Nature of Slip in γ-Titanium Aluminide Above the Yield Stress Anomaly Temperature

1998 ◽  
Vol 552 ◽  
Author(s):  
S. Jiao ◽  
N. Bird ◽  
P. B. Hirsch ◽  
G. Taylor
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Shear Stress ◽  
Yield Stress ◽  
Titanium Aluminide ◽  
Transmission Electron ◽  
Different Temperatures ◽  
Critical Resolved Shear Stress

ABSTRACTCrystals of γ-TiAl, containing ∼54.5 at% Al, with various orientations were deformed at different temperatures and examined by transmission electron microscopy (TEM). It was found that while in many cases slip and climb of ordinary dislocations tend to predominate, slip by [001] dislocations can be important also. The occurrence of [001] slip has not been reported before. The values of critical resolved shear stress were determined and strong locks on [001] dislocations have been identified as local segments of ½ ⟨112] dislocations arising from interactions between [001] and ½⟨110] dislocations.

On temperature dependence of deformation mechanism and the brittle–ductile transition in semiconductors

1999 ◽  
Vol 14 (7) ◽  
pp. 2783-2793 ◽  
Author(s):  
P. Pirouz ◽  
A. V. Samant ◽  
M. H. Hong ◽  
A. Moulin ◽  
L. P. Kubin
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Shear Stress ◽  
Deformation Mechanism ◽  
Low Temperatures ◽  
Partial Dislocations ◽  
Brittle Ductile Transition ◽  
Transmission Electron ◽  
Literature Evidence ◽  
Critical Resolved Shear Stress

Recent deformation experiments on semiconductors have shown the occurrence of a break in the variation of the critical resolved shear stress of the crystal as a function of temperature. These and many other examples in the literature evidence a critical temperature at which a transition occurs in the deformation mechanism of the crystal. In this paper, the occurrence of a similar transition in two polytypes of SiC is reported and correlated to the microstructure of the deformed crystals investigated by transmission electron microscopy, which shows evidence for partial dislocations carrying the deformation at high stresses and low temperatures. Based on these results and data in the literature, the explanation is generalized to other semiconductors and a possible relationship to their brittle–ductile transition is proposed.

Epitaxial Growth of NiSi2 on (011)Si

1983 ◽  
Vol 25 ◽  
Author(s):  
L.J. Chen ◽  
W.T. Lin ◽  
M.B. Chang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Shear Stress ◽  
Epitaxial Growth ◽  
Expected Value ◽  
Edge Type ◽  
Average Spacing ◽  
Transmission Electron ◽  
Interfacial Dislocations ◽  
Critical Resolved Shear Stress

ABSTRACTEpitaxial growth of NiSi2 on (011)Si was investigated by the transmission electron microscopy. Both epitaxial and twin related NiSi2 were formed, with the former being predominant, in samples annealed at 850°C for 1/2 h. The silicides were faceted with {111} interfaces being more prominent than {100} interfaces. Interfacial dislocations were found to be of edge type with 1/6<112> Burgers vectors. The average spacing is about 700 Å which is very close to the theoretically expected value 670 Å.The absence of twins formed on (111) and (111) planes for (011) samples as well as the results obtained for (001) and (111) specimens suggest that there exists a critical resolved shear stress at the interface for the initiation of the formation of twin related NiSi2.

Quantitative transmission electron microscopy of small agglomerates in HF-O

1978 ◽  
Vol 36 (1) ◽  
pp. 336-337
Author(s):  
M. Rühle ◽  
G. Elssner ◽  
O. Ruano
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Shear Stress ◽  
Physical Properties ◽  
Temperature Dependence ◽  
Hexagonal Lattice ◽  
Transmission Electron ◽  
Critical Resolved Shear Stress

High amounts of gases or carbon are soluble on interstitial sites of the hexagonal lattice of hafnium. The gas atoms influence nearly all physical properties; e.g., the critical resolved shear stress τ (CRSS) is drastically increased with an increasing content of gas atoms. Different authors measured the temperature dependence of τ for different 0 concentrations (cO ≲ 1.5 at%). The CRSS increases strongly with decreasing measuring temperature T. Ruano and Elssner concluded intuitively from the non continious shape of the τ-T curve, that besides the interstitially solved single gas atoms also agglomerates of gas atoms should be present in the specimens. These agglomerates act as strong barriers against plastic deformation. - A superposition of the 2 types of barriers (single interstitial gas atoms and agglomerates) could explain the shape of the τ-T curve. TEM studies were performed to prove this assumption of the existence of agglomerates. Hafnium specimens with different 0 content (0.13, 0.65 and 1.17 at%0) were electrolytically thinned and investigated with a Siemens ELMISKOP 102 operated at 125 kV.

