Characterization and fracture toughness on AISI 8620 with hard coatings

The present studies characterize and evaluate the fracture toughness at the surface AISI 8620 with hard coating. The hard coatings FeB and Fe₂B were formed using the boriding dehydrated paste at temperatures 1223 and 1273 K with 6 and 8 h exposure time, respectively. The presence of hard coatings formed on the surface AISI 8620 were confirmed by the classical metallographic technique combined with X-ray diffraction analysis. The distribution of alloying elements was determined by Energy Dispersive Spectroscopy (EDS). The fracture toughness of the hard coatings on AISI 8620 was estimated using a Vicker microindentation induced fracture testing of 15 and 35 μm from the surface, applying four load (0.49, 0.98,1.96 and N). The microcrack generated at the corner of the microindentation was considered as an experimental parameter and the tree model Palmqvist crack model was employed to determine the fracture toughness. The adherence of the hard coatings/substrate was evaluate in qualitative form though the VDI 3198 by testing Rockwell C and observed by Scanning Electron Microscopy (SEM). The formation of hard layers was obtained in the range of 100-130 μm, results of XRD present phases FeB, Fe₂B, CrB and MnB, the values obtained of Kc are in the range of 2.3 to 4.1 MPam^1\2 and results of acceptable adhesion HF4 patterns for conditions 6 h of treatment.