ISO-9227 states: "The test duration shall be as specified in the specification for the material or product to be tested, unless otherwise specified, this period shall be agreed between the contractors. Recommended working time is 2h, 6h, 24h, 48h, 96h, 168h, 240h, 480h, 720h, and 1008h ".

In "normal" language it means : "Do your test until the coating fails, and if that time is longer than the minimum given, you're in luck."

Good question

ISO-9227 states: "The test duration shall be as specified in the specification for the material or product to be tested, unless otherwise specified, this period shall be agreed between the contractors. Recommended working time is 2h, 6h, 24h, 48h, 96h, 168h, 240h, 480h, 720h, and 1008h ".

In "normal" language it means : "Do your test until the coating fails, and if that time is longer than the minimum given, you're in luck."

Dear Mr. Vadim Verlotski your answer is really helpful. Thank you very much.

The exposure time is based on the end use field application for example:

500-1000 hours ASTM B-117 for most things put outside is typical - cars, outside door hardware.

AAMA 2603 is about 3000 hour salt fog requirement (architectural aluminum)

250-500 hours for interior or appliance is not unusual.

Beware this is a tough test and thin PVD/CVD films are weak against it.

Quite often people apply clear coats over these finishes when used on aluminum car wheels for example to prevent the PVD from getting destroyed.

you should take into account that depending of the application aeronatics, other transportations it could neutral salt spray or acetic acid spray...

It's very hard to estimate the acceleration factor and it will be depend on the coating type. As a rule of thumb, polymeric coatings in 240h salt spray test at 35°C will age similarly to a 2-year period of marine use.

Many factors could influence the test severity :

- Temperature

- Activation energy of the degradation reactions

- Samples geometry and orientation

- Dry/wet cycling (if any)

In the case of TiN coatings, their columnar structure and propensity to form pinholes will not help...

What you can do, if you have one, is age a reference sample until it is considered "failed" and compare the time it takes for your TiN coated part to reach the same "failed" condition.

Dear Farid,

there are many standards, similar to each other, which illustrate the characteristics of a salt spray chamber and the parameters of use during the exposure of the samples:

- ASTM B-117

- ISO 9227

- JIS (Japanese Industrial Standard) Z2371

- SAE (Society of Automotive Engineers) J1563

- FIAT 50180

- etc.

I agree with what was said by Mr. Shawn Dolan; the exposure time of the proposed applications and by the results you get by viewing the samples.

Sometimes, it may be interesting to follow the progress of any corrosive attacks present (or deterioration of the coating) to have a temporal monitoring.

Best regards, PT

Farid - You have not said how and on what material, the TiN coating be applied, and also, no purpose has been given for testing. I presume it would be a mild or low alloy steel sample coated with a thin layer of TiN coating which is usually porous in nature unless double coating of Ti followed by TiN is applied.

There are many corrosion testing standards - e.g. ASTM B 117 or ISO 9227 using 5.0% NaCl solution at 35 C (to Start with) for various length of times say 100hr to 5000hr and examine the coated samples for rust spots or pits.

The best possible solution is to use a coating of nanocomposite of epoxy -- TiN nanopowder prepared by high speed dispesion. This coating would be non-pervious and provide your answer.

Dr. K

I agree 100% with the response given by Vadim Verlotski. However, I would add the following qualification on salt spray testing in general. Please bear in mind that this test was developed originally as a (cheap) quick-and-dirty screening test for chromium plated car bumpers in order to select the best local plating shop supplier, when cars still had chromium bumpers (fenders). It is a mistake to assume that there is any kind of predictable 'acceleration factor', compared to real-world exposure conditions. Where the test has value is purely and simply in terms of comparative performance testing of coatings that are of a similar type with perhaps minor variations in structure or composition, where you are trying to determine which coating might withstand the salt spray condition for longest time, and perhaps then examine the degradation condition to investigate how the specific coating might break down in such conditions. However, any kind of assumption that you can then place some kind of factor on how long the coating will withstand a practical service environment is fraught with risk, and there is no established evidence that says that the failure time or breakdown mechanism will have any reproducible relationship whatsoever to the rate of degradation in a real-world service environment.

Note that B-117 has been correlated to outdoor exposure by a number of different groups in the automotive and marine world. It is a nearly perfect simulation for marine testing of outboards for example but it is much more severe than realworld for automotive and we have special cyclic tests for that market such as SAE J2334 test which has the highest correlation to outdoor exposure for actual cars (between 85 and 90%). Also note that the acetic tests mentioned above are sometimes used but have very poor correlation because there is no acetic acid exposure anywhere outside - not much of a surprise. The Acetic based tests are good "gorilla" tests to tell you have a great product but they really are very far from real-world.