ASTM E81 Test Method for Preparing Quantitative Pole Figure

Scope:

ASTM E81 test method covers the use of the X-ray diffractometer to prepare quantitative pole figures. The test method consists of several experimental procedures. Some of the procedures permit the preparation of a complete pole figure. Others must be used in combination to produce a complete pole figure.

Procedure:

The ASTM E81 test method consists of characterizing the distribution of orientations of selected lattice planes with respect to sample-fixed coordinates. The distribution is usually obtained by measuring the intensity of X-rays diffracted by the sample. In such measurements, the detector and associated limiting slits are fixed at twice the appropriate Bragg angle, and the diffracted intensity is recorded as the orientation of the sample is changed. After the measured data has been corrected, as necessary, for background, defocusing, and absorption, and is normalized to have an average value of unity, the results may be plotted in stereographic or equal-area projection.

Figure 01: Geometry of Reflection Method

Figure 02: Geometry of Transmission Method

Specimen size:

Ordinarily, in ASTM E81, the test specimens are obtained from thicker sections by reducing them mechanically as far as possible and then etching them to the final required thickness. The sample must not be overheated or plastically deformed during the thinning process.

Data:

For an iron sample with molybdenum K-alpha radiation, the linear absorption coefficient is 303 cm⁻¹, and the optimum specimen thickness for transmission is approximately 0.03 mm (0.001 in.). It is extremely difficult to prepare specimens this thin, and in practice, iron specimens having a thickness between 0.05 to 0.1 mm (0.002 to 0.004 in.) are normally used in transmission with molybdenum K-alpha radiation.

Conclusion:

ASTM E81 test method covers the use of the X-ray diffractometer to prepare quantitative pole figures.