ICMCTF2011 Session B5-2: Hard and Multifunctional Nano-Structured Coatings

Thursday, May 5, 2011 1:30 PM in Room Golden West

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B5-2-1 Wear-Resistant PTFE Based Nanocomposites Thierry Blanchet, Sashi Kandanur (Rensselaer Polytechnic Institute) Polytetrafluoroethylene is known for low friction, however high wear rates ~10^-3 mm³/Nm have stymied PTFE as a bearing material. Conventionally, hard micron-scale fillers have been added to PTFE to yield composites typically two orders of magnitude more wear-resistant. Defying mechanisms hypothesized from microcomposite observations, some PTFE nanocomposites now display not only comparable but, particularly in the case of alpha phase alumina nanofiller, lower wear rates to ~10^-7 mm³/Nm. The goal of this research is thus to better understand PTFE nanocomposite wear resistance mechanism through studying effects of various parameters (filler size, weight fraction, dispersion technique, countersurface roughness and chemistry) on wear of alumina-PTFE composites. With 5 wt % alpha phase alumina nanoparticles (40 or 80nm) against polished steel, wear rates ~10^-7 mm³/Nm were measured, four orders of magnitude lower than unfilled PTFE and two orders of magnitude lower than with microparticles (0.5 or 20um). For alumina-PTFE microcomposites wear rate gradually increased towards that of unfilled PTFE as filler content was reduced, whereas alumina-PTFE nanocomposite maintained ~10^-7 mm³/Nm wear rate to as low as 0.32 wt % before reverting towards the rapid wear rate of unfilled PTFE. Lightly-filled alumina-PTFE nanocomposites depend upon low countersurface roughness for such low wear rate, and at a critical value of increasing roughness the wear rate transitioned to ~10^-5 mm³/Nm. Nanocomposites of higher filler content maintained wear resistance to higher roughness before such transition. At extremely high roughness Ra = 6-8um, nanocomposites at all filler contents increased in wear rate to ~10^-4 mm³/Nm. Among other observations, alumina-PTFE nanocomposite wear resistance was not changed by instead sliding against CoCr or alumina countersurfaces. Wear resistance of alpha alumina-PTFE nanocomposite was also greater than that provided by several other nanofillers investigated, including alumina of other phases, by at least two orders of magnitude. Finally, in the presence of water alumina-PTFE nanocomposite was observed to lose this wear resistance, with wear rates approaching that of unfilled PTFE. Countersurfaces of low wearing nanocomposites revealed thin uniform transfer films. It is hypothesized that alpha phase alumina’s influence on matrix PTFE is heightened by the higher surface-to-volume ratio, augmenting its intrinsic wear characteristic while forming thinner transfer films via increase ability to fibrillate. The low ~10^-7 mm³/Nm wear rate is considered a consequence of slowed removal rates of better-adhered thinner transfer films.
2:10 PM		B5-2-3 Comparison of Different Bionic Structures Coated with CrAlN Wolfgang Tillmann, Jan Herper (Technische Universität Dortmund, Germany) The reduction of friction and wear is an important goal for the extension of the tool life in many industrial applications. Especially the forming and cutting industry is very interested in new techniques in order to improve the tribological behavior of the tool surfaces. Biomimetics is a very promising approach where biological surfaces or phenomena are used to optimize technical components. The “Lotus Effect” is the most popular example, whereby the surface is made water- and dirt-repellent. Taking a closer look at nature, it can be noticed that many different natural surfaces have adapted perfectly to their environment in order to meet the respective requirements. Especially because of its excellent frictional behavior, the skin of many insects has the potential to be transferred onto technical surfaces. In this paper the surface structures of different beetles were investigated. Thereby, the main objective is the combination of nature-adapted surface patterns with wear‑resistant near‑netshape PVD‑coatings. A substrate composed of high speed steel material 1.3343 was structured by means of milling. The shells of dung and scarabaeus beetles served as patterns for the structurization of the surfaces. Afterwards a CrAlN multilayer coating system was deposited with the aid of magnetron sputtering. To compare the mechanical and tribological properties, the structured and coated surfaces were analyzed by a nanoindenter, a ball‑on‑disc‑tester as well as a scanning electron microscope.
