ICMCTF2007 Session B6-1: Hard and Multifunctional Nano-Structured Coatings

Thursday, April 26, 2007 8:40 AM in Room Golden West

Thursday Morning

Start	Invited?	Item
8:40 AM		B6-1-3 The Origin of Superhardness in nc-TiN/a-Si₃N₄ Nanocomposites S. Veprek (Technical University Munich, Germany); C. Stampfl (The University of Sydney, Australia); A.S. Argon (Massachusetts Institute of Technology); R.F. Zhang, M.G.J. Veprek-Heijman (Technical University Munich, Germany) The original finding that in nc-TiN/a-Si₃N₄ nanocomposites, which were deposited under the optimum conditions which allow a complete phase separation, the maximum hardness of ≥ 50 GPa is achieved when the thickness of the interfacial Si₃N₄ phase is about 1 monolayer, has been recently confirmed by both experiments and theory. In our paper we shall summarize these results and discuss some thermodynamics and kinetics limitation of the experiments on heterostructures and nanocomposites. First-principles DFT calculations confirm and explain that the maximum decohesion strength of TiN-Si₃N₄-TiN sandwich is achieved for one monolayer of Si₃N₄, and it is higher than that of bulk Si₃N₄. Combined ab-initio and thermodynamic calculations based on the sub-lattice model identify the conditions under which such nanostructure is formed by spinodal phase segregation. The decrease of the hardness for thicker Si₃N₄ interface is explained in terms of critical thickness of pseudomorhly grown Si₃N₄ on TiN with the corresponding misfit. It will be finally shown that the extraordinary mechanical properties of these and related superhard nanocomposites can be understood in terms of nearly flaw-free strong materials. One does not need to evoke any new mechanism of strengthening.
9:00 AM		B6-1-4 Metastable Phase Selection and Spinodal Decomposition in Ti_1-xSi_xN_y System Studied by ab Initio Thermodynamic Modeling: A Comparison with the TiN/CrN-AlN System R.F. Zhang, S. Veprek (Technical University Munich, Germany) The bulk properties of binary stable fcc-TiN and beta-Si₃N₄, hypothetical fcc-SiN and beta-Ti₃N₄, and mixed ternary Ti_1-xSi_xN_y phases of different stoichiometry are calculated by ab initio method and compared with the values from experiments and other theoretical calculations in order to verify the reliability of the numerical model used. Based on a good agreement of these data, the values of total energies are then used to calculate the lattice stabilities of binary fcc-TiN and hcp-Si₃N₄ and hypothetical of fcc-SiN and beta-Ti₃N₄ phases. The results are used to determine the interaction parameters of mixed quasi-binary Ti_1-xSi_xN_y phases. These data are then used in the semi-empirical sub-lattice thermodynamic method to calculate the Gibbs free energy diagrams and de-mixing energies of the different quasi-binary (TiN)_1-z(SiN_x)_z systems in order to study the relative phase stability of the metastable ternary hcp- and fcc-Ti_1-xSi_xN_y phases over the entire range of compositions. The predictions from these calculations are compared with, and supported by the published results from PVD and CVD experiments. Among these results to be reported it is shown that the substoichiometric, metastable fcc-Ti_1-xSi_xN phase has a smaller de-mixing energy with regard to fcc-TiN and fcc-SiN than to the stoichiometric fcc-TiN and beta-Si₃N₄ mixture. A comparison with the TiN/CrN-AlN system shows that, due to the much higher de-mixing energy of the (TiN)_1-z(SiN_x)_z phases, nanostructure with sharp interfaces may easily form through spinodal decomposition.
