Microstructures and Hydrogen Permeability of Nb-NiTi Eutectic Alloys Prepared by Directional Solidification

2006 ◽  
Vol 980 ◽  
Author(s):  
Yuji Yamaguchi ◽  
Kyosuke Kishida ◽  
Sho Tokui ◽  
Kazuhiro Ishikawa ◽  
Katsushi Tanaka ◽  
...  
Keyword(s):  
Hydrogen Embrittlement ◽  
Alloy Composition ◽  
Slow Growth ◽  
Hydrogen Permeability ◽  
Eutectic Structure ◽  
Eutectic Alloys ◽  
Directionally Solidified ◽  
Direction Parallel ◽  
Columnar Grains ◽  
Niti Matrix

AbstractThe Nb-NiTi eutectic alloys were directionally solidified (DS) in an optical floating zone furnace. Columnar grains of eutectic structures containing rod-shaped Nb in the NiTi matrix is observed in the DS ingots irrespective of the alloy composition. Well-aligned rod-type eutectic microstructures can be obtained for samples with a composition of Nb-41Ni-40Ti grown at relatively slow growth rates below 2.5mm/h. The hydrogen permeability along the direction parallel to the Nb rods of Nb-41Ni-40Ti DS alloy grown at 1mm/h is 2.60×10-8mol H2 m-1 Pa-1/2 at 673K, which is over 20 times higher than that measured perpendicular to the Nb-rod direction. No hydrogen embrittlement is observed between 573 and 673K indicating that the eutectic structure itself is favorable in suppressing the hydrogen embrittlement of Nb.

Hydrogen Permeation Properties of Nb-Based Two-Phase Compounds

2007 ◽  
Vol 561-565 ◽  
pp. 467-470
Author(s):  
Yuji Yamaguchi ◽  
Kyosuke Kishida ◽  
Katsushi Tanaka ◽  
Haruyuki Inui ◽  
Sho Tokui ◽  
...  
Keyword(s):  
Hydrogen Embrittlement ◽  
Hydrogen Permeation ◽  
Membrane Surface ◽  
Hydrogen Permeability ◽  
Eutectic Structure ◽  
Growth Direction ◽  
Directionally Solidified ◽  
Two Phase ◽  
Cast Sample ◽  
Lamellar Type

Nb-NiTi and Nb-CoTi eutectic alloys were directionally solidified in an optical floating zone furnace. Rod-type eutectic structures with Nb rods aligned parallel to the growth direction are obtained for Nb-41Ni-40Ti grown at relatively slow growth rates below 1.0mm/h, while lamellar-type eutectic structures are obtained for Nb-35Co-34Ti grown at the same condition. The hydrogen permeability for the Nb-41Ni-40Ti DS alloy with Nb rods perpendicular to the membrane surface is 2.60×10-8mol H2 m-1 Pa-1/2 at 673K, which is about 2.5 times higher than that of as-cast sample. No hydrogen embrittlement is observed between 573 and 673K, indicating that the Nb-NiTi rod-type eutectic structure effectively suppresses the hydrogen embrittlement of Nb during hydrogen permeation.

scholarly journals A Review for Consistent Analysis of Hydrogen Permeability through Dense Metallic Membranes

Membranes ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 120
Author(s):  
Asuka Suzuki ◽  
Hiroshi Yukawa
Keyword(s):  
Diffusion Coefficient ◽  
Hydrogen Embrittlement ◽  
Alloy Composition ◽  
Hydrogen Permeation ◽  
Hydrogen Permeability ◽  
Anomalous Temperature Dependence ◽  
Anomalous Temperature ◽  
High Hydrogen ◽  
Hydrogen Flux ◽  
Solubility Constant

The hydrogen permeation coefficient (ϕ) is generally used as a measure to show hydrogen permeation ability through dense metallic membranes, which is the product of the Fick’s diffusion coefficient (D) and the Sieverts’ solubility constant (K). However, the hydrogen permeability of metal membranes cannot be analyzed consistently with this conventional description. In this paper, various methods for consistent analysis of hydrogen permeability are reviewed. The derivations of the descriptions are explained in detail and four applications of the consistent descriptions of hydrogen permeability are introduced: (1) prediction of hydrogen flux under given conditions, (2) comparability of hydrogen permeability, (3) understanding of the anomalous temperature dependence of hydrogen permeability of Pd-Ag alloy membrane, and (4) design of alloy composition of non-Pd-based alloy membranes to satisfy both high hydrogen permeability together with strong resistance to hydrogen embrittlement.

