Thermal reactions and micro-structure of TiN-AlN layered nano-composites

Bilayer and multilayer structures of TiN and AlN thin films were synthesize d using pulsed laser deposition technique in a substrate temperature range 300-700 degrees C. The chemical reactions at TiN-AlN interfaces and the for mation of different alloy phases were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was observed that TiN-AlN i nterface remains sharp and stable for deposition temperatures up to similar to 650 degrees C. At higher deposition temperatures, however, substantial chemical reactions were found to occur. The ternary alloy phases such as Ti 3Al2N2 and Ti3AlN have been observed, for the first time. The composites sy nthesized at temperatures lower than 650 degrees C and subsequently anneale d at higher temperature were found to exhibit very limited or no interfacia l chemical reactions. The effect of layer thickness on the microstructure i s also studied. The studies revealed that by controlling the thickness of i ndividual layers and substrate temperatures, it was possible to control mic rostructure and obtain composite coatings consisting of ternary Ti-Al-N all oy phases. The results are discussed in terms of characteristic features of pulsed laser ablation process in which evaporated flux contains energetic ions, electrons and neutral particles. Preliminary nano-indentation measure ments and oxidation measurements reveal that these composites possess desir able mechanical properties at high temperatures. (C) 1999 Published by Else vier Science S.A. All rights reserved.