Formation and kinetics of FeB/Fe2B layers and diffusion zone at the surface of AISI 316 borided steels

The kinetics of the FeB/Fe2B layers and diffusion zone at the surface of AISI 316 steels exposed to the powder-pack bonding process were studied in this work FeB/Fe2B layers and diffusion zone measurements were taken at different temperatures and exposure times to validate diffusion-controlled growth during the bonding process. In order to obtain the boron diffusion coefficients at the FeB/Fe2B layers and diffusion zone, a mathematical model based on the mass balance at the growing interfaces was proposed. The activation energy values estimated for the FeB and Fe2B layers were 204 and 198 kJ mol(-1) respectively. In addition, the activation energy value obtained for the diffusion zone was 116 kJ mol(-1). The diffusion model was extended to estimate the FeB/Fe2B layer thicknesses, and the depth of the diffusion zone at the temperature of 1243 K with 3 and 5 h of exposure, based on the experimental parameters ascribed to the bonding process. Finally, the effects of the FeB/Fe2B growth and diffusion zone, on the weight gain of bonded steels and on the instantaneous velocity of the interfaces were incorporated in the model (C) 2010 Elsevier B.V. All rights reserved