ICMCTF1998 Session B3/F4: Microstructural Characterization - Structure & Properties of Hard Coatings

Wednesday, April 29, 1998 1:30 PM in Room San Diego

Wednesday Afternoon

Time Period WeA Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF1998 Schedule

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1:30 PM B3/F4-1 Advances in the Characterisation of Multilayered and Related Coatings Using Electron Energy Loss Spectroscopy in the TEM
A.J. Craven, C.P. Scott, M. MacKenzie (University of Glasgow, Scotland); P. Hatto, C. Davies (MultiArc, United Kingdom)

Multilayer coatings have been the subject of intense interest over the last few years. When the layer thickness is on the nanometre scale, techniques with high spatial resolution are required for their detailed microstructural characterisation. The micro-structure of the coating is determined by the deposition conditions and in turn determines the properties of the coating in use. The long term aim of such microstructural studies is to help to determine the relationship between deposition conditions, microstructure and coating performance.

Among the microstructural features of interest in a multilayer are the thickness of the individual layers, their uniformity, their composition, their crystallography, the defects present, the sharpness of the interfaces both crystallographically and chemically, the texture and its development, the internal stress and its variation through the film, the nature of the substrate coating/interface and the effects of any pre-treatment of the substrate prior to deposition of the coating. Many of these parameters are of interest in any coating whether multilayered or not.

Transmission electron microscopy of a cross-section through the coating and substrate is one well established way of gaining such information particularly when combined with x-ray and electron energy loss spectroscopy. The latter technique provides information about the composition, chemistry and crystallography on a nanometre scale and may even provide information on local stress.

Results will be presented for a range of multilayer coatings deposited in a commercial arc evaporation system. The results obtained suggested that further information could be obtained from such systems if the techniques in use were developed further. Progress in this area will be reported.

