Diffusion of phosphorus in α-titanium

Abstract

Diffusion coefficients of ³²P in single-crystal α-titanium have been measured over the temperature range 599–850°C. The phosphorus diffusivity is about five orders of magnitude larger than the self-diffusivity. The diffusivity perpendicular to the c−axis is larger than that parallel to the axis; this anisotropy is opposite to those observed for Fe, Co and Ni in α-Ti. The temperature dependence of the ³²P diffusivities perpendicular and parallel to the c−axis in the range 700–850°C can be expressed as D _⊥=1·55×10⁻¹ exp(−138·2±4·8 kJ mol⁻¹/RT)cm²s⁻¹, and D _∥ = 4·70exp(−172·3±1·9 kJ mol⁻¹/RT)cm²s⁻¹. Below 700°C, marked downward curvatures in the Arrhenius plots are found. A similar but more drastic effect is observed in the polycrystal Ti-2·35 at.% O alloy in the temperature range 720−849°C. This effect is interpreted as evidence for a trapping effect due to oxygen; the binding energy is estimated to be about 230 kJmol⁻¹.