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David N Seidman - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution and creep properties of precipitation strengthened al 0 06sc 0 02gd and al 0 06sc 0 02yb at Alloys
Acta Materialia, 2011Co-Authors: Marsha E Van Dalen, David C Dunand, David N SeidmanAbstract:Abstract The aging behavior at 300 °C of Al–0.06Sc–0.02Gd and Al–0.06Sc–0.02Yb (at.%) Alloys is studied by local-electrode atom-probe tomography, transmission electron microscopy and microhardness measurements. The Ternary Alloys exhibit high number densities of coherent L12 precipitates ( N v ≅ 10 22 m - 3 ) at aging times up to 1536 h (64 days). In the Al–0.06Sc–0.02Gd alloy, the Al3(Sc1−xGdx) precipitates are always Sc-rich, displaying a small Gd concentration (x
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effects of substituting rare earth elements for scandium in a precipitation strengthened al 0 08 at sc alloy
Scripta Materialia, 2006Co-Authors: Richard A Karnesky, David C Dunand, Marsha E Van Dalen, David N SeidmanAbstract:The microhardness of Al–0.06 Sc–0.02 RE Alloys (at.%, with RE (rare-earth) = Dy, Er, Gd, Sm, Y, or Yb) is measured as a function of aging time at 300 °C. As compared to Al–0.08 Sc, the Ternary Alloys exhibit: (i) the same incubation time, except for Al–0.06 Sc–0.02 Yb which hardens much faster; (ii) the same or reduced peak microhardnesses (which are higher than for Al–0.06 Sc); and (iii) the same over-aging behavior. All REs segregate to the core of Al3(Sc1−xREx) precipitates.
R D Noebe - One of the best experts on this subject based on the ideXlab platform.
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influence of hf solute additions on the precipitation and hardenability in ni rich niti Alloys
Journal of Alloys and Compounds, 2015Co-Authors: B C Hornbuckle, R D Noebe, Gregory B ThompsonAbstract:Abstract Very Ni-rich NiTi Alloys have recently been shown to have an unusually high hardness, comparable to tool steels, and other attributes that make them promising candidates for bearing and related applications. This high hardness has been associated with the precipitation of a large volume fraction of Ni 4 Ti 3 platelets, resulting in a matrix that consists of narrow B2 matrix channels. In this work, a series of Ni-rich Ternary Alloys with dilute solute additions of Hf (54Ni–45Ti–1Hf, 55Ni–44Ti–1Hf, 54Ni–44Ti–2Hf, and 56Ni–40Ti–4Hf (at.%)) have been investigated. Transmission electron microscopy confirmed a B2 NiTi matrix phase containing nanoscale Ni 4 Ti 3 platelets, H-phase precipitates, and R-phase; however, the H-phase and R-phase were not present initially but only after aging for a period of time. At aging times greater than ∼100 h at 400 °C, all Ternary Alloys showed a slight secondary increase in hardness, which was attributed to H-phase precipitation and growth within the B2 channels. In the particular case of the 56Ni–40Ti–4Hf alloy, hardness increased with aging to a maximum value of 679 VHN, which was greater than all other binary or Ternary Alloys examined. Additionally the H-phase appeared to alter or delay the typical breakdown sequence of the metastable Ni 4 Ti 3 strengthening phase by removing the excess Ni needed for its decomposition. The collective results provide new material insights for creating a next-generation NiTi based bearing alloy.
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tem study of structural and microstructural characteristics of a precipitate phase in ni rich ni ti hf and ni ti zr shape memory Alloys
Acta Materialia, 2013Co-Authors: R Santamarta, Raymundo Arroyave, J Pons, A Evirgen, I Karaman, H E Karaca, R D NoebeAbstract:Abstract The precipitates formed after suitable thermal treatments in seven Ni-rich Ni–Ti–Hf and Ni–Ti–Zr high-temperature shape memory Alloys have been investigated by conventional and high-resolution transmission electron microscopy. In both Ternary systems, the precipitate coarsening kinetics become faster as the Ni and Ternary element contents (Hf or Zr) of the bulk alloy are increased, in agreement with the precipitate composition measured by energy-dispersive X-ray microanalysis. The precipitate structure has been found to be the same in both Hf- and Zr-containing Ternary Alloys, and determined to be a superstructure of the B2 austenite phase, which arises from a recombination of the Hf/Zr and Ti atoms in their sublattice. Two different structural models for the precipitate phase were optimized using density functional theory methods. These calculations indicate that the energetics of the structure are not very sensitive to the atomic configuration of the Ti–Hf/Zr planes, thus significant configurational disorder due to entropic effects can be envisaged at high temperatures. The precipitates are fully coherent with the austenite B2 matrix; however, upon martensitic transformation, they lose some coherency with the B19′ matrix as a result of the transformation shear process in the surrounding matrix. The strain accommodation around the particles is much easier in the Ni–Ti–Zr-containing Alloys than in the Ni–Ti–Hf system, which correlates well with the lower transformation strain and stiffness predicted for the Ni–Ti–Zr Alloys. The B19′ martensite twinning modes observed in the studied Ni-rich Ternary Alloys are not changed by the new precipitated phase, being equivalent to those previously reported in Ni-poor Ternary Alloys.
