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

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 ~− 4 GPa and hardness increase from ~ 20 to ~ 24 GPa, 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 ~ 27 GPa 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.

► Quaternary (Ti,Zr)1 − xAlxN magnetron sputtered films are studied up to x = 0.37. ► Drastic change in structure is revealed depending on compositional range. ► Al addition inhibits TiZrN grain growth and favors a (200) preferred orientation. ► In situ stress measurements reveal a non-monotonous Al content dependency. ► A maximum hardness value of H = 27 GPa is obtained at x ~ 0.12 (nanocomposite region).