9:20 AM		B6-1-5 Ti-Si-C Thin Films Deposited by Magnetron Sputtering from a Ti₃SiC₂ Target P. Eklund, J. Frodelius, M. Beckers (Linköping University, Sweden); O. Wilhelmsson, U. Jansson (Uppsala University, Sweden); H. Högberg, L. Hultman (Linköping University, Sweden) The Ti-Si-C materials system is of growing interest for multifunctional coatings in, e.g., electrical and tribological applications. We have previously reported on beneficial electrical contact properties and a ductile deformation behavior for Ti-Si-C nanocomposite thin films deposited by magnetron sputtering at substrate temperatures below 300°C.¹Thus, we demonstrated the applicability of Ti-Si-C thin films in electrical-contact applications on technologically relevant substrates like Al and Cu. Here, we report on detailed characterization of the microstructure of Ti-Si-C thin films deposited from a Ti₃SiC₂ compound target² in the wide temperature range from room temperature to 900°C on Al₂0₃(0001), MgO(111), and metal substrates. XRD, TEM, and XPS demonstrated that Ti-Si-C films deposited at low temperature consist of TiC nanocrystallites or nanocolumns, and a matrix phase of amorphous SiC with presence of free carbon. ERDA and XPS showed carbon enrichment in the films compared to the target composition, while the Ti:Si ratio was close to 3:1. Mass spectrometry showed that the growth flux was elemental, i.e., only Ti, Si, and C species were detected. For temperatures from 400°C to 700°C, columnar TiC was observed, with amorphous SiC between columns. At 850°C, epitaxial Ti₃SiC₂(0001) was synthesized using an epitaxial TiC buffer layer on MgO(111) substrates, while temperatures of 700 - 850°C resulted in growth of polycrystalline Ti₃SiC₂. ¹P. Eklund et al J. Vac. Sci. Technol. B 23 2486 (2005) ²Maxthal, courtesy of Kanthal AB.
9:40 AM		B6-1-6 Room Temperature Deposition and Characterization of Hard Ti(X)N (X= Y, Si) Nanostructured Composite Films R Escobar Galindo (Instituto de Ciencia de Materiales de Madrid, Spain); J.L. Endrino (Lawrence Berkeley National Laboratory); O. Sanchez (Instituto de Ciencia de Materiales de Madrid, Spain); J.F. Marco (Instituto de Quimica-Fisica Rocasolano CSIC, Spain); A. Anders (Lawrence Berkeley National Laboratory); J.M. Albella (Instituto de Ciencia de Materiales de Madrid, Spain) In this work, we explore new alternatives for the synthesis of hard nanocomposite films to be used as protective coatings. Based on a TiN structure, the addition of a third element to the coatings (Si or Y) allows the tailoring of the desired properties (i.e. high hardness and toughness, improvement of oxidation resistance, etc.). The coatings were deposited at room temperature by using a pulsed "triggerless" arc source. Two different types of cathodes were used in the processes: pure Ti and mixed TiSi₃₀ for TiSiN and pure Ti and Y for TiYN deposition. The ratio of the arc pulses was tuned to control the stoichiometry of the films, resulting in a wide range of nanostructures (pure binary, ternary and nanocomposite). GDOES analysis were performed to obtain depth profiling spectra of the composition of the films, while the chemical state was studied by means of XPS. Structural changes were observed in the coatings by XRD studies revealing that TiYN can form a solid solution (NaCl-type) with a change of the TiN preferential orientation from (111) to (200) with the yttrium inclusion. Results on the mechanical properties of the coatings using nanoindentation and pin-on-disk tests are also discussed.
10:00 AM		B6-1-7 Characterisation of Hard Ti-Si-B Coatings Deposited by Pulsed Unbalanced Magnetron Sputtering M. Audronis, A. Leyland, A. Matthews (University of Sheffield, United Kingdom) Hard ceramic titanium-based boride and nitride thin films (e.g. Ti-B-N, Ti-Al-N, Ti-Si-N etc.) produced by plasma-assisted Physical Vapour Deposition are attracting increased scientific attention. This is due to the fact that these coatings can offer good wear performance and improved high temperature oxidation resistance; such parameters are critical when considering these coatings for industrial cutting tool applications for example. Optimal film properties can be achieved via the control of coating chemical composition, microstructure and morphology. For example, alloying of transitional metal nitride and boride coatings with Si is known to reduce the crystallinity, or to promote a nanophased composite structure in the film, and to improve thermal stability. The microstructure and morphology of these films are dependent largely on deposition process and parameters, which are therefore important factors determining the resultant properties. In this paper we report on the structure and resulting properties of Ti-Si-B thin films, a hard coating with the potential for excellent thermal stability and oxidation resistance deposited by an asymmetric bipolar pulsed unbalanced magnetron sputtering. The coatings produced are characterised by SEM, XRD, TEM, GDOES and nanoindentation methods.
