The impact of TiN coating on the performance of Al2O3-TiC ceramic tools in hard turning

. Ceramic tools are widely applied in machining processes due to their high level of hardness, chemical stability, and wear resistance. However, ceramic tools have low resistance to thermal shock, thus turning with these tools is usually carried out without cutting fluid. To limit the drawbacks of dry turning, the use of coated tools is typically adopted, but there is no consensus on the impact of coatings on mixed-ceramic tools. Although coatings on ceramic tools can improve the machining process, the cost is high and is usually not justified by the result because of the weak adhesion between the coating material and the ceramic substrate. In this context, this study investigates the impacts of TiN coating on the performance of Al 2 O 3 -TiC ceramic tools applied in dry turning of the hardened steel AISI 4340 (55 HRC). Radial turning experiments were performed with (v c ) = 150 m/min, feed (f) = 0.08 mm/rev, and depth of cut (a p ) = 0.20 mm. Machining forces, tool wear and surface roughness in turning with coated and uncoated mixed-ceramic tools were evaluated. The TiN-coated ceramic tool has a higher edge radius, which caused higher cutting force and passive force than the uncoated tool. On the other hand, the TiN coating provides higher toughness to the tool, leading to lower notch wear in coated tool. The flank and notch wear were the main forms of wear in the uncoated tool, while in the coated tool was formed a crater that contributed intensely to the volume of material removed from the tool (W RM ). The value of the W RM for the coated tool was approximately 22% higher than for the uncoated tool. Despite this, the lower notch wear in the coated tool was decisive for the quality of the machined surface. When using the TiN-coated tool a decrease around 40%, 44%, and 47% in the roughness S z , S a and S q occurred, respectively.