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

Hollow workpieces such as cylinders are often required to exhibit better pe rformance in wear and corrosion behaviour than the material the workpiece i s 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 ca n be overcome when the source of the material to be deposited is located in side the workpiece. This is possible when sputter coating with ions is perf ormed. A sputter target is located inside the workpiece. Energetic ions ext racted from a plasma in which the workpiece is immersed are accelerated tow ards the workpiece, enter it and impinge onto the sputter target. Thus, mat erial 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 b een tested with cylinders made of different materials and with different sp utter target materials. The deposited films are well adhering and dense and may act as protective coatings against corrosion. This is shown for corros ion of iron in acetic acid, pitting corrosion of aluminium in sodium chlori de solution, and hydrogen embrittlement of tantalum in hydrochloric acid. ( C) 2001 Elsevier Science B.V. All rights reserved.