Inner wall coating of cylinders by plasma immersion ion implantation for corrosion protection

Abstract

Hollow workpieces such as cylinders are often required to exhibit better performance in wear and corrosion behaviour than the material the workpiece is made of can offer. The problem can be overcome when a protective coating is deposited onto the inner walls. However, coating inner walls by means of physical vapour deposition techniques is difficult because the material to be deposited has to enter the hollow object under very flat angles to the wall, depending on the ratio of aperture to inner diameter. This problem can be overcome when the source of the material to be deposited is located inside the workpiece. This is possible when sputter coating with ions is performed. A sputter target is located inside the workpiece. Energetic ions extracted from a plasma in which the workpiece is immersed are accelerated towards the workpiece, enter it and impinge onto the sputter target. Thus, material is sputtered onto the inner wall. At the same time, ions impinge onto the growing film and lead to ion beam mixing effects. This technique has been tested with cylinders made of different materials and with different sputter target materials. The deposited films are well adhering and dense and may act as protective coatings against corrosion. This is shown for corrosion of iron in acetic acid, pitting corrosion of aluminium in sodium chloride solution, and hydrogen embrittlement of tantalum in hydrochloric acid.