Corrosion Behavior of CoCrNiNb0.1+B4C High Entropy Alloy Coating on A100 Ultra-high Strength Steel by Laser Cladding under Simulated Marine Environment
A100 ultra-high-strength steel is one of the ideal steel choices for the landing gear of amphibious aircraft.During actual service,it is often directly exposed to the marine environment,resulting in serious corrosion risks.Without affecting the mechanical properties of A100 ultra-high-strength steel,preparing a coating on its surface has become the first choice for surface protection.The high-entropy alloy coating prepared by laser cladding can achieve good protection on the surface of A100 ultra-high-strength steel.While ensuring the excellent mechanical properties and good corrosion resistance of the high-entropy alloy coating,it can achieve the metallurgical bonding of the coating and the substrate.Compared with traditional coatings and plating,the bonding strength is greatly improved.This paper designed high-entropy coating systems with different B4C contents to explore the effect of B4C content on the microstructure,mechanical properties and corrosion resistance of laser-clad CoCrNiNb0.1+B4C high-entropy alloy coatings on A100 ultra-high-strength steel,and elucidate the corrosion mechanism.This article explored the optimal laser processing process parameters,comprehensively considering the coating formability and performance,and finally determined the laser processing parameters as follows:laser power was 1.4 kW,scanning rate was 300 mm/min,and spot diameter was 3 mm.Heat-treated A100 ultra-high-strength steel with a size of 100 mm×15 mm×5 mm was selected as the base material,and different proportions(0％,2％,2.5％,3％,5％mass fraction)of B4C CoCrNiNb0.1 powder was used as coating raw material,and the coating was prepared after laser cladding.Then,the microstructure and element distribution of the coating were analyzed through SEM and EDS tests,and the phase composition of the coating was analyzed through XRD tests.The mechanical properties of the coating were characterized through microhardness testing,the corrosion resistance of the coating was characterized through electrochemical testing and immersion experiments,and the corrosion mechanism of the coating was analyzed.The results showed that the microstructure of the high-entropy alloy coating was composed of dendrites,in which Cr,Nb,B,and C elements were enriched in the interdendritic region,and Co,Cr,and Ni elements were evenly distributed.The physical phase composition of the coating was the matrix FCC phase and the ceramic phase.The contents of the ceramic phase Cr7C3,(Cr,Nb)23(C,B)6 increased with the increase of the B4C content.The emergence of the ceramic phase formed a second phase strengthening effect,which lead to an increase in the microhardness of the coating,with the highest hardness value reaching 1 090HV0.2.As the B4C content increased,the corrosion resistance of the coating decreased,which was manifested by a decrease in capacitive arc resistance,a decrease in impedance mode value,and a decrease in over-passivation potential.During the immersion experiment,the ceramic phase had a higher potential as the cathode phase,and the initiation site of the corrosion reaction was the FCC phase.The potential difference between the two phases lead to the occurrence of galvanic corrosion,which was the main corrosion failure mechanism of the coating.In conclusion,the addition of B4C leads to an increase in the microhardness of the coating and a decrease in corrosion resistance.
Co-Cr-Ni based high entropy alloy coatinglaser claddingmarine corrosion
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