Amorphization process by rod-milling Ti xAl 100 − x and the effect of annealing

Abstract

Amorphous Ti x Al 100 − x alloy powders with wide amorphization range (33 ⩽ x ⩽ 75) have been synthesized by rod-milling technique using a mechanical alloying (MA) process. The rod-milled alloy powders have been investigated by means of X-ray diffraction, differential scanning calorimetry, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results have shown that during the first few kiloseconds (11–360 ks) of the mechanical deformation via the rod-milling technique, the layered composite particles of Ti and Al are intermixed and form an amorphous phase when heated at about 700 K by so-called thermally assisted solid state amorphization (TASSA). The heat formation of an amorphous (enthalpy change of amorphization) Ti x Al 100 − x alloy via the TASSA process, ΔH a TASSA, has been measured directly as a function of the MA time. The crystallization characteristics indexed by the crystallization temperature T x TASSA and the enthalpy change of crystallization, ΔH x TASSA, of the amorphous phase formed via the TASSA process are also investigated as a function of the MA time. Comparable with the TASSA process, a homogeneous amorphous of Ti x Al 100 − x alloy has been formed directly without heating the composite particles after a longer MA time (1400 ks). The amorphization process in this case is attributed to a mechanical driven solid state amorphization (MDSSA). At the end of the MA processing time (360–1440 ks), the maximum heat formation of an amorphous Ti x Al 100 − x alloy via the MDSSA process ΔH a MDSSA has been estimated. Moreover, the thermal stability characterized by the crystallization temperature, T x MDSSA, and the enthalpy change of crystallization, ΔH x MDSSA, are also presented. The role of amorphization of Ti x Al 100 − x alloy powders for each process has been discussed.