Stress-controlled decomposition routes in cubic AlCrN films assessed by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction

Abstract

The dependence of decomposition routes on intrinsic microstructure and stress in nanocrystalline transition metal nitrides is not yet fully understood. In this contribution, three Al0.7Cr0.3N thin films with residual stress magnitudes of −3510, −4660 and −5930 MPa in the as-deposited state were in-situ characterized in the range of 25–1100 °C using in-situ synchrotron high-temperature high-energy grazing-incidence-transmission X-ray diffraction and temperature evolutions of phases, coefficients of thermal expansion, structural defects, texture as well as residual, thermal and intrinsic stresses were evaluated. The multi-parameter experimental data indicate a complex intrinsic stress and phase changes governed by a microstructure recovery and phase transformations taking place above the deposition temperature. Though the decomposition temperatures of metastable cubic Al0.7Cr0.3N phase in the range of 698–914 °C are inversely proportional to the magnitudes of deposition temperatures, the decomposition process itself starts at the same stress level of ~−4300 MPa in all three films. This phenomenon indicates that the particular compressive stress level functions as an energy threshold at which the diffusion driven formation of hexagonal Al(Cr)N phase is initiated, provided sufficient temperature is applied. In summary, the unique synchrotron experimental setup indicated that residual stresses play a decisive role in the decomposition routes of nanocrystalline transition metal nitrides.

Precipitation-based grain boundary design alters Inter- to Trans-granular Fracture in AlCrN Thin Films

“…The in situ high-energy high-temperature grazing incidence transmission X-ray diffraction (HE-HT-GIT-XRD) [21] experiments were performed at the P07B beamline of the PETRA III synchrotron source in Hamburg (D) in transmission geometry, using a pencil X-ray beam with a size of 400 μm × 100 μm and an energy of 87.1 keV. The samples were mounted into a DIL 805 dilatometer (TA Instruments) with the surface aligned with respect to the primary beam at an incident angle β of ∼2 deg.…”

“…The heating and cooling rates were adjusted for receiving sufficient diffracted signal at the 2D detector, which can be revised together with further experimental details in Ref. [21] .…”

“…9 a), applying the methodology from Ref. [21] . The aim was to identify structural changes, which might influence the mechanical behavior of the annealed film.…”

Quo Vadis: AlCr-Based Coatings in Industrial Applications

“…It was shown that the decomposition temperatures of the metastable fcc-(Al 63.5 Cr 36.5 )N phase depends significantly on the stress level in the coatings. The decomposition process starts at the same compressive stress level of around 4.3 GPa for all coatings that were investigated [75].…”

“…For example, thick coating layers are at risk of peeling off if the stress state is too high, while high compressive stresses can be advantageous in interrupted cutting operations. The stress state has also been pointed out as a key determining factor for thermal stability and decomposition pathways [75].…”