Youdou Zheng - One of the best experts on this subject based on the ideXlab platform.
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a band gap energy model of the quaTernary alloy in x ga y al 1 x y n using modified simplified coherent potential approximation
Chinese Physics Letters, 2013Co-Authors: Chuan-zhen Zhao, Rong Zhang, Bin Liu, Xiangqian Xiu, Zili Xie, Youdou ZhengAbstract:Based on modification of the simplified coherent potential approximation, a model for the band-gap energy of InxGayAl1−x−yN is developed. The parameters of the model are obtained by fitting the experimental band-gap energy of their Ternary Alloys. It is found that the results agree with the experimental values better than those reported by others, and that the band-gap reduction of InxGayAl1−x−yN with increasing In or Ga content is mainly due to enhanced intraband coupling within the conduction band, and separately within the valence band.
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a modified simplified coherent potential approximation model of band gap energy of iii v Ternary Alloys
Science China-physics Mechanics & Astronomy, 2012Co-Authors: Chuan-zhen Zhao, Rong Zhang, Bin Liu, Xiangqian Xiu, Zili Xie, Youdou ZhengAbstract:Based on the modification of the simplified coherent potential approximation (SCPA), a model is developed to calculate the composition dependence of the band gap energy of III-V Ternary Alloys with the same anion. The derived equation is used to fit the experimental band gap energy of InxAl1−xN, InxGa1−xN and AlxGa1−xN with x from 0 to 1. It is found that the fitting results are better than those done by using SCPA. The fitting results are also better than those obtained by using the formula with a small bowing coefficient, especially for InxAl1−xN. In addition, our model can also be used to describe the composition dependence of band gap energy of other III-V Ternary Alloys.
Oussama Moutanabbir - One of the best experts on this subject based on the ideXlab platform.
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indirect to direct band gap transition in relaxed and strained ge1 x ysixsny Ternary Alloys
Journal of Applied Physics, 2014Co-Authors: Anis Attiaoui, Oussama MoutanabbirAbstract:Sn-containing group IV semiconductors create the possibility to independently control strain and band gap thus providing a wealth of opportunities to develop an entirely new class of low dimensional systems, heterostructures, and silicon-compatible electronic and optoelectronic devices. With this perspective, this work presents a detailed investigation of the band structure of strained and relaxed Ge1−x−ySixSny Ternary Alloys using a semi-empirical second nearest neighbors tight binding method. This method is based on an accurate evaluation of the deformation potential constants of Ge, Si, and α-Sn using a stochastic Monte-Carlo approach as well as a gradient based optimization method. Moreover, a new and efficient differential evolution approach is also developed to accurately reproduce the experimental effective masses and band gaps. Based on this, we elucidated the influence of lattice disorder, strain, and composition on Ge1−x−ySixSny band gap energy and directness. For 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.2, we...
Yufeng Zheng - One of the best experts on this subject based on the ideXlab platform.
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effects of alloying elements ca and sr on microstructure mechanical property and in vitro corrosion behavior of biodegradable zn 1 5mg alloy
Journal of Alloys and Compounds, 2016Co-Authors: Yinghong Yang, Yufeng Zheng, Zhongjie Pu, Li LiAbstract:Abstract Zn, a promising biodegradable material, possesses excellent biocompatibility and biodegradability, however its low strength and hardness largely limit its application in biodegradable implants. The addition of alloying elements would generally be suggested as an effective method for improving the mechanical properties. In the current study, alloying with a minor amount of Ca or Sr in Zn–1.5Mg alloy, the Ternary Alloys were composed of the matrix Zn and precipitated phase (Mg 2 Zn 11 and CaZn 13 for Zn–1.5Mg–0.1Ca alloy, Mg 2 Zn 11 and SrZn 13 for Zn–1.5Mg–0.1Sr alloy, respectively). Besides, the grain size of Ternary Alloys became more homogeneous and smaller than that of Zn–1.5Mg alloy. Meanwhile, the effect of alloying elements on the mechanical properties and corrosion behavior of Zn–1.5Mg alloy were analyzed. The results showed that the Ternary Alloys exhibited much higher yield strength (YS), ultimate tensile strength (UTS) and elongation than those of Zn–1.5Mg alloy. The measured corrosion rates of the Ternary Alloys were slightly increased due to galvanic corrosion reaction. Besides, a model of the corrosion mechanism in the simulated body fluid was discussed here based on the results of the studied Alloys.
