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Projects / Programmes source: ARIS

Colour, absorption and protective nanolayer coatings for aluminium alloy

Research activity

Code Science Field Subfield
2.04.01  Engineering sciences and technologies  Materials science and technology  Inorganic nonmetallic materials 

Code Science Field
T155  Technological sciences  Coatings and surface treatment 

Code Science Field
2.05  Engineering and Technology  Materials engineering 
Keywords
aluminium alloys, PVD hard coating, nanocopmosite coatings, nanolayer coatings, magnetron sputtering, anodic oxidation, optical properties, color of coatings, metal island films, surface plasmons
Evaluation (rules)
source: COBISS
Researchers (18)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  20140  PhD Peter Cvahte  Materials science and technology  Researcher  2011 - 2014  165 
2.  03937  PhD Miran Čeh  Materials science and technology  Researcher  2011 - 2014  655 
3.  18271  PhD Miha Čekada  Materials science and technology  Researcher  2011 - 2014  445 
4.  13252  Vukašin Dragojevič  Materials science and technology  Researcher  2011 - 2014  89 
5.  32109  PhD Metka Hajzeri  Chemistry  Researcher  2012 - 2014  56 
6.  27704  PhD Nina Hauptman  Chemistry  Researcher  2011  106 
7.  13250  Marina Jelen  Materials science and technology  Researcher  2011 - 2014  62 
8.  12616  PhD Darinka Kek Merl  Materials science and technology  Researcher  2011 - 2014  129 
9.  04968  PhD Varužan Kevorkijan  Materials science and technology  Researcher  2011 - 2014  352 
10.  04423  PhD Marta Klanjšek Gunde  Electronic components and technologies  Researcher  2011 - 2014  562 
11.  15703  PhD Janez Kovač  Electronic components and technologies  Researcher  2011 - 2014  682 
12.  15912  Robert Kučič  Materials science and technology  Researcher  2011 - 2014 
13.  15603  Andrej Mohar    Technical associate  2011 - 2014 
14.  26463  PhD Matjaž Panjan  Electronic components and technologies  Researcher  2011 - 2014  230 
15.  09090  PhD Peter Panjan  Materials science and technology  Head  2011 - 2014  792 
16.  15597  PhD Zoran Samardžija  Materials science and technology  Researcher  2011 - 2014  583 
17.  15604  Tomaž Sirnik    Technical associate  2011 - 2014 
18.  28491  PhD Kristina Žagar Soderžnik  Materials science and technology  Researcher  2011 - 2014  211 
Organisations (3)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0104  National Institute of Chemistry  Ljubljana  5051592000  21,227 
2.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,836 
3.  0719  IMPOL Inustry of Metal Semimanufactures d.o.o.  Slovenska Bistrica  5040736  136 
Abstract
The goals of the proposed project are: a) Protection of aluminium moulds for plastic processing with environmentally friendly methods Aluminium moulds are increasingly used in plastic industry, because Al-alloys have good machinability, high thermal conductivity and low density. Using appropriate PVD hard coatings it is possible to improve wear and corrosion resistance of such moulds significantly. A still more important function of such  coatings is the non-sticking property of the surface. Thus we can avoid  the use of  environmentally harmful releasing agents. b) Deposition of decorative hard coatings on Al-alloy forging parts Practically all products made of Al-alloys by various manufacturing techniques (die casting, forging, rolling or extrusion) are treated with surface engineering procedures (anode oxidation, chromate conversion coatings, lacquering). The goal of such surface treatment is to improve the aesthetic appearance as well as to improve wear and corrosion resistance. Using surface engineering techniques the added value of aluminium products also increase significantly. In the scope of this project we will try to develop advanced, environmentally friendly surface engineering procedures for protection of Al-alloys products, in order to replace the existing environmentally harmful ones. Such are some of advanced PVD deposition techniques which allow to produce novel nanostructured coatings at low temperature. Thus we can improve the tribological properties of aluminium moulds and products. Coloring of these products can be obtained by variation of structure and composition of selected PVD coatings. In contrast to conventional PVD hard coatings advanced nanostructured coatings offer many more possibilities for colorization of Al products. Among them the interference effect on a surface grating structure (performed e.g. by laser) or on an array of holes (formed by the semiconductor microfabrication techniques) is commonly used. In some types of nanocomposite PVD coatings (e.g. transparent hard coatings with nanosized metal particles are embedded) the phenomenon of colorization by surface plasmon resonance can also be exploited. In the framework of this project we will prepare nanocomposite coatings composed from transparent layer and metal nanoparticles. The effect of surface plasmons will be tested also on thin film structures composed of three layers: bottom mirror metal layer (e.g. Al), dielectric interlayer (e.g. Al2O3 or SiO2, approximately 50 nm thick) and top metal island film. We expect that such thin film structure will give a colored appearance due to the surface plasmon resonance as well as interference. Besides PVD methods we will also develop and optimize an anodization process of Al and Al-based alloys with the final goal to produce colored surfaces by the use of different salts/pigments. Another approach to produce different colors will be by sputtering carbon on anodized surfaces of Al and Al-based alloys. The Stampal company (beneficiary of this project), which is a part of the holding Impol Group, produces forging parts. The customers of the high price bracket are nowadays increasingly opting for suppliers which can in addition to raw forging products also offer final finishing and surface protection. While anodic oxidation which is commonly used for this purpose is not appropriate for protection of the forging parts made of Al-alloys with a high content of copper (alloys series AA 2xxx), they are looking for other types of color, absorption and protective nanostructured coatings. One possibility is the use of PVD coatings, which should offer a much higher level of protection and durability, and variation of color hues. In the framework of this project we will prepare, characterize and test various conventional and advanced methods for colorizing of Al-alloys substrates at low temperature.
Significance for science
