Homogeneous Powder Mixtures Research Articles

Enhanced properties of ZrSiO4/ZrO2 composites produced by colloidal processing and spark plasma sintering

Zirconium oxide and silicate are well-known reference materials in ceramics. However, the performance of zircon/zirconia composites has not received the required attention considering the interesting properties and capabilities. Zircon and zircon/zirconia suspensions were optimised by colloidal processing routes. These suspensions were either slip cast to obtain pieces that were conventionally sintered or freeze-dried to obtain homogeneous powder mixtures for consolidation by non-conventional Spark Plasma Sintering (SPS). Pure zircon materials with densities up to 97.0 % and a hardness of 10.1 GPa were obtained by conventional sintering (1550 ºC/120 min) whereas densities higher than 99.5 % and hardness up to 12.7 GPa were achieved by SPS (1500 ºC/5 min). By introducing 20 vol.% zirconia as a sintering additive, densities up to 99.3 % and a hardness of 11.1 GPa were achieved by conventional sintering (1500 ºC/120 min) whereas densities of 99.9 % and a hardness of 13.5 GPa were obtained by SPS (1400 ºC/5 min).

Dry sliding wear behavior of sinter forged micrometric and nanometric yttrium oxide reinforced AA-7075 matrix composites

This study aims to investigate the dry sliding wear behaviour of AA-7075 based metal matrix composites developed by powder metallurgy route. AA-7075 metal matrix composites have been developed with 1–15 vol% micrometric yttrium oxide particulate reinforcement and 0.1–3 vol% nanometric yttrium oxide particulate reinforcement by sinter forging.The matrix and reinforcing powders were blended together to obtain a homogeneous composite powder mixture which was cold compacted and further sintered under pure nitrogen atmosphere. The sintered compacts were forged in a closed die to attain full density. The hot forged samples were further artificially age hardened to peak hardness. Wear behavior of AA-7075 and its composites at peak aged condition were investigated at various loads and sliding speeds. The coefficient of friction and wear rate were determined with respect to different volume fractions of micrometric and nanometric yttrium oxide additions to AA-7075 alloy matrix. The overall wear at a constant volume fraction was found to be lower for the compositions having nanometric Y2O3 as compared to micrometric Y2O3. Further the basic wear mechanism of pure aluminum 7075 alloy and reinforced composites consisted of adhesive wear with plastic deformation followed by abrasive wear (due to hard reinforcement particles).Material strengthening by precipitation hardening and reinforcement addition and the role of the forging operation and yttria reinforcements in the removal and uniform distribution of oxide layers present on the AA-7075 powder particles were accountable for the improvement in the wear resistance of the composites.

Fabrication and hardness of in-situ Al3Ti–Al2O3 composite

In this work, an in-situ Al3Ti–Al2O3 composite was optimally synthesized from raw powders via mechanical milling and conventional sintering processes. The strong influence of milling time on the promotion of the phase reaction between the initial TiO2 and Al materials was proven by using X-ray diffraction and surface morphology analysis. The obtained results showed that the milling process did not initiate any reaction between the raw TiO2 and Al materials. However, the milling process was important for creating a homogeneous powder mixture and refining the particle size of the powders. The Al3Ti–Al2O3 composites were completely formed after conventional sintering at 750°C for 30 min for a milling time of over 4 h. The highest obtained microhardness of the composite was approximately 130 HV, which was suggested to be related to the microstructure of the bulk composite specimen consisting of two main phases, the Al3Ti matrix and the Al2O3 particles dispersed in the matrix. A small portion of an unidentified phase, a Ti-rich compound, was found in the matrix together with a tiny fraction of AlTi3. We suggest that the optimal sintering process and mechanical milling are important key factors in fabricating bulk hardness Al3Ti–Al2O3 composite materials.

Micron- and Nanosized Alloy Particles Made by Electric Explosion of W/Cu-Zn and W/Cu/Ni-Cr Intertwined Wires for 3D Extrusion Feedstock.

