X-Ray Diffraction Study of HCP Metals II. Line Broadening in Polycrystalline Zn and Mg Powder

Microstructures of polycrystalline hexagonal close packed (hep) Zn and Mg have been studied by x-ray diffraction line broadening analysis using the integral breadth method, and the Fourier coefficient method. For these two methods, several diffraction peaks were considered to obtain two suitable peak combinations. For the room temperature powder samples, the root mean square (rms) strain was observed to be extremely small. The particle size was anisotropic in both samples with the Zn powder showing more particle size variation than Mg. The average particle size for Zn was about 750 Ä, which was over twice the average particle size of 295 Ä observed in Mg. The two fault probabilities for Zn turned out to be negligible or zero. Mg, on the other hand, was found to have small, but definite fault probabilities. The deformation fault probability a was 4 . 5 X 1 0 4 and the growth fault probability ß was 6.5 X 1 0 4 . These results can be compared with the previous work of hep Cd at room temperature, which was found to have no growth fault probability ß and a deformation fault probability a amounting to 3 X 1 0 3 . This value is higher than that observed in Mg, because for Cd the two fault probabilities were obtained by neglecting the particle size of about 650 Ä which actually did exist in the sample.