Papers by Paul H Mayrhofer
Applied Physics Letters, 2015
We combine continuum mechanics modeling and wafer curvature experiments to characterize the therm... more We combine continuum mechanics modeling and wafer curvature experiments to characterize the thermal expansion coefficient of AlN in its metastable cubic rock-salt (B1) structure. The latter was stabilized as nm thin layers by coherency strains in CrN/AlN epitaxial multilayers deposited on Si (100) substrates using reactive magnetron sputtering. The extraction of the B1-AlN thermal expansion coefficient, from experimentally recorded temperature dependent wafer curvature data, is formulated as an inverse problem using continuum mechanics modeling. The results are crossvalidated by density functional theory calculations. V
Calphad, 2017
Based on the experimental equilibrium data on spinodal decomposition in the literature together w... more Based on the experimental equilibrium data on spinodal decomposition in the literature together with the newly measured data in the present work, a complete metastable phase diagram for the pseudo-binary c-TiN/c-AlN system was constructed for the first time, from which a self-consistent thermodynamic description was then established by means of CALculation of PHAse Diagram (CALPHAD) method with the aid of first-principles computed free energies. By coupling with the CALPHAD thermodynamic database, two-and three-dimensional quantitative numerical simulations of microstructure evolution in metastable c-Ti 1−x Al x N coatings during spinodal decomposition were performed using Cahn-Hilliard model. Three sets of diffusivity data available in the literature were carefully screened by comparing the simulated microstructures with the experimental ones, and one of them was chosen for the final simulations. The simulated composition wavelengths during spinodal decomposition at different temperatures agree with the experimental data. Moreover, the effect of the composition fluctuation on the microstructure evolution during spinodal decomposition was also comprehensively investigated.
Surface and Coatings Technology, 2017
Alloying a fourth substantial element to Ti-Al-N coatings is a promising approach to tailor their... more Alloying a fourth substantial element to Ti-Al-N coatings is a promising approach to tailor their properties. Within this work, the effect of Ta-addition and multilayer architecture on structure, mechanical and thermal properties of arc-evaporated Ti-Al-N was investigated. The addition of Ta to Ti-Al-N coatings with chemical compositions right at the border for the face centered cubic metastable solubility limitation, can promote the formation of undesired hexagonal phases. Thereby, also the hardness further decreases from ~27.2 GPa for Ti 0.42 Al 0.58 N (with a small fraction of hexagonal phases) to 26.2 GPa for Ti 0.40 Al 0.54 Ta 0.06 N and 24.9 GPa for Ti 0.34 Al 0.54 Ta 0.12 N, due to their increased fraction of hexagonal phases. Nevertheless, the Ta-alloyed coatings exhibit higher hardness after vacuum annealing above 1000 °C. When fully stabilizing these Ta-containing nitrides in their face centered cubic structure through a multilayer arrangement with Ti 0.52 Al 0.48 N layers, the hardness can significantly be increased to ~32.8 GPa for Ti 0.40 Al 0.54 Ta 0.06 N/Ti 0.52 Al 0.48 N and ~34.3 GPa for Ti 0.34 Al 0.54 Ta 0.12 N/Ti 0.52 Al 0.48 N. These multilayers are also superior during the whole temperature range of vacuum annealing up to 1200 °C. Furthermore, only the Ta-containing coatings (monolithically or multilayered) can survive the 20 h exposure to ambient air at 900 °C.
International Journal of Materials Research, 2009
The influence of varying substrate temperature, N2 partial pressure, ion energy, and ion-to-Ti fl... more The influence of varying substrate temperature, N2 partial pressure, ion energy, and ion-to-Ti flux ratio on the texture development and mechanical properties of TiN is investigated in detail. We show that during low substrate temperature (T s = 300 °C) reactive sputtering of TiN in a mixed Ar + N2 discharge a change from 111- to 001-oriented growth occurs when increasing the ion-to-Ti ratio J i/J Ti above 2.5 while using a low ion energy E i of 30 eV. This texture change can be reversed to a 111-oriented growth by increasing the ion energy to 60 and 90 eV when using high ion-to-Ti ratios J i/J Ti of 2.5 and 9, without introducing strain. Thereby the hardness can be increased from ∼31 to 37 GPa with only minor changes in compressive stresses. Consequently, by defining the ion-to-Ti ratio and the ion energy during low substrate temperature reactive sputtering of TiN the texture development towards 111- or 001-oriented growth can be controlled. Based on previous studies and the textur...
Surface and Coatings Technology, 2018
The microstructural development of reactively sputter-deposited tantalum nitride thin films is in... more The microstructural development of reactively sputter-deposited tantalum nitride thin films is investigated as a function of the N 2-to-total-pressure ratio (p N2 /p T) and the operating mode of the metallic tantalum cathode; by direct current magnetron sputtering (DCMS), pulsed DCMS, and high power impulse magnetron sputtering (HiPIMS). For all sputtering modes investigated, the phase evolution of the TaN films strongly depends on the nitrogen partial pressure, p N2 , used when keeping the total pressure, p T , constant at 0.3 or 0.6 Pa. The major crystalline phases identified, with increasing the p N2 /p T-ratio, are α-Ta, orthorhombic o-Ta 4 N, hexagonal close packed (hcp) γ-Ta 2 N, face centred cubic δ-TaN, and hcp ε-TaN. Their development is basically determined by the N 2 partial pressure present. The deposition rate decreases slowest with increasing p N2 for the HiPIMS mode and fastest for the DCMS mode. The coatings with a dominating γ-Ta 2 N phase (which could be obtained for p N2 between 0.08 and 0.15 Pa) exhibit the highest hardness with 38.2 ± 4.6 GPa (HiPIMS), 38.0 ± 2.3 GPa (pulsed DCMS), and 40.0 ± 3.8 GPa (DCMS) among all samples studied. Higher p N2 lead to the formation of δ-and ε-TaN phases and a reduction in hardness. Especially, the ε-TaN rich coatings are comparably soft with only ~20 GPa. Based on our results we can conclude that coatings dominated by Ta-rich o-Ta 4 N or γ-Ta 2 N phases exhibit the most favourable mechanical properties, according to which the most important p N2-range is between 0.04 and 0.15 Pa, as for higher N 2-partial pressures the films undergo a transformation from γ-Ta 2 N (plus o-Ta 4 N) into mixed δ-and ε-TaN.
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Papers by Paul H Mayrhofer