Thermal Fatigue of NiAl Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
M. T. Kush ◽  
J. W. Holmes ◽  
R. Gibala
Keyword(s):  
Single Crystals ◽  
Thermal Fatigue ◽  
Thermal Stresses ◽  
Elastic Anisotropy ◽  
Thermal Strain ◽  
Cyclic Strain ◽  
Heating And Cooling ◽  
Tension And Compression ◽  
Temperature Heating ◽  
Shape Changes

ABSTRACTSingle crystals of [001]-oriented NiAI single crystals were subjected to thermal fatigue by a method which employs induction heating of disk-shaped specimens heated in an argon atmosphere. Several time-temperature heating and cooling profiles were used to produce different thermal strain histories in specimens cycled between 973 K and 1473 K. After thermal cycling, pronounced shape changes in the form of diametrical elongations along <100> directions with accompanying increases in thickness at and near the <100> specimen axes were observed. The deformations were analyzed in terms of operative slip systems in tension and compression, ratchetting (cyclic strain accumulation), and the elastic properties of NiAl. The experimental results correlate best with thermal stresses associated with the large elastic anisotropy of NiAl.

A rig for controlled cyclic strain and temperature testing

1982 ◽  
Vol 17 (1) ◽  
pp. 45-52 ◽  
Author(s):  
D J Beauchamp ◽  
E G Ellison
Keyword(s):  
Mechanical Strain ◽  
Thermal Strain ◽  
Cyclic Strain ◽  
Heating System ◽  
Temperature Cycle ◽  
Transient Temperature ◽  
Microprocessor System ◽  
Hydraulic Test ◽  
Heating And Cooling ◽  
Phase Temperature

A servo-hydraulic test rig capable of applying combined temperature and strain or load cycles has been developed and commissioned. The nature of the test has dictated the specimen form as a hollow, hour-glass type. The critical problem of a suitable extensometer for temperature and strain cycling has been solved. The device designed and produced shows negligible transient temperature effects, has a high resolution of better than 0.1 μm, and is mechanically very stable. The heating and cooling is controlled by an induction heating system with grip cooling; additional cooling is available using compressed air passing through the hollow specimen. The system is capable of following a temperature ramp to within 1°C linearity. The thermal strain associated with a temperature cycle is compensated for using a microprocessor system specially developed for the purpose, which also enables a mechanical strain-stress loop to be plotted during a test. Both ‘in-phase’ and ‘out-of-phase’ temperature/strain cycles have been carried out and development continues to include dwell periods.

Microstructural Stability Of a NiAI-Mo Eutectic Alloy

1998 ◽  
Vol 552 ◽  
Author(s):  
M. T. Kush ◽  
J. W. Holmes ◽  
R. Gibala
Keyword(s):  
Thermal Cycling ◽  
Thermal Stresses ◽  
Boundary Region ◽  
Microstructural Stability ◽  
Directionally Solidified ◽  
Columnar Microstructure ◽  
Heating And Cooling ◽  
Cellular Microstructure ◽  
Temperature Heating ◽  
Specimen Shape

ABSTRACTThe microstructural stability of a directionally-solidified NiA1–9 at.% Mo quasi-binary alloy was investigated under conditions of thermal cycling between the temperatures 973 K and 1473 K utilizing time-temperature heating and cooling profiles which approximate potential engine applications. Two different microstructures were examined: a cellular microstructure in which the faceted secondphase Mo rods in the NiAl matrix formed misaligned cell boundaries which separated aligned cells approximately 0.4 mm in width and 5–25 mm in length, and a nearly fault-free fully columnar microstructure well aligned along the [001] direction. Both microstructures resisted coarsening under thermal cycling, but plastic deformation induced by thermal stresses introduced significant specimen shape changes. Surprisingly, the cellular microstructure, for which the cell boundary region apparently acts as a deformation buffer, exhibited better resistance to thermal fatigue than the more fault-free and better aligned columnar microstructure.

scholarly journals The Elastic Constants of the Single Crystal of the Mg-Zn-Zr-REM Alloy from the Data of the Elastic Anisotropy and the Texture of the Polycrystalline Sheet

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
S. V. San’kova ◽  
N. M. Shkatulyak ◽  
V. V. Usov ◽  
N. A. Volchok
Keyword(s):  
Single Crystals ◽  
Young’S Modulus ◽  
Elastic Constants ◽  
Elastic Anisotropy ◽  
Young's Modulus ◽  
Rare Earth Metals ◽  
Alloy Sheet ◽  
Pole Figures ◽  
Integral Characteristics ◽  
Experimental Values

The measuring of the constants of single-crystals requires the availability of crystals of relatively big size. In this paper the elastic constants of the single crystals of magnesium alloy with zinc, zirconium, and rare earth metals (REM) were determined by means of the experimental anisotropy of Young’s modulus and integral characteristics of texture (ICT), which were found from pole figures. Using these constants the anisotropy of Young’s modulus of alloy sheet ZE10 was calculated. Deviation of calculated values from experimental values did not exceed 2%.

scholarly journals Potential of using inert gas flows for controlling the quality of as-grown silicon single crystal

