Relating Mechanical Properties with Dislocation Cores in Ni3Ge-Fe3Ge Intermetallic Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
T. John Balk ◽  
Mukul Kumar ◽  
Kevin J. Hemker
Keyword(s):  
Yield Stress ◽  
Mechanical Testing ◽  
Composition Range ◽  
Negative Temperature ◽  
Anomalous Behavior ◽  
Intermetallic Alloys ◽  
Complete Solid Solubility ◽  
Deformation Structures ◽  
Planar Fault ◽  
Fe Content

ABSTRACTThe transition from positive to negative temperature dependence of 0.2% yield stress is investigated m the model pseudo-binary Ni3Ge-Fe3Ge system. Ni3Ge and Fe3Ge, both Ll2 intermetallic alloys, show complete solid solubility as Fe is continuously substituted for Ni across the composition range. However, Ni3Ge exhibits the yield stress anomaly, whereas the yield stress of Fe3Ge shows a normal decline with temperature. Mechanical testing has verified this behavior, with the anomalous behavior gradually disappearing with increasing Fe content. It is proposed that this transition results from changes in the structure of dissociated superdislocation cores. Alloys with anomalous behavior from this system are characterized by the presence of screw superdislocations locked in the Kear-Wilsdorf (KW) configuration. Conversely, alloys with normal yield stress dependence are observed to contain curvilinear superdislocations that glide on the cube planes. Results from mechanical testing are presented and correlated with TEM observations of deformation structures. These results are discussed in light of planar fault energies determined through computer simulations of images.

Characterizing Deformation Mechanisms in Ni3Ge-Fe3Ge Intermetallic Alloys

1998 ◽  
Vol 552 ◽  
Author(s):  
T. J. Balk ◽  
Mukul Kumar ◽  
O. N. Mryasov ◽  
A. J. Freeman ◽  
K. J. Hemker
Keyword(s):  
Yield Strength ◽  
First Principles ◽  
Elastic Moduli ◽  
Intermetallic Alloys ◽  
First Principles Calculations ◽  
Anomalous Temperature ◽  
Weak Beam ◽  
Planar Fault ◽  
Fe Content ◽  
Mechanisms Of Deformation

ABSTRACTThe Ni3Ge-Fe3Ge model system provides us with a unique opportunity to characterize the mechanisms of deformation in both anomalous and normal L12 intermetallic alloys. The elastic moduli of alloys in this system have been measured and used as benchmarks for first principles calculations. At 77K, increasing the Fe content has been found to result in a dramatic increase in flow stress. The Ni-rich alloys exhibit a yield strength anomaly, but as Ni is replaced by Fe, the anomalous temperature dependence gradually disappears, and no yield strength anomaly is observed for alloys with more than 25 at% Fe. At low temperatures and Fe contents, the deformation microstructure has been found to be dominated by Kear-Wilsdorf locking; but a transition from octahedral glide and Kear-Wilsdorf locking to cube glide is observed as either Fe content or temperature is increased. This transition is related to changes that occur in the core structures of dissociated superdislocations and planar fault energies measured through computer simulations of weak-beam TEM images.

Deformation and its Structure in Llo Ti-Al-Nb Compound Alloys

1988 ◽  
Vol 133 ◽  
Author(s):  
Yoo-Dong Hahn ◽  
Sung H. Whang
Keyword(s):  
Temperature Dependence ◽  
Yield Stress ◽  
Uniaxial Compression ◽  
High Temperatures ◽  
Room Temperature ◽  
Fracture Strain ◽  
Positive Temperature ◽  
Deformation Structures ◽  
Miniature Specimens ◽  
Deformation Tests

ABSTRACTThe ternary TiAl-Nb (Llo) alloys stabilized at 1000°C for a week were prepared into miniature specimens for compressive deformation tests. The specimens were deformed in uniaxial compression at room temperature as well as various high temperatures. The yield stress and fracture strain were determined with respect to Nb concentration, and as a function of temperature to investigate positive temperature dependence.Dislocation structures and other deformation structures of the deformed alloys were studied by TEM.

