ICMCTF2006 Session B7-2: Properties and Characterization of Hard Coatings and Surfaces
Monday, May 1, 2006 1:30 PM in Golden West
B7-2-1 Nanostructure and Properties of TiC/a-C:H Composite Coatings
Y. Pei, D. Galvan, J.T.M. De Hosson (University of Groningen, Netherlands)
TiC/a-C:H nanocomposite coatings, deposited with closed-field unbalanced magnetron sputtering, have been scrutinized with atomic force, scanning and high-resolution transmission electron microscopy, nanoindentation and tribo-tests. These coatings consist of 2-5 nm TiC nanocrystallites embedded in an amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Toughening of the nanocomposite coatings has been achieved effectively on two different scales, namely by restraining the formation of columns on a microscale and by manipulating the nanostructure on a nanoscale. The hardness (H) and elastic modulus (E) of the coatings are found to increase monotonically with increasing substrate bias, whereas the ratio of the hardness to the elastic modulus (H/E) remains approximately constant. In contrast, the ratio H/E increases with C content. Ball-on-disc tribo-tests confirm that the nanocomposite coatings possess superior wear resistance and strong self-lubrication effects with a coefficient of friction as low as 0.05 in ambient air and below 0.02 in dry air, under dry sliding against uncoated bearing steel balls. Physical arguments are presented to explain the toughening mechanism and the ultra-low friction.
B7-2-3 Deposition of Nanometer- to Micron-Thick Crystalline TiC Films by Magnetron Sputtering
C.A. Freyman, Y.W. Chung (Northwestern University)
During magnetron sputter-deposition of TiC thin films, previous studies reported that the first 50 nm or so is always amorphous. This observation is intriguing because other Ti-based refractory coatings, such as TiN and TiB@sub 2@, grow as crystalline films at the nanometer scale without the presence of an intermediate amorphous layer. In our studies, we discovered that base pressure and target outgassing before deposition have significant effects on the crystalline growth of TiC. This observation parallels earlier studies of the growth of strontium titanate and cubic boron nitride. In these studies, it was found that trace amounts of water vapor and oxygen have drastic effects on the crystalline growth of respective compounds. Our studies suggest that the difficulty associated with the growth of crystalline alumina may be related to water vapor impurities present in the sputter-gas environment.
B7-2-4 Syntheses and Mechanical Properties of Cr-Mo-N Coatings by a Hybrid Coating System
D.S. Kang, J.W. Jeon, E.Y. Choi, K.H. Kim (Pusan National University, Korea)
Ternary Cr-Mo-N coatings were synthesized onto steel substrates (AISI D2) using a hybrid coating method of arc ion plating (AIP) using Cr target and DC magnetron sputtering technique using Mo target in N2/Ar gaseous mixture. The Cr-Mo-N coatings were synthesized with various Mo contents ranging from 0 to 30 at. %, and the mechanical properties such as microhardness, wear behavior of Cr-Mo-N coatings were systematically investigated. The Cr-Mo-N coatings showed largely increased hardness value of approximately 34 GPa at the Mo content of about 20 at. % while pure CrN coatings showed low hardness value of 18 GPa. The average friction coefficient of Cr-Mo-N coatings slightly decreased from 0.46 of CrN to 0.38. In this work, the effect of Mo addition on the microstructure and characteristics of CrN coatings are reported using instrumental analyses such as XRD, XPS, TEM.
B7-2-5 Effect of Al on the Thermal Stability of CrN Thin Films
H. Willmann (Materials Center Leoben, Austria); W. Ernst (University of Leoben, Austria); P.H. Mayrhofer (RWTH, Germany); A.E. Reiter (Balzers Ltd., Liechtenstein); L. Hultman (Linköping University, Sweden); C. Mitterer (University of Leoben, Austria)
CrN and CrN-based films are widely used for different industrial coating applications. Although, Al-additions to CrN improve the mechanical properties and oxidation resistance their high temperature applications are limited due to the N-loss of CrN-based materials, starting already at temperatures below 1000°C. Due to supersaturated phases, there is potential for several age-hardening processes in this system.@paragraph@In this work thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS) are used in combination with X-ray diffraction to study thermal stability and phase transformations occurring in Al@sub x@Cr@sub 1-x@N thin films. Pure CrN decomposes during annealing in inert atmosphere above 950 °C to Cr and N@sub 2@ via the formation of Cr@sub 2@N. The reaction steps are individually identified with simultaneous use of TGA/DSC/MS measurements at different heating rates.@paragraph@For as-deposited face-centered cubic (fcc) Al@sub x@Cr@sub 1-x@N films, the onset temperature of N-loss was found to increase with increasing Al content. However, fcc solid solution with Al contents approaching the solubility limit show a maximum in driving force for precipitation of AlN. This precipitation causes the remaining matrix to become Cr-rich and the onset temperature of N-loss decreases. For Al@sub 0.7@Cr@sub 0.3@N, the precipitation of AlN starts at ~650°C and the correspondingly Cr-enriched remaining matrix decomposes into Cr and N@sub 2@. Exceeding the solubility limit during deposition, results in the growth of hexagonal structured thin films with improved thermal stability, but decreased mechanical properties. The results show that by Al addition the onset temperature for decomposition of CrN into Cr and N@sub 2@ can be increased by ~100°C.
