ICMCTF2008 Session E2-1: Mechanical Properties and Adhesion

Thursday, May 1, 2008 8:00 AM in Room California

Thursday Morning

Start	Invited?	Item
8:00 AM		E2-1-1 Effect of Surfactants on the Mechanical Properties of Electroless (Ni - P) Coating R. Elansezhian, B. Ramamoorthy, P. Kesavan Nair (Indian Institute of Technology Madras, India) Electroless nickel (EN) coating is a well established surface engineering process that involves deposition of a metal-metalloid alloy coating on various substrates. Although a variety of metals can be plated, electroless Ni - P coating has received widespread acceptance as it provides high hardness and excellent resistance to wear, abrasion and corrosion. Electroless methods offer high-quality ultrathin films that are compatible with high-resolution patterns such as sub-100 nm interconnects, contacts and via contacts for ULSI and in high aspect ratio structures for MEMS. The effect of surfactants on the surface roughness, microhardness and microstructure of electroless Nickel - Phosphorus (EN) surface protective coating obtained from an alkaline bath is presented in this paper. In this study the influence of surfactants sodium dodecylsulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) on the surface roughness, microhardness and microstructure of coated samples are investigated. The variation on surface morphology was examined using high resolution scanning electron microscope (HRSEM) and surface roughness values were measured using a stylus instrument. It was observed that the surface roughness and surface morphology of Ni-P coating were affected by addition of surfactants SDS and CTAB. Different surfactant concentrations were added to the electrolyte bath. It was found that without surfactant mean surface roughness (Ra) value was 1.885 Ä. When SDS concentration was lower, the mean roughness (Ra) value was found to be much higher. When SDS concentration increased, the roughness value was found to be improving and stable. For lower CTAB concentration mean roughness (Ra) value was deteriorating and when CTAB concentration increased the roughness value was observed to be improving. It was found that without surfactant the micro hardness value of as-coated condition was 450 Hv. The micro hardness value was increasing with increased SDS and CTAB concentrations. When SDS concentration increased, beyond its critical micelle concentration (CMC) the hardness value has stabilized and found to be better. When CTAB concentration increased, the hardness value was stable and observed to be improving. A 100% increase in micro hardness was observed in the presence of surfactant. The complete experimental details, results obtained and their analysis is presented in this paper.
8:20 AM		E2-1-2 Mechanical Properties of Gradient and Multilayered TiAlSiN Hard Coatings Y.-Y. Chang (Mingdao University, Taiwan); S.-J. Yang (National Chung Hsing University, Taiwan); D.-Y. Wang (Mingdao University, Taiwan); W. Wu (National Chung Hsing University, Taiwan) Multicomponent coatings based on different metallic and non-metallic elements possess the combined benefit of individual components leading to further improvement of coating properties. In this study, TiAlSiN nanocomposite coatings prepared as monolithic single layer, multilayer and gradient films were synthesized by using a cathodic-arc deposition system with lateral rotating arc cathodes. Chromium and AlSi alloy cathodes were used for the deposition of TiAlSiN coatings. In this study, field emission scanning electron microscope, transmission electron microscope and X-ray diffraction using Bragg-Brentano and glancing angle parallel beam geometries were used to characterize the microstructure of the as-deposited and high temperature annealed films. The mechanical properties including hardness, elastic modulus, and fracture toughness of the deposited and annealed TiAlSiN coatings were analyzed by a nanoindenter with Berkovich indenter tip. It has been found that the mechanical properties of the deposited and annealed films were correlated with the gradient and multilayered structures.
8:40 AM	Invited	E2-1-3 The Strength of Thin Films, Small Structures and Materials Under Localised Stresses D.J. Dunstan (Queen Mary University of London, United Kingdom) Critical thickness theory explains an excess yield stress in thin films inversely proportional to the film thickness. However, in other contexts, an excess yield stress is often observed which is proportional to the inverse square-root of a relevant dimension. Work-hardening coefficients show both inverse and inverse square-root behaviours. We review recent experimental work which has demonstrated these effects unambiguously, and discuss the extent to which they can be theoretically explained.
