scholarly journals Synthesis, Characterization and Mechanical Properties of Nanocrystalline NiAl

1996 ◽  
Vol 457 ◽  
Author(s):  
M. S. Choudry ◽  
J. A. Eastman ◽  
R. J. DiMelfi ◽  
M. Dollar
Keyword(s):  
Room Temperature ◽  
Dark Field ◽  
Inert Gas ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Room Temperature Ductility ◽  
Cast Alloys ◽  
Bend Tests

ABSTRACTNanocrystalline NiAl has been produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100 to 300°C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range of 4 to 10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.

scholarly journals Forming pressure effect on microstructure and mechanical properties of nanocrystalline aluminum synthesized by inert gas condensation

2019 ◽  
Vol 79 ◽  
pp. 02002
Author(s):  
Shangshu Wu ◽  
Zhou Yu ◽  
Junjie Wang ◽  
Hanxin Zhang ◽  
Chaoqun Pei ◽  
...  
Keyword(s):  
Room Temperature ◽  
High Vacuum ◽  
Inert Gas ◽  
Helium Atmosphere ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
In Situ Forming ◽  
Nanocrystalline Aluminum ◽  
Al Powder

The preparation of nanocrystalline aluminum (NC Al) was conducted in two steps. After the NC Al powder was synthesized by an Inert gas condensation (IGC) method in a helium atmosphere of 500 Pa, the NC Al powder was in-situ compacted into a pellet with a 10 mm diameter and 250 μm-300 μm thickness in a high vacuum (10-6 Pa-10-7 Pa) at room temperature. The NC Al samples were not exposed to air during the entire process. After the pressure reached 6 GPa, the relative density could reach 99.83%. The results showed that the grain size decreased with the increased of in-situ forming pressure. The NC Al samples present obvious ductile fracture, and the tensile properties were greatly changed with the increase of forming pressure.

Combined In Situ Neutron Diffraction and Acoustic Emission of Twin Nucleation & Twin Growth in Extruded ZM20 Mg Alloy

2010 ◽  
Vol 652 ◽  
pp. 149-154 ◽  
Author(s):  
Ondrej Muránsky ◽  
Matthew R. Barnett ◽  
David G. Carr ◽  
Sven C. Vogel ◽  
E.C. Oliver
Keyword(s):  
Acoustic Emission ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Coarse Grained ◽  
Fine Grained ◽  
Grain Sizes ◽  
Twin Nucleation ◽  
Twin Growth ◽  
In Situ Neutron Diffraction

In the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy.

EFFECTIVE MAGNETIC ANISOTROPY AND COERCIVITY IN Fe NANOPARTICLES PREPARED BY INERT GAS CONDENSATION

2006 ◽  
Vol 20 (01) ◽  
pp. 37-47
Author(s):  
LUBNA RAFIQ SHAH ◽  
BAKHTYAR ALI ◽  
S. K. HASANAIN ◽  
A. MUMTAZ ◽  
C. BAKER ◽  
...  
Keyword(s):  
Room Temperature ◽  
Size Range ◽  
Magnetic Measurements ◽  
Uniaxial Anisotropy ◽  
Inert Gas ◽  
Condensation Process ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Fe Nanoparticles ◽  
Characterization Studies

We present magnetic measurements on iron ( Fe ) nanoparticles in the size range 10–30 nm produced by the Inert Gas Condensation process (IGC). Structural characterization studies show the presence of a core/shell structure, where the core is bcc Fe while the surface layer is Fe -oxide. Analysis of the magnetic measurements shows that the nanoparticles display very large uniaxial anisotropy, K eff ≈3 - 4 × 106 erg/cc. The observed room temperature coercivities lie in the range ≈600 – 973 Oe , much larger than those expected from the Stoner–Wohlfarth model using the bulk iron anisotropy. It can be inferred from the coercivity variation with the particle size that there is a general trend of the coercivity increasing with size, culminating finally in a decrease for high sizes (30 nm) possibly due to the onset of non-coherent magnetization reversal processes.

Characteristics of nanophase TiAl produced by inert gas condensation

1992 ◽  
Vol 7 (11) ◽  
pp. 2962-2970 ◽  
Author(s):  
H. Chang ◽  
C.J. Altstetter ◽  
R.S. Averback
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Large Fraction ◽  
Inert Gas ◽  
Full Density ◽  
Indentation Creep ◽  
Small Component ◽  
Grain Sizes ◽  
Transmission Electron ◽  
20 Nm

Nanophase TiAl, with grain sizes in the range of 10–20 nm, was synthesized by magnetron sputtering in an inert gas atmosphere and consolidated, in situ, under vacuum. The properties of the powders and sintered compacts were studied by transmission electron microscopy, scanning electron microscopy, calorimetry, Rutherford backscattering, and x-ray diffraction. Samples compacted at 1.0 GPa at room temperature had a large fraction of amorphous phase, while samples compacted at the same pressure and 250 °C were predominantly the equilibrium γ phase. An enthalpy change of 22 kJ/g-atom was measured during a DSC scan over the temperature range 125–450 °C, which is approximately the range over which crystallization occurs. Nearly full density could be achieved by sintering at 450 °C without significant, concomitant grain growth. The Vickers microhardness of these samples at room temperature and at −30 °C revealed an inverse Hall–Petch relationship at small grain sizes, 10–30 nm, and the usual Hall–Petch behavior at larger grain sizes. A small component of indentation creep was also observed. The maximum hardness is 4 times larger than that of a cast TiAl specimen of the same composition. The Vickers hardness was also observed to decrease rapidly with temperature above 200 °C.

