TiAlN Thin Films Research Articles

Influence of residual stress on mechanical properties of TiAlN thin films

Mechanical properties of TiAlN thin films with different residual stress, which were fabricated with magnetic filtered vacuum arc evaporation deposition method on silicon substrate, have been investigated. The mechanical properties of TiAlN thin films vary with the residual stress existed in TiAlN thin film. For a lower residual stress, the nanoindentation hardness (H) and modulus (Er) of TiAlN thin film are 18.96 and 210.16GPa respectively. With the increasing of the residual stress, the H and Er of TiAlN thin film decline from 18.96 and 210.16 GPa to 16.9 and 185.9GPa respectively. High residual stress induces the decreasing of the H and Er of TiAlN thin film. The empirical expressions of H and Er versus the mean residual compressive stress (σ) have been obtained for the TiAlN thin films.

Strain evolution during spinodal decomposition of TiAlN thin films

We use a combination of in-situ X-ray scattering experiments during annealing and phase-field simulations to study the strain and microstructure evolution during decomposition of TiAlN thin films. The evolved microstructure is observed to depend on the initial alloy composition, where the microstructure is finer and the TiN and AlN domains formed are more interconnected and aligned in the [100] directions in the higher Al content film. The simulations show strain formation in the evolving cubic AlN and TiN domains, which is a combined effect of increasing lattice mismatch and elastic incompatibility between the domains. The experimental results show that the strain of the film is a result of defect density, thermal strains, and the phase evolution during decomposition of the cubic TiAlN. The compressive strain increases at temperatures above ~850°C for Ti0.35Al0.65N and above ~930°C for Ti0.53Al0.47N due to the onset of transformation to hexagonal-AlN, which is similar to the temperature where the maximum hardness of similar TiAlN films has been found. The higher driving force for decomposition in the higher Al content film results in a higher decomposition rate revealed by the simulations and earlier formation of hexagonal-AlN in this film.

Origin of the nitrogen over- and understoichiometry in Ti0.5Al0.5N thin films

To identify the origin of the experimentally observed nitrogen over- and understoichiometry in TiAlN thin films, various point defect configurations were studied by ab initio calculations in terms of formation energies, equilibrium volume and elastic moduli. From formation energies and comparison to existing experimental equilibrium volume and elasticity data, it is shown that nitrogen vacancies and metal vacancies are responsible for nitrogen understoichiometry and overstoichiometry, respectively. Irrespective of the type of vacancies, the bulk modulus is decreased by approximately 7% as the nitrogen concentration is increased or decreased by 3 at.%.

Effect of Hf on structure and age hardening of Ti–Al-N thin films

Protective coatings for high temperature applications, as present e.g. during cutting and milling operations, require excellent mechanical and thermal properties during work load. The Ti1−xAlxN system is industrially well acknowledged as it covers some of these requirements, and even exhibits increasing hardness with increasing temperature in its cubic modification, known as age hardening. The thermally activated diffusion at high temperatures however enables for the formation of wurtzite AlN, which causes a rapid reduction of mechanical properties in Ti1−xAlxN coatings. The present work investigates the possibility to increase the formation temperature of w-AlN due to Hf alloying up to 10at.% at the metal sublattice of Ti1−xAlxN films. Ab initio predictions on the phase stability and decomposition products of quaternary Ti1−x−yAlxHfyN alloys, as well as the ternary Ti1−xAlxN, Hf1−xAlxN and Ti1−zHfzN systems, facilitate the interpretation of the experimental findings. Vacuum annealing treatments from 600 to 1100°C indicate that the isostructural decomposition, which is responsible for age hardening, of the Ti1−x−yAlxHfyN films starts at lower temperatures than the ternary Ti1−xAlxN coating. However, the formation of a dual phase structure of c-Ti1−zHfzN (with z=y/(1−x)) and w-AlN is shifted to ~200°C higher temperatures, thus retaining a film hardness of ~40GPa up to ~1100°C, while the Hf free films reach the respective hardness maximum of ~38GPa already at ~900°C. Additional annealing experiments at 850 and 950°C for 20h indicate a substantial improvement of the oxidation resistance with increasing amount of Hf in Ti1−x−yAlxHfyN.

