Powder Processing Technique Research Articles

High Performance Titanium Alloy Compacts by Advanced Powder Processing Techniques

In this paper, two kinds of advanced powder processing techniques such as Metal Injection Molding (MIM) and Direct Laser Forming (DLF) were introduced to fabricate complex shaped Ti alloy parts which have been widely used for various industrial and medical applications because of their excellent characteristics of low density, high corrosion resistance and high biocompatibility but need high processing cost because of poor workability. The MIM process has been tried to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe and Cr powders, and enhanced tensile strength of 1030 MPa with 15.1 % elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification but also the solution strengthening in beta phase. DLF process has been tried to improve the honeycomb porous structure from Ti-6Al-7Nb powder material, and the honeycomb structure with 300 m holes showed good mechanical compatibility and superb biocompatibility in osteoblasts culturing.

Fabrication and characterization of aluminum nitride polymer matrix composites with high thermal conductivity and low dielectric constant for electronic packaging

Abstract Polymethyl methacrylate (PMMA) composites filled with Aluminum Nitride (AlN) were prepared by powder processing technique. The microstructures of the composites were investigated by scanning electron microscopy techniques. The effect of AlN filler content (0.1–0.7 volume fraction (vf)) on the thermal conductivity, relative permittivity, and dielectric loss were investigated. As the vf of AlN filler increased, the thermal conductivity of the specimens increased. The thermal conductivity and relative permittivity of AlN/PMMA composites with 0.7 vf AlN filler were improved to 1.87 W/(m K) and 4.4 (at 1 MHz), respectively. The experimental thermal conductivity and relative permittivity were compared with that from simulation model.

Cobalt-based orthopaedic alloys: Relationship between forming route, microstructure and tribological performance

The average longevity of hip replacement devices is approximately 10–15years, which generally depends on many factors. But for younger generation patients this would mean that revisions may be required at some stage in order to maintain functional activity. Therefore, research is required to increase the longevity to around 25–30years; a target that was initially set by John Charnley. The main issues related to metal-on-metal (MoM) hip replacement devices are the high wear rates when malpositioned and the release of metallic ions into the blood stream and surrounding tissues. Work is required to reduce the wear rates and limit the amount of metallic ions being leached out of the current MoM materials, to be able to produce an ideal hip replacement material. The most commonly used MoM material is the cobalt-based alloys, more specifically ASTM F75, due to their excellent wear and corrosion resistance. They are either fabricated using the cast or wrought method, however powder processing of these alloys has been shown to improve the properties. One powder processing technique used is spark plasma sintering, which utilises electric current Joule heating to produce high heating rates to sinter powders to form an alloy. Two conventionally manufactured alloys (ASTM F75 and ASTM F1537) and a spark plasma sintered (SPS) alloy were evaluated for their microstructure, hardness, tribological performance and the release of metallic content. The SPS alloy with oxides and not carbides in its microstructure had the higher hardness, which resulted in the lowest wear and friction coefficient, with lower amounts of chromium and molybdenum detected from the wear debris compared to the ASTM F75 and ASTM F1537. In addition the wear debris size and size distribution of the SPS alloy generated were considerably small, indicating a material that exhibits excellent performance and more favourable compared to the current conventional cobalt based alloys used in orthopaedics.

Characterization and mechanical testing of alumina-based nanocomposites reinforced with niobium and/or carbon nanotubes fabricated by spark plasma sintering

Alumina-based nanocomposites reinforced with niobium and/or carbon nanotubes (CNT) were fabricated by advanced powder processing techniques and consolidated by spark plasma sintering. Raman spectroscopy revealed that single-walled carbon nanotubes (SWCNT) begin to break down at sintering temperatures >1150 °C. Nuclear magnetic resonance showed that, although thermodynamically unlikely, no Al 4C 3 formed in the CNT–alumina nanocomposites, such that the nanocomposite can be considered as purely a physical mixture with no chemical bond formed between the nanotubes and ceramic matrix. In addition, in situ single-edge notched bend tests were conducted on niobium and/or CNT-reinforced alumina nanocomposites to assess their toughness. Despite the absence of subcritical crack growth, average fracture toughness values of 6.1 and 3.3 MPa m 1/2 were measured for 10 vol.% Nb and 10 vol.% Nb–5 vol.% SWCNT–alumina, respectively. Corresponding tests for the alumina nanocomposites containing 5 vol.% SWCNT, 10 vol.% SWCNT, 5 vol.% double-walled-CNT and 10 vol.% Nb yielded average fracture toughnesses of 3.0, 2.8, 3.3 and 4.0 MPa m 1/2, respectively. It appears that the reason for not observing improvement in fracture toughness of CNT-reinforced samples is because of either damage to CNTs or possibly non-optimal interfacial bonding between CNT-alumina.