B7-2-6 Structure, Hardness and Thermal Stability of Ti(Al,N) Coatings
J.C. Oliveira, A. Manaia, A. Cavaleiro, M.T. Vieira (Universidade de Coimbra, Portugal)
Using hard coatings to improve the lifetime of prototyping moulds could allow the production of low and mid series from low strength materials moulds. However, a good compromise between high hardness and low friction coefficient must be reached. Coatings of Ti(Al) with low nitrogen content were deposited by magnetron sputtering on M2 (AISI) steel and aluminium substrates using two facing Ti targets incrusted with Al rods. Three sets of depositions with increasing number of Al rods were carried out. The Al/(Al+Ti)atomic ratio in the films was in the range of 21 to 27 at. %, as measured by Electron Probe Microanalysis (EPMA). For each deposition set increasing N fluxes were used leading to N/(Al+Ti+N) atomic ratios up to 33.2 at %.@paragraph@X-ray diffraction showed that the h.c.p. Ti phase with a <001> preferential orientation was always obtained for the as-deposited films without N. A decrease in the c lattice parameter was observed as Al was added to these films. On the contrary, N addition increased the c parameter. Collapse of the crystalline h.c.p. Ti lattice was also observed as a result of N incorporation. Amorphization of the films was favored by higher aluminum contents.@paragraph@A hardness of ±13 GPa was measured for the as-deposited films without nitrogen in spite of their different aluminium content. A continuous increase in hardness was observed with increasing nitrogen content. The highest harness values (up to 27 GPa) were obtained for the amorphous films.@paragraph@Annealing of the lower Al content films (Al/(Al+Ti) = ± 21 at. %) at 975 K for one hour in a dynamic hydrogenated argon atmosphere did not significantly affect their structure as h.c.p. Ti remained the only phase detected. On the contrary, annealing of the films deposited with higher Al contents (Al/(Al+Ti) = ± 24 and 27 at. %) induced the formation of new phases, including f.c.c Al and Ti@sub 3@Al, showing that the thermal stability of the films was degraded by Al incorporation.
B7-2-7 Effects of Substrate to Target Working Distance and the Nitrogen Pressure on Properties of CrAlN Coatings Deposited by Pulsed Closed Field Unbalanced Magnetron Sputtering (P-CFUBMS)
J. Lin, B. Mishra, J.J Moore (Colorado School of Mines); W.D. Sproul (Reactive Sputtering Consulting, LLC)
The aim of the research was to determine the dependence of the properties of CrAlN films deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) on the substrate to target distance (STD) and nitrogen pressure and resulting composition of the generated plasma. The microstructure, mechanical and tribological properties of the CrAlN films were characterized by X-ray diffraction (XRD), optical microscope (OM), Scanning electron spectroscopy (SEM), atomic force microscopy (AFM), pin-on-disk micro-tribometer and nanoindentation. The Hiden Electrostatic Quadrupole Plasma Analyser (EQP) has been used to investigate the plasma composition and energy spectra. In present research, the density, nano-hardness and wear resistance of CrAlN films improved with increasing STD at fixed substrate position. In order to compare the CrAlN film deposited under rotation condition with the films deposited at fixed substrate position, a planetary rotation system was designed and built. The CrAlN film deposited at a relatively short STD with the rotation system has comparable properties with those films deposited at long STD at fixed substrate position. The CrAlN films also exhibit improved microstructure and mechanical properties with increasing nitrogen pressure during the deposition.
