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NAPILIS Sintesi della relazione

Project ID: 505622
Finanziato nell'ambito di: FP6-NMP
Paese: Italy

Final Report Summary - NAPILIS (Nanocomposites for Piston/Liner Systems)

The purpose of the NAPILIS project was to develop self-lubricating metal and ceramic matrix nanocomposites for piston / liner systems using and refining the wide set of tools of modern surface engineering and engine simulation, in order to achieve significant improvements in fuel economy of modern diesel vehicles through a considerable reduction of engine friction. To fit these objectives new multiphase and multifunctional coatings and a new processing method to obtain bi-phase materials at nano-scale had to be developed.

Self-lubricating metal and ceramic matrix nanocomposites (SLMCMNCs) fulfil the specifications. These are materials consisting of a metal or hartstoff matrix with dispersed selflubricating nanoparticles; for piston / liner system the matrix may be a refractory metal like tungsten, molybdenum and chromium or a carbide or nitride of these materials. The solid lubricant would be graphite, disulfide, h-BN, etc.

SLMCMNCs have so far never been synthesised and there exists no process technology for their synthesis. They are produced by filling, sintering and casting, galvanic and electroless deposition, plasma spraying, but these technologies cannot be used for nanocomposites, because of worker's hygiene reasons and failure of PVD or CVD methods (since these technologies usually do not produce biphase materials).

In NAPILIS project, two solutions have been explored:
1. sputter deposition process, combining the selection of an appropriate metallurgy with the use of extremely short intense heat spikes to promote the appropriate segregation;
2. a combined arc and sputter process to obtain strong nano-particle emission from a graphite source which are expected to allow the PVD deposition of these new coatings.

The primary scientific objectives of the project were to:
- develop novel multiphase and multifunctional coatings. These may combine high wear resistance with low friction. Examples will include coatings with tailored composite structures of nano-particles of different composition. A hard matrix (chromium, molybdenum, tungsten, or a metastable solide solution of these metals with nitrogen or carbon, or a carbide or nitride of these metals) gives the required multifunctionality in combination with a solid lubricant like graphite, molybdenum disulfide or h-BN).
- develop a new processing method in order to obtain bi-phase materials on a nanoscale by using extremely short (msec) intense heat spikes in order to promote the appropriate segregation.
- up-scale those coatings to 'thick' coatings of at least 10 micrometre by studying stresses and stress reducing mechanisms in films (e.g. multilayer arrangement).
- reduce lubrication of components operating in hot environments, without friction rise or increase in wear, which leads to less particulate emission of engines.
- reduce friction loss in the engine to reduce CO2 emission.
- set-up methods for synthesising such nanostructured coatings at industrial scale and designing the necessary equipment.

The project was split into five work packages (WPs), of which WP1, WP2 and WP4 consist of research, technological development and innovation related activities; WP3 is based on both research and demonstration activities; and finally WP5 is fully dedicated to management, review and assessment activities.

In particular:

WP1 : Development and characterisation of a self-lubricating cermet coating in laboratory equipment
WP1 was dedicated to the development of a self-lubricating cermet coating in a laboratory equipment and its characterisation (first level of validation).

WP2 : Development and validation of a self-lubricating cermet coating on piston and liner components
WP2 was dedicated to the transfer of the process to a retrofitted production equipment, process scale-up and component coating. Coated components will allow the full validation of the new coating (second level of validation). The objective of WP2 was the deposition of self-lubricating cermets on piston rings made of nitrided steel and on aluminium liners.

WP3 Validation of self-lubricating cermets in engines and optimisation
WP3 was dedicated to the validation of the coatings in engine test rigs, including a demonstration. Engine testing represent the third level of validation. It was accompanied by a detailed simulation study of the behaviour of the piston / liner system with these new coatings that allows optimisation of piston segment geometry and finish, oil consumption friction losses and compatibility with alternative fuels. It was scheduled to be carried out on the 'virtual engine' of AVL. In parallel, engine tests were carried out to validate three targeted improvements: oil consumption, friction reduction, and wear reduction. The tests were carried out in different engines:
- diesel 1.9TDI VW engine
- gasoline 1.8L EW7 PSA engine
- L850 Fiat engine.
The targeted objectives were:
- reduced friction losses in engine, allowing a reduction of fuel consumption of 1.5 % and a reduction of CO2 emission by 3g/km;
- improved scuffing resistance, allowing a reduction of lubrication needs, oil consumption and particle emission.

During the course of the project and with the different results of other WPs, some modifications had to be done on objectives and the deliverables.

First variation concerns the application: the main work is done on coated rings and not liners. It has been discussed in the WP2 and decided to abandon the development of the coatings applied to liners because of the problems in coating optimisation. Coated liners were not tested in engine test, even if they have been tested with the Cameron-Plint test (in WP 1 and 2) to help understanding of phenomena.

The second variation concerns the engine test. Engine tests were carried out at Mahle and a high temperature scuffing test procedure was applied. The objective was to demonstrate the improvement of the engine performance, with a reduction of friction and an improvement of scuffing resistance. This improvement can then be associated to a reduction of fuel consumption and a reduction of particles emission. This topic was realised.

Concerning the friction evaluation mono-cylinder tests were carried out at CRF. Some mono-cylinder tests were also planned at PSA but they were cancelled because of other priorities occupying the benches within the time.

WP4 Development of equipment technology
WP4 was dedicated to the development of a dedicated scaled-up production equipment. The major objectives were:
- demonstrate production capability
- source and process operation stable;
- equipment costs: state of the art CrN plus 10 %.
The objectives of upscaling are to demonstrate the production capability of the laboratory scale developments by accomplishment of a stable operating process, including especially a stable operation of the sources. Upscaling of a prototype carbon source has been done by Vacotec and was successful implemented at CRT. Blueprints of the source were delivered (D33). A successful implementation of the MCL- and EIG processes, including pulsed heating, has been accomplished in a large industrial scale machine type HTC-1500, at CRT. Blueprints of the upscaled equipment design have been delivered by Hauzer.

An economic assessment has been done of the developed product. A model was developed, enabling to include parameters for three levels of cost projections: equipment and coating costs for dedicated equipment for piston rings on site of a piston ring producer, coating costs for dedicated equipment for piston rings in a dedicated or in a retrofitted equipment at a job coater's site.

Contrary to the original deliverable description, the developed cost model makes a comparison for the coating cost per piece, which is including all costs that are determining the coating cost per piece.

The conclusion to be drawn is that the goal of cost less than CrN plus 10 % is achievable for both CrC/C as well as for CrC/a-C:H systems developed in the project.

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