(45a) Atmospheric Pressure Plasma Effects On the Composition and Adhesive Bonding Properties of Titanium and Titanium Alloy

Atmospheric
pressure plasma effects on the composition and adhesive bonding properties of
titanium and titanium alloy

Edward W. Harris¹,
Justin T. Massey¹, Dick Cheng², Thomas Williams³
(speaker), and Robert F. Hicks²

¹NAVAIR North
Island, San Diego, CA 92135

²Surfx
Technologies LLC, Culver City, CA 90232

³Chemical and
Biomolecular Engineering Department, University of California, Los Angeles, CA 90095

            Titanium
alloy is a lightweight, high-strength material that has many structural
applications in aircraft, spacecraft, medical implants and dentistry. 
Preparing titanium surfaces for adhesive bonding is a complicated task that
requires specialized chemical formulations and procedures.  In this study, we
have examined the use of atmospheric pressure plasmas for surface preparation
of titanium and Ti-6AL-4V alloy.  Oxygen, nitrogen and hydrogen plasma
chemistries were used to clean the metal surface after it had been mechanically
deoxidized by sanding.  Following sanding, the samples were coated with a sol-gel
(AC technologies, AC-130-2), coated with a bond primer (Cytec BR6747-1), cured,
and joined together with an epoxy film adhesive (3M FM300-2).  Wedge crack-extension
tests (ASTM D3762) showed that the bonded titanium coupons exhibited 98% or 99%
cohesive failure (i.e., failed within the adhesive and not at the interface),
provided the metal surface was exposed to nitrogen-helium or hydrogen-helium
plasmas.  Oxygen-helium plasmas yielded only 77% cohesive failure, whereas
omitting the plasma process altogether yielded poorer results.  X-ray
photoemission spectroscopy indicated that the titanium alloy surface was
covered with a layer of carbonaceous material after sanding, and that 74% of
the atomic oxygen was present as (OH)₃^-3 species.  The
nitrogen and hydrogen plasmas removed the carbonaceous deposit and the (OH)₃^-3
species.  These results demonstrate the potential of atmospheric pressure
plasmas to improve the surface preparation of metal parts and achieve durable structural
bonds.