Microstructure, corrosive-wear and electrochemical properties of laser cladded CoCrFeNiMo-B4C coatings in 3.5%NaCl solution

Abstract

In order to improve the corrosive-wear and electrochemical properties of Ti6Al4V alloy, CoCrFeNiMo-B4C coatings were prepared on its surface by laser cladding (LC). The morphologies, chemical compositions and phases of obtained coatings were analyzed using a scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD), respectively, and the effects of B4C mass fraction on the corrosive-wear and electrochemical properties were analyzed using a corrosive-wear tester and an electrochemical workstation, respectively. The results show that the laser cladded CoCrFeNiMo-B4C coatings are mainly composed of Co2B, FeB, Fe2B, Fe2C and B4C phases, in which the B4C plays the role of grain refinement and crack reduction. The average coefficients of friction (COFs) of CoCrFeNiMo-5 %B4C, −10 %B4C and −15 %B4C coatings in 3.5 % NaCl solution are 0.44 ± 0.014, 0.28 ± 0.019, and 0.38 ± 0.021, respectively, and the corresponding wear rates are 1.942 × 10-7, 1.405 × 10-7, and 0.534 × 10-7 mm3•s−1•N−1, respectively, which are decreased with the increase of B4C mass fraction. The CoCrFeNiMo-15 %B4C coating has the highest wear resistance among the three kinds of coatings, and the wear mechanism is abrasive wear and fatigue wear. The corrosion current density icorr of CoCrFeNiMo-5 %B4C, −10 %B4C and −15 %B4C coatings is 4.860 × 10-8, 5.725 × 10-8, and 2.658 × 10-5 A•cm−2, respectively, and the corresponding charge transfer resistance Rct is 1.725 × 106, 3.229 × 105, and 2.897 Ω•cm2, respectively, which showed that the corrosion resistance is decreased with the increase of B4C mass fraction. Moreover, the galvanic corrosion prevents the formation of passive films by the B4C and other ceramic compounds, which is the main factor of corrosion performance degradation with the increase of B4C mass fraction.