Transmission electron microscopy of TiN and TiAlN thin films using specimens prepared by focused ion beam milling

The microstructures of a series of TiN and TiAlN wear resistant coatings on steel substrates are characterized using cross-sectional transmission electron microscopy. TiN coatings were deposited using both low-voltage electron beam evaporation and cathodic arc techniques, and a dual-layer TiN–TiAlN coating was prepared using cathodic arc deposition. All of the coatings consisted of columnar grains separated by high-angle grain boundaries. In all specimens, the substrate/coating interface was sharp and no Ti interlayer or modification of the substrate was observed. The TiN/TiAlN dual-layer coating contained a layered interfacial region where both the Ti and TiAl sources were operating concurrently. The TiAlN regions consisted of extremely fine sub-layers ∼2 nm thick, which are thought to result from the threefold planetary rotation of the specimen in the deposition chamber. The columnar grains grew epitaxially through the entire TiN/TiAlN interfacial region. TEM specimens were prepared using the focused ion beam, which allowed large, uniformly thin areas to be prepared with relative ease.