Investigation of fundamental deformation parameters on TiAlN films of different chemical composition and crystallographic structure using high-temperature nanoindentation

Malcolm Werchota

Research output: ThesisDiploma Thesispeer-review

48 Downloads (Pure)

Abstract

Metal nitrides, such as TiAlN films are one of the most common hard ceramic coatings in use today. These are primarily used as wear-resistant coatings for cutting tools, to improve among others, resistance to wear, oxidation and corrosion properties. Investigation at high temperatures, where dislocation activity is more significant, is therefore sensible. Using high temperature (HT) nanoindentation the typical hardness (H) and Young’s modulus (E) measurements were extended to calculate and extract the fundamental deformation parameters, such as activation volumes (V*) and activation energies (ΔGtot). For this investigation near-to epitaxial TiAlN films were grown on MgO single crystals (110) using a reactive magnetron sputtering system. After a multitude of pre-deposition runs, single-phased films with the following chemical compositions were achieved and analyzed: cubic-Ti0.44Al0.56N, cubic-Ti0.68Al0.32N and wurtzite-Ti0.36Al0.64N. Additionally cubic-Ti0.44Al0.56N was annealed at 600°C for 24 hours. HT-nanoindentation experiments were carried out in a temperature range from 25 - 350°C at 3 different loading rates of 0.5, 1 and 10 mN/s using a Berkovich indenter. Hardness values of the all cubic samples were stable(at ~28 GPa for cubic Ti0.68Al0.32N and Ti0.44Al0.56N, and ~28 GPa fort he annealed cubic Ti0.44Al0.56N) in the measured temperature range, with a slight decrease at 350°C. The H values of the wurtzite sample on the other hand decreased continuously from 19.8 ± 0.9 GPa at 25°C to 16.9 ± 1.4 GPa at 350°C. Young’s modulus values for all samples remained constant throughout the temperature range: 344 ± 34 GPa for c-Ti0.68Al0.32N, 336 ± 23 GPa for c-Ti0.44Al0.56N-as-deposited, 356 ± 21 GPa for c-Ti0.44Al0.56N-annealed and 219 ± 11 GPa for the wurtzite-Ti0.36Al0.64N. H values of the films were found to be strain rate sensitive at all temperatures, leading to an increase of up to 20% for the cubic films, when tested with 10mN/s. Dislocation activation volumes values, V*, for the cubic sample were in the range of 0.18 to 0.79 b3. V* values for the wurtzite sample were larger, ranging from 0.24 to 1.22 b3. The activation volume of the annealed sample only rose slightly compared to other samples. Ab-initio calculations using the VASP package showed that 1.63% rise of V* in the tested temperature range is due to thermal expansion. For further comparison purposes, V* values were determined for bulk-aluminium at room temperature using a population density function (PDF). V* values ranged between 0-4 b3 for the cubic films and 0-25 b3 for bulk-aluminium, which is a clear indication for a different deformation mechanism than present in ceramic films. Similarly to the V* values, ΔGtot for the cubic and wurtzite samples were very close and ranged between 0.19 and 0.86 eV. ΔGtot values rose linearly with the temperature, whereby both the thermal and the mechanical work equally influenced the calculated values. XRD analysis on powder samples of cubic-Ti0.44Al0.56N before and after annealing, indicates an increase of the integral width from 0.55 to 0.59 suggesting ongoing spinodal decomposition to form Ti- and Al-rich cubic domains. Summing up for the tested temperature range, the crystallographic structure of TiAlN films had the largest influence on all measured parameters. Calculation of the activation energies show that the obstacles encountered by moving dislocations are of weak nature and that lattice-resistance can be determined as rate-controlling deformation mechanism, due to the stiff nature of hard ceramic films, as V* values were smaller than the volume of one dislocation, E values were constant and ΔGtot of very low order. For soft bulk-aluminium dislocation-dislocation interaction was determined. This investigation proved that high temperature nanoindentation can be used to successfully extract fundamental deformation parameters and to conclude,
Translated title of the contributionUntersuchung der Verformungsparameter von TiAlN Schichten in Abhängigkeit ihrer chemischen Zusammensetzung und crystallographischen Orientierung mittels Hochtemperaturnanoindentierung
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Mayrhofer, Paul Heinz, Supervisor (internal)
Award date17 Dec 2010
Publication statusPublished - 2010

Bibliographical note

embargoed until null

Keywords

  • TiAlN
  • HT nanoindentation
  • dislocation activation volume
  • rate controlling mechanism

Cite this