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排序方式: 共有112条查询结果,搜索用时 15 毫秒
1.
Alexander Katsman Shalom Cohen Menachem Bamberger 《Journal of Materials Science》2007,42(16):6996-7003
This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved
by precipitation of binary phases such as MgZn2 and Mg2Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening
in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking
into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’
evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation
interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters
of the model, R
N
i and k
σ i
, were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The
effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated
from the hardness maximum positions on the aging curves. 相似文献
2.
3.
The CALPHAD method can be applied as a tool for both alloy development and process guideline determination. In this study, two Mg alloys were designed, their process parameters derived and, using the CALPHAD method, the final results simulated. These results were later confirmed using tangible experimental methods. It was found that γ- Mg17Al12 precipitates along the grain boundaries (GB), Mg2Sn forms both along the GB and as fine precipitates in the α-Mg matrix and the addition of Ce mishmetal (MM) leads to the formation of elongated Al- rare earth (RE) precipitates along the GB. The microstructural stability at 200 °C is high, showing no decrease in microhardness for 32 days. It is shown that the CALPHAD method considerably reduces the effort of alloy design and that the reliability of the results is high. 相似文献
4.
A. Munitz A. M. Bamberger S. Wannaparhun R. Abbaschian 《Journal of Materials Science》2006,41(10):2749-2759
The effects of supercooling and cooling rate on the microstructure of ternary Cu–Fe–Co alloys were investigated. Electromagnetic
levitation was used to supercool the liquids down by 180 K. Alloys with 11 at.% Cu and less than 19 at.% Fe contained fcc
(Fe, Co) and fcc Cu phases; those with 19 to 23 at.% Fe contained bcc (Fe, Co), fcc (Fe, Co) and fcc Cu; those with more than
23 at.% Fe contained bcc (Fe, Co) and fcc Cu. The primary dendrites contained 10 to 20 at.% Cu, with Fe and Co contents depending
on the alloy composition. Supercooling the melt below a certain temperature resulted in metastable separation of the melt
into two liquids, one (Co + Fe)-rich, the other Cu-rich. The metastable phase separation temperatures and the two liquid compositions
were determined experimentaly, and compared with calculated ones. Isothermal cross-sections at various temperatures were constructed
for stable and metastable cases based on thermodynamic and experimental data of the Cu–Co, Cu–Fe, and Co–Fe systems. A peritectic
reaction for the ternary alloys was found at approximately 1100°C. 相似文献
5.
Shara S. Shoup Tamara J. Haverlock Carlos E. Bamberger 《Journal of the American Ceramic Society》1995,78(5):1261-1264
A region of selected SrO-LnO1.5 -TiO2 (Ln = La, Ce, Pr, or Nd) systems was studied experimentally using X-ray diffractometry (XRD). A series of solid solutions with composition Sr4 x Ln2 x/ 3 Ti4 O12 having tetragonally distorted per-ovskite structures was found to exist along the tie line connecting SrTiO3 and Ln2 Ti3 O9 . Reactions of SrLn2 Ti4 O12 , representative compounds of the series, with SrO were also studied. Additionally, the solubility of TiO2 in Ln2 O3 -(3TiO2- m (Ln = La, Pr, or Nd) at 1300°C was investigated using XRD. 相似文献
6.
The chemistry of a new thermochemical cycle for splitting water is described. It consists essentially of three reactions: (a) Ce(IV), as CeO2, is reduced to Ce(III) by reaction with TiO2, evolving oxygen and forming one or more Ce(III) titanates; (b) the Ce(III) titanates react with molten NaOH to evolve hydrogen, and form CeO2 and Na-titanate; and (c) the sodium titanate is hydrolyzed by boiling water into a hydrous titanium dioxide and a sodium hydroxide solution. The cycle has been demonstrated with regenerated materials. 相似文献
7.
Creep properties of specimens taken from the core of AZ91D magnesium alloy ingots (9 pct Al, 1 pct Zn) were examined in the
temperature range of 120 °C to 180 °C and stress range of 40 to 115 MPa. Solution-treated and aged creep specimens were also
tested. The creep rates observed were about three orders of magnitude lower than those of pure magnesium, and elongations
to fracture were seen to be at least twice those of pure magnesium. A minimum creep rate was reached after approximately 2/3
of the creep life of the specimens (except for the aged specimens, in which the minimum creep rate appears at the beginning
of the test). A qualitative model for the creep process in proposed on the basis of the creep tests and optical, scanning
electron, and transmission electron microscopy. This model proposes that dislocation motion on additional slip systems is
the primary creep mechanism and that cracking acts as a stress relief mechanism. Structural instability dictates the amount
of hardening and, hence, creep resistance. 相似文献
8.
B. Rashkova W. Prantl R. Grgl J. Keckes S. Cohen M. Bamberger G. Dehm 《Materials Science and Engineering: A》2008,494(1-2):158
The microstructural evolution of a Mg–Zn–Sn alloy was studied by combining X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) in order to determine the individual phases, their size and volume fraction of the alloy. Solutionized and aged samples are analysed in detail concerning the nucleation, growth, morphology, and stability of precipitate phases. In the aged samples, firstly MgZn2 particles with a rod-like shape form, and secondly plate-like MgSn2 precipitates. The MgZn2 phase shows a well-defined orientation relationship with the Mg matrix. The formation of two types of precipitates is responsible for the occurrence of two pronounced hardness maxima. The growth behaviour of the MgZn2 phase is determined by combining TEM and SAXS measurements and the results are compared to the Lifschitz–Slyozov–Wagner (LSW) theory. 相似文献
9.
We have studied the distribution profiles of Cu and Sb introduced into Si substrates, and Sb introduced into Ge substrates by electron beam melting of thin (~30nm) layers of the dopant evaporated onto the substrate. Surface evaporation of the dopant during melting was reduced by a cover layer of the substrate material evaporated on top. We propose a novel model which explains solute surface accumulation phenomena oberved in laser and electron beam surface melting experiments. It is based on a mechanism of solute immobilization at the very surface. 相似文献
10.
This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We
analyzed the influence of Zn content on the precipitation of Mg2Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results
and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different
compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy
was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at
the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement
of the Mg2Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous
precipitation of Mg2Sn on the Mg–Zn precipitates, and Mg2Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool. 相似文献