Interfacial indentation test of FeB/Fe₂B coatings

The present study uses interfacial indentation testing to estimate the adhesion of the FeB/Fe₂B coating formed on the surface of borided AISI 316 steel. This technique creates and propagates a crack along the FeB/Fe₂B interface and defines the apparent fracture toughness, which can then be related to the adhesion and mechanical support of the aforementioned interface. The boriding process was performed on the surface of AISI 316 steel by means of the powder-pack method at temperatures of 1123, 1173, 1223 and 1273K with 2, 4, 6, 8 and 10h for each temperature. The Young's modulus for each surface layer was obtained by Knoop microindentation at a constant indentation load. Vickers microindentation fracture technique was used to generate microcracks at the FeB/Fe₂B interface with varying indentation loads. The applied load, Young's modulus, hardness, and lateral crack lengths generated from the corners of the indentations, along with the depth of the FeB layer, were used to determine the apparent fracture toughness and adhesion of the FeB/Fe₂B interface. The apparent fracture toughness of the FeB/Fe₂B interface varied between 3.56 and 4.45MPa m. Finally, the intensity of residual stress at the FeB/Fe₂B interface was estimated as a function of the FeB layer thickness.