RESUMO
A cold sprayed Al coating on S355 structural steel was processed using a laser remelting (LR). The surface and cross-section morphologies, chemical compositions, and phases of as-obtained Al coating before and after LR were analyzed using a scanning electronic microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD), respectively, and their hardness was measured using a micro-hardness tester. The friction-wear behaviors of Al coating before and after LR in 3.5% NaCl solution were conducted to simulate the sand and gravel scouring on its surface in seawater, the effects of wear loads and speeds on the tribological properties of Al coating were analyzed, and the wear mechanisms under different wear loads and speeds were also discussed. The results show that the Al coating after LR is primarily composed of an Al phase and its hardness is 104.66 HV, increasing 54.70 HV than the cold sprayed Al coating. The average coefficient of friction (COF) of cold sprayed Al coating at the wear load of 0.5, 1.0 and 1.5 N is 0.285, 0.239, and 0.435, respectively, while that after LR is 0.243, 0.227, and 0.327, respectively, decreased by 14.73%, 5.02% and 24.83% compared to the cold sprayed Al coating. The wear rate of cold sprayed Al coating at the wear load of 0.5, 1.0 and 1.5 N is 1.60 × 10-4, 2.36 × 10-4, and 2.40 × 10-4 mm³/m·N, respectively, while that after LR is 1.59 × 10-4, 1.70 × 10-4, and 1.94 × 10-4 mm³/m·N, respectively, decreased by 1%, 32%, and 23%, respectively, indicating that LR has high anti-friction performance. Under the wear load action of 1.0 N, the average COF of laser remelted Al coating at the wear speeds of 300, 400 and 500 times/min is 0.294, 0.279, and 0.239, respectively, and the corresponding wear rate is 1.06 × 10-4, 1.24 × 10-4, and 1.70 × 10-4 mm³/m·N, respectively. The wear mechanism of cold sprayed Al coating is primarily corrosion wear at the loads of 0.5 and 1.0 N, and that at the load of 1.5 N is abrasive wear and fatigue wear; while that after LR is abrasive wear and fatigue wear, with no corrosion wear, showing that LR improves its corrosion and wear resistance.
RESUMO
Cr-Ni coatings with the mass ratios of 17% Cr-83% Ni, 20% Cr-80% Ni and 24% Cr-76% Ni were fabricated on H13 hot work mould steel using a laser cladding (LC). The surface-interface morphologies, chemical elements, surface roughness and phase composition of the obtained Cr-Ni coatings were analysed using a scanning electron microscope (SEM), energy disperse spectroscopy (EDS), atomic force microscope (AFM) and X-ray diffractometer (XRD), respectively. The friction-wear properties and wear rates of Cr-Ni coatings with the different mass ratios of Cr and Ni at 600 °C were investigated, and the worn morphologies and wear mechanism of Cr-Ni coatings were analysed. The results show that the phases of Cr-Ni coatings with mass ratios of 17% Cr-83% Ni, 20% Cr-80% Ni and 24% Cr-76% Ni are composed of Cr + Ni single-phases and their compounds at the different stoichiometry, the porosities on the Cr-Ni coatings increase with the Cr content increasing. The average coefficient of friction (COF) of 17% Cr-83% Ni, 20% Cr-80% Ni and 24% Cr-76% coatings are 1.10, 0.33 and 0.87, respectively, in which the average COF of 20% Cr-80% Ni coating is the lowest, exhibiting the better anti-friction performance. The wear rate of 17% Cr-83% Ni, 20% Cr-80% Ni and 24% Cr-76% Ni coatings is 4.533 × 10-6, 5.433 × 10-6, and 1.761 × 10-6 N-1·s-1, respectively, showing the wear resistance of Cr-Ni coatings at a high temperature increases with the Cr content, in which the wear rate is 24% Cr-76% Ni coating with the better reducing wear. The wear mechanism of 17% Cr-83% Ni and 20% Cr-80% Ni and 24% Cr-76% coatings at 600 °C is primarily adhesive wear, and that of 24% Cr-76% coating is also accompanied by oxidative wear.
