Marc Leparoux

Dual-nanoparticulate-reinforced aluminum matrix composite materials

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.

The influence of process parameters on precursor evaporation for alumina nanopowder synthesis in an inductively coupled rf thermal plasma

The process parameters of an inductively coupled thermal plasma used for nanopowder synthesis are experimentally investigated using various plasma diagnostics and in situ powder monitoring methods. An enthalpy probe technique is applied to characterize the plasma properties under particle-free conditions. The nanoparticle synthesis from microscale alumina precursors is monitored in situ by optical emission spectroscopy and laser light extinction measurements to investigate the powder evaporation. The synthesized powders are collected in a sampling unit and characterized ex situ by particle size analysis as well as by electron microscopy. At low flow rates of the torch central gas, higher plasma enthalpy, a laminar powder flow and increased evaporation of the precursor have been observed. A precursor- and an energy-deficient regime related to the precursor feed rate and plasma enthalpy are found from the emission line intensities of aluminium metal vapour. The number fraction of plasma-treated precursors, which is an important process parameter, is calculated from the precursor number density obtained from laser extinction measurements.

The role of nano-particles in the field of thermal spray coating technology

Nano-particles play not only a key role in recent research fields, but also in the public discussions about health and safety in nanotechnology. Nevertheless, the worldwide activities in nano-particles research increased dramatically during the last 5 to 10 years. There are different potential routes for the future production of nano-particles at large scale. The main directions envisaged are mechanical milling, wet chemical reactions or gas phase processes. Each of the processes has its specific advantages and limitations. Mechanical milling and wet chemical reactions are typically time intensive and batch processes, whereas gas phase productions by flames or plasma can be carried out continuously. Materials of interest are mainly oxide ceramics, carbides, nitrides, and pure metals. Nano-ceramics are interesting candidates for coating technologies due to expected higher coating toughness, better thermal shock and wear resistance. Especially embedded nano-carbides and-nitrides offer homogenously distributed hard phases, which enhance coatings hardness. Thermal spraying, a nearly 100 years old and world wide established coating technology, gets new possibilities thanks to optimized, nano-sized and/or nano-structured powders. Latest coating system developments like high velocity flame spraying (HVOF), cold gas deposition or liquid suspension spraying in combination with new powder qualities may open new applications and markets. This article gives an overview on the latest activities in nano-particle research and production in special relation to thermal spray coating technology.

Methane dissociation process in inductively coupled Ar/H2/CH4 plasma for graphene nano-flakes production

The role of hydrogen and methane dissociation process in induction plasma synthesis of graphene nano-flakes (GNF) is studied by the optical emission spectroscopy of Ar/H2/CH4 plasma. The condensation of C2 species formed due to methane decomposition produces GNF, which depends on pressure. Electron impact and dehydrogenation processes dissociate methane, which promotes and hinders the GNF production, respectively. The effect of hydrogen is insignificant on quality, size and morphology of the GNF. The CH4 flow rate has no influence on particle temperature but has effect on cooling rate at the point of nucleation and, therefore, on production rate and thickness of GNF.

Optical emission spectroscopic study of Ar/H2/CH4 plasma during the production of graphene nano-flakes by induction plasma synthesis

Graphene nano-flakes using CH4 precursor were synthesized in a radio frequency inductively coupled plasma reactor with in-situ investigation of Ar/H2/CH4 plasma by optical emission spectroscopy at fixed H2 and Ar flow rates of 4 and 75 slpm, respectively, and at different plate powers (12 to 18 kW), pressures (400 to 700 mbar) and CH4 flow rates (0.3 to 2 slpm). Emissions from C2 Swan band, C3, CH and H2 are observed in the optical emission spectra of Ar/H2/CH4 plasma. Plasma temperature estimated analyzing the C2 Swan band emission intensities is found to be decreased with increasing pressure and decreasing plate power. The decreasing plasma temperature gives rise to increase in production rate due to increase in condensation process. The production rate is observed to be increased from 0 to 0.3 g/h at 18 kW and from 0 to 1 g/h at 15 kW with increase in pressure from 400 to 700 mbar at fixed CH4 flow rate of 0.7 slpm. Broad band continuum emission appears in the emission spectra at specific growth conditions in which the formation of vapor phase nanoparticles due to condensation of supersaturated vapor is facilitated. The production rate at 12 kW, 700 mbar, and 0.7 slpm of CH4 flow rate is found to be 1.7 g/h which is more than that at 15 and 18 kW. Thus, the broadband continuum emission dominates the optical emission spectra at 12 kW due to lower temperature and higher production rate, and is attributed to the emission from suspended nanoparticles formed in vapor phase. The synthesized nanoparticles exhibit flake like structures having average length and width about 200 and 100 nm, respectively, irrespective of the growth conditions. Nano-flakes have thickness between 3.7 to 7.5 nm and are composed of 11 to 22 graphene layers depending on the growth conditions. The intensity ratio (ID/IG) of D and G band observed in the Raman spectra is less than 0.33 which indicates good quality of the synthesized graphene nano-flakes.

