Additive Manufacturing of Ni/NiCr Thermocouples on Ceramic Substrates by Directed Energy Deposition

The direct integration of temperature sensors into thermally loaded components reduces the number of production steps and enables localized temperature measurements regardless of the selected contour. Directed Energy Deposition (DED) offers high potential for such applications due to its capability for multi-material processing; however, the direct deposition of metallic thermocouple tracks onto electrically insulating ceramic substrates remains challenging. In this study, Ni/NiCr thermocouples were fabricated directly onto thermally sprayed yttria-stabilized zirconia (YSZ) substrates using DED. Process parameters established for depositing Ni/NiCr on metallic steel substrates were found to be unsuitable for ceramic deposition due to excessive energy input and insufficient track formation. Dedicated parameter studies were therefore conducted for Ni and NiCr, focusing on scan velocity, powder mass flow rate, laser beam diameter, focal position, and NiCr powder particle size. The results demonstrate pronounced material- and particle-size-dependent differences in thermal interaction with the ceramic substrate. Fine NiCr powders caused significant heat-affected zones (HAZ) and substrate degradation, whereas coarser powder fractions substantially reduced thermal damage but required adapted focal conditions to achieve electrically functional tracks. Using optimized parameters, a functional Ni/NiCr thermocouple was fabricated and tested up to 300 °C, showing a stable and linear thermoelectric response with a systematic voltage offset relative to a conventional Type K thermocouple.