Interface Related Strength Phenomena in Two-Phase Titanium Aluminides

1999 ◽  
Vol 586 ◽  
Author(s):  
U. Christoph ◽  
M. Oehring ◽  
F. Appel
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Microscope Study ◽  
Lamellar Structure ◽  
Electron Microscope Study ◽  
Titanium Aluminides ◽  
Intermetallic Phases ◽  
Dislocation Loops ◽  
Two Phase ◽  
Interfacial Dislocations

ABSTRACTPhase equilibria and transformations in near-equiatomic titanium aluminides lead to the formation of a lamellar structure comprising of the intermetallic phases α2(Ti3Al) and γ(TiAl). Due to the differences in lattice parameters and crystal structure, coherency stresses and mismatch structures occur at various types of semicoherent interfaces present in the material. The present paper reports an electron microscope study of the atomic structure of the interfaces. The residual coherency stresses present at the interfaces were determined by analysing the curvature of dislocation loops which were emitted from the network of interfacial dislocations. The implication of these stresses on creep will be discussed.

An Electron Microscope Study of Diffusion Assisted Dislocation Processes in Intermetallic Gamma TiAl

1999 ◽  
Vol 589 ◽  
Author(s):  
F. Appel ◽  
U. Lorenz ◽  
M. Oehring
Keyword(s):  
Electron Microscope ◽  
Microscope Study ◽  
Electron Microscope Study ◽  
Structural Changes ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Strength Properties ◽  
Two Phase ◽  
Term Creep ◽  
Dislocation Sources

AbstractThe paper reports an electron microscope study of diffusion controlled deformation mechanisms in two-phase titanium aluminides which apparently cause the degradation of the strength properties at elevated temperatures. Climb velocities were analyzed in terms the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation sources. Particular emphasis was paid on structural changes occurring during long-term creep, which are apparently associated with dislocation climb.

An electron-microscope study of peristerite plagioclases

1965 ◽  
Vol 35 (269) ◽  
pp. 165-176 ◽  
Author(s):  
S. G. Fleet ◽  
P. H. Ribbe
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Transmission Electron Microscopy ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Microscope Study ◽  
Lamellar Structure ◽  
Electron Microscope Study ◽  
Transmission Electron

SummaryPlagioclase feldspars in the peristerite range An2-An17 have been investigated by transmission electron-microscopy and electron diffraction. All except the more anorthite-rich specimens were found to be unmixed into albite and oligoclase lamellae, between a few hundred and several thousand Å thick and approximately parallel to . A discussion is given of the part played by these lamellae when optical schiller is exhibited; and the effect of heat treatment on the lamellar structure and optical schiller is described.

The Structure and Stress State of Lamellar Interfaces in Two-Phase Titanium Aluminides

1993 ◽  
Vol 318 ◽  
Author(s):  
Fritz Appel ◽  
Ulrich Christoph ◽  
Richard Wagner
Keyword(s):  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Lattice Mismatch ◽  
Deformation Behaviour ◽  
Lamellar Microstructure ◽  
Misfit Strain ◽  
Shear Stresses ◽  
Dislocation Loops ◽  
Two Phase ◽  
Interfacial Dislocations

ABSTRACTTitanium aluminide alloys with compositions slightly on the Ti-rich side of stoichiometry consist of the intermetallic phases α2 (Ti3Al) and γ(TiAl). The two phases form a lamellar microstructure with various types of coherent and semicoherent interfaces. The lattice mismatch occurring at the semicoherent interfaces is largely accommodated by networks of interfacial dislocations. Nevertheless, a significant homogeneous straining seems to remain at these interfaces, resulting in long-range residual stresses. The present paper reports an electron microscope study of the correlation between the misfit strain of adjacent lamellae and the atomic structure of the interfaces. The residual coherency stresses were determined by analyzing the curvature of dislocation loops which were emitted from the network of the interfacial dislocations. The estimated stresses are close to the shear stresses applied during macroscopic deformation experiments. The effects of these stresses on the deformation behaviour of the material are discussed.

Ultrastructure of Plant Leaf Tissue Infected with Mite-Borne Viral-Like Pathogens

1970 ◽  
Vol 28 ◽  
pp. 178-179 ◽  
Author(s):  
O. E. Bradfute ◽  
R. E. Whitmoyer ◽  
L. R. Nault
Keyword(s):  
Triticum Aestivum ◽  
Zea Mays ◽  
Electron Microscope ◽  
Hordeum Vulgare ◽  
Microscope Study ◽  
Electron Microscope Study ◽  
Leaf Tissue ◽  
Leaf Ultrastructure ◽  
Double Membrane ◽  
Aceria Tulipae

A pathogen transmitted by the eriophyid mite, Aceria tulipae, infects a number of Gramineae producing symptoms similar to wheat spot mosaic virus (1). An electron microscope study of leaf ultrastructure from systemically infected Zea mays, Hordeum vulgare, and Triticum aestivum showed the presence of ovoid, double membrane bodies (0.1 - 0.2 microns) in the cytoplasm of parenchyma, phloem and epidermis cells (Fig. 1 ).

Sign in / Sign up

Export Citation Format

Share Document