Multipass scratch test behaviour of TiAlN thin film deposited on 316L stainless steel and Ti6Al4V alloy with dc biased and pulsed magnetron sputtering

In this study, TiAlN thin film was deposited with dc magnetron sputtering on 316L stainless steel and Ti6Al4V alloy which are widely used as hip joint implants. The adhesion behaviour of TiAlN thin films was investigated by multipass scratch tester. Multipass scratching with three progressive loads was performed on each sample. Observations of the scratch tests showed that there were three main failure events which were identified and labelled as Lc1, Lc2 and Lc3. Failure mechanisms were discussed according to SEM examinations of the scratch tracks. The TiAlN films with dense and homogeneous structure preferentially grew on the plane of (200) for 316L stainless steel and (111) for Ti6Al4V alloy. During the multipass scratch test, the friction coefficients were measured between 0·02 and 0·05. The best values for the friction coefficient were obtained from the films preferentially deposited on the plane of (111). After the scratch test, the thin film was damaged by mechanisms of chipping, flaking and spalling.

Cavitation Erosion of 6061 Aluminum Alloy Coated with TiAlN Thin Film

Cavitation erosion is one of the major problems to be solved in hydraulic machinery. Propellers of high speed boats require a light weight metallic material for their improved high performance. This example tells us that solutions are the developments of way for the improvement of cavitation erosion resistance of light weight metallic material. Coatings on aluminum alloy can enhance the cavitation erosion resistance. This study discussed the cavitation erosion behavior of 6061 aluminum alloy coated with TiAlN thin film. TiAlN coatings were deposited by DC magnetron sputtering method at various nitrogen partial pressures of the coating process using Ti based alloy cathode. The composition of target material was 90wt%Ti, 6wt%Al and 4wt%V. Using the TiAlN coated 6061 aluminum alloy specimen, cavitation erosion tests were carried out to investigate its resistance to the ultrasonic cavitation erosion. Prior to and after the tests, the specimen surfaces were analyzed by using the surface analysis techniques such as micro-hardness test, AFM, SEM, GXRD and scratch test to measure the microstructure of thin film and bonding properties of the applied TiAlN coatings to the substrate material. An improvement in cavitation erosion resistance could be seen with TiAlN coating on 6061 aluminum alloy. Especially, the coating at a nitrogen flow rate of 0.85 sccm or more were very effective in reducing the surface cavitation erosion from the ultrasonic cavitation. In the observation of surface damages during the cavitation erosion tests, the surface cracks in TiAlN were created by the bending of TiAlN coating which were resulted from the plastic deformation of the soft substrate material of aluminum alloy. Once the cracks initiate, drastic delaminations of TiAlN from the substrate material occured. The mean depth erosion rate (MDER) could be evaluated by critical and delamination loads measured by scratch test.

Oxidation Behavior of Nanostructured TiAlN and AlCrN Thin Coatings on ASTM-SA213-T-22 Boiler Steel

Metals and alloys gets oxidized when exposed to elevated temperatures in air or highly oxidizing environments, such as combustion gas with excess of air or oxygen. They often rely on the oxidation reaction to develop a protective oxide scale to resist corrosion attack. In the present study, nanostructured TiAlN and AlCrN thin films were deposited by physical vapour deposition process on T-22 boiler steel (ASTM-SA213-T-22). Cyclic oxidation studies in air were conducted at 900°C temperature in the laboratory using silicon carbide furnace. The weight gain was measured after each cycle and visually examined the surface morphology of the oxidized samples was studied using FE-SEM with EDAX attachment and XRD analysis. The results obtained showed the better performance of AlCrN coated T-22 boiler steels then the TiAlN coated and uncoated T-22 boiler steel.

Wear and corrosion behaviour of various surface treated medical grade titanium alloy in bio-simulated environment

Ti6Al4V alloy has been widely used as a suitable material for surgical implants such as artificial hip joints. Although this alloy is biocompatible, its wear resistance is inadequate. Therefore, three different surface treatments which were plasma nitriding, TiAlN thin film deposition by closed field unbalanced magnetron sputtering (CFUBMS) and Al 2O 3 coating using plasma spray method were applied to the alloy to improve the tribological and electrochemical properties. To simulate human body environment, wear experiments were performed by using pin-on-disc tribotester in Ringer's solution at 37 °C. Moreover, potentiodynamic corrosion tests were carried out in Ringer's solution. It was observed that each three surface treatments improved wear and corrosion resistance of Ti6Al4V alloy.

Surface brillouin scattering in opaque thin films

Simulations of surface Brillouin scattering (SBS) spectra of TiN, TiAlN, TiC and SiC thin hard films on silicon and diamond substrates have been carried out over a range of film thickness from 5nm to 1000nm. The simulations are based on the elastodynamic Green's function method that predicts the surface displacement amplitudes of acoustic phonons. These simulations provide information essential to understand and analyze experimental data emerging from SBS experiments currently in progress. There are striking differences in the simulated SBS spectra depending on the respective elastic properties of the film and the substrate. In fast on slow situations, the Rayleigh mode is accompanied by broadened resonances; in slow on fast situations, several orders of Sezawa modes are observed together with the Rayleigh mode and sharper resonances. In each case, use of a diamond substrate clearly provides optimal slow on fast conditions. Experimental studies are on process to demonstrate these effects. The velocity dispersion of the modes as a function of the product of surface wavevector and thickness (k//d) has also been simulated, allowing the elastic constants of the films to be determined.

