The structure of amorphous and nanocrystalline W---Fe alloys prepared by high-energy ball milling

Tungsten powder (99.9% purity, 12 μm particle size) was milled in a hardened steel vial with six 440C stainless steel balls for 1–50 h. Because of the hardness of W, contamination and later alloying with Fe from abrasion of the stainless steel balls occurred. X-ray chemical analysis and weight-gain measurements of the milled powder indicated Fe contents varying from 3 at.% after 1 h to approximately 40 at.% after 50h milling. The powder pattern peaks of the nanocrystalline W were subjected to a Fourier analysis to determine the effective particle size and the microstrains within these particles. After 20 h milling, a particle size of 35 Å and microstrains of 0.5% were observed. The diffraction patterns from the W powder milled for 20 and 50 h were also analyzed in terms of the structure factor (interference function) and the atomic distribution function. The 20 h sample was predominantly nanocrystalline with a broad diffuse peak under the (110) and (211) reflections, while the 50 h sample was predominantly amorphous. After subtracting the remnant crystalline peaks, the position of the first peak in the reduced atomic distribution function, G_I(r), was found to be 2.7 Å.