A novel approach to electric explosion of intertwined wires to obtain homogeneous powder mixtures intended for preparing feedstock for extrusion 3D printing has been applied. The powder were composed of spherical micron- and nano-sized W/Cu particles in-situ alloyed by Zn and Ni during electric explosion of intertwined dissimilar metal wires is offered. The mean particle size measured by micron-sized particles was not more than 20 μm. The average number size of these particles was 3 μm and it was dependent on the energy input. The powders contained phases such as α-W, β-W/W3O as well as FCC α-Cu(Zn) and α-Cu(Ni) solid solutions with the crystalline lattice parameters 3.629 and 3.61 A, respectively.

Synthesis of an Aluminum Alloy Metal Matrix Composite Using Powder Metallurgy: Role of Sintering Parameters

Powder metallurgy-based metal matrix composites (MMCs) are widely chosen and used for the development of components in the fields spanning aerospace, automotive and even electronic components. Engineered MMCs are known to offer a high strength-to-weight (σ/ρ) ratio. In this research study, we synthesized cylindrical sintered samples of a ceramic particle-reinforced aluminum metal matrix using the technique of powder metallurgy. The samples for the purpose of testing, examination and analysis were made by mixing aluminum powder with powders of silicon carbide and aluminum oxide or alumina. Four varieties of aluminum composite were synthesized for a different volume percent of the ceramic particle reinforcement. The hybrid composite contained 2 vol.% and 7 vol.% of silicon carbide and 3 vol.% and 8 vol.% of alumina with aluminum as the chosen metal matrix. Homogeneous mixtures of the chosen powders were prepared using conventional ball milling. The homogeneous powder mixture was then cold compacted and subsequently sintered in a tubular furnace in an atmosphere of argon gas. Five different sintering conditions (combinations of temperature and sintering time) were chosen for the purpose of this study. The density and hardness of each sintered specimen were carefully evaluated. Cold compression tests were carried out for the purpose of determining the compressive strength of the engineered MMC. The sintered density and hardness of the aluminum MMCs varied with the addition of ceramic particle reinforcements. An increase in the volume fraction of the alumina particles to the Al/SiC mixture reduced the density, hardness and compressive strength. The sintering condition was optimized for the aluminum MMCs based on the hardness, densification parameter and cold compressive strength. The proposed powder metallurgy-based route for the fabrication of the aluminum matrix composite revealed a noticeable improvement in the physical and mechanical properties when compared one-on-one with commercially pure aluminum.

A New High‐Entropy Alloy of Al–Fe–Co–Ni–Cu Possessing Single Face‐Centered Cubic Crystal Structure and Excellent Mechanical Properties at Room Temperature

A new powder combination of Al10(FeCoNiCu)90 is selected and verified for the potential to form solid solutions or else bulk metallic glasses (BMGs) in the alloy based on Guo et al.'s conditions and mismatch entropy criterion. The powder combination satisfies the above criteria to crystallize in solid‐solution phases and inhibits the formation of BMGs in the alloy. The alloy is fabricated by mechanical alloying of the powder mixture followed by sintering. A homogeneous powder mixture is obtained after ball milling for 80 h. The 80 h‐milled powder is crystallized in two face‐centered cubic (FCC) phases. The lattice parameters of the FCC1 and FCC2 phases are 3.60 Å and 5.21 Å, respectively. The microstructure of the alloy ingot reveals spinodal decomposition. The alloy ingot crystallizes in a single‐FCC structure. The lattice parameter of the corresponding FCC structure is determined as 3.66 Å. The compression test of the alloy ingot at room temperature reveals that the 0.2% offset yield stress of the high‐entropy alloy (HEA) is as high as 308 MPa. The compressive stress at 40% strain of the HEA is 1406 MPa. The overall Vickers hardness and density of the alloy ingot are 160 ± 14 HV0.5 and 7.7 g cm−3, respectively.

