Microbend tester and heat-treating apparatus development for study of high temperature protective coatings for refractory metal

Rexer, J.

English

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HIGH TEMPERATURE PROTECTIVE 
COATING$ FOR REFRACTORY METALS 
by 
J. Rexer  
PROGRESS REPORT NO. 5 
P r e p a r e d  under Contract No. NASw-1405 
UNION CARBIDE CORPORATION 
CARBON PRODUCTS DIVISION 
PAR XA , 0 E10 
fo r  
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
Q * * ' 
'd 
https://ntrs.nasa.gov/search.jsp?R=19680004268 2020-03-12T11:41:51+00:00Z
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TABLE O F  CONTENTS 
Section Page  
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . .  1 
11. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . .  2 
111. PROGRESS . . . . . . . . . . . . . . . . . . . . . . . . .  2 
A. Composites Mechanical Behavior . . . . . . . . . . . . .  2 
B. The Effect of Heat Treatment on Coating Thickness . . . .  
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . .  5 
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TABLES 
T ab1 e Page  
I. TEMPERATURE GRADIENTS WITHIN THE TUNGSTEN 
CRUCIBLE . . . . . . . . . . . . . . . . . . . . . . . . .  3 
ILL U ST R A T IO N S 
Figure  Page  
1. THERMOCOUPLE CALIBRATION CURVE . . . . . . . . . . .  4 
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HIGH TEMPERATURE PROTECTIVE 
COATINGS FOR REFRACTORY METALS 
J. Rexer  
I. INTRODUCTION 
This research ,  performed under Contract NASw- 1405, is a continuation 
of work initiated under Contract NASw-1030('). 
NASw-1405 was extended to Apri l  21, 1968 with slight modifications in  the pro-  
g r a m  objectives. 
the change in  thickness of an iridium coating on the re f rac tory  meta ls  tungsten, 
molybdenum, and niobium due to interdiffusion and intermetal l ic  compound forma-  
tion and 2) to examine microscopically with a microbend tes te r ,  the mechanical 
behavior of iridium-coated and heat-treated specimens. 
After the f i r s t  year ,  Contract 
The major objectives of the present  p rogram a r e  1) to measure  
The effort  during the f i r s t  year under Contract NASw-1405 indicated that 
sufficient work had been performed on the fused salt  electrodeposition of i r idium 
to evaluate i t s  potential a s  a method of cladding re f rac tory  metals.  
pa rame te r s  and apparatus made possible the consistent fused salt e lectro - 
deposition of coherent and adherent i r idium coatings on tungsten and molybdenum-. . 
Since niobium and tantalum reac t  chem-ically with the fused sal t  electrolyte,  these 
meta ls  could not be consistently electroplated with an adherent i r idium coating 
without the pr ior  application of a n  unreactive intermediate coating such a s  nickel. 
The amount of iridium depleted through intermetal l ic  compound formation can 
best  b e  determined directly f r o m  measurements  of the thickness of iridium r e -  
maining af te r  annealing r a the r  than f rom measurements  of changes in the thickness 
of the total reaction zone. 
polishing and etching techniques needed to reveal  the reaction zone interfacial  
boundaries, the total reaction zone thickness is still difficult to determine because 
The plating 
Although some success  was achieved in developing the 
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of i r regular i t ies  in  these boundaries. 
were a direct  consequence of the above findings. 
The changes in the p rogram objectives 
This repor t  discusses  the r e sea rch  effort for the period 21  April  1967 
to 21 July 1967. 
11. SUMMARY 
During - thepresent  repert pLl i d ,  a spring-loaded microbend t e s t e r  was 
designed and is being constructed. 
microscope platform permitt ing side -of -beam observations of metallographically 
polished surfaces  during deformation. 
means of a spring-loaded balance having a marke r  recording the maximum applied 
load. 
coated and heat-treated samples.  
The microbend t e s t e r  will be mounted on a 
The applied load will be measured by 
Flexural  strengths will be calculated f r o m  the data obtained with iridium 
A previous malfunction of the temperature  control unit resulted in exten- 
This apparatus and the control unit sive damage to the heat-treating apparatus. 
have been repaired.  The best  control settings for the controller were  established 
permitt ing set-point control of the temperature of the tungsten crucible within the 
