DYNAMIC STUDIES OF DEFORMATION AND FRACTURE AT GRAIN BOUNDARIES

1988 ◽  
Vol 49 (C5) ◽  
pp. C5-677-C5-680
Author(s):  
I. M. ROBERTSON ◽  
G. M. BOND ◽  
T. C. LEE ◽  
D. S. SHIH ◽  
H. K. BIRNBAUM
Keyword(s):  
Grain Boundaries ◽  
Dynamic Studies ◽  
Deformation And Fracture

Experimental Evidence For Sulfur Induced Loss Of Ductility In Copper Shaped-Charge Jets

1995 ◽  
Vol 409 ◽  
Author(s):  
D. K. Chan ◽  
D. H. Lassila ◽  
W. E. King ◽  
E. L. Baker
Keyword(s):  
Grain Boundaries ◽  
Sulfur Content ◽  
Fracture Behavior ◽  
High Strain ◽  
Shaped Charge ◽  
X Ray ◽  
Jet Breakup ◽  
Deformation And Fracture ◽  
Breakup Time ◽  
Content Of Oxygen

AbstractWe have observed that a change in the bulk sulfur content of oxygen-free electronic copper markedly affects its high temperature (400–1000°C), high strain-rate (> 103 s−1) deformation and fracture behavior. These conditions are typical of those found in "jets" formed from the explosive deformation of copper shaped-charge liners. Specifically, an increase in the bulk sulfur concentration from 4 ppm to 8 ppm shortens the breakup time, tb, of the copper jets by nearly 20% as measured using flash x-ray radiographs recorded during breakup of the jets. At bulk concentrations of 4 ppm, the jet was observed to be uniform and axisymmetric with a breakup time of 186 µs. Jet particles exhibited length-to-diameter ratios of roughly 8:1. The addition of sulfur transformed the jet breakup behavior to non-uniform, non-axisymmetric rupture and reduced the breakup time to 147 µs. The length-to-diameter ratios decreased to roughly 5:1 in the sulfurdoped samples. Previously measured sulfur solubilities and diffusivities in copper at the temperatures where this material was processed indicates nearly all of the sulfur was localized to grain boundaries. Therefore, we infer that the increase in sulfur content at grain boundaries is directly responsible for the change in breakup performance of the shaped-charge jets.

Atomistic Modeling of Extended Defects in Metalic Alloys: Dislocations and Grain Boundaries in Ll2 Compounds

1990 ◽  
Vol 186 ◽  
Author(s):  
V. Vitek ◽  
G. J. Ackland ◽  
J. Cserti
Keyword(s):  
Grain Boundaries ◽  
Dislocation Core ◽  
Extended Defects ◽  
Atomistic Modeling ◽  
Many Body ◽  
Deformation And Fracture ◽  
Governing Factor ◽  
Atomic Interactions ◽  
Total Energies ◽  
Physical Features

AbstractExtended defects, such as dislocations and grain boundaries, control a wide variety of material properties and their atomic structure is often a governing factor. A necessary precursor for modeling of these structures is a suitable description of atomic interactions. We present here empirical many-body potentials for alloys which represent a very simple scheme for the evaluation of total energies and yet reflect correctly the basic physical features of the alloy systems modeled. As examples of atomistic studies we show results of calculations of the core structures of screw dislocations in Ll2 compounds. The same potentials have also been used to calculate structures of grain boundaries in these compounds. The deformation and fracture behavior of Ll2 alloys is then discussed in the light of grain boundary and dislocation core studies.

