Study on wear mechanisms in drilling of Inconel 718 superalloy

The wear mechanisms and the approach to prolong the service life of the TiAlN coated carbide tool in drilling Inconel 718 superalloy are presented. It is found that the coated layer on the cutting edge is gradually abraded-off at the first stage of drill wear due to an excessive friction force on the tool–work interface. This in turns intensifies the friction force and leads to an increase of drilling force. Built-up edge (BUE) is then formed, and chipping starting from the relatively weaker cutting edge takes place subsequently. As a result, many micro-cracks are observed to distribute over the worn area. The subsurface fatigue cracks grow as the drilling process is proceeding. Together with the abrasion of hard carbide particles of the work material, the cutting edges break eventually parallel to the direction of fatigue cracks. At this moment, longer chip forms and cutting process is disturbed to an extent that the process can no longer be effectively continued. Failure of the drill is noted in a very short period of time once the long chips are observed. Finally, drilling experiments with the use of the cutting fluid containing the nano-particle low friction surface modifier are conducted. It is found that the service life of the drill is lengthened significantly and hence the machining cost can be greatly reduced.