XPS and AFM Investigations of Ti-Al-N Coatings Fabricated Using DC Magnetron Sputtering at Various Nitrogen Flow Rates and Deposition Temperatures

Abstract

Ti-Al-N coatings were deposited by direct current magnetron sputtering (DCMS) onto IN 718 at different nitrogen flow rates and deposition temperatures. The coatings' properties were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) as well as nanoindentation. It was found that higher deposition temperature leads to higher surface roughness and nitrogen flux influences the shape of grains. According to XPS, the bonding structure of all coatings exhibited the (Ti,Al)N phase. Mechanical properties depend on the Al content within the films. The coating with the best mechanical properties (deposited at 500 • C and 20 standard cubic centimeters per minute (sccm)) was further deposited onto tungsten carbide (WC) cutting tools for cylindrical turning experiments. A quasi-constant flank wear was observed until a machining volume of 23,500 mm 3 .

Effect of HPPMS Pulse-Frequency on Plasma Discharge and Deposited AlTiN Coating Properties

“…This is confirmed by the results from Obrosov et al [10], which show a surface roughness ms of 13.0 nm for AlTiN coatings deposited by dcMS at the same average power and nitrogen flow rate. According to Figure 14 (100 Hz), the surface is characterized by many elevated, rounded particle-like structures with various lateral dimensions (red marked), which may result from different velocities of coating growth or from the deposition of droplets caused by arcs.…”

“…So, AlTiN coatings deposited by HPPMS generally show a denser and smoother structure without column growth than coatings deposited by dcMS at the same average power due to increased metal ion bombardment [15]. This is confirmed by comparing the coating structure with published results from Obrosov et al [10]. Such a dense featureless, feathery coating structure is typical for coatings deposited with pulsed magnetron sputtering as, for example, Keunecke et al [48] and Jílek Jr. et al [49] have shown.…”

“…The constant pulse-on-time of 50 s has been chosen as it enables a high current density according to investigations on the effect of HPPMS pulse length with a comparable average cathode power (5 kW), similar process temperature (500 ∘ C), and pulse-frequency (500 Hz) from Bobzin et al [18]. The constant process temperature of 500 ∘ C and the nitrogen flow rate of 40 sccm (nitrogen partial pressure of 83 mPa) were chosen to compare the current results for AlTiN coatings deposited by HPPMS with previously published results for AlTiN coatings deposited by conventional dcMS at the same average power of 4 kW and argon pressure of 0.6 Pa from Obrosov et al [10].…”

“…Thus, the deposited AlTiN coatings belong to superhard coatings with low elastic moduli. In comparison, AlTiN films deposited by dcMS from Obrosov et al [10] reach a hardness of 21.5 GPa with elastic modulus of 238 GPa at the same average power, process temperature, and nitrogen flow rate. For different process conditions, AlTiN films deposited by dcMS from Jílek Jr. et al [49] reach a hardness of 33.4 GPa with elastic modulus of 466 GPa.…”

“…A well-known hard coating is Al Ti −1 N ( = 0.6), deposited by dc-magnetron/arc sputtering, which offers an increase in component life due to high hardness and resistance against wear, corrosion, and oxidation at high temperatures [5][6][7][8][9][10][11]. With increasing challenges of operating conditions, a constant need in improvement of material properties is required to withstand extreme loadings.…”