Micromechanisms of Deformation and Fracture in Rapidly Solidified Ni3Al Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
G. Liu ◽  
G.M. Bond
Keyword(s):  
Dislocation Motion ◽  
In Situ Tem ◽  
Intermetallic Alloys ◽  
Stress Concentrations ◽  
X Ray ◽  
Deformation And Fracture ◽  
The Subject ◽  
Rapidly Solidified ◽  
Degree Of Order

ABSTRACTRapidly solidified Ni76 Al24 ribbons, with and without boron, have been the subject of in-situ TEM deformation studies, as well as X-ray and TEM characterization and TEM fractography. The aim has been to gain a better understanding of the influence of a reduced degree of order on grainboundary behavior and ductility. This, in turn, allows fresh insights to be gained, both into the manner in which boron additions can enhance ductility, and into the potential usefulness of sequential ordering in intermetallic alloys with a tendency to intergranular failure. Lower degrees of order are found to reduce stress concentrations at grain boundaries; this effect is due to easier generation of dislocations from boundary sources, and, to a lesser extent, the braking action of thermal APB's on dislocation motion. The beneficial effect of boron on ductility is seen to result, at least in part, from enhanced boundary cohesive strength.

In-Situ TEM Study of Plastic Stress Relaxation Mechanisms and Interface Effects in Metallic Films

2005 ◽  
Vol 875 ◽  
Author(s):  
Marc Legros ◽  
Gerhard Dehm ◽  
T. John Balk
Keyword(s):  
Thin Films ◽  
High Strength ◽  
Dislocation Motion ◽  
Dislocation Nucleation ◽  
Film Stress ◽  
In Situ Tem ◽  
Metallic Films ◽  
Cross Sectional ◽  
Thin Foils

AbstractTo investigate the origin of the high strength of thin films, in-situ cross-sectional TEM deformation experiments have been performed on several metallic films attached to rigid substrates. Thermal cycles, comparable to those performed using laser reflectometry, were applied to thin foils inside the TEM and dislocation motion was recorded dynamically on video. These observations can be directly compared to the current models of dislocation hardening in thin films. As expected, the role of interfaces is crucial, but, depending on their nature, they can attract or repel dislocations. When the film/interface holds off dislocations, experimental values of film stress match those predicted by the Nix-Freund model. In contrast, the attracting case leads to higher stresses that are not explained by this model. Two possible hardening scenarios are explored here. The first one assumes that the dislocation/interface attraction reduces dislocation mobility and thus increases the yield stress of the film. The second one focuses on the lack of dislocation nucleation processes in the case of attracting interfaces, even though a few sources have been observed in-situ.

scholarly journals In situ TEM observations of high-strain-rate deformation and fracture in pure copper

2020 ◽  
Vol 33 ◽  
pp. 10-16
Author(s):  
T. Voisin ◽  
M.D. Grapes ◽  
T.T. Li ◽  
M.K. Santala ◽  
Y. Zhang ◽  
...  
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Pure Copper ◽  
In Situ Tem ◽  
Deformation And Fracture ◽  
High Strain Rate Deformation

In-Situ Tem Investigation During Thermal Cycling of thin Copper Films

1996 ◽  
Vol 436 ◽  
Author(s):  
R.-M. Keller ◽  
W. Sigle ◽  
S. P. Baker ◽  
O. Kraft ◽  
E. Arzt
Keyword(s):  
Grain Growth ◽  
Room Temperature ◽  
Dislocation Motion ◽  
In Situ Tem ◽  
Copper Films ◽  
Stress Evolution ◽  
Cu Films ◽  
Transmission Electron ◽  
Insight Into

AbstractIn-situ transmission electron microscopy (TEM) was performed to study grain growth and dislocation motion during temperature cycles of Cu films with and without a cap layer. In addition, the substrate curvature method was employed to determine the corresponding stresstemperature curves from room temperature up to 600°C. The results of the in-situ TEM investigations provide insight into the microstructural evolution which occurs during the stress measurements. Grain growth occurred continuously throughout the first heating cycle in both cases. The evolution of dislocation structure observed in TEM supports an explanation of the stress evolution in both capped and uncapped films in terms of dislocation effects.