Thermal conductivity and extinction coefficient of opacified expanded perlite for vacuum super insulation up to 1073 K

A vacuum super insulation for temperatures up to 1073 K has been developed using an opacified powder mixture with high-density (ρ= 180 kg m−3) expanded perlite as base material. To analyze radiative transfer, the mass-specific extinction coefficient e of expanded perlite and various opacifiers (SiC, B4C, FeTiO3, TiO2) has been determined by FTIR spectrometry. For reduction of radiative transfer, a SiC powder with mean grain diameter of 2 μm–4 μm and bulk density of 870 kg m−3 has been identified as most suitable opacifier, also under economic aspects. Subsequently, six homogeneous powder mixtures with weight fraction w of SiC between 0% and 60% have been prepared. In order to determine the optimum w, guarded hot plate (GHP) measurements under high vacuum conditions (p < 0.1 hPa) and at 673 K mean temperature have been performed on these mixtures, yielding a minimum effective thermal conductivity of λe = 13∙10−3 W m−1 K−1 for w = 40% and ρ = 263 kg m−3. This mean temperature corresponds to an insulation application with 950 K hot-side and ambient temperature cold-side. For the optimum mixture with w = 40%, e has likewise been determined with FTIR spectrometry. Furthermore, λe has been measured with the GHP method also at mean temperatures between 373 K and 873 K, where excellent values between 4∙10−3 W m−1 K−1 and 20∙10−3 W m−1 K−1 have been obtained. For the evaluation of these measurements, two different methods have been applied in order to separate radiative thermal conductivity λr and solid thermal conductivity λs: first the common plot of λe versus T3, and second an improved method, which includes the temperature dependencies of e and λs. Expanded perlite, opacified with SiC, has proven as a highly efficient and economic vacuum super insulation material for industrial applications up to 1073 K.

Study of structural and electrical properties of Al-Si-In-Sn quaternary semiconductor alloy

In the present work, we have investigated the structural and electrical properties of two quaternary semiconductor alloy viz. Al62Si12In6Sn20 (ASIS-1) and Al58Si16In6Sn20 (ASIS-2) fabricated through powder metallurgy technique in our laboratory. Thin powders of Al, Si, In, and Sn metals is carefully weighted by analytical weight balance and then used to obtain homogeneous powder mixtures to construct aforementioned quaternary semiconductor alloy. A mixed powder is compacted by a compressive testing machine (CTM) at a pressure of 800 MPa to achieve green compact. The hybrid phase sintering process is carried out at 500℃ temperature at isothermal holding time about 120 min in the steel furnace (i.e. muffle furnace). The obtained samples are than characterized by optical microscopy, electrical resistivity, density, UV–VIS spectroscopy and Hall effect measurements. The density of both samples is found by 3.01 gm/cm3 and 2.96 gm/cm3, respectively. From the overall study, it is concluded that the electrical resistivity of aforesaid alloy increases with increasing the silicon percentage.

Fiber Laser Cladding of WS2 + Cr on SS316 Substrate and its Characterization

Abstract In the present study, continuous wave fiber laser of 400W capacity with CNC controller is used for the cladding operation. SS316 +WS2+Cr powder mixture is taken as clad materials and SS316 of 5 mm thick plate as substrate materials. A homogeneous powder mixture is pasted over the substrate surface and laser beam is scanned by imparting motion to the XY table to get required cross-section area of the clad surface. By adjusting the (±) z–axis of working table the required size of spot diameter (divergence of laser beam) is obtained. For getting the required scan cross-section area, a CNC programmed was built with the help of SINUMERIK 828D SIEMENS controller. A gas chamber made of perpesx sheet having quartz window with different gas purging facility is used to creating required working environment. The laser beam is passed through a quartz window and strike on the surface of the powder layer. Various input process parameters were consider during the experiment such as laser power: 100-200 W, scanning speed: 500-1000 mm/min, % v/v composition of WS2: 5-15 and % v/v composition of Cr: 10 considered as variable process parameters and laser spot diameter: 0.4 mm, hatching gap: 0.2 mm, powder layer thickness: 0.7 mm. The prepared clad specimens were cut with the help of wire-EDM machine for characterization purpose. Then the sectioned specimens were polished using emery paper of different grit size followed by diamond paste polishing to get mirror finishing. Field emission scanning electron microscope (FESEM) (Model: Supra 55, Make: Zeiss, Germany) was used to study the microstructure and to do the elemental analysis. X- Ray diffraction (XRD) technique was used for phase analysis. The diffraction angle (2θ) was kept in the range of 20°-120° to detect the range of chemical compounds formed during the laser cladding process. From XRD analysis, it is can be observed that different intermetallic compounds were formed during laser cladding operation such as WS2, FeS2, FeS, CrS. The micro-hardness of the sectioned surface was measured along the clad depth using a Vickers micro hardness tester (Model: Economet VH-1 MD, Make: Chennai Metco, India). The dry sliding wear behaviour of the clad samples was analysed using a pin on disk tribometer (Make-DOCUM, India, Model: TR 201LE). The wear tests were conducted at an angular speed of 500 rpm at a radial distance of 60 mm. A dead load of 3kgf was maintained during the test for a period of 10 minutes

