Cold Spray Cobalt High Temperature Magnetostrictive EMAT Sensor

The Department of Energy’s Advanced Sensors and Instrumentation program seeks to develop and qualify advanced sensors for the nuclear industry. Reliable high temperature and high radiation sensors for detection, characterization, and monitoring of structural flaws in pipes, vessels, and structurally critical components are a weakness for both conventional light water reactors with coolant T-hot approaching 350°C, and for advanced reactors with T-hot temperatures in the range of 500 to 800°C and potentially higher. Magnetostrictive Electromagnetic Acoustic Transducers (EMATs) using a cold spray cobalt coating have been proposed as a sensor design that can withstand these temperatures and serve as online sensors to detect flaws before cracks, pits, or erosion/corrosion damage progresses to through-wall failures. This paper reports findings of cold spray cobalt (Co) as part of a magnetostrictive EMAT sensor for high temperature service. Co is known to have strong magnetostrictive properties; however, the effect of cold spray application is not well studied. Surprisingly, cold sprayed Co exhibited little or no magnetostrictive behavior until thermally annealed. Following annealing to 650°C however, cold spray Co did exhibit a magnetostrictive response, albeit with lower amplitude and higher acoustic noise than either Ni or FeCo. Work to date showed that Co magnetostrictive EMAT was successfully tested to 400°C with an