A comparative study on novel coated inserts for turning solution treated and aged (STA) Ti-6Al-4V

Machining titanium (Ti) alloys, such as Ti-6-Al-4V, presents significant challenge due to their poor thermal conductivity, low stiffness and its tendency to interact detrimentally with cutting tools. These characteristics often lead to accelerated tool wear and frequent tool fracture, posing significant challenges in machining. This study investigates the effectiveness of various coatings on carbide inserts for improving tool performance with the turning experiments on solution-treated and aged (STA) Ti-6Al-4V bars. A series of dry turning experiments were conducted at cutting speeds of 61, 91 and 122 m/min, comparing the performance of uncoated inserts with various coated inserts. The coated inserts examined includes commercially available AlTiN, TiAlN, and ZrN, as well as customized AlMgB14 (BAM) and (AlCrSi/Ti)N coatings with varying thicknesses. Tool wear progression was analyzed using a confocal microscope, focusing on the development of flank and crater wear. The experimental results revealed significant nose fracture in most inserts under the test conditions. Despite this, the (AlCrSi/Ti)N and BAM coatings demonstrated superior performance in mitigating both flank and crater wear compared to the uncoated carbide inserts. Notably, the (AlCrSi/Ti)N-coated insert with a 7 μm thickness showed at least threefold increase in tool life at the lowest cutting speed of 61 m/min compared to the uncoated carbide inserts. At the intermediate and high speeds, BAM-coated inserts proved effective in reducing crater wear and provided a moderate extension of tool life compared to the uncoated inserts. Through this work, the main wear mechanism for crater wear is determined to be diffusion.