Showing papers on "Sialon published in 2016"

Review on the properties of hexagonal boron nitride matrix composite ceramics

Abstract: Novel hexagonal boron nitride (h-BN) matrix composite ceramics exhibit versatile and greatly improved properties compared with the traditional h-BN ceramics, such as excellent mechanical properties, high-temperature resistance, thermal shock resistance, ablation resistance, and molten metal erosion resistance. They have potential important applications in the field of aerospace, electronics, metallurgy, machinery, nuclear energy, etc. As such, much attention are paid by both academia and industry on materials science and technology. In this paper, the special crystal structure and unique characteristics of h-BN are firstly briefly introduced. Then, the state-of-the-art development on mechanical properties, thermal shock resistance, ablation resistance, ion erosion resistances, molten metal erosion resistance and the damage mechanisms of novel h-BN matrix composite ceramics under harsh serving environments are reviewed, including textured h-BN matrix composite ceramics with anisotropic properties targeted for heat management applications. Moreover, the possible future research focus on h-BN and h-BN matrix composite ceramics are also forecasted.

Elucidating Structure–Composition–Property Relationships of the β-SiAlON:Eu2+ Phosphor

Abstract: In this work, we performed a systematic investigation of structure–composition–property relationships in Eu2+-activated β-SiAlON, one of the most promising narrow-band green phosphors for high-power light-emitting diodes and liquid crystal display backlighting with wide color gamut. Using first-principles calculations, we identified and confirmed various chemical rules for Si–Al, O–N, and Eu activator ordering within the β-SiAlON structure. Through the construction of energetically favorable models based on these chemical rules, we studied the effect of oxygen content and Eu2+ activator concentrations on the local EuN9 activator environment, and its impact on important photoluminescence properties such as emission peak position (using the band gap as a proxy), bandwidth, and thermal quenching resistance. Increasing oxygen content is shown to lead to an increase in Eu–N bond lengths and distortion of the EuN9 coordination polyhedron, modifying the crystal field environment of the Eu2+ activator, and result...

Tribochemical wear of cutting-tool ceramics in sliding contact against a nickel-base alloy

Abstract: The wear behaviour of a SiAlON and a SiC whisker reinforced Al 2 O 3 composite in dry sliding contact against Inconel 718 was investigated. For tribological characterization, the worn contact surfaces were analysed using tribometer data and calculation of wear volume in addition to SEM/EDX analysis. The surface contact temperatures were estimated by finite element simulations. The tribological behaviour is distinct for each ceramic. The wear in SiAlON undergoes an exponential decay with increasing frictional power due to the formation of lubricous tribolayers that separate both contacting surfaces; once the frictional power is high enough tribochemical wear dominates and delamination of the tribolayers takes place. The wear of Al 2 O 3 –SiC is lower than that of SiAlON especially at high frictional power, which can be mainly attributed to the chemical stability of the alumina matrix and the formation of stable lubricous tribolayers. FEM simulations indicated high contact temperatures with steep gradients in the depth.

Optical properties of solid-state laser lighting devices using SiAlON phosphor–glass composite films as wavelength converters

Abstract: In this work, SiAlON phosphor–glass films were investigated as wavelength converters in solid-state laser lighting. The phosphor–glass composite films were prepared by dispersing phosphor powders into a silica precursor solution and sintering at 500 °C. Both simulation and experiment were carried out to evaluate the optical properties of solid-state lighting devices using SiAlON:Eu or YAG:Ce–glass films. The device using SiAlON:Eu phosphors initially has lower brightness than that of the device using YAG:Ce at lower laser powers, but the latter has an illuminance saturation at 1000 lx whereas the SiAlON-based device is free of saturation even at higher laser powers. The device using SiAlON phosphor–glass composite films has a maximum illuminance 15% higher than that of the device using YAG when the temperature exceeds 250 °C. These better optical properties are ascribed to the higher thermal stability of SiAlON phosphors that are able to achieve high luminance and thermally robust solid-state lighting.

