APPLICATION OF PEEK COATINGS TO C PEEK SUBSTRATES BY PLASMA-SPRAY PROCESS/

This article describes the development of a method for applying PEEK c oatings to C/PEEK substrates by plasma spraying. Uniform, well-bonded PEEK coatings have been achieved using this technology. The process te mperature is a critical parameter. ''Hotter'' coatings exhibit less po rosity and better adhesion than ''colder'' coatings. No significant de gradation of the PEEK has been observed as a result of the plasma-spra y process as verified by DSC and TGA. Use of a plasma postheat cycle i mproves the uniformity and surface finish of the coating by reducing t he number of unmelted PEEK particles on the surface of the coating. Us e of a plasma preheat cycle provides a 52% increase in tensile bond st rength of the coating. Plasma and reactive gas surface treatments do n ot appear to have any significant effect on bond strength when used in conjunction with a plasma preheat cycle. The optimized plasma-spray p arameters developed in this study produce PEEK coatings 0.254 to 0.381 mm thick which are black in color and exhibit a moderate degree of po rosity which is evenly distributed. Individual pores are isolated rath er than interconnected acid do not vary in size or distribution with s ubstrate thickness, postheating, or annealing. No interface is visible between the PEEK coating and the C/PEEK substrate at magnifications u p to 500 x. Tensile bond strengths of 13.37 +/- 0.83 MPa have been mea sured on 3.175 mm thick C/PEEK substrates and similar tests on 12.7 mm thick C/PEEK substrates have yielded values of 24.28 +/- 0.65 MPa. Th e as-sprayed PEEK coatings are essentially amorphous and require an an nealing treatment in order to ensure a reasonable degree of crystallin ity. This treatment does not affect the bond strength of the coating.