Site Occupancy Determination by ALCHEMI of Nb and Cr in γ-TiAl and Their Effects on the a to γ Massive Phase Transformation

1999 ◽  
Vol 589 ◽  
Author(s):  
T.M. Miller ◽  
L. Wang ◽  
W.H. Hofmeister ◽  
J.E. Wittig ◽  
I.M. Anderson
Keyword(s):  
Solid State ◽  
Rapid Solidification ◽  
Titanium Aluminides ◽  
Site Occupancy ◽  
Solidification Structure ◽  
Two Phase ◽  
Alloying Additions ◽  
Massive Phase ◽  
Ternary Alloying ◽  
Solid State Cooling

AbstractAtom location by channeling enhanced microanalysis (ALCHEMI) has been used to characterize the site distributions of Nb and Cr alloying additions in the L10-ordered γ phase of ternary titanium aluminides. Two alloys, Ti50Al48Cr2 and Ti50A148Nb2, were processed by furnace cooling from 1300°C (within the α-γ two phase field) as well as by rapid solidification using twin-anvil splat quenching of electromagnetically levitated and undercooled samples. ALCHEMI studies of furnace cooled samples yield results generally consistent with those in the published literature. Nb alloying additions are found to partition exclusively to the ‘Ti’ sublattice, while Cr alloying additions exhibit an ‘Al‘ sublattice preference. However, a higher degree of disorder can be achieved with rapid solidification and high solid state cooling rates (105-106 K/s). Significant distribution of the ternary elements between the ‘Ti’ and ‘Al‘ sublattices has been measured in the splat quenched samples, with up to 12% of the Nb atoms occupying the ‘Al‘ sublattice and the fraction of Cr atoms on the ‘Ti’ sublattice doubling to ∼30%. Rapid solidification of TiAl produces an equiaxed hexagonal α phase solidification structure that transforms in a massive fashion to the tetragonal γ phase. Although the amount of massively transformed γ is dependent upon the solid state cooling rate, ternary alloying additions can more strongly influence the transformation kinetics. The Nb-modified alloy exhibits significant amounts of the massively tranformed γ, similar to the Ti52Al48 binary alloy, whereas little massively transformed γ is observed in the Cr-modified alloy. These results can be correlated with the relative atomic size, lattice distortion, and sublattice site occupancy of Nb and Cr in the L10 unit cell.

Infrared Joining of Titanium Aluminides by Using Ti-15Ni-15Cu Foil

1998 ◽  
Vol 552 ◽  
Author(s):  
S. J. Lee ◽  
S. K. Wu
Keyword(s):  
Solid State ◽  
Microstructural Evolution ◽  
Titanium Aluminides ◽  
Filler Metal ◽  
Isothermal Solidification ◽  
Joint Interface ◽  
Residual Liquid ◽  
Multilayered Structures ◽  
Two Phase ◽  
Liquid Filler

ABSTRACTThe infrared joining of titanium-aluminides Ti50A150, Ti60Al40and Ti70A130at Tw= 1100∼1200°C for 30–60sec using Ti-15Cu-15Ni foil as brazing filler-metal was investigated. Multilayered structures are formed by isothermal solidification following solid-state interdiffusion. The diffusion of Al atoms is the main controlling factor pertaining to the microstructural evolution of the joint interface. Seven characteristic zones at Twcan be distinguished in the Ti50Al50joint: γ-TiAl (I and II), α + β two-phase mixed, high Al% α-phase, α2-Ti3Al, β-Ti and residual liquid filler-metal. Five characteristic zones at Tw, are obtained in the Ti70A130joint: α2-Ti3Al, α2+ β two-phase mixed, α + β two-phase mixed, β-Ti and residual liquid filler-metal. The observed joint microsturctures at room temperature are obtained from the phase transformation of these well-established high-temperature phases during cooling. A step-by-step microstructural evolution mechanism at Tw= 1150°C is proposed individually for Ti50A150and Ti70A130alloys. These steps are in good agreement with the observed microstructures and are consistent with the multiphase diffusion theories in solid-state systems. The microstructural evolution of Ti60A140joint interfaces can also be explained by the proposed step mechanisms for Ti50A150and Ti70A130alloys.

scholarly journals β-Li0.37Na0.63Fe(MoO4)2

2014 ◽  
Vol 70 (2) ◽  
pp. i9-i10 ◽  
Author(s):  
Amira Souilem ◽  
Mohamed Faouzi Zid ◽  
Ahmed Driss
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Solid State Reaction ◽  
Title Compound ◽  
General Position ◽  
Site Occupancy ◽  
The Other ◽  
Main Structure ◽  
Axis Direction ◽  
A Site

The title compound, lithium/sodium iron(III) bis[orthomolybdate(VI)], was obtained by a solid-state reaction. The main structure units are an FeO6octahedron, a distorted MoO6octahedron and an MoO4tetrahedron sharing corners. The crystal structure is composed of infinite double MoFeO11chains along theb-axis direction linked by corner-sharing to MoO4tetrahedra so as to form Fe2Mo3O19ribbons. The cohesion between ribbonsviamixed Mo—O—Fe bridges leads to layers arranged parallel to thebcplane. Adjacent layers are linked by corners shared between MoO4tetrahedra of one layer and FeO6octahedra of the other layer. The Na+and Li+ions partially occupy the same general position, with a site-occupancy ratio of 0.631 (9):0.369 (1). A comparison is made withAFe(MoO4)2(A= Li, Na, K and Cs) structures.

