Why is Creep Temperature Higher than Melting Point?

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    Creep Temperature
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Discussion Overview

The discussion revolves around the phenomenon of creep in materials, particularly why the temperature at which alloys are at risk of creep is higher than the expected fractions of their melting points. Participants explore the factors influencing creep, such as stress, temperature, and material composition, and discuss methods to mitigate creep in materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants propose that creep becomes noticeable at around 30% of the melting temperature for metals, but significant effects occur at higher temperatures.
  • It is noted that the creep behavior of an alloy is influenced by its stress, temperature, and composition, with larger atoms potentially improving creep resistance.
  • Several participants discuss the role of grain boundaries in creep resistance, suggesting that fewer grain boundaries and larger grain sizes can enhance resistance to creep.
  • One participant inquires about methods to prevent or minimize creep in materials, indicating a need for practical solutions.
  • There are multiple requests for information on conducting creep rupture tests, specifically regarding specimen dimensions and furnace coverage.
  • A participant references a standard testing method for creep rupture, indicating the existence of established protocols.

Areas of Agreement / Disagreement

Participants express various views on the factors affecting creep and methods to mitigate it, with no consensus reached on the optimal approaches or the precise relationships between temperature, stress, and material properties.

Contextual Notes

Some discussions include references to specific materials and conditions, but there are unresolved questions regarding the exact parameters for testing and the influence of microstructure on creep behavior.

Who May Find This Useful

This discussion may be of interest to materials scientists, engineers working with high-temperature applications, and researchers studying creep behavior in alloys.

Ameya Joshi
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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?
 
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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.
 
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.
 
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can anyone of you guys please tell me different ways of preventing or minimizing creep in materials?
 
mpotsengshimi03 said:
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.
 
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yirmidokuz said:
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
 
yirmidokuz said:
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.
 
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
 
Inspector Eng said:
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.
 

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