ICMCTF2002 Session F4-1: Microstructural, Microanalytical and Imaging Characterization

Monday, April 22, 2002 10:30 AM in Room San Diego

Monday Morning

Start	Invited?	Item
10:30 AM		F4-1-1 Elemental Distributions in TiAlYN/VN Superlattice Hard Coatings Using Field Emission Gun Analytical Transmission Electron Microscopy Z. Zhou, W.M. Rainforth (The University of Sheffield, United Kingdom); P.Eh. Hovsepian, W-D. Münz (Sheffield Hallam University, United Kingdom) Superlattice structured PVD hard coatings have been the focus of study due to their properties, such as extremely high hardness (up to 60 GPa), excellent wear resistance and corrosion resistance.1,2 TiAlYN/VN superlattice PVD hard coatings, typically with periods of 3-4 nm, have been economically manufactured on an industrial scale by a combined steered cathodic arc evaporation and unbalanced magnetron sputtering technique and are now just at the point of commercialisation.2 An understanding of the relationship between microstructure and bulk properties is important for the optimisation of properties. Although coatings are routinely characterised by many methods, the problem remains that the ultra-fine structures requires the very best special resolution analytical electron microscopy techniques. In this paper we report field emission gun transmission electron microscope (FEGTEM, JEOL 2010F) coupled with energy filted TEM (EFTEM-GATAN GIF)3 to characterise TiAlYN/VN superlattice PVD hard coatings grown on stainless steel substrates as a function of bias voltage (75, 95 and 125V). For each individual coating, the superlattice period decreased significantly within the initial 10 layers due to the target poisoning effect, but remained relatively constant thereafter to the surface. As bias voltage increased from 75 to 125V, the average periodicity of coatings decreased. Qualitative elemental distributions from layers of periodicity of 3-4nm (bias 75 and 95V) were obtained from energy filtered images. These showed that the Ti-rich layers and V-rich layers had similar thickness to each other throughout the coating, attributed to similar sputtering yields of V and TiAl targets, although the absolute thickness decreased from the bottom to the top of coating. Interestingly, the elemental maps demonstrated an additional modulation superimposed on the basic period of coating, which was considered to the three-fold substrates rotation geometry^3,4 Reference: 1, U. Helmersson, S.Todorova, S.A. Barnett, J.-E. Sundgren, L.C. Markert, and J. E. Greene: J Appl. Phy., 62, 481 (1987). 2, W. –D. Munz, D.B. Lewis, P. Eh. Hovsepian, C. Schonjahn, A. Ehiasarian, and I.J. Smith: Surf. Eng., 17, 15 (2001). 3, J. Cawley, J. M. Titchmarsh, and L.A. Donohue: Surf. Coat.Technol., 86-87, 357 (1996). 4, B. Rother, G. Ebersbach, and H.M. Gabriel: Surf. Coat.Technol., 116-119, 694 (1999).
10:50 AM		F4-1-2 Indentation Behavior of Ultra Hard Bn Films Obtained by a New PACVD Technique K. Jozwiak (Institut Polytechnic de Poznan - PUT, France); K. Chicot (Laboratory of Mechanics, LML URA CNRS 1441, France); M. Kupcayk (Institut Polytechnic de Poznan - PUT, France); J. Lesage (Laboratory of Mechanics, LML URA CNRS 1441, France) Super hard materials like diamond and boron nitride (> 4000 HV) are among the materials well in used as coatings to improve the wear resistance of cutting tools. Compare to boron nitride, however, the diamond has the disadvantage of having a high chemical affinity to iron that renders it improper for the machining of iron alloys. On the other hand BN films can be obtained by PVD process at low temperature and are efficient to prevent oxidation. The purpose of the present work is to research the optimum conditions for the making of wear resistant BN films using a new Hot Filament Plasma Assisted Chemical Vapor Deposition process. BN nitride is a synthetic compound that exhibits four allotropic forms of different physico-chemical properties. The regular form, c-BN, is a specially attractive candidate as a coating for cutting tools aiming at hard materials machining. Using three levels of discharge potential, we obtained films of typically 3-4 μm thick which composition was demonstrate to be a combination of c-BN and h-BN phases as detected by electron diffraction and Raman spectroscopy. Concerning the mechanical properties, the objective was to determine the toughness of the film depending on its composition. For that purpose, indentations were performed at the surface of the film using several indentation loads. The cracks formed at the tip of the indents were then measured using scanning electron microscopy. The results fit perfectly a law associated to a half penny cracking process. It is the possible then, to calculate the toughness of the three different films and to discuss the results of the calculation in regards of the film composition.
