Investigation the Fatigue Impact Behavior and Wear Mechanisms of Bilayer Micro-Structured and Multilayer Nano-Structured Coatings on Cemented Carbide Tools in Milling Titanium Alloy

Hard coatings play an important role in increasing the ability of deformation and wear resistance due to the superior mechanical and tribological properties. Nano-structured coating is now being used for cutting tool and exhibits extremely fascinating and useful properties. In milling process, a typical failure mechanism of coating is the cyclic mechanical impact between the workpiece and cutting tool. This could induce intensive fatigue failure of coated tools. In this work, a novel cyclic impact tester has been designed by using the piezoelectric ceramic actuator to study the fatigue resistance of bilayer micro-structured and multilayer nano-structured TiSiN/TiAlN coating. Besides, the mechanical, tribological and adhesion properties of coatings were evaluated. The multilayer nano-structured coating showed higher hardness yet toughness, better adhesion and tribological properties, as well as more superior properties of fatigue impact resistance. The influence of coatings on the wear behavior and cutting performance of cutting tools was investigated in milling Ti-6Al-4V. The milling forces applied on the coated tools were measured and analyzed. It found that the friction force and normal force applied on the multilayer nano-structured coated tool were lower than that of bilayer micro-structured coated tool. The correlation between the mechanical properties in cyclic impact tests and cutting performance in milling experiments of coatings was studied. The multilayer nano-structured coated tool was much less susceptible to fatigue fracture and this could be attributed to the better fatigue resistance in the high frequency cyclic impact tests.