Dependence of protective effect of Ti1–xAlxN coatings in 3 wt.% NaCl solution on dissolution mechanism of their phases c-Ti0.5Al0.5N, c-AlN, and c-TiN

Abstract

The dissolution mechanism of phases c-Ti_0.5Al_0.5N, c-aluminium nitride (AlN), c-TiN, and Al₂Ti, and elements of the Ti_1–xAl_xN coatings (for x < 0.6) in 3 wt.% NaCl solution is described based on the results of X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and scanning electron microscope and previous electrochemical tests. Researchers studied the protective effectiveness of Ti_1–xAl_xN coatings in 3 wt.% NaCl solution by analyzing the factors: composition, thickness, porosity, total energy of ground state, stresses, structure, and texture. It was first established that the additional c-TiN phase with R_pmax and E_cormax, and secondary phase Ti_0.70–0.82N formed after Al's dissolution in the main phase c-Ti_0.5Al_0.5N increases the N content and prevents the Ti dissolution in the Ti_1–xAl_xN coatings. The phase c-AlN with i_cormin reduces the dissolution rate of Al in the c-Ti_0.5Al_0.5N phase. The stoichiometric c-Ti_0.5Al_0.5N is the most thermodynamically stable phase. The described phase transformations in Ti_1–xAl_xN coatings during phases dissolution in 3 wt.% NaCl can predict the coating protective effect. A multilayer coating with layers of c-AlN, c-TiN, and c-Ti_0.5Al_0.5N is recommended for industrial use.