Microstructure and Phase Stability Studies on Heusler Phase Ni2AlHf and G-phase Ni16Hf6Si7 in Directionally Solidified NiAl–Cr(Mo) Eutectic Alloyed with Hf

2000 ◽  
Vol 15 (6) ◽  
pp. 1261-1270 ◽  
Author(s):  
Y. X. Chen ◽  
C. Y. Cui ◽  
Z. Q. Liu ◽  
L. L. He ◽  
J. T. Guo ◽  
...  
Keyword(s):  
Hot Isostatic Pressing ◽  
Aging Treatment ◽  
High Resolution Electron Microscopy ◽  
Boundary Region ◽  
Dislocation Network ◽  
Directionally Solidified ◽  
Heusler Phase ◽  
Resolution Electron ◽  
Good Agreement ◽  
Nial Matrix

Small additions of Hf to directionally solidified NiAl–Cr(Mo) eutectic resulted in precipitation of a high density of Heusler phase Ni2AlHf along with fine G-phase Ni16Hf6Si7. The Heusler phase was mainly located on the grain boundary region. The fine G-phase formed in the presence of Si, which was a contamination resulting from contact with ceramic shell molds during directional solidification of the alloy. These fine G-phases were cuboidal in shape and coherent with the NiAl matrix. After hot isostatic pressing and aging treatment, the fine G-phases completely disappeared. The density of the Heusler phase was partially reduced, and the Heusler particles precipitated preferentially on the NiAl/Cr(Mo) interfaces and grain boundaries of the NiAl matrix. Some Heusler particles precipitated locally within the NiAl matrix, and small amounts of them precipitated within the Cr(Mo) phase. The structures of the NiAl/Ni2AlHf and NiAl/Ni16Hf6Si7 interfaces were investigated by high-resolution electron microscopy. The habit plane of the fine G-phase was {001}NiAl. This result was in good agreement with calculation based on the linear elastic theory. The misfit dislocation network on the NiAl/Ni2AlHf (110) interface was calculated from the O-lattice model and compared with the observation, which showed good agreement.

Misfit Dislocations at Metal/Ceramics Interfaces

1993 ◽  
Vol 319 ◽  
Author(s):  
G. Gutekunst ◽  
J. Mayer ◽  
M. RÜHle
Keyword(s):  
Lattice Mismatch ◽  
High Resolution Electron Microscopy ◽  
Dislocation Network ◽  
Misfit Dislocations ◽  
Burgers Vector ◽  
Resolution Electron ◽  
Substrate Surfaces ◽  
Atomistic Structure ◽  
Good Agreement

AbstractThe atomistic structure of the coherent regions of Nb/A12O3-interfaces of various substrate orientations have been determined by high-resolution electron microscopy (HREM). The substrate surfaces were parallel to (0001)A12O3, (0110)A12O3, (2110)A12O3 and (0112)A12O3. In all cases, the Al sublattice of the A12O3 substrate is continued in the first Nb layer at the interface. This principle results in the unique orientation relationship.The Burgers vectors of the misfit dislocations and the geometry of the dislocation network of all Nb/A12O3-interfaces have been determined by HREM. All Burgers vectors are lattice vectors. Thus no coherent regions with different atomistic structures are found. The Burgers vectors are of the type 1/2<111>. These Burgers vectors correspond to the Burgers vector of bulk dislocations. All Burgers vector components which do not accommodate the lattice mismatch are compensated in the networks. The network geometry is rectangular for the following interface planes: (0110)A12O3||(112)Nb (orientation 2) and (0112)A12O3||(001)Nb. If the interface is parallel to (0001)A12O3 and (111)Nb the geometry is rhombic.The core structure of misfit dislocations of orientation 2 with line direction ξ1=[110] are calculated with an atomistic model and a continuum approach. The calculated core structures are in good agreement with the experimental HREM-micrographs of misfit dislocations of orientation 2.

