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Multiple mechanisms in the thermally activated plastic flow of tantalum

Description: We argue that many of the features of the plastic flow behavior of tantalum can be described by a model that incorporates a two-component Peierls-type mechanism and an fcc-like obstacle mechanism in series. We compare the results of calculations based on such a model with flow data for unalloyed tantalum over a wide range of strain rates and a modest range of temperatures.
Date: June 27, 1995
Creator: Gourdin, W.H. & Lassila, D.H.
Partner: UNT Libraries Government Documents Department

Accurate atomistic simulations of the Peierls barrier and kink-pair formation energy for {lt}111{gt} screw dislocations in bcc-Mo

Description: Using multi-ion MGPT interatomic potentials derived from first- principles generalized pseudopotential theory, we have performed accurate atomistic simulations on the energetic of dislocation motion in the bcc transition metal Mo. Our calculated results include the (110) and (211) generalized stacking fault ({gamma}) energy surfaces, the Peierls stress required to move an ideal straight <111> screw dislocation, and the kink-pair formation energy for nonstraight screw dislocations. Many-body angular forces, which are accounted for in the present theory through explicit three- and four-ion potentials, are quantitatively important to such properties for the bcc transition metals. This is demonstrated explicitly through the calculated {gamma} surfaces, which are found to be 10-50% higher in energy than those obtained with pure radial-force models. The Peierls stress for an applied <111>/{l_brace}112{r_brace} shear is computed to be about 0.025{mu}, where {mu} is the bulk shear modulus. For zero applied stress, stable kink pairs are predicted to form for kink lengths greater than 4b, where b is the magnitude of the Burgers vector. For long kinks greater than 15b, the calculated asymptotic value of the kink-pair formation energy is 2.0 eV.
Date: May 23, 1997
Creator: Xu, W. & Moriarty, J.A.
Partner: UNT Libraries Government Documents Department

Dislocation Multiplication in the Early Stage of Deformation in Mo Single Crystals

Description: Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied using transmission electron microscopy (TEM) techniques in order to investigate dislocation multiplication mechanisms in the early stage of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. The jog height can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. The coalescence of superjogs results in an increase of both link length and jog height. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This ''dynamic'' dislocation multiplication source is suggested to be crucial for the dislocation multiplication in the early stage of plastic deformation in Mo.
Date: March 2, 2000
Creator: Hsiung, L. & Lassila, D.H.
Partner: UNT Libraries Government Documents Department

Dynamic Dislocation Mechanisms For the Anomalous Slip in a Single-Crystal BCC Metal Oriented for "Single Slip"

Description: Dislocation substructures of high-purity Mo single crystals deformed under uniaxial compression at room temperature to an axial strain of 0.6% were investigated in order to elucidate the underlying mechanisms for the {l_brace}0{bar 1}1{r_brace} anomalous slip in bcc metals [1], which is also known as the violation of Schmid law [2]. The test sample was oriented with the stress axis parallel to a nominal ''single-slip'' orientation of [{bar 2} 9 20], in which ({bar 1}01) [111] is the primary slip system that has a maximum Schmid factor (m = 0.5), which requires the lowest stress to operate among the twelve {l_brace}{bar 1}10{r_brace} &lt;111&gt; slip systems. Nevertheless, the recorded stress-strain curve reveals no easy-glide or single-slip stage; work hardening starts immediately after yielding. Moreover, the result of slip trace analysis indicates the occurrence of anomalous slip on both the (011) and (0{bar 1}1) planes, which according to the Schmid law requires relatively higher stresses to operate. TEM examinations of dislocation structures formed on the (101) primary slip plane reveal that in addition to the ({bar 1}01) [111] slip system, the coplanar ({bar 1}01) [1{bar 1}1] slip system which has a much smaller Schmid factor (m = 0.167) is also operative. Similarly, (0{bar 1}1) [111] (m = 0.25) is cooperative with the coplanar (0{bar 1}1) [{bar 1}11] slip system (m = 0.287) on the (0{bar 1}1) slip plane, and (011) [1{bar 1}1] (m = 0.222) is cooperative with the coplanar (011) [11{bar 1}] slip system (m = 0.32) on the (011) plane. The occurrence of {l_brace}0{bar 1}1{r_brace} anomalous slip is accordingly proposed to be originated from the cooperative dislocation motion of the {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations on the ({bar 1}01) slip plane; the mutual interaction and blocking of {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations not ...
Date: January 11, 2007
Creator: Hsiung, L & La Cruz, C
Partner: UNT Libraries Government Documents Department

