Effects of long-period superstructures on plastic properties in Al-rich TiAl single crystals

2004 ◽  
Vol 842 ◽  
Author(s):  
Takayoshi Nakano ◽  
Koutaro Hayashi ◽  
Yukichi Umakoshi ◽  
Yu-Lung Chiu ◽  
Patrick Veyssière
Keyword(s):  
Single Crystals ◽  
Annealing Time ◽  
Annealing Temperature ◽  
Microscopic Level ◽  
Vector Group ◽  
Two Phase ◽  
Plastic Properties ◽  
Long Period ◽  
The Matrix ◽  
Ti Particles

ABSTRACTIn Al-rich TiAl crystals, several long-period superstructures may appear depending on Al composition, annealing temperature and annealing time. Amongst these, Al5Ti3 and h-Al2Ti contain pure Al (002) layers, as in the L10 structure of the matrix, alternating with Ti (002) layers that exhibit an ordered arrangement of the Al atoms in excess. In single crystals with compositions ranging from Ti-54.7at.%Al to Ti-62.5at.%Al annealed at 1200°C, the Al5Ti3 long-period superstructure embedded in the L10 matrix develops with increasing Al concentration to finally transform fully into h-Al2Ti for Ti-62.5at.%Al. On the other hand, Al5Ti3 precipitates grow with annealing time at 500°C in Ti-58.0at.%Al.The effects of the Al5Ti3 and h-Al2Ti superstructures on slip properties of 1/2<110] ordinary dislocations are examined both at a macroscopic and a microscopic level. The CRSS for 1/2<110] ordinary slip increases with Al5Ti3 ordering depending on Al composition, or of annealing time in the case of Ti-58.0at.%Al. Dislocations with 1/2<110] Burgers vector group into fourfold configurations to avoid the trailing of extended APBs in Al5Ti3. The CRSS for slip in the <110] direction further increases with the formation of h-Al2Ti particles within the L10 matrix in Ti-62.5at.%Al. By contrast, Ti-62.5at.%Al fully transformed into Al5Ti3 exhibits a CRSS significantly lower than that of the two-phase alloy.

scholarly journals Effect of Reactive SPS on the Microstructure and Properties of a Dual-Phase Ni-Al Intermetallic Compound and Ni-Al-TiB2 Composite

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5668
Author(s):  
Paweł Hyjek ◽  
Iwona Sulima ◽  
Piotr Malczewski ◽  
Krzysztof Bryła ◽  
Lucyna Jaworska
Keyword(s):  
Intermetallic Compound ◽  
Tribological Properties ◽  
Matrix Material ◽  
Dual Phase ◽  
Compression Tests ◽  
Two Phase ◽  
Alloy Matrix ◽  
Plastic Properties ◽  
Mechanical And Tribological Properties ◽  
The Matrix

As part of the tests, a two-phase NiAl/Ni3Al alloy and a composite based on this alloy with 4 vol% addition of TiB2 were produced by the reactive FAST/SPS (Field Assisted Sintering Technology/Spark Plasma Sintering) sintering method. The sintering process was carried out at 1273 K for 30 s under an argon atmosphere. The effect of reactive SPS on the density, microstructure, and mechanical and tribological properties of a dual-phase Ni-Al intermetallic compound and Ni-Al-TiB2 composite was investigated. Products obtained were characterized by a high degree of sintering (over 99% of the theoretical density). The microstructure of sinters was characterized by a large diversity, mainly in regard to the structure of the dual-phase alloy (matrix). Compression tests showed satisfactory plastic properties of the manufactured materials, especially at high temperature (1073 K). For both materials at room temperature, the compressive strength was over 3 GPa. The stress–strain curves were observed to assume a different course for the matrix material and composite material, including differences in the maximum plastic flow stress depending on the test temperature. The brittle-to-ductile transition temperature was determined to be above 873 K. The research has revealed differences in the physical, mechanical and tribological properties of the produced sinters. However, the differences favourable for the composite were mostly the result of the addition of TiB2 ceramic particles uniformly distributed on grain boundaries.

Decarburization of 0.21C-1.3Mn-0.2Si Steel for Hot Stamping at Various Heating Temperatures

2011 ◽  
Vol 172-174 ◽  
pp. 887-892 ◽  
Author(s):  
Koutarou Hayashi ◽  
Toshinobu Nishibata ◽  
Nobusato Kojima ◽  
Masanori Kajihara
Keyword(s):  
Annealing Time ◽  
Single Phase ◽  
Annealing Temperature ◽  
Volume Diffusion ◽  
Hot Stamping ◽  
Ambient Atmosphere ◽  
Uniform Thickness ◽  
Two Phase ◽  
Annealing Conditions ◽  
Parabolic Relationship