2:10 PM B3/F4-3 Microstructure and Electronic Properties of the Refractory Semiconductor ScN Grown on MgO(001) by Ultra-High Vacuum Reactive Magnetron Sputter Deposition
D. Gall, I. Petrov, J.E. Greene (University of Illinois)
Polycrystalline and single crystal ScN layers, 180 nm thick, were grown on MgO(001) substrates at 750 °C by ultra-high vacuum reactive magnetron sputter deposition in 5 mTorr pure N2 discharges. Films deposited on grounded substrates were polycrystalline while applying a substrate bias of -50 V with a N2+-ion / metal flux ratio of 1.75 resulted in epitaxial growth. N/Sc ratios, determined by Rutherford backscattering spectroscopy, were 1.01±0.03. X-ray diffraction θ-2θ scans and pole figures combined with plan view and cross-sectional transmission electron microscopy showed that the films with no ion bombardment have a strongly textured columnar microstructure with both in-plane and growth direction preferred orientation and an average column width near the film surface of 30±5 nm. During nucleation and the early stages of film growth, 001 and 111 oriented grains are present in approximately equal volume fractions. However, preferred orientation evolves toward a purely 111 texture within 40 nm as the 001 grains grow out of existence in a kinetically-limited competitive growth mode. Ion bombardment changes the kinetics of growth so that only 001 grains nucleate, leading to 001 oriented single crystal ScN films. Room-temperature electrical resistivity ρ is 1.2x104 μΩ-cm for polycrystalline and 2x103 μΩ-cm for single crystalline films with a carrier density of 2.8x1020 cm-3 and a mobility of 12 cm2/Vs. The resistivity is higher at lower temperatures for both types of films, indicating semiconductor behavior. Optical absorption coefficients ranged from 1x104 cm-1 at 1.5 eV to 3x105 cm-1 at 3.5 eV with a well defined edge corresponding to a direct transition of 2.3 eV.
2:30 PM B3/F4-4 Growth and Properties of Epitaxial CrN(001) Layers Deposited by UHV Reactive Magnetron Sputtering
I. Petrov, C.S. Shin, M. Senna, D. Gall, J.E. Greene (University of Illinois); J.R.A. Carlsson, L.G. Hultman, J.-E. Sundgren (University of Linköping, Sweden)
CrN films, 0.5-1 μm thick film, have been grown on MgO(001) substrates by dc UHV reactive sputtering from a pure Cr target at substrate temperatures Ts ranging from 500 - 800 °C in 20 mTorr (2.7 Pa) N2 discharges. The target power was maintained constant at 140 W which resulted a film deposition rate of 25 nm min-1. The ion/metal flux ratio Ji/JMe incident at the substrate, determined by a combination of plasma probe measurements and RBS, was varied between 0.5 and 10 using an external electromagnetic field with constant N2+C ion energy of 12 eV. The films were stoichiometric CrN with N/Cr = 1.00±0.03, for Ts < 700 °C. Above that temperature, there was a rapid loss of nitrogen resulting in bcc CrNx (x< 0.1) films. X-ray diffraction (XRD) and electron diffraction showed that the stoichiometric films were epitaxial and had a B1 NaCl-structure. High-resolution XRD showed that the films had a lattice parameter approximately 2% larger than that for bulk CrN (ao = 0.4140 nm), indicating a small compressive strain. Plan-view and XTEM revealed that films deposited with Ji/JMe < 2 had voids, extending in the growth direction, with a typical diameter of 1-3 nm. Increasing Ji/JMe > 5 resulted in fully dense epitaxial CrN(001). The hardness of the as-deposited films, measured using a nanoindenter, ranged from 16 to 28 GPa with increasing Ji/JMe.
2:50 PM B3/F4-5 Tribological Properties of Graded Cr-N Coatings Deposited by Cathodic Arc Evaporation
A.M. Peters, J.J. Moore, B. Mishra (Advanced Coatings and Surface Engineering Laboratory (ACSEL))
Films of a graded Cr-N structure were deposited onto M4 tool steel by cathodic arc evaporation. Film structure was graded by changing deposition parameters such that high adhesion Cr-N was deposited at substrate surface and graded to yield high hardness Cr-N at the film surface. Nitrogen pressure and substrate bias were changed to obtain graded structure. Properties of hardness, critical load, and wear-resistance were examined. Graded structures were tested on soft (mill annealed) and heat-treated tool steel to examine the usage of these coatings under a wide range of applications.
3:10 PM B3/F4-6 Residual Stress in Coated Cemented Carbide Following Post Ion Implantation into the Coating
A.J. Perry (A.I.M.S. Marketing); D.E. Geist (Lockheed-Martin, Denver); D. Rafaja (Charles University)

In previous work we confirmed that the long range effect reviewed by Sharkeev 1 is also found in TiN coatings deposited by CVD methods 2 and in uncoated ground cemented carbide 3. The magnitude of the effect recorded in the TiN coating implanted with yttrium ions 4 is sufficiently great that it seemed likely that the residual stress in the cemented carbide substrate should also be impacted.

In the present work, first, the residual stress in cemented carbide following PVD and CVD coating processes is reported and, second, the effects of post ion implantation of the CVD coating on the stress in the substrate is studied. The coating process is found to change the compressive stress found in the WC phase to tensile in the plane of the surface, which is regarded as detrimental as it should enhance crack propagation. The subsequent ion implantation appears to have a beneficial effect by reducing the stress in the WC phase to near zero which should counteract the effect of the coating process.