Influences of dopants on microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites

Influences of addition of CaO, CoO and V2O5 on the microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites were investigated. The powders of (Mg0.476Mn0.448Zn0.007) (Fe1.997Ti0.002)O4 composition were prepared by using a conventional ceramic powder processing technique. The experimental results showed that the average grain size of the sintered ferrites codoped with 0.03wt% CaO, 0.04wt% CoO and 0.06wt% V2O5 was about 15 μm; the saturation magnetization of ferrites was 68.78 emu/g. The addition of V2O5 in the ferrites can not only increase value of the saturation magnetization, but also decrease the average grain size of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites. Simultaneous incorporation of CoO, CaO and V2O5 dopants into (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites can not only improve the saturation magnetization of the materials, but also inhibit abnormal grain growth.

The Development and Characterization of Zirconia-Silica Sand Nanoparticles Composites

The present study aims to develop zirconia-Silica sand nanoparticles composites through powder processing route and to study the physical properties, mechanical properties and microstructure of the composites. Zirconia based silica sand nanoparticles composite with 5, 10, 15 and 20 wt.% were developed through powder processing technique and sintered at 1500 ℃ for two hours. A decreasing trend of green density however an improvement in sintered density was observed. Also the addition of silica sand nanoparticles with 20 wt.% increased the hardness up to 12.45 GPa and microstructures indicated the diffusion mechanism of silica sand nanoparticles into pore sites of the composites.

Synthesis of nanocomposites by mechanical alloying

Nanocomposites were synthesized by the solid-state powder processing technique of mechanical alloying in Al–Al 2O 3, TiAl–Ti 5Si 3, and MoSi 2–Si 3N 4 systems. The mechanically alloyed powders were consolidated to full density by techniques such as vacuum hot pressing, hot isostatic pressing, and combinations of them. The as-milled powders as well as the consolidated compacts were characterized for their crystal structure features using X-ray diffraction and for the microstructural features using scanning and transmission electron microscopy techniques. Mechanical properties such as hardness, ductility, and fracture toughness were also measured. It has been shown that it is possible to produce a high volume fraction of the reinforcement of nanometer dimensions and that the properties of the nanocomposites are significantly better than those of the monolithic materials. Superplastic deformation has been demonstrated in TiAl–Ti 5Si 3 composite even when 60 vol.% of the ceramic reinforcement was present.

Processing characteristics and parameters in capacitor discharge sintering

A powder processing technique is here presented. The process consists in a single short impulse (5–40 ms) of electric current (with current densities greater than 10 8 A/m 2) combined with mechanical pressure and allows for nearly complete to complete densification of powders (>90% of theoretical density) with energy inputs from 1 to 4.5 kJ/g. The fundamental process parameter known as SEI is analyzed and is correlated with other known electro-discharge sintering techniques which present analogous values. An experimental equation correlating SEI and densities is proposed. Theoretical physical considerations on the amplification of mechanical and electrical energies during the process are made to explain the sintering process and the experimental evidence.

Thermal properties of low loss PTFE‐CeO2 dielectric ceramic composites for microwave substrate applications

AbstractPolytetrafluroethylene (PTFE) composites filled with CeO2 were prepared by powder processing technique. The PTFE is used as the matrix and the loading fraction of CeO2 in the composite varied up to 0.6 volume fraction. The thermal conductivity and coefficient of thermal expansion were studied in relation to filler concentration. The thermal conductivity increased and coefficient of thermal expansion decreased with increase in CeO2 content. For 0.6 volume fraction loading of the ceramic, the composite has a thermal conductivity of 3.1 W/m°C and coefficient of thermal expansion 19.6 ppm/°C. Different theoretical approaches have been employed to predict the effective thermal conductivity and coefficient of thermal expansion of composite systems and the results were compared with the experimental data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of coupling agent on the thermal and dielectric properties of PTFE/Sm 2Si 2O 7 composites