10:20 AM		B6-1-8 Improvement of the Cutting Performance of TiSiN Coated Cemented Carbide-Tools T. Ishikawa, F. Fujii (Hitachi Tool Engineering, Ltd., Japan) Si-containing ceramics coatings are widely used for cutting tools because of their high hardness and high oxidation resistance. Particularly, TiSiN coatings have higher hardness than other nitride coatings. It is considered that the higher hardness originates in nano-crystallization. Although TiSiN coatings have high hardness, they have higher residual stress simultaneously and the adhesion strength with substrate is remarkably low. Therefore TiSiN single layer coated tools show poor cutting performance. In the present work, using cathodic-arc-evaporation techniques (CAE), the cutting performance of TiSiN coatings on cemented carbide 6 flute-square-end-mills has been investigated for improvement of the cutting performance in high speed cutting (V=200m/min.) of die steels (AISI:D2-62HRC), which the combination of (Ti_1-0.6Si_0-0.4)N as the top layer and Al based nitride coating as the under layer (Al_0.25-0.75Ti_0.75-0.25)N, (Al_0.7Cr_0.3)N, (Al_0.6Cr_0.3Si_0.1)N (The number is the atomic ratio). The cutting test has shown that the tool life of the (Al_0.5Ti_0.5)N covered by the (Ti_0.8Si_0.2)N top layer coatings has been longer than the other combinations. After the cutting test, (Al_>0.6Ti)N, AlCrN, AlCrSiN under layer coatings have peeled off from the substrate of the cutting edge due to a poor resistance against plastic deformation. The cross-sectional TEM observation of the cutting edge after the cutting test has shown that the (Al_0.5Ti_0.5)N under layer deformed to axis direction accompanied by some micro cracks. It has been demonstrated that it was important not only the hardness, oxidation resistance but also the toughness of the coatings in high speed cutting of hardened die steel. In addition, the TEM-EDS analysis of the (Al_0.5Ti_0.5)N under layer coatings after the cutting test have shown Co-diffusions into the layer and spinodal-decompositions in the actual cutting process.
10:40 AM		B6-1-9 Mechanical Property and Cutting Test of Multilayer Coating System with Si Containing Layers K. Yamamoto, S. Kujime (Kobe Steel Ltd., Japan) Si containing coatings are drawing much attention due to their superior oxidation resistance and nature as a nano-composite structure. Authors proposed addition of Si to (Ti,Cr,Al)N coatings and reported improved mechanical as well as high temperature oxidation property, but found that in general it lacks of toughness and chipping type of failure is observed in severe cutting conditions. The idea is to form a multilayer structure of coating with higher toughness and Si containing coating for obtaining high higher toughness and oxidation resistance. Multilayer coatings with alternative layer of (Ti,Cr,Al)N and Si containing layers were deposited by cathodic arc evaporation method. Alloy targets with compositions of Ti_0.25Cr_0.1Al_0.65, Ti_0.3Cr_0.17Al_0.4Si_0.13 and Al_0.9Si_0.1 were evaporated in pure N2 atmosphere. The multilayer structure was facilitated using the rotation of the substrate table. The bi-layer period was changed from ca. 30 to 100 nm by changing the substrate rotation speed. X-ray diffraction measurement showed that the (TiCrAl)N/(Al,Si)N multilayer coating was a mixture of hexagonal (B4) and cubic (B1) at larger bi-layer period. The portion of hexagonal phase was decreased as the bi-layer period decreased. However, there was not significant change in hardness of the coating as measured by nanoindentation method. The indentation hardness of the (TiCrAl)N/(Al,Si)N multilayer coating decreased as the bi-layer period decreased. Dry cutting tests against hardened cold working die steel (D2, HRC60) and high-speed tool steel with extreme hardness of HRC68 was conducted with cutting speed of 150 m/min. Results showed that while (Ti,Cr,Al,Si)N mono-layer coating suffered from chipping of the cutting edge, the new multi-layer coating showed significantly improved cutting performance, compared to conventional mono-layer coatings such as (Ti,Al)N, (Ti,Cr,Al)N or (Ti,Cr,Al,Si)N.
