Influence of Al content on the phase formation, growth stress and mechanical properties of TiZrAlN coatings

Abstract

Quaternary (Ti,Zr)1−xAlxN transition metal nitride films, with Al content x ranging from 0 to 0.37, were reactively sputter-deposited from individual metallic targets under Ar+N2 plasma discharges on Si substrates at Ts=270°C. The influence of Al addition on the crystal structure, phase formation, growth morphology and intrinsic stress development, electrical and mechanical properties was systematically investigated. Three distinct compositional regions were evidenced: i) for 0≤x≤0.07, films develop a columnar structure consisting of cubic TiZr(Al)N grains with (111) and (200) preferred orientation, large compressive stresses up to ~−4GPa and hardness increase from ~20 to ~24GPa, ii) for 0.09≤x≤0.16, Al incorporation favors the growth of nanocomposite films consisting of (200)-oriented cubic TiZr(Al)N nanocrystals surrounded by a highly-disordered matrix, accompanied by a decrease of compressive stress, whereas a maximum hardness H~27GPa and H/E ratio of 0.105 is reached at x~0.12 and x=0.14, respectively, and iii) x>0.16, XRD amorphous films are formed, with reduced mechanical properties. The structure–stress-properties relationship is discussed based on evolutionary growth regimes induced by incorporating a high-mobility metal in a refractory compound lattice.