Investigation of Transformation Temperatures, Microstructure and Shape Memory Properties of NiTi, NiTiZr and NiTiHf Alloys

The influence of zirconium and hafnium additions in substitution to titanium, is investigated on TiNi shape memory alloy. Microstructural and thermomechanical studies are conducted on an arc-melted Ti38Ni50Hf12 alloy. Results are compared with those of an equiatomic TiNi. We confirm the increase of the phase transformation temperatures due to the additions of Zr and Hf. The presence of oxides in the cast alloy was detected. The lattice parameter is measured from a residue of electroextraction. It was found that a0=1,1547±0,0001nm. A stoichiometry of (Ti, Hf) 4Ni2 Ox (with x≤1) is suggested. It appears that this ternary alloy exhibit an improved shape recovery when it is pre-strained in austenite state (for Ms < T < As) . In this case it displays 100% of recovery for 4% of deformation

Effects of Impurities Content (Oxygen, Carbon, Nitrogen) on Microstructure and Phase Transformation Temperatures of Near Equiatomic TiNi Shape Memory Alloys

Investigation of precipitation is performed on several near equiatomic TiNi alloys elaborated by arc melting or by powder metallurgy (combustion synthesis mode). These alloys contain various amount of impurities (oxygen, carbon , nitrogen). We show that such impurities result in both oxides (Ti4Ni2Ox, with x ≤ 1) and carbonitrides (TiCxN1-x, with ≤ 1) precipitation. X-ray diffraction measurements are performed on residues of electrochemical extraction to determine the structure and the lattice parameters of these precipitates. The precipited fractions are quantified for various amount of impurities by image analysis. A very good correlation is obtained between the nominal content of impurities determined by chemical analysis and the precipited fraction measured by image analysis and X-ray measurements. Our results indicate that almost all the nominal oxygen has precipited to form Ti4Ni2O type oxides. As a consequence, an increase of the impurities content in near equiatomic TiNi alloys implies a lowering of the phase transformation temperatures. This phenomenon is attributed to the precipitates stoichiometry which induces a deficit of titanium content in solid solution.. On the other hand, we find that fine precipitation improve the grain size reduction during hot working. Possible explanation is that the precipitates act as grain refiners through a "pinning" or a "grinding" process

White beam microdiffraction experiments for the determination of the local plastic behaviour of polycrystals

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Effets des procedes de mise en forme sur les textures et les proprietes de traction des alliages ferritiques renforces par dispersion d'oxydes

Communication to : 1992 Powder Metallurgy World Congress, 21-26 juin, 1992, San Francisco, U.S.ASIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1221 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Modifications of structural and physical properties induced by swift heavy ions in Gd2Ti2O7 and Y2Ti2O7 pyrochlores

International audienceThe structural transformations induced by ionization processes in Gd2Ti2O7 and Y2Ti2O7 pyrochlores irradiated with swift heavy ions have been studied using XRD and Raman experiments. Results show that irradiation induces amorphization and that the phase transformation build-up can be accounted for in the framework of a model involving a single-impact mechanism. The radiation induced amorphization build-up is faster in Gd2Ti2O7 than in Y2Ti2O7. Moreover, a decrease of the thermal conductivity (measured by the laser flash method) is induced by irradiation both in Gd2Ti2O7 and Y2Ti2O7

X-ray absorption spectroscopy investigations on radioactive matter using MARS beamline at SOLEIL synchrotron

International audienceThe MARS beamline at the SOLEIL synchrotron is dedicated to the characterization of radioactive material samples. One great advantage of the beamline is the possibility to characterize about 380 radionuclides by different X-ray techniques in the same place. This facility is unique in Europe. A wide energy range from around 3.5 keV to 36 keV K-edges from K to Cs, and L3 edges from Cd to Am and beyond can be used. The MARS beamline is optimized for X-ray absorption spectroscopy techniques (XANES/EXAFS), powder diffraction (XRD) but x-ray fluorescence (XRF) analysis, High Energy Resolution Fluorescence Detected -XAS (HERFD-XAS), X-ray Emission (XES) and μ-XAS/XRD are also possible. A description of the beamline as well as its performances are given in a first part. Then some scientific examples of XAS studies from users are presented which cover a wide variety of topics in radiochemistry and nuclear materials