Abstract
Drilling micro-holes at different orientations on thermal barrier coated Inconel 718 superalloy surface is essential to protect turbine blades while operating in harsh environment. This work analyses integrity of micro drilled (600μm) surfaces on thermal barrier coated Inconel 718 sheets using TiAlN coated carbide micro-drills. Considering spindle speed, drill feed, and workpiece inclination, the drilling experiments were performed under dry environment with 100μm pecking length. Results show that, a higher tool life in terms of drilling length was observed in straight hole drilling at a combination of low speed (1000 rpm) and low feed (3μm/rev). The drilled surface roughness increased with the number of drilled holes and the highest value of roughness was observed to be 1μmRa on the 13th inclined hole surface. Smaller cavities were observed on the thermal barrier zirconia coated surfaces. In addition, drilled hole surfaces on metal showed alterations such as adhered chip particles and smeared material. Tensile residual stresses were observed in hoop direction and were found increase with the number of hole drilled in both straight and inclined surfaces. The highest compressive residual stress (1075.3 MPa) was observed in the axial direction on the 5th hole surface for inclined hole drilling, which shows an increase in the d spacing between two planes of machined surface.
Published Version
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