SLIDE 1
POWDER REQUIREMENTS
- Selection criteria: only the powders of materials that can deform plastically, can be sprayed by
cold‐spray.
- Ceramics and polymers cannot be applied by cold spray.
- Thus Metals and Alloys are the main choice.
– Face Centred Cubic (F.C.C.): structure metals, such as Al, Cu, Ag, Au, Pt, Ni, and γ‐Fe Having large number of planes and thus can be deformed and are thus best for cold spray – Body Centred Cubic (B.C.C.): structure metals, such as W, Ta, Mo, Nb, V, Cr, α‐Fe and β‐Ti. – Hexagonal Close‐Packed (H.C.P.): structure metals, such as Cd, Zn, Co, Mg and Ti.
- The H.C.P. metals have lesser deformability, while the B.C.C. metals have the lowest
deformability.
- M.P. is Another indication of sprayability. The low value of melting temperature is beneficial for
the ability to spray.
- On the other hand, materials that harden under mechanical stress, such as the stainless steel
316/304 or the alloy TiAl8V4, are difficult to spray.
- In practice, the most popular material sprayed by cold‐spray is Cu.
- Important technological metal and alloys, such as Ta, NiCr, NiCrAlY or CuAl, have been
successfully processed by this technique.
- Helium was used to spray most of these. Coating of metal‐ceramic composites, such as NiCr +
Cr3C2, have also been obtained in this way .
- Particle size: 5‐20μm.
- Particle temperatures and velocities: 500oCand particle velocities 600m/s for Cu particles
(15μm) with an optimized initial working gas (nitrogen).