AVS 46th International Symposium
    Vacuum Metallurgy Division Wednesday Sessions
       Session VM-WeM

Paper VM-WeM7
Interface Engineering in a Combined Arc/ UBM Deposition System during Growth of Ti@sub 0.5@Al@sub 0.5@N Films on Steel: Effects of Substrate Ion Etching

Wednesday, October 27, 1999, 10:20 am, Room 620

Session: Advanced Surface Treatments and Coatings
Presenter: C. Schönjahn, Sheffield Hallam University, UK
Authors: C. Schönjahn, Sheffield Hallam University, UK
L.A. Donohue, Sheffield Hallam University, UK
D.B. Lewis, Sheffield Hallam University, UK
W.-D. Münz, Sheffield Hallam University, UK
R.D. Twesten, University of Illinois, Urbana
I. Petrov, University of Illinois, Urbana
Correspondent: Click to Email
In-situ substrate cleaning by ion etching prior to deposition in PVD processes is a key step in achieving good film adhesion, which is essential for all coating applications. Irradiation with metal or gas ions alters substrate surface chemistry, topography and microstructure thus affecting subsequent film growth. This study compares Ti@sub 0.5@Al@sub 0.5@N/ steel interfaces formed after Cr- metal ion bombardment at negative substrate biases, Us, ranging from 600 to 1200 V during a Cr cathodic arc, stabilized with a 0.06 Pa Ar background pressure. Samples pretreated with a 1200 V Ar glow discharge at a pressure of 0.6 Pa were also investigated. Microstructure and microchemistry of the interfaces was studied by XTEM samples using STEM-EDX analysis. Cr ion etching with Us = 1200 V resulted in a net removal of over 100 nm of substrate material with the formation, through implantation and radiation-enhanced diffusion, of a Cr-enriched near-surface region extending to a depth of ~10 nm. As Us was reduced to 600 V, Cr accumulated at the surface as an ~5 nm thick layer. Ar was incorporated at the surface to levels of 4 and 5 at % during Cr arc-etching and Ar glow discharge, respectively. Microstructure of Ti@sub 0.5@Al@sub 0.5@N overlayers was dramatically affected by pre-treatment procedures. Ar sputter cleaned steel surfaces (Us = 1200 V) promote nucleation of randomly oriented grains leading to a competitive column growth with small column size and open boundaries. In contrast, Cr irradiation at the same bias voltage results in local epitaxial growth of Ti@sub 0.5@Al@sub 0.5@N on steel, which is expected to improve film/substrate adhesion. Coatings deposited after Cr treatment with Us = 600V still exhibit small areas of oriented growth but porosity is also present.