Small Angle Neutron Scattering Study of a Gehlenite-Based Ceramic Fabricated from Industrial Waste

This paper presents a small angle neutron scattering (SANS) study of a novel porous gehlenite-based ceramic, synthesised from a homogeneous powder mixture of soda-lime-silicate (SLS) glass, α-alumina, calcite and calcium fluoride via solid-state sintering at 1200 °C. The products of sintering at single temperatures from 600 to 1200 °C are examined by X-ray diffraction (XRD). Sintering of the mixture below 1200 °C forms two intermediate phases (Na2CaSi3O8 and Ca4Si2O7F2). Nepheline and α-alumina are minor phases in the gehlenite-based ceramic fabricated through sintering at 1200 °C. The microstructure of the gehlenite-based ceramic is investigated using field-emission scanning electron microscopy (FESEM) and SANS at the Australian Centre for Neutron Scattering. This study also evaluated the specific surface area of the gehlenite-based ceramic (~3.0 m2 cm–3) from quantitative analysis of SANS data.

Fabricating eco-friendly nanocomposites of SiC with morphologically-different nano-carbonaceous phases

A route based on aqueous colloidal processing followed by liquid-phase assisted spark-plasma-sintering (SPS) is described for fabricating eco-friendly nanocomposites of SiC with nano-carbonaceous phases (nanotubes, nanoplatelets, or nanoparticles). To this end, the conditions optimizing the aqueous colloidal co-dispersion of SiC nanoparticles, Y3Al5O12 nanoparticles (acting as sintering additives), and carbon nanotubes (CNTs), graphene oxide (GO) nanoplatelets, or carbon black (CB) nanoparticles were first identified. Next, homogeneous powder mixtures were prepared by freeze-drying, and densified by liquid-phase assisted SPS, thus obtaining nanocomposites of SiC with CNTs, reduced GO (rGO) nanoplatelets, or pyrolized + graphitized CB (p + gCB) nanoparticles. It is also shown that these nanocomposites are dense and have a high hardness of ∼20 GPa regardless of the nano-carbonaceous phase chosen, but are markedly tougher with CNTs and rGO (i.e., with high aspect ratio nano-carbonaceous phases). Finally, arguments are provided for the appropriate choice of nano-carbonaceous phases for engineering ceramic nanocomposites.

Improvement of the Manufacturing Process of Tungsten Carbide–Cobalt Hard Metals by the Application of Sound Assisted Fluidization for the Mixing of the Powders

In this work, the technology of sound assisted fluidization has been used as an alternative mixing method to obtain homogeneous powder mixtures (WC, Co, and polyethylene glycol (PEG)) to be used in the standard steps of hard metal production. A preliminary experimental campaign was carried out to optimize the process parameters (sound intensity/frequency and fluidization velocity) to perform the mixing process. After that, the obtained powder mixture was pressed and subjected to the sintering process. The quality of the final sintered products was assessed by using different techniques (SEM analysis, magnetic properties analysis, relative density, and Vickers hardness). The effects of two operating variables, mixing temperature and shaping pressure, were also studied aiming at improving the quality of the final products in terms of reduced porosity and enhanced density and hardness. Finally, also the effect of the addition of an inhibitor (Cr3C2) to the mixture was assessed.

