Abstract
Ion irradiation-induced changes in the structure and mechanical properties of metastable cubic (V,Al)N deposited by reactive high power pulsed magnetron sputtering are systematically investigated by correlating experiments and theory in the ion kinetic energy (Ek) range from 4 to 154 eV. Increasing Ek results in film densification and the evolution from a columnar (111) oriented structure at Ek ≤ 24 eV to a fine-grained structure with (100) preferred orientation for Ek ≥ 104 eV. Furthermore, the compressive intrinsic stress increases by 336 % to -4.8 GPa as Ek is increased from 4 to 104 eV. Higher ion kinetic energy causes stress relaxation to -2.7 GPa at 154 eV. These ion irradiation-induced changes in the thin film stress state are in good agreement with density functional theory simulations. Furthermore, the measured elastic moduli of (V,Al)N thin films exhibit no significant dependence on Ek. The apparent independence of the elastic modulus on Ek can be rationalized by considering the concurrent and balancing effects of bombardment-induced formation of Frenkel pairs (causing a decrease in elastic modulus) and evolution of compressive intrinsic stress (causing an increase in elastic modulus). Hence, the evolution of the film stresses and mechanical properties can be understood based on the complex interplay of ion irradiation-induced defect generation and annihilation.
Highlights
Cubic transition metal aluminum nitrides ((c-(TM,Al)N), space group Fm3 ̄ m, NaCl prototype structure) are commonly employed as protective coatings for forming and cutting applications due to their superior oxidation resistance [1,2], high thermal stability [3], high hardness and elasticity [4,5], and low wear [2]
The results reveal that ion irradiation-induced formation and annihilation of point defects define the stress state evolution and the elasticity of c-(V,Al)N
The influence of the ion kinetic energy ( Ek) on the structure evolution and mechanical properties of (V,Al)N layers deposited by high power pulsed magnetron sputtering (HPPMS) has been systematically investigated by correlation of experiments and Density functional theory (DFT) simulations
Summary
Cubic transition metal aluminum nitrides ((c-(TM,Al)N), space group Fm3 ̄ m, NaCl prototype structure) are commonly employed as protective coatings for forming and cutting applications due to their superior oxidation resistance [1,2], high thermal stability [3], high hardness and elasticity [4,5], and low wear [2]. Ion irradiation-induced defect formation has been discussed in the literature [22,31,37], very little is known about the nature of point defects and defect clusters generated during the interaction of plasma with the growing film surface and how these defects contribute to the stress state evolution. Music et al [27] developed a theoretical approach, known as DFT based thermal spike model, to explicitly take into account ion irradiation with Ek > 100 eV and its influence on the final defect structure, density, thermally induced stress state, and elastic properties.
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