Abstract
This work highlights the relationship between the preparation, crystallization behavior, microstructures, and mechanical properties of Cu-based bulk metallic glasses (BMGs) and their composites (BMGCs). (Cu47Zr45Al8)97.5Y1.5Nb in-situ BMGCs were prepared using isothermal annealing, and the experimental results indicate tunable mechanical properties of the alloys by processing parameter manipulation. The crystallinity of (Cu47Zr45Al8)97.5Y1.5Nb BMGCs increases with extended annealing temperature and time, while their phase transition with rising temperature follows Am (amorphous state) → Am + Cu10Zr7 →Am + Cu10Zr7 + AlCu2Zr + Al2Zr. Precipitation strengthening during annealing above 720 K (447 oC) can enhance the alloy microhardness remarkably and achieve an optimum of 712 HV by annealing at 800 K (527 oC) for 60 min. TEM results show that Cu10Zr7 with sizes of 12~15 nm precipitates out upon crystallization and thereby accounts for the superior compressive property. The alloy exhibits a fracture strength up to 2080 MPa after annealing at 680 K (407 oC) for 30 min. Morphological observation of the fracture surface reveals a transition of fracture characteristics from the typical amorphous ductile manner to a brittle manner with further annealing. The investigation provides novel thoughts of BMGs processing for further performance improvement.
Highlights
As an emerging class of advanced materials with huge potentials in technological benefits, bulk metallic glasses (BMGs) possess unique fracture mechanisms and superior mechanical properties such as ultra-high strength, high fracture toughness, low elastic modulus, and high hardness[1,2,3,4,5]
With the treatment time fixed at 30 min, X-ray diffraction (XRD) patterns corresponding to lower-temperature [i.e. temperature lower than 720 K (447 oC)] annealing only exhibit amorphous diffuse humps that are typically associated with the amorphous structures (Figure 2 (a))
With the annealing temperature raised to 740 K (467 oC), slight crystalline peaks show up on the top of the amorphous hump, and sharp crystalline peaks appear when further heating up to 760 K (487 oC), indicating that the crystallization phase has been extensively formed within the alloy
Summary
As an emerging class of advanced materials with huge potentials in technological benefits, bulk metallic glasses (BMGs) possess unique fracture mechanisms and superior mechanical properties such as ultra-high strength, high fracture toughness, low elastic modulus, and high hardness[1,2,3,4,5]. Numerous efforts have been given nowadays to develop diversiform BMG systems with enhanced functionality and improved mechanical performance, so as to better meet the requirements of structural and engineering materials[6,7,8]. The Cu-Zr system stands out for its ultrahigh strength, high hardness, great GFA (i.e. generally, compressive σf ≥1.5GPa; Hv ≥500; critical diameter ≥15 mm), and low preparation expense, thereby possessing much application value in the field of engineering[4,9]. BMGCs can be prepared with in-situ crystals by controlling the partial crystallization of BMGs10-13, of which the enhancement mechanism might be well expounded via scrutinizing the crystallization behavior.
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