Electron microscope studies of minerals: phase boundaries in an extremely slowly cooled clinopyroxene (augite)

1983 ◽  
Vol 387 (1792) ◽  
pp. 21-30 ◽  
Keyword(s):  
Phase Interface ◽  
Intermediate Formation ◽  
High Resolution Electron Microscopy ◽  
Cooling History ◽  
The North ◽  
North Side ◽  
Resolution Electron ◽  
History Of ◽  
Ambient Surface ◽  
Good Agreement

High resolution electron microscopy has been used to study the nature of exsolution lamellae that developed during extremely slow and prolonged cooling and depressurization of an aluminium rich augite (high Ca clinopyroxene) taken from a layer of garnet-augite rich gneiss that outcrops on the north side of Scourie Bay, Sutherland, northwest Scotland. The parent clinopyroxene structure evolved with an average cooling rate of ca . 6 x 10 -6 K per year and an average depressurization rate of ca . 0.75 Pa per year over a span of ca . 2 x 10 9 years between 3.0 x 10 9 and 1.0 x 10 9 years ago, and was subsequently stored at close to ambient surface conditions. Three sets of lamellae, which probably formed mainly during the middle of this evolution, were identified as amphibole, pigeonite and hypersthene. Coherent amphibole lamellae, ca . 10 nm thick, exsolved parallel to (010) of the host augite whereas hypersthene formed thicker lamellae 150-250 nm wide, parallel to (100) augite. Again the phase interface is coherent but contains ledges, a few lattice spacings wide, of a pigeonite structure suggesting that the growth of the hypersthene lamellae proceeded via the intermediate formation of pigeonite. Pigeonite forms ca . 90 nm thick lamellae, which extend parallel to an irrational plane (7.96, 0, 1) of host augite at 12° to (100) augite, yet at the same time maintains a coherent interphase boundary. The angle between lamellae of this type and (100) of the host augite is known to be dependent upon composition of the host augite. The quoted value indicates a (Fe+Mn)/(Fe+Mn+Mg) ratio of 0.30 ± 0.05, in good agreement with microprobe data for the host augite, which fall in the range 0.372–0.382. The micrographs also indicate that hypersthene lamellae precede amphibole. The above observations have enabled the relation between the phases and the cooling history of the rock to be established.

High resolution electron microscopy observation of interfacial structures in NiAl-matrix in situ composites reinforced by TiC particulates

1997 ◽  
Vol 12 (7) ◽  
pp. 1790-1795 ◽  
Author(s):  
L. G. Yu ◽  
J. Y. Dai ◽  
Z. P. Xing ◽  
D. X. Li ◽  
J. T. Guo ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Amorphous Layer ◽  
Interfacial Layers ◽  
Resolution Electron ◽  
Interfacial Structures ◽  
Tic Particulates ◽  
Nial Matrix

The structures of interfaces in NiAl-matrix in situ composites reinforced by TiC particulates were studied by means of high-resolution electron microscopy (HREM). No consistent orientation relationship between TiC particles and the NiAl matrix was found. In most cases, TiC particles bonded well to the NiAl matrix free from any interfacial phases. However, in some cases, an interfacial amorphous layer with a thickness of about 3 nm was found. The annealed NiAl–TiC composite showed a good chemical compatibility between the TiC particles and the NiAl matrix, though, some interfacial layers between TiC and NiAl, which were determined to be C-deficient TiC, were found. NiAl precipitates were observed in the TiC particles of the annealed specimens.

