This is an archive of messages from the space drives email list "lightly edited" to remove irrelevant headers, etc. Email addresses of participants have been removed because of spam and virus attacks in 2002.
You can download pdf files containing some of our reports on Space Mechanisms
and Aerospace Lubrication. You can find links for these at the following
URL:
http://WWW.grc.nasa.gov/WWW/spacemech/s-m-papers.html.
Note that These are scanned images of printed reports so the files are
rather large.
** "Fundamental Aspects of Polyamide Dry Film and Composite Lubrication
-- A Review"
** "How to Evaluate Solid Lubricant Films Using a Pin-on-Disk Tribometer"
** "Self-Lubricating Polymer Composites and Polymer Transfer Film Lubrication
for Space Applications"
** "Tribology Needs for Future Space and Aeronautical Systems"
** "Liquid Lubricants for Advanced Aircraft Engines"
** "Liquid Lubrication for Space Applications"
** "Space Mechanism Needs for Future NASA Long Duration Space Missions"
** "Lubrication of Space Systems"
Hello Space Drivers,
My thanks to the creator of this space drives list and to Fred who maintains it. It sounds like a wonderful resource. I've been subscribed for a month now. Since I haven't seen a single piece of mail come through, I thought I'd pose a few questions just to see if anyone is out there.
First of all, is there an archive of this list anywhere? I'd like to see what I've been missing all these years.
Second, I'd like to know if there any boundary lubricant additives (equivalents of fatty acid or EP additives) that work with Bray grease and don't evaporate away in vacuum? I've got a 10 year old paper from an obscure journal that talks about a new additive, but it doesn't mention vacuum, and besides, I'm not a chemist. We have a fellow here, (a rather slippery character... :-) who heard that a PFPE-soluble EP additive recently became available. Does anyone know what this might be and where I can get information on it?
And speaking of information... other than the Bray data sheet, does anyone know where I can get property data on Bray greases? i.e., data on viscosity as a function of temperature, density, etc? Our M&P guys were told that Bray doesn't have this data for Braycote 600. We're trying to see if Ausimont has it for their equivalent grease (http://WWW.Ausimont.com/docs/fom_grease.html) but it doesn't look promising. Alternately, does anyone have the test equipment for measuring viscosity per ASTM D-1092 "Measuring Apparent Viscosity of Lubricating Greases" ?
Thanks in advance for any assistance,
Mark Balzer
Mark -
I just recently became a member of this mailing list, but I saw your previous posting regarding additives for PFPE-based lubes on the list archives. There are some Krytox lubes that are being marketed with new (proprietary) additives. They have names like XP 1A5 and XP 1A6. (The viscosity of XP1A6 seems to be very similar to the old Krytox 143AC, so they may be trying to sell that as a drop-in replacement for 143AC.) One big caveat, however: I don't believe they are space-qualified, and seem to be intended for more common terrestrial uses. It may be they can be vacuum stripped to provide lower vapor pressures, but this would probably result in a viscosity increase.
Here's a website that talks about the lubes: http://WWW.dupont.com/lubricants/58547.htm
With regard to Braycote 600 grease, I believe it is just Bray 815Z oil
with a TFE thickener, so viscosity data on 815Z is probably what you need.
For example, I have a data sheet on Braycote 601 (I think Braycote 601 is the
same as Braycote 600, but with a corrosion inhibitor added), and the data sheets
for Braycote 601 and Braycote 815Z list virtually identical viscosities at
various temperatures, and both have a viscosity index of 350. Here's some
websites (or I can fax more detailed data sheet info to you):
http://WWW.2spi.com/catalog/vac/braycote-815z-base-oil.html
http://WWW.2spi.com/catalog/vac/braycote-601EF.html
(not very detailed info)
I hope this helps
Jeffrey R. Lince, PhD
Space Materials Laboratory, The Aerospace Corporation
>>>There are some Krytox lubes that are being marketed with
new (proprietary) additives. They have names like XP 1A5 and XP 1A6.
