Papers

ICMCTF2003 Session E3/F1-2: Mechanical Properties and Adhesion

Wednesday, April 30, 2003 1:30 PM in Room California

Wednesday Afternoon

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1:30 PM		E3/F1-2-1 Mechanical Property Measurement of Titanium/ Titanium Nitride and Aluminium-Magnesium/ Magnesium Free Standing Multilayer Foils M.G. Brookes, P.J. Kelly, R. D. Arnell (University of Salford, United Kingdom) The advent of the closed field unbalanced magnetron sputtering (CFUBMS) system has allowed a novel method for the production of ultra thick (above 50µm) multilayer coatings, which form free standing foils when removed from the substrate. Applications for this method range from the production of complex metal/ceramic probe tips to an alternative route for the production of axisymmetric high precision-machined components. In this study the CFUBMS system was developed to grow 50µm aluminium-magnesium/ magnesium (Al-Mg/Mg) and titanium/ titanium nitride (Ti/TiN) multilayer combinations. The Ti/TiN foils were deposited using opposing magnetrons, with the TiN layers produced by reactive sputtering. The Al-Mg/Mg foils were deposited from pure Al and Mg targets in a co-planar configuration; conditions having been initially found that produced high hardness/ high strength amorphous Al-Mg alloy foils. Both multilayer systems benefit mechanically from the combination of a high strength component (TiN; Al-Mg) and a ductile component (Ti; Mg). Global conditions were found that limited the stresses induced in these ultra thick coatings. Experimental arrays were then constructed to investigate the effect of relative percentage volume fraction, substrate bias and interlayer wavelength against the Young's modulus, tensile strength, UTS and other mechanical properties of the foils. These properties were determined using a modified Hounsfield tensometer. The study found that when in tension, the interlayer wavelength has no effect upon the tensile strength of the foil. However, as expected, tensile strength was strongly dependent upon the relative percentage volume fraction of the foil. The substrate bias was found to have a limited influence upon mechanical properties. Conditions were found that produced a tensile strength-to-film density ratio of 239, approaching that of tool steel.
1:50 PM		E3/F1-2-2 Evaluation of Microstructures and Mechanical Properties of Chromized Steels with Different Carbon Contents J.W. Lee (Tung Nan Institute of Technology, Taiwan, ROC); J.G. Duh (National Tsing Hua University, Taiwan, ROC) Chromization process is a method for developing a surface modified coating providing wear, corrosion resistance and high temperature surface protection. Three carbon steels with 0.25 wt%, 0.45 wt% and 1.0 wt% carbon contents, respectively, were chromized with pack cementation process at 950°C for 1, 4 and 9 hours. The phase transformation and microstructure phenomena of chromized coating layer and matrix of three steels were studied with X-ray diffractometer and electron probe microanalyzer. The mechanical and adhesion properties were evaluated by microhardness, scratch, Rockwell-C indentation and pin-on-disk wear tests. Atomic force microscopy was also employed to study microscratching, microwear, and nanoindentation behaviors of chromized surfaces. Chromium carbides and nitride phases were observed on the chromized surfaces. The thickness and hardness of chromized layers increase with carbon content. Chipping and micro radial cracking failures were found on the chromized layers after the Rockwell-C adhesion quality tests. Itâ€™s concluded that significant increase of the surfaces hardness were achieved on chromized alloys. Adhesion and wear properties of chromized layers were enhanced as carbon contents increased in the matrix.
2:10 PM		E3/F1-2-3 Study of the Effect of Ion Implantation of Carbon on TiBN Films S.M. Aouadi (Southern Illinois University); K.C. Wong, K.A.R. Mitchell (University of British Columbia); F. Namavar (University of Nebraska Medical Center / Spire Corp.); D.M. Mihut, S.L. Rohde (University of Nebraska - Lincoln) This paper presents a systematic study of the effect of carbon ion-implantation on the structural, optical, and mechanical properties of TiBN coatings. TiBN coatings with a functionally graded underlayer of Ti/TiN have been deposited at low temperatures (<200°C) on a silicon substrate using ion beam assisted deposition (IBAD). These coatings were subsequently implanted with carbon. The deposited and implanted structures were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and nanoindentation. The primary phases in the film were identified using XRD. The surface morphology and nanocrystalline nature of the coating were deduced using AFM. The chemical and phase compositions were determined from XPS measurements and were subsequently correlated to the optical data obtained from SE measurements. The hardness was found to strongly depend on chemical and phase composition and varied from 10 to 45 GPa. The difference between the properties of the as-deposited and implanted coatings was discussed.
