STUDY OF DAMAGE MECHANISMS IN COLD-SPRAYED 316L-MATRIX COMPOSITE COATINGS USING NOVEL IMPACT-SLIDING TESTING

摘要

Cold spray is now well recognized as one of the most powerful and efficient coating process because it is cost-attractive and "green". However, this process still shows limitations to achieve coatings for highly-demanding service conditions such as those required in certain automotive and/or aircraft applications. Beyond these limitations, cold spray is expected to compete with conventional P/M routes. The present work therefore focussed on the study of damage mechanisms in cold-sprayed AISI 316L and 316L-matrix-Cu composites coatings due to high-loading conditions. Different damage mechanisms could occur depending on the content of Cu particle addition, due to changes in the response of the microstructure to the loading. These mechanisms were studied using the newly-developed "impact-sliding" test. In this test, a steel ball impacts the coating surface at a given frequency, with a fixed angle. The influence of major testing parameters was investigated. Microstructures before and after testing were studied using optical microscopy, scanning electron microscopy (SEM), and microprobe analysis in addition to 3D optical profilometry of impacted areas. Damage mechanisms were seen to be of two types, i.e. plastic deformation and wear. These resulted in decohesion of splats, formation of wear debris and formation of a layer with a tribologically-transformed structure (TTS) at the contact surface. Results showed that cold spray could be claimed to be suitable for the achievement of high-performance coatings for industrial applications provided that the coating microstructure can be controlled. This could be done using a composite approach to the coating composition.