Papers

ICMCTF2002 Session F1/E4-2: Mechanical Properties and Adhesion

Tuesday, April 23, 2002 1:30 PM in Room San Diego

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		F1/E4-2-1 Hertzian Analysis of the Self-Consistency and the Reliability of the Indentation Hardness Measurements on Superhard Nanocomposite Coatings S. Veprek (Technical University Munich, Germany); S. Mukherjee (Bhabha Atomic Research Center, India); P. Karvankova, H.D. Mannling, J.L. He, K. Moto (Technical University Munich, Germany); A.S. Argon (Massasschusetts Institute of Technology) The measurement of elastic properties of superhard nanocomposite coatings can be subject to a number of possible errors, such as indentation size effects (ISE: indenter tip blunting, non-representatively small volume of the material to be tested upon nanoindentation and a too small stress under the indenter which does not reach the yield stress of that material if a small load of less than 10-20 mN is used), the composite effect of the system of superhard coating on a softer substrate, high compressive or tensile stress in the coatings, drifts and/or stiffness of the indenter etc.. We shall present a systematic study of these possible artefacts on superhard coatings using a large range of applied loads on a number of super- and ultrahard samples. Hertzian analysis of the non-linear elastic response upon unloading provides analytical solutions which can be used in order to check if the hardness values measured on the super- and ultrahard coatings are self-consistent. In particular, it is possible to estimate the maximum tensile stress which the coatings survive without failure. This stress occurs at the periphery of the contact between the coating and the indenter and, in the case of ultrahard coatings, it can reach values in the range of tens of GPa. The results show a very good agreement with the theoretical predictions based on the Universal Binding Energy Relation. The hardness values obtained from the indentation measurements are compared with the Vickers hardness calculated from the projected area of the plastic deformation. The data will be compared with Finite Element computer modeling in order to obtain a deeper insight into the complex problems. Reliable results can be obtained if sufficiently thick coatings can be used together with load independent values at sufficiently large indentation depths.
2:10 PM		F1/E4-2-3 Understanding of Automotive Clearcoats Scratch Resistance P. Bertrand-Lambotte, J.L. Loubet (Ecole Centrale de Lyon, LTDS, France); C. Verpy (PSA Peugeot Citroen, Velizy, France); S. Pavan (Ecole Centrale de Lyon, LTDS, France) Micrometric scratches, mainly due to car wash brushes, decrease the gloss of automotive clearcoats, alter their appearance and prevent them from protecting the car in the best way. Scratch resistance is estimated from the visible damage caused on the clearcoats. As the eye is more sensitive to brittle than ductile scratches, one way to improve scratch resistance it to decrease the proportion of brittle scratches and to favor the healing of ductile scratches. An analyze of the contact during a scratch test shows that the ductile/brittle transition is controlled by both an energetic and a size criterion. The energetic criterion is related to the tensile strain located at the rear of the contact between the indenter and the clearcoat. This strain can enlarge existing cracks, leading to fracture. This strain depends on the clearcoats viscoelastoplastic properties, the mean deformation imposed by the indenter and the environment (dry tests or tests in water or soapy water). The effect of these parameters on scratch resistance is studied : indentation and scratch tests with a Nanoindenter XP but also tensile tests are carried out. The healing of ductile scratches is estimated from scratched samples of clearcoats. The samples are heated at different temperatures and the remaining scratch depth is measured with an atomic force microscope. The importance of the "surface flash temperature" between clearcoats and car wash brushes is also emphasized. The aim of this paper is to highlight the significance of glass and secondary transitions on the clearcoat behavior.
2:30 PM		F1/E4-2-4 Scratch Resistance and Adhesion Testing of Optical Fiber Coatings E. Poiré (Micro Photonics, Inc.) Measuring the mechanical properties of optical fibers, in particular the adhesion between coating and fiber, is difficult due to the curved geometry of the surface and the problems of positioning a pointed diamond tip so that it moves along the longitudinal axis of the fiber during a scratch test. This paper will present the use of scratch testing as a tool to study the adhesion of layers, cracking, internal and external failures of coated optical fibers. A variety of coated fibers with different coatings and surface treatments were tested using a technique in which the mechanical response is measured by simultaneously recording friction transients, acoustic emissions and changes in surface morphology.
2:50 PM		F1/E4-2-5 Mechanical Properties Evaluation of Cathodic Arc Plasma Deposited CrN Thin Film on Fe-Mn-Al-C Alloy J.W. Lee (Tung Nan Institute of Technology, Taiwan, ROC); J.G. Duh (National Tsing Hua University, Taiwan, ROC) Chromium nitride is a promising hard coating applied in forming, drawing and plastic molding industries due to its good thermal stability and excellent resistance to wear and corrosion. An austenitic Fe-30Mn-5.8Al-1C alloy was deposited with 2µm thick CrN film by cathodic arc plasma deposition process. The mechanical and adhesion properties were evaluated by microhardness, scratch, Indentation and Cracking Test (ICT), Rockwell-C indentation and wear tests. The microhardness of CrN film reaches HK 2311±100 measured with 10 gf load. The elastic modulus of the combination is 540±69 GPa measured by ICT. The adhesion property of deposited CrN film on Fe-Mn-Al-C substrate is observed to be fairly satisfactory. Only few lateral cracking are observed. No radial cracking or chipping is found after the Rockwell-C indentation test. The adhesion strength of deposited CrN is better than HF1. The wear resistance of the Fe-Mn-Al-C matrix is also significantly improved with the presence of coated CrN film.
