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.