Microstructure And Mechanical Properties Of TiC Ceramic Coating Fabricated By High Energy Ball Milling Technique

During the process of high energy ball milling, balls, powder and the chamber intensely impacted each other. This action induces some powder to adhere to the surface of balls and the inner wall of the chamber, and then a coating film is formed. Based on the phenomenon, a novel method for surface engineering has been developed, which is called mechanical coating and armouring. The basic principle of this technique is cold welding, and now, it has provided a novel pathway for prepare coatings on metallic surfaces.In this dissertation, using the technique of mechanical coating and armouring, a planetary high-energy ball milling was applied to produce TiC coatings, TiC/Al composite coatings and Ti/Al/C composite coatings. The mass ratio of composition in latter two coatings is 4:1 and 107:30:13. The microstructure and mechanical properties of the coatings in different milling times were investigated by scanning electron microscope(SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD), scratch test technique and so on. Structural evolution and formation mechanism of the coatings were also discussed.Prolonged milling increased the thickness and dense of the coatings. But, the thickness of TiC coatings and Ti/Al/C composite coatings were decreased at the later stage of milling. The largest thickness of TiC coatings is 27μm, and 46μm for TiC/Al composite coatings, and 36μm for Ti/Al/C composite coatings. The micro-hardness, the strength of adherence and the tribological property of the coatings were also improved with the increase of milling duration. The highest value of micro-hardness for TiC coatings is 478HV0.1 with 12h milling, which is three times more than the value of the substrate. The well adherence has been obtained by the Ti/Al/C composite coating for 40h milling, and the value of strength of adherence is 56.4N. TiC/Al composite coatings get lower friction coefficient than TiC coatings.The combination between coating and substrate was formed by cold welding. The powders in the coatings were also cold welded together. In the process of ball milling, powders impacted the substrate through the movement of the milling balls, and then deposited on the substrate to form coating. Prolonged milling increased the strains. The coating produced with brittle powders is easy to be destroyed by the appearance of microcracks in coating. When the coatings, produced with ductile powders, have been under the condition of friction and impaction for a long time, the top coating layer tends to consolidate and densify into bulk materials, but we didn't find any new phase with the result of XRD test.