Nano-structural investigation of Ti-Al-N/Mo-Si-B multilayer coatings: A comparative study by APT and HR-TEM

Nano-composites often represent a challenge for spatially resolved analysing methods. The overlap of specific signals, for example in the mass-to-charge spectrum during atom probe tomography (APT) analysis or the intersection of electron energy loss edges in electron energy loss spectroscopy (EELS), leads to highly challenging results. Therefore, a complementary use of different techniques is essential to fully characterise a given system. Within this work, we studied our Ti-Al-N/Mo-Si-B multilayer (comprising alternating 31 nm thin arc evaporated fcc-Ti0.57Al0.43N layers and amorphous 6 nm thin Mo0.58Si0.28B0.14 layers), by high-resolution transmission electron microscopy, EELS as well as APT and completed the results by comprehensive X-ray diffraction measurements. We focused on the microstructure and crystallographic evolution during thermal loading - up to 1400 °C - and hence a detailed analytical description applying a wide set of high resolution techniques. When exposed to high temperatures, the as-deposited amorphous MoSiB layers form the oxidation resistant, intermetallic phases T1-Mo5Si3 and T2-Mo5SiB2. The layered arrangement between Ti-Al-N and Mo-Si-B allows to postpone the formation of the comparative soft, hexagonal wurtzite type AlN (due to the decomposition of fcc-Ti1-xAlxN layers) up to 1200 °C, which is by ∼200-300 °C above the typical formation temperature of w-AlN in homogeneously grown single phase fcc-Ti1-xAlxN thin films.