Hrtem Studies of Dislocations and Interfaces in TiAl

1996 ◽  
Vol 466 ◽  
Author(s):  
M. J. Mills ◽  
J. M.K. Wiezorek ◽  
H. L. Fraser
Keyword(s):  
Single Phase ◽  
Stacking Fault ◽  
Interface Plane ◽  
Two Phase ◽  
Transmission Electron ◽  
Interphase Boundaries ◽  
Common Observation ◽  
Interface Structures ◽  
Fully Lamellar

ABSTRACTIn this paper, we summarize the results of high resolution transmission electron microscopy investigations of the structure of dislocations and interphase boundaries in Ti-Al alloys. Dislocations of the type 1/2<110] and 1/2<112] have been examined in 60° and 90° orientations, respectively, in single-phase Ti-52 at%Al. The former dislocation exhibits an extremely compact core configuration, suggesting a high complex stacking fault energy, while the latter is dissociated the scale of several nanometers in a coupled intrinsic/extrinsic stacking fault configuration. Two types of α2/γ interface structures have been observed in nearly fully-lamellar Ti-48 at%Al. The first is consistent with the common observation of structural ledges due to 1/6<112> dislocations in the interface plane. The second interface type consists of a quasi-periodic array of 1/2<110] dislocations which do not lie in the interface, and appear to be contained wholy within the γ phase. The possible implications of these observations with respect to the mechanical behavior of both single-phase γ and two-phase lamellar microstructures are discussed.

The Effect of Deposition and Annealing Conditions on the Microstructure of Al-Cu and Al-Cu-Si Thin Films

1991 ◽  
Vol 229 ◽  
Author(s):  
M. Park ◽  
S. J. Krause ◽  
S. R. Wilson
Keyword(s):  
Single Phase ◽  
Alloy Composition ◽  
Phase Region ◽  
Annealed Condition ◽  
Two Phase ◽  
Annealing Conditions ◽  
Transmission Electron ◽  
Sputter Deposited ◽  
Cu Thin Film

AbstractThe effect of deposition temperature and the addition of Si to sputter deposited Al-Cu thin-film microstructure was studied with transmission electron microscopy. Films were studied in the as-deposited and annealed condition. The effects of thermal treatment were studied with in-situ hot stage microscopy. Al2Cu (θ) precipitated at the grain boundaries and the sublayer interface. At higher deposition temperatures, with alloy composition in single phase region (Al-1.5 wt.%Cu), Al2Cu precipitated during cooldown. At lower temperatures, in the two phase Al-0 region, Al2Cu precipitated during deposition. The addition of Si caused formation of Si precipitates and retarded Al2Cu precipitation during deposition or cooldown.

Ultra-Hard Nanostructured Al-Si Thin Films

2005 ◽  
Vol 494 ◽  
pp. 13-18
Author(s):  
Velimir Radmilović ◽  
D. Mitlin ◽  
U. Dahmen
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Mechanical Performance ◽  
High Rate ◽  
Hard Phase ◽  
Two Phase ◽  
Transmission Electron ◽  
Order Of Magnitude ◽  
Dense Distribution

We show that it is possible to use high rate co-evaporation of Al and Si onto room temperature substrates to achieve a novel two-phase nanoscale microstructure. These nanocomposites have a hardness as high as 4GPa (Al-23at.%Si), and display noticeable plasticity. Films with compositions of Al-12at.%Si and pure Al (used as baseline) were analyzed using transmission electron microscopy (TEM). The scale of the Al-12at.%Si microstructure is an order of magnitude finer compared to that of pure Al films. It consists of a dense distribution of spherical nanoscale Si particles separating irregularly-shaped small Al grains. These new structures may have a mechanical performance advantage over conventional single phase nanomaterials due to the role of the dispersed hard phase in promoting strain hardening.

On the Role of Lamellar Interfaces on the Strength and Ductility of Two-Phase Titanium-Aluminum

1998 ◽  
Vol 552 ◽  
Author(s):  
Jürg M. K Wiezorek ◽  
Xiao Dong Dong ◽  
Michael J. Mills ◽  
Hamish L Fraser
Keyword(s):  
Dislocation Slip ◽  
Two Phase ◽  
Shear Transfer ◽  
Transmission Electron ◽  
Fully Lamellar ◽  
Deformation Modes ◽  
Macroscopic Shape ◽  
Transfer Mechanisms ◽  
Strength And Ductility

ABSTRACTThe deformation mechanisms active in hard orientation compressed pst-TiAl have been studied by transmission electron microscopy (TEM). The observed deformation modes involved soft superdislocation and hard ordinary dislocation slip, and hard twin systems. The transfer of these twin shears occurred across all types of (γ/γ)-interfaces. Transfer mechanisms have been determined on the basis of crystallographic analyses of the TEM data. The active modes of deformation were consistent with macroscopic shape changes observed for the pst-TiAl when the twin shear transfer mechanisms were considered. Based on these observations it has been proposed that the strength and ductility of polycrystalline fully-lamellar TiAl may be improved by reducing the width of both γ- and α2-lamellae.

The Disordering Process in an Ll2 Ordered Alloy

1984 ◽  
Vol 39 ◽  
Author(s):  
J. A. Horton ◽  
A. Dasgupta ◽  
C. T. Liu
Keyword(s):  
Electron Microscopy ◽  
Phase Field ◽  
Room Temperature ◽  
Single Phase ◽  
Antiphase Boundary ◽  
Two Phase ◽  
Ripening Process ◽  
Transmission Electron ◽  
Complete Alignment ◽  
Single Phase Field

ABSTRACTThe antiphase boundary (APB) structure and the disordering process have been studied by transmission electron microscopy (TEM) in a long-rangeordered alloy with Ll2 structure and composition (Ni70Fe30)3(V58Al40Ti2). With an increase in temperature from a single-phase field into a two-phase field, disordering occurs both homogeneously within ordered domains and heterogeneously along APBs. Disordering continues by a ripening process with the disordered islands shrinking while the disordered bands on the prior APBs grow. The APBs are partially aligned on {100} while the material is single phase. As disordering proceeds, the degree of alignment of the disordered bands on {100} increases until complete alignment results. A correlation of the APB structure with room temperature mechanical properties indicates no dramatic change at the transition to the two-phase structure.

Microstructure and Mechanical Properties of Fe-Ni-Mn-Al Alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
M. W. Wittmann ◽  
I. Baker ◽  
J. A. Hanna
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Transmission Electron Microscopy ◽  
Single Phase ◽  
Al Alloys ◽  
Chemical Compositions ◽  
Two Phase ◽  
Microstructure And Mechanical Properties ◽  
Transmission Electron ◽  
Cast Alloys

ABSTRACTIn an attempt to produce a two-phase alloy consisting of a L21–structured (Fe, Ni)2MnAl-based phase in either a B2 or b.c.c. matrix, seven Fe-Ni-Mn-Al alloys were cast. Transmission electron microscopy (TEM) of the as-cast alloys revealed a range of microstructures including single phase L21, a f.c.c./B2 eutectic, and alternating, coherent 10–60 nm wide ordered and disordered b.c.c. rods aligned along <100>. A description of the phases, including chemical compositions and hardnesses is presented.

Influence of Heat Treatments on Microstructures in an Fe-Co-V Alloy

1974 ◽  
Vol 32 ◽  
pp. 512-513
Author(s):  
S. Mahajan ◽  
M. R. Pinnel ◽  
J. E. Bennett
Keyword(s):  
Single Phase ◽  
Alloy Composition ◽  
Supersaturated Solid Solution ◽  
Cell Formation ◽  
Heat Treatments ◽  
Air Cooling ◽  
Iced Brine ◽  
Transmission Electron ◽  
The Matrix ◽  
Bcc Structure

The microstructural changes in an Fe-Co-V alloy (composition by wt.%: 2.97 V, 48.70 Co, 47.34 Fe and balance impurities, such as C, P and Ni) resulting from different heat treatments have been evaluated by optical metallography and transmission electron microscopy. Results indicate that, on air cooling or quenching into iced-brine from the high temperature single phase ϒ (fcc) field, vanadium can be retained in a supersaturated solid solution (α2) which has bcc structure. For the range of cooling rates employed, a portion of the material appears to undergo the γ-α2 transformation massively and the remainder martensitically. Figure 1 shows dislocation topology in a region that may have transformed martensitically. Dislocations are homogeneously distributed throughout the matrix, and there is no evidence for cell formation. The majority of the dislocations project along the projections of <111> vectors onto the (111) plane, implying that they are predominantly of screw character.

A TEM study of the influence of microstructure on the superplastic behavior of a U-5.8 wt.% Nb alloy

1986 ◽  
Vol 44 ◽  
pp. 568-569
Author(s):  
G. Mackiewicz Ludtka
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Phase Field ◽  
Single Phase ◽  
Superplastic Behavior ◽  
Two Phase ◽  
Single Phase Field

Historically, metals exhibit superplasticity only while forming in a two-phase field because a two-phase microstructure helps ensure a fine, stable grain size. In the U-5.8 Nb alloy, superplastici ty exists for up to 2 h in the single phase field (γ1) at 670°C. This is above the equilibrium monotectoid temperature of 647°C. Utilizing dilatometry, the superplastic (SP) U-5.8 Nb alloy requires superheating to 658°C to initiate the α+γ2 → γ1 transformation at a heating rate of 1.5°C/s. Hence, the U-5.8 Nb alloy exhibits an anomolous superplastic behavior.

Interface structures in polycrystalline ceramic materials

1986 ◽  
Vol 44 ◽  
pp. 468-471
Author(s):  
K. J. Morrissey
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Physical And Mechanical Properties ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Polycrystalline Materials ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Interface Structures

Grain boundaries and interfaces play an important role in determining both physical and mechanical properties of polycrystalline materials. To understand how the structure of interfaces can be controlled to optimize properties, it is necessary to understand and be able to predict their crystal chemistry. Transmission electron microscopy (TEM), analytical electron microscopy (AEM,), and high resolution electron microscopy (HREM) are essential tools for the characterization of the different types of interfaces which exist in ceramic systems. The purpose of this paper is to illustrate some specific areas in which understanding interface structure is important. Interfaces in sintered bodies, materials produced through phase transformation and electronic packaging are discussed.

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