Lattice and grain-boundary diffusion of ⁵⁹Fe in 316 stainless steel

Abstract

In fine-grained polycrystalline solids both lattice and grain-boundary diffusion contribute to the effective volume diffusivity. In tracer diffusion experiments the concentration–penetration profiles can be suitably analysed to distinguish between these two components. This paper presents new data on ⁵⁹Fe diffusion in fine-grained molybdenum stabilized stainless steel in the temperature range 1178–1483 K. While the near surface regions of the concentration–penetration curves were analysed for lattice diffusion, the grain-boundary diffusion data were evaluated from the regions far away from the initial interface. The temperature dependence of these diffusivities can be described by the Arrhenius equations <disp-formula> <mml:math> <mml:mrow> <mml:msub> <mml:mi>D</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1·18</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> <mml:mtext> exp</mml:mtext> <mml:mo>[</mml:mo> <mml:mo>−</mml:mo> <mml:mo>(</mml:mo> <mml:mn>228·5</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2·99</mml:mn> <mml:mo>)</mml:mo> <mml:mo>/</mml:mo> <mml:mi>R</mml:mi> <mml:mi>T</mml:mi> <mml:mo>]</mml:mo> </mml:mrow> </mml:math> </disp-formula> and <disp-formula> <mml:math> <mml:mrow> <mml:msub> <mml:mi>D</mml:mi> <mml:mtext>b</mml:mtext> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>6·10</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mtext> exp</mml:mtext> <mml:mo>[</mml:mo> <mml:mo>−</mml:mo> <mml:mo>(</mml:mo> <mml:mn>177·21</mml:mn> <mml:mo>±</mml:mo> <mml:mn>6·01</mml:mn> <mml:mo>)</mml:mo> <mml:mo>/</mml:mo> <mml:mi>R</mml:mi> <mml:mi>T</mml:mi> <mml:mo>]</mml:mo> </mml:mrow> </mml:math> </disp-formula> where D ₁ and D _b are the lattice diffusivity and grain-boundary diffusivity respectively (both in m² s⁻¹) and the activation energies are given in kJ mol⁻¹.