11:10 AM		F4-1-3 The Microstructural Effect of Chemically Vapor Infiltrated SiC Whiskered Thin Film on the Green Body of SiC/C Composites. Y.J. Lee, S.M. Hwang, D.J. Choi (Yonsei University, Korea); S.H. Park (Korea Institute of Science and Technology); H.D. Kim (Korea Institute of Machinery and Materials, Korea) SiC films have been grown by chemically vapor infiltration and deposition method. Different microstructure so-called "whisker type" SiC films have been fabricated and the deposition and infiltration conditions of whisker growing have been optimized. By necking the SiC/C particles of the green body, the fractural strength and has been increased by whiskering process, the porosity of the body has been increased. The microstructure and composition of whiskered SiC has been investigated by means of SEM, TEM and XPS.
11:30 AM		F4-1-4 Influence of Deposition Conditions on the Microstructure and Mechanical Properties of Ti-Si-N Films by DC Reactive Magnetron Sputtering S.-H. Kim (Pusan National University, Korea); J.-K. Kim (Korea Institute of Machinery & Materials, Korea); K.H. Kim (Pusan National University, Korea) Ti-Si-N films based on a nanocomposite concept were codeposited on SKD 11 steels by a DC reactive magnetron sputtering technique using separate titanium and silicon targets, in Ar/NS₂ gas mixtures. The crystallinity and microstructure for the coatings were examined as a function of deposition variables such as Ar/N₂ gas ratio, bias voltage, and substrate temperature. The silicon incorporation into TiN film modified the microsturcture of TiN with respect to crystal size, preferred orientation. As the Si content increased, the grain size of TiN became finer to a nanoscale, and the strong (111) preferred orientation of TiN changed to multiply oriented microstructure. The deposited Ti-Si-N films were basically composed of nanocrystalline TiN and amorphous silicon nitride. The microhardness of the film droped again beyond a certain amount of Si content, while it increased monotonically with the initial increase of Si content. In this study we investigated the hardness drop at higher Si content using various instrumental analyses such as XRD, EPMA, XPS, and TEM. Besides, scratch and impact test of Ti-Si-N coating layers on the substrate were carried out.
11:50 AM		F4-1-5 Production and Clusterization of Single Point Defects in Pure Tungsten and its Slightly Diluted Alloys Under Ion Irradiation A.L. Suvorov (SSC RF Institute of Theoretical and Experimental Physics, Russia); A.G. Zaluzhnyi (Moscow State Engineering and Physics Institute, Russia); V.P. Babaev, A.A. Zaluzhnyi (SSC RF Institute of Theoretical and Experimental Physics, Russia) Results are presented of the field ion microscopy investigation of production and transformation of the defect structure in the very pure, commercially pure tungsten and its four slightly diluted alloys (W - HfC - C, W - 1,5% ThO₂, W - 5% Re ? W - 2%Fe) under irradiation by In⁺ and Yb⁺ ions with the energy 25 keV and by Ar⁺, Ni⁺ and Cr⁺ ions with the energy 35 keV. Density of the ion current in all cases has been fixed at the same level j = 2,0 μ?, the fluence of irradiation has been ?t = 5?10¹⁴ ions/cm². The greatest attention during this investigation has been paid to the particular features of clusterization of single vacancies in the irradiated specimens with regard to the volume and type of precipitates, presenting there. Distribution of complexes of vacancies in the irradiated specimens has been revealed and analyzed due to the number of single vacancies aggregated therein. A noticeable dependence of those distributions in the areas of development of cascades of atomic displacements (in the depleted zones) and away from those areas has been revealed. Specificity of distribution of the being investigated complexes "self atom - atom of impurity" (in the split configuration) in the volume of irradiated specimens has been investigated. Correlation between the type and concentration of components in alloys, concentration of the mentioned complexes (splits) and the dimensions and parameters of the depleted zones has been estimated. A theoretical analysis of the experimentally obtained laws from the point of view of representation of breakage of chains of focused replacing collisions at precipitates has been carried out. Average values of lengths of chains in the very pure specimens and in the specimens with precipitates of various levels and types have been measured indirectly. Efficiency of trapping of self interstitial atoms by precipitates in tungsten has been estimated using the obtained results.