Deformation of Diffusion-Bonded Bi-Pst and Directionally Solidified Crystals of TiAl

1996 ◽  
Vol 460 ◽  
Author(s):  
K. Kishida ◽  
D. R. Johnson ◽  
Y. Shimada ◽  
Y. Masuda ◽  
H. Inui ◽  
...  
Keyword(s):  
Directional Solidification ◽  
Diffusion Bonding ◽  
Flow Behavior ◽  
Lamellar Microstructure ◽  
Growth Direction ◽  
Current Status ◽  
Directionally Solidified ◽  
Lamellar Orientation ◽  
Columnar Grain ◽  
And Diffusion

ABSTRACTWith a data base now available on the microstructural characteristics and the deformation, fracture and macroscopic flow behavior of polysynthetically twinned (PST) crystals of γ/α2 TiAl-base alloys, an approach to achieve a good combination of strength, ductility and toughness in γ/α2 TiAl-base alloys was proposed using directional solidification (DS) techniques to produce a columnar grain material with the lamellar orientation aligned parallel to the growth direction. Such alignment of the lamellar microstructure was recently accomplished in γ/α2 TiAl-base alloys of near equiatomic compositions using an appropriately oriented seed crystal from the Ti-Al-Si system.At the same time, bi-PST crystals, each containing a planar boundary parallel to the loading axis were prepared by directional solidification and diffusion bonding of two PST crystals. Such bi-PST crystals were deformed in tension at room temperature and their deformation behavior was examined in terms of the compatibility requirements imposed at the grain boundary and the interaction of the two component PST crystals.In this paper, (i) the current status of our DS processing efforts, (ii) some results of microscopic characterization of grain boundaries in diffusion bonded bi-PST crystals and (iii) results of deformation experiments of bi-PST crystals prepared by DS processing and diffusion bonding, will be reported.

Growth Directions of Primary Phases in Directionally Solidified Ti-45Al-7Nb Alloys

2013 ◽  
Vol 32 (1) ◽  
pp. 69-75
Author(s):  
Jie Yan ◽  
Lijing Zheng ◽  
HuaRui Zhang ◽  
Zhixia Xiao ◽  
Hu Zhang
Keyword(s):  
Deflection Angle ◽  
Primary Dendrite ◽  
Growth Direction ◽  
Directionally Solidified ◽  
Electron Backscattered Diffraction ◽  
Lamellar Orientation ◽  
Primary Dendrite Arm Spacing ◽  
The Deflection Angle ◽  
Solidification Pathway ◽  
Liquid Metal Cooling

AbstractTi-45Al-7Nb alloys are produced by liquid-metal-cooling (LMC) directional solidification (DS) furnace with different temperature gradients (G) at a range of 40–80 K/cm. The growth directions of primary β phases and the deflection angles relative to the 〈100〉β direction were investigated. The solidification pathway of alloy is: Liq. → Liq. + β → β → β + α → α + γ → lamella (α2 + γ) + B2. Primary dendrite arm spacing λ reduced from 611.4 µm to 508.7 µm when G increased from 40 K cm−1 to 80 K cm−1. Grains with lamellar orientation aligned at the angles of 12–15° and 55° to growth direction were favored for various G. The orientations of the γ lamellas in steady-state regions were identified by the electron backscattered diffraction analysis (EBSD). The results indicated that the growth directions of primary bcc-β dendrites were 〈211〉β and 〈110〉β at 40 K/cm, 〈210〉β and 〈211〉β at 50 K/cm and 〈211〉β at 80 K/cm, the deflection angle of 〈211〉β relative to 〈100〉β direction is 35.3°.

