Difference between Metco 450NS and Metco 8400?

[Laurent]

Hello,
According to documentation available on web sites Metco 450NS and Metco 8400 are equivalent.
Metco 8400 is arc wire though.

Is there a difference between Metco 450NS and Metco 8400, used as a bond Ni 5Al?
If yes, could you please confirm?

Thanks for your help

Cheers
Laurent

[Gordon]

Hi Laurent

to the Surface Engineering Forum.

Equivalent in terms of similar chemistry and that they both produce good bond coat coatings.

Metco 450 is a powder consisting of nickel particles with fine aluminium particles glued to them. It is a clad composite powder and not an alloy. It is intended for use with low velocity combustion powder spray and plasma spray processes. Metco 480 and Diamalloy 4008 (HVOF variant) are similar products, but have NiAl alloy particles.

Metco 8400 and Taffa 75B are NiAl alloy wires for use with arc spray.

All the above and many other similar or so called equivalent materials will provide excellent bond coats. The best choice between them will depend on the application, top coat, economics, equipment availability and if you are required to work to a specific coating specification/certification.

[Laurent]

Hi Gordon,

Thanks very much for your prompt reply.

Our engineering would like us to change from Metco 450NS to either Metco 8400 (arc wire) or Diamalloy 4008 (HVOF).
Arc wire seems an "old" process, as HVOF is quite a huge equipment to invest for.

We would like to prove that still using Metco 450NS (low velocity spray)
as a bond won't make any diiference.
Top coat is Metco 320NS (abradable).

In the meantime Metco gave me a call to confirm what you previously explained.

Conclusion:
Bond strength is identical for both ( > 35-40 MPa )
Feed speed is higher for 8400 (3.5kg/h in place of 2.4kg for 450NS)
Therefore roughness is easier to monitor/control for 8400, so it could be easily used as a top coat.
(which is not the case for us, top coat of 320NS)
Should we really move from clad composite powder such as 450NS to an alloy (NiAl), Metco suggests that we go for 480NS (NiAl alloy).
We may be able to use existing spray equipment eventually, avoiding investment.


Cheers
Laurent

[Gordon]

Hi Laurent

For coating performance reasons only, I can't really see any benefit in changing. Even if other bond coats may show greater bond strengths, this is of little consequence, as the abradable coating will be the weak link in the chain anyway. The surface texture and how the top coat bonds to it are more important. For this reason I would not suggest Diamalloy 4008 with HVOF as this will produce a much finer texture coating, which may in fact give a weaker overall coating system strength.

I would consider changing only if I could see economic or ease of production benefits. I know people still use combustion wire sprayed Ni/20Al (Metco 405) as bond coats for combustion powder and plasma spray coatings. The reason being that they do not have to keep changing the main system between spraying bond coat and top coat. Also many believe the rougher texture of the bond gives benefits. Arc spray could be used in a similar way, possibly giving production benefits - faster spraying and leaving main spray unit to concentrate on top coat only.

Changing to Metco 480 will be relatively easy, just a change in powder. Not sure if you would realise any benefit though, but relatively easy to evaluate differences without investment in additional equipment.

Does your "engineering" give any reasons for wanting you to change from Metco 450?

[LEN WOOD]

Hi Gents,

If I may join the discussion. I certainly agree with Gordon, especially with regard to the HVOF bond coats - they would be too smooth 'spikiness' is a better interface! I think that Plasma sprayed bond coats are normally more reliable/dependable in their deposition/application than Arcsprayed equivalents. Mainly due to the nature of the beast, wire delivery, etc.

Funnily enough I can remember Plasma spraying 480 NS bond coats for a few months when 450 NS was in short supply for some reason. Rolls Royce had to grant a concession for its use. It was a few years ago but I do remember that we were glad to go back to 450 NS. If I remember correctly the 480 NS deposition was inferior and there was more smoke/bloom.

It does seem that someone in your Engineering Dept needs to give reasons - we are all in favor of improvement but this appears contrary.
Why fix it (or attempt to) if it isn't broke?

GlenB

[SimonH]

The fundamental difference between the materials is the particle / wire morphology.

Metco 450NS is a clad material, Metco 405 wire is a cored wire.

Metco 480NS and Sulzer Metco 8400 wire are both alloyed.

With the clad and cored materials there is a strong exothermic reaction between the nickel and the aluminium when spraying which improves the 'self bonding' properties of the material. This effect is either not as pronounced or absent with the alloyed materials.

How important this effect is to your coating is debateable, as has previously been mentioned, the weak point (deliberately so) in your coating is the abradeable top coat.