Effect of Fe content on glass-forming ability and crystallization behavior of a (Ti_(69.7)Nb_(23.7)Zr_(4.9)Ta_(1.7))_(100-x)Fe_x alloy synthesized by mechanical alloying

摘要

(Ti_(69.7)Nb_(23.7)Zr_(4.9)Ta_(1.7))_(100-x)Fe_x (x = 0, 2, 6, and 10) nanocrystalline, nanocomposite and metallic glass powders were synthesized by mechanical alloying. The glass-forming ability (GFA) and crystallization behavior of the synthesized alloy powders are investigated by X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. With the increased Fe content, the synthesized alloy powders after the steady state milling transform from full nanocrystalline structure for x = 0 to nanocomposite structure containing amorphous matrix surrounding nanocrystals for x = 2 and 6 and to full amorphous structure for x = 10, and thus has the increased enthalpy of crystallization and the increased GFA. The non-isothermal crystallization kinetics is analyzed by the modified Johnson-Mehl-Avrami (JMA) equation. The values of the Avrami exponent imply that the crystallization of (Ti_(69.7)Nb_(23.7)Zr_(4.9)Ta_(1.7))_(100-x)Fe_x nanocomposite/metallic glass powders with x = 6 and 10 is governed by diffusion-controlled three and two-dimensional growth, respectively. Moreover, the crystallized bulk alloys consolidated from the synthesized alloy powders have different crystallized phases, microstruc-tures and mechanical properties. The increased GFA with the increased Fe content could be explained by the total number of intermetallics present in the milled powders, appropriate atomic-size mismatch and large negative heat of mixing among constituent elements.