Microstructure and Creep of γ-TiAl Containing β-Stabilizer

2007 ◽  
Vol 539-543 ◽  
pp. 1543-1548 ◽  
Author(s):  
Dong Yi Seo ◽  
H. Saari ◽  
Peter Au ◽  
J. Beddoes
Keyword(s):  
Design Criterion ◽  
Grain Structure ◽  
Test Results ◽  
Directionally Solidified ◽  
Tial Alloys ◽  
Lamellar Orientation ◽  
Short And Long Term ◽  
Columnar Grain ◽  
Fully Lamellar

Fully lamellar structures of powder metallurgy (PM), investment cast, and directionally solidified (DS) TiAl alloys containing β stabilizer were produced after stepped cool heat treatment, and interface β precipitates were formed after aging at 950°C. In addition, a columnar grain structure combined with a fully lamellar structure aligned with the load direction and interface β precipitates were formed by directional solidification and subsequent heat treatments. Creep test results of PM TiAl indicate that controlling the initial microstructures is also critical for balancing the primary and steady-state creep resistance during short and long-term tests. DS TiAl alloy exhibits a significant reduction of the primary strain and creep rate compared to polycrystalline TiAl due to the unique DS microstructure. Therefore, a DS microstructure with proper lamellar orientation and controlled interface β precipitation is the ideal if maximum time to a relatively small (<0.5%) strain is the design criterion of merit.

Alignment of the lamellar orientation of multi-component TiAl alloys by directional solidification (DS) and mechanical properties of DS ingots

2002 ◽  
Vol 753 ◽  
Author(s):  
Y. Omiya ◽  
S. Muto ◽  
T. Yamanaka ◽  
D. R. Johnson ◽  
H. Inui ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Directional Solidification ◽  
Lamellar Structure ◽  
Growth Direction ◽  
Alloying Elements ◽  
Tial Alloys ◽  
Creep Properties ◽  
Lamellar Orientation ◽  
Loading Axis ◽  
Better Than

ABSTRACTBy using an appropriately oriented seed from the TiAl-Si system (Ti-43Al-3Si), the TiAl/Ti3Al lamellar structure has been successfully aligned parallel to the growth direction for TiAl ingots of the Ti-Al-Nb, Ti-Al-Nb-Si, Ti-Al-Ta-Si systems on the basis of the recently proposed method to predict the appropriate compositions. The Al equivalents for Nb and Ta are reevaluated in order to extend the proposed method to large addition (above a several at. %) of these alloying elements. These DS ingots with the lamellar structure all aligned parallel to the loading axis exhibit creep properties far better than conventionally produced TiAl ingots so far reported.

scholarly journals The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1203 ◽  
Author(s):  
Ning Cui ◽  
Qianqian Wu ◽  
Jin Wang ◽  
Binjiang Lv ◽  
Fantao Kong
Keyword(s):  
Directional Solidification ◽  
Deformation Behavior ◽  
Lamellar Microstructure ◽  
Microstructural Characterization ◽  
Zone Melting ◽  
Compression Tests ◽  
Directionally Solidified ◽  
Β Phase ◽  
Lamellar Interface ◽  
Loading Axis

A β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

Lamellar orientation and growth direction of α phase in directionally solidified Ti-46Al-0.5W-0.5Si alloy

2012 ◽  
Vol 27 ◽  
pp. 38-45 ◽  
Author(s):  
Xinzhong Li ◽  
Jianglei Fan ◽  
Yanqing Su ◽  
Dongmei Liu ◽  
Jingjie Guo ◽  
...  
Keyword(s):  
Growth Direction ◽  
Directionally Solidified ◽  
Α Phase ◽  
Lamellar Orientation

Magnetic and Mechanical Properties of Directionally Solidified Fe-6.5wt.%Si Alloy

2011 ◽  
Vol 687 ◽  
pp. 122-128
Author(s):  
Y. S. Deng ◽  
Xian Shi Fang ◽  
Feng Ye ◽  
Y. Qiao ◽  
Jun Pin Lin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Directional Solidification ◽  
Grain Growth ◽  
Magnetic Induction ◽  
Crystal Orientation ◽  
Grain Structure ◽  
Directionally Solidified ◽  
Columnar Grains ◽  
Columnar Grain ◽  
Saturation Magnetic Induction

Directional solidification technique was employed to produce Fe-6.5wt.%Si alloy with coarse columnar-grain structure, which was almost single crystal. The sectional diameters of columnar grains range from 2.2 to 6.8 mm. The saturation magnetic induction was 2.39 T. In this work, grain growth started from either a Fe-6.5wt.%Si crystal which was not melted at bottom of the specimen or a freely nucleated Fe-6.5wt.%Si crystal as the specimen was completely melted. It was found that the starting situation of the directional solidification plays an important role in the crystal orientation, and hence in properties.

