CALPHAD-Guided Design and Gas Atomization of a Fe-M(Nb,Mo,Cr)-C-B Alloy: Microstructure, Crystallographic Characteristics and Nanomechanical Properties

Severe wear is a frequent cause of failure in industrial machinery that lacks adequate surface protection. Iron-based alloys offer an attractive combination of hardness, fracture toughness, and low cost for addressing this problem. In this study, a CALPHAD-based thermodynamic approach was employed to design a novel Fe-M(Nb,Mo,Cr)-C-B alloy, which was cast and subsequently processed into powders by gas atomization. The powders showed a Hall flow rate of 27 s/50 g and an angle of repose of 26°. The alloy composition was determined by optical emission spectroscopy, X-ray fluorescence (Nb), and inductively coupled plasma mass spectrometry (B), while X-ray diffraction confirmed the presence of α-iron and complex borocarbide phases. SEM/EDS analysis revealed a spherical powder morphology and a refined, uniformly distributed borocarbide microstructure induced by rapid solidification. Electron backscatter diffraction indicated a near-random crystallographic texture, and grain orientation spread maps revealed increasing internal strain with decreasing particle size. Nanoindentation gave localized hardness values of approximately 1330–1590 HV0.0005, which decreased with increasing particle size. The refined borocarbide-reinforced microstructure, high localized hardness, and good flowability suggest that the developed powder is a candidate feedstock for wear-resistant coating applications, although its coating and wear performance remain to be verified.