Structure and Properties of Hard Coatings

Tuesday, April 11, 2000 1:30 PM in Room Golden West

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1:30 PM B3-2-1 Missing - Invited Hultman
Unknown Hultman ()
2:10 PM B3-2-3 Measurement and Control of Residual Stress in Multi-layer TiN and TiB@sub 2@ Films
R.A. Hoffman, A. Madan, K. Martin (Northwestern University)
The ability to measure and control film stress is critical for obtaining durable, adherent coatings for most applications; however, this is particularly true for tribological applications where stresses applied in use can be quite large. We have investigated the stress in TiN, TiB@sub 2@ and multi-layered TiN/TiB@sub 2@ films The films were deposited in a dual-opposed-cathode, unbalanced-magnetron sputtering system using TiN and TiB@sub 2@ ceramic targets. The stress was measured ex situ by determining the curvature of a Si beam and using Stoney’s equation. We will report on the stress in single and multi-layer films as a function of substrate bias and multi-layer period. We will also present data on the adhesion and hardness of these coatings. It was found, for example, that the stresses in monolithic TiN and TiB@sub 2@ films were greater than 7 GPa compressive. Deposition of a buffer layer of opposite stress or the use of multi-layers led to a reduction of the stress to less than 1 GPa which allowed the deposition of thick, adherent coatings of these materials.
2:30 PM B3-2-4 Mechanical Properties and Thermal Stability of TiN/TiB@sub 2@ Nanolayered Thin Films
K. Martin, A. Madan, S.A. Barnett (Northwestern University)
Hard coatings are widely used in extending the lifetime of cutting tools. High temperature structural stability and interfacial adhesion are both critical properties of coatings used for this application. We have investigated the structural and mechanical properties of nanolayered TiN/TiB@sub 2@ films deposited in a dual-opposed-cathode unbalanced-magnetron sputtering system using TiN and TiB@sub 2@ ceramic targets. Films deposited on sapphire substrates were annealed in an inert atmosphere at 1000@super o@C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nanoindentation were used to characterize the as-deposited and annealed films as a function of multilayer period. Monolithic TiB@sub 2@ and TiN films had a (001) and (111) orientation respectively whereas the nanolayered films had a predominant TiN (200) orientation. Annealing of the multilayered films showed that the TiB@sub 2@ layers, initially amorphous, crystallized in a mixed (001) and (101) orientation while the crystallinity of the (200) TiN layers was improved. Nanoindentation hardness of the as-deposited films was found to be approximately equal to the rule-of-mixtures value. Monolithic films showed a decrease in the hardness with annealing. On the other hand, annealed nanolayered films showed a substantial increase in hardness (as much as 29%), presumably due to the improved crystallinity. A maximum hardness of ~ 44 GPa was obtained for annealed multilayers having a period of 16.28 nm. The interfacial toughness at the coating-substrate interface of TiN/TiB@sub 2@ films deposited on M2 tool steel was investigated using a microscratch adhesion tester. A critical load to failure of 1.7 kg was measured for 1 micron TiN/TiB@sub 2@ films compared with 0.5 kg for pure TiB@sub 2@.
2:50 PM B3-2-5 Hard Nanocomposite Ti-Si-N Coatings Prepared by DC Reactive Magnetron Sputtering
L. Rebouta, C.J. Tavares (University of Minho, Portugal); R. Aimo (Savcor Coatings Oy, Finland); Z. Wang (Surfcoat Oy, Finland); E. Alves (ITN, Portugal); K. Pischow (Surfcoat Oy., Finland)
Nanocomposite thin films consisting of nanosized solid solutions or nanosized polycrystalline materials embedded in various amorphous matrix materials provide a great potential as hard coatings for future mechanical devices. Films resulting from additions of Si to TiN matrix, using a closed field unbalanced magnetron sputtering system, were prepared and characterised in this paper. @paragraph@ Physical and structural properties such as composition, texture and grain size, and mechanical properties such as hardness, Young´s modulus, residual stresses and adhesion were analysed. Nanoindentation tests and scratch tests were carried out for the mechanical characterisation. The atomic composition of the samples was obtained by Rutherford Backscattering Spectrometry (RBS). X-ray diffraction (XRD) experiments were used in order to obtain texture and grain size. The deflection method was used to evaluate the macroresidual stress states. @paragraph@ All properties will be characterised and discussed as a function of the Si content in the Ti-Si-N matrix, deposition rate, bias voltage, working pressure and distance from target and several relations will be made regarding important parameters such as texture, grain sizes and stress states. Regarding the preliminary results, the samples show hardness values as high as 45 GPa. Almost all samples showed high critical adhesion loads for total failure, generally higher than 80 N. The texture, as a function of Si content changes from a (111) orientation to a (200) orientation. Relations within these results, together with those of residual stresses will be made.