2:30 PM		B5-2-4 Surface Modification of Nanostructured NiTi Shape Memory Alloy Thin Films Using Various Passivation Layers by dc Magnetron Sputtering Nitin Choudhary, Davinder Kaur (Indian Institute of Technology Roorkee, India) NiTi based shape memory alloy (SMA) thin films have been recognized as promising and high performance materials in the field of biomedical and microelectromechanical systems (MEMS) applications due to their unique superelasticity and shape memory effect. However, the materials are vulnerable to surface corrosion, unsatisfactory mechanical and tribiological performances and biological reliability. The present study explored the insitu deposition of hard and adherent nanocrystalline protective coatings on NiTi thin films prepared by dc magnetron sputtering to improve the surface, mechanical and corrosion properties of NiTi thin films without sacrificing the phase transformation effect. Further the interfaces between a Silicon substrate and a NiTi thin film is also an important place where reaction between both these materials occurs during high temperature deposition. By controlling the chemical reaction, the interface can provide strong bonding and the reaction does not proceed excessively. In the present study a buffer layer of hard TiN was provided to control the diffusion at the interface. Following heterostructures were prepared; TiN/NiTi/TiN/Si, ZrN/NiTi/TiN/Si, CrN/NiTi/TiN/Si and TiAlN/NiTi/TiN/Si by dc magnetron sputtering technique. The structural, electrical, and mechanical studies of these heterostructures were performed and the results were compared. Nanoindentation studies were performed at room temperature to determine the hardness and reduced modulus. Surface modified NiTi thin films were found to exhibit high hardness, high elastic modulus and thereby better wear resistance as compared to pure NiTi films.
2:50 PM		B5-2-6 Mechanical Properties, Tribological and Corrosion Resistance Evaluation of Cathodic Arc Deposited ZrN/CrN Multilayer Coatings Siao-Fan Chen (National Taiwan University of Science and Technology, Taiwan); Jyh-Wei Lee (Mingchi University of Technology, Taiwan); Sung-Hsiu Huang (National Chiao Tung University, Taiwan); Chaur-Jeng Wang (National Taiwan University of Science and Technology, Taiwan); Tsung-Eong Hsieh (National Chiao Tung University, Taiwan); Yu-Chen Chan, Hsien-Wei Chen, Jenq-Gong Duh (National Tsing Hua University, Taiwan); Jai-Weh Chen (Gigastorage Corporation) Five nanostructured CrN/ZrN multilayer coatings were deposited periodically by the cathode arc deposition system. The bilayer periods of CrN/ZrN multilayer coating were controlled ranging from 8 to 30 nm. On the other hand, the thickness ratios of CrN to ZrN layer were changed for several multilayer coatings as comparison. The crystalline structure of multilayer coatings was determined by a glancing angle X-ray diffractometer. Microstructures of thin films were examined by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. A nanoindenter, scratch tester and pin-on-disk wear tests were used to evaluate the hardness, adhesion and tribological properties of thin films, respectively. Electrochemical tests in 3.5 wt.% NaCl aqueous solution were performed to evaluate the corrosion resistance of multilayered coatings. It was found that the hardness, tribological and corrosion resistance were strongly influenced by the bilayer period and thickness ratios of CrN to ZrN layer of the CrN/ZrN multilayer coatings.