Cutting performance and wear mechanism of Sialon ceramic cutting inserts with TiCN coating

Abstract: In this study, TiCN coating was deposited on Sialon ceramic cutting inserts by physical vapor deposition (PVD) technique. The properties of the coating were characterized by nano-indentation and scratch tests. The results showed that the elastic modulus, hardness, and adhesion force of the coating were 408.34 ± 16.25 GPa, 22.56 ± 0.99 GPa, and 33 N, respectively. Compared the Sialon ceramic cutting inserts with and without the coating, the surface hardness of inserts with the coating was higher than that of them without the coating, resulting in the outstanding cutting properties of the inserts. Cutting performance of the TiCN coated Sialon ceramic cutting inserts were investigated in turning nickel-based alloy under dry conditions. As a comparison, the uncoated Sialon ceramic cutting inserts for turning tests were performed under the same conditions. The results revealed that cutting performance of the inserts was improved remarkably by producing TiCN coating on the surface. The wear mechanisms of uncoated and TiCN coated Sialon ceramic cutting inserts were all abrasive and adhesive wear. However, the using life of TiCN coated inserts was much longer than that of the uncoated inserts, indicating that the coating can effectively protect the inserts from frictional wear.

Cutting performance and wear mechanisms of Sialon ceramic cutting tools at high speed dry turning of gray cast iron

Abstract: In the present work, the phase composition and microstructure of two Sialon cutting inserts (named sample A and sample B) were characterized by XRD and SEM. The cutting performance and wear mechanism of the cutting inserts were investigated at high-speed dry turning of gray cast iron. The results showed that the main phases of them were α- and β-Sialon, and the sample A contained more α-Sialon than that of sample B. The grains of the Sialon cutting inserts are mainly elongated shape, and the aspect ratios are about 5.32 and 5.09, respectively. The tool life of sample B was longer than that of sample A at low speed. However, with the speeds increased, the tool life of sample A was getting closer to that of sample B and then exceeded that of sample B. The wear mechanisms of the two cutting inserts were abrasive and adhesive wear, however, as the cutting speeds increased, the dominant wear mechanisms were different.

Development of a single-phase Ca-α-SiAlON ceramic from nanosized precursors using spark plasma sintering

Abstract: Nitrogen-rich Ca-α-SiAlON ceramics were synthesized using nanosized precursors via spark plasma sintering process for various holding times (10, 20, 30 min) at relatively low temperatures of 1500 °C and 1600 °C. The effects of the experimental conditions, namely sintering time and temperature, on the densification and mechanical properties of the processed α-SiAlON were investigated. All of the conditions yielded nearly completely densified ceramics. A remarkable combination of hardness and toughness was obtained for the samples at either sintering temperature; and these values were greatest after 30 min sintering time, with Vickers hardness values of 21.6 GPa and 20.5 GPa and fracture toughness values of 7.3 MPa√m and 9.7 MPa√m for sintering temperatures of 1500 °C and 1600 °C, respectively. The differences in the mechanical properties of these samples were related to differences in the phases formed during the sintering process.

Self-propagating high temperature synthesis of SiAlON

Abstract: In this work, a new method of SHS process has been investigated for the synthesis of SiAlON under low nitrogen pressure. A gel mixture of silica and sodium oxide (sodium silicate) as a reactant and catalyst was produced by alkali melting of silica, solving the results in water and heating in auto clave. Al powder was also used as reactants. Urea and aluminum nitrate hydrate was used as igniting agents. The addition of Mg also was necessary for reaching the combustion. Sodium azide as a good reactant addition for preparing both combustion and nitrogen supply was tested. Beta-Si 3 N 4 powder acted as diluting agent and by reducing the adiabatic temperature helped the nitrogen diffusion into the melted reactants which was not agglomerated. NH 4 Cl in some cases was used as a catalyst which showed good results for reaching SiAlON. For comparison possibility some experiments were made using silica powder instead of sodium silicate gel. These materials were mixed by pestle and mortar and laid into the combustion chamber cavity without pressing. The compound was heated by electrical element until the ignition happened by gases which were produced from urea and aluminum nitrate hydrate. The pressure of nitrogen in combustion chamber was kept constant near 0.1 Mpa. The products of syntheses were of agglomerated one mostly O′-SiAlON & β and β′-SiAlON. Effects of NH 4 Cl were examined by XRD results. TGA and DTA graphs showed the thermodynamics of reaction which were analyzed in some parts by XRD spectroscopy. In some cases nano material of SiAlON was produced which is demonstrated by XRD and FTIR spectroscopy.

