Age hardening of a magnetron sputtered V-Al-Si-N quaternary coating

A V0.38Al0.58Si0.04N coating was prepared by reactive magnetron sputtering, followed by isothermal annealing experiments with various temperatures from 700 °C to 1100 °C. The evolution of microstructure and mechanical properties as a function of the annealing temperature, was investigated by using nanoindentation tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An age-hardening effect, with an increase in hardness of ~ 24% after the isothermal annealing at 800 °C, was observed in the coating, which could be attributed to grain boundary segregation along with nanometer-size coherent domains formed locally. The sample annealed at 900 °C exhibited compacted columnar structure with defined boundaries, where more amorphous phase segregated along the boundaries of parent columns and the columns partially contained coherent nanometer-size domains of V-enriched and Al-enriched. However, accompanied by the appearance of hcp-AlN at 1100 °C, the hardness of coating decreased. Both fine cracks and delamination formed in the coating.