Service temperature increases material strength?

[no1speshal]

Hello All. I am getting my @$$ kicked by what seems to be a simple concept, and I hope someone can offer me a little help.

With some of the nickel based super-alloys such as what are used in turbine blades, why do the alloys get stronger as they get hotter? It seems counter-intuitive to me. Red hot metals are not typically "stronger" than those at room temperature. However, these blades withstand temperatures well beyond what it takes to melt most other metals and turbine blades remain strong. Is it because of the coatings? Is it because the additional heat creates a coalescence of the material and further heat treats it?

I hope I posted this in the correct forum. I only recently signed up with PF but I have frequented the site for some time now. I thank anyone and everyone for all the help provided.

Red

 

[Astronuc]

Strengthening (or hardening) by annealing occurs with solution annealing, precipitation (hardening) annealing or spinoidal decomposition. Alloy systems typical have specific thermal hardening mechanisms.

http://materion.com/~/media/Files/P...e No 18- Thermal Strengthening Mechanisms.pdf


See also Effect of Heat Treating on Superalloy Properties

http://www.keytometals.com/Article32.htm

See also Age hardening

See more on strengthening mechanisms here - http://dmseg5.case.edu/Classes/emse201/overheads/StreMech.pdf

 

[no1speshal]

Thank you very much for your help! That is exactly what I needed to make it make sense to me.

I am taking a metallurgy class on heat treatment, metal forming, and powder processing. Unfortunately, I am not grasping the material very well and the information my professor is offering assumes I know far more than I actually know! He moves far beyond my scope of comprehension at this point. Again, thank you so much for your help.

On a similar topic, while I was trying to learn more on this, I came across the Burgers vector. Do you know of anywhere I can get more information on this? The math on that seems to turn my brain into the equivalent of marshmallows in the microwave.

Again, thank you for your help.

 

[Astronuc]

Burger's vector is related to dislocations in crystalline materials, and both are part of the fundamental knowledge of metallurgy.

Dislocations are imperfections in the otherwise ordered array of the atomic lattice. Burger's vector "quantifies the difference between the distorted lattice around the dislocation and the perfect lattice."

http://www.doitpoms.ac.uk/tlplib/dislocations/burgers.php

http://en.wikipedia.org/wiki/Burgers_vector
http://en.wikipedia.org/wiki/Crystal_structure

http://www.princeton.edu/~maelabs/mae324/glos324/burgersvector.htm
http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_5/backbone/r5_1_1.html [this site has a pop-up that my browser blocks]

It's relatively straightforward in 2 dimensions (x,y), but it can be a bit more challenging in 3D.

Different authors may use different methods to describe it, and some methods are not so straightforward.

 

[alphy]

hot metals are not typically "stronger" than those at room temperature because at higher temperatures, the atoms in the material have more energy and are able to move more freely. This results in weaker bonds between the atoms and a decrease in strength. However, in some materials, such as nickel based super-alloys, the increase in temperature can cause a phenomenon called "strain hardening" which actually increases the strength of the material. This is because at higher temperatures, the material experiences more plastic deformation, which leads to a rearrangement of the atoms and an increase in dislocations. These dislocations act as barriers to the movement of other dislocations, making the material stronger. Additionally, the high temperatures can also cause chemical reactions within the material, forming intermetallic compounds that can increase strength. Coatings can also play a role in increasing strength, as they can provide a barrier against oxidation and corrosion, which can weaken the material. Overall, the increased strength of nickel based super-alloys at high temperatures is due to a combination of strain hardening, chemical reactions, and protective coatings.