Microstructure and Mechanical Properties of Magnetron Sputtered (Ti, Al)N Coatings with fcc Structure

Magnetron sputtered (Ti0.55, Al0.45)N and (Ti0.34, Al0.66)N coatings are deposited onto cemented carbide substrates at 350°C. The crystal structure and microstructure of the deposited coatings are characterized by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Nanoindentation is employed to determine the microhardness of the coatings. The adhesion between the coating and substrate is investigated using scratch test. Measurement of flank wear is used to evaluate the wear resistance of the coatings. XRD examination indicates that both (Ti0.55, Al0.45)N and (Ti0.34, Al0.66)N coatings are of fcc structure. The atomic ratios of Al against Ti for the two coatings are approximately close to those of the alloy targets according to EPMA measurement. In accordance with SEM observation, the fractured cross-section of (Ti0.55, Al0.45)N coating is characterized by dense columnar grain structure with most of grains extending from the interface of coating and substrate to the surface. SEM and TEM investigations show that the (Ti0.34, Al0.66)N coating indicates the nano-crystalline feature without appearance of the columnar structure. (Ti0.34, Al0.66)N coating exhibits higher microhardness and wear resistance, but lower adhesion with the substrate than (Ti0.55, Al0.45)N coating.