Ultrafast laser micromachining of thermal sprayed coatings for microheaters: Design, fabrication and characterization

This work presents an ultrafast laser (pulse duration < 1 ps) direct-write technique for rapid prototyping and manufacturing of embedded microheater structures on thermal sprayed NiCr (80wt.%/20wt.%) alloy coatings. By combining thermal spray, an additive material process, and ultrafast laser micromachining, a subtractive material process, this technique shows considerable potential in fabricating small scale embedded functional parts within thermal spray coatings. Heater patterns designed to produce a uniform heat flux, a linear distributed heat flux, and a non-uniform heat flux that compensates for edge losses to produce a uniform temperature distribution have been fabricated and characterized. A stable working temperature of up to 500°C measured in still air is observed, with fracture in the samples observed at higher operating temperatures. A mechanical analysis based on bimorph beam bending is presented to account for the failure mechanism of the laser-machined thermal spray microheaters at high temperatures, and recommendations are made for improved materials and fabrication parameters for high-temperature operation.