SOLID-STATE AMORPHIZATION REACTION BY ROD-MILLING ALXTA1-X POWDERS AND THE EFFECT OF ANNEALING

High thermal stable amorphous AlxTa1-x alloy powders with wide amorphi zation range (10 less than or equal to x less than or equal to 90) hav e been synthesized by rod-milling technique using a mechanical alloyin g (MA) method. During the first few kiloseconds (11-173 ks) of the MA time, the layered-composite particles of Al and Ta are intermixed and form an amorphous phase upon heating at about 680 K in a differential thermal analyzer by thermally assisted solid state amorphization (TASS A). The heat formation of an amorphous AlxTa1-x alloy via the TASSA pr ocess, Delta H-aT has been measured as a function of the MA time. The crystallization characteristics indexed by the crystallization tempera ture, T-xT and the enthalpy of crystallization, Delta H-xT of the amor phous phase formed via the TASSA process are also investigated as a fu nction of the MA time. Comparable with the TASSA process, a homogeneou s amorphous AlxTa1-x alloy is formed after longer MA time (1080 ks). T he amorphization process in this case is attributed to a mechanical so lid state amorphization (MDSSA). At the end of the MA time (1080-1440 ks), the maximum heat of formation of an amorphous AlxTa1-x alloy via the MDSSA process, Delta H-aM, has been calculated. Moreover, the ther mal stability characterized by the crystallization temperature, T-xM a nd the enthalpy of crystallization, Delta H-xM, are also estimated. Th e role of amorphization via each process has been discussed.