Effects of crystallization fractions on mechanical properties of Zr-based metallic glass matrix composites

Abstract

The Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (at.%) bulk metallic glass composites with various crystallization fractions were prepared by pretreating the bulk metallic glassy samples with pulsing current, and then by isothermal annealing at near initial crystallization temperature for different periods of time. The precipitations and crystallization fractions were studied by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), and their effects on mechanical properties of the composite were studied by microhardness, uniaxial compression test and scanning electron microscopy (SEM). The experimental results show that the primary precipitate is quasicrystalline phase and other metastable phases including Be 2 Zr, Zr 2 Cu and FCC would precipitate subsequently. In the initial crystallization process, in which the crystallization fraction increases from 0 to 8.2%, both fracture strength and plastic strain increase, with the maximum plastic strain up to 6.4%. When the crystallization fraction is larger than 8.2%, the fracture strength and the plastic strain decrease sharply. Furthermore, the alloy with low crystallization fraction is fractured by shearing, while for high crystallization fraction it is fractured by splitting and cleavage. The results show that the mechanical properties of the glassy alloy could be optimized by controlling the processing parameters. bulk metallic glass, pulsing current, crystallization fraction, plasticity, shear band PACS: 64.70.Pf, 81.40.Lm, 81.30.Mh, 61.50.KsBulk metallic glasses (BMGs) possess extraordinary properties, such as high strength and strong corrosion resistance, which has attracted much attention from scientists in the area of materials and physics [1][2][3]. Usually the strengths of BMGs come up to theoretical values, much higher than those of the crystalline alloys with the same chemical compositions [1-4]. But BMGs exhibit very limited global plasticity since they deform by shearing through the formation of shear bands that tend to form highly localized shear bands, resulting in crack formation and premature fracture [1][2][3][4][5]. Recently, however, investigations have reported that some BMGs exhibit large plastic strains in compression due to the generation of multiple shear bands [6][7][8][9][10][11]. This implies possibility to enhance the plasticity of BMGs through effectively hindering the highly localized shear along the primary shear bands and promoting the activation of shear bands. The reported results show that one way for improving the ductility of BMGs is to introduce second phases to BMGs by in-situ formation [6] or by isothermal annealing [7], which might benefit the generation of shear bands. For instance, Sun et al. [10] reported that 12% compressive plastic strain could be achieved by in-situ forming spherical crystals within the glassy matrix, while Hofmann et al. [11] reported that Zr-Ti-based bulk metallic glass matrix composites (BMGCs) display tensile plasticity of 8.6%-13.1%. However, effects of different second phases and their cryst...

Work toughening effect in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

“…Figure 3(a) shows the engineering strain-stress curves of the as-cast specimen and pre-deformed plus annealed specimens. The as-cast Vit1 BMG exhibits a yield strength of about 1800 MPa and a plastic strain of 0.3%, in agreement with the reported result [12][13][14][15]. When the BMG samples were pre-deformed by 5%, 10% and 15%, respectively, in a constrained state, vertical orientation specimens cut from the pre-deformed samples exhibited plastic strains of ~2.5%, ~5.0% and ~8.0%, respectively (Figure 3(b)).…”

“…So to enhance the plasticity of BMGs, it is necessary to promote the activation of multiple shear bands [2][3][4][5][6][7][8][9][10] and hinder the localization and rapid propagation of shear bands [11][12][13][14][15][16][17][18][19]. Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7].…”

“…Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7]. Because the partially relieved local heating and hindrance of the propagation of shear bands, both the strength and the ductility of a Zr-based BMG are enhanced at cryogenic temperatures [12].…”

Relationship between composite structures and compressive properties in CuZr-based bulk metallic glass system

“…Volume fractions of the crystal phase were found to severely affect mechanical properties in the dendrites reinforced composite [9,10,25]. Crystalline volume fractions can be varied by changing the applied cooling rates (i.e., the casting diameter) during fabrication of the composites and the longitudinal position of the as-cast rods.…”

Rolling-induced microstructure change in Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass

“…Moreover, with increasing deformation degree, the free-volume content in a pre-annealed/rolled specimen increases at a lower average rate than that in an as-cast/rolled specimen. Bulk metallic glasses (BMGs) have attracted much attention because of their properties such as high fatigue strength, high hardness, good castability, and excellent wear and corrosion resistances [1][2][3][4][5][6][7][8]. However, during compressive or tensile tests at temperatures far below the glass-transition temperature, failure of BMGs usually occurs along a single shear band without much macroscopic plasticity.…”