Denis Ansel

Interdiffusion in the body cubic centeredβ-phase of Ta–Ti alloys

Abstract Interdiffusion in the β -phase of Ta–Ti alloys is studied in the temperature range 1000–1900°C. Interdiffusion coefficients are calculated with Den Broeder’s method from concentration profiles determined by EPMA. These coefficients depend strongly on the composition: the interdiffusion coefficient for the lower tantalum concentrations is approximately 1000 times greater than the one for the higher concentrations. The activation energy (150–240 kJ/mol) is characteristic of a monovacancy diffusion mechanism. Except for the impurity diffusion of tantalum in titanium, determined by the Vignes and Birchenall method, anomalous behaviour of the diffusion in the β -phase of titanium is not observed. The diffusion in these alloys is characterized by an important Kirkendall effect, materialized by a marker’s shift towards the titanium rich part of the sample. The intrinsic diffusion coefficients have been calculated between 1000°C and 1600°C, at the composition of the Kirkendall plane, by Heumann’s method: the intrinsic diffusion coefficient of titanium is approximately five times greater than that of tantalum.

On the diffusion in the Mo–Ta refractory system

Abstract Diffusion in the Mo–Ta system is studied as regards interdiffusion and impurity diffusion over the temperature range from 1500 to 1900 ° C . Interdiffusion coefficients, calculated with the den Broeder or Hall methods, are found to be weakly composition-dependent. Their temperature-dependence leads to Arrhenius parameters consistent with (i) literature data obtained at higher temperatures and (ii) a monovacancy mechanism. The composition-dependence of the Arrhenius parameters implies repulsive interactions between unlike atoms. Linear relationships between those parameters are found to exist among composition. Impurity diffusion coefficients DMo(Ta)0 and DTa(Mo)0 are determined by the Vignes and Birchenall method and are consistent with the interdiffusion coefficient limits. By comparison with literature data, anomalous behavior is obvious over the range 1500– 2220 ° C for both coefficients.

The partial (Ti0.5Zr0.5)-N phase diagram from 0 to 50 at.%

Abstract We propose a partial (Ti0.5Zr0.5)–N pseudo-binary phase diagram by using two reactional methods: the isothermal nitrogen diffusion in the Ti0.5Zr0.5 alloy at 900, 1000, 1160, 1250, 1350, 1440 and 1520°C and the study of the isothermal phase equilibrium at 1000 and 1350°C. Conventional metallographic techniques and SEM observation with back scattered electrons, reported as SEM/BM and EPMA, were used. The alphagene character of nitrogen was observed with the Ti0.5Zr0.5 alloy. The two-phase fields (β+α) and (α+δ) are drawn. The lower limit of the δ-phase (Ti0.5Zr0.5)Nz was located at 25.5 at.% N, while 28 at.% N in TiNz and 35 at.% N in ZrNz are found.