I took a Mg-Ca alloy for cold rolling 20 percent reduction. XRD for as cast condition shows there are no peaks of Mg2Ca at 2theta=52. But after cold rolling a peak appears at 2theta=52. What would be the reason for this phenomena. Is it a dynamic precipitation or any other thing.
Please friends help me, I would be grateful to you all.
Thank you
Dear Ramkumar,
to my opinion it is a clear example of changing preferred orientation distribution of the crystallites of your sample due to strong mechanical load extending the limits of Hookes law, such as in your case by cold rolling.
There is no reason that for a casted sample the orientation of the crystallites behaves like in a powder sample, having homogenous orientational distribution over the full 4pi angular space. You will in general have preferred orientation of your crystallites. In the worst case of preferred orientation one or more XRD peaks are completely missing. Cold rolling changes this orientational distribution, so a missing peak will show up.
Dear Ramkumar,
to my opinion it is a clear example of changing preferred orientation distribution of the crystallites of your sample due to strong mechanical load extending the limits of Hookes law, such as in your case by cold rolling.
There is no reason that for a casted sample the orientation of the crystallites behaves like in a powder sample, having homogenous orientational distribution over the full 4pi angular space. You will in general have preferred orientation of your crystallites. In the worst case of preferred orientation one or more XRD peaks are completely missing. Cold rolling changes this orientational distribution, so a missing peak will show up.
Do you mean Ca as in calcium metal? Are you cold rolling in air or inert atmosphere? Take a look at: http://www.sciencedirect.com/science/article/pii/S1002007114001130
In case we are talking about hexagonal Mg2Ca with lattice parameter a=6.271 and c=10.17 measured with Cu radiation...there is a peak at about 52°: 213 at 52.042° having a relative intensity of 32%. This would underline G. Martens assumption of texture inluence, however, you should ask yourself why didn't you see it after casting?
A formation of new phase during cold rolling is quite unlikely. You need temperature for a recrystallization or phase transformation which certainly exists very locally, but then the entire material would be "unstable" if you only need a bit energy to transform it....except...you are cold-rolling in air (see the remark of Alan F Rawle).
Hi friends,
There are two questions in my mind.
I thankfull for your comments
1) I read an journal on dynamic precipitation of Zn during cold rolling.There zn atoms ejected out during cold rolling. Then why cann't I tell that the Ca atoms would eject from Mg during cold rolling, since the Ca atoms have higher atomic radius and forms substituional solid solution with Mg.
I just add an journal about Dynamic precipitation of Al–Zn alloy during rolling and accumulative roll bonding.
http://www.tandfonline.com/doi/full/10.1080/09500839.2015.1119322?src=recsys
2) How can I relate prefered orientation with respect to corrosion behavior.
once again thankyou to all.
http://www.tandfonline.com/doi/full/10.1080/09500839.2015.1119322?src=recsys
The review in the attached link may provide a little insight to the relation of preferred orientation/texture and corrosion behavior.
But I don't know whether 'Carbon Steel ' corrosion aspects are applicable to your sample system.
http://pubs.rsc.org/-/content/articlepdf/2017/ra/c6ra25094g
As far as I remember, one of the driving force for texture investigation in steel industry was the relation to corrosion. Unfortunately, there was no simple correlation as one would assume as for other chemical and physical properties. so, after several years again and again people try to proof it but I cannot remember that there is a paper which could prove it without any doubt. I guess, corrosion is a too complex process which is possibly more related to rain boundaries than to the orientation itself. Also precipitations are essential so that other influences possibly compensate the orientation effect. But G. Martens already added a paper which shows the diversity with respect of material, production, microstructure, and this is only carbon steel.
Dear Ramkumar,
The previous answers from Drs. Nolze and Martens strongly support preferred orintation of the matrix. I support thier suggestion and to cnfirm if this it you are encouraged to compare the intensities of the cast and cold worked conditions to see what peaks disappear and what peaks grow after cold rolling. In order for aging to occur you need enough temperature which is unlikely. However, in order to check whether the material undergone aging try transmission electron microscopy (TEM) to see if the percipitates appear.
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