9:20 AM		E2-1-5 The Effects of Alloying on the Mechanical Behaviour of In_xGa_1-xAs S. Korte, I. Farrer, W.J. Clegg (University of Cambridge, United Kingdom) The mechanical behaviour of In_xGa_1-xAs quantum wells is of interest in its own right, although these systems have also attracted interest as model systems for studying deformation behaviour, such as the effect of coherency strains. However, to the knowledge of the authors, only very little information is available on the deformation behaviour of InGaAs over the full compositional range from GaAs to InAs. Existing data on a range of systems suggests that a maximum in the yield stress or measured hardness occurs at some intermediate composition, for instance in ZnBeSe. In recent studies on InGaAs, a dependence of mechanical properties on composition has only been carried out in the range of normal dopant concentrations. Here, nanoindentation with different tip geometries was used to investigate the mechanical properties of InGaAs over its full compositional range, going into greater detail to either side of the maximum hardness at x ~ 0.25. Yield stress from spherical indentation, Berkovich hardness and Young modulus are reported for all samples. Stress-strain curves from spherical indentation suggest a difference in yield behaviour depending on composition and dislocation density of the volume under the indenter. These measurements are compared with observations using transmission electron microscopy.
9:40 AM		E2-1-7 Investigation of Magnetron Sputtered Titanium-Nickel Nitride Thin Films for Use as Mould Coatings H.R. Stock, M. Diesselberg, H.-W. Zoch (Stiftung Institut für Werkstofftechnik, Germany) Reactive magnetron sputtering of substoichiometric TiNx films (x < 1) with different amounts of nickel ranging from 8 to 32 at.% was undertaken. Moulding tools made of X42Cr13 (AISI 420) steel were used as substrates, ground and polished to a roughness of Ra = 12 nm. By varying the nitrogen gas flow, nickel content and deposition temperature the properties of the films change significantly. The morphology of the coatings is adjustable between amorphous and slightly columnar and the universal hardness between 7 and 21 GPa. After deposition the samples were heat treated at temperatures up to 700°C. Both chemical composition and heat treatment temperature were found to have a considerable effect on resulting hardness. Moulding experiments with PMMA (polymethylmethacrylate) revealed a remarkable performance of the coated tools. No delamination of the coating was observed. The only wear detectable was some abrasion occurring at the near surface region of the coating, also known as polishing wear. This results in a decrease of the roughness and even better surface smoothness of the moulded PMMA parts.
10:00 AM		E2-1-8 Structure and Mechanical Characteristics of Amorphous Carbon Film Deposited on Poly Aryl-Ether-Ether-Ketone (PEEK) Substrate M. Xu, Z. Wei, S.H. Pu, P.K. Chu (City University of Hong Kong) Poly aryl-ether-ether-ketone (PEEK) is a modern, high-temperature and radiation-resistant thermoplastic material used in a variety of applications in the aerospace industry, automotive industry as well as electronic and medical devices. However, the use of PEEK is limited because of its low hardness, poor scratch resistance, and high susceptibility to gases and chemicals. Surface modification by depositing an amorphous carbon film is one of the promising methods to improve the surface properties of the polymeric materials because amorphous carbon films have many desirable properties including improved hardness, excellent chemical, thermal stability, and so on. Recently, a number of techniques have been used to coat polymer substrates with amorphous carbon films, including plasma-enhanced chemical vapor deposition (PECVD), ion beam assisted deposition (IBAD), and pulsed laser deposition (PLD). In this work, plasma immersion ion implantation and deposition (PIII&D) is used for the first time to produce the amorphous carbon film on PEEK substrate. Medium to high energy ion bombardment which is intrinsic to PIII&D provides ion mixing ensuring successful deposition of a hard film on a soft substrate in spite of the large discrepancy in the mechanical properties between the two types of materials. We will report the structure and mechanical properties of the coated PEEK materials. The film structure is evaluated by X-ray photoelectron spectroscopy and glancing angle X-ray diffraction. The surface morphology is determined by atomic force microscope and hardness by nanoindentation measurements. The scratch resistance of the a-C:H/PEEK is assessed by nano-scratch tests.
10:20 AM		E2-1-9 Effect of the Ion Implantation Processing Variables on the Improvement of the Adhesion Strength Between the PET Polymer and the CrZrN Coatings B.S. Kim, S.Y. Lee, B.Y. Lee, Y.S. Hong (Korea Aerospace University, Korea); J.S. Lee (PEFP, KAERI, Korea); J.J. Lee (Seoul National University, Korea) The ion implantation on the surface of the polymers is known to improve the surface properties such as adhesion strength for the PVD coatings and the wettability, etc. In this study, the effect of the processing variables such as implantation energy, the nitrogen ion doses, etc on the enhancement on the adhesion strength between the PET polymer and the CrZrN coatings was investigated. The modification of chemical and structural properties of the implanted PET were analyzed in terms of the FT-IR(Fourier Transformation Infrared Spectroscopy), XPS(X-ray Photoelectron Spectroscopy), and AFM (Atomic Force Microscopy). The adhesion strength of coatings to the implanted polymer surfaces was evaluated by measuring the critical load using a revetest scratch test. Preliminary results showed that the surface roughness of the PET was modified in a great extent and the scratch test showed that the adhesion strength of the CrZrN coating on the implanted PET was much better than that of CrZrN coating on the PET without ion implantation. Detailed experiment results will be presented.
