The effect of laser energy density on the geometric characteristics, microstructure and corrosion resistance of Co-based coatings by laser cladding

Abstract

In view of the urgent problem of oil pipeline corrosion in the petroleum industry, Co-based coating was prepared on 42CrMo pipeline steel through laser cladding technology to realize the surface strengthening. The objective of the paper is to investigate the effects of process parameters (Led = 64–100 J/mm2) on the geometric characteristics, microstructure and corrosion resistance of the coating. It can be seen from the results that the increase of Led led to the increase of the dilution ratio and the Marangoni convection effect. At the Led of 90 J/mm2, the grain size of the coating was refined, and the dendrite growth direction was clearly visible. In the electrochemical test, the corrosion resistance of the coating first increased and then decreased with the increase of Led. Using the appropriate process parameters, the corrosion current density of the coating was only 1.740 × 10−7 (A/cm2), and a dense passive film was formed on the Co-based coatings. The Led was closely related to the properties of the coating. While at the Led of 64 J/mm2, the passive film resistance reached 6.474e+003 Ω cm2, and many microcracks appeared on the surface of the coating after corrosion. However, at the Led of 90 J/mm2, the corrosion products on the coating surface were less with excellent corrosion resistance. Therefore, the process parameters of laser cladding showed great effect on the forming quality and corrosion resistance of the coating. The coating with excellent corrosion resistance could be obtained by the adjustment of the process parameters.