Rate-Controlling Mechanisms in Five-Power-Law Creep

Description: OAK-B135 Rate-Controlling Mechanisms in Five-Power-Law Creep. The initial grant emphasized the rate-controlling processes for five power-law creep. The effort has six aspects: (1) Theory of Taylor hardening from the Frank dislocation network in five power law substructures. (2) The dual dynamical and hardening nature of dislocations in five power law substructures. (3) Determination of the existence of long-range internal stress in five-power law creep dislocation substructures. (4) Dynamic recovery mechanisms associated with dislocation heterogeneities during five power law creep. (5) Versatility of five power law creep concept to other (hcp) crystal structures. (6) Writing of a book on ''Fundamental of Creep in Metals and Alloys'' by M.E. Kassner and Maria-Teresa Perez-Frado (postdoctoral scholar, funded by this project) Elsevier Press, 2004, in press. These areas are consistent with the original goals of this project as delineated in the original proposal to Basic Energy Sciences. The progress in each of these areas will be discussed separately and there will be an attempt to tie each aspect together so as to allow a summary regarding the conclusions with respect to the rate-controlling mechanisms of five power-law creep.
Date: April 20, 2004
Creator: Kassner, Michael E.
Partner: UNT Libraries Government Documents Department

LDA Calculations of Dislocation Mobility in Fe & Mo

Description: This Project was a collaborative effort between Murray Daw (Clemson) and Daryl Chrzan (LBNL/UCB). The main goal of this project was to accomplish the first-ever first principles calculations of the structure of the screw dislocation in Fe and to study the effects of stress and magnetization. The calculations were completed and reported at conferences. During the work on this project, the collaboration also tackled an important related question - the effect of periodic boundary conditions in dislocation dalculations on the stress-state. The solution to the problem for this particular case has had much broader impact than the specific results of the calculation in iron. This technique was published in Computational Materials Science, and has been applied recently to the study of dislocations on nanotubes (submitted). Finally, the collaboration considered the application of scaling formalism to a simple problem of dislocation emission from a single, stress-actived source. The result is a very elegant, compact solution to a simple textbook problem, which was published in Phil Mag. This result lays the foundation for continuing work on applying scaling formalism to dynamics of more complex dislocation problems.
Date: July 13, 2007
Creator: Daw, Murray S. & Chrzan, Daryl
Partner: UNT Libraries Government Documents Department

Role of interfaces in deformation and fracture: Titanium aluminides

Description: Available experimental data on deformation and fracture behavior of polysynthetically twinned (PST) TiAl crystals are analyzed on the basis of the calculated results of bulk and defect properties and shear fault, cleavage and interfacial energies of TiAl and Ti{sub 3}Al. The extent of dissociation width of and ordinary dislocation is calculated to be larger at {alpha}{sub 2}/{gamma} and {gamma}/{gamma} interfaces by about two-fold as compared to the bulk of {gamma}-phase, suggesting the enhances slip along the interfaces when the crystal is a soft orientation. Propagation of (111) cleavage cracks is influenced by the mixed mode (II and III) of external loading applied to the coplanar deformation twinning and ordinary slip, leading to translamellar fracture. According to the calculated interfacial fracture energies, cleavage cracking si to occur on {alpha}{sub 2}/{gamma} boundaries and least likely on true-twin boundaries. Discussion is given on the roles of misfit dislocations, kinetics of dislocation-interface interactions and hydrogen embrittlement in deformation and fracture processes.
Date: September 1, 1996
Creator: Yoo, M.H. & Fu, C.L.
Partner: UNT Libraries Government Documents Department

