The texture of sheet diffractometer methods

The photographic method is now obsolete, because the diffractometer permits direct measurement of reflected intensities and yields quantitative pole figures. 

The ideal diffractometer specimen would be a small sphere cut out of the sheet, because a sphere presents the same aspect to the incident beam whatever its orientation. Normally, however, the sheet is examined directly, and then the paths of incident and diffracted beams within the sheet change with sheet orientation. It is then necessary to correct the measured intensities for these geometrical effects or to design the x-ray optics so that corrections are not required. 

There is not one, but several, diffractometer methods for measuring sheet texture. They fall into two groups, transmission and reflection, both being normally necessary for complete coverage of the pole figure. 

The two methods described below both require a specimen for which nt is of the order of 1, where /x is the linear absorption coefficient and t the thickness. This means a thickness of the order of 35 fxm for iron examined with Mo Koi radiation or 75 fim for aluminum with Cu K(x. Thicker sheet has to be thinned by grinding and etching. 

The method of Decker, Asp, and Marker [9.9] was the first application of the diffractometer to texture measurements. The sheet specimen, in a special holder, is positioned initially with the rolling direction vertical and coincident with the diffractometer axis, and with the plane of the specimen bisecting the angle between incident and diffracted beams (Figs. 9-12 and 9-13). The specimen holder allows rotation of the sheet in its own plane and about the diffractometer axis. 

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Sheet textures may also be represented by inverse pole figures. Here three separate projections are needed to show the distribution of the sheet normal, rolling direction, and transverse direction. Figure 9-24(b) is such a projection for the normal direction of the steel sheet whose (110) pole figure was given in Fig. 9-20 it was calculated from the crystal orientation distribution mentioned in Sec. 9-8. The distribution of the normal direction is also shown in (c), for the same material. This distribution was measured directly in the following way. A powder pattern is made of the sheet in a diffractometer by the usual method, with the sheet equally... 

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