This looks a little like a nematic liquid crystal (LC) where there is one-directional order in the system (specified by a parameter called the director and given the symbol n tilde). The XRD of these liquid crystals is interesting (although I only have book not practical knowledge of this facet) and provides indication of molecules 'swarming' around in local groups. Observed under cross polarizers should show anisotropic behavior. Not sure I can add more but this may simply be an off-the-wall (or Rawle!) comment that you can ignore. There's plenty of literature on XRD of LC's.

Dear Alan, unfortunately, this is a metallic microstructure. Quite common material like copper or aluminium. In other words, it is really nothing special, however, the habit of the crystals combined with the pole figures surprise me. Nature is again and again astonishing :-). From my personal view it does not match in (my simple) correlation concept.

Hi Gert I realized that this wasn't a LC material. However, this reminded me of the pictures of nematic phases I've seen under polarized light (see Hartshorne's Microscopy of Liquid Crystals). I spent 7 years in this field of research without ever undertaking any XRD work. The alignment of the crystals is like sardines in a can and obviously attributable to the aspect ratio of the individual 'grains' making up the structure. Now if there was some magnetism in the material one could perhaps speculate that the constituents could align parallel to a magnetic field in the same way that LC's orient along rubbed polymer layers (and the basis of the twisted nematic LCD).

Thanks, Alan. I will keep it in mind. The question for me is: what is the driving force which is able to generate elongated grains without any effect of the crystal orientation? A directed material transport without growth competition? Electric field? (it is not magnetic...)

In general, elongated grains do not necessarily imply development of crystallographic texture (and conversely non-elongated grains may be textured).

It looks like this specimen might have been deformed either by wire drawing or some similar uniaxial compression method. In that case, the expected deformation texture would be (110)||deformation direction, which is visible in the pole figure (assuming Y is deformation direction).

Yes, the fibre is not well developed, that may be due to insufficient grains counted, or (in my opinion) more likely, that the texture has not developed at this level of strain.

My understanding is that the grains which did develop the deformation texture (here perhaps the green grains, ) are simply those which could easily rotate into the preferred orientation , whereas the remaining grains could not (too much rotation required and not enough time due to high deformation rate etc.). Nevertheless, the applied load forces the grains to elongate even if they can't rotate, hence the high aspect ratio but no texture. I would love to hear if there is a more refined explanation for this phenomenon.

For the broader question, If different materials (of the same crystal structure too) are deformed under identical conditions, some would form stronger textures and some weaker; the difference is attributed to the stacking fault energy and chemical composition. A nice summary of these aspects is in:

Article Texture of Metals

fcc does not form (111) preferred orientation?

Um that depends on the state of stress; in tension it would form (111) and (001) split texture (the degree of split again changes with SFE), while in compression it would form (110).

Well, it is neither compression nor tension...."Simply" grown...and the goal of the investigation is to know how. But actually no tension or compression.

Alright, no deformation, so definitely no deformation texture. I got that impression because you mentioned fibre textures, which usually develop during axisymmetric deformation (if they form in other cases too, I would be glad to learn).

If these are grown during solidification, then the a preferred heat transfer direction might cause the long grains.

right...but it is freely grown...look like wires but they are not..

That is quite interesting, if this forms naturally. Are scans on the perpendicular planes available? Those might indicate if heat transfer plays some role.

Yes, naturally grown, but I do not think that there is any heat transfer. How, and from where? They are either growing in "water" or some gas atmosphere, or vacuum. There might be an electric potential...but in all that cases I do not see any way how wire-like crystals can grow and if, why do they form rod-like crystals without any according fiber texture (despite the existing anisotropy in growth). Very weird...

i do agree withGert Nolze specially about the form rod-like crystal without fiber texture. I have never seen something like that before.

Can we have any information on the initial manufacturing process of the material and type of material (without giving away too much information, as you seem to have a confidentiality issue ;-) )?

My first guess for an undeformed material would also have been a thermal gradient during grain growth (although depending on the material I would not necessarily be expecting a relatively random crystallographic texture).

Did you do any combined EBSD/EDS measurement to see if there is a difference in chemical composition (I am implicitly assuming that you are sure it is a single phase material)?

Why you are assuming single phase materials

This is a really curious microstructure.

My only input to all the discussion so far is given the lack of preferred orientation, this suggests that (a) the surface energies and/or mobilities are relatively isotropic and (b) the starting nuclei are all randomly orientated. The rod-shape of the grains is, in my opinion, driven by some gradient in the processing.

Dear colleages, there is no considerable change in chemistry (checked by microprobe), and...the surface energies are anisotropic. Since there seems to be some tendency for a texture (but it might be not true...) I would assume the opposite: no random orientation distribution. Unfortunately, the parent matrial is not electron-stable so that I cannot test this. Therefore, we do not really know this. I have to check bigger maps. I was only irritated by the very well alignedlong grains and no pronounced fibre texture.

single phase: the chemical composition as well as the structure seem to be identical. Thus I concluded that it is a single phase. However, I have to admit that it is investgated many times but nobody checked the microstructure properly.

I still have doubt about the crystal growth with respect to the fiber texture.

Which doubts? Maybe, I did not explain everything properly.

Single phase (let us assume it is Cu) having the same chemical composition. I do not know anz thing about the growth, but I can exclude something like a tension or compression. There is no thermal gradient which could explain the elongated shape.

