Nanoindentation study of chemical effects on the activation volume controlling shear band initiation in metallic glasses (original) (raw)
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Journal of Alloys and Compounds, 2009
Zr 57 Cu 20 Al 10 Ti 8 Ni 5 and modified composition by adding Sn, W or Ta are studied using standard mechanical test and nanoindentation. Addition of refractory elements with a Sn micro-addition increases clearly the Young's modulus and the hardness of basic BMG. However, Sn reduces plasticity. Moreover these experiments allowed, in confine plasticity conditions, estimating an apparent activation volume associated to a plastic deformation (≈150 Å 3 ). (Y. Champion). mentary deformation process, delaying consequently shear bands propagation and catastrophic fracture. 0925-8388/$ -see front matter
Influences of Sample Preparation on Nanoindentation Behavior of a Zr-Based Bulk Metallic Glass
Influences of two different sample preparation methods, mechanical polishing and plunge cutting, on nanoindentation behavior of a Zr-based bulk metallic glass were studied. Mechanical polishing suppresses the serrated flow but promotes the creep. In contrast, plunge cutting promotes the serrated flow but suppresses the creep. However, hardness and elastic modulus obtained from these two methods are nearly the same.
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Materials Science and Engineering A, 2004
This paper presents studies on mechanical properties of a Zr-based metallic glass by using spherical indentation and nano-indentation techniques. The spherical indentation investigates mechanical properties of the Zr-based metallic glass as a function of indentation strain. The results show that the Zr-based metallic glasses have almost perfect plasticity with little strain hardening. During fully plastic stage, spiral shear bands appear inhomogeneously around the impression of the spherical indentations. The shear bands initiate from the impressions at an angle slightly deviating from the pure shear stresses in the free surface. Further nano-indentations by using Berkovich tip made around the spherical indentation impression show that there is a zone of lower hardness around the impression of the spherical indentation. SEM and AFM images show that there exists significant different pile-up behaviors of the impressions by the nano-indentation far away and near the spherical indentation impression. Near the spherical indent, less pile-up is formed around the impression of nano-indentation, and this is assumed to be the result of the intersection between the pre-introduced shear bands by the spherical indentation and the new shear bands induced by nano-indentation.
Effect of temperature on mechanical behavior of Zr-based bulk metallic glasses
Applied Physics Letters, 2006
The compressive tests and Vickers microhardness measurements were conducted on the as-cast Zr-based bulk metallic glasses at different temperatures. The results show that the strength is proportional to the temperature. Furthermore, at cryogenic temperatures, more shear bands were observed near the fracture surface and surrounding the indentation marks. The analysis suggests that both the formation and propagation of the shear bands are thermally activated processes.
A new and unique alloy formulation design strategies has been developed in order to fabricate thin layered metallic glasses (TFMG) with superior fracture resistance and low coefficient of friction (COF) during nano-scraching test. Due to the outstanding properties, TFMG could be applied for different uses uch as surface coating, biomedical, bio implant, electronic devices, spacecraft and railway, all of which need surface fracture resistance. The fabricated Zr-based metallic glass having the composition of Zr60Cu25Al5Ag5Ni5 (at.%) was annealed for 10, 30, and 60 min below the glass transition temperature. Nanoindentation and nanoscratch tests were used to investigate mechanical and nanotribological properties. Atomic force microscopy (AFM) was used to examine the surface morphology and microstructures. The annealing effect and applied forces change over the chemical structure and stability, morphological change, elastic modulus, hardness, wear rate, and coefficient of friction of th...
International Journal of Plasticity, 2022
Unraveling the microstructural heterogeneity is an important issue to understand the physical and mechanical properties of bulk metallic glasses (BMGs). Physical aging below the glass transition temperature and cold rolling at ambient temperature are effective ways to tune the state within the potential energy landscape of BMGs, modifying the microstructural heterogeneity. With the help of nanoindentation measurements, scrutinizing the local reduced modulus and hardness of a Zr50Cu40Al10 MG in different states, from physical aged to rejuvenated materials, we demonstrate here that the enhancement of microstructural heterogeneity plays an important role in the mechanical behavior. The internal friction coefficient , obtained from modelling by finite element simulation the experimental load-displacement curves, is found to decrease with the increase of concentration of flow defects and the stress exponent obtained from the creep stage shows a strong dependence on the structural state. The effect of physical aging and rejuvenation on the structural state is rationalized in terms of the relative flow defects concentration. Finally, the statistics of discrete displacement bursts were investigated. Importantly, we found that the displacement bursts behavior is significantly different depending on the structural state, changing from obvious to unapparent behaviors. The potential mechanisms originating this phenomenon are discussed. By given a physical schematic, the correlation between the displacement burst size and the shear band size in the local plastic zones is well illustrated, which will lead to a deeper understanding of the rejuvenation-induced plasticity of BMGs.
Advances in Materials Science and Engineering
The present study reveals the role of Nb and Ni minor addition on the nanomechanical properties and nanostructure of ZrCuAl bulk metallic glass (BMG). For this purpose, atomic force microscopy (AFM) was used to evaluate the viscoelastic response of the BMG surface at the nanoscale, while the nanoindentation technique was applied to show the mechanism of plastic deformation. The results indicated that minor Nb addition decreased the relaxation of enthalpy accompanied by the weakening of structural heterogeneity. On the other hand, Ni addition improved the stored energy of the material and intensified the distribution of loosely packed regions in the microstructure. Moreover, the mechanical test unveiled that Ni addition enhanced the viscoelastic response; however, it came at the expense of creep resistance. The evaluation of the magnitude of the derivative in the nanoindentation test also demonstrated that the Ni-added sample exhibited a multiple shear-band mode for plastic deformation.
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Materials Science and Engineering: A, 2007
In the present investigation, Cu 47 Ti 33 Ni 6 Sn 2 Si 1 (numbers indicate at.%) bulk metallic glass (BMG), fabricated by injection casting has been used for indentation experiments. Microindentation and nanoindentation tests were conducted to study the indentation responses of this material. The nanohardness and the Young's modulus were calculated following the standard procedure in literature. Around the indent, shear bands can be clearly observed under scanning electron microscopy examination. Atomic-force microscopy shows the pile of the material in a step-wise manner. The thinned sample near the indent shows the evolution of nanocrystals (∼20-30 nm) by transmission electron microscopy. During nanoindentation (in single-and multi-indent mode) experiments, the load-displacement P-h curves show displacement bursts, which are also known as pop-ins or serrations. The total displacement during indentation can be accounted for by sum total effect of the individual displacement of all the displacementbursts observed in the P-h curve. Thus the plastic deformation of this glassy material appears to proceed in a discrete manner unlike ductile metallic alloys.
Micro and nano indentation studies on Zr60Cu10Al15Ni15 bulk metallic glass
Materials & Design (1980-2015), 2015
Partially vitrified Zr 60 Cu 10 Al 15 Ni 15 bulk metallic glass has been synthesized using water cooled copper mold drop casting technique. Kinetically favorable microstructures having different morphologies are observed throughout the volume of the bulk metallic glass sample. X-ray diffraction studies indicate formation of hard intermetallic compounds such as Zr 3 Al 2 and Zr 2 Ni in certain regions along with amorphous structures. Microindentation studies carried out in different regions of the sample reveal microstructure dependent deformation behavior. Highest hardness is observed in the fully crystallized regions compared to pure glassy regions in the same sample. Further nanoindenation in the same sample is used to understand dynamic mechanical properties of microstructures in different regions. The pileup morphologies around the indent and differences in load-displacement curves provide vital information on deformation behavior of sample in different microstructure sensitive regions.