Measurement of fracture toughness in AISI 1018 borided steels by vickers indentation

This study evaluates the fracture toughness of Fe₂B boride layers formed by the paste bonding thermochemical process on an AISI 1018 steel surface. The samples were placed in acrylic molds for the impregnation of boron carbide paste with thickness of 4mm over the sample surfaces to produce the diffusion into the steel. The aforementioned treatment considered one temperature, T= 1273 K, and three exposure times t=5, 6 and 8 h. Later, the bonded samples were prepared metallographically to determine the mean values of the layer thicknesses and to produce Vickers microindentations at 45 μm from the surface, applying four loads (1.9, 2.9, 4.9 and 9.8 N). The microcracks generated at the corners of the Vickers microindentation were considered as experimental parameters, which are introduced into two Palmqvist cracks models to determine their corresponding fracture toughness K_C. As a result, the experimental parameters, such as exposure time and applied load are compared with the resulting fracture toughness of the bonded phase.