Quantitative measurements of stresses at grain boundaries in polycrystalline metals

1988 ◽  
Vol 46 ◽  
pp. 620-621
Author(s):  
W. A. T. Clark
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Direct Transmission ◽  
Static Mode ◽  
Quantitative Measurements ◽  
Polycrystalline Metals ◽  
Dynamic Studies ◽  
Pile Up ◽  
Mode A

It has long been recognized that the deformation of polycrystalline metals proceeds by the movement of individual dislocations both within the grains and across the grain boundaries which separate them. It is known, for example, that the yield stress is directly affected by the density of grain boundaries in a metal; in the familiar Hall-Petch relationship it is inversely proportional to the grain diameter. Various models have been proposed to account for this behaviour, all of which involve the interaction between dislocations and grain boundaries (for a review see e.g. ref. 1). Microscopically, these interactions can be accomplished by several different mechanisms, which include the nucleation of new dislocations, direct transmission of dislocations across the interface, the absorption and desorption of dislocations into and out of the interface.The TEM can be used for both static and in-situ dynamic studies of these interactions. In the static mode, a TEM is used to analyze fully the crystallography of dislocation pile-up/grain boundary interactions; one such pile-up is shown in Fig. 1.

Deformation and fracture of high-entropy AlCoCrFeNi alloy

2021 ◽  
pp. 103-108
Author(s):  
Yu.F. Ivanov ◽  
◽  
V.E. Gromov ◽  
K.A. Osintsev ◽  
S.V. Konovalov ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Tensile Tests ◽  
High Entropy Alloy ◽  
Second Phase ◽  
High Entropy ◽  
Deformation And Fracture ◽  
Distribution Of Elements ◽  
Microscopy Method ◽  
Second Phases ◽  
Wire Arc Additive Manufacturing

Using wire-arc additive manufacturing (WAAM)technology in an atmosphere of argon gas a non - equatomic high entropy alloy (HEA) of AlCoCrFeNi system is obtained: Al (35.67±1.34 at%), Ni (33.79±0.46 at%), Fe (17.28±1.83 at%), Cr (8.28±0.15 at%), Co (4.99±0.09 at%). Scanning electron microscopy method revealed that HEA is a polycrystal material having the grain size (4-15) µm with the particles of second phase located along the grain boundaries. Mapping methods showed that grain volumes are enriched in aluminum and nickel, while grain boundaries contain chromium and iron. Cobalt is distributed in the crystal lattice of the resulting HEA quasi-uniformly. It is shown that during tensile tests, the material was destroyed by the mechanism of intra-grain cleavage. The formation of brittle cracks along the boundaries and at the junctions of grain boundaries, i.e., in places containing inclusions of the second phases, is revealed. It was suggested that one of the reasons for the increased brittleness of HEA, is revealed uneven distribution of elements in the microstructure of the alloy and also the presence in the volume of material discontinuities of various shapes and sizes.

Effect of Strain Rate on Hydrogen Evolution during Deformation in Al-Zn-Mg Alloys

2012 ◽  
Vol 706-709 ◽  
pp. 295-300
Author(s):  
Keitaro Horikawa ◽  
Hiroyuki Yamada ◽  
Masahide Mutsuo ◽  
Hidetoshi Kobayashi
Keyword(s):  
Strain Rate ◽  
Grain Boundaries ◽  
Testing Machine ◽  
Hydrogen Gas ◽  
Mg Alloys ◽  
Second Phase ◽  
Gas Evolution ◽  
Hydrogen Atoms ◽  
Deformation And Fracture ◽  
The Moment

Hydrogen gas evolution behaviour during deformation and fracture in Al-Zn-Mg alloys with and without copper additions was examined by using a testing machine equipped with a quadrupole mass spectrometer in an ultrahigh vacuum chamber (QMS-UHV) and by a hydrogen microprint technique (HMT). The QMS-UHV testing revealed that hydrogen gas was evolved at the moment of grain boundary fracture, in particular. This suggested that hydrogen atoms primarily dissolved were trapped at the grain boundaries before the fracture. It was also revealed that hydrogen gas evolution behaviour was changed according to the testing strain rate. The HMT also revealed that silver particles, which represented the emission sites of hydrogen, were observed mainly around the second phase inclusions and the grain boundaries.

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