Analysis Of Components Depth Profile At The Interface Of Ti6242 Alloy And Tini Coatings After High Temperature Oxidation In Air

We have analyzed the interfacial elemental depth profile evolution after high temperature isothermal oxidation of NiTi coatings deposited by dynamic ion mixing on a Ti6242 alloy (Ti-6Al-2Sn-4Zr-2Mo). NiTi coatings (thickness 0.4 mu m) were deposited at room temperature (RT) by ion beam sputtering. High temperature isothermal oxidation tests in 1 atm flowing synthetic air (80% N-2, 20% O-2) have been conducted at 500 degrees C and 600 degrees C during 100 hours. We have observed a non-monotonous depth distribution of nickel in GDOES depth profiles after oxidation of TiNi/Ti6242: nickel segregates to the surface of TiNi coating and to the interface between TiNi coating and Ti6242 alloy. We propose a kinetic model based on rate equations for analyzing the depth profile. This model includes microprocesses taking place during oxidation in air such as: adsorption of nitrogen and oxygen, diffusion of components through the film and interface, formation of chemical compounds. It is shown by modeling that non-monotonous depth profile of nickel occurs because nickel from TiNi coating is forming a nickel oxide compound when oxygen atoms reach the film/alloy interface. XRD analysis confirms the presence of nickel oxide in the TiNi/Ti6242 interface after oxidation at both temperatures 500 degrees and 600 degrees C. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim