Riassunti di Aerospace Materials

NANOSTRUCTURED MATERIALS

A nanocrystalline material is a single or multi-phase polycrystalline solid with a grain size of few nanometers (<100 nm) in at least one dimension, while ultrafine grain size materials have grain size of 100-300 nm.Generated without any changes in chemical composition with respect to the bulk nanostructured material, they have:

• higher strength, hardness, ductility and toughness; stiffness; thermal expansion coefficient (CTE); magnetic properties and electrical resistivity;
• lower elastic modulus, thermal conductivity.

The presence of low creep temperature and superplasticity, which both helps in industrial applications because then all the material can be shaped easily at lower temperature and creating very thin pieces or extremely high deformations (up to 600%) without the risk of cracking or narrowing.Regarding creep see the slides at 25/02/12.Nanomaterials are classified bearing on their dimensions as 0-D, 1-D, 2-D or 3-D, depending on the number of sizes having a nan nanoscale dimension (<100 nm).

In general, 0-D, 1-D and 2-D nanomaterials are used as nanofillers to create nano composites made of a matrix that can be polymeric, metallic or ceramic. In general, nanocomposites have a % reinforcement of about 5% in volume, and this is due to the fact that with respect to conventional composites for the same area, the reinforcement superficial area is much higher and there is a higher tendency to agglomerate, which would lead to a loss of mechanical properties and non-uniform dispersion. Despite that, even if the volume % is lower (5% instead of 10-50%) mechanical properties are much better.

Some fields of application for nanostructured materials are:

• thermal barrier coatings (TBC) (because of the higher CTE (more similar to metal) are used for turbine blades; alumina, so lower mechanical stresses and the lower thermal conductivity, so the inner temperature is lower and the life-time longer (or operating temperature higher));
• against crack propagation, because thanks to an higher presence of grain boundaries, cracks are more deviated;
• antifouling and anti-corrosion coatings;
• coatings for anti-icing thanks to an nanohydrophobic behavior, so that the droplets impacting the surface at higher angle have a rotation movement and goes away detaching from the surface.
• electrode coatings, to develop nanohydrophobic behavior, in order to make droplets with imposed magnetic field without orient on surface.

NANOSTRUCTURED MATERIALS

A nanocrystalline material is a single or multiphase polycrystalline solid with a grain size of few nanometers (<100nm) in at least one dimension (while ultrafine grain size materials have grain size of 100-300 nm).

In general, without any change in chemical composition with respect to the bulk non nanostructured material, they have:

• higher strength, hardness, ductility and toughness; affiniuries; thermal expansion coefficients; magnetic properties and electrical resistivity;
• lower elastic moduli or thermal conductivity.

The presence of a low creep temperature and superplasticity, which both helps in industrial applications because then all the material can be shaped easily at lower temperature and creating very thin pieces or extremely high deformations, up to 600% without the risk of cracking or narrowing.

Regarding creep see the slides at 25/02/22.

Nanomaterials are classified having on their dimensions as 0-D, 1-D, 2-D or 3-D depending on the number of sizes having a non nanoscale dimension (<100nm). In general, 0-D, 1-D and 2-D nanomaterials are used as nanofillers to create nanocomposites, made of a matrix that can be polymeric, metallic or ceramic. In general, nanocomposites have a % of reinforcement of about 5% in volume and this is due to the fact that with respect to conventional composites for the same area, the reinforcement superficial area is much higher and so there is a higher tendency to agglomerate, which would lead to the loss of mechanical properties and non-uniform diffraction. Despite that, even if the volume % is lower (5 instead of 40-50%), mechanical properties are much better.

Some fields of application for nanostructured materials are:

• thermal barrier coatings ^(TBC) (because of the higher CTE (more similar to metal) are used for turbine blades alumina, so lower mechanical stresses and the lower thermal conductivity, so the inner temperature is lower and the life-time longer (or working temperature higher);
• against crack propagation, because thanks to an higher presence of grain boundaries, new cracks are more deviated;
• antifouling and anti-corrosion coatings;
• coatings for anti-icing thanks to an nonphysicophobic behavior, so that the droplets impacting the surface at high angle have a rotation movement and goes away detaching from the surface.
• adhesives coatings to develop nanophysiophobic behavior, in order to make droplets with nanospheres beyond interfounds on a surface.

In general, for nanocrystalline materials, the volume fraction of the material in the grain boundary is much higher than the one for microcrystalline, and it can r