Chemical partitioning of elements in Ni-base MC-carbide reinforced eutetic superalloys

1983 ◽  
Vol 41 ◽  
pp. 250-251
Author(s):  
E. F. Koch ◽  
E. L. Hall ◽  
S. W. Yang
Keyword(s):  
Alloy Composition ◽  
Volume Fraction ◽  
Lattice Mismatch ◽  
Turbine Blades ◽  
Eutectic Alloys ◽  
Alloy Matrix ◽  
X Ray ◽  
Gas Turbine Blades ◽  
Analytical Electron ◽  
Analytical Electron Microscope

The plane-front solidified eutectic alloys consisting of aligned tantalum monocarbide fibers in a nickel alloy matrix are currently under consideration for future aircraft and gas turbine blades. The MC fibers provide exceptional strength at high temperatures. In these alloys, the Ni matrix is strengthened by the precipitation of the coherent γ' phase (ordered L12 structure, nominally Ni3Al). The mechanical strength of these materials can be sensitively affected by overall alloy composition, and these strength variations can be due to several factors, including changes in solid solution strength of the γ matrix, changes in they γ' size or morphology, changes in the γ-γ' lattice mismatch or interfacial energy, or changes in the MC morphology, volume fraction, thermal stability, and stoichiometry. In order to differentiate between these various mechanisms, it is necessary to determine the partitioning of elemental additions between the γ,γ', and MC phases. This paper describes the results of such a study using energy dispersive X-ray spectroscopy in the analytical electron microscope.

scholarly journals Evolution of Microstructure and Microsegregation of Ti-45Al-8Nb Alloy during Directional Solidification

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Xiangjun Xu ◽  
Rui Hu ◽  
Junpin Lin ◽  
Jian Guo
Keyword(s):  
Mushy Zone ◽  
Solidification Rate ◽  
Solidus Temperature ◽  
Melting Zone ◽  
Optical Microscope ◽  
Directionally Solidified ◽  
Good Oxidation Resistance ◽  
Columnar Grains ◽  
Columnar Grain ◽  
Evolution Of Microstructure

High Nb-containing TiAl alloys have good oxidation resistance and mechanical properties, but the microstructure and the properties are substantially affected by the segregation. To quantitatively investigate the segregation behavior of Al during solidification, microstructures of directionally solidified (DS) Ti-45Al-8Nb (in atomic percent) alloy prepared at withdrawing rates of 30 μm/s and 200 μm/s and a temperature gradient of 4200 K/m were observed by optical microscope and electronic probe microanalyzer. The microsegregations were characterized by wave dispersive spectroscopy. The results show that the DS ingots include the no melting zone, directionally solidified zone with columnar grains, mushy zone, and quenched liquid zone. The primary dendritic arm spacings are 353 μm and 144 μm, respectively, for the two ingots. But the solidified microstructures of the ingots are large lamellar colonies, which contain a few B2 patches and γ bands induced by microsegregation. From dendritic zone to columnar zone, the volume fractions of B2 patches and γ bands decrease. The segregation extents of Al and Nb decrease with the increase of solidification rate. There exists an obvious back diffusion process of Al during solidification and cooling after solidification. According to evolution of Al concentration profiles from mushy zone to columnar grain zone, interdiffusion coefficient for Al in β-Ti at near solidus temperature is semiquantitatively calculated, and the value is (6 – 11) × 10−11 m2/s.