Exfoliation of MoS2 and h-BN nanosheets by hydrolysis of LiBH4

Efficient preparation of two-dimensional materials is still a great challenge. These materials possess unique electrical, optical, and thermal properties. In this study, few-layer MoS2 nanosheets and nanoflakes were exfoliated by the hydrolysis reaction of LiBH4. First, the layered MoS2 powder materials were mixed with LiBH4 to obtain a homogeneous powder mixture, and then the mixture was heated above the melting point of LiBH4 under 300 °C and 4 MPa H2 for 2 h, during which the layered materials were curled by liquid LiBH4. In the subsequent hydrolysis of LiBH4, the layered materials were split into nanosheets by H2 gas generation. The obtained MoS2 nanosheets show almost uniform thickness of ~4 nm, with a width of 2–10 μm and a yield of more than 1.5 wt.%. The effectiveness of this method has also been verified by the preparation of few-layer h-BN. This work provides a new high-yield route to producing two-dimensional materials.

Synthesis and Study on Ionic Conductive (Bi1−x,Vx)O1.5−δ Materials with a Dual-Phase Microstructure

Homogeneous Bi2O3-V2O5 powder mixtures with different amounts of V2O5 content (≤15 mol%) were prepared by colloidal dispersion and sintering to high density. The sintered and annealed samples were studied by thermal analysis, quantitative X-ray diffraction and scanning electron microscopy. The electrical and ionic conductivities of the conductors were also measured by a four-probe direct current (DC) method. The results of the samples prepared at 600–800 °C and annealed for as long as 100 h show that the sintered samples consisting of a pure γ phase or δ + γ binary phase perform differently in conductivity. The highly conductive δ phase in the composition of Bi0.92V0.08O1.5−δ enhances the electric conductivity 10-times better than that of the pure γ-sample (Bi0.94V0.06O1.5−δ) between 400 and 600 °C. The compatible regions of the γ phase with the α- or δ phase are also reported and discussed, so a part of the previously published Bi2O3-V2O5 phase diagram below 800 °C is revised.

Europium(III)‐Doped MgAl2O4 Spinel Nanophosphor Prepared by CO2 Laser Co‐Vaporization

Photoluminescent nanoparticles (NPs) are of specific interest for biomedical applications, bioimaging, and cell tracking. Here, we report on the synthesis of europium(III)‐doped MgAl2O4 spinel NPs by the CO2 laser co‐vaporization of a homogeneous raw powder mixture consisting of micrometer‐sized MgAl2O4 and Eu2O3 (2 and 4 mol%, respectively). The resulting NPs are spherically shaped, show a narrow size distribution (mean diameter: ~30 nm), and are well dispersed. The as‐prepared NPs are highly crystalline and consist of MgAl2O4 with small amounts of the secondary phases MgO (~10 mass%) and Eu2O3 (&lt;0.5 mass%). The photoluminescence spectra of the doped spinel nanopowders show an intense red emission (λem = 615 nm) resulting from the 5D0→7F2 transition with a maximum intensity at an excitation wavelength of 470 nm.

Bioactive nano fluorapatite/polyetheretherketone composite for orthopedic Implants

