Real-time remote temperature and thickness measurement of titanium nitride thin coatings growing on steel using laser thermoreflectance optical thermometer
Center for Advanced Diffusion Wave Technologies (CADIFT), Mechanical Engineering Department, 5 King College Rd., Toronto, Ontario, M5S 3G8, Canada
A novel optical thermometer based on the principle of laser thermoreflectance has been introduced to monitor the surface temperature of thin coatings on steel parts undergoing an industrial titanium nitride (TiN) alloy deposition process. To study the feasibility of the optical thermometer, various thermo-optical parameters of TiN affected by the deposition process have been investigated; namely, the reflectance-temperature relation, the thermoreflectance coefficient, and the coating thickness dependence of thermoreflectance and of total reflectance. A theory of interferometric thermoreflectance has been introduced to model the total reflectance variations during the coating process. An inverse reflectance-temperature relation for the TiN-D2 steel substrate system has been found and a first-order Taylor series expansion used to model thermoreflectance has been shown to yield a thermoreflectance coefficient which is independent of temperature. Both results are in quantitative agreement with the Drude-Zener theory of conductors and semiconductors. An empirical formula has been derived to effectively model the experimental thermoreflectance coefficient dependence of the TiN-D2 steel system on TiN coating thickness, in qualitative agreement with scattering mechanisms of the Boltzmann transport theory in conductors and semi-conductors.
© EDP Sciences, Springer-Verlag, 2008