Properties and Characterization of Hard Coatings and Surfaces

Wednesday, May 1, 2013 2:10 PM in Room Royal Palm 4-6

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2:10 PM B4-3-1 Novel Method for Deposition of Protective Coatings on Internal Surfaces
Thomas Casserly, John Bae, Jason Wickersham (Sub-One Technology, US); Barry Williams (URS Flint, US)

A novel hollow cathode plasma immersion ion processing method is utilized to deposit diamond like carbon (DLC) coatings on the internal and select external surfaces of metallic pipes and components. The hollow cathode effect (HCE) occurs when high energy electrons oscillate between opposing cathodes causing multiple ionization events. Plasmas taking advantage of the HCE typically have ion and electron densities hundreds of times higher than conventional plasma discharges. This phenomenon allows for very high deposition rates in excess of 3 microns per minute for optimized DLC coating applications as compared to typical chamber based deposition rates on the order of 1-2 microns per hour. DLC coatings have high density, high hardness, and strong adhesion while providing excellent wear resistance with low friction. DLC coatings are also chemically inert in most environments providing protection of the coated substrate from corrosive attack. By introducing different precursor gases, the vacuum-based plasma deposition process can produce coatings with properties tailored for specific applications. In summary, this high speed hollow cathode plasma deposition technology enables DLC based coatings to increase component life in applications where the internal surface of pipes and other parts are exposed to corrosive and abrasive environments.

2:50 PM B4-3-3 Prediction of DLC Friction Lifetime Based on a Local Archard Factor Density Approach
Fathia Alkelae, Siegfried Fouvry (LTDS - Ecole Centrale de Lyon, France)
Diamond-like carbon coatings, displaying low and stable coefficient of friction, are potentially very interesting palliatives for fretting wear applications. The purpose of the research work is to investigate the coating endurance as a function of the fretting loadings conditions such as the contact pressure, sliding amplitude. Fretting wear tests have been performed applying a 12.7 mm radius 52100 steel ball against a 2µm DLC coating deposited on 52100 plane substrate. Normal forces between 5 and 57 N, inducing maximum Hertzian contact pressures from 430 to 1000 Mpa have been tested. Sliding amplitudes from ± to ±100 µm have been investigated. The coating endurance (Nc) is related to a friction coefficient criterion fixed at a 0.3 threshold value (Fig. 1). This analysis demonstrates that above a 650 Mpa contact pressure, the coating endurance is unstable and controlled by a coating delamination process. Below this threshold pressure, the coating endurance is monitored by a progressive abrasive wear process. This analysis shows that the coating endurance in the low pressure domain can be formalized using a single local Archard’s wear parameter expressed as a function of the contact pressure (pmax), the sliding amplitude (dg) and the contact radius (a). By considering this analysis, a single master endurance curve along which all the studied test conditions are aligned has been identified (Fig. 2). In addition the endurance modeling, dedicated expertises of fretting scars combining SEM, EDX and micro raman investigations have been performed to elucidate the fretting wear damage scenario.

Fig. 1 : Definition of the coating endurance criterion related to a threshold friction condition.

Fig. 2 : Identification of the DLC coating endurance in the low pressure domain (pmax < 650 Mpa)

3:10 PM B4-3-4 Time- and Space-resolved High-throughput Characterization of Stresses during Sputtering and Thermal Processing of Al-Cr-N Thin Films
Dario Grochla (Ruhr-Universität Bochum, Germany)

Mechanical stresses (extrinsic or intrinsic) are a crucial feature of thin films. The mechanical behaviour of thin film-substrate combinations are strongly affected by internal stresses, especially with respect to the adhesion, durability and tribological performance. Thus, gaining a better understanding of stress-inducing mechanisms is an important concern for surface engineering. Interfacial stress components due to lattice mismatch or different thermal expansion coefficients contribute to the overall film stress as well as dislocations, impurities, voids and grain boundaries. To gain closer insight into the mechanisms of stress development and relaxation, real-time measurements during film growth are necessary. Furthermore, it is of interest to correlate the stresses to the chemical composition and the corresponding microstructure. This is possible in composition spread type materials libraries, where thin films of different compositions are fabricated simultaneously. In order to understand the stress development during sputtering and annealing as a function of composition, high-throughput measurement methods are needed which are both time-resolved and space-resolved.

