MoAlB is the first and, so far, the only transition-metal boride that forms alumina when heated in air and is thus potentially useful for high-temperature applications. Herein, the thermal stability in argon and vacuum atmospheres and the thermodynamic parameters of bulk polycrystalline MoAlB were investigated experimentally. At temperatures above 1708 K, in vacuum and inert atmospheres, this compound incongruently melts into the binary MoB and liquid aluminum metal as confirmed by differential thermal analysis, quenching experiments, x-ray diffraction, and scanning electron microscopy. Making use of that information together with heat-capacity measurements in the 4-1000-K temperature range-successfully modeled as the sum of lattice, electronic, and dilation contributions-the standard enthalpy, entropy, and free energy of formation are computed and reported for the full temperature range. The standard enthalpy of formation of MoAlB at 298 K was found to be −132 ± 3.2 kJ/mol. Lastly, the thermal conductivity values are computed and modeled using a variation of the Slack model in the 300-1600-K temperature range.

T2-Al2MgC2 was synthesized from the elements in a Mg-Al melt at 1000°C using sealed Ta crucibles. Single crystals of T2-Al2MgC2 were extracted by evaporating the Mg-Al matrix. The crystal structure of T2-Al2MgC2 was refined for the first time on the basis of single-crystal X-ray diffraction. The crystal is trigonal (space group P-3m1, Z=1) with lattice parameters of a=3.3767(11) Å, c=5.807(2) Å and V=57.34(5) Å 3. Based on the refined crystal structure, DFT calculations were conducted to evaluate the thermodynamic properties and the electronic structure of the phase. The heat of formation of T2-Al2MgC2 was calculated to be-23.6 kJ/moles of atoms at 298K. The heat capacity of T2-Al2MgC2 was measured by DSC from 300 to 871K and calculated by DFT from 0 to 1000K. Based on the calculated heat capacity, the entropy of formation of the phase at 298K was determined to be 70.0 J/mol/K. The band structure and the electronic density of state of T2-Al2MgC2 was calculated leading to an indirect band gap value of 1.73 eV.

International audience"Microstructure and mechanical properties of an Al-TiC metal matrix composite obtained by reactive synthesis", Composites: Part A (2015), 72, 50-57." Abstract: A metal matrix composite has been obtained by a novel synthesis route, reacting Al 3 Ti and graphite at 1000°C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al-TiC composites and to its high reinforcement volume fraction, with a Young's modulus of ~110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%

The nature of liquid-solid phase equilibria in the Al-rich corner of the Al-Si-Ti system are determined by drawing three isothermal sections at 620, 680 and 727°C. The solubility of Ti in Al-Si liquids is determined for four different compositions (0, 9, 13 and 18 at.%Si) at temperature below 800°C. Combination of the two sets of experimental results leads to an attempt of liquidus projection. The primary crystallization surface of Al 3 Ti is found to extend up to 9.5 at.%Si in the liquid phase at 620°C and 11 at.%Si at 727°C. The solubility of Ti is found to be not significantly dependent on the Si content of the liquid. From DSC measurements and deduction on microstructure, the last invariant reaction of the solidification path is found to be quasi-peritectic: L

International audienceThe evolution of TiC reinforcement during the high-temperature consolidation step of a particulate-reinforced Ti matrix composite has been studied. A four-step scenario has been highlighted starting with the dissolution of the smallest particles to reach C saturation of the Ti matrix, followed by a change in the TiC stoichiometry from the initial TiC 0.96 composition to the equilibrium composition (TiC 0.57). This change in composition induces an increase in both the total mass fraction of reinforcement and the particle diameter. The diameter increase promotes contact between individual particles in the most reinforced domains and initiates an aggregation phenomenon that is responsible for the observed high growth rate of particles for heat treatment times shorter than 1h. Finally Ostwald ripening is responsible for the growth of particles for longer heat treatment times. 1. Introduction In the general context of structural lightening in the aerospace industry, Metal Matrix Composites (MMC) materials have attracted much interest over the past decades because of their high specific mechanical properties (relative to density) compared to existing metallic alloys. Of the fibers or particulate materials used as reinforcement for Ti-based composites, titanium carbide (TiC) has been widely investigated because of its excellent chemical compatibility with the matrix alloys [1–3]. Ti-TiC composites can be prepared by different routes although the most widely used is the classical powder metallurgy route [4, 5]. The nature of bonding at the matrix-reinforcement interface and the existence and extent of any reaction zone determine, to a large extent, the properties of the composite material. From the binary TiC phase diagram (see Figure 1-[6]), the expected interaction between a Ti-based matrix and commercial stoichiometric TiC particles, consists of the formation of a sub-stoichiometric form of the carbide according to reaction (1)

The solubility of group IV transition metals Ti, Zr, and Hf in liquid Al was measured by the settling technique coupled with ICP-AES analysis after dissolution in hydrochloric acid. The kinetic aspect of the settling technique was studied in order to show that, after a cooling step, thermodynamic equilibrium between the liquid and solid phases could be achieved after only 1 h. Finally, it was verified that solubility values obtained after a cooling or a heating step were fully consistent. The present results demonstrate that the immersion-and-settling technique allows reliable solubility values to be determined. The results confirm the values previously reported in the literature and the good description for the three binaries by the existing CALPHAD optimizations concerning the liquidus below 800°C.

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