Strain-hardening and suppression of shear-banding in rejuvenated bulk metallic glass

Abstract

Strain-hardening (the increase of flow stress with plastic strain) is the most important phenomenon in the mechanical behaviour of engineering alloys because it ensures that flow is delocalized, enhances tensile ductility and inhibits catastrophic mechanical failure 1,2. Metallic glasses (MGs) lack the crystallinity of conventional engineering alloys, and some of their properties-such as higher yield stress and elastic strain limit 3-are greatly improved relative to their crystalline counterparts. MGs can have high fracture toughness and have the highest known 'damage tolerance' (defined as the product of yield stress and fracture toughness) 4 among all structural materials. However, the promise of MGs for structural applications is largely thwarted by the fact that they show strain-softening, instead of strain-hardening; this leads to extreme localization of plastic flow in shear bands, and is associated with early catastrophic failure in tension. Although rejuvenation of an MG (raising its energy to values that are typical of glass formation at a higher cooling rate) lowers its yield stress, which might enable strain-hardening 5 , it is unclear whether sufficient rejuvenation can be achieved in bulk samples while retaining their glassy structure. Here we show that plastic deformation under triaxial compression at room temperature can rejuvenate bulk MG samples sufficiently to enable strain-hardening through a mechanism that has not been previously observed in the metallic state. This transformed behaviour suppresses shear-banding in bulk samples in normal uniaxial (tensile or compressive) tests,

Pulling Metallic Glasses Ductile

“…3b). The maximum absolute value of ΔH rel of 0.81 kJ/mol is comparable to previously reported sub T g mechanical rejuvenation techniques, including high pressure torsion and notched triaxial strain, 16,20,42 and is among the highest reported changes in enthalpy of relaxation when compared to the reference sample.…”

“…[7][8][9] Recognizing such limitations in realizing a ductile state under BMG forming conditions has led to the development of processing strategies to enhance ductility after the glass has already been formed. Such strategies are based on mechanical means, 10 and include irradiation, [11][12][13][14][15] static loading, [16][17][18][19][20] cyclic loading, 21 shot peening, 22 rolling, 23 twin roll casting, 24 thermal cycling, [25][26][27][28] and severe plastic deformation. 29,30 A summary of previous results can be found in the supplementary material in table 1.…”

Renin–Angiotensin System: An Important Player in the Pathogenesis of Acute Respiratory Distress Syndrome

“…The SARS epidemic in 2003 as well the current COVID-19 pandemic, caused by two members of the Coronavirus family SARS-CoV and SARS-CoV-2, respectively, have directed attention towards the interaction of Coronaviruses with the RAS. mACE2 serves as a binding site for SARS-CoV [64,65] and SARS-CoV-2 [66,67], mediating the entry of the virus into the host cell. A mutation in the receptor-binding domain of the SARS-CoV-2 spike protein S compared to SARS-CoV is responsible for a higher affinity of SARS-CoV-2 to ACE2 [67].…”

Rejuvenation of Zr-Based Bulk Metallic Glasses by Ultrasonic Vibration-Assisted Elastic Deformation

“…Bulk metallic glasses (BMGs) are materials with excellent performance and mechanical properties, such as high yield strength [ 1 ], high toughness [ 2 ], high hardness [ 3 ] and exceptional “damage tolerance” [ 4 , 5 ]. However, the nonuniform deformation caused by the highly localized deformation at room temperature directly causes its brittleness [ 6 , 7 ], which has become the bottleneck for the widespread application of BMGs.…”

“…Through plastic deformation under triaxial compression at room temperature, Y. Li and A.L. Greer [ 4 ] rejuvenated BMGs samples and found that the rejuvenated amorphous material showed excellent plastic deformation ability. However, elastic loading [ 17 ], ion radiation [ 18 ], thermal cycling [ 19 , 20 ], and plastic deformation [ 21 ] methods require a substantial amount of time to rejuvenate the BMGs, and during this time, a relaxation effect inevitably occurs, weakening the rejuvenation effect.…”