RESUMO
This paper aims to explore the influence mechanism of powder particle sizes on the microstructure and properties of coatings and identify the effect of powder particle size difference on the coating graphite phase. NbC-reinforced Ni-based coatings were in-situ synthesized by laser cladding to investigate the impact of powder particle sizes on the morphology, structure, and properties of coatings. The results indicate that increasing powder particle size enlarges the coating area and decreases the coating width and dilution ratio. Meanwhile, the defect ratio first increases and then decreases. The XRD test suggests that the coating mainly consists of NbC, solid solution (Fe, Ni), B4C, Cr2C, and CrB2. Different powder particle sizes do not change the phase composition of coatings but affect the graphite phase morphology. The morphology transforms from spherical to flocculent as the powder size varies from micrometer to nanometer. The hardness of coatings gradually increases, and the friction and wear properties decrease with the growth of powder particle size. The dispersed graphite phase in the nano coating plays a self-lubricating role in the friction and wear process. This research provides a reference and theoretical basis for selecting powder particle size in laser cladding.
RESUMO
This paper aims to explore the mechanism of an ultrasonic applied field on the microstructures and properties of coatings, and clarify the evolution of the molten pool under different ultrasonic frequencies. The Taguchi experimental design method was adopted in this paper. NbC-reinforced Ni-based coatings were in situ synthesized by laser cladding to investigate the effects of ultrasonic vibration process parameters on the microstructure, pore area, microhardness, and wear resistance of the cladding layer. The results show that the pore area decreases first and then increases as ultrasonic power increases from 600 to 900 W and ultrasonic frequency from 23 to 40 kHz. On the contrary, the hardness and wear resistance increase at first and then decrease. The pore area is minimized at 800 W ultrasonic power and 32 kHz ultrasonic frequency, and the hardness is maximized at 600 W ultrasonic power and 40 kHz ultrasonic frequency. Meanwhile, the highest wear resistance can be obtained when ultrasonic power is 700 W and ultrasonic frequency is 32 kHz. Based on the phase structure analysis, the cladding layer mainly consists of FeNi3, NbC, B4C, and CrB2. Ultrasonic vibration will not change the phase composition of the layer. Combined with the varying G/R value and cooling rate, the reasons for the change in grain morphology in different areas were analyzed to reveal the evolution mechanism of the molten pool under the influence of ultrasound.