Effect of Trace Boron Addition on the Microstructure and Tensile Elongation of Ti2AlNb-Based Orthorhombic Titanium Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1439-1444
Author(s):  
Masuo Hagiwara ◽  
Tomoyuki Kitaura
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Tensile Elongation ◽  
Boron Addition ◽  
Grain Sizes ◽  
Solution Treated Condition ◽  
Room Temperature Ductility ◽  
Solution Treated ◽  
Treated Condition ◽  
Orthorhombic Titanium

The grain sizes of two kinds of orthorhombic alloys, namely (O+B2) Ti-22Al-11Nb-2Mo -1Fe and (O+2) Ti-27.5Al-13Nb have been successfully reduced by the addition of trace boron (B) (less than 0.12 wt.%). For example, the grain size in the B2 solution-treated condition was reduced from 1 mm to 80 m by the addition of 0.05% B for both alloys. The tensile elongation of Ti-22Al-11Nb-2Mo-1Fe at room temperature and 650C was increased from 0.3% to 4.3%, and from 8.2% to 30.3%, respectively, by the addition of 0.10% B. Ti-27.5Al-13Nb also showed an improved room temperature ductility by the minor B addition.

Microstructure of Titanium-Aluminides after Thermomechanical Treatment

1990 ◽  
Vol 213 ◽  
Author(s):  
J. Seeger ◽  
C. Hartig ◽  
A. Bartels ◽  
H. Mecking
Keyword(s):  
Heat Treatment ◽  
Dynamic Recrystallization ◽  
Thermomechanical Treatment ◽  
Phase Field ◽  
Room Temperature ◽  
Titanium Aluminides ◽  
Subsequent Heat Treatment ◽  
Grain Sizes ◽  
Room Temperature Ductility ◽  
Residual Amount

ABSTRACTForging in the α2+γ-phase field results in grain refined zones by dynamic recrystallization, but still coarse γ-grains and a residual amount of α2/γ-lamellae are observed. During subsequent heat treatment in the α+γ-phase field the recrystallization leads to inhomogeneous distributions of α2-Ti3Al and grain sizes of γ-TiAl. Due to these inhomogeneities a significant increase of the room temperature ductility is not found.

Synthesis, characterization, and properties of nanophase TiO2

1988 ◽  
Vol 3 (6) ◽  
pp. 1367-1372 ◽  
Author(s):  
R. W. Siegel ◽  
S. Ramasamy ◽  
H. Hahn ◽  
L. Zongquan ◽  
L. Ting ◽  
...  
Keyword(s):  
Sintering Temperature ◽  
Positron Annihilation Spectroscopy ◽  
Sintering Aids ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Conventional Sintering ◽  
Hardness Values

Ultrafine-grained, nanophase samples of TiO2 (rutile) were synthesized by the gas-condensation method and subsequent in situ compaction. The samples were studied by a number of techniques, including transmission electron microscopy, Vickers microharness measurements, and positron annihilation spectroscopy, as a function of sintering temperature. The nanophase compacts with average initial grain sizes of 12 nm were found to densify rapidly above 500 °C, with only a small increase in grain size. The hardness values obtained by this method are comparable to or greater than those for coarser-grained compacts, but are achieved at temperatures 400 to 600 °C lower than conventional sintering temperatures and without the need for sintering aids.

Dislocation Motion in λ Tial Studied by in situ Straining Experiments in the Hvem

1994 ◽  
Vol 364 ◽  
Author(s):  
Ulrich Messerschmidt ◽  
Martin Bartsch ◽  
Dietrich Häussler ◽  
Mark Aindow ◽  
Rainer Hattenhauer ◽  
...  
Keyword(s):  
Room Temperature ◽  
Precipitation Hardening ◽  
Dislocation Motion ◽  
Coarse Grained ◽  
Orientation Factor ◽  
Slip Mechanism ◽  
Voltage Electron ◽  
Slip Bands ◽  
Kinematic Behaviour

AbstractMicro-tensile specimens of coarse-grained Ti52at%Al crystals have been deformed in situ in a high voltage electron microscope at room temperature. In addition to some twinning, “simple” 1/2〈110] dislocations as well as superdislocations were moving, with the simple dislocations prevailing even if their orientation factor is lower than that of the superdislocations. Both types of dislocations are pinned, probably by small precipitates having a distance along the dislocations of about 100 nm. The precipitates consist most probably of Al2O3. Under stress, the dislocations bow out between the obstacles. The bowing is stronger for 1/2〈110] dislocations. An effective stress of about 41 MPa is estimated from their curvature. The kinematic behaviour of the dislocations is in accord with precipitation hardening. The dislocations are generated by the double-cross slip mechanism. Their density within the slip bands corresponds to a long-range internal stress of about 40 MPa. These data are consistent with the flow stress of PST crystals in the easy orientation, taken from the literature.

TEM Observation of Nanocrystalline Copper During Deformation

2000 ◽  
Vol 634 ◽  
Author(s):  
Carl J. Youngdahl ◽  
Richard C. Hugo ◽  
Harriet Kung ◽  
Julia R. Weertman
Keyword(s):  
Grain Size ◽  
Stress Concentration ◽  
Real Time ◽  
Dislocation Motion ◽  
Inert Gas ◽  
Nanocrystalline Copper ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Small Cracks

ABSTRACTNanocrystalline samples of copper were prepared using inert gas condensation and an optimized sequence of powder outgassing and compaction. TEM specimens were cut, electropolished, and mounted in a straining stage. In situ TEM observations including real-time video were captured during straining in the microscope. Areas of presumed increased stress concentration were identified near small cracks around the perimeter of the electropolished hole. Such locations were observed in the TEM while the specimen was pulled in tension. Several microstructural changes were captured during deformation including numerous sudden shifts in contrast of grains and parts of grains, occasional dislocation motion, opening and propagation of the crack. Relationships between grain size and deformation are described.

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