Test conditions and results are reported for various coatings on a 1 percent zirconium columbium alloy at a temperature of 2000 deg F. Molybdenum silicide over molybdenum is most effective coating, tin-aluminum coating is adequately protective, chromium-molybdenum silicides are not protective

Phillips, W. M.

English

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December 1970	 Brief 70-10674 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Oxidation-Resistant Coatings for Refractory Metals Used in Inert Atmospheres 
Portions of refractory-metal parts of high-temper-
ature power systems are commonly exposed to inert 
atmospheres containing traces of oxygen and other 
impurities. Protection by an oxidation-resistant coat-
ing may be desirable and/or necessary. Selection of 
the coating must be based on its effectiveness in pre-
venting oxidation, and on its reactive effect on and 
protection of the substrate. The test results reported 
are for various coatings on a 1%-zirconium columbium 
alloy at a temperature of 2000°F. The 2-by-0.5-in. 
specimens were cut from 1/8-in. sheet stock. The argon 
atmosphere contained oxygen at from 1 to 3 ppm. 
The water-vapor content decreased from an initial 
value of less than 10 ppm to from 1 to 3 ppm within 
24 hours. 
Specimens PCA and PCB received single-cycle 
coatings of a proprietary material; specimens PCC and 
PCD received two-cycle coatings. Specimens S-1, 
S-2, and S-3 received tin-aluminum coatings. Four 
more specimens were coated with KA-1, K-2, KA-3, 
and KA-4. (KA refers to a specific manufacturer's 
designation.) Three specimens, VCA, VCB, and VCM, 
received 0.003-in, coatings of modified chromium-
molybdenum disilicide. A fourth (VCM-5) in this 
series was coated (by halide decomposition)with 0.005 
in. of molybdenum topped with an unmodified 
molybdenum disilicide. 
After 500 hours at 2000°±25°F, the specimens were 
cooled five times to 70°F before being reheated to 
2000°F. Each cooling cycle took approximately 12 
hours; the heating cycles required approximately 6 
hours. The depth to which the coating diffused into 
or contaminated the substrate was evaluated by 
metallography, microhardness testing, and micro-
probe analysis. A diamond-pyramid indenter and 
a 25-g load on a Tukon tester were used for the
microhardness. 
Molybdenum silicide over molybdenum appeared 
to be the most effective coating. The chromium-molyb-
denum silicides were not protective and caused dif-
fusion of chromium into the substrate. All PC and KA 
coatings permitted some oxidation of the substrate. 
The tin-aluminum coating adequately inhibited oxida -
tion in two of the three specimens, with little evidence 
of contamination in the third; thus it is believed to 
be adequately protective. 
Note: 
The following documentation may be obtained 
from:
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Springfield, Virginia 22151 
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Reference: 
N67-15683, Evaluation of Oxidation-Resis-
tant Coatings for Inert-Atmosphere Applica-
tions 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code I 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: W. M. Phillips of
Caltech/J PL
under contract to
NASA Pasadena Office
(N PO- l 1477) 
Category 04 
This document was prepared under the sponsorship of the National
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Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately ownedrights.
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Oxidation-resistant coatings for refractory metals used in inert atmospheres

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