Why is Creep Temperature Higher than Melting Point?

[Ameya Joshi]

Why is the actual value of temperature, at which alloy is at a risk of creep, higher than the expected 0.3 (or 0.4)
of melting point?

 

[PhanthomJay]

Creep is the time dependent inelastic deformations of materials that is a function of stress and temperature as well as time. Creep is more significant at temperatures near the melting point, but it can occur at normal ambient air temperatures also. I believe that 30 percent of melting temperature value is established for metals as the point where creep becomes noticeable, but it's greater effect occurs at temperatures higher than that, if that is what you mean. Deformations due to creep are not recoverable. I haven't worked much with creep except for its effects on long cables under high tension, especially aluminum cables.
,and at temperatures below 100 degrees C. After 10 years, Inelastic deformations are sometimes significant.

 

[Astronuc]

Fundamentals of Creep in Metals and Alloys

Creep of an alloy depends on stress, temperature and composition. Larger atoms in a bulk metal will interfere with dislocation glide, so they can improve creep resistance. Some second phase particles and intermetallic compounds can improve creep resistance.

See also - http://ame-www.usc.edu/research/advanced_materials/science.pdf - for example.

 

[mpotsengshimi03]

can anyone of you guys please tell me different ways of preventing or minimizing creep in materials?

 

[yirmidokuz]

can anyone of you guys please tell me different ways of preventing or minimizing creep in materials?

Grain boundaries are very weak areas when compared to lattice structure. Thus, they are prone to creep behavior. Therefore less grain boundaries you have, high creep resistance you have. That means, if you can increase your average grain size, you will have higher creep resistance compared to small grain sized material.

 

[mpotsengshimi03]

Grain boundaries are very weak areas when compared to lattice structure. Thus, they are prone to creep behavior. Therefore less grain boundaries you have, high creep resistance you have. That means, if you can increase your average grain size, you will have higher creep resistance compared to small grain sized material.

thank you so much

 

[Astronuc]

Grain boundaries are very weak areas when compared to lattice structure. Thus, they are prone to creep behavior. Therefore less grain boundaries you have, high creep resistance you have. That means, if you can increase your average grain size, you will have higher creep resistance compared to small grain sized material.

Which is why turbine blades are preferably single crystal.

http://iweb.tms.org/SUP/selectedreadings/01-1022-205.pdf

I should have added microstructure to the list with stress, temperature and composition.

 

[Inspector Eng]

I am trying to do a creep rupture test at high temperature to a tube with dia. 5'', thick. 6.5mm. Can anyone help me with the standard specimens diamensions, especially the length of this specimen. Is the whole specimen covered with the furnace ?
thanks for any effort

 

[yirmidokuz]

I am trying to do a creep rupture test at high temperature to a tube with dia. 5'', thick. 6.5mm. Can anyone help me with the standard specimens diamensions, especially the length of this specimen. Is the whole specimen covered with the furnace ?
thanks for any effort

This file, astm standard e139, elucidates the standard testing method for determining the creep rupture of a material.
I hope you can find the details you need, in the file.