ZrO2+yttrium oxide TBC Coating Colour
09-11-2009, 04:18 PM,
ZrO2+yttrium oxide TBC Coating Colour
Posted by Gordon England ( on 11:07:42 31/05/06

In Reply to: Re: contamination in TBC bond coat posted by Leon

1. Ventilation air flow can play an important role in coating quality in some circumstances. You will notice this particularly when spraying into internal spaces where good ventilation is difficult to achieve. Over-spray material and dust are not removed, then get entrained back into the spray stream and get included in the coating.
2. For any given powder (as mentioned by Leon powder chemistry, size etc. will produce different effects) the colour of the coating will be effected by the coating temperature during application. Generally, a grey/white colour indicates coating is too cool and a yellow/orange colour too hot. You should not use that as a rule of thumb for coating quality, but noting colour changes can be useful during coating development and monitoring coating quality as this reflects changes in spraying parameters.
Regards Gordon

[color] a grey/white colour indicates coating is too cool and a yellow/orange colour too hot.[/color]
the coating is too cool/hot means the cooling is too strong/less or the spray temperature ? Generally what the desired colour of TBC coating although it's not defined in any document?
09-11-2009, 05:24 PM,
RE: ZrO2+yttrium oxide TBC Coating Colour
Hi joanwang

Link to start of thread in old SE message board for those that may want to read full discussion - Contamination in TBC bond coat

Assume all spray conditions/parameters are constant, except coating/substrate temperature. Many TBC coatings will show a different colour depending on this temperature. An old guide to some coatings was "antique white" with "grey/white" indicating too low coating/substrate temperature and "orange/yellow" indicating too high. To be honest, I'm not sure if this is very helpful in itself - except in the case where a colour change is noticed say during production spraying, as this will be a sensitive indicator of changing process conditions and should be investigated.

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