2:30 PM		E3/F1-2-4 Nanohardness of Nanocrystalline Transition-Metal Nitride Coatings by Ion-beam-assisted-deposition C.-H. Ma (University of Illinois at Urbana Champaign); J.-H. Huang (National Tsing Hua University, Taiwan, R.O.C.); H. Chen (City University of Hong Kong) In this study, highly textured nanocrystalline titanium nitride (TiN), chromium nitride (CrN) and vanadium nitride (VN) thin films were prepared by ion-beam-assisted deposition method (IBAD). The nanohardness increased as the result of the improvement of microstructure; however, the nanohardness was not sensitive to the texture strengthening mechanism. Compared to the data published by other groups, it was found that the application of texture strengthening mechanism should also take the grain size into account. The nanohardness of the single crystal and nanocrystalline samples were not sensitive to the sample orientations. On the other hand, the preferred orientation was important on the nanohardness of polycrystalline samples with the grain size ~150nm. A simple explanation of this dilemma was given based on the scales of indentation depth, deformation zone, surface force (the St. Venant's Principle) affective zone, and the grain size.
2:50 PM		E3/F1-2-5 Characterization and Mechanical Properties of Silicon Nitride Films with Various Nitrogen Contents J. Yun, B. Kim, C. Go, H. Lee (Kyungnam University, South Korea); S.R. Choi, S.-Y. Yoon, K.H. Kim (Pusan National University, South Korea) Silicon nitride is a matrix phase and plays an important role in the properties of Ti-Si-N coating films having TiN nano-crystallites in it. To understand the role of silicon and/or nitrogen in the film, silicon nitride thin film was prepared by a magnetron sputtering technique in gaseous mixtures of nitrogen and argon. Different nitrogen flow rate with constant argon flow rate or with constant total flow rate were used for producing Si-N films of different nitrogen contents. The hardness and elastic modulus of thin film was characterized by nanoindentation and scanning probe microscopy. The hardness of Si-N film was almost constant with changing nitrogen flow rate. However, the elastic modulus decreased with increasing nitrogen/argon ratio. When the nitrogen flow rate was zero, the film composition was almost free of nitrogen, but showed lower hardness and modulus values than those of pure silicon. Wear and oxidation resistance were examined by the proper methods. The microstructures of Si-N thin films were examined by SEM and TEM and the mechanism of hardness variation was discussed.
3:30 PM		E3/F1-2-7 Mechanical Properties and Scratch Resistance of Large-area Optical Coatings P.D. Warren (Pilkington plc, United Kingdom) With the increasing demands for energy-efficiency (in both buildings and automobiles) the use of energy-efficient glazings is increasing rapidly. The essential requirement is that of high transmission of visible radiation and high reflection of infra-red radiation. For glass, these requirements can be satisfied by the use of so-called low-emissivity coatings. There are two basic types of coating that can be used either "on-line" or "off-line". For "on-line" coatings, a relatively thick (~0.5um) coating of a transparent conducting oxide (typically tin oxide) is deposited onto hot glass via a CVD process. For "off-line" coatings, a very thin (~10nm) layer of silver, plus various other thin (~10's nm) oxides for anti-reflection purposes, is sputtered onto the glass when it is cool. Once the coated glass has been produced, it undergoes a variety of processing and transport steps in order to turn it into a window. During these operations, the coating may come into contact with other objects and if care is not taken mechanical damage to the coating may result. This paper will describe some of the problems that arise when one tries to understand and improve the mechanical properties of these coatings bearing in mind that they have been optimised for their optical, not mechanical, performance.
4:10 PM		E3/F1-2-9 Structure, Thermal Stability, and Mechanical Properties of Electroless Ni-P-W Alloy Coatings During Cycle Test S.K. Tien, F.B. Wu, J.G. Duh (National Tsing Hua University, Taiwan, ROC) The electroless Ni-P-W coatings were deposited on the mild steel and 420 stainless steel in the alkaline solutions. The compositions of Ni-P-W and Ni-P coatings were evaluated by electron probe microanalysis. The effect of thermal cycle at 400 and 450°C on the crystal of the electroless deposit structure was studied by X-ray diffraction. The thermal stability of electroless Ni-P and Ni-P-W coatings with the identical of phosphorus content was analyzed by differential scanning calorimetry (DSC). The variation of adhesion strength between as-deposited and heat treated Ni-P-W coatings was appraised by scratch test. With identical molar ratio of precipitated Ni₃P in both heat treated Ni-P and Ni-P-W films, the tungsten, addition into the nickel-phosphorus based coatings effectively increases microhardness and thermal stability. After over 30 times of thermal cycling test at 400°C, the X-ray diffraction analysis shows that Ni-P films have completely crystallized and the hardness is degraded to a lower value. On the contrary, the Ni-P-W films have not completely crystallized and thus a high value of hardness can be retained without appreciable degradation.