Several physical mechanisms can be exploited to generate a color. In general, the color of solid materials results from the interaction of light with the free and bound electrons. If the color is determined solely by the electronic band structure of the material, then we refer to such color as an intrinsic color. In most decorative applications the intrinsic color of hard coatings is exploited. The color is determined by the stoichiometry of the material, therefore it can be varied only in a limited range. If a coating is thin enough and is fully or partially transparent in the visible part of the light spectrum then the light reflected at the interfaces will interact with each other resulting in the interference-based colors. In such case, the color of the coating is determined not only by the electronic band structure (or optical constants of the materials) but also by the geometry, i.e. by the thickness of the thin film. Another physical mechanism, which is also exploited for generating the color in the thin films, is surface plasmon resonance. Localized surface plasmons are collective oscillations of free electrons confined to metallic nanoparticles embedded in a dielectric matrix. Metallic particles strongly absorb particular wavelengths of a visible spectrum giving rise to specific colors that strongly depend on the material, size and shape of the particles. All of the above described mechanisms can be used to generate color yet not all of these color designs can be used in the applications where good protective and decorative functionality is required. There is not a single solution: in different circumstances, different coatings should be selected. In the framework of this project we demonstrated a simple single-layer design where color of commonly used hard coating material AlTiN can be varied over large part of color spectrum. Color is achieved through interference and absorption effect of a thin AlTiN layer deposited over a substrate with high reflectivity. This new approach offers an additional degree of freedom in the color design of protective/decorative coatings without significant color shift with the viewing angle and without sacrificing tribological performance of the coatings. Using conventional magnetron sputtering a relatively high temperature (about 450°) is needed to obtain optimal functional properties of hard coatings. Such a high temperature cannot be used for the protection of temperature-sensitive materials such as Al-alloys. We have shown that with the pulsed magnetron sputtering the deposition temperature can be reduced bellow 180°C, while the functional properties of hard coatings remain similar to high temperature ones. We studied also anodic aluminium oxidation processes in different alluminium alloys. It is well know that hexagonal arrangement of nanopores can be made by anodization process. Such surface has become a popular template system for the synthesis of various functional nanostructures. In our case we applied such nanoporous structure in oxide layer to for generation of a color. We optimized an anodization process of four different Al-alloys (2014, 2017, 7075, 6082) with the final goal to produce colored surfaces by the use of different salts/pigments. We studied the influence of growth parameters (voltage, temperature, type and concentration of electrolyte, anodization time) on the diameter of pores, the average distance between them and oxide layer thickness.
Significance for the country
Prolonged tool lifetime reduces repair and maintenance, which has a substantial impact on costs and productivity. The project was proposed to meet these challenges by development of a variety of tool surface modifications and coatings that will be tailored for specific surface properties to extended tool lifetime and to enable the premium esthetic appearance. In tribological applications the color of the protective coating is not an essential feature, however, it adds significant value to the product. For example, in the manufacturing process, the color of a coated tool indicates when the coating has been worn out. Thus one can stop the machining before larger damages occur. From a practical perspective, the color can be also used to distinguish between the coated tools of similar shape and size. Decorative coating on components also adds to the economic value of the product (e.g. bathroom appliances). Today many new products in the automotive and other industries are made from temperature sensitive Al- or Mg-alloys. A protection of components with decorative hard PVD coatings is a big challenge for job coaters. A product with a specific color can be a recognizable brand of a manufacturer and its esthetic appearance will more likely attract the attention of a consumer. Hence, the color of protective coatings is important feature even in the cases when the coatings are not exclusively used for the decorative purpose. It is therefore very useful to have flexibility over the design of the color. In the framework of this project a new concept of color design of PVD hard coatings by exploiting the interference effect through the use of semi-transparent thin film and reflective substrate has been proposed. This approach offers an additional degree of freedom in the color design of protective/decorative coatings without sacrificing tribological performance of the coatings. This is a new approach in the protection of tools and components. The results of this project will enable the beneficiary and broader industrial branch in Slovenia to stay competitive for a long term. Some years ago we implemented blue nanolayer hard coatings (AlTiN/TiN) in industrial production and is now used in more than 20 customers in Slovenia. Company Stampal SB associated companies in the holding Impol Group is an aluminum forging company that produces forging parts. Typical characteristic of such products ia a combination of good mechanical properties, dimensional accuracy and surface finish. Besides appropriate mechanical properties the wear and corrosion resistance and esthetic appearance are very important. Conventional technique for protection of aluminum parts is the anodic oxidation with an addition of various pigments which provide the desired color. Its principle disadvantage is that it is not applicable for Al-alloys with a high percentage of copper. These alloys are due to their machinability and mechanical properties one of the most appropriate for production of forging products. In order to achieve additional advantages both the producers aluminum forging products are looking for PVD coatings. These coatings should offer a much higher level of protection and durability, variation of color hues. Impol has an interest to offer on market surface treated Al-products with higher add value. This will enable Impol to be a developmental supplier. Ecological aspect should not be forgotten. The PVD technologies are ecologically acceptable. They do not leave any hazardous waste, no wet chemicals, no aerosols or dust. The consumption of raw materials is minimal, and water is needed only for cooling and even this is minimal by using a closed loop. By scrapping the ecologically problematic chemical coating techniques and implementing PVD techniques instead the broader society benefits substantially. It is expected that the technologies and products emerging from the project will be in future exploited commercially.
Most important scientific results Annual report 2011, 2012, 2013, final report, complete report on dLib.si
Most important socioeconomically and culturally relevant results Annual report 2011, 2012, 2013, final report, complete report on dLib.si
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