Modified criterions for phase prediction in the multi-component laser-clad coatings and investigations into microstructural evolution/wear resistance of FeCrCoNiAlMox laser-clad coatings

摘要

Based on the analyses of a large number of investigations related to laser cladding, the modified criterions in terms of the atomic size difference (delta), the mixing enthalpy (Delta H-mix), the mixing entropy (Delta S-mix) and the specific laser energy (K) had been proposed to precisely predict phase constituents of the multi-component laser-clad coatings fabricated in a typical nonequilibrium state. The criterions were followed: 10.8 = Delta S-mix = 16.2 J.K-1.mol(-1), -17 = Delta H-mix = 7 kJ.mol(-1), 0 = delta = 14 and 0.04 = K = 0.14 kJ.mm(-2), in which the simple solid solution was obtained in a multi-component alloy coating prepared by laser cladding. Among them, delta as the most important criterion was double that proposed in the previous studies, K as a new criterion was first proposed. Moreover, FeCrCoAlNiMox (x = 0.25, 0.75, 1.00, 1.25 and 1.50) high-entropy alloy (HEA) coatings were synthesized on 45# steel substrates by laser cladding, and the investigations into the effect of Mo on dilution rates, macro morphologies, microstructures and mechanical properties (microhardness and wear resistance) of the coatings were carried out. Results showed that the dilution rates of the coatings presented the increasing tendency with the increase in x. The coatings with x = 0.75/1.00 were composed of the single solid solution with a BCC structure. Besides the solid solution, an intermetallic compound rich in Fe and Mo (CrFeNiMo) was also formed in the other three coating with x = 0.25/1.25/1.50. A model was established to estimate the content of each component in the coatings, based on which Delta S-mix, Delta H-mix and delta were further calculated. The calculated results of the four parameters (delta, Delta H-mix, Delta S-mix and K) in the five coatings confirmed the validity of the above criterions. With the increasing in x, the average microhardness of the coatings (660, 664, 706, 681 and 642 HV0.2) was first increased and then decreased. The maximum value was obtained in the coating with x = 1.00, which was improved about 3.5 times when compared with that of the substrate (about 200 HV0.2). The average friction coefficient (0.514, 0.462, 0.443, 0.494 and 0.503), wear volumes (0.281, 0.154, 0.119, 0.177 and 0.254 mm(3)) and wear rates (8.29, 5.64, 4.41, 6.28, and 7.43 mm(3).N-1.m(-1)) of the coatings also confirmed that the coating with x = 1.00 exhibited the optimum wear resistance among the five coatings, which were significantly improved when compared those of the substrate (0.579, 0.34 1 mm(3) and 8.42 mm(3).N-1.m(-1)).