Développement d’une ailette d’obus en composite magnésium renforcé de fibres de carbone

Report (2012)

This report describes the accomplished breakthrough for the manufacturing of long carbon fibres reinforced magnesium alloy (AZ91). Infiltration can be performed with non-equilibrium conditions such as ... [more ▼]

This report describes the accomplished breakthrough for the manufacturing of long carbon fibres reinforced magnesium alloy (AZ91). Infiltration can be performed with non-equilibrium conditions such as fibres preheating, high liquid compacting pressure and low contact times. Thanks to specific TEOS sol/gel treatment, the reached fibre rate is 60 vol.% and the measured Young's modulus of the composite is ca. 110 GPa. The presence of defects including fibre yarns misorientation, unreinforced areas seems very detrimental to the bending properties. Other advanced infiltration techniques with Al pretreatment (K2ZrF6) of fibres is also considered. [less ▲]

Friction Stir Processing of Magnesium Matrix Composites reinforced with Carbon Fibres: Influence of the Matrix Characteristics and of the Processing Parameters on Microstructural Developments

in W.J.Poole, K.U.Kainer (Ed.) Proceedings of the 9th International Conference On Magnesium Alloys and their Apllications (2012, July 12)

Processing of magnesium matrix composites reinforced with C fibres by ‘liquid state’ methods such as squeeze casting are usually impaired by the poor wettability of C substrates by liquid Mg. As a ... [more ▼]

Processing of magnesium matrix composites reinforced with C fibres by ‘liquid state’ methods such as squeeze casting are usually impaired by the poor wettability of C substrates by liquid Mg. As a consequence, ‘solid state’ processes such as Friction Stir Processing (FSP) appear as very promising alternative processing routes for the production of C-Mg composites. And, more particularly, FSP of a C fabric between two sheets of the fairly ductile Mg alloy AZ31B was shown to be a simple and innovative process for a large-scale production of magnesium matrix composites reinforced with short C fibres. In the present work, FSP of a C fabric between two metal sheets or thin plates has been performed using two different Mg alloys exhibiting quite different mechanical behaviours, i.e. alloy AZ31B and the more brittle alloy AZ91D. And the effect of the matrix characteristics, along with the influence of the FSP experimental parameters such as the rotational and advancing speeds, on the microstructural changes occuring upon processing have been carefully studied. A particular attention has been given to the fragmentation and distribution of the C fibres, as well as to the recrystallisation, solutionising and precipitation processes taking place in the Mg matrix. [less ▲]

Influence of the addition of functionalized MWCNT on mechanical properties on epoxy/carbon fiber and epoxy/carbon-aramid fiber composites

in Proceedings of the 1st Brazilian Conference on Composite Materials (2012, July)

We investigated the effect of the inclusion of carbon nanotubes (CNT) on the mechanical properties and wear behavior of epoxy/carbon and epoxy/carbon-aramid composites in this study. Epoxy/carbon and ... [more ▼]

We investigated the effect of the inclusion of carbon nanotubes (CNT) on the mechanical properties and wear behavior of epoxy/carbon and epoxy/carbon-aramid composites in this study. Epoxy/carbon and epoxy/carbon-aramid composites with 0 wt.% CNT and 0.3 wt.% CNT were manufactured by RTM, amino functionalized multi-walled CNT (MWCNT) were used to modify the matrix. Tensile, compression, two rail shear, Charpy impact tests and Pin On Disc (POD) were performed on the four composites. The EP/CAF composites showed better impact resistance than the ones containing carbon woven. The addition of CNTs improves the shear modulus in 5% for EP/CF composites and 6% for EP/CAF. The results also show that the dynamic friction coefficient is independent of the CNT content, and the specific wear rate shows no improvement with the selected test parameters. [less ▲]

Microstructure and mechanical properties of stir processed magnesium matrix composites reinforced with carbon fibres

Conference (2012, January 26)

Mg-Al-Zn alloys have been reinforced with carbon fibres using friction stir processing (FSP) which appears as a promising alternative for the large-scale production of C-Mg composites. The process has ... [more ▼]