Anisotropic Microstructure and Hydrogen Permeability of Nb-Ti-Ni Duplex Phase Alloy Prepared by Hot Forging-Rolling Technique

2006 ◽  
Vol 980 ◽  
Author(s):  
Sho Tokui ◽  
Kazuhiro Ishikawa ◽  
Kiyoshi Aoki
Keyword(s):  
Solid Solution ◽  
Hydrogen Embrittlement ◽  
Hydrogen Permeability ◽  
Rolling Direction ◽  
Hot Forging ◽  
The Other ◽  
Rolling Reduction ◽  
Eutectic Microstructure ◽  
Ni Alloys ◽  
Other Hand

AbstractIt has been demonstrated that the as-cast Nb40Ti30Ni30 duplex phase alloy, which consists of the primary (Nb, Ti) solid solution and the fine lamellar type eutectic {TiNi+(Nb, Ti)} phase, shows higher hydrogen permeability ¶ than that of pure Pd without the hydrogen embrittlement at 673K. In this alloy, the eutectic phase contributes to the suppression of the hydrogen embrittlement, while the primary one does mainly to the hydrogen permeation. It is important to note that even if the eutectic microstructure disappears and is replaced by the small spherical (Nb, Ti) phase embedded in the TiNi matrix by rolling and subsequent annealing, its high hydrogen permeability and large resistance to the hydrogen embrittlement are sustained. Furthermore, the present authors have observed that the primary (Nb, Ti) phase is largely elongated along the rolling direction. Consequently, it is expected that rolled and annealed Nb-Ti-Ni alloys show the large anisotropy of the microstructure and the hydrogen permeability. In the present work, the microstructure and hydrogen permeability ¶nof the Nb40Ti30Ni30 alloy after rolling and annealing treatments are examined in order to develop highly hydrogen permeable alloys utilizing the anisotropic microstructure.The primary (Nb, Ti) phase and the very fine eutectic {TiNi+(Nb, Ti)} phase are observed in the as-cast Nb40Ti30Ni30 alloy by scanning electron microscopy (SEM). The X-ray diffractometry (XRD) indicates that this alloy consists of the B2-TiNi intermetallic compounds and the bcc- (Nb, Ti) solid solution. The primary (Nb, Ti) phase is largely elongated along the rolling direction by forging and subsequent rolling at 1173 K. On the other hand, the eutectic microstructure becomes unclear with increasing the rolling reduction. The composite alloys in which the (Nb, Ti) phase is elongated along to the rolling direction are obtained by 69 % rolling reduction. ¶n of this sample is four times higher than that of as-cast one. On the other hand, ¶ for the sample vertical to the rolling direction is reduced to about one third of that of as-cast one. Thus, the hydrogen permeability of the Nb40Ti30Ni30 alloy varies about ten times or more depending on the direction of the primary¡]Nb, Ti¡^ phase. We conclude that it is possible to produce highly hydrogen permeable Nb-Ti-Ni alloys using the anisotropy of the microstructure prepared by hot forging and rolling.

Resonant Response and Random Response Analysis of Mistuned Bladed Disk Consisting of Directionally Solidified Blade

2015 ◽  
Author(s):  
Yasutomo Kaneko ◽  
Kazushi Mori ◽  
Hiroharu Ooyama
Keyword(s):  
Elastic Constants ◽  
Rupture Strength ◽  
Turbine Blades ◽  
Response Analysis ◽  
Resonant Response ◽  
Random Response ◽  
Directionally Solidified ◽  
Columnar Crystal ◽  
Bladed Disk ◽  
Columnar Grains

Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventional Casting) alloys, in order to improve the creep rupture strength. The DS blade consists of several columnar grains of SC, where the growing direction of the columnar crystal is set to the direction of the centrifugal force. Because the elastic constants of the DS blade are anisotropic, the mistuning characteristics of the bladed disk consisting of the DS blades seem to be different from those of the CC blade. In this study, the resonant response and random response analysis of mistuned bladed disks consisting of the DS blades are carried out, considering the deviations of the elastic constants and the crystal angle of the DS blade. The FMM (Fundamental Mistuning Model) and the conventional modal analysis method are used to analyze the vibration response of the mistuned bladed disk. The maximum resonant response and random response of the mistuned bladed disk consisting of the DS blades are estimated by the Monte Carlo simulation combining with the response surface method. These calculated results for the DS blades are compared with those of the CC blades. From these results, it is concluded that the maximum response of the mistuned bladed disk consisting of the DS blades is the nearly same as that of the CC blades. However, in the design of the tuned blade, where the blade resonance should be avoided, it is necessary to consider that the range of the resonant frequency of the DS blade becomes wider than that of the CC blade.

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