(Al100-xCrx)N thin film materials libraries were fabricated on micro-machined cantilever arrays, in order to simultaneously investigate the evolution of stresses during film growth as well as during thermal processing by analyzing the changes in cantilever curvature. The issue of the dependence of stress in the growing films on composition, at comparable film thicknesses, was investigated. Among the various experimental parameters studied, it was found that the applied substrate bias has the strongest influence on stress evolution and microstructure formation. The compositions of the films, as well as the applied substrate bias, have a pronounced effect on the lattice parameter and the coherence length. For example, applying a substrate bias in general leads to compressive residual stress, increases the lattice parameter and decreases the coherence length. Moreover, bias can change the film texture from [111] orientation to [200]. Further detailed analysis using X-ray diffraction and transmission electron microscopy clearly revealed the presence of a [111] highly textured fcc (B1 type) Al-Cr-N phase in the as deposited state as well as the coexistence of the hexagonal [110] textured Cr2N phase, which forms in the Cr-rich region. These results show that the combinatorial approach provides insight into how stresses and compositions are related to phases and microstructures of different Al-Cr-N compositions fabricated in the form of materials libraries.

3:30 PM B4-3-5 Mechanical Properties and Microstructures of Cr-O-N Coatings Deposited by Arc Ion Plating Method
Toru Minami, Satoru Nishio (Kanefusa Corporation, Japan); Yoshinori Murata (Nagoya University, Japan)
Using AIP (Arc Ion Plating) method, Cr-O-N coatings with different O contents, and CrN coating were prepared in a gas mixture of N2 and O2. Their mechanical properties and microstructures were investigated.As the Oxygen flow rate increased, the O content in the coatings also increased. X-ray diffraction measurements revealed that Cr-O-N coatings have the NaCl type cubic CrN phase until the oxygen flow rate increased to 20%, and other phases such as oxides were not detected. The diffraction peaks of the cubic CrN phase became broad and shifted to a lower angle in proportion to the O content. As the amount of O increased, hardness of the Cr-O-N coatings increased because the grain sizes became smaller and the compressive residual stresses increased.FE-SEM observations revealed that the CrN coating has a columnar structure, while the Cr-O-N coatings have very fine microstructure and nm-scale periodic layered structures regardless of their O content. We have found that the period of the lines depends on the rotation speed of the substrate holder in the PVD equipment. Microstructures of the Cr-O-N coatings were also investigated by TEM to find the details of the periodic lines. TEM observations clearly showed that the Cr-O-N coating has the fine periodic layered structure. It was also found by STEM/EDS analysis that the oxygen concentration at the periodic lines is higher than in other areas. Furthermore, we have examined reasons why fluctuation in oxygen concentration occurs during a coating process.
3:50 PM B4-3-6 Effect of Bias Voltage on the Mechanical-tribological Properties of AlCrN Coatings
Fernando Lomello (DEN/DANS/DPC/SEARS/LISL CEA Saclay, France); Alain Billard (IRTES-LERMPS-UTBM, France); Frédéric Sanchette (LRC CEA-ICD LASMIS, Nogent International Center for CVD Innovation (Nicci), France); Frédéric Schuster (CEA Cross-Cutting Programme on Advanced Materials, France); Michel Tabarant (DEN/DANS/DPC/SEARS/LISL CEA Saclay, France)

In recent years, the application of AlCrN-type coatings in processes which involve attrition, chipping and/or cracking due to the impacts, such as the industrial metal forming has increased [1]. The cutting edge of coated tools may exceed 1000°C, therefore the oxidation resistance is a very important issue [2]. The oxidation resistance and high temperature mechanical properties of AlCrN are improved comparing with other ternary nitride such as AlTiN [3]. Furthermore, it presents good tribological properties up to 500°C, since a low friction coefficient is generally found even at high temperatures [4].

