Mechanical and Structural Characterization of Laser-Cladded Medium-Entropy FeNiCr-B₄C Coatings

Equiatomic medium-entropy alloy (MEA) FeNiCr-B₄C (0, 1, and 3 wt.% B₄C) coatings were deposited onto an AISI 1040 steel substrate using pulsed laser cladding. Based on an SEM microstructural analysis, it was found that the cross-sections of all the obtained specimens were characterized by an average coating thickness of 400 ± 20 μm, a sufficiently narrow (100 ± 20 μm) "coating-substrate" transition zone, and the presence of a small number of defects, including cracks and pores. An XRD analysis showed that the formed coatings consisted of a single face-centered cubic (FCC) γ-phase and the space group Fm-3m, regardless of the B₄C content. However, additional TEM analysis of the FeNiCr coating with 3 wt.% B₄C revealed a two-phase FCC structure consisting of grains (FCC-1 phase, Fm-3m) up to 1 µm in size and banded interlayers (FCC-2 phase, Fm-3m) between the grains. The grains were clean with a low density of dislocations. Raman spectroscopy confirmed the presence of B₄C carbides inside the FeNiCr (1 and 3 wt.% B₄C) coatings, as evidenced by detected peaks corresponding to amorphous carbon and peaks indicating the stretching of C-B-C chains. The mechanical characterization of the FeNiCr-B₄C coatings specified that additions of 1 and 3 wt.% B₄C resulted in a notable increase in microhardness of 16% and 38%, respectively, with a slight decrease in ductility of 4% and 10%, respectively, compared to the B₄C-free FeNiCr coating. Thus, the B₄C addition can be considered a promising method for strengthening laser-cladded MEA FeNiCr-B₄C coatings.