Corinne Arvieu

Correlation between microstructures of SiC-reinforced titanium matrix composite and liquid route processing parameters

A new procedure for filamentary metal matrix composite processing is described here. It consists in running carbon-coated SiC filaments through a liquid titanium bath in levitation. The liquid metal/carbon interaction must be significant enough to enable filament wetting and sufficiently low to avoid composite embrittlement. To insure both requirements, different configurations of the initial ceramic filament can be used: (1) SiC(C) filament free of any other coating, (2) SiC(C) filament coated with a carbide obtained by reactive chemical vapour deposition (R-CVD), or (3) SiC(C) previously coated by a first metal layer. In order to choose the best conditions for developing the process, the different processing configurations were studied through modelling and numerical simulations of the filament/matrix interaction. The microstructure of the interfacial zone between filament and matrix was investigated through SEM and Auger electron spectroscopy (AES) analyses. The microstructure of the interfacial zone between filament and matrix was investigated through SEM and AES analyses. The results show that in comparison to the first processing configuration, the best way to obtain filamentary composite semi-products without excessive fibre/matrix interaction is to use the second configuration. However, the latter requires preliminary R-CVD operations, while the third configuration leads to moderate carbon embrittlement effect without requiring additional equipment.

Heat and Mass Transfer Modeling and Simulation during Liquid Route Processing of SiC/Ti Filamentary Composites

To process SiC/Ti filamentary composites using a liquid route method, it is first necessary to overcome various major difficulties such as, high speed filament/matrix coupling, liquid titanium wetting of filament surfaces, and reduction of filament/matrix interaction. All of these requirements depend mainly on the heat and mass transfer, which occurs as the filament runs through a liquid titanium bath. Consequently, these transfers were modeled and simulated numerically during the different processing steps, particularly the cooling step. The results describe the physical phenomena which occur during the process: the carbon transfer from the carbon coated SiC filament to the liquid titanium, heat exchanges, formation of the TiC interphase at the filament surface, and, finally, the solidification of the titanium coating. Numerical simulation has shown the strong influence of running speed which governs the wettability of the filament by the liquid metal. Furthermore, the effects of an additional specific cooling device have been highlighted.

Numerical Simulation of Segregation Phenomena Coupled with Phase Change and Fluid Flow: Application to Metal Matrix Composites Processing

The injection of a liquid metal through a fibrous preform, located in an initially preheated mold, is one of the techniques used to manufacture metal matrix composites (MMCs). In order to reduce the chemical reactions between the fibers and the metal matrix, the fibrous reinforcement and the mold are commonly preheated up to initial temperatures much lower than the metal solidification temperature. Therefore, local metal solidification instantaneously occurs on fiber during liquid metal infiltration. When infiltrating metal alloy, unlike what happens when infiltrating a pure metal, both temperature and composition may vary within the matrix; this heterogeneity induces segregation within composites. A fiber scale numerical simulation was developed taking into account coupled physical phenomena which occur during the processing: flow of the liquid metal around the fibers, phase change phenomena, solute redistribution at the liquid/solid interface during alloy solidification, and species diffusion. This model predicts the segregation phenomena associated with fibrous preform infiltration by a binary alloy.

Matrix consolidation mechanism in 1D-Ti/SiC/C composites produced by continuous binder-powder coating

In this workmatrix consolidation mechanism has been investigated in 1D-Ti/SiC/C composites produced by Continuous Binder-Powder Coating - CBPC. Titanium metal matrix composites reinforced with continuous SiC/C filaments were analysed in different densification conditions. The results show that during processing, densification occurs by several mechanisms including a complex elasto-viscoplastic flow and diffusion bonding. The matrix consolidation depends on many processing conditions such as pressure and temperature, mainly. Using correct conditions of pressure and temperature, the titanium matrix composites produced by this process present a good matrix consolidation without porosity and a weak interaction between matrix and fiber. These good agreements between matrix consolidation and weak chemical interaction between matrix and fibre are obtained when pressures up to 150 MPa and temperatures below β-transus are applied. In these conditions, supplementary heat treatments can be performed either in alpha or beta domains.

Validity of powder metallurgy-based method for processing carbon fibers reinforced titanium matrix composites:

Titanium matrix composites reinforced by continuous carbon fibers were prepared using powder metallurgy (PM) and hot compression. The study of fiber—matrix interfaces has shown that direct coupling between carbon and titanium is possible without interposing any diffusion barrier, provided compression temperatures are lower than 700°C. However, high pressures of about 200 MPa for 1 h must be applied. The validity of the used PM-based processing method has been discussed and some discrepancy between expected and measured mechanical performance has been justified, which enables directions for processing improvement to be proposed.

Continuous Binder-Powder Coating for the Production of Ti/SiC/C Composites

Continuous Binder-Powder Coating (CBPC) is a new fabrication route for the titanium metal matrix composites reinforced with continuous SiC filaments. Based on powder-cloth process, this alternative fabrication route is characterised, analysed and application viability is discussed considering the other related routes. In addition, effects of the pressure and temperature on the Ti/SiC/C composites were considered for matrix consolidation. Results have shown that the titanium matrix composites processed by Continuous Binder-Powder Coating present, simultaneously, good matrix densification, consolidation and also a weak interaction between matrix and fibers, when the hot pressing is performed under 150 MPa at temperature below β-transus. Most important characteristics of the CBPC process and its application viability are reported, in this paper.

Evaluation of an original use of spark plasma sintering to laminate carbon fibres reinforced aluminium

An alternative route for producing aluminium matrix reinforced with continuous carbon fibres is proposed in this paper. On the one hand, liquid aluminium does not wet carbon; on the other hand, however, the two form a reactive system leading to carbide formation. A novel way to obtain continuous carbon fibre-reinforced aluminium was investigated, using spark plasma sintering with aluminium foils as raw material. Sintering parameters were adjusted to achieve the effective welding of aluminium foils and penetration of the metal between the filaments. A quality assessment of the fibre/aluminium coupling is presented. Interfaces were then investigated by scanning electron microscopy, transmission electron microscopy and energy-dispersive ray spectroscopy. An effective cohesion of fibres with the matrix was shown. The manageable fibre positioning could result in unidirectional architecture and reinforcement rate should be handled through foil thickness and yarn properties. Using tensile tests, cohesion between aluminium and carbon fibres can be quantified.

Influence of Post-Laser Welding Heat Treatment on Assembling Performance of Aluminum Alloy Structure

The need to reach the mechanical performance of age hardened Al-Mg-Si (6000 series) base alloy of structures, the assemblies of which are processed by laser welding, has required the efficiency evaluation of age hardening heat treatment performed after welding. It has been established that post-laser aging treatments are not efficient enough to give laser welded assemblies the expected performance of hardened Al base alloy in term of micro-hardness, ultimate tensile strength, and failure deformation. This lack of efficiency has been attributed to insufficient cooling kinetic during laser welding rather than to composition deviation of the bead due to the use of Si rich filler. The interposition of solution heat treatment between welding and aging treatment has been proposed and has shown its efficiency to give the laser welded zone a sufficient strength, similar to that of Al base alloy.