load which is impressed on single ball, the larger the amplitude of residual tensile stress is; the smaller the abrasive particle, the stronger the trend of plastic deformation is and the larger the amplitude of residual tensile stress is.

Electrochemical characteristics of ternary and quadruple lithium silicon nitrides as anode material for lithium ion batteries:the influence of precursors

Ternary and quadruple lithium silicon nitride anode materials for lithium ion batteries with different precursors were prepared by the simple process of high-energy ball milling. High capacity and excellent cyclability were obtained. The influence of precursor introduction on the electrochemical performance of products was investigated. This research reveals that the electrochemical performance of lithium silicon hitilde can be enhanced significantly by doping O. The cyclability of quadruple lithium silicon nitfide can be optimized remarkably by controlling the introduction quantity of the precursors. It is possible for the composite to be used as a capacity compensator within a wide voltage cut-off window.

Low-power electro-optic phase modulator based on multilayer graphene/silicon nitride waveguide

Electro-optic modulator is a key component for on-chip optical signal processing.An electro-optic phase modulator based on multilayer graphene embedded in silicon nitride waveguide is demonstrated to fulfill low-power operation.Finite element method is adopted to investigate the interaction enhancement between the graphene flake and the optical mode.The impact of multilayer graphene on the performance of phase modulator is studied comprehensively.Simulation results show that the modulation efficiency improves with the increment of graphene layer number,as well as the modulation length.The 3-dB bandwidth of around 48 GHz is independent of graphene layer number and length.Compared to modulator with two-or four-layer graphene,the six-layer graphene/silicon nitride waveguide modulator can realizeπphase shift at a low-power consumption of 14 fJ/bit when the modulation length is 240μm.

TiC Particle Reinforced Silicon Nitride Composite Joined With Y_2O_3-Al_2O_3-SiO_2 Mixture

Silicon nitride composite is joined to itself by heating interlayer of Y2 O3 -AL2O3 -SiO2 mixtures above their liquidus temperatures in flowing nitrogen. The joined specimens are tested in four point flexure from room temperature to 1373 K. The interface microstruclure and fractured surfaces after testing are observed and analyzed by SEM, EPMA and XRD respectively. The results show that F2 O3 -A12 O3 -SiO2 glass reacts with Si3 N4 at interface, forming the Si3 N4/Si2 N2 O( Y-AlrSi-O-N glass/ Y-Al- Si-O glass gradient interface. With the increase of bonding temperature and holding time, the joint strength first increases, reaching a peak, and then decreases . According to interfacial analyses , the bonding strength depends on joint thickness .

Silicon Nitride Supported Cobalt Catalyst for Enhanced Hydrogen Production from Ethanol Steam Reforming

Silicon nitride(Si_(3)N_(4))supported cobalt catalysts(Co/Si_(3)N_(4))were fabricated by using wetness impregnation procedure.The microscopic morphology,phase composition,and electronic states were characterized by XRD,TEM,SEM,and XPS,respectively.For comparison,cobalt catalyst supported on SiO_(2)(Co/SiO_(2))was also investigated.XPS studies and DFT calculations show that the cobalt species in Co/Si_(3)N_(4) have lower valence state than those in Co/SiO_(2).The catalytic ESR reactions demonstrate that Co/Si_(3)N_(4) exhibits distinctly higher catalytic activity and hydrogen selectivity than Si_(3)N_(4) support and Co/SiO_(2) catalyst with the identical cobalt loading,indicative of the favorable effect of Si_(3)N_(4) support on the catalytic performance of supported cobalt catalyst.Durability tests and TG-DSC studies show that Co/Si_(3)N_(4) catalyst exhibits better stability and resistance to coke during the same catalytic experiment period.