A fractal approach to predict the oxidation and corrosion behavior of a grain boundary engineered low SFE high entropy alloy

The current study presents a method to predict the oxidation and corrosion properties in a grain boundary engineered low stacking fault energy (SFE) FCC high entropy alloy (HEA) Ni14Cr21.5Co21.5Fe21.5Mn21.5 through fractal analysis. Two thermo-mechanical processing (TMP) routes namely, unidirectional rolling (UDR) and multistep cross rolling (MSCR) with intermediate annealing, were employed to enhance the percentage of coincident site lattice (CSL) boundaries and break the random boundary network (RBN) in the alloy. Electron backscattered diffraction (EBSD) was utilized to analyze the microstructure and local texture of the samples before and after subjecting the samples to TMP. Fractal analysis (box-method) was carried out to analyze and quantify the RBN in the processed samples. Potentiodynamic polarization experiments were carried out to study the corrosion resistance as a function of CSL boundaries in the processed samples. Thermogravimetric analysis (TGA) was carried out to study the oxidation behavior in the samples. Elemental segregation in the oxide layer was also analyzed using Energy dispersive spectroscopy (EDS) line scan analysis. In the final part of the study, empirical relationships were established between fractal number, oxide layer thickness, and corrosion rate respectively. It was observed that Fractal numbers could be used as a powerful and reliable tool to predict some of the grain boundary character dependent properties like corrosion and oxidation in the alloy system under study.