Microstructure evolution during the isostructural decomposition of TiAlN—A combined in-situ small angle x-ray scattering and phase field study

Abstract

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.

Thermal stability of wurtzite Zr1−xAlxN coatings studied by in situ high-energy x-ray diffraction during annealing

“…The lack of a SAXS signal does not rule out the possibility of composition fluctuations in the as-deposited sample as random compositional fluctuations have been observed by atom probe tomography in as-deposited TiAlN coatings grown by cathodic arc evaporation, 40 while these fluctuations were too weak and disordered to be detected by SAXS using a similar experimental setup. 1 Thus, while compositional fluctuations cannot be excluded in the as-deposited w-ZrAlN samples, they are either weak or non-existent considering the stronger SAXS contrast expected between ZrN-and AlN-rich domains compared to that between TiN-and AlN-rich domains. The formation of layers during decomposition should thus not be influenced by compositional fluctuations in the as deposited sample, which was the case in a previous study.…”

“…Transition metal (Me) aluminum nitride coatings with a cubic crystal structure generally exhibit high hardness values and may undergo high temperature age hardening due to a phase separation of the unstable cubic (c)-MeAlN phase, making them suitable for high temperature wear protection. One frequently used industrial coating is c-TiAlN, which exhibits spinodal decomposition when exposed to temperatures above 800 C. 1 The evolving microstructure consists of nanosized c-TiN and c-AlN rich domains that result in an enhanced hardness 2,3 due to a combination of coherency strains and the elastic modulus difference between the domains. [4][5][6] The subsequent transformation of c-AlN to wurtzite (w)-AlN results in a loss of coherency between the binary phases and a concomitant decrease in hardness.…”

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.…”

Wear behavior of ZrAlN coated cutting tools during turning

“…One of the most commonly used PVD coating materials is TiAlN, for which the cubic (c) solid solution TiAlN phase decomposes as the coating is exposed to high temperatures, resulting in a fine nanostructure that improves the mechanical properties of the coating [8][9][10]. Thus, c-TiAlN coated tools typically exhibit good wear resistance [11,12].…”