The Effects of Substrate Bias and Edge Proximity on the Mechanical Properties and Machining Performance of TiN-Coated Carbide Inserts

摘要

The effects of substrate bias on magnetron sputter-deposited TiN-coated carbide inserts were examined with a focus on the property changes that occur near the cutting tool edge. Sandvik SPG-422 polished carbide inserts were coated with TiN using substrate bias levels ranging from -25 to -150 V. The hardness was measured using the nano-indentation method and x-ray diffraction was used to measure residual stress. The bias strongly affected the appearance of the region 1-2 mm from the tool edge with defect formation, cracking, and delamination observed at the higher substrate bias levels. For samples deposited at bias levels of up to -50 V, the coating composition was not strongly affected by edge proximity and the hardness exhibited only a small increase with bias of about 3 GPa. The residual stresses were measured using the sin~2ψ method, and it was found that both the increasing bias level and proximity to the edge increased the degree of compressive stress, reaching -3.2 GPa at edge location of the -50 V bias sample. The machining performance was assessed by turning hardened 4340 steel, and only the samples deposited at -25 and -35 V exhibited substantial improved tool wear in comparison to an uncoated edge. These results correlated well with the appearance of the cutting tool edge and the measured stress levels.