(The viscosity of XP1A6 seems to be very similar to the old Krytox 143AC, so
they may be trying to sell that as a drop-in replacement for 143AC.) One
big caveat, however: I don't believe they are space-qualified, and seem to be
intended for more common terrestrial uses. It may be they can be vacuum
stripped to provide lower vapor pressures, but this would probably result in a
viscosity increase. Here's a website that talks about the lubes:
http://WWW.dupont.com/lubricants/58547.htm<<<
Thanks very much - these Krytox pages have much more info than I have been able to find about the Bray versions. In looking over the chart on the web page above, one question comes immediately to mind: How is the "Estimated Useful (temp) Range" determined? Take a look at the numbers:
The Bray 600 lists a base oil viscosity of of 140 cSt @ 40 °C
but lists a min temp of -80 °C
The Krytox XP2A3 lists a base oil viscosity of 30 cSt @ 40 °C
but lists a min temp of -60 °C
and
The Fomblin ZLHT lists a base oil viscosity of 150 cSt @ 20 °C
but lists a min temp of -80 °C
The Krytox XP2A3 lists a base oil viscosity of 80 cSt @ 20 °C
but lists a min temp of -60 °C
Unless the viscosity/temperature slopes are different, this doesn't appear to make sense... Do you know if the temp range might come out of tests per ASTM D1478 "Standard Test Method for Low-Temperature Torque of Ball Bearing Grease" where they pack a 1" bearing _full_ of grease and rotate it at 1 rpm while measuring the torque absorbed? If so, what is the peak torque that defines the end of the useful range? Is it arbitrarily defined (so each manufacturer picks whatever they like), or is it the torque that takes the test equipment off scale (75000 g-cm or about 7.5 N-m)? Or is this really just a test for comparing two candidate greases because the conditions are so unreal?
And as a somewhat off-topic diversion, the Krytox page says:
Proper lubrication is achieved by using the correct amount of grease. Too little grease in the bearings causes premature failure. Too much grease at the initial fill or during relubrication can cause overheating of bearings that are running at medium to high speed, resulting in bearing failure. The amount of grease put in the bearing depends on the application and operating speed. For applications such as conveyor rollers and low-speed machinery with DN values (inner race ID in mm x rpm) below 50,000, the bearing can be filled to capacity. For medium-speed applications, i.e., DN 50,000 to 200,000, the bearing can be filled 50-70%. For higher-speed systems, the fill is typically 30-40%. Some extreme-speed special applications have grease fills of only 10-15%.
Admittedly, I haven't made a study of this, (most limited life things here are grease plated) but Krytox provides much more detail than I've ever read regarding grease packing bearings, so I have to ask, is this Krytox-specific advice, or a general recommendation that they are just repeating, w/o listing the source?
>>> With regard to Braycote 600 grease, I believe it is just Bray 815Z oil with a TFE thickener, so viscosity data on 815Z is probably what you need. For example, I have a data sheet on Braycote 601 (I think Braycote 601 is the same as Braycote 600, but with a corrosion inhibitor added), and the data sheets for Braycote 601 and Braycote 815Z list virtually identical viscosities at various temperatures, and both have a viscosity index of 350.<<<
Jeff, this last sentence of yours is what led me to write my first email to this list. The Bray grease data sheets only list the viscosity of the BASE OIL and not the grease. At the time I figured, "What good is that?... I need the viscosity of the grease!" (I need a lube for a 5 stage planetary gearbox with a 4.333 reduction per stage that has to be qualified at -80°C ( no heaters allowed :-( ) and am worried about how to estimate torque losses due to the viscosity.)
As a newbie to all this, I had to put a number of puzzle pieces together to find the answer, but a rheology textbook shed some light on it. It turns out that grease is decidedly non-newtonian... the tests in ASTM D-1092 "Measuring Apparent Viscosity of Lubricating Greases" measure just that... the APPARENT viscosity which is a function of shear rate... and a rather dramatic one at that! Grease is a shear thinning fluid and the apparent viscosity of PFPE greases is roughly halved every time you double the shear rate. (if anyone cares, you can think of it as viscoelastic and define a complex viscosity with a storage and loss moduli...). It gets messy trying to make any real world predictions from this.
But then I found a couple of great papers which say that for estimating torque losses in grease lubed ball bearings, it isn't the grease viscosity that matters... viscous torque loss depends primarily on the base oil viscosity! This jives with Doug Packard's (JPL mechanism designer) observation that "A well run in grease plate has friction levels which approach `oil only.'" So the world is beginning to make sense again :-)
>>> Here's some websites (or I can fax more detailed
data sheet info to you):
http://WWW.2spi.com/catalog/vac/braycote-815z-base-oil.html
http://WWW.2spi.com/catalog/vac/braycote-601EF.html
(not very detailed info) <<<
Right now I'm waiting for info to arrive on some new Bray 700 series greases
with a non-soluble EP additive mixed in. Maybe we can trade :-)
Mark Balzer, NASA / JPL
Hello Space Drivers,
I'm really getting snowed under with all the emails you guys post to this list... I may have to drop off the list for a while just to get caught up :-) :-) :-)
Anyway, my problem du jour is an offshoot of the questions I asked in my last email... first the "micro" part:
Do any of you lubrication guru's out there know of any good books or papers that discuss the effect of surface finish and lay on the performance of boundary lubricated (intermittent, slow, heavily loaded, grease lubricated once at the beginning of life...) shafts/bushings/gears? I'm looking for something that talks about how surfaces that are too smooth will squeegee the lube away, surfaces that are too rough will wear out rather than wear in, etc.
