In situ embedment of type K sheathed thermocouples with directed energy deposition

Abstract

Advanced nuclear reactor systems require new technologies for heat transfer and system monitoring to achieve autonomous operations and improved performance. Additive manufacturing offers the design flexibility to allow in situ sensor embedment to realize new manufacturing techniques that can improve the smart manufacturing, real-time monitoring, and performance of these systems. This study focuses on experiments investigating the feasibility of in situ sensor embedment using directed energy deposition (DED). We embedded type K thermocouples into 316L stainless steel (SS) samples using two different configurations (e.g., exposed and embedded tips) and two designs, one with the sensor placed directly onto the substrate (e.g., flush to substrate) and the second using an additive manufacturing base. Embedded sensor samples are analyzed via in situ measurements and high-temperature performance validation tests at 350 and 900 ºC. Temperature performance results at both temperatures show good agreement with manufacturer specifications, proving that these sensors could still capture accurate temperature readings after experiencing the high-heat laser processing during DED fabrication. Additional optimization experiments were performed on the exposed tip configuration using a surrogate thermocouple to improve tolerances and the embedment process. These experiments lead to improved tolerances, lower porosity, smaller gaps between the sensor and base, and better junction contact for the sensor. Further optimization of this embedment strategy will improve the structural stability and tolerances within the component. This embedment strategy demonstrates a proof of feasibility for DED embedment with commercial sheathed thermocouples. Further investigations into fabrication strategies should be conducted to fully realize smart manufacturing and an advanced real-time monitoring system.