Report describes growth of silver-alloy crystals under widely varying conditions of growth rate, temperature gradient, and magnetic field. Role of gravitation and convection on crystal substructure is analyzed, as well as influence of magnetic fields applied during crystallization

Gelles, S. H.

Miller, J. F.

English

NASA Technical Reports Server

October 1975
	 875-10268 
•	 NASA TECH BRIEF 
Marshall Space Flight Center 
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Single Crystals of Metal Solid Solutions: A Study 
A published report describes the growth of 
silver-alloy crystals under widely varying conditions of 
growth rate, temperature gradient, and magnetic 
field. The role of gravitation and convection on the 
crystal substructure is analyzed, as well as the 
influence of magnetic fields applied during crystal- 
lization. The study, entitled "Single Crystals of Metal 
Solid Solutions," indicates that magnetic fields of 
moderate strength damp out convective currents. 
Single crystals grown within the field will form with a 
preferred orientation. Without the presence of the 
magnetic field, polycrystals having a random orienta-
tion are formed. 
The report divides the study objectives into four 
tasks: (1) "Investigation of the Influence of Convec-
tion and Crystal Growth," (2) "Investigation of the 
Influence of Magnetic Fields on Crystal Growth," (3) 
"Characteristics of Crystals and Analysis of the 
Effects of Growth Conditions," and (4) "Space Flight 
Experiment Definition." A summary of the report 
follows. 
Experiments determined the characteristics and 
effects of convection currents in molten Ag-20Zn alloy 
in a' horizontal boat. Temperature fluctuations, 
resulting from the convection currents, were moni-
tored at overall longitudinal temperature gradients of 
1.50, 2.5°, 550 ,
 750, 8°, 12°, and 16.5° C/cm in the 
region of the thermocouples. No significant short-
term temperature fluctuations were observed with 
longitudinal temperature gradients less than 8° C/cm. 
Magnetic fields applied in the range of 50 to 4,000 
gauss showed that low-to-moderate fields (50 to 250 
gauss) decreased the amplitude of convection-current
induced temperature oscillations and damped out 
some, of the complex oscillations, while fields in the 
range of 300 to 350 gauss appeared to damp out all 
oscillations caused by turbulent convection. No 
additional effect was detected when higher magnetic 
fields (up to 4,000 gauss) were applied. 
Several horizontal Bridgman crystal-growth runs 
were made with and without seeds, both under 
conditions calculated to produce constitutional 
supercooling 'and cellular growth and to give planar 
interface growth and banding. The single-crystal seed 
material of the Ag-20Zn alloy had been grown in 
vertical Bridgman growth runs. The examination of 
ingots crystallized under conditions calculated to give 
constitutional supercooling revealed expected cellular 
growth. The results of electron microprobe analysis of 
the cellular structure indicated that cell-wall thickness 
and composition differed from ingot to ingot, 
presumably due to differences in crystallization rate 
and melt composition. 
Metallographic examination of some ingots, grown 
under conditions calculated to give planar interface 
growth (with and without magnetic fields up to 4,000 
gauss) revealed no unusual microstructural features. 
However, distinct changes in macrostructure were 
found to correlate with the application and removal of 
the magnetic field. Limited X-ray Laue diffraction' 
analysis, conducted on one of the ingots containing 
sections grown with and' without a magnetic field, 
indicated that there was a preferred growth direction 
in both the single-crystal and polycrystalline portions. 
(continued overleaf) 
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r
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writing to: 
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Marshall Space Flight Center 
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Marshall Space Flight Center, Alabama 35812 
Reference: B75-10268
Patent status: 
NASA has decided not to apply for a patent. 
Source: J. F. Miller and S. H. Gelles of

Battelle Memorial Institute

(MFS-23268)
S 
Categories: 03 (Physical Sciences) 
04 (Materials) 
B75-10268
	
08 (Fabrication Technology)


Single crystals of metal solid solutions: A study

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