4:30 PM		E3/F1-2-10 Hardness Evolution of Electroless Nickel-phosphorus Deposits with Thermal Processing K.G. Keong, W. Sha, S. Malinov (The Queen's University of Belfast, United Kingdom) Four samples of electroless nickel-phosphorus (EN) deposits coated on mild steel substrate have been analysed for their hardness changes in relation to the deposit phosphorus contents as well as different heating temperatures at isothermal (100-500°C for 1 hour) and linear heating (300-600°C at 20°C/min) conditions. It was found that the hardness of the EN samples increased with decreasing phosphorus content at as-deposited condition, and could be enhanced by appropriate heating. The results of Vickers microindentation testing show that the peak hardness of the EN samples could be achieved after heat treating at 400-450°C. This is caused by the formation of intermetallic Ni₃P stable phase at this temperature range, acting as a function of precipitation hardening. The Knoop microindentation testing on the cross sections of the samples indicates variations of hardness across the depth (distance from the sample surface towards the sample/substrate interface), but for most samples the tendencies of change were not monotonous. Scanning electron microscopy (SEM) analysis has shown that the lamellar structure present in the cross sections of the as-deposited EN samples tends to disappear, and agglomeration occurs as the heat treating temperature is increased. The concept of kinetic strength (K_s) is adopted to interpret the kinetic energy (Q) of increased hardening effects using the Vickers hardness data from the isothermal experiments, but the result has not been satisfactory.
4:50 PM		E3/F1-2-11 Structural and Tribological Studies of Nanocrystalline Ti-C-N Composites Coatings Prepared by Reactive Sputtering D. Martínez-Martínez, J.C. Sánchez-López, T.C. Rojas, A. Fernández (Instituto de Ciencia de Materiales de Sevilla, Spain); P. Eaton (Instituto de Investigaciones Químicas, Sevilla, Spain); M. Belin (Ecole Centrale de Lyon, France) The development of a nanocomposite coating that combines good mechanical and tribological properties results a research activity of high technological interest for the improvement in performance of cutting and forming tools. In this sense, a singular microstructure formed by nanodomains of a hard phase (transition metal carbides or nitrides) embedded in an amorphous matrix that would act as lubricant may succeed this goal by diminishing the friction coefficient without lost of mechanical properties. Nanocrystalline Ti-C-N composite films were synthesized at near room temperature by reactive magnetron sputtering of titanium and graphite targets in Ar or Ar/N₂ mixtures. A set of coatings was prepared varying the Ar/N₂ ratio, sputtering power, and total pressure. The film microstructure and chemical composition of the coatings were studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). For high Ar/N₂ ratios, a microstructure constituted by small grains (20-40 nm) surrounded by thin walls is observed. AFM lateral force mapping shows a strong frictional contrast between the two phases. The existence of TiC, TiN and/or TiCN phases is demonstrated by the XPS technique for these samples. When increasing the nitrogen content, the granular microstructure is not seen and the chemical composition is enriched in amorphous non-stoichiometric CN_x phases. The friction coefficient and durability of the coatings were evaluated using pin-on-flat and pin-on-disk tribometers. The type of structure and chemical bonding of the Ti-C-N films are correlated with the tribological properties at the nano- and microscopic level in order to establish the best synthesis conditions.
5:10 PM		E3/F1-2-12 Nanoindentation with Scanning Force Microscope for Complete Characterization of Mechanical Properties of Carbon Nitride Thin Films S. Chowdhury, M. Laugier, Z. Rahman, M. Serantoni (University of Limerick, Ireland, RO) It is found that hardness and Young's modulus values are significantly overestimated by nanoindentation using the Oliver and Pharr analysis [1]. SFM imaging of the residual indent, in conjunction with the nanoindentation results provides a more complete understanding of the response of a material at small scales to indentation. The true residual contact area directly measured from the SFM images can subsequently be used to recalculate the hardness of the material more accurately. In this study, nanoindentation with SFM has been used to investigate the mechanical properties of thin CN_x films deposited by RF magnetron sputtering on silicon (100) substrates. Hardness was determined at different loads and depths from nanoindentation using the Oliver and Pharr method. The indents were imaged using SFM and true residual contact areas as well as hardness values were determined. Residual depths and hardness values obtained by SFM were found to be consistently lower than the values calculated by the Oliver and Pharr method. [1] Tusi, T.Y., G.M. Pharr, 1999, J. Mater. Res., 14, 292.