Thermal spray coatings are widely used to rebuild worn parts to original dimensions, and to restore or modify surface properties. Twin wire arc spray (TWA) is among the most common methods used to spray metallic coatings. Two infrared (IR) methods, flash thermography and thermal wave imaging, were evaluated for detection of porosity and disbonds in TWA coatings. Test samples were flat coupons of grey iron coated with 12 or 24 layers (1mm or 2mm total thickness) of AISI420 stainless steel. Porosity was introduced by spraying graphite powder between the layers, and disbonds by locally oxidizing a single layer of coating near the mid-depth. The coatings were inspected in the as-sprayed condition, without removing the inherent surface roughness. The data will show that both IR methods detect the defects. Strategies for data analysis of the thermal response, and correlation to the adhesive strength of the coating will be explored. Finally, the merits and shortcomings of the two methods will be discussed.
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M. Ravi Shankar, Ph.D.
In 2006, Shankar earned his Ph.D. in Industrial Engineering from Purdue University and started as an assistant professor at the University of Pittsburgh. His primary appointment was in Industrial Engineering, with a secondary appointment in Mechanical Engineering and Materials Science. In 2009, he was awarded the Whiteford faculty fellowship by the Swanson School of Engineering. In 2012, he was tenured and promoted to the rank of associate professor. In 2016, he was promoted to the rank of full professor and continued to hold the Whiteford endowed position. In 2019, he was awarded the Swanson Professorship. Shankar received the SME’s Outstanding Young Manufacturing Engineer award in 2010 and was named the Institute of Industrial Engineer’s Outstanding Early Career IE in 2014.
Shankar’s research program is broadly in the areas of manufacturing and materials engineering with a particular focus on bulk nanomaterials, nanomanufacturing, 3D printing, microrobotics and adaptive metamaterials. He has been supported by the NSF, Navy, Air Force, DARPA, Manufacturing Innovation Institutes, the State of PA, philanthropic foundations, and Industry partners. His work has appeared in an array of archival journals ranging from the Proceedings of the National Academy of Sciences, Nature Communications, Advanced Functional Materials, Acta Materialia, Applied Physics Letters, as well as ASME, IIE and ACS families of journals. His work also resulted in 4 published patents and 2 pending applications. He has overseen 10 postdocs, 9 Ph.D students, several of whom have gone on to build academic careers of their own.