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.
Highlights
Precision products made of heat-resistant nickel alloys, such as Inconel 718 and Nicrofer 5219 Nb, are more than 50% of the mass of modern aircraft gas turbine engines due to the unique physical and mechanical properties of these materials and their ability to function under conditions of increased contact stresses, high operating temperatures, and corrosive and erosive effects of vapors and gases [1,2,3,4,5]
It can be seen that the nitride and diamond-like carbon (DLC) coatings were uniformly formed on the working surfaces of the end mills and did not radically change the cutting edge radius
The Transmission electron microscopy (TEM) image of the structure of the surface layer of cemented carbide samples coated with CrAlSiN–DLC (Figure 5c) demonstrates that the nitride sublayer had a classic columnar structure, and the outer DLC layer based on architecture of the CrAlSiN–DLC coating (a-C):H:Si had an amorphous structure, in which no pronounced grains and boundaries between them were observed
Summary
Precision products made of heat-resistant nickel alloys, such as Inconel 718 and Nicrofer 5219 Nb, are more than 50% of the mass of modern aircraft gas turbine engines due to the unique physical and mechanical properties of these materials and their ability to function under conditions of increased contact stresses, high operating temperatures, and corrosive and erosive effects of vapors and gases [1,2,3,4,5]. [3] discussed the bulk properties of a military aircraft’s gas turbine engine parts that determine the product life and are decided by the aero-thermal degradation and microstructure degeneration of nickel alloy despite aluminide coating. [4] investigated the microstructure of gas turbine engine aircraft parts after heat treatment of granulated heat-resistant nickel alloys characterized by high long-term strength at 750 ◦C and confirmed the phase stability of the material. The results of numerical simulations showed that the laser path strategy favors a thermal gradient that partially induces geometrical distortions
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