Effects of Severe Plastic Deformation

[darkelf]

Hello,

I'm a bit confused here about this topic. I can't seem to find a proper book on it so reading loads of papers of try and get a grip on it. I had come to the understanding that the high tensile and yeild strength developed here was due to the subgrain/micrograin size and the partial dislocations that they emitted.

But I read this paper that says that the high strength doesn't always come with the decrease in grain size and that the increase in strength is due to dispersion hardening. And another that explains that the good ductility experienced is due to annealing during the process and that this doesn't affect the strength.

Could someone set me straight please. Does this process just apply to nanocrystalline structures or to SPD in general?

Thanks

 

[Mapes]

Can you give the references?

 

[darkelf]

Y. P Kolobov, E. V. Naidenkin and E. F Dudarev. Russian Physics Journal.

Would anyone have the name of a good paper that just essentially says, SPD is occurs at dislocation saturation so grain size reduces and the reduced grain size is responsible for the strength increase? Or do I have this wrong?

 

[Mapes]

Try Valiev and Aleksandrov's (Alexandrov's) papers. There's also a book called Severe Plastic Deformation that is partially available on Google Books. Your summary looks right.

 

[darkelf]

Thanks, gotten a few Valiev papers but he's more into nanocrystals and assumes one knows all about SPD. So does the SPD, its a bunch of papers on nanocrystal formation from SPD not the mechanism of SPD which is what I'm looking for.
the grain size is reduced due to the subgrains forming new grains and from Hall Petch the smaller the grain size the higher the yield strength but that's not meant to hold in nanocrystals.

 

[Mapes]

From what I've seen, Hall-Petch holds until the grain size is approximately 10 nm. Is the typical grain size for SPD-treated samples in the range of 20-200 nm? So it looks like the strength increase can be explained by a Hall-Petch mechanism; i.e., dislocation buildup in individual grains due to an inability to cross-slip into the next grain.

 

[darkelf]

yeah but when grain sizes are lower and hall-petch doesn't hold, what is the strengthening mechanism? Its assumed that the nanoparticles are responsible for the strength but why and how?

 

[Mapes]

Yip discusses some alternatives in "Mapping plasticity," Nature Materials 3(1) (2004).

 

[darkelf]

Thanks, is that some alternatives to SPD?

 

[Mapes]

SPD is just a process--cold working taken to an extreme--that increases a material's yield strength. The effect appears to be explained by the Hall-Petch theory of strengthening. That may be why researchers don't go into great detail; they just mention that the grain size is reduced and assume that the reader knows about the Hall-Petch effect.

Now if you're interested in the reverse Hall-Petch effect, which has been observed for grain sizes less than 10 nm, Yip's paper is a brief introduction to the subject.

 

[darkelf]

Thanks. Will go through the paper. But you did point out that Hall-Petch doesn't not hold sway at below grain sizes of 10nm and the formation of grains during SPD has the same effect as recrystallization? I'm sorry to be a bother just asking.

 

[Mapes]

But you did point out that Hall-Petch doesn't not hold sway at below grain sizes of 10nm

I got this from Yip's paper and from a number of reviews.

and the formation of grains during SPD has the same effect as recrystallization?

? When did I say this?

 

[darkelf]

thanks, i'll get the paper then.
the second part i got explained to me by someone else, is this right?

 

[yilmazerh]

Hi friends
i am studying in special titanium alloy, TNTZ by SPD treated. i need some information about effects of SPD on properties of material except mechanical properties. i read some articles valiev, horita and langdon but these papers are about processing of producing nanostructural materials, UFG etc. may you advice some paper about effects of SPD on properties of material.
Besides, superelastisite is important in my research. may you advice some paper about Superelastisite applications of SPD

thank you
yilmazerh.

 

[darkelf]

Try Radik Mulyukov's work on the physical properties of nancrystals. That would be a good start.