3:10 PM B3-2-6 High Temperature Behaviours of Hard 9Ti,Al)N Coatings Deposited in a Cathodic Arc Evaporation Device
S. Anderbouhr, F. Sanchette, P. Jacquot (Innovatique (Groupe HIT), France); J.J. Hantzpergue, S. Benayoun (ENSAM, France); M.F. Guimon (Université de Pau et des Pays de L'Adour, France); G. Pfister (Universit@aa e@ de Pau et des Pays de L'Adour, France)
(Ti,Al)N coatings with several Ti/Al ratios were deposited on HSS substrates by Arc cathodic evaporation from different TiXAlY alloy targets. and oxidized in air at 400 and 700°C. The build-up of the oxide overlayer was analyzed by means of X-ray Photoelectron Spectroscopy (XPS) with sputter depth profiling. Tribological films properties were investigated by pin-on-disc testing under hot air atmosphere (400, 700°C). The results clearly indicate that both aluminum content and oxidation temperature have important effects on the tribological performance of such coatings : the steady friction coefficient is found to decrease with increasing working temperature. Further, the optimun composition of a film having excellent tribological properties was found to be Ti0.4Al0.6N. These results are correlated with the coatings microstructural properties.
3:30 PM B3-2-7 Source and Effect of Impurity Incorporation During Thin Film Growth by Physical Vapor Deposition in a High Vacuum Ambient
J.M. Schneider (Linköping University, Sweden); B. Hjörvarsson (Royal Institute of Technology); A. Anders (Lawrence Berkeley National Laboratory); L. Hultman (Linköping University, Sweden)
Impurity incorporation during thin film growth was investigated for oxide thin films grown by magnetron sputtering and cathodic arc deposition. The residual gas in a high vacuum chamber mainly consists of water, but also nitrogen and carbon containing species may be present. We find that chemical reactions of the species contained in the residual gas with the growing film occur. Furthermore we show that impurity incorporation has large implications for the microstructure evolution of the grown films, and hence for their properties. For strontium titanate thin films for example we found an amorphous structure if several atomic percent of hydrogen are incorporated during growth. If the hydrogen incorporation is limited to < 0.6% the formation of a crystalline structure was observed.
3:50 PM B3-2-8 Plastic Flow and Related Wear Mechanisms of CVD Ceramic Coatings
K.J. Ma (Chung-Cheng Institute of Technology, Taiwan); C.G. Chao (Chiao-Tung University, R.O.C.); D.S. Liu (Chung-Cheng Institute of Technology, Taiwan)
Ceramic coatings have been widely used in cutting tools and various machine parts. Even though high strengths have been obtained in most ceramic coatings, it has also been shown that ceramic coatings undergo extensive plastic deformation during scratch and wear tests. It is essential to understand the plastic flow and related friction and wear behaviour. Reciprocating multipass wear tests have been carried out on various CVD coatings. Deformation and failure mechanisms were identified based on high resolution microstructural examination through cross-sectional fracture surfaces @paragraph@ Obvious plastic flow was observed on the surface of CVD ceramic coatings in the first sliding, due to the extremely high contact pressure developed on the contact asperities. However, shake down may quickly be reached after several subsequent traverses. In further repeated traverses, the plastic-elastic flow accumulates residual strain energy may reach certain level where stress induced cracking, microbuckling, and microflaking will occur along the elastic-plastic interfaces behind the indenter. The new surface will appear after the detachment of the heavily strained plate-like wear debris. The repeated sliding allows the process- “plastic flow of asperities - flatten the surface and shake down - microbuckling and detachment of strained layer to continue until the coating is totally worn out.