SiAlON–epoxy nanocomposite coatings: Corrosion and wear behavior

Abstract: In this study, epoxy powder as a matrix was combined with different contents of silicon–aluminum–oxygen–nitrogen (SiAlON) nanoparticles using a planetary ball mill Pure epoxy and nanocomposite powders were applied on the surface of plain carbon steel components by the electrostatic spraying method Curing of the coatings was done in an oven or microwave for the appropriate time The coating structure and morphology of the SiAlON nanoparticles were studied by scanning electron microscopy and transmission electron microscopy, respectively The corrosion properties of the coatings were assessed by immersion, Tafel polarization, and electrochemical impedance spectroscopy tests in 35% NaCl solution The results show that addition of 10 wt % SiAlON nanoparticles markedly increases the corrosion resistance of epoxy coatings Thus, it can be inferred that the corrosion rate of these coatings is 15 to 18 times lower than that of pure epoxy samples and 8 to 11 times lower than coatings with 20 wt % SiAlON The higher corrosion resistance of nanocomposite coatings can be attributed to the barrier properties of SiAlON nanoparticles The tribological performance of the coatings was studied with the pin-on-disk test The results of wear testing show that the samples containing 10 wt % SiAlON provide about five times more wear resistance than pure ones and about two times more than coatings with 20 wt % SiAlON However, the coefficient of friction for nanocomposite coatings is reduced about 50% compared to the pure sample Also, the curing process in either regime (oven or microwave) has the same effect on the corrosion and wear properties, and the coatings are completely crosslinked © 2016 Wiley Periodicals, Inc J Appl Polym Sci 2016, 133, 43855

Sintering behavior and mechanical properties of spark plasma sintered β–SiAlON/TiN nanocomposites

Abstract: In this study, fully dense β-SiAlON/TiN composites were produced by Spark Plasma Sintering (SPS) method. Si3N4, Al2O3, AlN and TiO2 powders were used as precursors. Starting powders were mixed with high energy ball milling and then were sintered by SPS method (at 1750 °C under pressure of 30 MPa for 12 min.). The milled powders had an average particle size of below ~ 155 nm. The XRD patterns of SPS-ed composites showed that the entire β-SiAlON phase constituent was in the form of Si4Al2O2N6 phase and cubic TiN phase can be formed by the phase transformation of TiO2 in relation with other precursors. FESEM micrographs confirmed that TiN particles were distributed homogeneously throughout β-SiAlON matrix. Mechanical properties evaluation revealed that by adding micro sized TiO2, optimal mechanical properties with a hardness ~ 14.6 GPa and a fracture toughness ~ 6.3 MPa m1/2 were obtained. The improvement in the fracture toughness was attributed to the presence of the crack deflection as the dominant toughening mechanism in the SPS-ed β–SiAlON/TiN composites.

Experimental Investigation on Sialon Ceramic Inserts for Ultra-high-speed Milling of Inconel 718

Abstract: A series of milling aerospace material Inconel 718 experiments were conducted with a sialon ceramic tool to investigate chip evolution, cutting force, and tool wear at different cutting speeds. Round inserts were used at ultra-high-speeds under dry cutting conditions. A scanning electron microscopy and an optical microscope were used to observe the worn surfaces and to reveal the wear mechanisms of the inserts. The experiment results showed that the macroscopic shape of the chips was small scraps and fan-shaped. With the increase in the cutting speed, the plastic deformation of the chips was increasingly serious. The minimal average cutting forces were obtained at vc = 700 m/min. The rise of cutting temperature was resulted from the increase in cutting deformation work and friction work with cutting speed. The combined effect of thermal stress and mechanical stress contributed to the tool chipping, flaking, microcrack propagation, abrasion, and adhesion which were the primary reasons of the sialon ceramic...

