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Coatings for the Aeronautic Industry
CPT Opportunities


NIF: Q0818001J
TIPUS PROJECTE: Incorporació a centre Tecnio
TÍTOL PROJECTE: Novel Intermetallic coatings for high temperature oxidation resistance
DR Núria Cinca

Corrosion protection is still a worldwide problem; several types of material degradation are involved which affect to many industry fields. Considering the cost of maintenance, prevention, replacement of parts, loss of efficiency and interruption of services due to maintenance, the World Corrosion Organization (New York, N.Y.) says that the annual cost of corrosion worldwide is $2.2 trillion, more than 3 percent of the world's gross domestic product (GDP).
In terms of the aeronautic industry, it is still seeking for the development of new alloys for aircraft-propulsion systems with the aim to substitute superalloys and improve the engine efficiency. In such field, great effort is being done with the aim to find high temperature resistant materials. Intermetallic compounds are regarded as promising for such purpose but their manufacture presents some drawbacks that make their commercialization still difficult. Therefore, new alloying compositions are an important topic of investigation for metallurgists. Also their load-carrying capabilities must be a compromise with the oxidation performance and sometimes this is not accomplished for bulk materials. Therefore, the use of such materials as coatings is regarded as a good option to balance the different requirements. In addition, they could also provide protection for steam turbine components or on heat exchanger tubes. They combine low density with high strength and modulus, which gives rise to very attractive specific properties, which are especially important for rotating machinery and aerospace applications.  It is their high aluminium content makes them to be considered for high temperature and / or aggressive environments.
In this project, the new cost-effective and environmental friendly technology, Cold Gas Spray is proposed to be used with the aim to produce intermetallic coatings that would provide much better improvements to the current technologies. Conventional thermal spray processes have been used to produce transition metal aluminide coatings with oxidation resistances up to 950ºC but still the coatings are porous and oxidated. The main problem is then, that conventional spraying techniques involve feedstock melting, therefore leading to non-equilibrium structures or non-desired phases after rapid cooling. In terms of aluminides, thus, this produces aluminium depleted areas that will strongly affect the corrosion behaviour.
Cold Gas Spray is an emerging technology that provides dense and oxide-free coatings whenever the process parameters are optimized. It does not involve melting; therefore, the structure of the initial feedstock powder could be preserved. An additional difficulty is that such technique is mainly based on the capacity of plastic deformation of the sprayed material; since IMCs show very low ductility, the process variables will have to be accurately optimized. Normally, due to the lack of ductility of intermetallics, necessary for the powders to be sprayed with this technology, the authors tend to use blends or ball milled of the elemental powders and the resulting deposit is annealed in order to obtain the ordered alloy. Our intention would be to try to produce the coatings directly from the ordered alloys, which a challenging topic. For that purpose a deep knowledge of the system and technology is required and that is the goal pursued with this project.
Another even interesting and innovative application of intermetallics such as FeSe, MgB2, Nb3Sn or Nb3Ge is as superconducting coatings. Here, since production costs are a very serious issue with superconductors, it would be extremely interesting the attempt on using the Cold Gas Spray technique to contribute to decrease the commercial price of any product. Nowadays, the coating techniques that have been studied are physical vapor deposition (PVD), chemical vapor deposition (CVD), molecular beam epitaxy (MBE), electrochemical plating, pulsed laser deposition (PLD), hybrid physical CVD (HPCVD), reactive evaporation, coaxial energetic arc deposition, and sputtering. Among these, HPCVD and reactive evaporation methods seem to give highest quality films but the vacuum requirements impose high costs to the final product.
There are several applications were we could use intermetallic superconducting coatings like for example superconducting cavities, magnetic screening and tapes for high power cables and high field magnets.
The Thermal Spray Center is a TECNIO center which has already such technology and a lot of experience in such field.
By optimizing the manufacturing process for such purposes, the implementation on the different industry fields would provide an increase of components life, while reducing the costs.
The main objectives can be summarised as follows:
• To find the best suitable materials to reach the expected performance.
• To optimize the spraying conditions in order to produce dense coatings with good adherence.
• Test these coatings under oxidizing or aggressive conditions.
• To extrapolate the laboratory results to real components.