Powder-pack boronizing of CoCrFeNiAl0.5Nb0.5 HEA: Modeling of kinetics, microstructural, mechanical, and tribological characterizations

Abstract

This study is dedicated to the detailed investigation of boronization kinetic, microstructural, mechanical, and wear properties of high entropy alloys (HEAs) considering their sluggish diffusion effect properties. A CoCrFeNiAl0.5Nb0.5 HEA was powder-pack boronized in the interval of 850–1050 °C for 2, 4, and 6 h in the boronizing medium containing 90 wt% of boron carbide and 10 wt% of sodium tetrafluoroborate. Boronizing of CoCrFeNiAl0.5Nb0.5 HEA was successfully produced. The obtained multi-phase boronized layers were characterized by compactness and flatness showing up inside its typical dendritic zones. The X-Ray Diffraction (XRD) studies showed the presence of ternary phases inside the boronized layers having a thickness of 4.38–92.16 µm. The nano and microhardness values were also determined and the adhesion force was analyzed through the Rockwell indentation tests. In addition, the Vickers fracture toughness values (0.46–1.83 MPa m−1/2) of the treated samples were found to be very dependent on the boronizing temperature. The wear losses have decreased due to the increase in hardness and an improvement of up to 99% has been achieved. The average diffusion coefficient model was implemented to deduce the boron activation energy in the CoCrFeNiAl0.5Nb0.5 HEAs. Finally, the predicted layers’ thicknesses were coincident with the experimental data.