Effect of chemical composition, defect structure, and stress state on the elastic properties of (V_1−x Al _x )_1−yN _y

Abstract

For (V 1−x Al x ) 1−y N y an extensive and theoretically unexplained spread in experimentally obtained elastic moduli ranging from 254 to 599 GPa is reported in literature. To identify its origin, the effect of chemical composition (0 ⩽ x ⩽ 0.75), non-metal to metal ratio (N/Mratio: 0.48 ⩽ y ⩽ 0.52), and stress state (−6 ⩽ σ ⩽ 2 GPa) on the elastic modulus at room temperature is studied sytematically by density functional theory employing the Debye-Grüneisen model. As the Al concentration is increased from x = 0 to x = 0.75, strong Al-N sp 3 d 2 hybridization causes an increase in elastic modulus of 26%. The effect of the N/M-ratio on the elastic properties is also Al content dependent. As y is increased from y = 0.50 to y = 0.52, decreasing bond distance upon vacancy formation causes an anomalous increase in the elastic modulus of 6% for V 1−y N y , while a decrease in elastic modulus of up to 5% occurs for (V 1−x Al x ) 1−y N y . A stress state variation from +2 to −6 GPa increases the elastic modulus e.g. for (V 0.5 Al 0.5 ) 0.5 N 0.5 by 70 GPa and hence 13% due to shifts in density of states towards lower energies implying bond strengthening. Thus, it is suggested that the extensive spread of 58% in reported elastic moduli for (V 1−x Al x ) 1−y N y can at least in part be rationalized based on variations in chemical composition, off-stoichiometry induced point defects, and stress state.

Structure, stress, and mechanical properties of Mo-Al-N thin films deposited by dc reactive magnetron cosputtering: Role of point defects

“…Here, when the ternary Mo 1−x Al x N solid solution is formed, the influence of vacancy concentration (10% V Me or V N are considered here) on C 44 is more complex and may change as a function of Al fraction. A complex dependence of the elastic properties of V 1−x Al x N y alloys to point defect and Al content was also reported recently by Rueß et al 68 using DFT calculations.…”

Orientation dependence of the fracture mechanisms in (V,Al)N coatings determined by micropillar compression

“…Transition metal nitride (TMN) and boride protective coatings have already been valued for several years in technical processes because of their excellent properties, such as high hardness and elasticity [1][2][3][4], high thermal stability [5] and good electrical conductivity [6][7][8]. The application as thin protective layers deposited by physical vapour deposition (PVD) has therefore already been investigated towards its applicability for various industrial applications [9][10][11][12].…”

“…Measurements of hardness and stiffness of thin coatings are usually carried out by means of nanoindentation [20][21][22][23][24]. Several studies have investigated nitride systems similar to the (V,Al)N coatings used here, including the binary systems VN [1], CrN [25] and TiN [26] as well as the ternary systems (X,Al)N with X = V, Cr, Ti [1,25,27,28], so that Young's Article modulus, and hardness are known in addition to lattice parameters. It was found that thin films usually have a slightly higher hardness than the corresponding bulk material [29] and the cubic ternary films with higher Al content also show a higher hardness [5,29,30] but a more brittle behaviour [31] as long as they have the same crystal structure.…”