The effect of back-melting on the continuity of crystallographic orientation and composition in HgZnTe

1992 ◽  
Vol 50 (2) ◽  
pp. 1696-1697
Author(s):  
H.J. Zuo ◽  
M.W. Price ◽  
R.D. Griffin ◽  
R.A. Andrews ◽  
G.M. Janowski
Keyword(s):  
Directional Solidification ◽  
Space Shuttle ◽  
Solidification Process ◽  
Space Experiment ◽  
Infrared Detection ◽  
Directionally Solidified ◽  
Crystallographic Defects ◽  
Semiconducting Alloys ◽  
Uniform Composition ◽  
Growth Experiments

The II-VI semiconducting alloys, such as mercury zinc telluride (MZT), have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities and crystallographic imperfections adversly affect the performance of MZT infrared detectors. One source of imperfections in MZT is gravity-induced convection during directional solidification. Crystal growth experiments conducted in space should minimize gravity-induced convection and thereby the density of related crystallographic defects. The limited amount of time available during Space Shuttle experiments and the need for a sample of uniform composition requires the elimination of the initial composition transient which occurs in directionally solidified alloys. One method of eluding this initial transient involves directionally solidifying a portion of the sample and then quenching the remainder prior to the space experiment. During the space experiment, the MZT sample is back-melted to exactly the point at which directional solidification was stopped on earth. The directional solidification process then continues.

Effects of Initial Nucleation Condition at the Start Block on the Grain Size and Growth Direction in Directionally Solidified CM247LC Superalloy

2011 ◽  
Vol 49 (01) ◽  
pp. 58-63
Author(s):  
Hye-Young Yoon ◽  
Je-Hyun Lee ◽  
Hyeong-Min Jung ◽  
Seong-Moon Seo ◽  
Chang-Young Jo ◽  
...  
Keyword(s):  
Grain Size ◽  
Growth Direction ◽  
Directionally Solidified ◽  
Initial Nucleation

Impurity-Induced Layer Disordering in AlxGa1−xAs-GaAs Quantum well Heterostructures -

1988 ◽  
Vol 126 ◽  
Author(s):  
D. G. Deppe ◽  
L. J. Guido ◽  
N. Holonyak
Keyword(s):  
Experimental Data ◽  
Quantum Well ◽  
Laser Diodes ◽  
Growth Direction ◽  
High Power Laser ◽  
Power Laser ◽  
Frenkel Defects ◽  
Buried Heterostructure ◽  
And Diffusion ◽  
Disordered Regions

ABSTRACTSelective interdiffusion of Al and Ga at AlxGa1−x As-GaAs heterointerfaces can be carried out by conventional masking procedures and diffusion of acceptor impurities (e.g., Zn), or donor impurities (e.g., Si), or also by ion implantation. This process, impurity-induced layer disordering (IILD), makes it possible to convert quantum well heterostructures (QWHs) such as AlxGa1−xAs-GaAs superlattices (SLs) into bulk homogeneous AlyGa1−yAs where y is the average Al composition of the QWH or SL. Since th IILY process is maskable and thus selective, heterojunctions can be formed in directions perpendicular to the crystal growth direction, i.e., between as-grown “ordered” and IILD “disordered” regions. To date this process has been used most effectively in the fabrication of buriedheterostructure QW lasers, single and multiple stripe, where the disordered regions provide both optical and electrical confinement. The IILD process has also been used to advantage in the fabrication of high power laser diodes with non-absorbing “windows” at the laser facets and thus with better immunity from facet damage. In this paper we present data on the application of the IILD process to the fabrication of buried-heterostructure QW laser diodes. We also describe possible mechanisms by which the impurity-induced layer disordering proceeds based on Column III “Frenkel” defects and the influence of the crystal Fermi level on the defect solubility. These mechanisms are supported by experimental data.

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