Impact of B4c In-Situ Alloying on Microstructure and Mechanical Properties of Laser Deposited Medium-Entropy Fenicr Coatings

Laser cladding of the equiatomic medium-entropy alloy (MEA) FeNiCr-B4C coatings on AISI 1040 steel substrate was carried out by pulsed laser deposition. X-Ray diffraction analysis showed that the formed coatings consist of a single face-centered cubic (FCC) γ-phase, space group Fm-3m, independently of the B4C content. However, additional TEM analysis of the FeNiCr coating with 3 wt.% B4C showed that it is characterized by two-phase FCC structure consisting of the grains up to 1 µm in size and banded interlayers between the grains. The grains are clean; the density of dislocations inside the grains is low. Based on the SEM analysis of the microstructure, it was found that the cross-sections of all obtained specimens are characterized by average coating thickness of 400 ± 20 μm, sufficiently narrow (100 ± 20 μm) “coating-substrate” transition zone and the presence of a small number of defects: cracks and pores. The characterization of the mechanical properties showed that in-situ alloying with 1 and 3 wt.% B4C is resulted in noticeable increase in microhardness, i.e. 16 and 38%, with a slight decrease in ductility, i.e. 4 and 10%, compared to the B4C-free FeNiCr coating. Thus, in-situ alloying with B4C can be considered as a promising method for hardening of laser deposited MEA FeNiCr coatings.