Growth kinetics and mechanical properties of Fe₂B layers formed on AISI D2 steel

231-243In the present study, the growth kinetics and mechanical properties of Fe2B layers formed on the AISI D2 steel are investigated. A mathematical model for studying the growth kinetics of Fe2B<span style="mso-bidi-font-size:9.0pt;position:relative;top:6.0pt;mso-text-raise: -6.0pt;mso-ansi-language:EN-US" lang="EN-GB"> <span style="mso-bidi-font-size: 9.0pt;mso-ansi-language:EN-US" lang="EN-US">layers on the AISI D2 steel is proposed for the powder-pack boriding. This process is carried out in the temperature range of 1123-1273 K for treatment time ranging from 2 to 8 h. This kinetic model is based on solving the mass balance equation at the (Fe2B/ substrate) interface to evaluate the boron diffusion coefficients through the Fe2B<span style="mso-bidi-font-size:9.0pt;position:relative;top:6.0pt; mso-text-raise:-6.0pt;mso-ansi-language:EN-US" lang="EN-GB"> layers in the temperature range of 1123-1273 K. The formed boride layers are characterized by different experimental techniques such as light optical microscopy, scanning electron microscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. A tribological characterization is also performed using a Plint TE77 tribometer under dry sliding conditions. The boron activation energy for the AISI D2 steel is estimated as 201.5 kJ mol-1 based on our experimental results. This <span style="mso-bidi-font-size: 9.0pt;color:black;font-style:normal" lang="EN-GB">kinetic model is also validated by comparing the experimental Fe2B layer thickness with the predicted value at 1243 K for 5 h of treatment. A contour diagram relating the layer boride thickness to the boriding parameters is suggested to be used in practical applications.