This is usually the common procedure since with the IPF and the selection of  the loading (rolling) direction you have to find a correlation. You only need to the given poles define plane perpendicular to this direction, i.e. glidening occurs in these planes, and commonly not only in one.

Hi Gert,

     thanks for your answer. I believe we met last year at Glasgow, at the EBSD conference.

Why is it the vertical planes? I would have imagined that the planes that lie 45 degrees (to the RD) are highly activated during rolling operations.

So in my case the vertical of 111 orientation leads to strong slip bands, while the vertical of 101, is an orientation where the grains deform uniformly and behave like 'hard' grains. At least that is the correlation I obtained from the tests I did.

Imaging the FCC unit cell, isn't it the case that the perpendicular plane to the 101 lies 45 degrees to the TD, so it doesn't take much plastic deformation. While the vertical to the 111 has tensor components along both the RD, TD and ND. Thus has the potency to form strong slip bands.

Is that right?

All the best,

Panos

Misunderstanding :-). With vertical I mean that the plane are vertically aligned to their poles which are displayed in the IPF. 

Hi Panos,

Hard Vs Soft orientations can be confirmed using crystal plasticity to correlate the loading vector, the CRSS on slip systems, and each crystal orientation. Due to the interplay of of various slip systems in polycrysalline material, capturing the slip system activities will answer your question per grain. A Taylor-type crystal plasticity model should not take much time to run. Good luck! 

I presume that the fatigue testing is done on samples which are cyclically stressed parallel to RD (the same as the IPF). If so you would not expect the grains stressed along - directions to be hard - they should be soft with a low Taylor factor (or high Schmid factor). Conversely the grains should be relatively hard, at least in tensile tests. However, cracking during fatigue testing does not necessarily follow the rules of simple hard or soft tensile behaviour. So "hard" grains could crack before the more ductile soft grains. Ideally you should measure the stress in the grains.

Hi Julian,

       thank you for your answer. That is correct. I am cyclically loading the sample along the RD. Yet it is a 4-point bending sample. The vertical displacement is along the thickness (ND). I have a hole in the middle to act as a stress concentrator. And I am trying to see the effect of grain orientation.

It is surprising that the grains do behave oppositely! So the hard grains form strong slip bands and the soft ones are the ones that have fatigue tolerance. Could it be because in the soft grains more slip systems can get activated?

Because I have the formation of strong slip bands prior to cracking, it does raise a few questions as there is plasticity involved (even though highly localised) prior to cracking.

Let me know if you want to have a look into the figures to have a better idea about the analysis. I am a bit puzzled that it is opposite to what I expected.

Best regards,

Panos

I suppose that the strong slip bands are visualized by SEM or optical microscopy. If so, they usually indicate concentrated slip which often favours crack nucleation. In the (soft) grains where you do not see these strong slip bands they could well have deformed plastically but by very fine homogeneous slip which cannot be detected by SEM (but can be seen by TEM). What you see depends upon the technique.

Hi Julian,

       your comments are very correct. I used SEM to see and observe the performance of the individual grains. It is very true that the soft grains deform by homogeneous slip. But the hard grains form strong slip bands. In these slip bands I have seen very fine voids forming. Suddenly these voids form a micro-crack and crack grows along these slip bands. However I noticed that the cracks can later change slip band when approaching a second grain. Crack deflection did occur before reaching the GB.

I have attached the paper I intend to publish sometime soon, so you can see the figures/results. Of course my section about IPF is wrong and needs editing.

I have to really thank you for your comments, as it has been a really fruitful discussion. Please feel free to make any comments and other suggestions.

I have not yet read the manuscript in detail but have seen what was done and have a couple of comments, or rather references you might look at. First many years ago we noted shear bands developing by fatigue in near crystals of a ferritic steel - Acta Metall 1982! Secondly and more recently, we have looked at the influence of hard and soft grains in promoting localized shear during bending - Mater Sci & Eng 2013.

And I see that you are publishing with Christophe Pinna whom I know so I send my regards.

Julian thank you very much for the articles. The 1982 article on fatigue crack development in ferritic steels is spot on. I wish I had my samples in front of me so I could do some TEM in the hard and soft grains. I am still a bit confused why a hard grain would need to form localised slip. Could someone say/conclude that less slip systems get activated in the hard grains?

I am certainly missing references in my article. It certainly needs more work.

My main problem was that I was not confident about the IPF observations and certainly I do not want to remove it. Your comments and articles are really spot on!

I will do mention your help and greetings to Christophe. He was my PhD advisor back in Sheffield (2010-2013). We have drafted now an additional paper where we model the exact microstructure from this study to evaluate the FCI parameters available from the literature.