The process uses a high energy ion beam of aluminum impinging on a cobalt-chrome substrate in an oxygen ambient gas to grow the alumina from beneath the metal's surface. Angstroms thick have been observed. To date, flat coupons and hip balls, have been coated with coatings 1 micron thick. The coatings were evaluated for polyethylene wear using a laboratory screening tribometer which has been designed to simulate non- linear tracking of the femoral ball on the UHMW polyethylene. The adhesion was measured using a diamond point scratch tester.
Surface roughness is equal to or slightly improved over the cobalt-chrome substrate.
Polyethylene wear debris is one of the primary causes of loosening resulting in the need for subsequent revision surgery in total joint replacement. These Ceramic advantages have not yet been realized on a widespread basis for total knee replacement components. In order to specifically address the femoral knee application, an adherent alumina coating is being developed. However, aluminum oxide is not readily compatible with cobalt chrome alloy with respect to chemical affinity. Failure occurred at the metal-ceramic interface.