The effect of back-melting on the continuity of crystallographic orientation and composition in HgZnTe

1992 ◽  
Vol 50 (2) ◽  
pp. 1696-1697
Author(s):  
H.J. Zuo ◽  
M.W. Price ◽  
R.D. Griffin ◽  
R.A. Andrews ◽  
G.M. Janowski
Keyword(s):  
Directional Solidification ◽  
Space Shuttle ◽  
Solidification Process ◽  
Space Experiment ◽  
Infrared Detection ◽  
Directionally Solidified ◽  
Crystallographic Defects ◽  
Semiconducting Alloys ◽  
Uniform Composition ◽  
Growth Experiments

The II-VI semiconducting alloys, such as mercury zinc telluride (MZT), have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities and crystallographic imperfections adversly affect the performance of MZT infrared detectors. One source of imperfections in MZT is gravity-induced convection during directional solidification. Crystal growth experiments conducted in space should minimize gravity-induced convection and thereby the density of related crystallographic defects. The limited amount of time available during Space Shuttle experiments and the need for a sample of uniform composition requires the elimination of the initial composition transient which occurs in directionally solidified alloys. One method of eluding this initial transient involves directionally solidifying a portion of the sample and then quenching the remainder prior to the space experiment. During the space experiment, the MZT sample is back-melted to exactly the point at which directional solidification was stopped on earth. The directional solidification process then continues.

scholarly journals Microstructures and compressive properties of AlxCoCrFeNi high entropy alloys prepared by arc melting and directional solidification

2022 ◽  
Author(s):  
Zhuhuan Yu ◽  
Yawen Yan ◽  
Wei Gao ◽  
Xiaohui Wang ◽  
Xuliang Liu ◽  
...  
Keyword(s):  
Directional Solidification ◽  
Energy Dispersive Spectrometer ◽  
Solidification Process ◽  
High Entropy Alloys ◽  
Directionally Solidified ◽  
High Entropy ◽  
Phase Constituent ◽  
Arc Melting ◽  
The Difference ◽  
Fcc Phase

Abstract The AlxCoCrFeNi (molar radio, x=0.6 and 1.2) high entropy alloys (HEAs) were prepared by arc melting and directional solidification at the withdrawal rate of 150 μm/s. All microstructures were characterized by x-ray diffraction, optical microscopy and scanning electron microscopy with an energy-dispersive spectrometer. Strong similarities in phase constituent were observed between the as-cast samples and directionally solidified samples. The Al0.6CoCrFeNi HEA and Al1.2CoCrFeNi HEA fabricated by two different techniques respectively consisted of Cr-Fe-Co enriched FCC phase + Al-Ni enriched BCC phase and Al-Ni enriched B2 phase + Cr-Fe-Co enriched A2 phase. It was micromorphology found that directional solidification could not only make the microstructures arranged regularly but also coarsen the grains. This has been attributed to the preferred grain orientation and lower cooling rate during directional solidification process. Compression testing showed that the compressive ductility of directionally solidified samples decreased obviously. The ultimate compressive strength of Al0.6CoCrFeNi HEA increased from 1 675 MPa to 1 903 MPa, but the strength of Al1.2CoCrFeNi HEA decreased from 2 183 MPa to 1 463 MPa. The difference in strength has been suggested to be the result of micropores in the matrix.

Precipitate size refinement by CeO2 and Y2BaCuO5 additions in directionally solidified YBa2Cu3O7

1997 ◽  
Vol 12 (1) ◽  
pp. 38-46 ◽  
Author(s):  
N. Vilalta ◽  
F. Sandiumenge ◽  
S. Piñol ◽  
X. Obradors
Keyword(s):  
Directional Solidification ◽  
Strong Influence ◽  
Solidification Process ◽  
Small Concentration ◽  
Precipitate Size ◽  
Directionally Solidified ◽  
Bridgman Technique ◽  
Efficient Procedure ◽  
Size Refinement ◽  
Peritectic Decomposition

Directional solidification of YBa2Cu3O7 has been carried out through a Bridgman technique, and the influence of Y2BaCuO5 and CeO2 additives on the size of Y2BaCuO5 precipitates has been investigated. It is demonstrated in this work that the most efficient procedure to reduce the size of the Y2BaCuO5 precipitates is to increase the concentration of nucleation centers present in the peritectic decomposition of YBa2Cu3O7−x. A small concentration (0.3−1 wt. %) of CeO2 has a strong influence on the solidification process and on the size of Y2BaCuO5 precipitates. It is shown that when CeO2 is added, further refinement of the size of precipitates results from the formation of nanometric Y2O3 particles which further enhance the multinucleation effect. We have also observed that coarsening effects are avoided with CeO2 additives.

