TEM Studies of Shear Bands in a Bulk Metallic Glass Based Composite

2001 ◽  
Vol 7 (S2) ◽  
pp. 1120-1121
Author(s):  
E. Pekarskaya ◽  
C.P. Kim ◽  
W.L. Johnson
Keyword(s):  
Metallic Glasses ◽  
Shear Bands ◽  
High Yield ◽  
In Situ Tem ◽  
Two Phase ◽  
University Of Illinois ◽  
Glass Forming ◽  
The University ◽  
Very High

In 1980’s the discovery of multicomponent systems with exceptional glass forming ability enabled the synthesis of metallic glasses at relatively low cooling rates, 10−1 — 102 K/s and at a larger thicknesses. Bulk metallic glasses normally have very high yield stress, σy = 0.02 · Y (Y is Young’s modulus), high elastic limit of about 2%, but fail with very little global plasticity, typically along a localized shear band at a 45 degree angle with respect to the applied stress.The material studied in the present work is a two-phase Zr56.3Ti13.8Cu6.9Ni5.6Nb5.0Be12.5 alloy,prepared by in-situ processing. The alloy consists of amorphous and crystalline phases. In-situ TEM straining (tensile) experiments were performed at room temperature in JEOL 4000EX operating at 300kV. The experiments were carried out in the Center for Microanalysis of Materials in the University of Illinois at Urbana-Champaign. The goal of the study was to understand the deformation mechanisms of such composite material.

Deformation-Induced Nanocrystallization in Al-Rich Metallic Glasses

2006 ◽  
Vol 114 ◽  
pp. 123-132 ◽  
Author(s):  
Nancy Boucharat ◽  
Rainer J. Hebert ◽  
Harald Rösner ◽  
Gerhard Wilde
Keyword(s):  
Metallic Glasses ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
In Situ Tem ◽  
Number Density ◽  
High Number Density ◽  
Glass Forming ◽  
Processing Strategies ◽  
Improved Performance

Deformation-induced nanocrystallization has been investigated in a marginally Al88Y7Fe5 glass forming alloy. Conventional calorimetry and microstructural analyses of materials that have been subjected to high pressure torsion straining (HPT) at room temperature indicate the development of an extremely high number density of small Al nanocrystals. The nanocrystals appear to be distributed homogeneously throughout the sample without any evidence of strong coarsening. Moreover, the comparison between nanocrystallization caused by the application of either HPT, cold-rolling or in-situ TEM tensile straining yielded the identification of the probable mechanisms underlying the formation of nanocrystals. These results form the basis for the development of advanced processing strategies for producing new nanostructures with high nanocrystal number densities which allow increased stability and improved performance.

scholarly journals Fracture in Bulk Amorphous Alloys

1998 ◽  
Vol 554 ◽  
Author(s):  
J. A. Horton ◽  
J. L. Wright ◽  
J. H. Schneibel
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Shear Bands ◽  
Bulk Amorphous Alloy ◽  
In Situ Tem ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Crack Tips ◽  
Temperature Fracture

AbstractThe fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 Al-5 Ti-17.9 Cu-14.6Ni (at.%), was examined by transmission electron microscopy (TEM) and x-ray diffraction forany evidence of crystallization preceding crack propagation. No evidence for crystallizationwas found in shear bands in compression specimens or at the fracture surface in tensile specimens.In- situ TEM deformation experiments were performed to more closely examine actualcrack tip regions. During the in-situ deformation experiment, controlled crack growth occurredto the point where the specimen was approximately 20 μm thick at which point uncontrolledcrack growth occurred. No evidence of any crystallization was found at the crack tips or thecrack flanks. Subsequent scanning microscope examination showed that the uncontrolledcrack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN2) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN2 temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture surfaces may also be a result of localized melting.

Glass-Forming Ability and Crystallization of High Purity Pd-Cu-Ni-P Alloy

2000 ◽  
Vol 644 ◽  
Author(s):  
Nobuyuki Nishiyama ◽  
Mitsuhide Matsushita ◽  
Akihisa Inoue
Keyword(s):  
High Purity ◽  
Isothermal Annealing ◽  
Glass Forming Ability ◽  
In Situ Tem ◽  
Nucleation Behavior ◽  
Spherical Region ◽  
Glass Forming ◽  
High Purity Alloy ◽  
Nose Temperature