3:10 PM		F1/E4-2-6 Mechanical Characterization of Ni-P-based Ternary Coatings by RF Magnetron Sputtering F.B. Wu, Yi-Ying Tsai, J.G. Duh (National Tsing Hua University, Taiwan, ROC) The Ni-P-based ternary coating with a third element, including Cu, Cr, and W, is fabricated by the RF magnetron sputtering. It is revealed that the P/Ni ratio and the amount of the third element in the ternary coating can be controlled through power adjustment and target design during sputtering. All the ternary coatings exhibit the amorphous microstructure in the as-deposited state. The introduction of the third element in the ternary coatings, especially in the cases of Cr and W, effectively retards the on-set of precipitation for Ni₃P phase and raises the recrystallization temperature to a higher temperature as compared to that for the Ni-P electroless plated alloy. Mechanical properties, including microhardness and scratch behavior are characterized and analyzed with respect to the addition element concentration and thermal history. It is observed that the hardness of the coatings can be effectively modified with the composition control of the third elements. Embrittlement caused by the third element elements through scratch test is also discussed.
3:30 PM		F1/E4-2-7 Functionally Gradient Nitrogen Diffusion/Cr Ion Plating Treatment on 4340 Steel V. Singh, E.I. Meletis (Louisiana State University) Ion-plated hard metal or ceramic coatings on steels have high potential in improving wear resistance but they suffer from low load bearing capacity. Diffusion treatments prior to coating can significantly increase surface hardness and create a functional gradient in hardness alleviating this drawback. The present study is focused on such functionally gradient treatments on 4340 steel. Intensified plasma-assisted processing (IPAP) was utilized to produce a functional hardness gradient by developing a nitrogen diffusion zone and dense Cr coating. Scanning electron microscopy, x-ray diffraction and cross sectional microhardness profiles were utilized to characterize the treated specimens. Wear and corrosion resistance of the substrate was studied prior to and after the IPAP treatment. The results show that the present functionally gradient treatments can cause marked improvements in wear resistance.
3:50 PM		F1/E4-2-8 New Unidirectional Single Pass Procedure Using Wear Tester Equipment for Assessment of Suitable Coatings and Other Materials for Forming Operations N.M. Renevier, S. Poulat, M. Jarrat, J. Codwell, D.G. Teer (Teer Coatings Ltd., United Kingdom) The ST-3001 is a multi-mode testing system which can be used for scratch adhesion tests, linear wear tests either reciprocating or uni-directional and hardness testing. The system was based on an earlier tester ST-2000 [1] and was further developed in a join project supported by the European Commission [2]. In conventional pin on disc or reciprocating wear tests, the same track is rubbed repetitively and such tests can be used to simulate the wear conditions for components but they do not simulate cutting or forming operations where new material is continuously bought into the contact zone. Recently, the ST-3001 has been used to provide an initial assessment for suitable coatings and substrate materials used in cold forming operations. Tests have performed at several loads under several environmental conditions (dry and lubricated) and a conditions for a new accelerated test have been established. The new testing procedure will be fully described in the paper and results will be correlated with industrial results. This is a powerful technique for simulation sticking of gummy materials such as aluminium, copper, stainless steel, led, zinc...for forming operation. [1] V. Bellido-Gonzalez, N. Stefanopoulos, F. Deguilhen, Surface and Coatings Technology 74-75 (1995) 884-889. [2] Multimode scratch testing project SMT4-CR1997-2150
4:30 PM		F1/E4-2-10 Structual and Mechanical Properties of Sputtered Tin-nitride Thin Films Y. Inoue, K. Sano, H. Sugimura, O. Takai (Nagoya University, Japan) Metallic tin and its alloys have been utilized since the Bronze Age, and their properties have been well-known as well as tin oxides, which have also been extensively studied and already put to practical use to gas-sensing and transparent-conductive devices. On the other hand, the characteristic of any binary tin-nitrogen compound has not been clarified. In this study, we report on synthesis of tin-nitride thin films by reactive sputtering and the dependence of the structure and mechanical properties of the films on deposition conditions in the sputtering process. Tin-nitride films were prepared by using an rf magnetron sputtering system. The nitrogen pressure was kept at 1 Pa. We varied a substrate bias in the ranges of 0 ~ -200 V. The crystal structure of the deposited films was characterized by X-ray diffraction (XRD). The chemical bonding states and the chemical compositions were investigated by X-ray photoelectron spectroscopy (XPS). Cross-sectional structure of the films was observed by using both a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The mechanical properties of the films were investigated by nanoindentation method. Some sharp diffraction peaks were observed in the XRD patterns. From the peak positions, we confirmed the crystal structure of the tin-nitride film is spinel. The crystallinity of the films was influenced by the substrate bias. XPS analyses revealed that the Sn-N bonds in the films are more covalent than Sn-O in tin oxide. In the cross-sectional SEM images, we observed that the films consist of two layers: the surface-side layer shows clear columnar structure while the substrate-side one has no texture, which means the polycrystalline tin-nitride grow on amorphous tin-nitride buffer layers. The hardness of the film prepared at the substrate bias of 0 V was found to be around 7 GPa with the elastic modulous of 100 GPa.