Evaluation of Cold Spray Coatings by Ultrasonic Washing

Abstract

This paper proposes application of ultrasonic washing to the evaluation of the strength of cold spray coatings.The ultrasonic washing test exploits the phenomenon that when a polished surface of a cold sprayed coating is subjected to ultrasonic washing,powder particles that are not well bonded come off the surface while leaving those that are well-bonded in the surface.In this study,polished surfaces of copper coatings,fabricated at spray gas temperatures of 200-800℃,were ultrasonically washed in water for various times up to 30 minutes,and the apparent(surface)porosity due to particle detachment was determined by image analysis.For all specimens,the surface porosity increased with increasing ultrasonic washing time but the increase leveled off after about 15 minutes.The final surface porosity at 30 minutes,which was as high as 9% at 200℃,decreased drastically with increasing gas temperature,with values of the coatings sprayed 600 and 800℃ reduced to well below 1%.The final porosity was found to inversely correlate with the tensile strength of the coatings.The ultrasonic washing test may provide an effective means for rapid evaluation of cold spray coatings.