The present study investigates the dielectric and thermal properties of PTFE/Sm 2Si 2O 7 composites. The composites were prepared by powder processing technique followed by hot pressing. The variation of the dielectric properties with filler content (0–0.5 V f ) was studied at 1 MHz and 9 GHz. The filler surface was chemically modified using phenyl trimethoxy silane (PTMS) as a coupling agent. The microstructural study using scanning electron microscopy (SEM) showed that the particles were well dispersed in the matrix when coupled with PTMS. The surface modification led to an improvement in the dielectric properties. The PTFE filled with 0.4 V f silane treated Sm 2Si 2O 7 composite showed a low dielectric loss of 0.0054 and slightly higher relative permittivity of 3.92 when compared with the untreated composite of the same composition. The experimental values of relative permittivities were compared with the theoretical predictions and the Effective Medium Theory was found to agree well even for higher content of silane treated filler. It was found that the addition of silane coupling agent is very effective in improving the thermal properties of the PTFE/Sm 2Si 2O 7 composites.

On the synthesis and performance of flame-made nanoscale La 0.6Sr 0.4CoO 3− δ and its influence on the application as an intermediate temperature solid oxide fuel cell cathode

Flame spray synthesis (FSS), a large-scale powder processing technique is used to prepare nanoscale La 0.6Sr 0.4CoO 3− δ powder for solid oxide fuel cell cathodes from water-based nitrate solutions. Influence of processing is investigated on basis of the as-synthesised powders by X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), nitrogen adsorption (BET) and electron microscopy (SEM and TEM). Against the background of a nanostructured cathode morphology for an intermediate temperature solid oxide fuel cell (IT-SOFC) at 600 °C, an optimised and high surface area flame-made La 0.6Sr 0.4CoO 3− δ nanopowder of 29 m 2 g −1 is used to investigate its performance and chemical reaction with common electrolytes (Y 0.16Zr 0.84O 2− δ , Ce 0.9Gd 0.1O 2− δ and Sc 0.20Ce 0.01Zr 0.79O 2− δ ). Secondary phase analysis from XRD measurements revealed a substantially lower La 2Zr 2O 7 and SrZrO 3 formation in comparison to conventional spray pyrolysed and submicron powder of about 9 m 2 g −1. TGA and resistivity measurements proofed that La 0.6Sr 0.4CoO 3− δ is non-sensitive towards carbonate formation under CO 2 containing atmospheres. Electronic bulk conductivity of 2680 S cm −1 (600 °C) and 3340 S cm −1 (500 °C) were measured in air and as function of oxygen partial pressure (2 × 10 5 Pa > p(O 2) > 1.2 × 10 −2 Pa) in the temperature range between 400 and 900 °C. Electrochemical performance is determined by impedance spectroscopy on symmetrical cells of screen printed nanoscale La 0.6Sr 0.4CoO 3− δ on Ce 0.9Gd 0.1O 2− δ substrates from which an area specific resistance (ASR) of 0.96 Ω cm 2 at 600 °C and 0.14 Ω cm 2 at 700 °C were obtained.

Development of high DC-bias Mn–Zn ferrite working at frequency higher than 3 MHz

Modern high-frequency electronic technology demands Mn–Zn soft ferrite for high DC-bias and low power loss applications. In this study, DMR50B ferrite material with a very attractive DC-bias property and with a lower power loss at high frequency up to 3 MHz was developed employing a conventional ceramic powder processing technique based on our previous study of DMR50 material, indicating its magnetic properties can be further improved by microstructure homogeneity. The core loss is around 200 kW/m 3 at 3 MHz, 10 mT and 100 °C, and only around 20 kW/m 3 at 700 kHz, 30 mT and 100 °C; its cutoff frequency f r is ∼4 MHz and its incremental permeability μ Δ remains constant until H DC = 100 A/m. Furthermore, the electromagnetic characteristics and the microstructure of this new DMR50B material are also discussed.

Antibacterial Property of Cold Sprayed Chitosan-Cu/Al Coating

The antibacterial behavior of CS-Cu (chitosan-copper complex) powder and their composite coatings were investigated against Escherichia coli (DH5α). CS-Cu powder and Al (aluminum) based CS-Cu composite powders were synthesized using in-house powder processing techniques. The results indicated that the antibacterial effect of all the powders increased with the proportion of CS-Cu powder. These composite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of CS-Cu to Al in their composite powders were 25:75, 50:50, and 75:25 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and FTIR. Antibacterial composite CS-Cu/Al coatings were successfully deposited using cold spraying parameters of 6-8 bars at preheated helium gas, temperature between 140 and 150 °C. The coatings retained the antibacterial properties of the original feedstock powders.

