Numerical evaluation of scratch tests on boride layers

• Scratch tests on boride layers were evaluated using the finite element method.
• Normal and shear stresses during the scratch test were analyzed.
• Cohesive and adhesion failures were observed in the boride layers.

An experimental and numerical study of the scratch test on FeB/Fe2B bilayers is presented. The boride layers were formed at the surface of AISI 304 steels by developing the powder-pack boriding process at temperatures of 1223 K for 2, 6 and 10 h of exposure times. From the set of experimental conditions of the boriding process, scratch tests were performed with a linearly-increasing load mode of 1 to 90 N on 7 mm in length to determinate the most effective and informative testing conditions and to estimate the critical load (Lc) at which the boride layer fails. The damage in the boride layer was examined by high resolution SEM. Experiments tests indicated that at a critical load the boride layer fails through brittle fracture. Numerical calculations considering the residual stress field generated by the scratch load showed that at this load the tensile stresses inside the boride layer become large enough to cause brittle failure. The residual stress fields generated by the scratch load were analyzed and related with the failure mechanisms observed by the experimental tests.