This paper describes details of the spinodal decomposition and coarsening in metastable cubic Ti0.33Al0.67N and Ti0.50Al0.50N coatings during isothermal annealing, studied by in-situ small angle x-ray scattering, in combination with phase field simulations. We show that the isostructural decomposition occurs in two stages. During the initial stage, spinodal decomposition, of the Ti0.50Al0.50N alloy, the phase separation proceeds with a constant compositional wavelength of ∼2.8 nm of the AlN- and TiN-rich domains. The time for spinodal decomposition depends on annealing temperature as well as alloy composition. After the spinodal decomposition, the coherent cubic AlN- and TiN-rich domains coarsen. The coarsening rate is kinetically limited by diffusion, which allowed us to estimate the diffusivity and activation energy of the metals to 1.4 × 10−6 m2 s−1 and 3.14 eV at−1, respectively.

In the present work, we have studied the decomposition of arc-evaporated Ti 0.55 Al 0.45 N and Ti 0.36 Al 0.64 N during heat treatments in vacuum by in situ synchrotron wide-angle X-ray scattering primarily to characterize the kinetics of the phase transformation of AlN from the cubic (c) NaCl structure to the hexagonal (h) wurtzite structure. In addition, in situ small-angle X-ray scattering measurements were conducted to explore details of the wavelength evolution of the spinodal decomposition, thus providing information about the critical size of the c-AlN-rich domains prior to the onset of the transformation to h-AlN. We report the fractional cubic to hexagonal transformation of AlN in Ti 1Àx Al x N as a function of time and extract activation energies between 320 and 350 kJ mol À1 depending on the alloy composition. The onset of the hexagonal transformation occurs $50 K lower in Ti 0.36 Al 0.64 N compared to Ti 0.55 Al 0.45 N where the high Al content alloy also has a significantly higher transformation rate. A critical wavelength for the cubic domains of $13 nm was observed for both alloys. Scanning transmission electron microscopy shows a c-TiN/h-AlN microstructure with a striking morphology resemblance to the c-TiN/c-AlN microstructure present prior to the hexagonal transformation.

No abstract

No abstract

No abstract

In this study, the influence of substrate surface finish on scratch resistance and associated failure mechanisms is investigated in the case of a TiN-coated hardmetal. Three different surface finish conditions are studied: as-sintered (AS), ground (G), and mirror-like polished (P). For G conditioned samples, scratch tests are conducted both parallel and perpendicular to the direction of the grinding grooves. It is found that coated AS, G and P samples exhibit similar critical load for initial substrate exposure and the same brittle adhesive failure mode. However, the damage scenarios are different, i.e. the substrate exposure is discrete and localized to the scratch tracks for G samples while a more pronounced and continuous exposure is seen for AS and P ones. Aiming to understand the role played by the grinding-induced compressive residual stresses, the study is extended to coated systems where ground substrates are thermal annealed (for relieving stresses) before being ion etched and coated. It yielded lower critical loads and changes in the mechanisms for the scratch-related failure; the latter depending on the relative orientation between scratching and grinding directions. Please find attached electronic files corresponding to our contribution on influence of substrate surface finish on scratch response and induced failure modes for TiN-coated hardmetals, which we (all authors do agree to the submission of the manuscript) offer for publication in Surface and Coatings Technology.I hope it is found satisfactory. Regarding reviewer 1's suggestion for improvement of the manuscript, although it seems rational and suitable, we feel that an additional figure (sketch) in a paper including already 10 other Figures (and most of them with multiple captions) may go beyond the (not written) limit associated with space limitation. Sincerely yours, Luis LlanesAnd aiming to clarify locations in the various surfaces where residual stresses occur, text has been slightly modified (Within last paragraph in section 3.1):… The coated G condition has a maximum compressive stress of about -1.0 GPa in the substrate surface (i.e. just at the coating-substrate interface). As expected, this value is one order of magnitude higher than those assessed for the coated AS and P conditions at similar substrate surface location, i.e. -0.2 and -0.1 GPa respectively. However, it should be noted that such residual stress level at the substrate surface for coated G specimen is lower ( (1) Several authors (Steinmann et. al., Thin Sol. Film., 1987; Bromark et. al., Surf. & Coat. Technol. 1992) We do have the data for plotting the requested curves but we do not see that they provide any additional useful information to the understanding of the results presented. In addition, the length of the scratch grooves is much smaller than the scratch track and sliding distance (as it may be seen in Figures 3, 4, 7 and/or 8). To provide the requested overlays would therefore require additional figures and corresponding text and consequently extend...

The effect of metal alloying on mechanical properties including hardness and fracture toughness were investigated in three alloys, Ti~0 .33 Al 0.50 (Me)~0 .17 N (Me = Cr, Nb and V), and compared to Ti 0.50 Al 0.50 N, in the as-deposited state and after annealing. All studied alloys display similar as-deposited hardness while the hardness evolution during annealing is found to be connected to phase transformations, related to the alloy's thermal stability. The most

Through a combination of theoretical and experimental observations we study the high temperature decomposition behavior of c-(TixZryAlzN) alloys. We show that for most concentrations the high formation energy of (ZrAl)N causes a strong tendency for spinodal decomposition between ZrN and AlN while other decompositions tendencies are suppressed. In addition we observe that entropic  effects due to configurational disorder favor a formation of a stable Zr-rich (TiZr)N phase with increasing temperature. Our calculations also predict that at high temperatures a Zr rich (TiZrAl)N disordered phase should become more resistant against the spinodal decomposition despite its high and positive formation energy due to the specific topology of the free energy surface at the relevant concentrations. Our experimental observations confirm this prediction by showing strong tendency towards decomposition in a Zr-poor sample while a Zr-rich alloy shows a greatly reduced decomposition rate, which is mostly attributable to binodal decomposition processes. This result highlights the importance of considering the second derivative of the free energy, in addition to its absolute value in predicting decomposition trends of thermodynamically unstable alloys.

On the day of the defence date the status of this article was Manuscript.