Abstract
In order to improve material service life under a fatigue and corrosion coupling environment, a high-velocity oxygen fuel (HVOF) Cr3C2–NiCr coating with a bonding layer was prepared. The objective was to obtain the optimum bonding layer for the HVOF Cr3C2–NiCr coating, which included a laser cladding (LC) Ni625 layer, extreme high-speed laser material deposition (EHLA) Ni625 layer and HVOF NiCr layer. Fatigue properties of the samples with various bonding layers were investigated by means of a four-point bending fatigue test. Electrochemical impedance spectroscopy (EIS) and the salt spray test were executed after the bending fatigue test to simulate the interactive effect of fatigue and corrosion atmosphere. Failure surfaces were characterized by scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS) to indicate the details of corrosion products. Corrosive behaviors of samples were adequately demonstrated according to the results, which included the curves of potentiostatic polarization, impedance magnitude and phase degree, and corrosion products. The result showed that the cycles of perforative cracking for the sample with the EHLA Ni625 bonding layer was almost three times than that of the sample with the HVOF NiCr layer. The magnitude of EIS reduced from ~105 to ~103 for the sample after BFT. Eventually, the main improvement mechanism of the HVOF Cr3C2–NiCr coating with the EHLA Ni625 bonding layer was attributed to the grain refinement of the bonding layer and performed a good level of metallurgical bonding with the substrate.
Highlights
Hydro cylinders were the key components of a hydraulic system, which can effectively and steadily convert hydraulic energy to mechanical energy
The cross-sections of NO. 1–3 samples were presented in Figure 3a, including surface coating, bonding layer and substrate
This was ascribed to the particles to be a semi-melting state before arriving at the bonding layer and some semi-melting particles at the fringe of flame flow to be oxidation
Summary
Hydro cylinders were the key components of a hydraulic system, which can effectively and steadily convert hydraulic energy to mechanical energy. Hydro cylinders were widely used in marine equipment, construction machineries, mining machineries, etc. Since the frequent reciprocating motion or the prolonged exposure to air, the surface performance of piston rod directly affected the service life of the whole hydraulic system. High-velocity oxygen fuel was widely used to reinforce the surface properties because of the advantage of high flame velocity, high spray particle velocity and high kinetic energy [1]. The piston rod with the Cr3 C2 –NiCr coating fabricated by HVOF presented excellent performance in the coal mine, desert, ocean and oil field atmosphere [2,3,4,5,6]. Varis [7] et al
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