Ion-assisted growth of Ti1-xAlxN/Ti1-yNbyN multilayers by combined cathodic-arc/magnetron-sputter deposition

The microstructure and microchemistry of polycrystalline Ti1-x-yAlxNbyN alloys and Ti1-xAlxN/Ti1-yNbyN multilayers grown on bcc ferritic stainless steel substrates at 450 degrees C by unbalanced-magnetron (UBM) sputter deposition and combined UBM/cathodic-arc (UBM/CA) deposition have been investigated using X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy (XTEM), and scanning transmission electron microscopy with energy-dispersive X-ray microanalyses of XTEM samples. The growth experiments were conducted in a deposition system in which the substrates are continuously rotated past one Ti0.85Nb0.15 and three Ti0.50Al0.50 cathodes, each capable of being operated independently in either UBM or CA mode. CA ion-etching of the steel substrates prior to deposition produced a polycrystalline compositionally-graded altered layer with a depth of similar or equal to 20 nm when operating the are on the Ti0.50Al0.50 target and a much narrower, similar or equal to 6 nm, amorphous layer with the Ti0.85Nb0.15 target. Subsequent UBM or UBM/CA growth on substrates subjected to the former treatment resulted in local epitaxy with underlying grains for film thicknesses up to similar or equal to 200 nm before the growth front gradually broke down locally to initiate columnar deposition. Film growth on substrates CA ion-etched using the Ti0.85Nb0.15 target resulted in much smaller average column diameters with competitive grain growth. However, the fraction of the sample area covered by nodular defects arising from are-ejected droplets was reduced by a factor of similar or equal to 102. Thus the latter procedure was used for substrate preparation prior to multilayer growth. Ti1-xAlxN/Ti1-yNbyN multilayers with periods between 2.17 and 2.29 nm were grown by combined UBM/CA deposition. The multilayers exhibited flat, regular interfaces throughout film total thicknesses of up to 3 mu m. (C) 1997 Elsevier Science S.A.