2020 ◽  
Vol 6 (1) ◽  
pp. 1-7
Author(s):  
Tatyana V. Kritskaya ◽  
Vladimir N. Zhuravlev ◽  
Vladimir S. Berdnikov
Keyword(s):  
Single Crystal ◽  
Carbon Content ◽  
Single Crystals ◽  
Gas Flow ◽  
Thermal Stresses ◽  
Crystal Surface ◽  
Gas Flows ◽  
Reaction Products ◽  
Crystal Silicon ◽  
Argon Gas

We have improved the well-known Czochralski single crystal silicon growth method by using two argon gas flows. One flow is the main one (15–20 nl/min) and is directed from top to bottom along the growing single crystal. This flow entrains reaction products of melt and quartz crucible (mainly SiO), removes them from the growth chamber through a port in the bottom of the chamber and provides for the growth of dislocation-free single crystals from large weight charge. Similar processes are well known and have been generally used since the 1970s world over. The second additional gas flow (1.5–2 nl/min) is directed at a 45 arc deg angle to the melt surface in the form of jets emitted from circularly arranged nozzles. This second gas flow initiates the formation of a turbulent melt flow region which separates the crystallization front from oxygen-rich convective flows and accelerates carbon evaporation from the melt. It has been confirmed that oxygen evaporated from the melt (in the form of SiO) acts as transport agent for nonvolatile carbon. Commercial process implementation has shown that carbon content in as-grown single crystals can be reduced to below the carbon content in the charge. Single crystals grown with two argon gas flows have also proven to have highly macro- and micro-homogeneous oxygen distributions, with much greater lengths of single crystal portions in which the oxygen concentration is constant and below the preset limit. Carbon contents of 5–10 times lower than carbon content in the charge can be achieved with low argon gas consumption per one growth process (15–20 nl/min vs 50–80 nl/min for conventional processes). The use of an additional argon gas flow with a 10 times lower flowrate than that of the main flow does not distort the pattern of main (axial) flow circumvention around single crystal surface, does not hamper the “dislocation-free growth” of crystals and does not increase the density of microdefects. This suggests that the new method does not change temperature gradients and does not produce thermal shocks that may generate thermal stresses in single crystals.

scholarly journals Progressive Damage in Unidirectional Ceramic Composites Under Transient Thermal Fatigue

1991 ◽  
Author(s):  
A. Sinha ◽  
K. Kokini ◽  
K. J. Bowman
Keyword(s):  
Thermal Fatigue ◽  
Ceramic Composites ◽  
Ultrasonic Pulse ◽  
Unidirectional Composite ◽  
Progressive Damage ◽  
Cyclic Heating ◽  
Heating And Cooling ◽  
Stiffness Properties ◽  
Transient Thermal ◽  
Pulse Echo

The changes in stiffness properties for a CAS matrix-Nicalon fiber unidirectional composite resulting from cyclic heating and cooling are presented. The measurements are made using an ultrasonic pulse-echo technique. It is shown that a significant decrease in stiffness is observed after 30 cycles.

Cyclic strain localization in copper single crystals and polycrystals

1990 ◽  
Vol 24 (2) ◽  
pp. 415-419 ◽  
Author(s):  
Jaroslav Polák ◽  
Jan Helešic ◽  
Karel Obrtlík
Keyword(s):  
Single Crystals ◽  
Strain Localization ◽  
Cyclic Strain ◽  
Copper Single Crystals

Superelastic response in 〈1 2 2〉-oriented single crystals of FeMnAlNi shape memory alloy in tension and compression

2018 ◽  
Vol 233 ◽  
pp. 195-198 ◽  
Author(s):  
V.V. Poklonov ◽  
Y.I. Chumlyakov ◽  
I.V. Kireeva ◽  
V.A. Kirillov
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Single Crystals ◽  
Tension And Compression

Processing and Properties of Mo5Si3 Single Crystals and Alloys

1998 ◽  
Vol 552 ◽  
Author(s):  
F. Chu ◽  
D. J. Thoma ◽  
K. J. McClellan ◽  
P. Peralta ◽  
F. X. Li ◽  
...  
Keyword(s):  
Single Crystals ◽  
Elastic Properties ◽  
Elastic Anisotropy ◽  
Orientation Dependence ◽  
High Melting ◽  
Design Strategies ◽  
Solubility Range ◽  
Metal Silicides ◽  
Deformation And Fracture ◽  
Indentation Tests

ABSTRACTAmong the high-temperature intermetallic systems, transition-metal silicides are attractive because of their high melting temperatures (many greater than 2273 K) and potential oxidation resistance. In particular, Mo5Si3 exhibits a very high melting point (2453 K) and also has a solubility range of 2 – 3 atomic percent, which can aid in processing and alloy design strategies. The focus of this study is to evaluate the processing and properties of Mo5Si3 and Mo5Si3-base ntermetallics. For the optimal baseline comparison, high-purity single crystals have been fabricated, and thermal and elastic properties have been experimentally measured. Although Mo5Si3 has a strong thermal expansion anisotropy, ts elastic anisotropy factors and the Poisson's ratios indicate that Mo5Si3 is less anisotropic in elasticity. The combination of the thermal and elastic properties has been employed to calculate the thermal residual stress and to explain the potential for grain boundary cracking during processing. Room temperature Vickers indentation tests of Mo5Si3 have been performed. The orientation dependence of hardness and fracture toughness of Mo5Si3 single crystals have been obtained. The corresponding deformation and fracture modes have been revealed by microscopy studies. Finally, micro- and macroalloyed Mo5Si3 with aluminum and boron will be briefly explored with property assessments.

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