Study On Process Conditions Of Laser Cladding Of CNTs On Titanium Alloy

Carbon nanotube (CNT) precoating was fabricated on TC4titanium alloy by dip-coating technique from the CNT dispersion solution prepared by using carboxymethylcellulose sodium(CMC) as dispersing agent under ultrasonic agitation. And then, a clad coating was fabricated by laser cladding with the CNT precoating under the protection of Ar gas. The effects of process parameters on the thickness of CNT precoating were discussed, such as the ultrasonic power, the concentration of CMC and the withdraw velocity. The effects of laser scanning velocity on the phase structure and properties of the clad coating were also studied.For CMC concentration of15g/1, CNT addition quantity of5g/1, standing time of12h, the viscosity of CNT dispersion decreases from40.76mm2/s at200W to19.18mm2/s at1800W. For CNT addition quantity of5g/1, ultrasonic power of1000W, standing time of12h, the viscosity of CNT dispersion increases from4.44mm’/s to95.26mm7/s when the CMC concentration increases from5g/1to20g/1. For ultrasonic power of1000W, CMC concentration of20g/1, CNT addition quantity of5g/1. standing time of12hours, drying horizontally in the oven, the thickness increases and then decreases with withdraw velocity, the peak thickness of precoating is5.83μm and22.03μm for4and8dip-coating cycles respectively at withdraw velocity of150mm/min.For laser power of400W. scanning velocity of1400-1800mm/min, the ablation and roughness became lighter with the increase in scanning velocity. The laser clad samples have three zones along the cross section, including laser clad coating, heat affected zone and substrate. The thickness of the laser clad coating decreases with the laser scanning velocity and a lot of nanocrystallines, some undecomposed CNTs and reinforced phase of TiC were observed in the laser clad coatings. Heat affected zone has a needle-like martensitic structure and get more sparse with the increase in scanning velocity.The surface micro-hardness of the laser clad coating decreases from HV0.25N8.38GPa to HV0.25N6.81GPa when the laser scanning velocity increases from1400mm/min to1800mm/min. The friction coefficient of the laser coating is0.25-0.27. and the wear mass of laser coating was also decreased significantly compared with that of TC4substrate.