Experimental Investigation of Micro-Machinability of Nano-TiC Reinforced Inconel Fabricated by Direct Metal Laser Melting

The objective of this paper is to experimentally investigate the machinability of nano-TiC reinforced Nickel based super alloy Inconel 718 fabricated by direct metal selective laser melting (SLM). Four 10×10×3 square test coupons were fabricated with different amount of nano-TiC: (1) pure Inconel 718, (2) Inconel 718+0.25% TiC, (3) Inconel 718 + 0.5% TiC, of 508 microns. The machinability of the four materials were examined in terms of cutting forces, tool wear and chip morphology. Three level of federates (1.0, 1.5 and 2.0 um/flute) and three level of spindle speeds (12,000, 15,000 and 18,000 rpm) were selected and a 3² full factorial experiment was performed on each test coupon. Full immersion slotting was selected with a fixed axial depth of cut at 20 microns. The SEM images of the tools reveal that the dominant wear mechanisms were abrasive wear at the tool tip and flank face. The adhesion and build up edge were also common. The wear rate increases with the addition of nano-TiC. The loss of the AlTiC coating will result in accelerated wear, which was observed for machining of nano-TiC reinforced Inconel 718, but not on pure Inconel 718. The edge chipping and abrasive wear at the tool tip reduced the effective cutting diameter, enlarged the edge radius, and caused the increase of the cutting force. For all the materials tested, the cutting chips had serrated edge on the free surface and much smoother surface on the other side, which suggests that a cyclic chip formation of alternating high shear strain followed by low shear strain. This is in agreement with the chip formation mechanism for the Inconel 718 fabricated with conventional method rather than DMLS. The serration is more severe with the and (4) Inconel 718 + 1% TiC. Tensile tests were performed on all four material and the material strength increases with the increase of the TiC content up to 0.5% then plateaued. The elongation drop significantly with the inclusion of TiC in Inconel substrate. Micro-endmilling experiments were conducted using AlTiN coated WC micro-mill with nominal diameter addition of nano-TiC. The cutting forces were collected with a Kistler 3-axial load cell 9017B. The cutting forces increases with the increase spindle speed (hence surface speed) within the range examined, but the effect of feedrate is not statistically significant. The cutting forces were much higher for TiC reinforced Inconel and the magnitude of the cutting forces increases with the increase of the weight percentage of TiC contents.