Precipitation kinetics of W2B5 in (Ti0.4W0.5Cr0.1)B2 solid solutions

Roland Edith Fotsing (1) , Harald Schmidt (2) , Günter Borchardt (1) , C Schmalzried (3) , Rainer Telle (4)

1 IMET
2 IMET
3 Institut fur Gesteinshuttenkunded
4 RWTH - Rheinisch-Westfälische Technische Hochschule Aachen University

The isothermal precipitation kinetics of W2B5 secondary phase from supersaturated polycrystalline (Ti0.4W0.5Cr0.1)B2 solid solutions were investigated with X-ray diffractometry (XRD) and secondary electron microscopy (SEM) in the temperature range between 1500 and 1700 °C. The precipitate formation is described by a modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, where W2B5 particles nucleate preferably at grain boundaries and subsequently grow into the volume by a two-dimensional process controlled by volume diffusion of the transition metals. Numerical calculations are used to quantitatively describe the time dependence of the precipitated fraction and to determine a differential JMAK exponent, ndiff, which gives information on nucleation and growth modes. ndiff decreases during the precipitation process from 2 to about 0.8 for all temperatures investigated. The first limit corresponds to the classical JMAK model (two-dimensional diffusional growth and constant nucleation rate) and the decrease of ndiff is the consequence of an impingement of the nucleating and growing particles in the late stages of the process. Nucleation and growth rates are determined as a function of reciprocal temperature, where the first quantity shows a non-monotonic behaviour with a maximum at about 1650 °C and the second quantity exhibits an Arrhenius behaviour with an activation enthalpy of 3.6 eV. Herefrom it can be concluded that the overall precipitate formation is dominated by the kinetics of atomic motion at low temperatures and by the thermodynamics of nucleation at high temperatures.

Mots clés: Physical Sciences

Roland Edith Fotsing, Harald Schmidt, Günter Borchardt, C Schmalzried, Rainer Telle. Precipitation kinetics of W2B5 in (Ti0.4W0.5Cr0.1)B2 solid solutions. Philosophical Magazine, 2005, 85 (36), pp.4409-4427. ⟨10.1080/14786430500333323⟩. ⟨hal-00513617⟩