10:40 AM		E2-1-10 Surface Morphology of Compressively Stressed Film Deposited on a Soft Polymer Using PECVD M.W. Moon, J.W. Yi, K.-R. Lee (Korea Institute of Science and Technology, Korea) It has recently been shown that focused ion beam (FIB) irradiation induces a wrinkled skin on the surface of polydimethylsiloxane (PDMS), providing a robust technique for creating wrinkling patterns on selective areas of PDMS. However, a key limitation of this technique is the size of the area exposed to ion beam (confined to 500 micron 500 micron maximum due to the magnification limitation of the FIB system). This restriction hinders the application of this technique where the desired area size of the created patterns is in the order of square millimeter or even square centimeter (e.g. cell templates for tissue engineering and surface modification for enhancing the wear characteristics of polymers). This restriction is overcome in our recent experiments by coating the compressively stressed thin film on soft polymer surface where ordered wrinkles can be created over a large area of the polymeric substrate. Using plasma enhanced CVD technique (PECVD), a diamond-like carbon (DLC) film with a elastic modulus of ~100GPa was deposited on a soft PDMS with the range of 1~10MPa in elastic modulus. The wavelength of the wrinkling patterns of DLC films was controlled by varying the thickness of DLC film and the deposition condition of the acceleration voltage between 100 to 1000eV with precursor gas of C₂H₂ using PECVD. The surface morphologies from simple herringbone to hierarchical shape of wrinkle patterns have been measured by AFM with respect to the thickness and deposition power of DLC film. Moreover, the exact modulus of the DLC film was estimated using a simple theory for wrinkled thin films on compliant substrates.
11:00 AM		E2-1-12 Nano and Micro Indentation and Scratch Tests of Mechanical Properties of Thin Films N. Gitis, L. Hermann, S. Kuiry (Center for Tribology, Inc.) Experimental comparison of common nano and micro scales for hardness evaluation has been performed on metal and ceramic coatings of different thickness and discussed in details. Instrumented indentation was found advantageous in both repeatability and a number of measured parameters over classical hardness methods for metals, while sclerometry was advantageous for thin films. All the indentation and scratch (sclerometry) techniques were compared on the same samples on the same instrument (Universal Nano+Micro Tester UNMT-1). In the micro-indentation and nano-indentation tests, the indents under 5-10% of the film thickness have produced repeatable and apparently substrate-independent results. In the micro-scratch and nano-scratch, the scratches under 30-35% of the film thickness have produced repeatable substrate-independent results. In the micro-indentation tests, traditional Rockwell and Vickers hardness tests produced more data variability than the instrumented-hardness tests with the same indenters in the same test setup, though the statistics requires more data.
11:20 AM		E2-1-13 The Relationship Between Top-Layer Tensile Strength and Optical Gloss Retention in Multi-Layer Coated Surfaces via Nanoindentation, Parametric Optimization, Scratch Testing and Finite Element Modeling T. Ovaert (University of Notre Dame); B.-R. Kim (L.G. Chemical, Ltd., Korea); J. Wang (A.B.B. Robotics) Multi-layered coatings are often specified to maintain a high-gloss protective finish for both structural and decorative applications. Furthermore, the relationship between optical gloss properties and coating mechanical properties after random micro-scratch type events is a complex phenomenon. In this investigation, multi-layered coating visco-elastic/plastic properties were determined using parametric modeling; derived from nanoindentation, gradient-based optimization, and finite element analysis. The individual layers, once characterized, were assembled into two- or three-layered structures and subject to micro-scratch tests. These tests determined an experimental critical scratch indentation load for the layered structures, as designated by the first appearance of visible surface layer tensile cracks during sliding. Scratch tests were carried out for three different conical scratch tip radii. The top-layer tensile strength of the layered structures was then estimated, utilizing the individual layer properties, the top layer friction coefficients, the micro-scratch test critical loads, and a finite element scratch model, for each scratch tip radius. The top-layer scratch tensile strengths were then used to correlate with the results of gloss measurements on several multi-layered structures after a full-scale scratch/wear process. The method is proposed as a candidate for coating selection, comparison, and performance testing in scratch-resistant coating applications.