In this study, AlCrN coatings were prepared by vacuum cathodic arc deposition (CAD). This technique has been chosen due to its versatility, allowing an easy industrial up-scaling.

The correlation of processing parameters was focused on the influence of bias voltage on the resulting mechanical-tribological properties. Indeed, it was demonstrated that the variation of bias voltage by means of the ion peening effect has an important role in modifying the morphological properties - such as surface roughness, crystallite sizes and the associated residual stresses which influences the final properties.

Interesting mechanical properties such as hardness were measured. These properties were strongly affected by the combination of the grain size (Hall-Petch effect) and the intrinsic residual stress.

The tribological behaviour was a consequence of the resulting properties, especially ruled by the H/E ratio.

References

[1] G.S. Fox-Rabinovich et al. Surf. Coat. Technol. 200 (2006) 5738.

[2] H.O. Gekonde et al. Surf. Coat. Technol. 149 (2002) 151.

[3] O. Banakh et al. Surf. Cat. Technol. 163-164 (2003) 57.

[4] R. Franz et al. Tribol. Lett. 23 (2006) 101.

4:10 PM B4-3-7 Influence of Substrate Bias on the Structure and Mechanical Properties of ZrN Thin Films Deposited by Arc Ion Plating
Min Zhang (Liaoning Normal University, China); Kim Kwang Ho (Pusan National University, Republic of Korea); Huang Ye, Hu Xiaogang, Pan Yunli (Liaoning Normal University, China)
In this study, zirconium nitride thin films were fabricated using arc ion plating under different negative substrate biases. To enhance the adhesion property of ZrN films, at the first 15min of deposition process, nitrogen flow rate was zero to form a Zr interlayer with thickness of 120nm. The phase structure, composition, resistivity and mechanical properties of ZrN films, with respect to substrate bias, were studied by means of X-ray diffraction, electron probe microanalyzer, four point probe method, nanoindentation, and tribotester. Cubic ZrN and hexegenol Zr phases were formed in the films. The competition between surface energy and strain energy made the preferred orientation of ZrN films change from (111) to (200) and then back to highly (111) preferred orientation as a function of substrate bias. With the increase of bias voltage, the crystallite size of ZrN films decreases, resultantly the nanohardness of the ZrN films increases. Meanwhile, film microstructure evolves from an apparent columnar structure to a highly dense one, indicating that ion bombardment enhanced by substrate bias can suppress columnar growth in ZrN films. The deposition rate and impurity oxygen content of ZrN films were substantially influenced by the resputtering effects due to the ion bombardment on the film surface. The electrical resistivity of ZrN films ranges from 0.07 to 0.15 Ω•μm, and shows a slight increase with substrate bias.
4:30 PM B4-3-8 Effect of Cr/Al Content on Creep Resistance of AlCrN Coatings Applied by Reactive Magnetron Sputtering
Zuhair Gasem, Shahnawaz Alam (King Fahd University of Petroleum and Minerals, Saudi Arabia); Allan Matthews (University of Sheffield, UK)
The main objective of this work is to characterize the creep resistance of reactive magnetron sputtered AlCr nitride coatings as influenced by the Cr/Al content. The coating composition was varied by using a pure aluminium target with variable number of Cr plugs inserted along the sputtering track. A comparative creep test has been carried out for high and low Cr/Al coating compositions sputtered on H13 tool steel substrates. Creep testing was carried out by applying a constant load for a short period of time and monitoring the extent of penetration in the coating over a range of temperatures (25-150oC). The loads applied were 20 mN, 40 mN, and 60 mN with a fixed loading rate of 20 mN/min. The coatings were characterized in terms of their elemental composition, phase composition, mechanical, and tribological properties. Preliminary results indicate that the creep resistance of AlCrN based coatings is sensitive to CrN and AlN phase distribution. At low temperatures, creep resistance is higher for the high Cr/Al coating. As the temperature is increased, the creep resistance of AlCrN coatings demonstrates less sensitive response to the Cr/Al content. The dependence of the creep resistance behaviour of AlCrN coatings on the temperature level will be discussed in terms of the coatings phase character and distribution.