HREM of Rapidly Solidified Al-Li-Zr Based Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 54-55
Author(s):  
V. Radmilovic ◽  
G. Thomas ◽  
R. Kilaas ◽  
N. J. Kim
Keyword(s):  
Volume Fraction ◽  
Solution Treatment ◽  
Aging Treatment ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Large Volume Fraction ◽  
Heat Treated ◽  
Resolution Electron ◽  
Rapidly Solidified

During aging of Al-Li-Zr based alloys δ'(Al3Li) precipitates heterogeneously around β'(Al3Zr), forming so-called composite precipitate[l-4], that has important effects on the mechanical behavior of these alloys. As has been observed in several investigations, the addition of small amount of Zr results in a fairly large volume fraction of β' in the microstructure, and this suggests that there may be a partitioning of Li in the β'. In the present investigation, high resolution electron microscopy (HREM) and image simulation have been used to perform detailed characterization of the chemistry and structure of β' precipitate.The alloy Al-3Li-1Cu-0.5Mg-0.5Zr (wt.%) has been heat treated as follows: a) solution treatment at 550°C for 2 hours and water quenching, b) aging treatment at 150°C for 4 hours or at 200°C for 8 hours and c) 10% cold working followed by aging at 175°C for 64 hours. HREM images were taken on a JEOL ARM electron microscope operating at 400 and 800kV. Simulated HREM images of the composite δ'/β' precipitate were calculated using CEMPAS multislice program described by Kilaas[5].

Tem/Hrem Structural Characterization of Directionally Solidified Gaas-Cras Eutectic Crystals

1995 ◽  
Vol 398 ◽  
Author(s):  
Sergei Ruvimov ◽  
Zuzanna Liliental-Weber ◽  
Wendy Swider ◽  
Jack Washburn ◽  
Douglas E. Holmes
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Czochralski Method ◽  
High Resolution Electron Microscopy ◽  
Structural Defects ◽  
Directionally Solidified ◽  
Gaas Matrix ◽  
Resolution Electron ◽  
Ordered Array

ABSTRACTConventional and high resolution electron microscopy have been applied to characterize the microstructure of the CrAs-GaAs eutectic. The CrAs-GaAs eutectic crystals were directionally solidified by the Czochralski method in order to produce an ordered array of CrAs rods embedded in a GaAs matrix. The CrAs rods of 2-3 μm in diameter align parallel to the growth axis of the ingot. Where the GaAs matrix is found to contain structural defects, the CrAs rods are effectively defect-free. The CrAs has an orthorombic structure with the parameters a=3.5±0.1 Å, b=6.2±0.1 Å,c=5.7±0.1 Å.The c-axis is close to the direction of solidification.

A Comparative Study of the Nanocrystalline Material Produced by Sliding Wear and Inert Gas Condensation

1990 ◽  
Vol 206 ◽  
Author(s):  
S. K. Ganapathi ◽  
M. Aindow ◽  
H. L. Fraser ◽  
D. A. Rigney
Keyword(s):  
Sliding Wear ◽  
Nanocrystalline Material ◽  
Rate Sensitivity ◽  
High Resolution Electron Microscopy ◽  
Inert Gas ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Fine Grain ◽  
Resolution Electron ◽  
Good Agreement

ABSTRACTA High Resolution Electron Microscopy (HREM) study of grain boundaries in nanocrystalline copper produced by sliding wear and by inert gas condensation is described. The results in both cases are essentially the same and similar to those in conventional polycrystals. Contrary to reports in the literature, these results do not indicate the presence of a fundamentally different structure in nanocrystalline materials. Measurements of the mechanical properties (such as yield strength, elastic modulus and strain rate sensitivity) of these materials using nanoindentation are also presented. These are found to be in good agreement with values expected from a polycrystalline material with a very fine grain size.

Relaxation of Metamorphic III-V Heterostructures Studied by Digital Processing of HREM Images

1998 ◽  
Vol 523 ◽  
Author(s):  
André Rocher ◽  
Etienne Snoeck ◽  
Léon Goldstein ◽  
Joël Jacquet ◽  
Catherine Fortin
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Transition Zone ◽  
Epitaxial Layer ◽  
Digital Processing ◽  
High Resolution Electron Microscopy ◽  
Dislocation Network ◽  
Misfit Dislocations ◽  
Misfit Stress ◽  
Resolution Electron

AbstractThe crystalline structure of metamorphic heterostructures grown by epitaxy has been studied by digital processing of High Resolution Electron Microscopy (HREM) images. Two systems have been investigated: the GaSb/(001)GaAs, known to be fully relaxed by a perfect Lomer dislocation network and the GaAs/(001)InP relaxed by partial and 60° dislocations randomly distributed. A transition zone can be defined between the perfect substrate and the relaxed epitaxial layer: its thickness is less than 20Å in GaSb/GaAs and more than 80Å in GaAs/InP. These results indicate that the misfit dislocations are only one of the elements involved in the relaxation of misfit stress.

