Abstract
Structural relaxation and nanomechanical behaviors of La65Al14Ni5Co5Cu9.2Ag1.8 bulk metallic glass (BMG) with a low glass transition temperature during annealing have been investigated by calorimetry and nanoindentation measurement. The enthalpy release of this metallic glass is deduced by annealing near glass transition. When annealed below glass transition temperature for 5 min, the recovered enthalpy increases with annealing temperature and reaches the maximum value at 403 K. After annealed in supercooled liquid region, the recovered enthalpy obviously decreases. For a given annealing at 393 K, the relaxation behaviors of La-based BMG can be well described by the Kohlrausch-Williams-Watts (KWW) function. The hardness, Young’s modulus, and serrated flow are sensitive to structural relaxation of this metallic glass, which can be well explained by the theory of solid-like region and liquid-like region. The decrease of ductility and the enhancement of homogeneity can be ascribed to the transformation from liquid-like region into solid-like region and the reduction of the shear transition zone (STZ).
Highlights
Bulk metallic glasses (BMGs) have attracted much attention owing to their excellent strength, high elastic limit, and outstanding soft magnetic properties [1,2,3,4], which originate from its disordered structure [5,6,7]
After being annealed at 350 ◦ C for 12 h, Zr55 Cu30 Ni5 Al10 BMG undergoes obvious brittle fracture, and its fracture energy density is reduced by 75%, which is consistent with the increase in the degree of ordered structure characterized by high resolution transmission electron microscopy (HRTEM) [12]
The effects of annealing temperature and time on thermal stability, enthalpy recovery, and nanomechanical behaviors of La65 Al14 Ni5 Co5 Cu9.2 Ag1.8 BMG have been investigated by differential scanning calorimetry (DSC) and nanoindentation
Summary
Bulk metallic glasses (BMGs) have attracted much attention owing to their excellent strength, high elastic limit, and outstanding soft magnetic properties [1,2,3,4], which originate from its disordered structure [5,6,7]. Compared with thermodynamically stable crystalline counterparts, BMGs are in a high-energy metastable state and tend to relax to a stable state. This process, called structural relaxation, has no effect on non-crystalline nature [8]. The investigation on structural relaxation is of great significance for grasping thermal stability and mechanical properties of BMGs. The annealing treatment is commonly used to eliminate the thermal history of amorphous alloys and induce its structural relaxation. Liang et al have found that a La-based BMG can promote the local atomic rearrangement (β relaxation) after being annealed for a short time at a high temperature close to Tg by dynamic mechanical analysis [22]. The influence of annealing temperature on nanomechanical properties has been investigated by using nanoindentation and atomic force microscope (AFM)
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