Mg-Al-Zn alloys have been reinforced with carbon fibres using friction stir processing (FSP) which appears as a promising alternative for the large-scale production of C-Mg composites. The process has shown its ability to produce sound composites with enhanced strength compared to the non-reinforced alloys. The C fabric is fragmented in short fibres leading to a reduction in grain size and an improved hardness. [less ▲]

Interfacial phenomena in carbon fibre reinforced magnesium alloys processed by squeeze casting and thixomolding

Conference (2011, September)

Composite materials are known to combine interesting properties of different materials. This research concerns magnesium alloys reinforced by carbon fibre weaves. Such a material can theoretically exhibit ... [more ▼]

Composite materials are known to combine interesting properties of different materials. This research concerns magnesium alloys reinforced by carbon fibre weaves. Such a material can theoretically exhibit a high yield strength/density ratio. This composite is thought to be especially promising for aeronautics. A pre-treatment of carbon weaves ensure two fundamental functions. The first is to provide stiffness and cohesion. It helps keeping fibres aligned and well placed in the mould during casting to ensure optimal properties of the final part in the main load directions. This is imperative when the composite is formed with thixomolding for which semi liquid metal is injected with a very high speed. Nevertheless the problem of geometrical carbon weaves stability is also encountered with squeeze casting. The second objective of the pre-treatment is to provide a porous network in the weaves to enhance infiltration by the capillary action. The two functions can be assumed by coating fibres with Al(H2PO4)3, SiO2 combined with starch, or some other oxide containing mixtures. The general process is to assemble carbon weaves, infiltrate them in an aqueous solution or dispersion of oxides and lastly heat them at high temperature to promote covalent bonds with fibres and vaporize or crack carbonaceous agents to let a porous medium. Further the chemical interaction between the coated fibres and the liquid metal during infiltration can influence the species which are present at the interfaces. As magnesium oxide is stable magnesium can react with oxides. This could lead to better wettability of treated weave. However such chemical reactions seem to be thermally activated and take many seconds to initiate, whereas solidification of magnesium is achieved faster. Furthermore the addition of some carbide former elements (Si, Ti, Zr) to a magnesium based alloy can also influence chemical affinity. In conclusion CMg-MMC research concerns composites with low density, high potential mechanical properties and possibility of processing through thixomolding. Firstly the reach of the theoretical performance of the composite includes the ability of dealing with the interaction between fibres and liquid metal. Secondly primary treatment could help to form bonds between matrix and fibres, make rigid weaves and promote a further infiltration. Thirdly chemical affinity between the fibres, magnesium alloy and coating can influence the infiltration. [less ▲]

Study of Carbon Fibre-Reinforced Magnesium Composites (Introduction to interfacial phenomenon)

Conference (2009, November 06)

Composite materials are known to combine interesting properties of different materials. This research concerns magnesium alloys reinforced by carbon fibres weaves. Such a material can theoretically ... [more ▼]

Composite materials are known to combine interesting properties of different materials. This research concerns magnesium alloys reinforced by carbon fibres weaves. Such a material can theoretically exhibit a yield strength/density ratio around 500 compared to ~200 for Ti6Al4V and ~125 for Al2024-T6. This composite is thought to be especially promising for aeronautics if interaction between fibres and magnesium can be controlled and optimized. The strategy studied to enhance interaction between matrix and fibres consists in covering a thin layer of carbide former metal (Zr, Ti) by PVD as a primary treatment of carbon weaves. This intermediate product can then be heated up between 300-700°C in an argon atmosphere in order to form stable carbides. The wetability of treated weaves by liquid magnesium is potentially higher because carbides are not fully covalent (partially metallic) and so they can have more interface interaction with liquid metals. Further crystal lattice parameters of particular carbides can be close to the ones of metal crystal lattices and interface energy can consequently be reduced when they form carbide-metal bonds. Furthermore magnesium is known for its high oxygen attraction and is able to reduce a lot metallic oxides. It is a key fact because liquid magnesium easy wets its oxide in certain conditions. [less ▲]

Etude de dépôts en alliage Nickel - Diamants fabriqués par Laser Cladding

Report (2008)