Effect of Zr on structure and properties of Ti–Al–N coatings with varied bias

Ti–Al–N coatings exhibit considerable mechanical and thermal properties, which make them promising candidates for advanced machining and other high temperature application. Here, the effect of Zr addition on the structure, mechanical and thermal properties of Ti–Al–N coatings deposited by industrial cathodic arc evaporation system is studied. Furthermore, we researched the machining application of Ti–Al–Zr–N coated inserts with varied bias from − 50 to − 150 V. Addition of Zr leads to a structural transition from cubic to mixed cubic–hexagonal, and an increased hardness from ~ 31.2 to 33.1 GPa. The high hardness value of ~ 35.8 GPa for Ti–Al–Zr–N coating after annealing at 1000 °C indicates the improved thermal stability. Oxidation experiments yield fully oxidized Ti–Al–N coating for 16 h at 850 °C, whereas Ti–Al–Zr–N coating only forms of a layered oxide scale ~ 1.0 μm. Therefore, an increased machining performance in continuous turning is obtained by Ti–Al–Zr–N coated insert. Increasing of deposition bias favors the growth of cubic structure, and thereby results in a structure transition from a mixed cubic–hexagonal structure to finally a single phase cubic structure for bias of − 150 V. With consideration of its structure, hardness, defect densities, stress and cohesion with substrate, Ti–Al–Zr–N coated inserts with bias of − 100 V behaved the best performance in both continuous turning and milling.

► Zr addition into Ti-Al-N results in a structural transition from cubic to mixed cubic-hexagonal structure.
► Zr-containing coating exhibits high hardness value of ~ 35.8 GPa after annealing at 1000 °C.
► Increasing bias promotes the formation of cubic structure, and leads to an increased hardness.
► Alloyed with Zr improve the oxidation resistance and machining performance.