Speaker
Description
Wear resistant coatings are widely used for cutting applications due to their high hardness and chemical stability. Their low thermal conductivity is equally important, as it limits heat transfer into the tool during cutting. Accurate knowledge of this property enables targeted thermal design and effective heat management. Besides time domain thermoreflectance, the 3ω method is a widely accepted technique for measuring thermal conductivity of thin films.
For 3ω measurements a thin flim heater was first sputter deposited onto the sample surface and subsequently structured. This step is typically based on lithographic processes, which are often elaborate and time consuming. This study integrates femtosecond (fs) laser ablation into the fabrication of Al and Cu thin film heaters by structuring the sputtered films directly from CAD defined geometries. Particular emphasis was placed on a systematic investigation of fs laser parameters, including variations in average power, repetition rate, work angle, scan regime, pulse distance and line distance. Optionally, a photoresist sacrificial layer was applied on top to reduce the taper angle and capture debris.
The method was first validated on well known, electrically non conductive reference substrates, namely amorphous SiO2 (fused silica) and single crystalline 0001 oriented α Al2O3. Measurements on electrically conductive samples, with Ti serving as a model metallic substrate, were enabled using an additional thin Al2O3 dielectric layer beneath the heater. Finally, the approach was applied to wear resistant coatings, including CVD Al2O3, PVD AlN and TiN based coatings.
Optimised fs laser parameters enabled well defined heater geometries. The taper angle was reduced without significant damage to the underlying Al2O3 dielectric layer. Compared with lithography, fs laser structuring offers greater flexibility in adjusting heater geometries while maintaining sufficient accuracy for 3ω measurements. This simpler, faster and potentially more cost effective heater fabrication method may facilitate wider use of the 3ω method for thermal conductivity characterisation of wear resistant coatings.