range 1100" to 2100°C. In additiwrr, a calibration curve was obtained for the new 
thermocouple, and the radial  temperature distribution within the tungsten crucible 
was established a t  various temperature settings. 
111. PROGRESS 
A .  Composites Mechanical Behavior 
( 1 )  A microbend tes te r  was constructed under Contract No. NASw-1030 
so that we might obtain more  knowledge concerning the mechanical behavior of 
i r id iumcoated  and heat-treated composites; the basic  design of the microbend 
tes te r  follows that proposed by Flinn and Trojan(2).  
permitted microscopic observation of the side of the beam while a bending s t r e s s  
was applied. 
attached to two outer loading pins while the center pin was  held stationary. 
Consequently, neither the load being applied nor the maximum load at f rac ture  
The microbend tes te r  
Three-point loading was accomplished by turning a thumbscrew 
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could be measured. 
structed which will  permi t  the load  to be applied to two outer loading pins through 
the plunger of a spring balance. The spr ing balance is calibrated to within 1 / 8  lb. 
and has  a marke r  to measure  the maximum applied load. 
new microbend t e s t e r  is not significantly diiferent f r o m  the previous one. 
F o r  the present program,  a s imi la r  device is being con- 
In other respec ts ,  the 
B. The Effect of Heat Treatment oncoa t ing  Thickness 
The apparatus for heat treating i r idium coated samples  and the electronic  
The var ious adjustments of the con- temperature  controller have been repaired. 
t ro l le r  were  systematically tuned for set-point control of the temperature  of the 
tungsten crucible.  
variations of five degree,; af the desired tempera tures ,  at  100°C intervals ,  with- 
in the range 1100" to 2100°C. 
inside of the tungsten crucible,  was calibrated against  a calibrated micro-  
optical pyrometer .  
plotted is the average of five determinations at  each thermocouple output setting. 
In addition, the radial  temperature  distribution within the tungsten crucible was 
established at severa l  temperatures  through the use of a crucible lid containing 
five 1/16 inch diameter holes. 
located in the center of the lid and the remaining four holes were  uniformly 
distributed between the inner crucible surface and the center hole. 
gradients which could be determined by the optical pyrometer  were observed. 
Optimum control sett ings were  established for  temperature  
A w-570 R / W - 2 6 7 0  Re thermocouple, positioned 
The calibration curve i s  given in Figure 1. The tempera ture  
In the accompanying table, hole number one was 
No temperature  
TABLE I 
Temperature Gradients Within the Tungsten Crucible 
Tem at Ave.  Temp. 
Hole % Hole E, " C  "C Temp. at * Temp. at Tern at Hole #1, "C Hole #2, "C Hole &;, " C  
1288 i 10 1278 f 10 1278 f 10 1288 f 10 1280 f 10 1282 
1497 f 10 1491 f 10 1500 f 10 1503 f 10 1497 f 10 1498 
1683 f 12 1675 & 12 1700 f 12 1696 f 12 1689 f 12 1689 
1900 f 15 1885 i 15 1870 i 15 1900 f 15 1879 f 15 1887 
* Each recorded temperature is the average of 10 trials. 
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Black Body Temperature, t"C x 
Figure 1 .  Thermocouple Calibration Curve 
N-18111 
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REFERENCES 
1. Criscione, J. M.,  Rexer,  J. , and Fenish,  R. G. , "High Tempera ture  
Protective Coatings for  Refractory Metals", under Contract NASw- 1030. 
2. Flinn, R. A .  , and Trojan, P. K . ,  "Examination of Microstructure  Under 
Varying Stress",  Metal P rogres s ,  July, 1955. 
Upion Carbide Corporation 
C arbon Product s Divi sion 
Parma, Ohio 44130 
December 18, 1967 
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DISTRIB UTI0 N 
NASA Headquarter s ( 15) 
Code RRM 
Washington, D. C. 20546 
NA SA He adquar t e r s 
Code RRM 
Washington, D. C. 20546 
Attn. : Mr. Joseph Maltz 
Attn. : NASA Representative (2) 
Scientific and Technology Information Facil i ty 
P. 0. Box 5700 
Bethesda, Maryland 
Inspector of Naval Mater ia ls  
Ferguson Building 
1793 Eas t  11 Street  
Cleveland, Ohio 441 14 
M r  . William Klopp 
Lewis Resea rch  Center 
21000 Brookpark Road 
Cleveland, Ohio 


High temperature protective coatings for refractory metals Progress report

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