Functionally Graded Dual-Nanoparticulate-Reinforced Aluminum Matrix Composite Materials

Functionally graded carbon nanotubes (CNT) and nano Silicon carbide (nSiC) reinforced aluminum (Al) matrix composite materials were fully densified by a simple ball milling and hot-pressing processes. The nSiC was used as a physical mixing agent to increase dispersity of the CNT in the Al particles. It was observed that the CNT was better dispersed in the Al particles with a nSiC mixing agent compared to without it used. SEM micrograph showed that the interface of the each layers had very tightly adhesion without any serious pores and micro-cracks. This functionally graded dual-nanoparticulate-reinforced Al matrix composite by powder metallurgical approach could also be applied to comples matrix materials.

Mechanical behaviour of dual nanoparticle-reinforced aluminium alloy matrix composite materials depending on milling time:

Aluminium 6061 alloy matrix composite materials reinforced with carbon nanotubes (CNTs) and silicon carbide nanoparticles (nSiCs) were prepared by high-energy ball milling and hot pressing. In addition to inducing fine particle strengthening, nSiCs were also used as a solid mixing agent to improve the dispersion of the CNTs in the Al matrix powder. The dependence of the densification and mechanical strength of the composites reinforced with the dual nanoparticles on the milling time is discussed. The crystallite sizes of Al in the composites were also investigated. Moreover, the relative defect ratios of the CNTs in the composites were calculated from the intensities of the D and G peaks of the Raman spectra. With this new approach to composite fabrication, a hardness and tensile strength of 334 HV and 293 MPa, respectively, were achieved. The high-energy ball milling time significantly affected the microstructure and mechanical properties of the composites; however, the dual nanoparticle reinforcement can potentially be used in a variety of industrial component materials with precisely controlled material properties.

Additive Manufacturing of Semiconductor Silicon on Silicon Using Direct Laser Melting

Currently, Additive Manufacturing (AM) is limited to three classes of materials: ceramics, polymers and metals. Even within these classes, only a small number of materials can be processed by AM, either in a powder bed approach or in a direct energy deposition approach.

Microstructure Evolution and Mechanical Properties Investigation of Friction Stir Welded AlMg5-Al2O3 Nanocomposites

The present study has investigated the influence of friction stir welding (FSW) on the microstructure and mechanical properties of powder metallurgy processed unmilled AlMg5, AlMg5 milled with 0.3 wt. % stearic acid (SA) and milled AlMg5–0.5 vol% Al2O3 nanocomposites. FSW of unmilled AlMg5 resulted in grain refinement due to dynamic recrystallization induced by the thermo-mechanical processing, thereby increasing the stir zone yield strength (YS) and ultimate tensile strength (UTS) to 160 MPa and 326 MPa when compared to 135 MPa and 300 MPa of base metal, respectively. The friction stir AlMg5–0.5 vol% Al2O3 nanocomposite exhibited superior mechanical properties compared to almost all commercial 5xxx series of Al alloy friction stir welds. However, the friction stir welded AlMg5 milled with 0.3 wt. % SA and AlMg5–0.5 vol% Al2O3 samples showed a slight reduction in UTS values (373 MPa and 401 MPa) compared to 401 MPa and 483 MPa of respective base metal values.

Nanoparticulate Reinforced Aluminum Alloy Composites Produced by Powder Metallurgy Route

High energy planetary ball-milling was used to effectively disperse 3, 6 and 9 wt. % multiwall carbon nanotubes (MW-CNTs) into commercially available aluminum alloys (Al6061, AlMg5, S250 and S790). Composite bulks were manufactured by uniaxial hot pressing. For the Al6061- CNT composites, standard heat treatments (T4, T5 and T6) were performed and their influence on the structural evolution (grain coarsening, CNT reaction) and hardness was recorded. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Raman spectroscopy were used to characterize the produced composites. The study shows that CNTs can be effectively mixed with high-strength aluminum alloys. Up to 5 fold increase in hardness was achieved compared to unreinforced alloys ranging up to 390 HV20 for the S250 alloy with 6 wt. % of MW- CNTs. The applied standard heat treatments did not lead to any improvements of the mechanical properties. The developed nanocomposite materials could find applications where high hardness of aluminum is needed, or in functionally graded composites.