## Co-efficient of thermal expansion and NIST

## Co-efficient of thermal expansion and NIST

(OP)

Hi,

I'm working on some tolerances after cool down, and have up until now been using CTE's; typically 17,3um/mK for 304SS, 16um/mK for 316SS, and 16,7um/mK fro BeCu

I've been refining my design, and have been double checking with the NIST cryo materials page, where I have worked out expected shrinkage, based on their linear expansion equations.

Firstly, on NIST there is the same equation given for 304 & 316, which doesn't fit the with the CTE's.

Secondly, when I evaluate the expressions then I get a higher shrinkage for BeCu than for 304 (&316) at the temp (100K). If I use the CTE for 304 vs BeCU, then I'd get a lower shrinkage for BeCu than for 304.

Can anyone shed any light on this? It's rather important due to the tight tolerances I'm working with.

Thanks in advance,

Chris

I'm working on some tolerances after cool down, and have up until now been using CTE's; typically 17,3um/mK for 304SS, 16um/mK for 316SS, and 16,7um/mK fro BeCu

I've been refining my design, and have been double checking with the NIST cryo materials page, where I have worked out expected shrinkage, based on their linear expansion equations.

Firstly, on NIST there is the same equation given for 304 & 316, which doesn't fit the with the CTE's.

Secondly, when I evaluate the expressions then I get a higher shrinkage for BeCu than for 304 (&316) at the temp (100K). If I use the CTE for 304 vs BeCU, then I'd get a lower shrinkage for BeCu than for 304.

Can anyone shed any light on this? It's rather important due to the tight tolerances I'm working with.

Thanks in advance,

Chris

## RE: Co-efficient of thermal expansion and NIST

Secondly you have to cycle the material through the full range a few times before you can expect to get good repeatability. Residual stresses (and their non-uniformity) are a big deal.

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P.E. Metallurgy, Plymouth Tube

## RE: Co-efficient of thermal expansion and NIST

## RE: Co-efficient of thermal expansion and NIST

We would heat samples to about 600F (depending on the alloy), hold that temp and cool very slowly.

Then cycle the samples across the temperature range of interest a few times before we started measuring.

Even doing this we would have samples of 304L that would be different by 20% or more.....

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P.E. Metallurgy, Plymouth Tube

## RE: Co-efficient of thermal expansion and NIST

I've always used the Cryogenic Materials Data Handbook:

http://www.dtic.mil/dtic/tr/fulltext/u2/438718.pdf

See page D.11.p for 304

## RE: Co-efficient of thermal expansion and NIST

I guess it is a computerised version of all the data mentioned in your link (which I have also used by the way!) , plus more.

## RE: Co-efficient of thermal expansion and NIST

I haven't purchased his computerized database. Instead, I have spreadsheets to do the same thing.

## RE: Co-efficient of thermal expansion and NIST

I know that there are not many options, butt hat would greatly improve your results.

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P.E. Metallurgy, Plymouth Tube

## RE: Co-efficient of thermal expansion and NIST

## RE: Co-efficient of thermal expansion and NIST

## RE: Co-efficient of thermal expansion and NIST

Invar (Fe 36%Ni) is the only metallurgical discovery to ever be awarded a Nobel Prize.

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P.E. Metallurgy, Plymouth Tube