Stéphane Gorsse

In situ preparation of titanium base composites reinforced by TiB single crystals using a powder metallurgy technique

The feasibility of Ti/TiB composite by in situ precipitation of the reinforcement have been investigated. The titanium monoboride can be obtained by the chemical reaction between TiB2 and Ti powders. The fabrication method requires two stages: the first stage corresponds to the compacting of the pre-blended powders and the second one to the nucleation and growth of the TiB needles. By controlling the second stage, it is possible to monitor the density and the aspect ratio of the reinforcement. Bend tests have been performed on these composites reinforced with 20% in volume of discontinuous TiB needles and it has been demonstrated that the load transfer is efficient to get a 50% improvement of the Youngs modulus of the titanium. The simplicity of this technique makes this material very attractive for numerous applications.

Investigation of the Young's modulus of TiB needles in situ produced in titanium matrix composite

In situ Ti/TiB composites with different volume fractions of discontinuous TiB reinforcements were produced by powder metallurgy. After compacting Ti� /TiB2 powders by hot unidirectional pressure, heat treatments led to the in situ formation of distinctive needles of TiB, randomly distributed in the titanium matrix. The Young’s modulus of TiB was evaluated using the ASW computation method and experimental Vickers micro-indentation. Three point bend tests were performed on Ti/TiB composites as a function of the TiB volume fraction in order to extract the Young’s modulus of TiB from the elastic properties of the composite. The different values obtained according to these three methods were discussed and compared with the literature. # 2002 Elsevier Science B.V. All rights reserved.

Additive manufacturing of metals: a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys

Abstract We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process–microstructure–property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts.

A new approach in the understanding of the SiC/Ti reaction zone composition and morphology

Abstract The morphology of the SiC/Ti reaction zone has been analysed by scanning electron microscopy. The composition of the different constituents was determined by Auger and X-ray microprobes. It was found that the two main constituents through the reaction zone were Ti 5 Si 3 (C) and TiC x . The TiC x crystals were measured from the inner part of the reaction zone (against the SiC) to the outer part of the reaction zone (against the titanium). By changing the scale of space by the scale of time, it has been possible to get the age of the TiC x crystals. This new approach has been useful to determine the kinetic rate of the SiC/Ti reaction and also to understand what was the driving force for the SiC/Ti reaction zone growth.

Magnetic behavior and magnetocaloric effect of neodymium-based amorphous alloy

The Nd49Al13Ni38 amorphous alloy has been prepared by melt-spinning in the form of ribbons. Its magnetic properties have been investigated via superconducting quantum interference device magnetometry and its magnetic phase diagram was established. Hysteresis and temperature-dependent magnetization measurements show the occurrence of a reentrant spin-glass behavior on cooling. With increasing applied field, the spin-freezing temperature decreases and disappears at very high field, and the Curie temperature increases, broadening the temperature range of the ferromagnetic state. The resulting magnetocaloric effect was evaluated and compared to other interesting magnetic refrigerant materials.

Stabilization by Si Substitution of the Pseudobinary Compound Gd2(Co3–xSix) with Magnetocaloric Properties around Room Temperature

We report the discovery of a new solid solution Gd2(Co3-xSix) with 0.29 < x < 0.50 in the Gd-Co-Si ternary system. Members of this solid solution crystallize with the La2Ni3-type structure and correspond to the stabilization of Gd2Co3 through silicon substitution. The structure of the member Gd2(Co2.53(3)Si0.47) was determined by X-ray diffraction on a single crystal. It crystallizes with the space group Cmce and cell parameters a = 5.3833(4), b = 9.5535(6), and c = 7.1233(5) Å. Co/Si mixing is observed on two crystallographic positions. All compounds studied in the solid solution present a ferrimagnetic order with a strong composition-dependent Curie temperature TC with 280 K < TC < 338 K. The magnetocaloric effect, which amounts to around 1.7 J K(-1) kg(-1) for ΔH = 2 T, is interestingly tunable around room temperature over a temperature span of 60 K through only 4-5% of composition change.