Processing and characterization of aluminium-based MMCs produced by gas pressure infiltration

International audienceA device has been designed and built for unidirectional infiltration of ceramic preforms with a molten metal. It allows production of Al or Mg alloys reinforced with short or continuous ceramic fibres. The apparatus has been tested for different alloys and preforms by varying the process parameters (infiltration pressure, fibre content, melt superheat, preform preheat and solidification speed). As an example, full infiltration of Al 2 O 3-SAFFIL chopped preforms with an Al-4wt.%Cu-1wt.%Mg-0.5wt.%Ag alloy has been achieved under controlled conditions by using a gas pressure between 1 and 3 MPa. The resulting metal matrix composite has been characterised by microscopical observations and mechanical tests. Measurements of Young's modulus, density, microhardness and mechanical loss show that the optimal process conditions for Al-4wt.%Cu-1wt.%Mg-0.5wt.%Ag-SAFFIL composites are a temperature of 750°C for both preform and melt and the maximum infiltration pressure of 3 MPa. Preliminary tests have shown that the gas pressure infiltration apparatus is also suitable to produce continuous fibre reinforced and hybrid metal matrix composites

An anticorrosive magnesium/carbon nanotube composite

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 92(6):63105 (2008) and may be found at https://doi.org/10.1063/1.2842411 .ArticleAPPLIED PHYSICS LETTERS. 92(6):63105 (2008)journal articl

Thermal Properties of Carbon Nanotube–Copper Composites for Thermal Management Applications

Carbon nanotube–copper (CNT/Cu) composites have been successfully synthesized by means of a novel particles-compositing process followed by spark plasma sintering (SPS) technique. The thermal conductivity of the composites was measured by a laser flash technique and theoretical analyzed using an effective medium approach. The experimental results showed that the thermal conductivity unusually decreased after the incorporation of CNTs. Theoretical analyses revealed that the interfacial thermal resistance between the CNTs and the Cu matrix plays a crucial role in determining the thermal conductivity of bulk composites, and only small interfacial thermal resistance can induce a significant degradation in thermal conductivity for CNT/Cu composites. The influence of sintering condition on the thermal conductivity depended on the combined effects of multiple factors, i.e. porosity, CNTs distribution and CNT kinks or twists. The composites sintered at 600°C for 5 min under 50 MPa showed the maximum thermal conductivity. CNT/Cu composites are considered to be a promising material for thermal management applications

Strain-amplitude-dependent mechanical loss at intermediate temperatures in a Ni-3(Al, Ta) single crystal

Dislocation dynamics in a Ni-3(Al, Ta) single-crystal alloy have been studied by means of mechanical spectroscopy at intermediate temperatures, that is in the temperature range of the flow stress anomaly. The mechanical loss of specimens predeformed at 300 K was found to be strongly dependent on temperature, pre-deformation level and heating rate. Thermal cycling (heating-cooling) and ageing experiments were also performed, which provided additional information about the annealing time dependence of the mechanical loss, elastic modulus of the material and plastic deformation of the specimens. The obtained results can be explained by a combination of two phenomena simultaneously occurring as the temperature is increased from 300 to about 500 K exhaustion of the mobile dislocation parts (superkinks) and pinning of the screw dislocation segments via cross-slip from the (111) onto the (010) planes

Investigation of hydrogen storage in carbon nanotube-magnesium matrix composites

Magnesium (Mg) and magnesium nickel (Mg-23.5 wt%Ni) reinforced with multiwalled carbon nanotubes (CNTs) were processed by powder metallurgy and then charged with hydrogen by annealing at 620 K under a pressure of 0.4 MPa of hydrogen. Mechanical spectroscopy revealed that such a treatment has no effect in the composites with pure Mg matrix. On the other hand, Mg-23.5 wt%Ni alloys, unreinforced as well as reinforced with CNTs, exhibit a mechanical loss spectrum, which is deeply modified by hydrogen charging. Two relaxation peaks are observed at similar to 190 K and similar to 330 K (frequency similar to 6 kHz), the height of which increases strongly with hydrogen charging. These peaks may be interpreted by atomic relaxation due to hydrogen in the Mg2Ni phase. Both peaks decrease strongly in height by degassing under vacuum at 750 K. In bulk specimens of Mg-23.5 wt%Ni/CNTs composites a concentration of hydrogen as high as 6.1 wt% (similar to 6% of specific weight of liquid hydrogen) has been obtained by the mentioned hydrogenation process. (C) 2009 Elsevier B.V. All rights reserved

Hydrogen storage properties of as-synthesized and severely deformed magnesium - multiwall carbon nanotubes composite

We prepared a Mg-2 mass % multiwall carbon nanotubes composite employing a powder metallurgy technique. The kinetics of hydrogen absorption/desorption of the as-synthesized composite was much faster than that of reference samples of pure Mg. The pressure-composition isotherm (measured at 300 degrees C) of the as-synthesized composite exhibited no measurable pressure hysteresis, with the equilibrium hydrogen pressures in the plateau region being higher than those of pure Mg by a factor of up to 1.8. Equal channel angular pressing of the as-synthesized composite led to a slow down of the absorption/desorption processes at the initial stages of the processes, and to their acceleration at the later stages. We suggested that the mechanism responsible for the good kinetic performance of the as-synthesized composite was fast diffusion of hydrogen through the cores of carbon nanotubes. We put forward a hypothesis relating the increase in equilibrium hydrogen pressure in the as-synthesized composite to the elastic constraints imposed by carbon nanotubes on the Mg matrix. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved

Epstein Barr virus Latent Membrane Protein-1 enhances dendritic cell therapy lymph node migration, activation, and IL-12 secretion

Dendritic cells (DC) are a promising cell type for cancer vaccines due to their high immunostimulatory capacity. However, improper maturation of DC prior to treatment may account for the limited efficacy of DC vaccine clinical trials. Latent Membrane Protein-1 (LMP1) of Epstein-Barr virus was examined for its ability to mature and activate DC as a gene-based molecular adjuvant for DC vaccines. DC were transduced with an adenovirus 5 vector (Ad5) expressing LMP1 under the control of a Tet-inducible promoter. Ad5-LMP1 was found to mature and activate both human and mouse DC. LMP1 enhanced in vitro migration of DC toward CCL19, as well as in vivo migration of DC to the inguinal lymph nodes of mice following intradermal injection. LMP1-transduced DC increased T cell proliferation in a Pmel-1 adoptive transfer model and enhanced survival in B16-F10 melanoma models. LMP1-DC also enhanced protection in a vaccinia-Gag viral challenge assay. LMP1 induced high levels of IL-12p70 secretion in mouse DC when compared to standard maturation protocols. Importantly, LMP1-transduced human DC retained the capacity to secrete IL-12p70 and TNF in response to DC restimulation. In contrast, DC matured with Monocyte Conditioned Media-Mimic cocktail (Mimic) were impaired in IL-12p70 secretion following restimulation. Overall, LMP1 matured and activated DC, induced migration to the lymph node, and generated high levels of IL-12p70 in a murine model. We propose LMP1 as a promising molecular adjuvant for DC vaccines