Jeon G. Han

High temperature wear resistance of (TiAl)N films synthesized by cathodic arc plasma deposition

(TiAl)N films were deposited on M2 high speed steel by cathodic arc plasma deposition process employing two separate targets of Al and Ti, and the formation behavior of the film was investigated by Auger electron spectroscopy (AES), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The composition of (TiAl)N films was varied by controlling the cathode current ratio (IAl/ITi) of Al and Ti targets at constant arc voltage. As the ratio IAl/ITi increased from 0.31 to 0.73, the Al/Ti atomic ratio linearly increased from 0.49 to 1.29. The hardness of (TiAl)N reached 3000 kg mm−2 at the Al/Ti atomic ratio of 1.10. The high temperature wear resistance of (TiAl)N films was consequently enhanced up to 600°C. A significant improvement of the high temperature wear resistance could be obtained below the temperature of 500°C. The wear mechanisms were discussed and correlated with changes in dynamic friction coefficient and microstructural wear track analysis.

A study on the high rate deposition of CrNx films with controlled microstructure by magnetron sputtering

Abstract High rate deposition of CrNx films with control of microstructure was carried out by magnetron sputtering. For these purposes, the deposition processes parameters were varied: N2 flow rate and especially substrate bias voltage, duty cycle and frequency using a pulsed DC power supply. The microstructure was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and mechanical properties were evaluated by a microhardness test and adhesion test. The maximum deposition rate for CrNx compound films could be reached to nearly 90% compared with that for pure Cr coating due to the increase of ionization efficiency caused by a negative-pulsed DC bias. As N2 flow rate is increased, the microstructure of CrNx films was changed from Cr+Cr2N to CrN. Also, a phase transformation occurred between Cr2N+CrN multi-phase and CrN mono-phase by control of a negative DC and/or pulsed DC bias voltage, duty cycle and frequency. Microhardness for CrNx films were measured to be up to 1600 kg/mm2 and the maximum hardness value of 2250 kg/mm2 was obtained for CrNx film deposited with a N2 flow rate of 20 sccm at a negative DC bias of −100 V.

A study on the synthesis and microstructure of WC-TiN superlattice coating

Abstract WC–TiN superhard coatings are formulated to form a nanoscaled superlattice by separate arc reactive evaporation of Ti and WC. The microstructure of WC–TiN films was identified to be a superlattice of TiN and β-WC1−x phases with modulation period (λ) of 5–13 nm and the lattice planes were continuous through the TiN and β-WC1−x layers. The residual stress of WC–TiN films was measured to be 7.9 GPa. This high stress was reduced to 2.2 GPa by introducing Ti or Ti–WC interlayers. Ti–WC interlayer also increased the film adhesion strength. In spite of almost the same residual stress of 2.2–2.3 GPa, Ti–WC/WC–TiN film showed a higher adhesion strength of 48.5 N than that of Ti/WC–TiN film. These results are attributed to the low residual stress and higher stiffness of the Ti–WC interlayer than the soft Ti interlayer. The microhardness of Ti–WC/WC–TiN film on cemented carbide was measured to be 40 GPa and the maximum hardness was obtained as the period (λ) was approximately 7 nm. This value is approximately 1.5 times higher than that of the TiN single layer film. Other WC–TiN superlattice coatings with Ti and WC interlayers showed a hardness range of 38–40 GPa. The ratio H3/E2 (plastic deformation resistance) of WC–TiN superlattice films with various interlayers was calculated to be in a range from 0.18 to 0.33. This paper reports the preparation of WC–TiN superlattice coatings on WC–Co and Si substrates using a multi-cathode arc ion-plating system. The microstructures and mechanical properties of WC–TiN superlattice films were investigated, too.

Deposition behaviours of CrN films on the edge area by cathodic arc plasma deposition process

Abstract The deposition behaviours of CrN films were evaluated on the various geometrical angles of H13 steel in the cathodic arc plasma deposition process. Specimens were prepared with edge angles of 30°, 60° and 90° and deposited with CrN at various DC bias voltages of 0–400 V in continuous or interrupted modes. The film surface morphology and growth rate were significantly changed with the edge angle. The deposition rate was enhanced with an increase in edge sharpness. The noted feature of the CrN coating on the sharp edge region is the remarkable surface roughening due to accelerated accumulation of deposited vapour molecules at many localized spots during continuous DC biased coating. The atomic ratio of Cr to nitrogen was also varied from the edge tip to the bottom zone for angled specimens. Interrupted DC biasing at 100 V during deposition could effectively reduce the particle accumulation, thereby providing the confirmed smooth coating.

The shear impact wear behavior of Ti compound coatings

Abstract The failure behavior of Ti compound coatings was evaluated under normal and shear impact conditions at room and elevated temperatures. Monolayers and combined multilayers of TiAlN and TiAlCN were deposited onto high speed steel by a cathodic arc ion plating process. The shear impact loading mode was obtained by rotating the coated disk specimen at a speed of 0.8 m s −1 under repetitive normal impact loading of 10 N using a CoWC ball indentor with a frequency of 5 Hz. The impact resistance under normal impact loading appeared to be higher in the order TiAlN, TiAlN/TiAlCN and TiAlCN in accordance with the adhesive strength measured by HRC indentation tests. Meanwhile the addition of shear force during repetitive normal impact loading by specimen rotation reduced significantly the failure resistance of all the films, both at room temperature and 600°C, with a change in failure mode. It was observed through progressive failure analysis with increasing repetitive loading cycles that the failure under shear impact loading was accelerated owing to the promotion of crack formation as well as laminated fragmentation by increasing tensile and shear stresses at the ball trailing zone resulting from tracking forces during repetitive instantaneous impacting and sliding. The propensity for failure became more severe owing to substrate softening for all the coatings as the temperature increased to 600°C.

The ion current density and spectroscopic study in a straight magnetic filtering arc deposition system

Abstract The changes of plasma states during cathodic arc discharges of Ti and TiAl under various magnetic fields of straight magnetic solenoid were analyzed by Langmuir probe method and optical emission spectroscopy (OES). The ion emission intensity of Ti II for Ti arc discharge was enhanced by a factor of 2. with increasing magnetic field up to 150 Gauss compared to that under no magnetic fields. For discharging TiAl with ambient N2 under 150 Gauss, however, the emission of Al exhibited dominant neutral emission of Al I only with slight increase of ionized Al II emission while Ti II emissions were increased at a similar ratio as measured in Ti discharge. The enhancement of electron density induced by a straight solenoid magnetic field promoted the effective ionization of metal vapors, therefore producing a high fraction of ionized vapor flux including macroparticles, which contributed to the increase of deposition rate and sputtering of macroparticles seated on the film surface by energetic metal ion flux. The changes of surface morphology and film formation behaviors of TiN and (TiAl)N arc was evaluated with a variation of external magnetic field in conjunction with plasma conditions obtained from Langmuir probe, OES and XRD analyses. The corresponding hardness and friction coefficient variations are also illustrated.