ICMCTF2004 Session E3/F1-1: Mechanical Properties and Adhesion

Monday, April 19, 2004 10:30 AM in Room California

Monday Morning

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10:30 AM E3/F1-1-1 Structure and Mechanical Properties of Ceramic Nanocomposite Coatings
W.J. Meng, B. Shi (Louisiana State University)
Ceramic coatings consisting of mixtures of two or multiple phases with characteristic length scales ranging from a few to a few tens of nanometers have recently been under intense scrutiny. Interests in these coatings are partly application driven, stemming from the ability to vary their mechanical properties and tribological characteristics systematically by varying their composition and structure, and partly curiosity driven, stemming from the presently incomplete understanding of the dominant mechanism(s) governing deformation and fracture of these materials. Here we present results of our recent investigations into the structure and mechanical properties of pseudo-binary ceramic nanocomposite coatings. We will concentrate on two prototypical ceramic nanocomposite coating families, namely, metal-containing amorphous hydrocarbon (Me-C:H) coatings and metal-containing amorphous silicon nitride (Me-Si-N) coatings. Protocols for nanoscale structure determination by combining the techniques of high-resolution transmission electron microscopy and X-ray absorption spectroscopy will be illustrated with examples from the Ti-C:H and Ti-Si-N coating systems. Attention will be paid to the influence of the nanoscale structure on the mechanical properties of nanocomposite coatings.
11:10 AM E3/F1-1-3 Micro-mechanical Properties of Ternary Transition-metal Nitrides
D. Mihut (University of Nebraska-Lincoln); S.M. Aouadi, M. Debessai (Southern Illinois University); S.L. Rohde (University of Nebraska-Lincoln)
Ternary transition-metal nitrides (TTMN's), such as CrBN, TaZrN, NbZrN, etc., are significant because they yield a rich array of structural, chemical and physical forms that give rise to numerous useful properties, including exceptionally low chemical reactivity, extreme hardness, and desirable optical characteristics; often coupled with good electrical conductivity. These materials are difficult to produce in bulk, but can be readily synthesized at low temperatures via thin film techniques and often in novel nanostructured forms. The TTMN's in this study were deposited on Si(100) wafers using reactive magnetron sputtering. While there have been some studies assessing the chemical and structural composition of these alloys, little is known about the mechanical behavior of TTMN's, especially on the micro- or nano-scale. In the present study, the micro-mechanical properties of several TTMN alloys were assessed using AFM surface profilometry to determine the surface topography and an AFM-Hysitron Triboscope system to make nanoindentation and microwear measurements. These micro-mechanical properties are correlated with previous phase and chemical analyses. For example in CrBN films an amorphous structure is observed for all samples, except those produced at the lowest nitrogen levels. While the highest hardness occurred using either very low (0.5 sccm) nitrogen levels or in nitrogen saturated films (15 sccm), where the hardnesses were 24 and 17.5 GPa, respectively. In addition, scanning electron microscopy was used to image and analyze the microwear tracks of several thin films in order to study typical failure modes.
11:30 AM E3/F1-1-4 Fatigue Behavior of a Ti-6 Al-4 V Alloy Coated with Balinit Futura
L.M. Fernandez, C.J. Villalobos-Gutierrez (Universidad Central de Venezuela); G. Mesmacque (IUTA, France); E.S. Puchi-Cabrera (Universidad Central de Venezuela)
The fatigue behavior of a Ti-6 Al-4 V alloy coated with a commercial film known as Balinit Futura® has been investigated. The tests were carried out in air and in a NaCl solution under rotating bending conditions. The coating is a multilayer film composed of 24 alternate layers of TiAlN/TiN, of approximately 3 µm in thickness. It was deposited industrially in a PAPVD reactor by arc enhanced magnetron sputtering at a temperature of less than approximately 500°C. The substrate material had been previously annealed at a temperature of 704°C and air cooled. The evaluation of the monotonic mechanical properties by means of tensile tests showed an increase in both the yield and tensile strength of the coated material. The fatigue behavior of both the coated and uncoated material was evaluated at stresses of the order of 68-78% of the yield stress. The stress versus number of cycles to failure data were described by means of a simple parametric relationship similar to that proposed by Basquin for the correlation of this kind of data. It has been determined that the presence of the coating on this alloy gives rise to a decrease in the fatigue properties of the substrate that can achieve up to about 21% at high alternating stresses and 45% at low alternating stresses. The fatigue limit of the coated substrate was also reduced by approximately 10% in comparison with that of the uncoated alloy. Some selected fracture surfaces and sections normal to such surfaces, of the fatigue samples tested both at high and low alternating stresses have been analyzed by means of SEM techniques in order to determine the initiation sites of the fatigue cracks and their subsequent propagation. The preliminary observations of such samples indicates that the deposition process gave rise to significant changes in the substrate microstructure and mechanical properties which could be responsible for the decrease in the fatigue performance of the coated alloy.
11:50 AM E3/F1-1-5 Improving Surface Wearing of Tools by Magnetization when Cutting Dry
M. El Mansori (Labortaire de Mecanique et Procedes de Fabrication, France); D. Paulmier (ERMES - INPL, France)

Wear of magnetized cutting contacts results from thermo-mechanical and magnetic actions. Theses actions are closely interrelated during cutting process.

This contribution highlights these phenomena when investigating the dry cutting of ferromagnetic 0.38% carbon steel using ferromagnetic HSS and non-magnetic carbide tools in drilling and turning experiments.

The results These results suggest that even the magnetic effect seems to be manifold, it can be basically grouped into two categories (i) a change in the cutting mechanics (ii) a material properties variation of workpiece and tool.

12:10 PM E3/F1-1-6 On the Influence of Residual Stress on Hardness and Elastic Modulus
E. Coronel, M. Smid, U. Wiklund, S. Hogmark (The Angstrom Laboratory, Sweden)
It is widely accepted that the residual stress of surface coatings influences measurements of other mechanical properties of the coatings. The hardness is often reported to increase by a compressive stress in the coating. Less consistent information is available regarding e.g. the influence on elastic modulus although there are reports that also the elastic modulus increases with increasing stress. In this work we approach this issue from a somewhat different experimental point of view. Nanoindentation is used to access the hardness and elastic modulus of coatings. The residual stress of the coating is determined using either plate deflection techniques or XRD techniques. To isolate the influence of residual stress small parts of the coating is cut from the coating using a focused ion beam. After mounting nanoindentation is again used to measure the mechanical properties of the stress relieved coating fragments. This experimental route presents an easy and straightforward way to investigate the role of residual stress. TiN and similar coatings with large differences in level of stress are investigated with this experimental method and to elucidate its applicability.
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