Creep of Anomalous Ni3Ga

1996 ◽  
Vol 460 ◽  
Author(s):  
M J Lunt ◽  
Y Q Sun
Keyword(s):  
Yield Stress ◽  
Creep Strength ◽  
Rapid Decrease ◽  
Steady State Creep ◽  
Intermetallic Alloys ◽  
Creep Tests ◽  
Screw Dislocations ◽  
Cube Plane ◽  
Ordered Intermetallic ◽  
Inverse Creep

ABSTRACTNi3Ga is among a number of LI2 ordered intermetallic alloys whose yield stress increases with temperature. In this work we have examined the creep strength of [123] and [001] oriented Ni3Ga specimens in the temperature regime of the yield stress anomaly and confirmed that the creep strength shows the normal rapid decrease with temperature. Inverse creep occurs in the [001] specimens where slip is on the {111} planes only. [123] specimens exhibit steady-state creep and slip line and TEM observations have shown slip on the cube plane and dislocations of both <110> and <100> Burgers vectors are present. We have carried out creep tests of prestrained [123] samples and demonstrated that the storage of primary <110> {111} screw dislocations, locked in the Kear-Wilsdorf configuration, has no effect on creep.

Dislocation Structure, Phase Stability and Yield Stress Behavior of Ultra-High Temperature L12 Intermetallics: Combined First Principles-Peierls-Nabarro Approach

2004 ◽  
Vol 842 ◽  
Author(s):  
Oleg Y. Kontsevoi ◽  
Yuri N. Gornostyrev ◽  
Arthur J. Freeman
Keyword(s):  
High Temperature ◽  
Mechanical Behavior ◽  
Yield Stress ◽  
Dislocation Structure ◽  
First Principles ◽  
Platinum Group Metals ◽  
Intermetallic Alloys ◽  
Stress Behavior ◽  
Restoring Forces ◽  
Ultra High Temperature

ABSTRACTWe present results of comparative studies of the dislocation properties and the mechanical behavior for a class of intermetallic alloys based on platinum group metals (PGM) which are being developed for ultra-high temperature applications: Ir3X and Rh3X (where X = Ti, Zr, Hf, V, Nb, Ta). For the analysis of dislocation structure and mobility, we employ a combined approach based on accurate first-principles calculations of the shear energetics and the modified semi-discrete 2D Peierls-Nabarro model with an ab-initio parametrization of the restoring forces. Based on our analysis of dislocation structure and mobility, we provide predictions of temperature yield stress behavior of PGM-based intermetallics, show that their dislocation properties are closely connected with features of the electronic structure and the L12 → D019 structural stability, and demonstrate the dramatic difference in dislocation structure and the mechanical behavior between PGM alloys with IVA and VA group elements.

Dislocation Dynamics and Yield Stress Anomalies in Intermetallic Alloys

1994 ◽  
Vol 364 ◽  
Author(s):  
Daniel Caillard
Keyword(s):  
Yield Stress ◽  
Rate Sensitivity ◽  
Short Review ◽  
Dislocation Dynamics ◽  
Positive Temperature ◽  
Intermetallic Alloys ◽  
Transient Effects ◽  
Slip Mechanism ◽  
Double Cross

AbstractMany intermetallic alloys with L12, L10 and BCC related structures exhibit yield-stress anomalies, which have strong influence on their mechanical properties at intermediate temperatures. A short review is made of the anomalous glide systems in various intermetallics. They are shown to exhibit several common characteristics, which allow it to classify them into three groups with possibly similar dislocation mechanisms. In the second half, the well-known case of octahedral glide in Ni3Al is considered again, and a new model is proposed, based on the formation and the unlocking process of incomplete Kear-Wilsdorf locks by a double cross-slip mechanism. This model is supported by several microscopic and macroscopic observations including “in situ” straining experiments in a TEM. It accounts for the positive temperature dependence of the yield-stress with fairly good orders-of-magnitude estimates of the stress. It also explains satisfactorily the small stress-strain rate sensitivity and the transient effects.

