Development of high quality thermal spraying process by shielding control

Abstract

The shielding controlled plasma spraying process was investigated to improve corrosion resistance of metal surfaces. In this process, a shielding nozzle that covered only spraying area was attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet was controlled by nitrogen flow. When the oxygen concentration in the shielding nozzle was maintained at 0·5%, the metal oxide contents in CoNiCrAlY coating and the porosity of the coating reduced to 0·2 and 0·3% at optimal spray particle size respectively. The corrosion potential in an acid solution including chloride ions was almost constant for 1000 h for CoNiCrAlY coating deposited by shielding controlled plasma spraying. On the other hand, those obtained by atmospheric plasma spraying process decreased in the corrosion potential largely after 10 h. Thus, it can be concluded that the shielding controlled plasma spraying process improves the corrosion resistance of the metal.

Keywords:

• PLASMA SPRAYING
• SHIELDING CONTROL
• OXIDE CONTENTS
• POROSITY
• CORROSION RESISTANCE