Preparation of Five China Sea and Continental Shelf Sediment Reference Materials (MSCS‐1–5) with Ultra‐Fine Particle Size Distributions

We report the preparation and characterisation of five sediment reference materials MSCS‐1–5 from the China Sea and continental shelf. The raw samples were individually collected from the East China Sea and the South China Sea. They were first ground by ball mill to a homogenous powder of ‐200 mesh (< 74 μm). Then, half of each sample was further processed by an ultra‐fine powder processing technique, a jet mill, to form a powder with an average particle size of < 4 μm (about 800 mesh). The homogeneity was tested by high‐precision WD‐XRF and the precision was found to be less than 1% RSD, which is compatible with the precision range for modern analytical techniques. An F‐test showed that all five samples were homogeneous. Twelve laboratories participated in the cooperative study and sixty constituents were determined. Between fifty and fifty‐two analytes were characterised as recommended values in MSCS‐1–5 in compliance with Chinese national norms. The sum of the major and minor elements or components in the five reference materials MSCS‐1–5 was 99.91%, 99.86%, 100.43%, 100.12% and 99.66%, respectively.

New Generation of Synthetic, Bioresorbable and Injectable Calcium Phosphate Bone Substitute Materials: Alpha-bsm<sup>®</sup>, Beta-bsm<sup>TM</sup> and Gamma-bsm<sup>TM</sup>

Alpha-bsm® is a first generation self-setting, injectable and moldable apatitic calcium phosphate cement (CPC) based on amorphous calcium phosphate (ACP). ACP was prepared using low temperature double decomposition technique, from a calcium solution (0.16 M), and phosphate solution (0.26 M) in a basic (pH~13) media. ACP was than stabilized using three crystal growth inhibitors (CO32-, Mg2+, P2O74-), freeze-dried, and heated (450 °C, 1h) to remove additional moisture and some inhibitors. Dicalcium phosphate dehydrate (DCPD) was also prepared using wet chemistry at room temperature from calcium and phosphate solution, respectively, 0.3 M and 0.15 M. ACP and DCPD powder were combined at a 1:1 ratio and ground to produce Alpha-bsm® bone cement. The cement is supplied as a powder and when mixed with an appropriate amount (0.8 ml/g) of physiological saline at room temperature, forms an injectable putty-like paste. The paste has a working time of about 45 minutes at room temperature, when stored in a moist environment. The setting reaction proceeds isothermically at body temperature (37°C) in less than 20 minutes, forming a hardened, porous (total porosity 50 to 60%), low crystalline (40% comparing with HA), apatitic calcium phosphate cement with a compressive strength range of 10 to 12 MPa. Extensive pre-clinical studies (rabbit radius critical sized defect, canine tibia osteotomy, sheep tibia, primate fibula fracture healing, and primate fibula critical size defect) demonstrate that Alpha-bsm® undergoes remodeling in conjunction with new bone formation. The next generation of Bone Substitute Materials (Beta-bsmTM and Gamma-bsm TM) are formulated based on the Alpha-bsm® chemistry but differ in powder processing (e.g. milling) technique. These materials are also self-setting, injectable and/or moldable apatitic calcium phosphate cements with improved handling and mechanical properties. The setting & hardening reaction of these new CPCs proceeds isothermically in less than 5 minutes at 37°C and once hardened demonstrate a compressive strength of 30 to 50 MPa. The final product (after full conversion) is a low crystalline (40% compared with Hydroxyapatite), calcium deficient (Ca/P atomic ratio = 1.45) carbonated apatite similar to the composition and structure of natural bone mineral (crystal size: length = 26 nm, width thickness = 8 nm). A desirable feature of these cements is their high surface chemistry (with specific surface area of about 180-200 m2/g) which is ideal for remodeling and controlled release of growth factors. A pilot rabbit critically sized femoral defect study comparing the three synthetic family products demonstrate that they share similar remodeling and resorption characteristics up to 52 weeks. Physico-chemical and mechanical performance of these next generation CPCs are favorable when compared with existing CPCs in the market, specifically material working time (at room temperature), cohesivity in a wet environment and fast setting & hardening rate (at body temperature).