Compositional analysis of mercury zinc telluride by EDS and WDS

1991 ◽  
Vol 49 ◽  
pp. 748-749
Author(s):  
M. W. Price ◽  
H. Zuo ◽  
G. M. Janowsk ◽  
R. N. Andrews
Keyword(s):  
Growth Parameters ◽  
Compositional Analysis ◽  
Zinc Telluride ◽  
Methanol Solution ◽  
Infrared Detection ◽  
Device Performance ◽  
Directionally Solidified ◽  
Compositional Homogeneity ◽  
Semiconducting Alloys ◽  
Bulk Alloys

Semiconducting alloys of II-VI compounds have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities in II-VI materials can adversely affect device performance. Extensive work has been conducted to evaluate the influence of growth parameters on the compositional redistribution in directionally solidified bulk alloys. Energy Dispersive Spectroscopy (EDS) has proven to be a valuable tool both in evaluating the compositional homogeneity of II-VI alloys and gaining information about the influence of growth parameters on compositional redistribution.In the work reported here, samples of directionally solidified mercury zinc telluride (MZT) were analyzed by SEM/EDS. The specimens were prepared by longitudinal sectioning, polishing to a 0.25 am finish, chemical polishing with a 2 vol% bromine/methanol solution, and rinsing with distilled water, acetone, and ethanol. Standards of Zn, Te, ZnTe, and HgTe were prepared in a similar manner for the quantitative analysis.

Thermal Parameters, Tertiary Dendritic Growth and Microhardness of Directionally Solidified Al-3wt%Cu Alloy

2016 ◽  
Vol 869 ◽  
pp. 452-457 ◽  
Author(s):  
André Santos Barros ◽  
Maria Adrina Paixão de Souza da Silva ◽  
Otávio Fernandes Lima da Rocha ◽  
Antonio Luciano Seabra Moreira
Keyword(s):  
Growth Rate ◽  
Directional Solidification ◽  
Cooling Rate ◽  
Dendritic Growth ◽  
Solidification Process ◽  
Flow Conditions ◽  
Directionally Solidified ◽  
Cu Alloy ◽  
Cu Alloys ◽  
Transient Heat Flow

The main purpose of this paper is to evaluate both tertiary dendritic arm growth and microhardness of Al-3wt%Cu alloy during horizontal directional solidification under transient heat flow conditions. Experimental thermal profiles recorded during solidification process allowed to determine growth rate and cooling rate values which are associated with both tertiary dendritic arm spacings and microhardness. The results show that initial tertiary branches growth only occurs when a cooling rate value of 1.14 K/s is reached. Variation of tertiary spacings is expressed as-1.1 and-0.55 power law functions of growth rate and cooling rate, respectively. A comparative analysis with other studies published in the literature that analyze tertiary dendritic growth of Al-Cu alloys considering transient directional solidification is carried out. Dependence of microhardness on dendritic arrangement is evaluated by experimental laws of power and Hall-Petch types with a view to permitting the applicability of the resulting expressions.

A TEM and EDS Study on the effect of back melting on directionally solidified HgZnTe

1993 ◽  
Vol 51 ◽  
pp. 1194-1195
Author(s):  
H.J. Zuo ◽  
R.D. Griffin ◽  
R.A. Andrews ◽  
G.M. Janowski
Keyword(s):  
Space Shuttle ◽  
Crystal Defects ◽  
Device Performance ◽  
Directionally Solidified ◽  
Initial Composition ◽  
Low Gravity ◽  
Flight Experiment ◽  
Bulk Growth ◽  
Uniform Composition ◽  
Limited Duration

Bulk growth of II-VI semiconductors such as HgZnTe (MZT) is difficult because of the gravity-induced convection that occurs during solidification. This convection can lead to crystal defects (primarily dislocations and subgrain boundaries) and composition inhomogeneities which may limit device performance. Crystals grown in the low-gravity environment of space should have fewer of these defects. However, the limited duration of space shuttle experiments and the need for uniform composition make it imperative that the initial composition transient that occurs in directionally solidified alloys be eliminated. One proposed solution to this problem is back-melting. In the first stage of this process, a section of the specimen is directionally solidified and the remainder is quenched. The quenched portion is then remelted and directionally solidified. In the flight experiment, the remelting and second directional solidification step will be carried out in space.

Movable partition designed for the seed-assisted silicon ingot casting in directional solidification process

2014 ◽  
Vol 49 (6) ◽  
pp. 405-413 ◽  
Author(s):  
Changlin Ding ◽  
Meiling Huang ◽  
Genxiang Zhong ◽  
Lijun Liu ◽  
Xinming Huang
Keyword(s):  
Directional Solidification ◽  
Solidification Process ◽  
Ingot Casting ◽  
Silicon Ingot ◽  
Directional Solidification Process

Interpenetrating Network-Structured Al2O3–Y3Al5O12 Eutectic Composite Grown by Containerlessly Directional Solidification Process

2015 ◽  
Vol 15 (12) ◽  
pp. 5652-5655 ◽  
Author(s):  
Xiaoguang Ma ◽  
Jianqiang Li ◽  
Zhijian Peng ◽  
Bingqian Ma ◽  
Xiaoyu Li ◽  
...  
Keyword(s):  
Directional Solidification ◽  
Solidification Process ◽  
Eutectic Composite ◽  
Interpenetrating Network ◽  
Directional Solidification Process
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