Structural and Chemical Properties of MBE Grown Niobium Overlayers on (110) Rutile

1996 ◽  
Vol 441 ◽  
Author(s):  
J. Marien ◽  
T. Wagner ◽  
M. Rühle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Defect Structure ◽  
Chemical Properties ◽  
High Energy ◽  
Initial Growth ◽  
High Energy Electron ◽  
Transmission Electron ◽  
Different Temperatures ◽  
And Chemical Properties

AbstractThin Nb films were grown by MBE in a UHV chamber at two different temperatures (50°C and 950°C) on the (110) surface of TiO2 (rutile).At a growth temperature of 50°C, reflection high energy electron diffraction (RHEED) revealed epitaxial growth of Nb on rutile: (110)[001] TiO2 ¦¦ (100)[001] Nb. In addition, investigations with Auger electron spectroscopy (AES) revealed that a chemical reaction took place between the Nb overlayer and the TiO2 substrate at the initial growth stage. A 2 nm thick reaction layer at the Nb/TiO2 interface has been identified by means of conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM).At a substrate temperature of 950°C, during growth, the Nb film was oxidized completely, and NbO2 grew epitaxially on TiO2. The structure and the chemical composition of the overlayers have been investigated by RHEED, AES, CTEM and HRTEM. Furthermore, it was determined that the reaction of Nb with TiO2 is governed by the defect structure of the TiO2 and the relative oxygen affinities of Nb and TiO2.

Preparation and Property of Al87Ce3Ni8.5Mn1.5 Nanophase Amorphous Composites

2011 ◽  
Vol 412 ◽  
pp. 263-266
Author(s):  
Hong Wei Zhang ◽  
Li Li Zhang ◽  
Feng Rui Zhai ◽  
Jia Jin Tian ◽  
Can Bang Zhang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Single Phase ◽  
Volume Fraction ◽  
Material Structure ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Transmission Electron ◽  
Different Temperatures

The higher mechanical strength of Al87Ce3Ni8.5Mn1.5 nanophase amorphous composites has been obtained with two methods. The first nanophase amorphous composites are directly produced by the single roller spin quenching technology. The method taken for the second nanophase amorphous composites is at first to obtain amorphous single-phase alloy, followed by annealed at different temperatures .The formative condition, the microstructure, the particle size, the volume fraction of α-Al phase and microhardness of nanophase amorphous composites etc have been investigated and compared by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The microstructure of composites produced by the second method is higher than the former, the fabricated material structure of the system is more uniform and the process is easier to control.

Dislocations around precipitates in AlGaN epilayers

2002 ◽  
Vol 17 (8) ◽  
pp. 2007-2011 ◽  
Author(s):  
Junyong Kang ◽  
Shin Tsunekawa ◽  
Atsuo Kasuya
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Shear Stress ◽  
Dislocation Loop ◽  
Edge Dislocation ◽  
Concentration Change ◽  
Homogeneous Shear ◽  
Transmission Electron ◽  
Shape And Size ◽  
Chemical Force

Dislocations around precipitates in undoped AlGaN were investigated by transmission electron microscopy. The dislocation images were taken under different diffraction conditions. The dislocations are classified into two types, a pure edge dislocation loop and a close-;coiled helical dislocation. Both types of dislocations were found to depend on the shape and size of the precipitate sources. It is suggested that the pure edge dislocation loop results from homogeneous shear stress and the close-;coiled helical dislocation is caused by spherically symmetrical stress concentration at round ends of the precipitates and chemical force due to defect concentration change.

In situ Transmission Electron Microscopy and Nanoindentation Studies of Phase Transformation and Pseudoelasticity of Shape-memory Titanium-nickel Films

2005 ◽  
Vol 20 (7) ◽  
pp. 1808-1813 ◽  
Author(s):  
X.-G. Ma ◽  
K. Komvopoulos
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Phase Transformation ◽  
Shape Memory ◽  
Heating And Cooling ◽  
Transmission Electron ◽  
Different Temperatures ◽  
Titanium Nickel ◽  
In Situ Heating

Transmission electron microscopy (TEM) and nanoindentation, both with in situ heating capability, and electrical resistivity measurements were used to investigate phase transformation phenomena and thermomechanical behavior of shape-memory titanium-nickel (TiNi) films. The mechanisms responsible for phase transformation in the nearly equiatomic TiNi films were revealed by heating and cooling the samples inside the TEM vacuum chamber. Insight into the deformation behavior of the TiNi films was obtained from the nanoindentation response at different temperatures. A transition from elastic-plastic to pseudoelastic deformation of the martensitic TiNi films was encountered during indentation and heating. In contrast to the traditional belief, the martensitic TiNi films exhibited a pseudoelastic behavior during nanoindentation within a specific temperature range. This unexpected behavior is interpreted in terms of the evolution of martensitic variants and changes in the mobility of the twinned structures in the martensitic TiNi films, observed with the TEM during in situ heating.

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