The Effectiveness of Diamond-like Carbon a-C:H:Si Coatings in Increasing the Cutting Capability of Radius End Mills When Machining Heat-Resistant Nickel Alloys

Abstract

The main purpose of this paper was to study the efficiency of using diamond-like carbon (DLC) coatings based on a-C:H:Si with a pre-formed CrAlSiN sublayer to increase the cutting ability of ball end mills made of KFM-39 cemented carbide at a speed of 150–250 m/min in milling aircraft-grade Inconel 718, and to assess the DLC coating effect on the quality of the machined surface. DLC coating performance was quantified against uncoated carbide ball end mills and the proven TiN–AlN–TiAlN gradient multilayer coating at elevated temperatures measured by the natural thermocouple method. The temperature near the cutting edge is the factor determining the wear intensity in the tool contact surfaces in milling hard-to-machine nickel alloys to the greatest extent. Thermo-EMF (electromotive force) was recorded and converted into temperatures by calibration charts. The behavior of CrAlSiN–DLC and TiN–AlN–TiAlN coatings was compared with the results of high-temperature tribological tests on a ball-on-disc friction machine. For the CrAlSiN–DLC coating at cutting speeds of 150 and 200 m/min (<650 °C), the milling time until critical flank face wear (0.4 mm) was more than 67 and 50 min, respectively (1.4–1.5 times longer than an uncoated tool and about 1.3 times longer than the TiN–AlN–TiAlN coating). The CrAlSiN–DLC coating was characterized by a minimum adhesion amount.