Deposition of single-crystal Ti2AlN thin films by reactive magnetron sputtering from a 2Ti:Al compound target

Single-crystal Ti2AlN (0001) thin films were grown on (111) oriented MgO substrates kept at 830°C by ultrahigh vacuum dc reactive magnetron sputtering from a compound 2Ti:Al target in a mixed Ar∕N2 discharge. The effects of variations in the nitrogen partial pressure on the phase composition of the films were studied. Results from transmission electron microscopy, x-ray diffraction, and elastic recoil detection analysis show a narrow region for growth of Ti2AlN MAX phase with respect to the nitrogen content in the discharge. Perovskite Ti3AlN and intermetallic Ti3Al and TiAl phases dominate at nitrogen depletion. For overstoichiometric deposition conditions with respect to Ti2AlN, a phase mixture with NaCl-structured TiN is obtained. Epitaxial growth is observed with a layer-by-layer mode on the 0001 basal planes for all phases. A superstructure in the TiN phase is also observed along [111] with the repetition distance of 7.34Å, most likely related to Al segregation. Nanoindentation shows that the film hardness increases from 11to27GPa with increasing nitrogen content and corresponding phase transformations from Ti–Al intermetallics to Ti3AlN, Ti2AlN, and TiN.

Nucleation and growth of Ti2AlN thin films deposited by reactive magnetron sputtering onto MgO(111)

The nucleation and growth of Ti2AlN thin films on MgO(111) substrates during dual direct current reactive magnetron cosputtering from Ti and Al targets in an Ar∕N2 atmosphere at a substrate temperature of 690 °C have been investigated. Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy reveal the formation of competing phases for slight N superstoichiometry with respect to Ti2AlN. The stoichiometry deviations initiate the layer-by-layer growth of a ∼380 Å thick epitaxial N-substoichiometric cubic (Ti1−xAlx)Ny layer. N-vacancy driven diffusion of Ti and Al leads to decomposition of this metastable solid solution into nanosized cubic TiNy′ and AlNy″ domains as well as to a solid-state reaction with the MgO(111) by formation of a Mg2(Al:Ti)O4 spinel, reducing the transformed (Ti1−xAlx)Ny layer thickness down to ∼60 Å. Local AlNy″ domains serve as templates for Ti2AlN nucleation at higher thicknesses. At the same time TiNy′ and AlNy″ serve as a sink for excess gas phase N during the subsequent polycrystalline Ti2AlN growth with random (Ti1−xAlx)Ny renucleation as a tissue phase along Ti2AlN grain boundaries. The individual Ti2AlN grains with vertical sizes up to the total thickness retain local epitaxy to the substrate, with basal planes nonparallel to the substrate interface. Concurrently the (Ti1−xAlx)Ny layer is further reduced by inward Ti2AlN grain growth along the basal planes.

Off-axis texture in nanostructured Ti 1 − xAl xN thin films

Standard θ-2 θ and pole figure X-ray diffraction techniques were used to study structural properties and preferred orientation of nanostructured TiAlN thin films prepared using cathodic arc deposition. Systematic collection of reflections from lattice planes {111}, {200}, {220}, and {311} showed that the in-plane orientation of crystallites exhibits cylindrical symmetry with random distribution of crystallites, while the out-of-plane growth presents strong texture which is inclined with respect to the surface normal. This brings the crystallographic orientation of fibre texture towards high indices lattice planes (113) and (115) contrary to traditionally grown films that develop a preferred orientation following to low indices close-packed planes (111) and (200). The origin of inclined growth is discussed taking into account the role of crystallographic defects in particular twin faults that develop in the lattice of growing crystal and change the stacking sequences of atom layers.

Properties of TiAl and TiAlN Thin Films by Pulsed Cathodic ARC

TiAl and TiAlN thin films are deposited on glassy carbon and Si substrates by the pulsed cathodic arc deposition process. In our pulsed cathodic arc system, because the spatial position of plasma on the surface of the evaporation source can be controlled by pulsed arc discharge, the thickness of the TiAl and TiAlN films can be controlled at nanometer scale. Amorphous stoichiometric Ti-Al films are synthesized from one Ti-Al alloy target at room temperature by changing the number of pulses of the arc discharge.

