Modification of the Structure-Phase State of Coatings by Ion Implantation Techniques
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Electronics Institute, 4 Akademichesky Ave., Tomsk, 634055, Russia
ABSTRACT Transmission electron microscopy was used to study the effect of nitrogen-ion irradiation on the microstructure of ion-plasma TiN coating deposited on a substrate of austenitic stainless steel. The principal peculiarities of the changes in the fine structure at the substrate-coating interface and in the bulk of the coatings having a thickness of several micrometers have been revealed for the conditions of ion-beam-assisted deposition and plasma-assisted deposition. Possible mechanisms for the effect of ion irradiation on the microstructure of the substrate-coating composition are discussed.
INTRODUCTION With the widespread use of the techniques for improving the service and operational properties of articles and tools by depositing type TiN coatings, the tasks concerned with increasing the adhesion of a coating to the substrate and optimizing the coating composition and structural state still remain actual. Currently a new, highly promising technique for modification of the structure and properties of coatings by irradiating the latter with low-energy (E • 100-1000 eV) and high-energy (E > 1--3 keV) ions has been developed [1-10]. The potentialities of this technique improving specific service properties of coatings, its promise and fields of application have motivated considerable interest in investigating the features of the structural phase states of coatings produced under the conditions of ion-beam-assisted deposition (IBAD) and plasma-assisted deposition (PAD). A major part of this work was carried out with TiN coatings. It has been revealed unambiguously that the adhesion of these coatings is improved, their porosity decreases [1, 2], the texture changes [1-3] and so does the composition (including a reduced contamination of the coating-substrate interface with oxygen [1, 2, 4]), and so on. There is some evidence [2, 5] on the formation, upon ion irradiation, of nanocrystalline coatings with a grain size d< 10 nm. Some studies [2, 3], however, have shown that the texture formation is related to a column-like growth of coatings and to the absence of equiaxial grains in them. The data on the effect of ion irradiation on the level of internal stresses in coatings also remain controversial [2, 6, 7]. In low-energy ion irradiation, because of the absence of cascaded collisions and temperature peaks, the physical possibilities for the ions to affect the coating structure are very limited. Nevertheless, even for the ion energy equal to some hundreds of electron-volts a substantial change in the structural state of ceramic coatings has been found [2, 8, 9], in particular, a decrease in their porosity [2], formation of equiaxial grains instead of a columnar structure, etc. It is supposed [2, 9, 10] that in this case the principal factors affecting the structure of a growing structure are an increased mobility of adatoms and atomic mixing in a thin (2-3 interatomic 119 Mat. Res. Soc. Symp. Proc. Vol. 396 0 1996 Materials Res
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