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New beta‐metastable Ti alloys containing Ta, Mo and Fe biocompatible elements were synthesized by arc melting and then quenched in water from the beta phase field. For each alloy, the beta‐metastable phase decomposition was characterized by electric resistivity measurements and differential scanning calorimetry upon heating from room temperature to the beta transus. The formation of omega and alpha nanophases was detected and observed and the different phase transitions behavior was discussed in connection with the beta‐stabilizer content in each alloy.

Ti-based biocompatible alloys are especially used for replacing failed hard tissue. Some of the most actively investigated materials for medical implants are the β-Ti alloys, as they have a low elastic modulus (to inhibit bone resorption). They are alloyed with elements such as Nb, Ta, Zr, Mo, and Fe. We have prepared a new β-Ti alloy that combines Ti with the non-toxic elements Ta and Mo using a vacuum arc-melting furnace and then annealed at 950 °C for one hour. The alloy was finally quenched in water at room temperature. The Ti–12Mo–5Ta alloy was characterised by X-ray diffraction, optical microscopy, SEM and EDS and found to have a body-centred-cubic structure (β-type). It had a lower Young’s modulus (about 74 GPa) than the classical α/β Ti–6Al–4V alloy (120 GPa), while its Vickers hardness remained very high (about 303 HV). This makes it a good compromise for a use as a bone substitute. The cytocompatibility of samples of Ti–12Mo–5Ta and Ti–6Al–4V titanium alloys with various surface roughnesses was assessed in vitro using organotypic cultures of bone tissue and quantitative analyses of cell migration, proliferation and adhesion. Mechanically polished surfaces were prepared to produce unorientated residual polished grooves and cells grew to a particularly high density on the smoother Ti–12Mo–5Ta surface tested.

The purpose of this work is to precisely study the martensitic transformation in a plutonium-gallium alloy. Thus, the thermodynamics and kinetics of the d-a'+d phase transformation in a Pu-Ga alloy were studied under isochronal and isothermal conditions. The activation energy of the d-a'+d phase transformation at a constant cooling rate (0.5 K.min[?]1) was determined by using Kissinger and Ozawa models. The average value of the activation energy was found to be at [?]56 kJ.mol[?]1. Dilatometry measurement was also used to trace 'in situ' the entire transformation for several temperatures. The kinetics of the d-a'+d transformation were modelled under isothermal conditions in the theoretical frame of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. It is proposed that the transformation consists of three stages. The a' transformation begins with a nucleation of pre-existing embryos. Then, both nucleation and rapid growth of a' occurs simultaneously and finally, the plates width expend. Apparent activation energies for nucleation and growth transformation were determined from the temperature dependence of the constant K at respectively [?]34 kJ.mol[?]1 and [?]60 kJ.mol[?]1. Adler et al. [1] investigated also the thermodynamics and the kinetics of the martensitic transformation in Pu alloys. These nucleation energies were found by modelling of heterogeneous martensitic nucleation via strain interaction with observed superdislocation-like nucleation sites in PuGa alloys. The values obtain by this model was very close to those we find. Investigations in steels alloys indicate that these energies are of the same order for nucleation near dislocation. Then, it could be indicating a strong relationship between these dislocations and martensitic nucleation sites.

The partial martensitic d-a' transformation in plutonium alloys is sensitive to chemical composition, sample thermal history, as well as crystalline defects. The present work investigates the d-Pu phase microstructure before and after the martensitic transformation d-d+a'. More precisely, microstructural modifications of the host d-phase, resulting from the stress induced by a cell volume difference of 19% between the d and a'-phases, were analysed. Microstructural information about crystallite size and microstrain of a highly homogenized Pu-Ga alloy was extracted from x-ray diffraction patterns using a three dimension crystallite size and microstrain model. This is available in Rietveld refinement software and consists in anisotropic broadening analysis of diffraction peaks. Crystallite size doesn't significantly change with the phase transformation contrary to microstrain that is multiplied, on average, by five. Furthermore, internal normal and shear microstress are multiplied, respectively, by 2 and 13 when a'-phase appears. Last, dislocation densities, calculated from crystallite size and microstrain, are compared to TEM results available in the literature.