________________________ I N Ż YNIERIA MATERIA Ł OWA ___________________ROK XXIX 732 KRZYSZTOF LUKASZKOWICZ, JAROSŁAW MIKUŁA, KLAUDIUSZ GOŁOMBEK, LESZEK A. DOBRZAŃSKI, JANUSZ SZEWCZENKO, MIECZYSŁAW PANCIELEJKO Structure and mechanical properties of nanocomposite coatings deposited by PVD process onto tool steel substrates Struktura i własności mechaniczne nanokompozytowych powłok naniesionych w procesie PVD na podłoże ze stali narzędziowych ABSTRACT This paper presents the research results on the structure and mechanical properties of nanocomposite coatings deposited by PVD process onto the tool steel substrates. The tests were carried out on TiAlSiN, CrAlSiN and AlTiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range of 15÷30 nm, depending on the coating type. The coatings demonstrated columnar structure and dense cross-section morphology as well as good adherence to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L C2 lies within the range of 46÷54 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa) and corrosion resistance. The good properties of the PVD nanocomposite coatings make them suitable in various engineering and industrial applications. STRESZCZENIE W pracy przedstawiono wyniki badań struktury i własności mechanicznych nanokompozytowych powłok naniesionych w procesie PVD na podłoże ze stali narzędziowych. Badania wykonano na powłokach TiAlSiN, CrAlSiN i AlTiCrN. Stwierdzono, że struktura powłok PVD złożona jest z drobnych krystalitów, a ich średnia wielkość zawiera się w przedziale 15÷30 nm w za- leżności od rodzaju powłoki. Badane powłoki wykazują strukturę kolumnową oraz strukturę o zagęszczonych krystalitach, jak również dobrą przyczepność do podłoża, o której decyduje nie tylko adhezja, lecz również warstwa przejściowa pomiędzy powłoką a podłożem powstała w wyniku dyfuzji i na skutek działania jonów o dużej energii, powodujących przemieszanie się pierwiastków w strefie połączenia. Obciążenie krytyczne L C2 zawarte jest w przedziale 46÷54 N, w zależności od powłoki i materiału podłoża. Badane powłoki wykazują wysoką twardość (~40 GPa) i odporność korozyjną. Dobre własności nanokompozytowych powłok PVD powodują, że warstwy te są odpowiednie do różnych technicznych i przemysłowych zastosowań. INTRODUCTION The research issues concerning the production of coatings is one of the more important directions of surface engineering development, ensuring the obtainment of coatings of high usable properties in the scope of mechanical characteristics and wear resistance. Giving new operating characteristics to commonly known materials is frequently obtained by laying simple single-layer, multi-layer or gradient coatings using PVD methods [1, 2]. While selecting the coating material, we encounter a barrier caused by the fact that numerous properties expected from an ideal coating is impossible to be obtained simultaneously. For example, an increase of hardness and strength causes the reduction of the coating’s ductility and adherence to the substrate. The application of the nanostructural coatings is seen as the solution of this issue [3, 4]. According to the Hall-Petch equation, the strength properties of the material rise along with the reduction of the grain size. In case of the coatings deposited in the PVD processes, the structures obtained, with grain size ~10 nm cause the obtainment of the maximum mechanical properties. Coatings of such structure present very high hardness >40 GPa, ductility, stability in high temperatures, etc. [5÷7]. The known dependency between the hardness and abrasion resis- tance became the foundation for the development of harder and harder coating materials. The progress in the field of producing coatings in the physical vapour deposition process enables the obtainment of coatings of nanocrystal structure presenting high mechanical and usa- ble properties. The coatings of such structure are able to maintain a low friction coefficient (self-lubricating coatings) in numerous working environments, maintaining high hardness and increased resistance [8, 9]. The main concept in the achievement of high hardness of nano- crystal structure coatings and good mechanical properties and high strength related to it, particularly in case of nanocomposite coatings [10-12] is the restriction of the rise and the movement of dislocations. High hardness and strength of the nanocomposite coatings are due to the fact that the movement of dislocations is suppressed at small grains and in the spaces between them. When the grain size is reduced to that of nanometers, the activity of dislocations as the source of the material ductility is restricted. This type of coatings is also charac- terized with a large number grain boundaries with a crystal- line/amorphous transition across grain-matrix interfaces, restricting the rise and development of cracks. Such mechanism explains the resistance to fragile cracking of nanocomposite coatings [13÷15]. Simultaneously, the equiaxial grain shapes, high angle grain boundaries), low surface energy and the presence of the amorphous boundary phase facilitating the slide along the grain boundaries causes a high plasticity of the nanocomposite coatings [3]. The purpose of this paper is to examine the structure, mechanical properties and corrosion resistance of nanocomposite coatings deposited by PVD process on substrates made from X40CrMoV5-1 hot-work tool steel and gradient tool materials obtained by using the powder metallurgy of the chemical composition corresponding to the HS6-5-2 high-speed steel reinforced with the WC and TiC type hard carbide phases with the growing portions of these phases in the outward direction from the core to the surface. EXPERIMENTAL DETAILS The tests were made on samples of the X40CrMoV5-1 hot work tool steel with 56 HRC (2.1 GPa) hardness and the gradient tool materials ___________________________ Ph. D. Krzysztof Lukszkowicz, Ph. D. Jarosław Mikuła, Ph. D. Klaudiusz Gołombek, Prof. Leszek A. Dobrzański (rmt1@polsl.pl), Ph. D. Janusz Szewczenko – Institute of Engineering Materials and Biomaterials, Silesian University of Technology, Gliwice, Ph. D. Mieczysław Pancielejko – Institute of Mechatronics, Nanotechnology and Vacuum Technique, Koszalin University of Technology, Koszalin