In order to examine the decarburization behavior in the hot stamping (HS) method, the dependence of the microstructure evolution on the annealing temperature was experimentally studied using a Fe-0.21 mass% C-1.3 mass% Mn-0.2 mass% Si steel. The steel was isothermally annealed in the temperature range ofT= 773-1173 K for various times oft= 100-12800 s in an ambient atmosphere. Here, the steel possesses the ferrite (α) + cementite (θ) two-phase microstructure atT= 773-923 K, the α + austenite (γ) two-phase microstructure atT= 1013-1073 K, and the γ single-phase microstructure atT= 1093-1173 K. During annealing atT= 1013-1073 K fort= 1600 s, however, the α layer with a uniform thickness is formed at the surface of the steel due to decarburization and gradually grows into the inside. Such formation of the a layer was not clearly observed atT973 K and T1093 K. Thus, the formation of the α layer hardly occurs under the HS annealing conditions. AtT= 1033 K, the thickness of the α layer is mostly proportional to the square root of the annealing time. Such a relationship is called the parabolic relationship. Furthermore, the grain size of the α layer monotonically increases with increasing annealing time. Hence, the parabolic relationship guarantees that the growth of the α layer is controlled by volume diffusion.

The Mechanical Properties of Near-equiatomic B2/f.c.c. FeNiMnAl Alloys

2013 ◽  
Vol 1516 ◽  
pp. 249-254 ◽  
Author(s):  
Xiaolan Wu ◽  
Ian Baker ◽  
Hong Wu ◽  
Paul R. Munroe
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Temperature Dependence ◽  
Orientation Relationship ◽  
Annealing Time ◽  
Two Phase ◽  
Chemical Partitioning ◽  
The Matrix ◽  
In Situ Heating

ABSTRACTTwo types of as-cast microstructures have been observed in a series of near-equiatomic FeNiMnAl alloys: 1) an ultrafine microstructure in Fe30Ni20Mn20Al30 [1] and Fe25Ni25Mn20Al30, which consists of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases aligned along <100>; and 2) a fine two-phase microstructure in Fe30Ni20Mn30Al20 and Fe25Ni25Mn30Al20, which consists of alternating (Fe, Mn)-rich f.c.c. and (Ni, Al)-rich B2-ordered platelets with an orientation relationship close to f.c.c (002) // B2 (002); f.c.c. [011] // B2 [001] [2]. The phases in Fe25Ni25Mn20Al30 coarsened upon annealing with no significant change in the chemical partitioning. The hardness behavior was studied as a function of the annealing time at 823 K. AnL21-to-B2 transition, which occurred at 573-623K, was observed using in-situ heating in a TEM. After annealing at 973 K for 100 h, needle-shaped clusters of (Fe, Mn)-rich precipitates were observed along the grain boundaries and in the matrix. The temperature dependence of the yield strength of as-cast Fe25Ni25Mn20Al30 was also studied.

Effect of A12Ti Phase on Plastic Behavior in Ti-62.5at%Al Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
Takayoshi Nakano ◽  
Koutarou Hayashi ◽  
Keishi Ashida ◽  
Yukichi Umakoshi
Keyword(s):  
Single Crystals ◽  
Annealing Temperature ◽  
Volume Fraction ◽  
Plastic Behavior ◽  
Research Article ◽  
Structure Morphology ◽  
Plastic Deformation Behavior ◽  
The Matrix ◽  
Higher Temperature ◽  
Loading Axis

ABSTRACTThe microstructure and plastic deformation behavior in Ti-62.5at.%Al single crystals were investigated focusing on effect of the formation of h- and r-AI2Ti precipitates. Crystal structure, morphology and volume fraction of the precipitates depended strongly on the annealing temperature. The r-A12Ti phase precipitated as a plate in the Li0 matrix containing A15Ti3 superstructure below 1200°C, while the h-Al2Ti phase appeared at the higher temperature. The r-A12Ti had six-fold periodicity along the c-axis of the L10 structure and formed a semi-coherent boundary with the matrix maintaining an orientation relationship with {101)r-A12Ti//{101)L10 In contrast, small particles of h-A12Ti with three-fold periodicity along the b-axis were homogeneously distributed in the matrix forming an obscure coherent phase boundary.Yield stress for specimens with a [201] loading axis anomaly increased showing a maximum peak around 800°C and then rapidly decreased. [111] <110] slip was dominant in the Li0 matrix and research-article-Al2Ti precipitates at temperatures below the peak, while slip occurred on (001) above the peak temperature. The anomalous strengthening and the change in operative slip system were discussed focusing on the effect of anisotoropy of APB energy and formation of Al2Ti precipitates.

Effects of Carbide Precipitate Formation on the Change in Ultrasonic Velocity in Austenitic Stainless Steels

2014 ◽  
Author(s):  
Taira Okita ◽  
Junji Etoh ◽  
Mitsuyuki Sagisaka ◽  
Takashi Matsunaga ◽  
Yoshihiro Isobe
Keyword(s):  
Stainless Steels ◽  
Annealing Time ◽  
Annealing Temperature ◽  
Austenitic Stainless Steels ◽  
Velocity Change ◽  
Precipitate Formation ◽  
Annealing Conditions ◽  
The Matrix ◽  
Velocity Changes ◽  
Carbide Precipitate

Ultrasonic tests were conducted for 304 type austenitic stainless steels with different annealing conditions and effects of carbide precipitate formation on the velocity changes were evaluated. The velocity increased with higher annealing temperature and/or longer annealing time. SEM observations indicated that carbide precipitates were formed mainly on grain boundaries. Results show that it is not the precipitation itself but the removal of carbon from the matrix that determines the velocity change.

Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

1978 ◽  
Vol 36 (1) ◽  
pp. 594-595
Author(s):  
N.J. Long ◽  
M.H. Loretto ◽  
C.H. Lloyd
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Thin Foil ◽  
Age Hardening ◽  
Dispersion Strengthening ◽  
Accurate Picture ◽  
The Matrix ◽  
Very High ◽  
Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

Transition alpha structure in beta-isomorphous Nb-Hf alloys

1987 ◽  
Vol 45 ◽  
pp. 232-233
Author(s):  
R.W. Carpenter ◽  
Changhai Li ◽  
David J. Smith
Keyword(s):  
Solid Solution ◽  
Solution Phase ◽  
Miscibility Gap ◽  
Large Strains ◽  
Solid Solution Phase ◽  
Two Phase ◽  
Diffuse Intensity ◽  
Metastable Form ◽  
The Matrix ◽  
Equilibrium Morphology

Binary Nb-Hf alloys exhibit a wide bcc solid solution phase field at temperatures above the Hfα→ß transition (2023K) and a two phase bcc+hcp field at lower temperatures. The β solvus exhibits a small slope above about 1500K, suggesting the possible existence of a miscibility gap. An earlier investigation showed that two morphological forms of precipitate occur during the bcc→hcp transformation. The equilibrium morphology is rod-type with axes along <113> bcc. The crystallographic habit of the rod precipitate follows the Burgers relations: {110}||{0001}, <112> || <1010>. The earlier metastable form, transition α, occurs as thin discs with {100} habit. The {100} discs induce large strains in the matrix. Selected area diffraction examination of regions ∼2 microns in diameter containing many disc precipitates showed that, a diffuse intensity distribution whose symmetry resembled the distribution of equilibrium α Bragg spots was associated with the disc precipitate.

Using crystallographic symmetry in diffraction and contrast analysis

1989 ◽  
Vol 47 ◽  
pp. 504-505
Author(s):  
U. Dahmen ◽  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
High Symmetry ◽  
Two Phase ◽  
Tem Analysis ◽  
Crystallographic Symmetry ◽  
The Matrix ◽  
Contrast Analysis ◽  
Practical Tool ◽  
Convergent Beam ◽  
Beam Diffraction

Despite the increased use of convergent beam diffraction, symmetry concepts in their more general form are not commonly applied as a practical tool in electron microscopy. Crystal symmetry provides an abundance of information that can be used to facilitate and improve the TEM analysis of crystalline solids. This paper draws attention to some aspects of symmetry that can be put to practical use in the analysis of structures and morphologies of two-phase materials.It has been shown that the symmetry of the matrix that relates different variants of a precipitate can be used to determine the axis of needle- or lath-shaped precipitates or the habit plane of plate-shaped precipitates. By tilting to a special high symmetry orientation of the matrix and by measuring angles between symmetry-related variants of the precipitate it is possible to find their habit from a single micrograph.

scholarly journals Growth of single crystals in the (Na1/2Bi1/2)TiO3–(Sr1–xCax)TiO3 system by solid state crystal growth

2021 ◽  
Author(s):  
Phan Gia Le ◽  
Huyen Tran Tran ◽  
Jong-Sook Lee ◽  
John G. Fisher ◽  
Hwang-Pill Kim ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Solid State ◽  
Single Crystal ◽  
Single Crystals ◽  
Piezoelectric Properties ◽  
Single Crystal Growth ◽  
Crystal Growth Rate ◽  
Large Strains ◽  
Growth Technique ◽  
The Matrix

AbstractCeramics based on (Na1/2B1/2)TiO3 are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1−x)(Na1/2Bi1/2)TiO3-xSrTiO3 system exhibits a morphotropic phase boundary at x = 0.2–0.3, leading to high values of inverse piezoelectric constant d*33, which can be further improved by the use of single crystals. In our previous work, single crystals of (Na1/2B1/2)TiO3-SrTiO3 and (Na1/2B1/2)TiO3-CaTiO3 were grown by the solid state crystal growth technique. Growth in the (Na1/2B1/2)TiO3-SrTiO3 system was sluggish whereas the (Na1/2B1/2)TiO3-CaTiO3 single crystals grew well. In the present work, 0.8(Na1/2Bi1/2)TiO3-0.2(Sr1−xCax)TiO3 single crystals (with x = 0.0, 0.1, 0.2, 0.3, 0.4) were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate. The dependence of mean matrix grain size, single crystal growth distance, and electrical properties on the Ca concentration was investigated in detail. These investigations indicated that at x = 0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced. Replacing Sr with Ca increased the shoulder temperature Ts and temperature of maximum relative permittivity Tmax, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.

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