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Service temperature increases material strength?

  1. Oct 20, 2012 #1
    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
     
  2. jcsd
  3. Oct 20, 2012 #2

    Astronuc

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    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
     
  4. Oct 20, 2012 #3
    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.
     
  5. Oct 21, 2012 #4

    Astronuc

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    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.
     
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