Plasma Immersion Ion Processing

Plasma immersion ion processing (PIIP) is a relatively new vacuum technology for the application of hard, wear-resistant coatings. Like conventional physical vapor deposition (PVD) methods, PIIP is used to deposit various coatings, but the non-line-of-sight PIIP approach allows simultaneous treatment of large components and complex shapes without requiring component manipulation.

Building on established capabilities in ion beam surface modification techniques, Southwest Research Institute (SwRI) is committed to the advancement of PIIP technology. The recent availability of inexpensive, high-power pulsed modulator equipment, and the inherent scalability of PIIP, lend an economy to this surface modification process which is difficult to match using other methods.

PIIP technology was originally developed at the University of Wisconsin and principally refined at Los Alamos National Laboratory (LANL). The PIIP process occurs as follows:

  • Components are inserted into vacuum chamber

  • Chamber is evacuated to base pressure below 10-5 torr

  • Plasma (mixture of ions and electrons) is generated from gas introduced into chamber

  • All exposed surfaces are completely surrounded by plasma

  • High-voltage pulse modulator generates negative voltage pulses applied to components

  • Positive ions are extracted out of plasma

  • Ions impinge on all exposed surfaces simultaneously

  • Voltage pulses >20 kV are used to produce ion implantation 

  • Voltage pulses <10 kV are used to deposit coatings

  • Ion implantation or interlayer deposition can be used to improve coating adhesion 

The versatility of the “plasma” approach to surface modification allows the use of any gas with the same equipment. Thus, a single vacuum chamber can use argon gas for sputter-cleaning or nitrogen gas for ion implantation. The same equipment can be used to deposit coatings from hydrocarbon gases or organometallic compounds. 

PIIP techniques for the deposition of diamond-like carbon (DLC) from acetylene gas and chromium oxycarbide from chromium carbonyl have been demonstrated. Researchers at LANL have demonstrated the scalability of PIIP by simultaneously coating 16 m2 with DLC. Analysis of a large-scale PIIP-based DLC deposition process indicates that the treatment cost would be comparable to electrodeposited hard chrome. Thus, PIIP offers an affordable alternative to more expensive and smaller-scale processes for the deposition of coatings for tribological (wear and friction) applications. 

SwRI can also perform plasma immersion ion implantation (PIII), which was principally refined at the University of Wisconsin. PIII efforts have concentrated primarily on nitrogen implantation to improve the wear resistance of metals, and also on other implantation processes for the semiconductor industry. 

SwRI’s state-of-the-art PIII and PIIP facility uses combinations of ion implantation and coating deposition to engineer adherent coatings on the exterior surfaces of metals, plastics, and ceramics.

Large vacuum chambers treating large components (or large numbers of components) significantly reduce the treatment cost per part. Shown is the interior of SwRI’s PIIP chamber (4-ft diameter, 8-ft long) during processing. 

The large-area, non-line-of-sight PIIP process promises a number of advantages over conventional vacuum coating processes including higher throughput (at lower cost), reduced component heating, and the ability to treat external surfaces simultaneously without manipulation.

SwRI has state-of-the-art equipment in place and technical personnel dedicated to building a world-class PIIP capability.

This flyer was published in April 2000. For more information about plasma immersion ion processing, contact Dr. Kent E. Coulter, Phone (210) 522-3196, Fax (210) 522-6220, Materials Engineering Division, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510.

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