Fabrication and erosion resistance of dense α-Si3N4/Sialon coating on porous Si3N4 ceramic

Abstract: A dense α-Si3N4/Sialon ceramic coating was fabricated on porous Si3N4 ceramic using the liquid infiltration and filling method. The effect of sintering temperature on microstructures, water absorption, mechanical properties and erosion resistance of the coatings were investigated in detail. The results showed that the coatings mainly consisted of α-Si3N4, O′-Sialon and Y–Si–Al–O–N glass, and the content of O′-Sialon increased gradually with the increase of sintering temperature. As-prepared coatings exhibited good waterproof ability though some pores were produced within the coating, and water absorption of porous Si3N4 ceramic decreased obviously after fabricating the coatings. Hardness, elastic modulus and E/H value of the coatings increased gradually as the sintering temperature increased from 1400 to 1450 °C, but they began to decrease when the sintering temperature reached 1500 °C. The coating prepared at 1450 °C displayed the best erosion resistance, and mass loss was only 0.91 wt% after eroding 2 h.

Microstructure and erosion resistance of in-situ SiAlON reinforced BN-SiO 2 composite ceramics

Abstract: BN-SiO2-SiAlON composite ceramics were successfully prepared by the means of hot pressed sintering. Xe plasma flow generated by Hall Thruster was used for sputtering the surface of the samples in order to evaluate the plasma erosion resistance. XRD, TEM, SEM, and LSCM were used to characterize the phase composition and morphologies of as-made composite ceramics before and after Xe plasma erosion. The ceramics were composed of h-BN, fused silica, and SiAlON, which maintained structural stability during the process of Xe plasma sputtering. In conclusion, comparing with BN-SiO2 composite ceramics, the plasma erosion rate of BN-SiO2-SiAlON composite ceramics decreases significantly at first then rises with the increase of AlN addition. Erosion pits can be observed by using SEM on the surface after plasma sputtering, which demonstrates that the BN grains have dropped off the surface. In addition, mechanical denudation by high-speed Xe ions is recognized as the injury mechanism for the BN-matrix composite materials.

Inorganic phosphors in lead–silicate glass for white LEDs

Abstract: Luminescent composites of the “phosphor-in-glass” type, based on a highly reflective lead–silicate matrix and fine-grained powders of YAG:Ce3+ and SiAlON:Eu2+ crystals, are developed and synthesized. Phosphor and glass powders are sintered at a temperature of 550°C to obtain phosphor samples for white LEDs. The composites are analyzed by X-ray diffraction and luminescence spectroscopy. The dependence of the light quantum yield on the SiAlON:Eu2+ content in the samples is investigated. A breadboard of a white LED is designed using a phosphor-in-glass composite based on lead–silicate glass with a low glasstransition temperature. The total emission spectra of a blue LED and glass-based composites are measured. The possibility of generating warm white light by choosing an appropriate composition is demonstrated.

Na-α'-GeGaON Solid Solution Analogous to α'-SiAlON: Synthesis, Crystal Structure, and Potentiality as a Photocatalyst.

Abstract: We demonstrated, for the first time, formation of the Na-α′-GeGaON (NamGe12–(m+n)Gam+nOnN16–n) solid solution, an analogue of the well-established α′-SiAlON system. We successfully synthesized single-phase powder samples by reduction–nitridation of Na2CO3–GeO2–Ga2O3, in the solubility range of m ≈ 0.8–1.7 with n ≈ 0.2–0.3. The Rietveld refinement of powder X-ray diffraction data for Na-α′-GeGaON was conducted on the basis of the space group P31c of α′-SiAlON, and the refinement converged with RB = 1.78% and RF = 1.02% for the composition of Na1.26(1)Ge10.50Ga1.50O0.24(1)N15.76(1), indicating reliably the isomorphism between the SiAlON and GeGaON systems. The results of 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy clearly showed a single peak at the chemical shift of ∼16 ppm, further proving the accommodation of Na in the α′-GeGaON matrix with the expected coordination environment. The synthesized Na-α′-GeGaON exhibited stable photocatalytic activity for the evolution of H2 from water und...