Article Article
Magnetostrictive Cold Spray Sensor for Long-Term or Harsh Environment Ultrasound

Ultrasound sensors are frequently used to generate acoustic waves capable of detecting cracks, pits, erosion, inclusions, etc. One problem with piezoelectric transducers, particularly in harsh environment applications, is the difficulty to achieve coupling between the transducer and the structure. This work explores the behavior of a magnetostrictive (ms) cold-spray patch on a stainless steel inspection target, and compares it to the performance of a standard adhesively bonded ferrous-cobalt (FeCo) ms strip. Cold spray is a process where powdered metal is accelerated to 2–3 × speed of sound and impacted on the surface forming a metallurgically bonded coating. If the powder is nickel or cobalt with high ms coefficients, this surface can serve as the base of an SH-0 or A-0 Lamb wave mode EMAT sensor suitable for crack or pitting corrosion damage monitoring that is not subject to temporal or environmental degradation. Guided-wave ultrasound edge reflection signals from adhesively applied FeCo strips were compared to nickel or nickel alloy cold-spray coatings applied with various process parameters. The ms coefficient of nickel is less than half of FeCo so some reduction in amplitude was expected. Cold-spray responses ranged from a moderate increase to > 40 dB reduction. The signal/noise ratios though were > 26 dB. Based on the edge reflection amplitudes and signal/noise, the inspection sensitivity is inferred to be manageable by instrument gain adjustments and, therefore, the cold-spray patch would be a viable alternative to an adhesive strip sensor that is not subject to coupling or adhesive degradation.

DOI: 10.32548/RS.2019.009

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