Colossal Barocaloric Effects with Ultralow Hysteresis in Two-Dimensional Metal–Halide Perovskites

2021 ◽  
Author(s):  
Jarad Mason ◽  
Jinyoung Seo ◽  
Ryan McGillicuddy ◽  
Adam Slavney ◽  
Selena Zhang ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Phase Transitions ◽  
Solid State ◽  
Hydrostatic Pressure ◽  
Metal Halide ◽  
Two Dimensional ◽  
Vapor Compression ◽  
Entropy Changes ◽  
Halide Perovskites ◽  
Solid State Cooling

Abstract Nearly 4,400 TWh of electricity—20% of the total consumed in the world—is used each year by refrigerators, air conditioners, and heat pumps for cooling. In addition to the 2.3 Gt of carbon dioxide emitted during the generation of this electricity, the vapor-compression-based devices that provided the bulk of this cooling emitted fluorocarbon refrigerants with a global warming potential equivalent to 1.5 Gt of carbon dioxide into the atmosphere. With population and economic growth expected to dramatically increase over the next several decades, the development of alternative cooling technologies with improved efficiency and reduced emissions will be critical to meeting global cooling needs in a more sustainable fashion. Barocaloric materials, which undergo thermal changes in response to applied hydrostatic pressure, offer the potential for solid-state cooling with high energy efficiency and zero direct emissions, as well as faster start-up times, quieter operation, greater amenability to miniaturization, and better recyclability than conventional vapor-compression systems. Efficient barocaloric cooling requires materials that undergo reversible phase transitions with large entropy changes, high sensitivity to hydrostatic pressure, and minimal hysteresis, the combination of which has been challenging to achieve in existing barocaloric materials. Here, we report a new mechanism for achieving colossal barocaloric effects near ambient temperature that exploits the large volume and conformational entropy changes of hydrocarbon chain-melting transitions within two-dimensional metal–halide perovskites. Significantly, we show how the confined nature of these order–disorder phase transitions and the synthetic tunability of layered perovskites can be leveraged to reduce phase transition hysteresis through careful control over the inorganic–organic interface. The combination of ultralow hysteresis (< 1.5 K) and high barocaloric coefficients (> 20 K/kbar) leads to large reversible isothermal entropy changes (> 200 J/kg•K) at record-low pressures (< 300 bar). We anticipate that these results will help facilitate the development of barocaloric cooling technologies and further inspire new materials and mechanisms for efficient solid-state cooling.

Hot work processing, microstrructure and mechanical properties of two-phase γ titanium aluminides

1994 ◽  
Vol 185 (1-2) ◽  
pp. 17-24 ◽  
Author(s):  
X.D. Zhang ◽  
R.V. Ramanujan ◽  
T.A. Dean ◽  
M.H. Loretto
Keyword(s):  
Mechanical Properties ◽  
Titanium Aluminides ◽  
Two Phase

Microstructural Characterization of α2 + γ Titanium Aluminides

1997 ◽  
Vol 3 (S2) ◽  
pp. 701-702
Author(s):  
D. J. Larson ◽  
M. K. Miller
Keyword(s):  
Titanium Aluminides ◽  
Base Alloy ◽  
Significant Proportion ◽  
Weight Ratio ◽  
High Strength ◽  
Microstructural Characterization ◽  
Two Phase ◽  
Tial Alloys ◽  
Boron Doped

Two-phase α2+γ TiAl alloys with microalloying additions, Fig. 1, are of interest due to the high strength-to-weight ratio they can provide in automotive and aircraft applications. In boron-doped α2+γTiAl containing Cr, Nb, and W, the B levels were found to be significantly depleted below the nominal alloy content in both the α2 andγ phases. The boron solubilities in the γ and α2 phases were 0.011 ± 0.005 at. % B and 0.003 ± 0.005 at. % B, respectively in Ti-47% Al-2% Cr-1.8% Nb-0.2% W-0.15 % B that was aged for 2 h at 900°C (base alloy). The majority of the B was in a variety of borides including TiB, TiB2 and a Cr-enriched (Ti,Cr)2B precipitate. With the exception of the smaller (< 50 nm thick) Cr-enriched (Ti,Cr)2B precipitates, Fig. 2, most of the borides were larger than ∼100 nm. A significant proportion of the microalloying additions is in these borides, Table 1.

A new two-phase kinetic model of sporulation of Clonostachys rosea in a new solid-state fermentation reactor

2013 ◽  
Vol 48 (8) ◽  
pp. 1119-1125 ◽  
Author(s):  
Yuan Yuan Zhang ◽  
Jun Hong Liu ◽  
Yuan ming Zhou ◽  
Yu Yan Zhang ◽  
Ying Liu ◽  
...  
Keyword(s):  
Solid State ◽  
Kinetic Model ◽  
Solid State Fermentation ◽  
Clonostachys Rosea ◽  
Two Phase
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