11:00 AM		B6-1-10 Comparative Study of Nanocomposite Ti-B-C, Ti-B-C-N, and Ti-B-C-N-Si Films Deposited by Unbalanced Magnetron Sputtering I.W. Park (Advanced Coatings & Surface Engineering Laboratory (ACSEL)); J.J. Moore, B. Mishra (Colorado School of Mines); A.A. Voevodin (Air Force Research Laboratory); K.H. Kim (Pusan National University, Korea); E.A. Levashov (Moscow State Institute of Steel and Alloys, Russia) Multifunctional nanocomposite, based on nanocrystalline (nc-) and amorphous (a-) phases, films attract considerable interest to extend the lifetime of cutting tools, press-forming tools and various other mechanical components. Films for most tribological applications require combinations of properties such as a relatively high hardness, high fracture toughness, wear- and oxidation-resistance, and a low friction coefficient. The present work investigates the co-deposition of Ti-B-C, Ti-B-C-N, and Ti-B-C-N-Si nanocomposite films from a composite target of TiB₂-TiC and a pure boron doped Si target using DC unbalanced magnetron sputtering in Ar/N₂ gas mixtures. The microstructures, mechanical, wear and oxidation properties for the films were investigated in various N and Si contents. The microstructures of the synthesized films were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscope (XPS), high-resolution transmission electron microscope (HRTEM), respectively. Nano-indentation was conducted to assess the hardness and Young's modulus of the films. Wear- and oxidation-resistance of these films were evaluated using a CETR micro-tribometer and TG-DSC, respectively. The adhesion behavior between films and AISI 304 substrates was evaluated with a scratch tester using a Rockwell C diamond stylus. In the present work, the comprehensive microstructures and various properties of the films were investigated and correlated with deposition parameters.
11:20 AM		B6-1-11 Hard Tribological Ti-(Al,Cr,Si)-(B,N) Films with Enhanced Thermal Stability, Corrosion- and Oxidation-Resistance D.V. Shtansky, Ph.V. Kiryukhantsev-Korneev, A.N. Sheveiko, A.E. Kutyrev, M.I. Petrzhik, E.A. Levashov (Moscow State Institute of Steel and Alloys, Russia) Many engineering materials require a combination of properties: wear-, corrosion-, and oxidation-resistance, thermal and chemical stability, high fatigue strength, and low friction coefficient. These properties can be achieved in hard coatings based on borides and nitrides by alloying with elements such as Al, Si, and Cr. In the present work, films Ti-(Al,Si,Cr)-(B,N) were deposited by DC magnetron sputtering of TiBN, TiCrB, TiSiB, and TiAlSiB composite targets in a gaseous mixture of argon and nitrogen. The structure, phase and chemical composition of films were studied by means of X-ray diffraction, transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. To evaluate the thermal stability and oxidation resistance, the Ti-B-N, Ti-Cr-B-N, Ti-Si-B-N, and Ti-Al-Si-B-N films were annealed at 600, 800, and 1000°C in vacuum and at 600, 700, 800, and 900°C in air, respectively. The Ti-B-N and Ti-Cr-B-N films demonstrated thermal stability up to 1000°C. A threshold temperature of 800°C was determined, below which these films acted as a diffusion barrier for Ni diffusion from metallic substrate. Annealing in the range of 600-800°C improved mechanical and tribological characteristics of the films. In order to reveal the influence of the alloying elements on high-temperature tribological performance, the films were also tested at 500°C using high-temperature ball-on-disc tribometer. The Ti-Cr-B-N and Ti-Al-Si-B-N films were more resistant against high-temperature oxidation than the Ti-B-N and Ti-Si-B-N films. The electrochemical tests were carried out in an electrolyte corrosion medium 5N H₂SO₄ and 1N HCl at room temperature. The films used in the corrosion tests were deposited on Si substrates. The results obtained showed that the Ti-Cr-B-N films were most corrosion-resistant and posses the best passivation characteristics.