Inhomogeneous Deformation in Compression – Comparison of Two Bulk‐Metallic Glasses

Abstract

Over the last decade, a significant advancement has been made in exploring multicomponent glass-forming metallic alloys with substantially sluggish crystallization kinetics, which resulted in the development of numerous bulk-metallic glasses (BMGs) with a thickness of several millimeters or even centimeters. This progress makes the applications of metallic glasses as structural materials become a reality. [1] The BMGs have outstanding mechanical properties, such as the high strength of up to 5 GPa, [2] large elastic deformation limit of around 2 %, [1] as well as good fatigue properties, [3][4][5][6] and, thus, they may be critical for advanced structural applications. However, the BMGs exhibit very limited plasticity, which is generally less than 2 % of the plastic strain in compression and almost zero in tension, and subsequent premature fracture. Undoubtedly, the poor plasticity and catastrophic fracture endanger the structural safety and hinder the extensive applications of the BMGs. The unfavorable mechanical behaviors/properties of the BMGs are imputed to their highly-localized inhomogeneous deformation.At low temperatures (e.g., room temperature) and high strain rates, the BMGs exhibit the inhomogeneous deformation, which is limited to highly-localized narrow regions, i.e., shear bands. [7] The formation of the shear bands affects plastic-flow and fracture behaviors substantially. [7][8][9][10] The excessive propagation of individual shear bands causes the premature failure. Various strategies have been developed to improve BMGs' ductility such as the insertion of crystalline phases or pores into the amorphous matrix, which forms crystalline or porosity/amorphous matrix composites. [11][12][13][14][15] These BMG composites display the improved ductility that results from the multiplication of shear bands.Recently, Das et al. [16] reported a new class of Cu 47.5 -Zr 47.5 Al 5 (atomic percent, at.-%) BMGs that exhibit an obvious work-hardening behavior and large ductility. These extraordinary mechanical behaviors/properties are attractive, which are different from those of common BMGs that show work softening and poor plasticity. The origin of this unique work-hardening behavior is still in debate. [16][17][18][19][20] In this paper, we re-examined the mechanical behavior of the work-hardening Cu 47.5 Zr 47.5 Al 5 in quasistatic compression and compared it with that of a common Zr 55 Ni 5 Al 10 Cu 30 BMG. It is expected that the present work can provide insight to the relationship between the plastic flow and shear-banding behavior of the BMGs and it may be helpful for improving the ductility of the BMGs. Figure 1 shows the engineering stress-strain curves of the Cu 47.5 Zr 47.5 Al 5 and Zr 55 Ni 5 Al 10 Cu 30 BMGs in the quasistatic compression at a strain rate of 2 × 10 -4 s -1 . From the engineering stress-strain curves, we derive the yield strength, compressive strength, and plastic strain for both the BMGs, and the results are listed in Table 1. It is noted that the compression tests for the Cu 47.5 Zr ...

Role of crystalline precipitates on the mechanical properties of (Cu0.50Zr0.50)100−xAlx (x=4, 5, 7) bulk metallic glasses

“…[37], some of the discrepancies in plasticity reported in the literature [13][14][15][16][17][18] for Cu 47.5 Zr 47.5 Al 5 BMG could be due to the presence of not irrelevant amounts of crystals that were not detected by laboratory scale XRD. Furthermore, it appears clear that plastic deformations higher than 3% and work hardening behaviour are observed only when considerable amounts of the B2-CuZr phase (at least 20%) are present.…”

“…The values of ε f and 0.2 for Cu 47.5 Zr 47.5 Al 5 and Cu 46.5 Zr 46.5 Al 7 BMGs obtained in this work (open symbols) and taken from the literature (filled symbols) [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] are reported as a function of the sample diameter in Fig. 5(a) and (b), respectively.…”

Mechanical behaviours of workhardening and worksoftening bulk metallic glasses

“…They attribute it to smaller intervals between shear banding operations. 14 It is important to note that no appreciable distinction in serrations between the as cast and predeformed Cu 47?5 Zr 47?5 Al 5 can be made in the plastic flow curves (Fig. 3).…”

“…In Zr 52?5 Cu 17?9 Ni 14?6 Al 10?0 Ti 5?0 , shear bands are straight and approximately parallel to each other, which is a typical characteristic of BMGs, 12,13 while in Cu 47?5 Zr 47?5 Al 5 , the shear bands are wavy and deflected, which are similar to previous observations. 4,14 There are more shear bands in Cu 47?5 Zr 47?5 Al 5 than in Zr 52?5 Cu 17?9 Ni 14?6 Al 10?0 Ti 5?0 .…”

“…The serrated plastic flow has been observed extensively under various loading modes in metallic glasses. [12][13][14]18,19,23,24 Wright et al suggested that the serrated plastic flow is caused by the formation of individual shear bands. 24 Using an infrared camera, Jiang et al recently observed in situ dynamic shear banding processes during uniaxial compression of a Zr based BMG and demonstrated that the serrations in the plastic flow correspond to individual shear banding events.…”