Plasma spray of Nichrome matrix composite contains dispersed glass for oxidation protection and calcium fluoride for lubrication. Coatings can be applied to bearing journals and bearing bores. Coating was easily machinable and had excellent bond strength on substrate metal

Sliney, H. E.

English

NASA Technical Reports Server

June 1974	 B74-10016 
NASA TECH BRIEF S	 Lewis Research Center 
NASA Tech Briefs announce now 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, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Plasma-Sprayed Metal-Glass Fluoride 
Coatings for Lubrication to 1170 K (1650°F) 
. 
.
The Problem: 
A need exists for the development of improved 
high-temperature, self-lubricating materials. In advanced 
aircraft, the aerodynamic heating at speeds of Mach 3 and 
higher can result in vehicle skin temperatures well above 
the temperature limitations of presently available airframe 
bearings. 
Solid lubricants such as graphite, molybdenum disul-
phide, and graphite fluoride oxidize or dissociate below 
770 K (930°F). Self-lubricating composites of a sintered 
porous nickel base superalloy, in which the pore structure 
is impregnated with calcium fluoride (CaP 2
 )-barium 
fluoride (BaF2 ) eutectic, have been successfully tested for 
long duration in non-oxidizing atmospheres to 1170 K 
(16500 F). In air, however, usefulness is limited to 920 K 
(1200°F) for long durations and 1070 K (1470°F) for 
short durations, because oxidation of the sintered metal 
structure occurs and causes swelling and distortion of the 
part. Previously, considerable improvement was achieved 
by partially filling the pore structure of a metal matrix 
with oxidation-protective glasses. The lubricating fluorides 
were introduced in a second infiltration. The resulting 
composites had improved oxidation resistance and were 
self-lubricating at 1170 K (1650 0 F). However, the double 
infiltration was complex and time consuming. 
The Solution: 
The plasma spraying of a Nichrome matrix composite 
containing dispersed glass for oxidation protection and 
calcium fluoride for lubrication. The coatings can be 
applied to bearing journals and bearing bores. 
How It's Done: 
A special glass of the composition 21.2 w/o BaO -7.8 
w/o CaO - 13.0 w/o K2 0 - bal Si02 is prepared. The glass 
is pebble milled to a fine powder. The powdered glass is 
then mixed with powdered Nichrome metal and CaF 2 to 
the desired composition - 67 w/o Nichrome - 16.5 w/o 
glass - 16.5 w/o CaP 2 for plasma spraying. 
The substrate surfaces are grit blasted with coarse 
alumina grit. The composites are sprayed to a thickness of
about 0.050 cm (0.02 in) and subsequently machined 
back to a thickness of 0.025 cm (0.01 in). During 
spraying, argon is used as the carrier gas and the arc gas. 
An arc current of 350 amperes is used. 
The coating is machined at low speeds and with light 
cuts to prevent smearing of the Nichrome matrix metal. 
The surface is then enriched in the lubricant by heat 
treating the specimens in air at 1145 K (1600°F) for four 
hours. The heat treatment causes a solid state migration of 
fluorides along the surface and serves the added beneficial 
purpose of mildly preoxidizing the exposed metal. The 
surface becomes entirely covered with a combined 
fluoride-oxide film which is very desirable to prevent 
direct metal to metal adhesive contacts during sliding. 
Bearings with a composite liner in the bore were in 
good condition and exhibited very good oxidation resist-
ance after over 50,000 .oscillating cycles. The bearing 
temperatures were controlled, and these temperatures 
were cycled between 300 and 1170 K (77 and 16500F). 
Notes: 
1. During the sliding process, any wear that takes place 
exposes more lubricant thereby preventing an increase 
in wear rate or galling of the surfaces. The lubricating 
material prevents gaffing from room temperature to 
1170 K (1650°F), but is especially effective from 810 
to 1170 K (1000 to 1650°F) at which temperatures 
the glass and particularly the fluorides are soft enough 
to form a smear or glaze of lubricating film on the 
surface. 
2. In general, better results were obtained with the 
coating on the bearing bore rather than on the journal 
surface. The coating was easily machinable and had 
excellent bond strength on the substrate metal. 
3. In addition to aircraft requirements, other areas in 
which high temperature lubrication is needed include 
sliding contact seals for automotive turbine regenera-
tors, shaft seals for turbopumps, piston rings for high 
performance reciprocating compressors, and lubricants 
for hot glass processing machinery. 
(Continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
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 owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000016 2020-03-17T13:42:36+00:00Z
4. Further information is available in the following 
report: 
NASA TN-D-7556 (N74-16146), Self-Lubricating 
Plasma-Sprayed Composites for Sliding-Contact 
Bearings to 900°C 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B74-10016 
5. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B74-10016 
Patent Status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
NASA Patent Counsel 
Mail Stop 500-113 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135
Source: Harold E. Sliney
Lewis Research Center
(LEW-1 1930)
. 
S 
B7440016	 Category 04,07


Plasma-sprayed metal-glass fluoride coatings for lubrication to 1170 K (1650 F)

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