AbstractGlass-forming ability, thermal stability and nucleation behavior of a Pd40Cu30Ni10P20 alloy prepared using a high purity polycrystalline phosphorus are investigated. The critical cooling rate for glass formation for the high purity alloy is the same as that for the previous result, but the improvement of undercooling reaches about 80 K as compared with the fluxed ordinary alloy. In comparison with the non-fluxed alloy, the solidified structure of the present highly purified alloy is significantly different. The non-fluxed sample shows the characteristic “island-like” structure consisted of acicular fcc-Pd2Ni2P solid solution and Cu3Pd intermetallic compound. These acicular phases appear to be caused by the growth of quenched-in nuclei. In the isothermal experiment, nucleus density exhibits time dependence even at 683 K near the nose temperature. It is assumed that the crystallization behavior for the highly purified alloy is closer to homogeneous nucleation from quenched-in nuclei dominant behavior. In order to investigate the nucleation behavior, in-situ TEM observation was carried out. Spherical Pd15P2 particle with a diameter about 15 nm is observed, and this spherical region repeats generation and annihilation during isothermal annealing. The reason for the high glass-forming ability is discussed on the basis of the obtained results.

In-Situ Observations of the Effect of Electron Irradiation on the Defect Microstructure of Alumina

1997 ◽  
Vol 3 (S2) ◽  
pp. 601-602
Author(s):  
S.-J. Chen ◽  
U. Dahmen ◽  
D.G. Howitt
Keyword(s):  
High Temperature ◽  
Electron Irradiation ◽  
Shear Bands ◽  
Valuable Insight ◽  
High Velocity Impact ◽  
Dislocation Densities ◽  
In Situ Observations ◽  
Very High ◽  
Insight Into

The interaction of radiation produced point defects with a dislocation microstructure at high temperature is of considerable interest and careful high voltage microscopy experiments can provide valuable insight into the mechanisms. Veyssière and Westmacott carried out in-situ experiments monitoring the partial dislocation climbs in Ni3Al induced by thermal vacancies as well as by Frenkel pairs produced during irradiation.1 We report here the results of some preliminary experiments we performed on alumina (A12O3) single crystals with high dislocation densities to study the modification of the microstructure by electron irradiation at high temperature.The dislocation microstructures were produced by shock wave deformation using a high-velocity impact technique. The technique is capable of producing a very high density of defects consisting primarily of basal twins, and slips on the basal, pyramidal and rhombohedral planes in alumina. The dislocations are all of glide type, mostly forming shear bands. A typical microstructure prior to irradiation is shown in figure la.

Correlation between the Enhanced Plasticity of Glassy Matrix Composites and the Volume Fraction, Size and Intrinsic Mechanical Property of Reinforcements

2014 ◽  
Vol 783-786 ◽  
pp. 1967-1970
Author(s):  
Z.H. Chu ◽  
Hidemi Kato ◽  
Guo Qiang Xie ◽  
D.R. Yan ◽  
Guang Yin Yuan
Keyword(s):  
Mechanical Properties ◽  
Metallic Glasses ◽  
Volume Fraction ◽  
Shear Bands ◽  
Ex Situ ◽  
Glassy Matrix ◽  
Matrix Composites ◽  
Micro Scale ◽  
Fraction Size

In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.

Enhancement of glass-forming ability and mechanical behavior of zirconium–lanthanide two-phase bulk metallic glasses

2015 ◽  
Vol 618 ◽  
pp. 795-802 ◽  
Author(s):  
Jie He ◽  
Norbert Mattern ◽  
Ivan Kaban ◽  
Fuping Dai ◽  
Kaikai Song ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Metallic Glasses ◽  
Bulk Metallic Glasses ◽  
Glass Forming Ability ◽  
Two Phase ◽  
Glass Forming

An easy approach to dihydrochalcones via chalcone in situ hydrogenation

2016 ◽  
Vol 88 (4) ◽  
pp. 349-361 ◽  
Author(s):  
Ana R. Jesus ◽  
Ana P. Marques ◽  
Amélia P. Rauter
Keyword(s):  
Room Temperature ◽  
Aromatic Aldehydes ◽  
Iron Chloride ◽  
High Yield ◽  
Microwave Assisted ◽  
Olefinic Double Bond ◽  
Single Reaction Product ◽  
Very High ◽  
Single Reaction

AbstractDihydrochalcones are polyphenols that exhibit a diversity of bioactivities, namely anti-inflammatory, antimicrobial and antiviral. We have explored the synthetic access to such molecular entities, and describe now an easy and scalable approach based on reduction of the olefinic double bond of chalcone precursors via in situ hydrogenation with the system Et3SiH-Pd/C in very high yield. The intermediate chalcones were synthesized also by a simple and efficient microwave-assisted Claisen–Schmidt condensation of aromatic aldehydes with acetophenones, conveniently protected with ethoxymethyl ether, if required. Chalcones were obtained as single reaction product in high yield in 2–3 h, while under conventional conditions at room temperature the reaction was carried out with completion only after 24 h. In addition, microwave irradiation has proven very efficient for deprotection of ethoxymethyl ether with iron chloride in only 10 min and very high yield.

