Multifunctional Composite Coating
New Composite Multifunctional Coatings Produced Using SHS-Electrodes
Tech Area / Field
- CHE-THE/Physical and Theoretical Chemistry/Chemistry
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Mitina L M
MISIS (Steel and Alloys), Russia, Moscow
- TsNIIChermet (Ferrous Metallurgy), Russia, Moscow\nAll-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
- Colorado School of Mines, USA, CO, Golden\nAirbus Deutschland GmbH, Germany, Munich\nDaimler Chrysler AG, Germany, Stuttgart\nUniversity of Tokyo, Japan, Tokyo\nTomei Diamond Co., Ltd., Japan, Tokyo
Project summaryThe purpose of the Project is the development of scientific and technological principles to produce multi-functional composite thin and thick films by methods of d.c. and r.f. reactive bias magnetron sputtering and thermoreactive electrospark alloying. The problem to produce wear- and corrosion-resistant coatings with the properties, which are superior than analogues known from the literature, consists of two important aspects: the development of new promising super-hard and corrosion-resistant film compositions (aspect of physical metallurgy); the development of effective methods to produce strong adhesion of a coating to the base (technological aspect). As to the method of thermoreactive electrospark surface strengthening (TRESS), it, by its nature, produces high adhesive resistance of a coating to the base because of partial fusion penetration of the base surface and running of the processes similar to micro welding.
The TRESS method, first proposed by project authors from the MISiS, is based on the exothermal and chemical reaction in the interelectrode space between electrode components under the stimulation by pulse discharge energy. The reaction (synthesis) products are formed on both the charge electrode tip and the workpiece surface. In this case the energy evolved as the result of the chemical reaction is comparable or exceeds the energy of the chemical discharge. Therefore the total energy of the TRESS-process is significantly higher than the energy typical for the known electrospark alloying process. This makes it possible to increase the efficiency of the coating formation process 2ё3 times. Electrical discharge initiates the synthesis reaction which, depending on the mix composition, can carry both in the regime of guided burning, and locally only within spark gap between the consumable electrode (anode) and the base (cathode).
The Project’s authors carried out a series of experiments to realize the TRESS-process using mixture (charge) electrodes of the following compositions: Ni-Al and Ti-Al. The synthesis of diamond-containing coatings is found as possible by addition of diamond powder directly into the electrode composition. In spite of high local temperatures in the interelectrode gap, the transfer of diamond component from the electrode to the base surface (of steel and titanium tools) is shown to be possible with formation of coatings up to 300 µm thick which consist of ceramic matrix (for example, on the TiB, NixAly or TixAly based) impregnated with diamond grains of 8 through 250 µm in size. During the fulfillment of this part of the Project, 12 new coating compositions will be developed, the regimes of their synthesis on the part surface (dies, mill rollers, etc.) having hard alloying, wear-resistant including self-lubricating coatings of low friction coefficient. This makes it possible to use the process for surface strengthening and restoration of machine and mechanism parts, die and press tools, farm equipment, choosing the optimal composition for an every given problem. American collaborators will participate in researching the structure and properties (adhesion) of TRESS-coatings and promote this process, equipment and materials in the US market after getting the results of industrial tests. Thin film coatings (less than 5ё10 µm thick) produced by magnetron sputtering of composite targets (cathodes) are the other objective of searching fundamental and applied researches. Multi-component coatings in Ti-C-N and Ti-B-N systems as well as solid solutions containing elements (Al, Si) interest because of their high mechanical properties, physical and chemical stability. Usually these properties are attributed to the crystalline structure, which is characterized by stoichiometric composition, small grain size, compressive residual stresses, strong growth orientation and dense microstructure. However some questions on the existence of solid solutions on the basis of phases of AlB2, NaCl, FeB (Ti-B-N, Ti-Si-B-N, Ti-Si-C-N) types and the solubility limit of the third component for the middle region of a phase diagram are discussed by many authors and remain unsolved. Limited information on Ti-B-N ternary diagram shows that there are minimum boron solubility in TiN and negligible nitrogen solubility in titanium boride phase.
Besides coatings, which have a lattice of NaCl type in Ti-B-N, Ti-Si-N, Ti-Si-C-N systems, earlier the authors of the Project have found also the hexagonal state in Ti-B-N and Ti-Si-B-N films and the orthorhombic state of Ti-B-N. It was found that the transition from one type of crystalline lattice to another is defined by B and N to titanium ratio. In addition, a good correlation has been shown between structure, wear-resistance, coating microhardness and their corrosion-resistance in the corrosive environment.
The composition of magnetron films is mainly defined by the composition of sputtered targets. The SHS-method makes it possible to produce composite targets of the various compositions. Being experts in the field of combustion and explosion physics, the authors of the Project, jointly with the collaborators from the Colorado School of Mines (USA), developed a method of SHS-pressing targets, for example, on the titanium carbide and borides, titanium and molybdenum silicides, silicon and chromium carbides, aluminum oxide based. Variation of the regimes of reactive bias magnetron sputtering (temperature of the base, voltage bias, partial pressure of nitrogen) and the composition of sputtered targets makes it possible to control the composition, structure, and properties of coatings. For example, a composite SHS-target of TiB2+Ti5Si3+Si is promising for deposition of Ti-Si-B-N coatings with a record high microhardness up to 70 GPa, that is half as much again the microhardness of diamond polycrystalline films, high wear-resistance, and good adhesion to steel. The structure of these coatings is a mixture of hexagonal Ti(BN)2 phase crystallites of 2–4 nm in size and amorphous intergranular ingredients. The films in the Ti-Si-C-N system produced by sputtering of TiC+Ti5SiC2+SiC (TiSi2) targets are the other example. The film structure is shown to change with the growth of silicon content in the target, and the crystalline state passes into the nanocrystalline one and then into the amorphous one. Simultaneously the last coating has high corrosion-resistance, wear-resistance, and heat-resistance (up to 1000°C in the air). A group of the researchers from the Mine Academy of Colorado (USA) participates in the following phases of the second part of the Project: development and synthesis of new promising compositions of the targets by the SHS-method; study of the magnetron sputtering process; making studies of adhesion properties and mechanical characteristics of the coatings.
The authors of the Project have a large experience of international cooperation in the SHS-field and surface engineering. There are 36 joint publications in the SHS-field and surface engineering for the period of 1995 through 1999. During the fulfillment of the second part of the Project, more than 8 new materials of targets, promising for the following application in the processes of magnetron and ion-plasma sputtering, will be developed and produced. During optimization of the regimes of thin-film coating sputtering, a wide fundamental and applied research and development is to be carried out to find an interrelation between the composition and structure of SHS-cathodes (targets), on the one hand, and the composition, structure, properties of coatings, and sputtering regimes, on the other hand. It should be noted that the development data corresponds to the world level. New composite coatings with record high service characteristics as well as the processes of their production are the end result.
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