COMPUTER SIMULATION OP FRANK LOOP CONTRAST IN FIELD IONIMAGES

Description: A computer model for simulation of the image contrast caused by Frank dislocation loops in field ion tips of fcc materials is presented. The model is based on the shell model for ion image simulation, whereas the displacement field of Frank loops is computed from the exact displacement equation for a closed dislocation loop in an isotropically elastic continuum. A method for taking surface effects into account by superposition of the displacement field of an image loop is introduced. The results indicate that Frank loops will cause image contrast while wholly beneath the surface of the tip, and that vacancy and interstitial loops will cause qualitatively different contrast. The effect of surface relaxation, while quantitatively substantial, does not qualitatively alter these results. Special emphasis is placed on small loops, with respect to which existing contrast theory is inadequate. Some micrographs of ion bombarded iridium tips are presented. These micrographs display contrast effects in excellent agreement with computer plots of interstitial loop contrast.
Date: September 1, 1973
Creator: Stolt, Kaj Gunnar
Partner: UNT Libraries Government Documents Department

Atomistic simulations for multiscale modeling in bcc metal

Description: Quantum-based atomistic simulations are being used to study fundamental deformation and defect properties relevant to the multiscale modeling of plasticity in bcc metals at both ambient and extreme conditions. Ab initio electronic-structure calculations on the elastic and ideal-strength properties of Ta and Mo help constrain and validate many-body interatomic potentials used to study grain boundaries and dislocations. The predicted C(capital Sigma)5 (310)[100] grain boundary structure for Mo has recently been confirmed in HREM measurements. The core structure, (small gamma) surfaces, Peierls stress, and kink-pair formation energies associated with the motion of a/2(111) screw dislocations in Ta and Mo have also been calculated. Dislocation mobility and dislocation junction formation and breaking are currently under investigation.
Date: September 25, 1998
Creator: Belak, J.; Moriarty, J.A.; Soderlind, P.; Xu, W.; Yang, L.H. & Zhu
Partner: UNT Libraries Government Documents Department

Atomistic studies of jogged screw dislocations in {gamma}-TiAl alloys

Description: The behavior of jogged screw dislocations in {gamma}-TiAl alloys has been investigated with large-scale molecular dynamics (MD) simulations. The authors find a new mechanism for formation of pinning points in jogged screw dislocations. They also find that the critical height for the jogs in the {+-}[{bar 1}10] directions on the (001) plane to move nonconservatively is between 3r{sub 0} and 4r{sub 0}, where r{sub 0} is the nearest neighbor distance of aluminum atoms. Interstitials and vacancies are created during the nonconservative motions of the jogs. In addition, the formation of dislocation dipole and loops around the jogs is also observed.
Date: March 1, 1999
Creator: Chen, K.Y.; Li, M. & Zhou, S.J.
Partner: UNT Libraries Government Documents Department

On the Micromechanisms of Anomalous Slip in BCC Metals

Description: Dislocation substructures developed in high-purity Mo single crystals deformed under uniaxial compression at room temperature to a total strain of {approx} 0.5% with a strain rate of 1 s{sup -1} have been investigated using transmission electron microscopy (TEM) techniques in order to elucidate the underlying micromechanisms of the anomalous operation of {l_brace}0{bar 1}1{r_brace} slip systems, i.e. Schmid-law violation, in bcc metals. The crystals were oriented with the stress axis parallel to a nominal single-slip orientation of [{bar 2}920], in which the ({bar 1}01)[111] slip system is the only system having a maximum value of Schmid factor (m = 0.5). Nevertheless, the recorded stress-strain curve reveals no single-slip or easy-glide stage, and the anomalous slip occurs in both (011) and (0{bar 1}1) planes. TEM examination of the dislocation structure in the ({bar 1}01) primary slip plane reveals that in addition to the operation of the ({bar 1}01)[111] slip system, the coplanar ({bar 1}01)[1{bar 1}1] slip system that has a much smaller Schmid factor (m = 0.167) is also operative. Similarly, the (0{bar 1}1)[111] slip system (m = 0.25) is cooperative with the coplanar (0{bar 1}1)[{bar 1}11] system (m = 0.287), and the (011)[1{bar 1}1] slip system (m = 0.222) is cooperative with the coplanar (011)[11{bar 1}] system (m = 0.32). The occurrence of {l_brace}0{bar 1}1{r_brace} anomalous slip is accordingly proposed to be initiated from the cooperative dislocation multiplication and mutual trapping and blocking of 1/2[111] and 1/2[1{bar 1}1] coplanar dislocation arrays in the ({bar 1}01) plane. The resulted internal stresses render the propagation of both 1/2[111] and 1/2[1{bar 1}1] screw dislocations from the ({bar 1}01) plane onto the {l_brace}0{bar 1}1{r_brace} planes and subsequently result in the occurrence of anomalous slip.
Date: September 6, 2005
Creator: Hsiung, L L
Partner: UNT Libraries Government Documents Department

Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED Studies

Description: We investigate the atomic structure of the fivefold surface of an icosahedral Al-Cu-Fe alloy, using scanning tunneling microscopy (STM) imaging and a special dynamical low energy-electron diffraction (LEED) method. STM indicates that the step heights adopt (primarily) two values in the ratio of tau, but the spatial distribution of these two values does not follow a Fibonacci sequence, thus breaking the ideal bulk-like quasicrystalline layer stacking order perpendicular to the surface. The appearance of screw dislocations in the STM images is another indication of imperfect quasicrystallinity. On the other hand, the LEED analysis, which was successfully applied to Al-Pd-Mn in a previous study, is equally successful for Al-Cu-Fe. Similar structural features are found for both materials, in particular for interlayer relaxations and surface terminations. Although there is no structural periodicity, there are clear atomic planes in the bulk of the quasicrystal, some of which can be grouped in recurring patterns. The surface tends to form between these grouped layers in both alloys. For Al-Cu-Fe, the step heights measured by STM are consistent with the thicknesses of the grouped layers favored in LEED. These results suggest that the fivefold Al-Cu-Fe surface exhibits a quasicrystalline layering structure, but with stacking defects.
Date: April 15, 2001
Creator: Cai, T.; Shi, F.; Shen, Z.; Gierer, M.; Goldman, A.I.; Kramer, M.J. et al.
Partner: UNT Libraries Government Documents Department

Screw dislocations in GaN

Description: GaN has received much attention over the past few years because of several new applications, including light emitting diodes, blue laser diodes and high-power microwave transistors. One of the biggest problems is a high density of structural defects, mostly dislocations, due to a lack of a suitable lattice-matched substrate since bulk GaN is difficult to grow in large sizes. Transmission Electron Microscopy (TEM) has been applied to study defects in plan-view and cross-sections on samples prepared by conventional techniques such as mechanical thinning and precision ion milling. The density of dislocations close to the sample surface of a 1 mm-thick HVPE sample was in the range of 3x109 cm-2. All three types of dislocations were present in these samples, and almost 50 percent were screw dislocations. Our studies suggest that the core structure of screw dislocations in the same material might differ when the material is grown by different methods.
Date: February 15, 2002
Creator: Liliental-Weber, Zuzanna; Jasinski, Jacek B.; Washburn, Jack & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Screw dislocations in GaN grown by different methods

Description: A study of screw dislocations in Hydride-Vapor-Phase-Epitaxy (HVPE) template and Molecular-Beam-Epitaxy (MBE) over-layers was performed using Transmission Electron Microscopy (TEM) in plan-view and in cross-section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.
Date: May 27, 2003
Creator: Liliental-Weber, Z.; Zakharov, D.; Jasinski, J.; O'Keefe, M.A. & Morkoc, H.
Partner: UNT Libraries Government Documents Department

{l_brace}311{r_brace} Defects in ion-implanted silicon: The cause of transient diffusion, and a mechanism for dislocation formation

