Effects of Cr Microalloying on Structural Evolution, Crystallization Behavior and Micromechanical Properties of ZrCoAlCr Bulk Metallic Glass

This paper deals with the role of minor addition of Cr on the atomic rearrangement and crystallization evolution in a Zr-based bulk metallic glass. For this purpose, Cr elements with 1–4% atomic percentage were added into the alloying composition. The X-ray diffraction results indicated that the trace element led to the increase in disordered structures in the glassy alloy and the decline in population of short and medium scale orders. This event was due to the intensification of structural heterogeneity which was manifested in the change of enthalpy relaxation. The differential scanning calorimetry analysis also showed that all ZrCoAlCr BMG samples included two distinct crystallization peaks during the heating process. However, the increase in Cr content led to the intensification of low temperature peak. This result was consistent with viscosity analysis, in which the viscosity decrement was intensified at the range of low temperature crystallization peak with the rise in Cr content. Moreover, it was found that although the plasticity improved in samples with Cr-content, the strength showed a slight decrease

The effects of Ni or Nb additions on the relaxation behavior of Zr<inf>55</inf>Cu<inf>35</inf>Al<inf>10</inf> metallic glass

Many questions raised in the field of metallic glasses (MGs) are inherently attributed to β relaxation. Therefore, this study investigated the behavior of β relaxation in the Zr55Cu35Al10 MG by differential scanning calorimetry (DSC) under different heating rates. Minor additions of Ni and Nb into the base alloy and pre-annealing process were also carried out to highlight the features of β relaxation in the thermal curves. The results showed that the pre-annealing process led to the appearance of an endothermic peak under the glass transition temperature (Tg), which is a sign of reversible β relaxation in the glassy structure. Moreover, the peak position of the endothermic event was at 0.78 Tg, 0.83 Tg, and 0.87 Tg for Zr55Cu35Al10, (Zr55Cu35Al10)98Ni2, and (Zr55Cu35Al10)98Nb2, respectively, which indicated the crucial role of minor addition on the evolution of β relaxation. In addition, the pre-annealing process from 3 h to 48 h demonstrated that the endothermic peaks in the minor-added samples tended to shift to higher temperatures. Furthermore, structural characterization of MGs revealed various types of short-range and medium-range orders in the Ni- and Nb-added alloys, leading to a different relaxation behavior in the glassy structure