Ion-assisted growth of Ti 1− xAl xN/Ti 1− yNb yN multilayers by combined cathodic-arc/magnetron-sputter deposition

Abstract

The microstructure and microchemistry of polycrystalline Ti 1− x− y Al x Nb y N alloys and Ti 1− x Al x N/Ti 1− y Nb y N multilayers grown on bee ferritic stainless steel substrates at 450 °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 Ti 0.85Nb 0.15 and three Ti 0.50Al 0.50 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 ⋍ 20 nm when operating the arc on the Ti 0.50Al 0.50 target and a much narrower, ⋍ 6 mm. amorphous layer with the Ti 0.85Nb 0.15 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 ⋍ 200 nm before the growth front gradually broke down locally to initiate columnar deposition. Film growth on substrates CA ion-etched using the Ti 0.85Nb 0.15 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 arc-ejected droplets was reduced by a factor of ⋍ 10 2. Thus the latter procedure was used for substrate preparation prior to multilayer growth. Ti 1− x Al x N/Ti 1− y Nb y N 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 μm.