Influence of N2 Flow Rate on the Microstructure, Mechanical, and Tribological Properties of Ti-Al-Cr-N Coating: Dry Milling Investigation on 6061 Aluminum Alloy

Ti-Al-Cr-N coatings were synthesized by manipulating the nitrogen (N2) flow rate and via a hybrid physical vapor deposition process. The morphologies, microstructures, mechanical properties, tribological behavior, and milling performance of Ti-Al-Cr-N coatings were systematically investigated. Results indicated Ti-Al-Cr-N coatings were composed of Ti(Al, Cr)N, which grew preferentially along the (111), (200), and (220) crystal planes. Furthermore, low N2 flow rates of 40 sccm and 60 sccm facilitated the formation of the amorphous-like metallic. Ti-Al-Cr-N coating with the N2 flow rate of 100 sccm showed the maximum hardness (18.5 GPa) and elastic modulus (207.7 GPa), inferior toughness, a minimum friction coefficient of 0.62, and the lowest wear rate of 1.68 × 10−11 m3·N−1·m−1. Meanwhile, the Ti-Al-Cr-N-coated mill with the N2 flow rate of 100 sccm presented an enhanced wear life of about 1.8 times than that of the uncoated mill when dry milling aluminum alloy and the wear modes were mainly abrasion and diffusion wear. This article provides a novel way of processing soft metal materials, such as aluminum alloy.