My mai question is: If a microstructure shows such elongated grains perfectly aligned parallel by theyr shape...wouldn't this indicate a fiber texture? And if not, as in this case...how it can be interpreted?

I agree with Ke Huang: the microstructure is typical of rolled and annealed Al-Mn alloys used in car radiators for example. The long elongated grains improve corrosion resistance. The manufacturer must have been very clever to avoid developing a strong texture.

Indeed, deformation would be the simplest explanation, but it seems from the discussion that neither deformation nor heat treatment has been imparted.

The main discussion is about elongated grains and texture. I am little confused about the fiber texture relation. Would somebody elaborate

In some grains (like "green ones" in the centre of the image) there can be additional grain boundary visible, right? Could be possible, that this is twin boundary? Like, usually elongated Cu crystals (natural) are twinned according to spinel-type (111) twinning (attached image). This can also propagate grain growth in certain direction...

It could be twin boundary. It make more sense according to spinel (111)

I think, application of the structural hierarchy model may give new directions in thinking on this problem. Anyway, what about martensite?

It is an fcc material without transformation. Even if it would be a martensitic like transformation you would see a perfect relationship (in case you have packets in mind). However, hierarchic model is certainly a good idea. The question is only, from what?

May I propose the paper on this topics: Structural hierarchy: Article STRUCTURAL HIERARCHY: Teaching sciences more effectively

I agree with Gert

Dear Oleg, yes, these are macroscopic samples. Wire-like strings. The microstructure displays a part of naturally grown silver. The question is, how is this possible and why do we have these elongated grains and no texture?

Oleg, there is certainly some texture. I was only irritated that it is "some" texture" and not a clear fiber texture the habit of the grains suggests.

BTW: The shown IPF is the growth directions (I only showed a full map and not the edges of the wire, but I have some).

Well, K. Huang and J. Driver already pointed out that there are certain cases where elongated grains may appear (after some treatment), but not without any treatment. I wouldn't ask here if I would see a simple solution for this problem, but I admit that there must be an explanation. I only do not have any idea...what was the reason to ask around. Maybe, somebody already had a similar experience, and this phenomenon is easy to explain.

The main assumption is: it is a growing texture, and I guess silver is anisotropic. And even if not, how do you explain the formation of long grains? They grow in hot water...:-)...without any thermal gradient.

I need to understand if some texture is dominant or there is some fiber texture in some grains.

Dear Gert, I have just seen your data. Your data shows that there is a texture maximum intensity of about 5. Thus, there is considerable texture in your sample. According to the aspect ratio, the texture intensity should more larger than 5. I think the initial texture and microstructure is responsible for the final texture of your material. The fiber texture will be achieved if you continue the process.

My believe is that one should not trust these numbers that much since in case of a low number of grains this number is more related to the grain size than to a really existing texture. Don't misunderstand me, I do not assume that there is no texture (although the number of grains presented are too small so that the maximum intensity has no real meaning), I am only surprised that with such a aspect ratio and a parallel arrangement no fibre texture results. There are special reasons as mentioned by J. Driver and K. Huang but this microstructure has never seen and external loading. It is naturally grown...but nobody knows how. This is one of the main questions I am interested in here...

Dear Gert, although such growth is expected to result in fibre texture, I think one should also consider the nucleation of differently oriented grains (different from fibre orientations) due to energy reasons. The differently oriented grains seem to be more discontinuous along the growth direction. The shape of the differently oriented grains seems to be elongated, this is possible due to the higher kintetics of growth of favourably oriented grains along "Y" direction impinging the growth of differently oriented grains.

I think differently oriented grains will not have great influence when considering the growth in fiber texture.

Dear Bharat, I guess what you are describing is a growth competition which you will observe in castings. Finally these crystals win which are directed in a way that the fastest growing speed direction is nearly parallel to the later visible grain axis....which ends in a fiber texture. In other words, I of course know about the anisotropic speed. The interesting fact is that the results shown would only work if there would be NO anisotropy....but as far as I know, silver has an (strong) ansiotropy...This is the dilemma I do not understand...or do not have a really acceptable explanation.

I totally agree with Gert

This is not answering your central question, but why do you insist that there is no thermal gradients during growth. Shouldn't growth involve some form of latent heat evolution which needs to be conducted away from the growing interface.

Even though, it should not have much influence

Dear Rajesh, in fact, I cannot exclude anything since I do not know the formation conditions (this is the actual question :-)). However, if the silver was formed hydrothermally (as expected) then we can practically exclude a considerable thermal gradient. However, even if there would be a thermal gradient, it would explain the elongated grains, but not the missing fiber texture (at least from my point of view). Another theory assumes that there is a electropotential formation which might be possible. But from my point of view I do not see any reason, how this should form elongated fibers.

If this would be all correct...the only consequence is that the major assumption for these microstructures is that they are not formed hydrothermally at all....which changes everything. If not hydrothermally...how then? Therefore my central question: If a microstructure shows elongated grains but no considerable texture...how this might be possible? Mechanical loading as given as example by J. Driver we can definitely exclude. Heat is a perfect explanation since this has been demonstrated already hundreds of years ago, however, from this would follow that all silver examples on rocks exhibited in mineral collections are fakes....which would be a very strong claim...:-). A comparably natural explanation seems to be very unlikely...but maybe I oversaw something...

Very good explanation

thank you