FAILURE MODES AND WEAR MECHANISMS OF M35 HIGH-SPEED STEEL DRILLS WHEN MACHINING INCONEL-901

High-Speed Steel drills (M35) with different drill-point geometries were used to machine a nickel base, Inconel 901, superalloy at various combinations of cutting speed and feed in order to assess their overall performance and to identify their failure modes as well as the wear mechanisms responsible for drill failure. Test results show a general reduction in drill performance at higher cutting conditions due to increased temperature and pressure during machining in addition to the rapid rate of work hardening of the Inconel 901 work material. The increased temperature usually causes over-tempering of the drill lips, as evidenced by a significant reduction in the hardness of the cutting edges of the worn drills. Rapid work-hardening of the Inconel 901 alloy was a major cause of the rapid drill wear at particular cutting conditions due to the increased hardness values of the work-hardened region (up to 90% greater) relative to the hardness of the base material. Unground 120 degrees, split-point drills gave the greatest wear resistance of all the drill geometries investigated, hence they gave longer service life. Study of the worn drills revealed wear on the flank face, the chisel edge and the margin, and crater wear. The flank and crater wears are most critical for drill performance and often lead to severe chipping of the drill lips or fracture of the entire drill. The wear mechanism study showed that attrition, abrasion, adhesion and plastic deformation could singly or jointly contribute to the wear of High-Speed Steel drills when machining Inconel 901.