Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.

Microstructural evolution during film growth

Microstructural design of hard coatings

Different approaches to superhard coatings and nanocomposites

The paper is devoted to an assessment of the mechanical behavior of hard and superhard nanocomposite coatings from loading/unloading curves measured by a computer-controlled Fischerscope H 100 microhardness tester and a maximum depth d max of the diamond indenter impression into the coating at a given load L . It is shown that: (1) the area between the loading/unloading curve and the value of d max decreases with increasing (i) hardness H , (ii) effective Young's modulus E * = E /(1−ν 2 ) and (iii) universal hardness HU, where E and ν are the Young's modulus and the Poisson ratio, respectively; and (2) there is no simple relation between the mechanical response of the coating and H or E * alone; however, this response is strongly dependent on the ratio H / E * . The last fact gives a possibility of tailoring the mechanical properties of a coating for a given application, e.g. to prepare coatings with high hardness H , high resistance to plastic deformation (∼ H 3 / E *2 ), high elastic recovery W e , but with low E * and high d max . Special attention is also given to the analysis of problems in accurately measuring the hardness of superhard (≥60 GPa) coatings. It is shown that a high elastic recovery W e ≥80% of superhard films with H ≥60 GPa (1) strongly decreases the gradient d H /d L and (2) shifts the region L , where H ( L )≈constant and the hardness H is correctly measured, to higher values of L . This means that the lowest load L used in the hardness measurement must be higher than L used in measurements of coatings with H H measured from being significantly higher than the real hardness of the coating.

Relationships between hardness, Young's modulus and elastic recovery in hard nanocomposite coatings

The phenomenon of age hardening could be evidenced in thin film applications. A model system, Ti1-xAlxN was chosen as such coatings are known for their excellent wear resistance enabling improved m ...

Self-organized nanostructures in the Ti–Al–N system

The mechanical properties and machining performance of Ti 1− x Al x N-coated cutting tools have been investigated. Processing by arc evaporation using cathodes with a range of compositions was performed to obtain coatings with compositions x =0, x =0.25, x =0.33, x =0.50, x =0.66 and x =0.74. As-deposited coatings with x ≤0.66 had metastable cubic structures, whereas x =0.74 yielded two-phase coatings consisting of cubic and hexagonal structures. The as-deposited and isothermally annealed coatings were characterised by nanoindentation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cutting tests revealing tool wear mechanisms were also performed. Results show that the Al content, x , promotes a (200) preferred crystallographic orientation and has a large influence on the hardness of as-deposited coatings. The high hardness (∼37 GPa) and texture of the as-deposited Ti 1− x Al x N coatings are retained for annealing temperatures up to 950 °C, which indicates a superior stability of this system compared to TiN and Ti(C,N) coatings. We propose that competing mechanisms are responsible for the effectively constant hardness: softening by residual stress relaxation through lattice defect annihilation is balanced by hardening from formation of a coherent nanocomposite structure of c-TiN and c-AlN domains by spinodal decomposition. This example of secondary-phase transformation (age-) hardening is proposed as a new route for advanced surface engineering, and for the development of future generation hard coatings.

Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools

The thermal stability of Ti1−xAlxN films deposited by arc evaporation from Ti–Al cathodes with 67 and 75 at. % aluminum, respectively, has been investigated. The microstructure of as-deposited and ...

Thermal stability of arc evaporated high aluminum-content Ti1−xAlxN thin films

Influence of residual stresses on the mechanical properties of TiCxN1 x (x=0, 0.15, 0.45) thin films deposited by arc evaporation

TiCxN1-x films with x ranging from 0 to 1 were grown by arc evaporation by varying the flow ratio between the reactive gases. The substrates were cemented carbide inserts (WC-6 wt.% Co) which were negatively biased at 400 V, resulting in a deposition temperature of similar to 550 degrees C. The film composition, as measured by glow discharge optical emission spectroscopy, was found to vary almost linearly with the gas flow ratio. Cross-sectional transmission electron microscopy in combination with X-ray diffraction (XRD) showed that the films were of single-phase NaCl-structure with a dense columnar microstructure. The intrinsic stress analyzed using the XRD sin(2)psi method, was found to have a maximum of - 5.9 GPa in the composition range of 0.4 less than or equal to x less than or equal to 0.7 which correlated with a maximum in XRD peak broadening due to inhomogeneous strains. The hardness and Young's modulus of the as-deposited TiCxN1-x films were measured by the nanoindentation technique. A maximum in hardness of 45 GPa was found at the same composition range (0.4 Ix I 0.7) as the intrinsic stress maximum. The hardness for x = 0 (TiN) and x = 1 (TiC) were found to be 28 and 36 GPa, respectively. The Young's modulus was constant similar to 610 GPa for films with compositions up to x = 0.6, thereafter it decreased to 540 GPa at x = 1. The increase in intrinsic stress with increasing carbon content is suggested to be due to increased stability of defects created from the collision cascade or/and by a change in the defect structure itself. The fact that hardness showed a maximum at the same composition as residual stress and FWHM indicates that obstruction on dislocation movement has a major influence on the hardness of these films. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Lennart Karlsson

Papers

Self-organized nanostructures in the Ti–Al–N system

Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools

Thermal stability of arc evaporated high aluminum-content Ti1−xAlxN thin films

Influence of residual stresses on the mechanical properties of TiCxN1 x (x=0, 0.15, 0.45) thin films deposited by arc evaporation

Growth, microstructure, and mechanical properties of arc evaporated TiCxN1-x (0 <= x <= 1) films