Abstract
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.
Highlights
As a structural steel, S355 structural steel has the characteristics of high strength, plasticity and impact toughness etc. [1,2] and is mainly used in manufacturing of offshore platforms
Cold spraying is a fabrication method of Al coating with plastic deformed Al powders impacted by high speed gas to combine with the substrate [3,4,5,6,7,8], because the cold sprayed Al coating presents a typical layered structure with micro-porosity, it is difficult to adapt to the harsh environment, which limits its scope of application and service life on offshore platforms [9,10]
Wang et al fabricated a MCrAlY coating on Ti–Al alloy using plasma spraying: the lamellar micro-structure disappeared and the density increased and other defects disappeared after laser remelting (LR) [15]; Astaritaa et al used LR to modify the cold-sprayed Ti coating: the remelted zone (RZ), heat affected zone (HAZ) and base zone (BZ) were formed after LR [16]; Yao J et al analyzed the beneficial effects of laser irradiation on the deposition process of cold-sprayed diamond and Ni60 composite coatings [17]
Summary
S355 structural steel has the characteristics of high strength, plasticity and impact toughness etc. [1,2] and is mainly used in manufacturing of offshore platforms. Cold spraying is a fabrication method of Al coating with plastic deformed Al powders impacted by high speed gas to combine with the substrate [3,4,5,6,7,8], because the cold sprayed Al coating presents a typical layered structure with micro-porosity, it is difficult to adapt to the harsh environment, which limits its scope of application and service life on offshore platforms [9,10]. Forms a uniform and compact structure, which is an effective way to improve the properties and expand the application range of cold sprayed Al coating [20,21,22]. Al coating were investigated to simulate the sand wear in seawater, which provided an experimental basis for the Al coating protection of S355 steel on offshore platforms
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