scholarly journals The impacts of spring basal and side dressing on maize yield

2014 ◽  
pp. 83-86
Author(s):  
Péter Ragán
Keyword(s):  
Maize Yield ◽  
Yield Potential ◽  
High Yield ◽  
Chernozem Soil ◽  
Maize Production ◽  
Yield Increase ◽  
Stress Effects ◽  
Humus Layer ◽  
The University ◽  
Very High

The yield potential of maize is very high. According to Tollenaar (1983), maize yield potential is as high as 25 t ha-1 (absolute dry yield) which is the highest among all cereals. In order to fully utilise this high yield potential, proper nutrient replenishment is of chief importance among all agrotechnical factors. The aim of research was to examine the effect of nitrogen fertiliser applied as basal and side dressing on maize yield. The measurements were performed at the Látókép experiment site (47° 33’ N, 21° 26’ E, 111 m asl) of the Centre for Agricultural Sciences of the University of Debrecen on mid-heavy calcareous chernozem soil with deep humus layer in an established experiment in 2011, 2012 and 2013. The trial design was split-split-plot with two replications. Based on the experiment results, it can be established that the nutrient uptake of maize is greatly dependent on the amount of water store in the soil. From the aspect of the development of the maize plant and water supply, the most determinant factor was the distribution of precipitation over the growing season and not the amount precipitation. This is shown by the fact there was only 276 mm precipitation – which was favourably distributed – in 2012 to increase the availability of nutrients and the main average was the highest in this year (14.394 t ha-1). Spring basal dressing helped maize development in all three years even on chernozem soil which is well supplied with nutrients. Although the effect of side dressing did not result in any yield increase, it could still contribute to mitigating the stress effects caused by environmental factors. Altogether, nutrient supply adapted to the various development stages of maize can favourably affect the success of maize production.

HREM study of phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal

1996 ◽  
Vol 54 ◽  
pp. 722-723
Author(s):  
L.F. Chen ◽  
L.M. Wang ◽  
R.C. Ewing
Keyword(s):  
Phase Transformation ◽  
Ion Irradiation ◽  
National Laboratory ◽  
Research Field ◽  
In Situ Tem ◽  
Decagonal Quasicrystal ◽  
University Of New Mexico ◽  
Fundamental Understanding ◽  
The University

Irradiation-induced phase transformation in crystals has been an interesting research field for the past twenty years. Since the discovery of quasicrystals in Al-based alloys, there have been some reports on irradiation-induced phase transformation in quasicrystals by in situ TEM observations. However, detailed study on phase transformation in quasicrystals under ion irradiation at atomic level using HREM is necessary for the fundamental understanding of the process. In this paper, we report the results from a systematic HREM study on phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal (31.4 wt.% Cu, 21.8 wt.% Co and 5.4 wt.% Ge).The TEM specimens of single decagonal quasicrystal were prepared perpendicular to the tenfold axis. The transformation in single quasicrystal was studied by in situ TEM during 1.5 MeV Xe+ ion irradiation at room temperature using the HVEM-Tandem Facility at Argon National Laboratory and examined in detail by HREM using a JEM2010 microscope at the University of New Mexico after the irradiation.

Microfracture Observation of Zr-Based Bulk Metallic Glasses

2007 ◽  
Vol 345-346 ◽  
pp. 645-648
Author(s):  
Jung G. Lee ◽  
Kee Sun Sohn ◽  
Sung Hak Lee ◽  
Nack J. Kim ◽  
Choong Nyun Paul Kim
Keyword(s):  
Shear Band ◽  
Metallic Glasses ◽  
Fracture Resistance ◽  
Shear Bands ◽  
Stable Crack Growth ◽  
Curve Analysis ◽  
Fracture Properties ◽  
Apparent Fracture Toughness ◽  
Crack Blunting

Microfracture mechanisms of Zr-based bulk metallic glass (BMG) alloy containing ductile crystalline particles were investigated by directly observing microfracture processes using an in situ loading stage. Strength of the BMG alloy containing crystalline particles was lower than that of the monolithic BMG alloy, while ductility was higher. According to the direct microfracture observation, crystalline particles initiated shear bands, acted as blocking sites of shear band or crack propagation, and provided the stable crack growth which could be confirmed by the R-curve analysis, although they negatively affected apparent fracture toughness. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloy containing crystalline particles, and could be explained by mechanisms of blocking of crack or shear band propagation, formation of multiple shear bands, crack blunting, and shear band branching.

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