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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CREATe-Network (Processing and Characterization of Advanced Nano-Composites for Resource-efficient Applications and Technologies)

Teaser

Summary

CREATe-Network is composed of 3 academic institutions in Europe (Saarland University; Technical University of Catalonia; and INM - Leibniz Institute for New Materials), 3 non-academic institutions in Europe (AB Sandvik Coromant; Materials Engineering Center Saar; and Nanoforce Ltd.), as well as 8 academic partners outside Europe (CSIR - Council for Scientific and Industrial Research; Universidad CatÃ³lica de Uruguay; INTEMA; Universidad de ConcepciÃ³n; Univ. Sao Paulo, Georgia Institute of Technology, Universidad CatÃ³lica de Chile and Universidad TecnolÃ³gica Nacional Argentina).
The network cooperates in the field of design, processing and characterization of novel composite materials for resource-efficient applications and environmentally friendly technologies, in particular energy storage, bearings, electrical contacts, and cutting tools.
The purpose of the network is to combine the expertise of the academic and industrial network members in order to design new composite materials with superior properties and performance. The cooperation is based on the exchange of researchers from academy and industry, complemented with network workshops and conferences.

Work performed

Top 1: First, metal nitrides were studied for electrochemical energy storage technologies. However, its electrochemical stability was insufficient. Therefore, we moved on to carbon nanoparticle/metal oxide systems. Using hydrothermal synthesis, we showed a 10-fold increase in energy storage capacity when using manganese oxide/carbon hybrids. Using atomic layer deposition, we achieved battery-like energy storage capacities when using titania/vanadia metal oxides. Using nanoscale engineered carbon fiber/carbon nanoparticle electrodes, we enhanced the energy storage capacity by a factor of 5-6. This was possible by capitalizing on the high electrical conductivity of the carbon fibers and the large surface area provided by carbon nanoparticles. A key factor to enable the high performance was the use of redox-active surface groups at the fluid/solid interface.

Top 2 and 3: production of composites reinforced with carbon materials. The best distribution of carbon nano particles (CNP) within the metallic matrix was achieved for the nanodiamond (ND)-containing composites, followed by onion like carbon (OLC) and by carbon nanotube (CNT). This feature is related primarily to the hybridization of the C atoms in the nanoparticles and in the case of OLCs and CNTs (both sp2) the difference is related to their shape, since CNTs tends to enhance their interlinking, resulting in larger agglomerates. A new developed processing route which takes advantage of the optimal dispersability of sp3 carbon (nanodiamonds), allows to control the sp3/sp2 ratio by a thermal treatment, and thus to tailor the global physical properties. Very high densification was achieved by hot pressing and by spark plasma sintering, without compromising the structure of the CNTs.
Top 2: with tribological tests and modeling of contact mechanics, we were able to identify the self-lubricating mechanisms brought by the CNPs and its influence on friction and wear. The embedded nanoparticles produce a continuous feeding of solid lubricant which reduces the overall coefficient of friction. This effect has been even enhanced by combining composites with a surface structuring and a coating with CNPs.
Top 3: test facilities were developed for studying contact resistance of composites. The thermal diffusivity and electrical conductivity of the composite could be slightly increased against the pure metal, having the reduction of contact resistance a much more significant effect, opening good perspectives for this material to be used as electrical contact. Low voltage sparking experiments showed that the composites have a reduced arc duration and energy input, which translates into a larger duty-life.

Top 4: cemented carbides with different binders were produced by hot pressing consolidation and liquid phase sintering, presenting a functionally graded microstructure regarding chemical composition, particle size of WC and hardness profiles. We developed a method to analyze in-situ the thermal stress behavior during an individual thermal cycle. Despite of the functionalization of the surface, the alternating stress behavior cannot be avoided indicating that the overall composition of the cemented carbide strongly affects the stress behavior of the system. The addition of Cr and (Ta,Nb)C to the WC-Co substrate enhances the corrosion resistance of the binder, reducing fatigue induced cracks. Differences between the coatings (ZrCN and TiCN) in thermomechanical experiments could be explained with the help of Finite Elements Simulations and is based on the different mechanical behavior. Finally, prototypes of different carbide variants and coatings could be tested in plane milling of motor blocks made of cast iron, showing that Zr(CN) coatings improved the resistance to crack formation and propagation.

Final results

The novel solutions proposed in the fields of energy storage, low friction materials, electrical contacts and cutting tools have shown very promising results in performance under operating conditions, highlighting the fact that they could indeed replace current typical materials. The solutions are based in green, low-environmental impact materials (i.e. carbon-based), which further supports the initial goal of developing resource-efficient alternatives.

Following conclusions can be drawn:
â€¢ Energy storage: New carbon based materials show enhanced specific energy and power when compared to current materials. The developed synthesis route is straightforward and optimizes the utilization of resources.
â€¢ Low-friction self-lubricating materials: Increased duty life by the efficient reduction of wear and improved energy efficiency by a significant reduction in friction. These advanced composite materials with reduced friction and wear may help saving energy costs.
â€¢ Electrical contacts in automotive branch: increased reliability through efficient circuit breaking and extended duty life. Metal matrix composites reinforced with carbon materials improve the performance of electrical contacts, allowing for a reduction of weight in the contact system. This is especially important in transportation, since a reduction in weight and energy loses implies a reduction of fuel consumption. Finally, with the proposed solution, it is possible to reduce the use of expensive noble metals like Ag or rare elements like In.
â€¢ Cutting tools: An extension of the applicability range to hard-to-machine metals was achieved. Furthermore, the extension of the duty life of machining tools can reduce, on one side the energy consumed in machining pieces and, on the other side the consumption of strategic important materials like for instance tungsten.

The scientific impact of the project is evident in the large amount of publications in important journals (37). Finally, highly-qualified human resources could be developed. Through extensive knowledge exchange, participating early stage researchers were able to not only gain insights into relevant scientific topics, but also to be in permanent contact with leaders of the industry. Through the enhancement of existing scientific cooperation and the cultivation of new ones, the participants of the network were able to found new common interests and start new cooperative research lines.