Event Abstract Back to Event Bioactive nano fluorapatite/polyetheretherketone composite for orthopedic Implants Liang Cai1 and Jie Wei1 1 East China University of Science and, School of Materials Science and Engineering, China Introduction: Nano fluorapatite (n-FA) is a bioactive material with chemical and crystallographic similarity to that of natural apatite in bones and dentals, and has been currently used in hard tissue engineering for bone regeneration. Furthermore, the effects of FA on oral bacteria and plaque due to the release of fluorine ions, which can act as an antimicrobial agent, are well documented by a considerable amount of literature[1]. Lack of antibacterial activity and binding ability to natural bone tissue has significantly limited polyetheretherketone (PEEK) for many challenging in bone implant applications[2]. Hence, we have developed the n-FA/PEEK composite and evaluated the antibacterial activity and osseointegration. Materials and Methods: The PEEK powder and n-FA powder were mixed together to obtain a homogeneous powder mixture via solvent evaporation method. Then the compression molding method was used to fabricate n-FA/PEEK composite. The hydrophilicity of n-FA/PEEK was evaluated via water contact angle test, the mechanical strength was tested by mechanical testing machine, and the antibacterial ability of composite was evaluated by Live/Dead cell staining. The MG-63 cells were cultured on the composites with different time, and the cell attachment, proliferation and differentiation were evaluated by confocal laser scanning microscope (CLSM), CCK-8 assay and alkaline phosphatase (ALP) activity, respectively. The Micro CT, histological and immunostaining analysis were used to evaluated osteoconductivity of composite, which the composite samples were implanted into the femoral bone of rabbits with different time. Results and discussions: The results showed that the hydrophilicity and mechanical strength of the composite obviously improved as compared with PEEK. In addition, the composite could inhibit bacterial attachment, with the number of viable bacteria on the composite obviously lower than on PEEK, indicating good antibacterial ability. Moreover, the attachment and proliferation of MG-63 cells on the composite was significantly higher than on PEEK, and the ALP of the cells on the composite was expressed at significantly higher levels compared to PEEK. Furthermore, the cells showed intimate contact with the composite surface and the cells spread and grew significantly better on the composite as compared with PEEK. Therefore, incorporation of n-FA into PEEK is a good method to prepare an inorganic–organic bioactive composite of nanometer inorganic materials and polymers, which supports cell attachment, proliferation and differentiation. The implantation of the composite into the femoral bone of rabbits showed that the new bone tissue could form on the composite surfaces, and the composite combined directly with the natural bone tissue without fibrous capsule tissue, showing good osseointegration. Conclusions: In short, the n-FA/PEEK biocomposite with good biocompatibility and bioactivity might be a promising implant material for using in orthopedic clinics.

(Invited) Properties of the Electrode-Ammonium Polyphosphate-Composite Interface at Temperatures up to 250°C

Introduction: Ammonium polyphosphate (APP) based composites as proton conducting electrolyte for the development of an intermediate temperature (200-400°C) fuel cell have drawn a lot of interest and attention in the past, as APP is non-toxic, commercially available and inexpensive. The intermediate temperature operation range of a fuel cell is in particular interest for mobile and stationary applications, as the thermal management of the cell will be similar to an internal combustion engine, without facing the high material requisitions of a solid oxygen fuel cell. In addition, the elevated operation temperature offers enhanced kinetics, an efficient conversion of some liquid fuels (e.g. small alcohols) in the cell, which have a relatively high volumetric energy density. Because pure APP decomposes at intermediate temperatures, thermally stable composites with metal oxides (e.g. SiO2, TiO2) were developed during the last years (1-5). For the usability of the ceramic composites of APP as a flexible fuel cell membrane, the electrolyte was recently successfully imbedded in a polymer (6). Tests with commercial HT-PEM electrodes as MEA have shown, that this composite membrane can be used as hydrogen and alcohol fuel cell (7). Here, we want to report investigations of the electrode-solid electrolyte interface. These were performed by obtaining capacity values of the solid-solid interface from impedance spectroscopy measurements. In addition, the kinetics of interfacial charge transfer reactions were considered. Experimental: The composite electrolyte, (NH4)3Si0.5Ti0.5P4O13 (ASi0.5Ti0.5PP) was prepared according to the procedure of Wang et al. (4). The membrane was manufactured by imbedding ASi0.5Ti0.5PP in a polymer (7). For the electrodes, a homogeneous powder mixture of unsupported Pt (black) and ASi0.5Ti0.5PP was prepared and pressed on a platinized titanium expanded metal, which served as current collector and was cleaned before use in a HF/HNO3/H2O bath. To fabricate a membrane electrode assembly (MEA), these electrodes were pressed on the membrane and were put into two layers of Klingersil-C4400, which served as sealing material. The geometric surface area of the electrodes, anode and cathode, were 2 cm² each. The experimental set-up was described earlier in detail (7). Results: From impedance measurements at different temperatures the interfacial capacity was evaluated. The values are comparable to other solid-solid electrolyte contacts and were of the order of µF/cm2. It is interesting to note that the capacity showed only a small temperature dependence. Further insight was obtained from evaluating the kinetics of charge transfer reactions at the solid-solid electrolyte interface. The results will be discussed in terms of the charge distribution at the interface and what kind of potential distribution can be assumed. This will impact the understanding of charge transfer reactions taking place at the same interface.