Mechanical Properties of Fe-Modifie Ll2-Type Al3Ti

1990 ◽  
Vol 213 ◽  
Author(s):  
H. R. P. Inoue ◽  
C. V. Cooper ◽  
L. H. Favrow ◽  
Y. Hamada ◽  
C. M. Wayman
Keyword(s):  
Room Temperature ◽  
Boundary Energy ◽  
Large Population ◽  
Hot Isostatic Pressing ◽  
Antiphase Boundary ◽  
High Resolution Electron Microscopy ◽  
Room Temperature Ductility ◽  
Strain Fracture ◽  
Resolution Electron ◽  
Crystallographic Planes

ABSTRACTThe room temperature ductility of an L12-type A13Ti alloy containing 7.5 at.% Fe has been improved substantially by hot isostatic pressing (HIP) after arc casting. This L12-type alloy can be deformed in compression to 11.4 % at room temperature after HIPing, retaining the original shape of compressive specimens, while compressive specimens without HIPing following heat-treatment for homogenization (HHT) fracture into small pieces when deformed to similar strain. At temperatures higher than 400°C, specimens for both HHTed and HIPed conditions show similar behavior, having strains to failure of greater than 12 % plastic strain. Fracture occurs at room temperature by brittle transgranular cleavage with a smooth surface in HHTed specimens, while in HIPed specimens, fracture occurs by both transgranular and intergranular modes. Transgranularly fractured surfaces in the latter case have rough surfaces with fine structure, indicating ductile fracture as compared with that for HHTed specimens. In both HIPed and HHTed specimens, no fracture surfaces are flat and parallel to any crystallographic planes. High resolution electron microscopy has revealed that a pair of superlattice partial dislocations on a (111) plane have a spacing of approximately 11 nm (2–3 times larger than that for Al-23Ti-6Fe-5V) giving an antiphase boundary energy of 95 mJ/m2. Since this energy is relatively low, the present alloy may be ductile because of its ready emission of dislocations at crack tips, according to the Rice-Thomson criterion. Improvement of room-temperature ductility of this alloy is attributed primarily to the reduction of a large population of cavities formed upon arc casting.

The effect of beam and crystal tilt on quantitative HREM measurememts of grain boundary volume expansion

1993 ◽  
Vol 51 ◽  
pp. 982-983
Author(s):  
M. I. Buckett ◽  
Karl L. Merkle
Keyword(s):  
Grain Boundary ◽  
Volume Expansion ◽  
High Resolution Electron Microscopy ◽  
Boundary Region ◽  
Hrem Image ◽  
Linear Least Squares ◽  
Strain Fields ◽  
Resolution Electron ◽  
Least Squares Fit ◽  
The Difference

The effects of both beam and crystal tilt on quantitative high resolution electron microscopy (HREM) measurements of grain boundary volume expansion have been investigated. As volume expansion - or rigid body translation normal to a given boundary - has been found to directly vary with the grain boun-dary energy, it is important that accurate measurements of this quantity can be made. The type of measurement we consider is a technique first outlined by Stobbs and co-workers and modified by Merkle. The technique utilizes a linear least squares fit to the centers of gravity of either peak or valley positions in the HREM image. The interplanar distances on both sides of the boundary outside the strain fields of the core are first determined, and the measured width of the boundary region is extrapolated. The volume expansion is then determined as the difference between this measured width and the effective unrelaxed width of an ideal boundary.

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