Self-organized nanostructures in the Ti–Al–N system

Abstract

The phenomenon of age hardening could be evidenced in thin film applications. A model system, Ti1−xAlxN was chosen as such coatings are known for their excellent wear resistance enabling improved machining processes like high-speed and dry cutting. Here, we show unambiguously that metastable Ti1−xAlxN coatings initially undergo spinodal decomposition into coherent cubic-phase nanometer-size domains, causing an increase in hardness at elevated temperatures. These intermediate metastable domains transform into their stable phases TiN and AlN during further thermal treatment. Activation energies for the processes indicate defect-assisted segregation of Ti and Al. The findings are corroborated by ab initio calculations. A long-standing discussion on the thermal stability of this important class of ceramics is thus resolved.

Pressure and temperature effects on the decomposition of arc evaporated Ti0.6Al0.4N coatings in continuous turning

“…Although several studies previously reported on the decomposition of post annealed Ti 1-x Al x N [3,7,14], a detailed study of the Ti 1-x Al x N decomposition at the cutting edge is still 2 lacking. This is the motive of the present study where the microstructure evolution of Ti 0.6 Al 0.4 N after cutting was compared to reference heat treatments performed with isothermal steps of 10 min.…”

“…A contributor to this is the observed age hardening during annealing, which is an effect of the decomposition of the as-deposited unstable cubic (c)-Ti 1-x Al x N (B1) structure into nanometer sized c-TiN rich and c-AlN rich coherent domains [3,4]. The lattice mismatch between the coherent domains introduces microstresses at the domain borders which in combination with evolving elastic property differences hinder dislocation motion [5].…”

Effect of Al substitution on Ti, Al, and N adatom dynamics on TiN(001), (011), and (111) surfaces

“…However, when subjected to high temperatures, e.g., during highspeed cutting-tool operations, such metastable coatings separate into TiN and either NaCl-or wurtzite-structure AlN as bulk diffusion becomes active. [12][13][14][15] This is believed to be responsible in part for the improved wear resistance of TiAlN coatings which has been extensively studied both experimentally [12,13,15] and theoretically. [12,[15][16][17][18] During growth, limited short-range clustering is likely to occur [19] and must be taken into account in order to obtain a complete atomistic understanding of these materials.…”

Temperature dependence of TiN elastic constants fromab initiomolecular dynamics simulations

“…23 Furthermore, the elastic anisotropy is essential for understanding and modeling the spinodal decomposition, 24 which occurs in some alloys of transition-metal nitrides and it is believed to be the main reason for the age hardening effect. 7,8,25 At the same time, experimental information on elastic properties of transition-metal nitrides is mostly limited to their Young's moduli. 23,[26][27][28][29] With rare exceptions it does not include data on the single-crystal elastic constants.…”