Thermally Sprayed Y2O3-Al2O3-SiO2 Coatings for High-Temperature Protection of SiC Ceramics

The suitability of certain glass compositions in the Y2O3-Al2O3-SiO2 (YAS) system as protecting coatings for silicon carbide components has been prospected. One particular YAS composition was formulated considering its glass formation ability and subsequent crystallization during service. Round-shaped and homogeneous granules of the selected composition were prepared by spray drying the corresponding homogeneous oxide powder mixture. Glassy coatings (197 µm thick) were obtained by oxyacetylene flame spraying the YAS granules over SiC substrates, previously grit blasted and coated with a Si bond layer (56 µm thick). Bulk glass of the same composition was produced by the conventional glass casting method and used as reference material for comparative evaluation of the characteristic glass transition temperatures, crystallization behavior, mechanical, and thermal coating properties. The mechanical properties and thermal conductivity of the coating were lower than those of the bulk glass owing to its lower density, higher porosity, and characteristic lamellar structure. The crystallization of both bulk glass and coating occurred during isothermal treatments in air at 1100-1350 °C. Preliminary data on ablation tests at 900 °C using the oxyacetylene gun indicated that the YAS glassy coating was a viable protective shield for the SiC substrate during 150 s.

Particle properties of submicron-sized WC–12Co processed by planetary ball milling

In this study, a conventional nano-grained tungsten carbide (WC) powder was mixed with 12wt.% of a submicron cobalt (Co) powder in a ball mill for varying milling time periods, producing a homogeneous powder mixture which can be used to sinter near-nanocrystalline cemented carbides using short-duration sintering processes. Parameters of the wet milling process were adapted in order to maximise the mixing effect on the one hand, and to avoid particle growth during the milling process on the other. Surface analysis and microscopic examination of the milled powders showed a milling-time-dependent evolution of particle size and surface roughness. X-ray diffraction (XRD) investigation indicated a decrease of the crystallite size of WC in combination with an increase in defect density, as well as a strong increase in stacking faults in the Co. The main action of the milling mechanism is the fracturing of the WC particles. Co is distributed consistently around the WC particles. The preparation method used is a useful technique to prepare homogeneous powder mixtures of WC–Co with particle sizes below 200nm on a laboratory scale.

Characteristics of Ti(C, N)-30%WC-5%Mo2C-20%Co Sintered Body Prepared via Mechanical Milling

Ti(C, N)-30mass%WC-5mass%Mo2C-20mass%Co was synthesized by a mechanical milling of Ti(C, N) powder, WC powder, Mo2C powder and Co powder for 1.8 ks in a dry process. The mechanical milling used a planetary ball milling. Various powders were prepared by changing a rotational speed of main disk, rotational speed of grinding bowl and the size of crushing ball. The obtained powders were sintered at 1693 K in a vacuum after the press forming. The effects of the absolute acceleration and the ball size in the mechanical milling on the mechanical properties of the sintered bodies were examined by the microstructural observation, the transverse rupture strength test and the Rockwell hardness A-scale test.The homogenous powder mixture was accomplished by using the small size ball even in a dry milling. The large absolute acceleration promoted the formation of a brittle phase in the sintered body because of the adhesion improvement between hard particle and metal powder during the milling. In our experimental condition, it was suitable for the preparation of a homogeneous powder mixture to apply the absolute acceleration of 2.5-10 G using cemented carbide balls with 2 mm in diameter. Additionally, the compact prepared using the homogeneous mixture with high carbon content at 1653 K showed 1313 MPa in transverse rupture strength.