Adhesive wear mechanism of coated tools and its influence on cutting performance during machining of Zr-based bulk metallic glass

Abstract

Adhesive wear is the primary failure form of coated tools in zirconium-based bulk metallic glasses (Zr-based BMGs) machining. This work investigated the adhesion formation and failure of TiN/Al2O3/Ti(C,N), Al2O3/Ti(C,N), and TiAlN-coated tools when machining Zr41.2Ti13.8Cu10Ni12.5Be22.5 BMG. Characterization of tool-chip interfacial material responses revealed the mechanism of adhesive wear. The relationship between the wear resistance and micro-mechanical properties of coatings was established. The cutting performance of coated tools is also discussed. According to the results, the adhesive wear of coated tools results because the temperature at the tool-chip interface is above the glass transition temperature, reducing the viscosity of chips. Low-viscosity chips were welded to the tool surface under high pressure. Subsequently, high interfacial friction tore the adhesive interface, causing coatings to peel off layer by layer. The exposed tool substrate also generated secondary adhesion, which triggered the diffusion of tungsten and cobalt atoms towards the chip. This was accompanied by redox reactions that exacerbated tool failure. The wear resistance of coatings depended on the elastic modulus (E) and the ratio of nano hardness to elastic modulus (H/E). The TiAlN coating had a lower E of ∼410 GPa and higher H/E of 0.064, and it exhibited better wear resistance than the TiN/Al2O3/Ti(C,N) (E ∼ 436 GPa, H/E = 0.051) and Al2O3/Ti(C,N) (E ∼ 469 GPa, H/E = 0.061) coatings. The lifespan of the TiAlN-coated tool was more than three times longer that of the other two, and the obtained machined surface roughness was less than half that of the others.