4:10 PM B3-2-9 On the Wear and Failure Mechanisms of PVD TiN/TaN Coated Tools When Milling Austenitic Stainless Steel
M. Nordin (Uppsala University, Sweden); R. Sundström, T. Selinder (AB Sandvik Coromant, Sweden); S. Hogmark (Uppsala University, Sweden)
Multilayered PVD coatings have shown enhanced mechanical and tribological properties as compared to homogeneous coatings. In this work, multilayered PVD TiN/TaN coatings deposited on cemented carbide tools are presented and compared with homogeneous TiN and TaN. TiN/TaN has in earlier investigations shown high abrasive and erosive wear resistance as well as good properties in milling austenitic stainless steel. The purpose of this work is to increase the understanding of the wear and failure mechanisms during milling. For this reason milling to a certain cutting distance, facilitating a direct comparison of the coatings, has been performed.@paragraph@It was found that by multilayering TiN with TaN, a coating suitable for tools used in milling austenitic stainless steel can be obtained. The reason is that it is possible to take advantage of the good properties of TaN, such as low thermal conductivity and high hot hardness, as well as the high toughness obtained through crack deflection in lamella interfaces.@paragraph@Keywords: PVD, TiN, TaN, milling, wear
4:30 PM B3-2-10 Deposition of Si-DLC Films With High Hardness, Low Stress and High Deposition Rate
J.C. Damasceno (University of Rio de Janeiro, Brazil); F.L. Freire Jr. (PUC-Rio, Brazil); R. Carius (Forschungszentrum Juelich, Germany); S.S. Camargo Jr. (University of Rio de Janeiro, Brazil)
In this work a-C:H:Si (Si-DLC) films were produced onto crystalline silicon substrates by the PECVD technique from gaseous mixtures of CH@sub 4@ and SiH@sub 4@. The effects of self-bias and gas composition upon mechanical and structural properties of the films were investigated. Raman spectroscopy, RBS, ERDA, micro-hardness, residual stress and gas effusion measurements were employed for characterization. Results show that internal stress of the films presents a maximum at self-bias voltages of about -200V and decreases for higher values. On the other hand, hardness could be increased by increasing self-bias so that for high values (around -800V) films with high hardness (~30 GPa), low stress (~1 GPa) and high deposition rate (~30 nm/min) could be obtained. Raman results show that these films present reduced sp@super 3@ character when compared with those produced with self-bias around -200V while RBS shows rather low silicon contents (~1 at.%). Gas effusion measurements suggest that these films also present a less compact structure. Increasing self-bias results in a decrease on hydrogen content and increases the carbon incorporation into the film so that, at high bias values, the C / (C + Si) ratio tends to achieve the same value as in the gas phase. On the other hand, the increase of the SiH@sub 4@ concentration in the plasma increases the sp@super 3@ character of the films, making their properties less dependent on the self-bias voltage employed.
4:50 PM B3-2-11 New Cr-B-N Thin Films Synthesized by Inductively-Coupled-Plasma Assisted Planar Magnetron Sputtering
M. Zhou (Osaka University, Japan); M. Nose (Takaoka National College, Japan); Y. Makino, K. Nogi (Osaka University, Japan)
Thin film coating techniques have become more and more important in the deposition of wear resistant coatings for tribological applications. Thin film coatings have proved to be remarkably effective for the increment of lifetime for cutting tools or moulds.@paragraph@For improving the wear performance and toughness of thin films, ternary or multiphase coatings become attracting as they provide the possibility of tailoring material properties by synthesizing the coating with a suitable combination of different phases. In the ternary family of transitional boron nitrides, Ti-B-N and Zr-B-N are developed and well studied. As CrN thin films have very good oxidation, wear and corrosion resistant as compared to TiN, the Cr-B-N ternary coatings may be a promising candidate for tribological properties. As yet only very limited studies of Cr-B-N thin films have been carried out.@paragraph@Newly developed rf inductively coupled plasma assisted planar magnetron sputtering apparatus is one of the most promising method for preparation of protective layers since it allows:(1)almost unlimited freedom to choose among elements, alloys and compounds as layering constituents;(2)to design and produce materials with compositional and structural periodicties approaching the atomic scale by sputtering several targets simultaneously;(3)to ensure minimal component distortion due to deposition temperatures being well below 500@super o@C.@paratraph@New Cr-B-N thin films were synthesized by rf inductively coupled plasma assisted planar magnetron sputtering apparatus in this study. The influence of nitrogen on the phase composition and mechanical properties of the Cr-B-N thin film is evaluated in this study. The XRD and XPS results indicate that h-BN phase appears in all Cr-B-N thin films and a phase transformation from CrB@sub 2@to BN and Cr@sub 2@N occurred in the Cr-B-N films with increasing the nitrogen partial pressure. Hardness and friction coefficient of the films were determined using nanoindentation and pin-on-disk apparatus, respectively. Both hardness and Young's modulus of the films decrease due to the formation of soft h-BN phase in the Cr-B-N films. However, h-BN shows itself as a kind of high efficient lubricant. The friction coefficient of the films decreases sharply from 0.8 to 0.2 when just a very small amount of nitrogen is introduced. These results indicate that it is possible to synthesize lubricating coatings with proper hardness and Young's modulus by controlling the coating composition to obtain the suitable proportion of the soft and lubricating h-BN phase.