Impact of O concentration on the thermal stability and decomposition mechanism of (Cr,Al)N compared to (Ti,Al)N thin films

Kümmerl, Pauline and Nayak, Ganesh Kumar and Leinenbach, Felix and Czigány, Zsolt and Primetzhofer, Daniel and Kolozsvári, Szilárd and Polcik, Peter and Hans, Marcus and Schneider, Jochen M. (2026) Impact of O concentration on the thermal stability and decomposition mechanism of (Cr,Al)N compared to (Ti,Al)N thin films. ACTA MATERIALIA, 312. No. 122250. ISSN 1359-6454

Preview

Text 1-s2.0-S135964542600354X-main.pdf - Published Version Available under License Creative Commons Attribution. Download (19MB) | Preview

Abstract

The composition-dependent thermal stability of (Cr0.47±0.03Al0.53±0.03)z(OyN1-y)1-z thin films (z = 0.475 ± 0.015) with O concentrations of y = 0, 0.15, and 0.40 is investigated up to 1200 ◦C and then compared to (Ti0.56Al0.44)z(OyN1-y)1-z. X-ray diffraction reveals a thermal stability limit of 1150 ◦C independent of the O concentration, as witnessed by the formation of decomposition products, namely h-Cr2N for (Cr0.50Al0.50)0.49N0.51 and c-Cr for both (Cr0.48Al0.52)0.48(O0.15N0.85)0.52 and (Cr0.44Al0.56)0.46(O0.40N0.60)0.54. Based on transmission electron microscopy and elastic recoil detection analysis data, the thermal stability limit is extended to 1100 ◦C – 1150 ◦C for all films. Chemical environment-dependent DFT calculations indicate that bond breaking limits the thermal stability. In (Cr,Al)N, N has the lowest activation energy for migration. Furthermore, the O vacancy formation energy is highest in (Cr,Al)(O,N). It has to be overcome to enable diffusion on the non-metal sublattice, which is necessary for forming decomposition products like w-AlN or c-Cr. However, once Cr-N bonds break, decomposition into hCr2N and subsequent c-Cr together with N2 is triggered. This results in N evaporation, generating sufficient nonmetal vacancies that greatly enhance diffusion and render the extensive vacancy formation energies for nonmetals irrelevant. This reduction of the activation energy for mass transport on the non-metal sublattice to the migration barrier causes the similar thermal stability in (Cr0.47±0.03Al0.53±0.03)z(OyN1-y)1-z. In contrast, Al bonds break first without creating non-metal vacancies in (Ti,Al)(O,N). Thus, the high O vacancy formation energy in (Ti,Al)(O,N) significantly increases the thermal stability compared to (Ti,Al)N as well as the here investigated films.

Actions (login required)

Edit Item