Kinetics of boron diffusion and characterization of Fe2B layers on AISI 9840 steel

In this work, the AISI 9840 steel was subjected to the powder-pack boriding in the temperature range of 1123–1273 K for various times ranging from 2 to 8 h. A kinetic model based on the principle of mass conservation at the growing interface was used to estimate the boron diffusion coefficients through the Fe 2 B layers. The pack-borided samples were experimentally characterized by different techniques such as: Scaning electron microscopy, XRD analysis, Microhardness Vickers testing. The Daimler-Benz Rockwell-C indentation technique was used to assess the adhesion quality of boride coatings on AISI 9840 steel. Finally, the scratch and pin-on-disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions. The boron activation energy for the AISI 9840 steel was estimated as 193.08 kJ /mol by applying the present model. To confirm and extend the validity of the diffusion model, the experimental values of Fe 2 B layers thicknesses obtained for other boriding conditions were compared with the predicted values.