Description: Ion implantation is used at several critical stages of Si integrated circuit manufacturing. The authors show how {l_brace}311{r_brace} defects arising after implantation are responsible for both enhanced dopant diffusion during annealing, and stable dislocations post-anneal. They observe {l_brace}311{r_brace} defects in the earliest stages of an anneal. They subsequently undergo rapid Ostwald ripening and evaporation. At low implant doses evaporation dominates, and they can quantitatively relate the interstitials emitted from these defects to the transient enhancement in diffusivity of dopants such as B and P. At higher doses Ostwald ripening is significant, and they observe the defects to undergo a series of unfaulting reactions to form both Frank loops and perfect dislocations. They demonstrate the ability to control both diffusion and dislocations by the addition of small amounts of carbon impurities.
Date: April 1995
Creator: Eaglesham, D. J.; Stolk, P. A.; Cheng, J. Y.; Gossmann, H. J.; Poate, J. M. & Haynes, T. E.
Partner: UNT Libraries Government Documents Department

High-Resolution Spore Coat Architecture and Assembly of Bacillus Spores

Description: Elucidating the molecular architecture of bacterial and cellular surfaces and its structural dynamics is essential to understanding mechanisms of pathogenesis, immune response, physicochemical interactions, environmental resistance, and provide the means for identifying spore formulation and processing attributes. I will discuss the application of in vitro atomic force microscopy (AFM) for studies of high-resolution coat architecture and assembly of several Bacillus spore species. We have demonstrated that bacterial spore coat structures are phylogenetically and growth medium determined. We have proposed that strikingly different species-dependent coat structures of bacterial spore species are a consequence of sporulation media-dependent nucleation and crystallization mechanisms that regulate the assembly of the outer spore coat. Spore coat layers were found to exhibit screw dislocations and two-dimensional nuclei typically observed on inorganic and macromolecular crystals. This presents the first case of non-mineral crystal growth patterns being revealed for a biological organism, which provides an unexpected example of nature exploiting fundamental materials science mechanisms for the morphogenetic control of biological ultrastructures. We have discovered and validated, distinctive formulation-specific high-resolution structural spore coat and dimensional signatures of B. anthracis spores (Sterne strain) grown in different formulation condition. We further demonstrated that measurement of the dimensional characteristics of B. anthracis spores provides formulation classification and sample matching with high sensitivity and specificity. I will present data on the development of an AFM-based immunolabeling technique for the proteomic mapping of macromolecular structures on the B. anthracis surfaces. These studies demonstrate that AFM can probe microbial surface architecture, environmental dynamics and the life cycle of bacterial and cellular systems at near-molecular resolution under physiological conditions.
Date: March 14, 2011
Creator: Malkin, A J; Elhadj, S & Plomp, M
Partner: UNT Libraries Government Documents Department

Growth modes of InN(000-1) on GaN buffer layers on sapphire

Description: In this work, using atomic force microscopy and scanning tunneling microscopy, we study the surface morphologies of epitaxial InN films grown by plasma-assisted molecular beam epitaxy with intervening GaN buffer layers on sapphire substrates. On smooth GaN buffer layers, nucleation and evolution of three-dimensional InN islands at various coverages and growth temperatures are investigated. The shapes of the InN islands are observed to be predominantly mesa-like with large flat (000-1) tops, which suggests a possible role of indium as a surfactant. Rough GaN buffer layers composed of dense small GaN islands are found to significantly improve uniform InN wetting of the substrates, on which atomically smooth InN films are obtained that show the characteristics of step-flow growth. Scanning tunneling microscopy imaging reveals the defect-mediated surface morphology of smooth InN films, including surface terminations of screw dislocations and a high density of shallow surface pits with depths less than 0.3 nm. The mechanisms of the three-dimensional island size and shape evolution and formation of defects on smooth surfaces are considered.
Date: January 24, 2005
Creator: Liu, Bing; Kitajima, Takeshi; Chen, Dongxue & Leone, Stephen R.
Partner: UNT Libraries Government Documents Department

