Micro-channels by Nd:YAG laser beam machining: fabrication, microstructures, and micro-hardness profiles

This study presents the investigation results of micro-channel fabrication in nickel-based super alloy (Inconel 718) by Nd:YAG laser beam machining. The effects of laser parameters on the machining performance characteristics over dimensional sizes are evaluated. Three number of laser parameters have been reserved as predictors to the naming of laser intensity, pulse frequency, and laser scanning speed. The channel's top width, bottom width, depth, and taperness are considered as the process responses. Micrographs by SEM have been organized to study and measure the micro-sized dimensions of fabricated channels. The results showed that the selection of channel size is critical to achieve desired machining results. Wider-sized channels (for example 200 x 100 mu m and 1000 x 500 mu m) can more confidently be machined than narrower-sized channels (50 x 50 mu m). The possible reasons behind the failure of narrow-sized micro-channel fabrication are identified. The appropriate combination of parameters that can yield the better results for 100 x 100 mu m channel size are the laser intensity of 92.7 %, repetition rate of 30 kHz, and scan speed of 300 mm/s. At this combination, the channel geometries of wider-sized channels are more close to the designed geometries as compared to narrow-sized channels. Microstructures of the machined channels are also studied showing the recast layer with lamellar grain structure and phase transformation near the edges of micro-channels. The channel edges and their adjacent areas show variation in hardness relative to bulk material. This has been validated via micro-hardness profiles of the close vicinity of machined micro-channels.