An investigation on the transformation of the icosahedral phase in the Al-Fe-Cu system during mechanical milling and subsequent annealing

摘要

Icosahedral quasicrystalline material in the Al-Fe-Cu system was mechanically milled in an attritor ball mill (Szegvari attritor) for 1, 3, 6 and 10 h in dry air, at a speed of 400 rev min(-1) and with a ball-to-powder ratio of 20 to 1. Structural transformations and the consequent phase evolutions during mechanical milling and subsequent heat treatments were studied by X-ray diffraction, differential thermal analysis (DTA) and transmission electron microscopy techniques. After milling for 1 h, the evolution of disordered B2 phase (a = 0.29 nm) was observed to coexist with the parent icosahedral phase, whereas a microstructure consisting of nanosized B2 particles distributed in an amorphous matrix was observed after further milling (3-10 h). However, no sharp peak corresponding to the phase transformation was identified in DTA, but the microstructure of the powder milled for 10 h after the DTA experiment was found to transform to a mixture of icosahedral and B2 phases, where B2 appears to be the major phase in contrast with that in as-cast material. Isothermal heat treatment of powder mechanically milled at 850degreesC for 10 and 20 h led to complete transformation to a single B2 phase with a high degree of long-range ordering. The implication of these transformations will be discussed with reference to their relative stabilities among the competing phases during milling and subsequent heat treatment. [References: 31]