Dislocation core in GaN

Description: Light emitting diodes and blue laser diodes grown on GaN have been demonstrated despite six orders of magnitude higher dislocation density than that for III-V arsenide and phosphide diodes. Understanding and determination of dislocation cores in GaN is crucial since both theoretical and experimental work are somewhat contradictory. Transmission Electron Microscopy (TEM) has been applied to study the layers grown by hydride vapor-phase epitaxy (HVPE) and molecular beam epitaxy (MBE) (under Ga rich conditions) in plan-view and cross-section samples. This study suggests that despite the fact that voids are formed along the dislocation line in HVPE material, the dislocations have closed cores. Similar results of closed core are obtained for the screw dislocation in the MBE material, confirming earlier studies.
Date: February 20, 2002
Creator: Liliental-Weber, Zuzanna; Jasinski, Jacek B.; Washburn, Jack & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Cracking behavior and microstructure of austenitic stainless steels and alloy 690 irradiated in BOR-60 reactor, phase I.

Description: Cracking behavior of stainless steels specimens irradiated in the BOR-60 at about 320 C is studied. The primary objective of this research is to improve the mechanistic understanding of irradiation-assisted stress corrosion cracking (IASCC) of core internal components under conditions relevant to pressurized water reactors. The current report covers several baseline tests in air, a comparison study in high-dissolved-oxygen environment, and TEM characterization of irradiation defect structure. Slow strain rate tensile (SSRT) tests were conducted in air and in high-dissolved-oxygen (DO) water with selected 5- and 10-dpa specimens. The results in high-DO water were compared with those from earlier tests with identical materials irradiated in the Halden reactor to a similar dose. The SSRT tests produced similar results among different materials irradiated in the Halden and BOR-60 reactors. However, the post-irradiation strength for the BOR-60 specimens was consistently lower than that of the corresponding Halden specimens. The elongation of the BOR-60 specimens was also greater than that of their Halden specimens. Intergranular cracking in high-DO water was consistent for most of the tested materials in the Halden and BOR-60 irradiations. Nonetheless, the BOR-60 irradiation was somewhat less effective in stimulating IG fracture among the tested materials. Microstructural characterization was also carried out using transmission electron microscopy on selected BOR-60 specimens irradiated to {approx}25 dpa. No voids were observed in irradiated austenitic stainless steels and cast stainless steels, while a few voids were found in base and grain-boundary-engineered Alloy 690. All the irradiated microstructures were dominated by a high density of Frank loops, which varied in mean size and density for different alloys.
Date: February 16, 2010
Creator: Chen, Y.; Chopra, O. K.; Soppet, W. K.; Shack, W. J.; Yang, Y.; Allen, T. R. et al.
Partner: UNT Libraries Government Documents Department

Mechanical effects of electron irradiation in iron single crystals

Description: Electron irradiation (2 MeV, up to 6 x 10$sup 18$ e/cm$sup 2$) decreased the yield stress of iron single crystals in the temperature range from 4.2 to 80$sup 0$K. The softening effect was highly dependent on the tensile axis orientation. The temperature and strain rate dependency of the yield stress was increased by the irradiation. The annealing of the softening took place between 90 and 150$sup 0$K. The observation is consistent with an intrinsic solid solution softening mechanism based on the enhancement of screw dislocation motion due to dispersed interstitials. (auth)
Date: January 1, 1976
Creator: Meshii, M. & Sato, A.
Partner: UNT Libraries Government Documents Department

Irradiation softening in pure iron single crystals

Description: The characteristics of irradiation softening in Fe were studied. Results show that irradiation softening effect can be explained by the intrinsic mechanism, namely, the interaction of screw dislocations with randomly dispersed interstitials. At least some of the solid solution softening phenomena observed in alloys can be explained by the same mechanism. However, the alloying may be accompanied by an additional effect such as solute segregation to dislocations which may also strongly affect the yield stress. This effect may mask the softening effect partially or totally. Changes in the dislocation structure of deformed specimens caused by alloying, which are often reported in electron microscopic investigations, support this contention. The alloying, therefore, may not be as good as the low temperature irradiation in studying the effect of random solutes on dislocation motion and yield stress. (auth)
Date: January 1, 1975
Creator: Meshii, M.
Partner: UNT Libraries Government Documents Department