Phase Transformations in the Fe-Al System Studied by “In-Situ” Tem Heating

1994 ◽  
Vol 364 ◽  
Author(s):  
A. Korner
Keyword(s):  
Transition Temperature ◽  
Single Crystal ◽  
Domain Structure ◽  
Type A ◽  
Bimodal Distribution ◽  
Dislocation Motion ◽  
In Situ Tem ◽  
Transmission Electron ◽  
The Matrix

AbstractThe domain structure and the evolution of antiphase boundaries (APBs) have been investigated in Fe-Al by means of “in-situ” transmission electron microscopy (TEM) heating experiments. Single crystals with composition Fe22.1at%Al and Fe25.6at%Al have been used.The grown-in structure of the Fe22.1at%al single crystal is composed of DO3 ordered particles embedded in the disorderd ±-matrix. A bimodal distribution of the particles was found. Small ordered particles are in between the large precipitates which are surrounded by particle-free zones. Numerous of this large ordered precipitates contain APBs. Crossing the transition temperature to the disordered phase, the small particles dissolve into the ±-matrix and the large particles start to shrink by dissolving.The single crystal with composition Fe25.6at%Al was found to be completely DO3 ordered. The grown-in domains are separated by APBs of type a′0/2〈100〉. At temperatures far below the transition temperature to the B2 phase no significant change in the APB and domain structure has been detected. In contrast, a remarkable evolution in the APB structure has been observed approaching the transition temperature. Coarsening of the domains has been found. Furthermore, APBs of B2-type (a′0/4〈lll〉 shear) are dragged out by dislocation motion. B2- and DC3-type APBs react and junctions are formed. With increasing annealing time, the density of B2-type boundaries increases. The TEM image is dominated by B2-type boundaries linked by the D03-type boundaries. The DO3 superlattice spots are clearly excited approaching the transition temperature to B2. Above the transition temperature, the DO3 spots disappear completely and the diffraction pattern reveals B2 long range order.

In-Situ Tem Studies of Recrystallization and Grain Growth in Al-Mg-Mn-Zr Alloys

1995 ◽  
Vol 404 ◽  
Author(s):  
John S. Vetrano ◽  
Steve M. Bruemmer ◽  
Ian M. Robertson
Keyword(s):  
Grain Growth ◽  
Boundary Migration ◽  
Dislocation Motion ◽  
Precipitate Size ◽  
In Situ Tem ◽  
Eutectic Constituent ◽  
Cold Worked ◽  
Superplastic Properties ◽  
Zr Alloys

AbstractRecrystallization and grain growth studies of Al-Mg-Mn-Zr alloys have been carried out in-situ in the transmission electron microscope. Nucleation sites were primarily on large (>I μm diameter) eutectic constituent particles. The sub-micron A16Mn dispersoids were observed to be effective as nuclei if present in clusters, and were effective at retarding grain boundary migration and dislocation motion. The smaller A13Zr precipitates seemed to have little effect on nucleation and growth, but were effective in pinning dislocations. These results have been analyzed in terms of precipitate size and shape in both the as-cold-worked microstructure and during recrystallization. The implications on the microstructural refinement of these alloys for improved superplastic properties will be discussed.

Deformation mechanisms at epitaxial semiconductor interfaces studied by in situ TEM

1992 ◽  
Vol 50 (1) ◽  
pp. 248-249
Author(s):  
R. Hull ◽  
J.C. Bean ◽  
F. Ross
Keyword(s):  
Strain Relaxation ◽  
High Stress ◽  
Dislocation Motion ◽  
Dislocation Nucleation ◽  
Deformation Mechanisms ◽  
Dynamic Strain ◽  
In Situ Tem ◽  
Stress Regime ◽  
Semiconductor Interfaces

We have studied deformation mechanisms at epitaxial semiconductor interfaces, primarily in the GexSi1-x/Si and InxGa1-xAs/GaAs systems, by in-situ annealing of metastably strained films in the transmission electron microscope (TEM). This allows direct, real-time, observation and recording of dynamic strain relaxation phenomena such as misfit dislocation nucleation, propagation and interaction mechanisms. This geometry also allows considerable insight into fundamental dislocation physics, as we are able, for example, to accurately quantify dislocation propagation velocities as functions of well-defined effective stresses (in the 108 - 109 pa regime)in the epitaxial layers, and to vary dislocation structure and character by varying the orientation of the epitaxial interface. Comparison with measurements of dislocation velocities in bulk semiconductors and with models of dislocation motion via kink propagation, allows extension of existing measurements and models to the thin film, high stress regime.

Understanding the Deformation and Fracture of Nitinol Endovascular Stents Using In Situ Synchrotron X-Ray Microdiffraction

2007 ◽  
Vol 19 (9) ◽  
pp. 1183-1186 ◽  
Author(s):  
A. Mehta ◽  
X.-Y. Gong ◽  
V. Imbeni ◽  
A. R. Pelton ◽  
R. O. Ritchie
Keyword(s):  
Endovascular Stents ◽  
X Ray ◽  
Deformation And Fracture
Sign in / Sign up

Export Citation Format

Share Document