1 Y.P. Sharkeev et al, Surf. Coat. Technol., in press.

2 D.E. Geist et al, Adv. X-ray Anal., 38 (1995) 471.

3 A.J. Perry et al, Surf. Coat. Technol., 86-87 (1996) 364.

4 A.J. Perry and D.E. Geist, Nucl. Instr. Meth., B 127/128 (1997) 967.

3:30 PM B3/F4-7 The Influence of the Ion Bombardment on the Optical Properties of TiNx and ZrNx Coatings
P.H. Mayrhofer, W. Waldhauser, C. Mitterer, E. Kelesoglu, P. Losbichler (The University of Leoben, Austria)
The aim of this work was to investigate the interrelationships between the ion bombardment during film growth, the resulting chemical composition and microstructure and the optical properties of TiNx and ZrNx coatings. Samples were prepared by non-reactive d.c. unbalanced magnetron sputtering from TiN and ZrN targets. The energy and intensity of the argon ions impinging on the film surface was varied systematically using different bias voltages and different external magnetic fields applied via a Helmholtz coil system. Coating characterization was done using cross-sectional scanning electron microscopy, wave-length dispersive electron-probe microanalysis, X-ray diffraction, spectroscopic ellipsometry and CIE-L*a*b* colorimetry. For a brilliant appearance the formation of coatings with a well defined crystal lattice and a chemical composition close to stoichiometry was found to be necessary. The optical properties of TiNx coatings are mainly determined by their chemical composition. Contrary to that, the coloration of coatings based on ZrN is controlled by the microstructure. The influence of both energy and intensity of the ion bombardment on film structure and optical properties (reflectivity, dielectric constant, plasma frequency) is presented and discussed.
3:50 PM B3/F4-8 Structure and Properties of Compositionally Graded Aluminum Oxynitride Thin Films
R.J. Lad, O.D. Greenwood, S.D. Dvorak (University of Maine)
The aluminum oxynitride (AlOxNy) thin film system offers the opportunity of combining the hardness and oxidation resistance of alumina with the high thermal conductivity and toughness of aluminum nitride. We have grown aluminum oxynitride thin films with graded compositions and controlled microstructure on sapphire substrates, and have characterized their structural and tribological properties. Films having thicknesses ranging from several nanometers to one micron were grown by two different methods, O2/Ar magnetron sputtering of an AlN target and O2/N2 ECR microwave plasma-assisted electron beam evaporation of metallic aluminum. In situ RHEED analysis during growth was used to verify the film structure, which ranged from amorphous to polycrystalline to epitaxial depending on deposition parameters. The O and N content, phase identification, and film compositional depth distributions were measured with XPS, UPS and AES sputter profiles. Pin-on-disk measurements using a sapphire ball indicate that films with N-rich surface compositions have higher friction coefficients than O-rich compositions. Single-pass and multiple-cycle scratch tests performed using a diamond probe in a nanotribometer instrument developed at Maine indicate that friction and wear of the AlOxNy films at the nanometer to micron size scale are very dependent on compositional gradients in the film. Film hardness values measured as a function of composition using a Hysitron picoindenter will also be reported.
4:10 PM B3/F4-9 Physical, Structural and Mechanical Characterization of Ti1-xSixN Films
F. Vaz, L. Rebouta (University of Minho, Portugal); M.F.da Silva (ITN, Portugal); J.C. Soares (University of Lisbon, Portugal)

The increasing importance and use of surface coatings in tribological applications bring with them a need for fundamental understanding of their properties if the optimum coating for a particular purpose is to be selected. Furthermore, in order to achieve a coating tailored for a particular task, a knowledge of the interrelationship between their physical, structural and mechanical properties needs to be studied in some detail. Within the frame of this work we produced Ti1-xSixN hard coatings, with 0 ≤ x ≤ 0.3 by r.f. reactive magnetron sputtering. The films, with thicknesses ranging from 1 to 3 micrometers, were produced with and without Ti interlayer. Some of the physical properties, such as oxidation resistance, structural properties such as texture and grain size and mechanical properties such as hardness, adhesion and residual stress were analysed. The atomic composition of the samples was obtained by Rutherford Backscattering Spectrometry (RBS). Texture and grain size were characterised by X-ray diffraction (XRD). The deflection method was used to evaluate the residual stress. The hardness and adhesion were characterised using a ultarmicrohardness tester and a scratch tester, respectively.

All properties will be characterised and discussed as a function of the Si content in the (Ti,Si)N matrix, bias voltage and thickness of the adhesion layer. Regarding the preliminary results, and although all samples with x > .05 present good results, the Ti0.70Si0.30N sample presented not only an oxidation resistance several orders higher than that of TiN and similar to that of (Ti,Al)N, but also good results in the mechanical properties, presenting a hardness value of about 36 GPa and a critical load for total failure around 115 N.