Fe doped Ni-Mn-Co-O ceramics with varying Fe content as negative temperature coefficient sensors

2017 ◽  
Vol 43 (13) ◽  
pp. 10528-10532 ◽  
Author(s):  
HyukSu Han ◽  
Sungwook Mhin ◽  
Kyoung Ryeol Park ◽  
Kang Min Kim ◽  
Jung-Il Lee ◽  
...  
Keyword(s):  
Temperature Coefficient ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Fe Content

Synthesis and thermoelectric properties of p-type barium-filled skutterudite BayFexCo4−xSb12

2002 ◽  
Vol 17 (11) ◽  
pp. 2953-2959 ◽  
Author(s):  
X. F. Tang ◽  
L. D. Chen ◽  
T. Goto ◽  
T. Hirai ◽  
R. Z. Yuan
Keyword(s):  
Single Phase ◽  
Lattice Thermal Conductivity ◽  
Composition Range ◽  
Solid State Reaction Method ◽  
Filling Fraction ◽  
Filled Skutterudite ◽  
Reaction Method ◽  
Fe Content ◽  
P Type ◽  
Type Conduction

Single-phase barium-filled skutterudite compounds, BayFexCo4−xSb12 (x = 0 to 3.0, y = 0 to 0.7), were synthesized by a two-step solid-state reaction method. The maximum filling fraction of Ba (ymax) in BayFexCo4–xSb12 increased with increasing Fe content and was found to be rather greater than that of CeyFexCo4–xSb12. The ymax varied from 0.35 to near 1.0 when Fe content changed from 0 to 4.0. BayFexCo4–xSb12 showed p-type conduction at a composition range of x = 0 to 3.0, y = 0 to 0.7. Carrier concentration and electrical conductivity increased with increasing Fe content and decreased with increasing Ba filling fraction. The Seebeck coefficient increased with increasing Ba filling fraction and with decreasing Fe content. Lattice thermal conductivity decreased with increasing Ba filling fraction and reached a minimum at a certain Ba filling fraction (y = 0.3 to 0.4). The greatest ZT value of 0.9 was obtained at 750 K for p-type Ba0.27Fe0.98Co3.02Sb12. It is expected that further investigation on the optimization of filling fraction would result in a higher ZT value at the moderately low Fe content region.

Temperature dependence of yield stress, tensile elongation and deformation structures in polysynthetically twinned crystals of Ti-Al

1995 ◽  
Vol 72 (6) ◽  
pp. 1609-1631 ◽  
Author(s):  
H. Inui ◽  
K. Kishida ◽  
M. Misaki ◽  
M. Kobayashi ◽  
Y. Shirai ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Yield Stress ◽  
Tensile Elongation ◽  
Deformation Structures

Anomalous behavior of yield stress upon an increase in temperature under high strain rate conditions

2007 ◽  
Vol 52 (12) ◽  
pp. 691-694 ◽  
Author(s):  
Yu. V. Petrov ◽  
A. A. Gruzdkov ◽  
E. V. Sitnikova
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Yield Stress ◽  
High Strain ◽  
Anomalous Behavior

Relation between Diffuse Scatterings and Fermi Surface Nesting in Iron Doped Ti-Ni Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 2337-2340
Author(s):  
Takuya Yamamoto ◽  
Mi Seon Choi ◽  
Sho Majima ◽  
Takashi Fukuda ◽  
Tomoyuki Kakeshita ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Negative Temperature Coefficient ◽  
Reciprocal Lattice ◽  
Negative Temperature ◽  
Lattice Points ◽  
Intensity Maximum ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
Ni Alloys ◽  
Fe Content

We have studied diffuse scatterings appearing in Ti-(50-x)Ni-xFe (x = 6, 7, 8, 10) alloy, which shows negative temperature coefficient in electrical resistivity below a temperature Tmin. Electron diffraction pattern of each alloy exhibits diffuse scatterings below Tmin on cooling. The intensity maximum of the diffuse scatterings is located at an incommensurate position of g+<ζζ0>, where g represents reciprocal lattice points of the B2-phase. The value ζ is slightly smaller than 1/3 and decreases with increasing Fe content. The diffuse scatterings of the present alloys are well explained by the nesting effect of the Fermi surface in the B2-type structure, i.e., ζ of each alloy agrees with the length of nesting vector in the [110] direction, which is evaluated by a first-principle calculation.

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