The Fabrication And Properties Analysis Of Metal-Cermet Composite Coatings

Titanium alloys have been widely used in the field of civil and national defense for their unique properties,such as low density,high specific strength and high corrosion resistance.However,high friction coefficient and low adhesive wear resistance have greatly affected the safety and reliability of the titanium alloys in high friction conditions.In order to improve the wear resistance of titanium alloy,composite coatings on TC4 alloy with thickness about 2mm was prepared by semiconductor laser with pre-laid powers protected by argon shielding gas.Cladding layers with no obvious pores and crackles were obtained.We utilized X-ray diffraction(XRD),scanning electron microscopy(SEM)which has an energy dispersive spectrometer(EDS)and microhardness tester to analysis all the specimens.The results showed that metallurgical bond between coatings and substrates can be achieved by laser cladding Ti40Ni20Zr20Cu20 powders on TC4 alloys.Coating of pure Ti-based alloy powders was composed of Ti dendrites,Ti-riched equiaxed grains and reticular structures.Ni60 alloy powders had small influence on phase formation when the content was less than 10wt.%.When the content of Ni60 reached 20wt.%,Ti dendrites disappeared when massive Ti-reached needle and lath structures emerged.Size of these needle and lath structures decreased when the content of Ni60 reached 40wt.%.Meanwhile,secondary enhanced phases were founded.They included equiaxed grains at the length of 7?m and the fine TiC cellular dendrites.XRD results showed that TiB2 and TiC were generated in the coatings.When the content of Ni60 reached 60wt.%,needle and lath structures disappeared thoroughly.Content of the equiaxed grains cellular dendrites increased obviously.Surface microhardness was 3 times of the substrate.The microhardness results indicated that the increase of the surface hardness mainly came from the second phase strengthening and fine grain strengthening.Ceramic grains of TiC and TiB2 can significantly improve the surface hardness of the cladding layer as well as inhibit the growth of the dendrite.In order to improve the performance of cladding layer,the contents of B and Si can be reduced.Meanwhile,the scanning speed can be improved to refine the grain size and generated the TiB which has better combination with the metal matrix.