AMORPHIZATION PROCESS BY ROD-MILLING TIXAL100-X AND THE EFFECT OF ANNEALING

Amorphous TixAl100-x alloy powders with wide amorphization range (33 l ess than or equal to x less than or equal to 75) have been synthesized by rod-milling technique using a mechanical alloying (MA) process. Th e rod-milled alloy powders have been investigated by means of X-ray di ffraction, differential scanning calorimetry, optical microscopy, scan ning electron microscopy and transmission electron microscopy. The res ults have shown that during the first few kiloseconds (11-360 ks) of t he mechanical deformation via the rod-milling technique, the layered c omposite particles of Ti and Al are intermixed and form an amorphous p hase when heated at about 700 K by so-called thermally assisted solid state amorphization (TASSA). The heat formation of an amorphous (entha lpy change of amorphization) TixAl100-x alloy via the TASSA process, D elta H-a(TASSA), has been measured directly as a function of the MA ti me. The crystallization characteristics indexed by the crystallization temperature T-x(TASSA) and the enthalpy change of crystallization, De lta H-x(TASSA), Of the amorphous phase formed via the TASSA process ar e also investigated as a function of the MA time. Comparable with the TASSA process, a homogeneous amorphous of TixAl100-x alloy has been fo rmed directly without heating the composite particles after a longer M A 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 TixAl100-x alloy via the MDSSA process Delta H-a(MDSSA) has been estimated. Moreover, the thermal stability characterized by t he crystallization temperature, T-x(MDSSA) and the enthalpy change of crystallization, Delta H-x(MDSSA), are also presented. The role of amo rphization of TixAl100-x alloy powders for each process has been discu ssed.