Non-isothermal and isothermal crystallization kinetics and their effect on microstructure of sintered and crystallized TiNbZrTaSi bulk alloys

Non-isothermal and isothermal,crystallization kinetics of mechanically alloyed Ti65Nb23.33Zr5Ta1.67Si5 metallic glass (MG) powder and their effect on microstructure and mechanical property of spark-plasma-sintered and crystallized bulk counterparts were investigated by using Johnson-Mehl-Avrami-Kolmogorov equation. Results show the MG powder has two distinct crystallization steps, which precipitates bcc beta-Ti and hexagonal (Ti, Zr)(2)Si phases successively. The larger apparent activation energy of the second crystallization step than that for the first one indicates the easier occurrence of precipitation for bcc beta-Ti phase. Comparative analysis of crystallization kinetics indicates that regardless of non-isothermal and isothermal crystallization types, the first crystallization step is dominated by diffusion-controlled three- and two-dimensional growth of nuclei for the early and late crystallization stage, respectively, while the second one is governed by diffusion-controlled three-dimensional growth of nuclei in the whole crystallization process. Both nucleation rates of these two steps increase firstly and then reduce in the early and late crystallization stage, respectively. The processing technologies combined with crystallization kinetics decide different grain sizes and yield strengths for the sintered and crystallized bulk alloys. The results obtained provide a new insight into tailoring microstructure and mechanical property of bulk alloys by designing and optimizing processing technologies based on crystallization kinetics. (C) 2015 Elsevier B.V. All rights reserved.