Electronic Structure Investigation of MAX-Phases by Soft X-ray Emission Spectroscopy

AbstractThe electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAX-phase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.

Oxidation and wear behaviors of Ti-based thin films

The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO 2) at their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear tests with alumina ball were characterized to identify the compounds, particularly titanium oxides, to gain a better understanding of the tribochemical reactions. The coatings that were examined include TiN, TiCN (N rich), TiCN (C rich), TiAlN, AlTiN, TiSiN, and TiCNO thin films. These coatings were characterized using Raman spectroscopy, scanning electron microscopy, and X-Ray diffractometer. The results show that TiSiN and AlTiN have the highest oxidation resistance, comparing with other coatings. As for the analyses of wear debris, all of the Ti-based coatings are worn by the mechanism of forming TiO 2, except AlTiN. AlTiN is worn by ploughing wear.

Phase stability of epitaxially grown Ti2AlN thin films

The phase stability of Mn+1AXn phase (M: early transition metal, A: A-group element, and X: C and∕or N) Ti2AlN thin films reactively sputtered onto MgO(111) and Al2O3(0001) substrates has been investigated by in situ x-ray diffraction and Rutherford backscattering. High substrate temperature deposition results in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. In contrast to reported high thermal stability for bulk Ti–Al–N Mn+1AXn phases in air, Ti2AlN thin films in vacuum decompose already at ∼800°C. The decomposition proceeds by outward Al diffusion and evaporation, followed by detwinning of the as-formed Ti2N atomic layers into cubic TiNx and intermediate phases.

Characterisation of TiN and TiAlN thin films deposited on ground surfaces using focused ion beam milling

TiN and TiAlN/TiN PVD coatings deposited onto as-ground surfaces have been characterised via direct cross-sectional imaging and transmission electron microscopy with the aid of a focused ion beam system. Cross-sections showed that the coatings exhibit consistent coverage, even in sheltered areas such as at the base of grooves resulting from prior grinding. A columnar grain structure was observed in all coatings. A number of defects were observed such as seams and voids resulting from coating onto the as-ground surface and macroparticles which were shown to be deposited during the metal ion etching stage. Cross-sections through nanoindents revealed that the coatings deform by through-thickness shear cracking.

Evaluation of Internal Stresses in Single-, Double- and Multi-Layered TiN and TiAlN Thin Films by Synchrotron Radiation

Evaluation of Internal Stresses in Single-, Double- and Multi-Layered TiN and TiAlN Thin Films by Synchrotron Radiation

A possibility of application of MTDIL to the Residual stresses analysis

The work demonstrates a proof of application of the modulated-temperature dilatometry (MTDIL) to the stresses investigations of the well known and commonly used hard coatings e.g. TiN, TiCN, TiAlN thin films deposited mainly on different type of tools for its higher performances. In the PVD (physical vapour deposition) processes such kind of coatings are formed in meta stable state caused, between other, by strong stresses between coating and substrate. These stresses have an important influence on the fundamental properties of the coatings, for example, adherence to the substrate, so they are the subject of many investigations by use of different methods, mainly XRD (X-ray diffraction). For the purpose of presentation of application of MTDIL for such kind of investigation two reference substrate materials were chosen: ARMCO steel and cemented carbide in the form suitable for dilatometric analysis covered, by actually the most conventional, TiN hard coating. In the article the experimental results are presented, discussed and compared with simple model formed by means of finite elements method (FEM).

Transmission electron microscopy of TiN and TiAlN thin films using specimens prepared by focused ion beam milling

The microstructures of a series of TiN and TiAlN wear resistant coatings on steel substrates are characterized using cross-sectional transmission electron microscopy. TiN coatings were deposited using both low-voltage electron beam evaporation and cathodic arc techniques, and a dual-layer TiN–TiAlN coating was prepared using cathodic arc deposition. All of the coatings consisted of columnar grains separated by high-angle grain boundaries. In all specimens, the substrate/coating interface was sharp and no Ti interlayer or modification of the substrate was observed. The TiN/TiAlN dual-layer coating contained a layered interfacial region where both the Ti and TiAl sources were operating concurrently. The TiAlN regions consisted of extremely fine sub-layers ∼2 nm thick, which are thought to result from the threefold planetary rotation of the specimen in the deposition chamber. The columnar grains grew epitaxially through the entire TiN/TiAlN interfacial region. TEM specimens were prepared using the focused ion beam, which allowed large, uniformly thin areas to be prepared with relative ease.