The Research And Improvement About The Characteristics Of Laser Cladding On Titanium Alloy Surface

Titanium alloy possesses excellent comprehensive properties of high strength, low density, anti-corrosion safety. And they are high-performance material which have been widely used in many fields, such as the machinery, electronics, metallurgy, petrochemical, aerospace and other fields. However, titanium alloy exhibits low hardness and poor wear resistance which restrict its further application. Laser cladding is one kind of surface modification process for materials which use high-energy laser cladding on metal surface to form a layer of high hardness, good thermal stability, excellent wear resistance and good fusion bonding between coating and substrate. The cobalt-based composite powder with good wear property and anti-high temperature which is used as coating material cladded on TA15 surface, through trying to add other strengthening phase and improve the process conditions,in order to improve the quality of the coatings,thus improve the performance of the coatings.The cobalt-based composite powder Stellite-6 is as Cladding materials,in which the rare earth oxide Y2O3 or ceramic zirconia particles is added.the effect of laser remelting on cladding layer is studied. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings were determined by X-ray diffraction (XRD), the Vickers hardness and wear resistance of the coatings were measured by hardness tester (DHV-1000)and wear testing machine(UMT-2 Multi-functional wear tester).The TA15 titanium alloy was selected as substrate which the cobalt-based composite powder with different content of Y2O3 were cladded on.Through analyzing, rare earth oxide can reduce the secondary dendrite spacing, decrease the cracks and pores, refine the grains and carbides and improve the compactness of the coatings, therefore the microhardness and wear resistance of the coatings have improved.The coating with 0.8wt% Y2O3 content has better wear property and higher microhardness. Wear resistance is as 53 times as the substrate and the microhardness (HV1181.1)is 3 times of the substrate.Transformation toughening and dispersion toughening are the main toughening mechanisms on zirconia.It is used for the toughening phase of laser cladding layer, and the TA15 titanium alloy is selected as substrate on which the cobalt-based composite powders (Stellite-6) with 5wt% content of ZrO2 is cladded. The results indicate that the zirconia can refine and purify the microstructure of the coating and improve compactness of the coating to some extent. Moreover,the cracks which appear in the coating have been repaired, the microstructure of the coating has been improved.The XRD spectrum has proved phase structure of zirconia ceramic in the coating is monoclinic, which has indicated the appearance of transformation toughening. At one time, the microhardness and wear resistance of the coating have improved with the addition of zirconia.The laser remelting technology is combined with laser cladding technology, the effect of laser remelting on cladding layer is studied.The results show that the laser remelting technology can relieve the residual thermal stress of cladding layer effectively, improve the content of hard phase, refine the dendrite, reduce the cracks and pores in the cladding layer.Thus the density and roughness of the cladding layer have improved. The highest microhardness value of the coating is HV1170, is more than three times as TA15 titanium alloy substrate.