4:30 PM B3/F4-10 Improving the Properties of TiN by Incorporation of Silicon
M. Diserens (Swiss Federal Institute of Technology, Switzerland); J. Patscheider (Swiss Federal Laboratories for Materials Testing and Research, Switzerland); F. Lévy (Swiss Federal Institute of Technology, Switzerland)
Thin films of TiSixN have been prepared in a PVD setup with the intention to improve the tribological properties of TiN coatings. The coatings were prepared by reactive unbalanced magnetron sputtering using two separate Ti and Si targets on a rotating substrate holder. The silicon concentration in the deposited films was varied between 0 and 15 atomic percent. SEM observations and X-ray diffraction analysis of these coatings showed that the addition of Si to TiN coatings transforms the (111) oriented columnar structure into a dense fine grained structure. TEM investigations as well as X-ray diffraction showed crystallite sizes of TiN below 20 nm. XPS investigations showed the presence of Si3N4 while diffraction methods showed no indication of crystalline Si3N4. These findings are indicative for the formation of nanocrystallites of TiN together with amorphous silicon nitride. The microhardness of the TiSixN coatings as determined from load/displacement curves is at least twice as high as for TiN films deposited under the same conditions. The wear resistance measured by ball cratering is also enhanced by a factor of three. Investigations of the structure and properties relevant to wear of these TiSixN coatings will be presented.
4:50 PM B3/F4-11 The Influence of Yttrium Distribution in the Growth Direction on the Structure and Properties of TiAlCrYN Coatings
D.B. Lewis, L.A. Donohue, W.-D. Münz (Sheffield Hallam University, United Kingdom); R. Kuzel (Charles University, Czech Republic); V. Valvoda (Chalres University, Czech Republic); C.J. Blomfield (Kratos Analytical, United Kingdom)

Ti0.43Al0.52Cr0.03Y0.02N coatings have been grown in a multiple target PVD coater using the combined steered arc evaportion / unbalanced magnetron deposition technique. Coating properties and yttrium distributions have been found to change significantly when 3 targets with equal yttrium content (Ti0.495Al0.495Y0.01) or one yttrium containing target (Ti0.48Al0.48Y0.04) neighboured by 2 pure Ti0.5Al0.5 targets to produce a non-homogenous distribution were used.

The structural characteristics and residual stress of the coatings were determined by x-ray diffraction using both Bragg-Brentano and glancing angle parallel beam (sin2 U method) geometries. The residual stress state for all cases was found to be compressive, with -6.5GPa using a single 4 atomic %yttrium containing target and -3.25GPa deposited using three TiAlY targets each containing 1 atomic % Y. Line broadening measurements demonstrated that the domain size within the in-homogeneously grown TiAlCrYN coatings was also significantly smaller than the other films examined.

The surface chemistry of as-deposited and thermally treated films was further analsed by high resolution monochromatic XPS. Large area (700x200 um) and small spot (55um) spectroscopic analysis was used to examine the role of low concentrations of Cr and Y during the oxidation process whilst 0 1s imaging has been used to elucidate the spatial distribution of the oxides formed. High resolution analysis of the yttrium 2p core level identified two chemical species for the as-deposited TiAlCrYN films at positions y 2P3/2 156.4eV and 158.3eV respectively, whilst only single species were identified in heat treated films at Y 2p3/2 157.9eV.

5:10 PM B3/F4-12 Microstructural Changes in CVD Coated Cutting Tools During Turning Operations.
A. Larsson, M. Halvarsson (Chalmers University of Technology, Sweden); S. Vuorinen (SECO Tools AB, Sweden)

Wear resistant CVD coatings on cemented carbide inserts are widely used in metal cutting operations. The wear on cutting tool inserts during metal machining might result in microstructural changes in the coatings and the cemented carbide substrates. In this investigation, these changes in microstructure during turning operations were studied.

Experimental multilayer coatings were deposited in a hot wall CVD reactor on TiC coated cemented carbide cutting tool inserts. The coatings consisted of eight κ-Al2O3 layers separated by thin intermediate layers of TiC. After coating, the inserts were used in turning tests of steel. The influence of the turning operation on the microstructure of the cutting tool inserts were characterised using a combination of SEM, TEM and EDX.

Time Period WeA Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF1998 Schedule