B7-2-8 The Microstructure and Mechanical Properties of Pulsed DC Magnetron Sputtered Nanocomposite Cr-Cu-N Thin Films
J.W. Lee, Y.-C. Kuo (Tung Nan Institute of Technology, Taiwan); S.-K. Tien (National Tsing Hua Univerisity, Taiwan)
The nanocomposite Cr-Cu-N thin films have been deposited by the bipolar asymmetric pulsed DC reactive magnetron sputtering. Different substrate bias and substrate temperature were employed during sputtering. Oscilloscope traces of the I-V wave forms were recorded. The chemical compositions of the Cr-Cu-N films were determined by a field emission electron probe microanalyzer. The structures of Cr-Cu-N thin films were analyzed by XRD. The surface and cross sectional morphologies of thin films were examined by scanning electron microscopy and atomic force microscopy, respectively. The nanoindentation, scratch and wear tests were adopted to evaluate the mechanical properties of Cr-Cu-N coatings. The effects of the Cu content, substrate bias and substrate temperature to the structure and mechanical properties were discussed. It was concluded that the nanohardness of the Cr-Cu-N coating increased with decreasing Cu content. The scratch and Daimler-Benz Rockwell-C adhesion strength test results of the Cr-Cu-N coatings showed good adhesion properties. A sufficient wear resistance of the Cr-Cu-N thin films was also obtained.
B7-2-9 Influence of Oxygen Content in Powder Metallurgical TiAl33/67at% Targets on Characteristics of TiAlN Coatings
P. Polcik (PLANSEE Metall GmbH, Austria); M. Kathrein (CERATIZIT Austria GmbH, Austria); A. Kolbe (Technische Universitaet Bergakademie Freiberg, Germany); C. Michotte, M. Penoy (CERATIZIT Luxembourg S.à.r.l., Luxembourg)
TiAl targets produced by powder metallurgy are characterized by several advantageous properties such as high density, uniform microstructure as well as homogeneity concerning chemical elements and distribution of impurities. The quality of targets depends on the manufacturing process and for the most part on the quality of the powder ingredients used. In the choice of powder components great importance is given to the oxygen content because of formation of non conductive oxides having negative influence on coating quality. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA), glow discharge optical spectrometry (GDOES) and X-ray diffraction (XRD). Coating hardness and adhesion properties were evaluated by Vickers micro-indentation and scratch tests. On the target side special attention was paid to microstructure investigated by means of optical microscopy (OM) as well as to thermal diffusivity and specific heat capacity measured using the laser flash technique and calorimetric method, respectively. The aim of this work was to investigate the influence of oxygen content in aluminum powder, used for the production of TiAl33/67at% targets, on specific characteristics of TiAlN coatings deposited on cemented carbide samples in a commercial PVD unit. A relationship was found between the oxygen content in the target and the thermal conductivity of target material, roughness of sputtered target surface and finally the density and distribution of droplets on the coating surface. It was found that over a wide range of oxygen content in the target there is no significant influence on the coating characteristics examined.
B7-2-10 Effect of Oxygen Flow Rate on the Structure and Properties of Nanocrystalline Zr(N,O) Thin Films Deposited by Ion Plating
J.-H. Huang, K.H. Chang, G-.P. Yu (National Tsing Hua University, Taiwan)
Nanocrystalline Zr(N,O) thin films were deposited on (111) Si wafers using hollow cathode discharge ion-plating (HCD-IP) system. The effect of oxygen flow rate (ranging from 0 to 8 sccm) on the composition, structure and properties of the Zr(N,O) thin films was investigated. The oxygen content of the thin film determined using X-ray Photoelectron Spectroscopy (XPS) increased significantly with the increase of the oxygen flow rate. As the oxygen content increased, the color of Zr(N,O) thin film changed from golden yellow to blue and then slate blue; the microstructure observed by Scanning Electron Microscopy (SEM) changed obviously. Phase separation of ZrN and monoclinic ZrO@sub 2@ was observed in X-ray Diffraction (XRD) patterns when the oxygen content was higher than 9.7 at%. The grain sizes of the ZrN and ZrO@sub 2@ phases in the Zr(N,O) films were ranged from 12 to 5 nm and 8 to 2 nm, respectively. A phase separation mechanism was proposed: the ZrO@sub 2@ phase precipitated on grain boundaries as the oxygen content was lower than 32 %, and above which, a growth competition between ZrN and ZrO@sub 2@ occurred. The hardness of the film increased slightly as the oxygen content was less than 9.7 % and decreased to 15.7 GPa, a typical value of ZrO@sub 2@ phase, as the oxygen content further increased. The total residual stress of the film was measured using an optical method and the residual stresses of ZrN and ZrO@sub 2@ phase were measured separately using modified XRD sin method. The total stress was close to that in ZrN phase as the fraction of ZrO@sub 2@ phase was less than 30 %, and was close to that in ZrO@sub 2@ phase as the fraction was over 30 %. The electrical resistivity of the film increased significantly with the increase of oxygen content. Phase separation showed consistent effects on film properties. As the fraction of ZrO@sub 2@ phase was small, the properties were more close to those in ZrN. When ZrO@sub 2@ fraction was about 30 %, the properties of ZrO@sub 2@ would dominate the film properties.