3:10 PM		B5-2-7 High Temperature Crystallisation of Cr₂AlC MAX-Phase Coatings Sputter-Deposited at Room Temperature John Colligon, Ovidiu Crisan, Piotr Dobrosz, Vladimir Vishnyakov (Manchester Metropolitan University, UK) Chromium Aluminium Carbide, which belongs to so named MAX-phases, has been deposited by ion sputtering from combined elemental targets onto Silicon and Stainless Steel at room and elevated temperature of the substrate. The material was annealed at 700^oC in air for 20 min. Material composition was determined by Energy dispersive and Wave dispersive X-Ray (EDX and WDX) Analysis. The crystallinity of the films was accessed by X-Ray Diffraction (XRD) and Raman spectroscopy. As- deposited and annealed films are homogeneous and dense over large areas. Negligible, below 1 at %, traces of Oxygen are detected by WDX in as-deposited films which are predominantly amorphous. Raman spectra of as-deposited films show characteristic but not well structured MAX-phase bands in the region of 100-400 cm^-1 and broad amorphous Carbon D-band. After annealing Cr₂AlC single-phase is well-formed, with small traces of oxides or other phases (occurring, in the 5% error range), as estimated from the Rietveld-type refinement of the XRD patterns of the samples. It is evident that the oxides are mostly confined to the surface layers. The MAX-phase region in the Raman spectra becomes well structured and shows good correspondence to crystallinity. Surprisingly, Carbon also develops a G-band signature and this probably indicates presence of some carbon nano-clustering in the system. It is possible that the nanoclustering is only happening in the oxidised top layers. It is thought that this carbon can be partially responsible for the low friction coefficient of the Cr₂AlC phase. Ion assistance during film deposition shows significant preferential sputtering of Carbon, which can be explained on the basis of weak incorporation of carbon into the growing amorphous film and indicates that magnetron sputtering from stoichiometric targets in the presence of even small ion assistance from the plasma will lead to carbon depletion in the deposited film. The results for coatings formed using ion beams are designed as a first step towards optimisation of the synthesis procedures that will be required for production of large area samples in view of the potential industrial applications of MAX phase materials.
3:30 PM	Invited	B5-2-8 Recent Advances in Transition Metal Nitride–Based Nanostructured Hard and Superhard Coatings Harish Barshilia, K. Rajam (NAL, Bangalore, India) Current research problems in surface coating technology include development of various thin coatings with exotic properties as part of an effort to modify the surfaces of a variety of engineering materials at lower cost. The role of coatings as a surface modification technique has grown significantly in recent years for applications in cutting tool, automobile, aerospace, biomedical, and other industrial sectors, since they can impart specific properties such as high hardness, high wear resistance, etc. to a surface. Binary and ternary transition metal nitride/carbide coatings with hardness in the range of 20-35 GPa have been widely used as protective hard coatings to increase the lifetime of various engineering components. However, for most of the technological applications, it is desirable to develop a coating with a combination of properties such as high hardness, high fracture toughness, high oxidation and corrosion resistance, etc. In this direction, in recent years, great advances have been made in the field of nanostructured coatings with improved properties using nano-scale engineering. In particular, transition metal nitride-based nanolayered multilayer coatings and nanocomposite coatings have emerged as novel superhard coatings (hardness > 40 GPa), which can operate across multiple extreme environments. Both nanolayered multilayer coatings and nanocomposite coatings provide enormous flexibility in choice of materials and, therefore, provide an opportunity to design novel coating properties. In this paper, we describe the state-of-the-art in the deposition and characterization of transition metal nitride-based nanolayered multilayer coatings and nanocomposite coatings. Various physical vapor deposition techniques used for the preparation of the nanostructured superhard coatings are described, in brief. It is shown that reactive magnetron sputtering is a promising technique for the deposition of these coatings on small engineering components. However, development of these coatings on large scale and deposition at production scale at affordable cost still needs considerable efforts. We discuss in detail the growth process, microstructure, mechanical and tribological properties, oxidation resistance and thermal stability, and corrosion resistance of sputter deposited transition metal nitride nanostructured coatings. We also present the potential applications of the transition metal nitride nanostructured superhard coatings.