Nanostructured Materials Prepared by Mechanical Alloying and Mechanochemical Process

Mechanical alloying and mechanochemical treatment are the major powder processing techniques on the nano scale. In these processes a high energy ball mill has been applied to synthesize compounds and nanocomposites such as aluminum metal matrix nanocomposite, hydroxyapatite and bionanocomposites based on hydroxyapatite. These processes involve deformation, cold welding, fracturing, and rewelding of powder particles. Due to the applied mechanical forces, chemical reactions and phase transformations could also take place. In the present research work, the effects of milling time, milling media, and sonication process on the microstructures and morphology of the obtained materials were evaluated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The results indicate that increasing the milling time leads to an increased lattice strain and decreased crystallite sizes. Furthermore, the results show that the sonication process leads to the morphological improvement of nanocrystalline hydroxyapatite. The obtained data show that the nanocrystalline hydroxyapatite with low contamination and suitable morphology can be produced in Polyamide6 vials similar to stainless steel vials, therefore it seems that using polymeric and polymeric based nanocomposite vials with high strength and wear resistance could lead to a new way for the mass production of nanocrystalline hydroxyapatite with high performance, low contamination and low cost.

Microstructure, electrical properties and Hall coefficient of europium-doped Li–Ni ferrites

Europium-doped Li–Ni soft ferrites with the general formula of (Li 0.5Fe 0.5) 0.5 Ni 0.5Eu y Fe 2− y O 4 (where 0 ≤ y ≤ 0.1), were prepared by using powder processing technique. The effect of Eu addition on the AC and DC electrical resistivity, Hall coefficient, charge mobility and charge carrier concentration of the prepared ferrites were characterized at room temperature. Seebeck coefficient was also calculated from the carrier concentration. Hall and Seebeck coefficients confirmed that all of the prepared samples are p-type semiconductors. The formation of the single-phase spinel ferrites structure was verified by X-ray diffraction. Lattice parameter, X-ray density, apparent density and A- and B-sites radii were calculated. The microstructure, which plays an important role in determining electrical properties, was analyzed by scanning electron microscopy and EDS, and found to have a major effect on the electrical properties. The dielectric loss was calculated from the AC conductivity and found to increase with firing temperature. This study provides information to optimize the composition and microstructure of the europium-doped Li–Ni ferrite with desired performance.

Antibacterial Property of Cold-Sprayed HA-Ag/PEEK Coating

The antibacterial behavior of HA-Ag (silver-doped hydroxyapatite) nanopowder and their composite coatings were investigated against Escherichia coli (DH5α). HA-Ag nanopowder and PEEK (poly-ether-ether-ketone)-based HA-Ag composite powders were synthesized using in-house powder processing techniques. Bacteria culture assay of HA-Ag nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of HA-Ag nanoparticle in these composite powders. These nanocomposite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of HA-Ag to PEEK in their composite powders were 80:20, 60:40, 40:60, and 20:80 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite HA-Ag/PEEK coatings were successfully deposited using cold spraying parameters of 11-12 bars at preheated air temperature between 150 and 160 °C. These as-sprayed coatings of HA-Ag/PEEK composite powders comprising varying HA-Ag and PEEK ratios retained their inherent antibacterial property as verified from bacterial assay. The results indicated that the antibacterial activity increased with increasing HA-Ag nanopowder concentration in the composite powder feedstock and cold-sprayed coating.

A study on preparation of Mo–0.6Ti–0.2Zr–0.02C alloy by mechanical alloying and hot isostatic pressing, and its characterization

Mo–0.6Ti–0.2Zr–0.1C alloy was prepared by mechanical alloying (MA) and subsequently consolidated by powder processing techniques. The pellets prepared from the fine size MA powder showed a high rate of densification during sintering in the temperature range of 1300–1500 °C. Close to theoretical density was attained by hot isostatic pressing (HIP) at 1250 °C and TEM studies revealed the uniform distribution of complex carbide precipitates (<100 nm) in the fine grain microstructure of the consolidated alloy. The alloy consolidated by HIP showed a high hardness of the order of 500 HK due to the presence of the carbides in the fine grain microstructure.

Compaction and sintering response of mechanically alloyed Cu–Cr powder

The present paper discusses the powder processing techniques of mechanically alloyed Cu–Cr powder. Mechanical alloying is required to obtain a nano-scale homogeneous mixture of Cu and Cr. Two processes to prepare Cu–Cr contacts are proposed from the present study for obtaining compacts having better properties. While the explosive compaction of the mechanically alloyed powder forcibly fills the pores to show excellent density and electrical conductivity, application of Cu coating to the mechanical alloyed powder gives a short-circuit diffusion path during sintering and thus, shows the best combination of properties compared to the presently used Cu–Cr compacts. Both the processes show near theoretical density, exceptionally high electrical conductivity and comparable hardness. Moreover, both the processes change the sintering process of Cu–Cr compacts from liquid phase sintering to solid-state sintering, thus making the process more energy efficient.