4:10 PM		B5-2-12 Comparison of Superhard and Superelastic Ti-Based Nanocomposite Erosion Resistant Coatings on Ti-6Al-4V Substrates Prepared by PECVD Salim Hassani, Etienne Bousser, Srinivasan Guruvenket, Duanjie Li, Jolanta Klemberg-Sapieha, Ludvik Martinu (Ecole Polytechnique de Montreal, Canada) Enhanced tribological erosion resistant coatings require high toughness. This can be obtained by an appropriate combination of hardness and elasticity that allows one to optimize energy dissipation during particle impact. In the present work we investigated two types of coating systems deposited on Ti-6Al-4V substrates and prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD), namely (A) superhard Ti-Si-C-N multilayer coatings consisting of TiN, (nanocomposite) nc-TiN/a-SiN_x and nc-TiCN/a-SiCN, and (B) hard superelastic Ti-Si-C multilayer systems consisting of a sputter deposited chromium adhesive layer followed by the deposition of a-SiC:H and nc-TiC/a-SiC:H/a-C:H films. The Ti-Si-C-N multilayer architecture (A) provided an effective (composite) hardness of 5000HV 0.05, and very high resistance to plastic deformation and elastic resilience, expressed by H³/E_r² and H²/E_r ratios, respectively. The Ti-Si-C multilayer coatings (B) exhibited an unusual but highly desirable combination of hardness, low friction, and high elastic strain to failure with a ratio H/E_r > 0.2, thus exceeding the superelastic threshold. Both coating systems resulted in a significant improvement of erosion resistance compared to the bare Ti-6Al-4V substrate. Under conditions simulating compressor blades in aircraft engine, the erosion resistance was improved by a factor of 50.
4:30 PM		B5-2-10 Effects of Nanostructure Formation on the Fundamental Physical Properties of Epitaxial Hf_1-xAl_xN(001) Alloys Brandon Howe (University of Illinois at Urbana-Champaign); Thomas Oates (ISAS, Germany); Shawn Puttnam (Air Force Research Laboratory); Jian-Guo Wen (University of Illinois at Urbana- Champaign); Mauro Sardela, Jr. (Frederick-Seitz Materials Research Laboratory); Andrey Voevodin (Air Force Research Laboratory); Hans Arwin (Linköping University, Sweden); Joseph Greene (University of Illinois at Urbana-Champaign); Lars Hultman (Linköping University, Sweden); Ivan Petrov (University of Illinois at Urbana-Champaign) Transition metal nitrides (TMN) are well known to have a remarkable range of unique physical properties and thus find their place in a variety of applications. By employing highly kinetically-limited growth techniques including low growth temperatures and high-flux, low-energy ion bombardment during film growth, metastable TMN alloys can be synthesized and have shown to exhibit novel and exotic physical properties. The most famous example is Ti_1-xAl_xN; many have reported drastically enhanced hardness, elevated oxidation resistance, age-hardening behavior, as well as the ability to tune the reflectance of optical coatings. Many of these properties are often accompanied by the formation of self-organized nanostructures due to the onset of spinodal decomposition. However, very little has been reported on the ability to control the nanostructure formation and as a result, the systematic effects of nanostructure on the bulk fundamental physical properties of TMN alloys are relatively unknown. Here, we report on an investigation into the effects of nanostructure formation on the optical, electronic, and thermal transport, as well as elastic properties of high-quality Hf_1-xAl_xN(001) single crystal layers using ellipsometry, temperature-dependent hall effect, picosecond probe acoustic and thermal transport measurements, in combination with advanced HR-TEM and STEM techniques. The layers were grown on MgO(001) by reactive magnetron co-sputter deposition. Films with 0 ≤ x ≤ 0.17 are random Hf_1-xAl_xN solid solutions with moderate changes in film properties. The onset of spinodal decomposition with x > 0.17, as indicated by the observation of 3D-nanoscale composition modulations using HR-STEM, results in abrupt changes in the thermal and optical properties, while gradual changes occur in the electronic properties. For instance, the thermal conductivity drops over an order of magnitude while the effective carrier concentration maintains values >10²² cm^-3. Dielectric functions are determined for all compositions 0 ≤ x ≤ 0.54 using ellipsometry at various degrees of incidence and simultaneously well fit using a combination of Drude-Lorentz behavior and a Bruggeman effective medium approximation. These fits suggest a percolated network of spherical metallic particles exists in a semiconducting medium with 0.24 ≤ x ≤ 0.32, while films with x ≥ 0.37 fall below the percolation limit, and carrier localization is observed (using electronic transport measurements). Comparisons are made with changes in film properties and those observed using advanced HR-TEM and HR-STEM techniques.