Now the "macro" part: Other than the old advice not to put grooves where they will destroy the pressure distribution developed in a bushing, have you ever come across any design recommendations for sizing the lubricant reservoir pockets or grooves that are often seen in bushings designed for boundary lubricated service (intermittent, slow, heavily loaded, grease lubricated once at the beginning of life... for example, http://WWW.garlockbearings.com/dx/dx.htm) ? Would you even consider designing a bushing for this kind of service without some type of lubricant reservoir feature (or porosity) ?
Finally, do you know of any databases of material combinations (metals, coatings, polymers, etc.) that run well together (preferably when PFPE lubed in vacuum, but I'll take any info I can get my hands on), or just as importantly, a list of material combinations that don't work well together (i.e., seize up immediately) ?
Thanks in advance for any assistance,
Mark "squeaky wheel" Balzer
--
Mark Balzer, NASA / JPL
Mark Balzer asked and Bob Fusaro answers:
>> DO ANY OF YOU LUBRICATION GURU'S OUT THERE KNOW OF ANY GOOD BOOKS OR PAPErs that discuss the effect of surface finish and lay on the performance of boundary lubricated (intermittent, slow, heavily loaded, grease lubricated once at the beginning of life...) shafts/bushings/gears? I'm looking for something that talks about how surfaces that are too smooth will squeegee the lube away, surfaces that are too rough will wear out rather than wear in, etc. <<
I would suggest looking at the CRC Handbook of Lubrication, edited by Booser. If you are really in boundary lubrication, it is not the lubricant but the reaction film on the surface that is providing the lubrication. These films function much like a solid lubricant, and they tend to wear off with time; but if additional oil is present they can reform. Under high load, "edge effects" due to stress risers in un-smooth surfaces can cause wear of a counterface.
>> Now the "macro" part: Other than the old advice not to put grooves where they will destroy the pressure distribution developed in a bushing, have you ever come across any design recommendations for sizing the lubricant reservoir pockets or grooves that are often seen in bushings designed for boundary lubricated service (intermittent, slow, heavily loaded, grease lubricated once at the beginning of life... for example, http://WWW.garlockbearings.com/dx/dx.htm ) ? Would you even consider designing a bushing for this kind of service without some type of lubricant reservoir feature (or porosity) ? <<
Don't have any answer for this one, other than the fact that it may be possible to design the bearing so that it could be actively lubricated without affecting the contact areas.
>> Finally, do you know of any databases of material combinations (metals, coatings, polymers, etc.) that run well together (preferably when PFPE lubed in vacuum, but I'll take any info I can get my hands on), or just as importantly, a list of material combinations that don't work well together (i.e., seize up immediately) ? <<
The CRC Handbook of Lubrication, edited by Booser recently has come out with a new volume with data on material properties. Tribology is so systems dependent, what you use is dependent on the end use conditions of load, speed, temperature, contact geometry, atmosphere, etc. I would say what you want to use is a good bearing material. 440C stainless steel is one of the best. In general, solid lubricants do not work well with oils, they debond and do very little good.
I would contact Bill Jones at NASA, he has worked in this area for years
and has written many papers.
also
Fred Morales of NASA has done a lot of work in this area, especially on the decomposition of it.
For myself, I would not want to use PFPE in vacuum under boundary conditions. The work by Morales shows that it will eventually decompose under boundary conditions. Pennzain grease would be a better choice.
Bob Fusaro
NASA/Glenn Research Center
Space Mechanisms Website: http://WWW.grc.nasa.gov/WWW/spacemech/
> and Bob Fusaro answers:
> I would suggest looking at the CRC Handbook of Lubrication, edited by Booser.
Thanks very much for the reference - I will try to obtain that book tomorrow.
> If you are really in boundary lubrication, it is not the lubricant but the reaction film on the surface that is providing the lubrication.
Understood. Maybe I should have said "mixed" rather than "boundary."
My reason for asking this is as follows: Buried in Annex A of AGMA 2001-C95
"Rating factors and calculation methods for involute spur and helical gear
teeth" is this wonderful little "KISS" equation for mean coefficient of
friction of mating gear teeth when operated in the partial EHD regime:
u = 0.06 x 50 / ( 50 - S )
where S is the surface finish of the active profile of meshing gear
teeth (they claim this applies for S < 32 ).
This implies that the smoother I can make my gear teeth, the better the mesh efficiency will be. Plus when the temps are cold, my lube turns to molasses and I'm losing efficiency left and right, wouldn't it be great if the the smooth finishes help the gear meshes shift to full EHD and become more efficient? :-)
So we sent a co-op student who is helping me to a gear superfinishing meeting to see what he could learn, and he came back singing the praises of mirror finishes on oil-lubricated high speed helicopter gears... which really isn't my situation.
Anyway, I'm sure that as-ground gears get the job done in countless
intermittent, slow, heavily loaded, grease lubricated once at the beginning of
life applications, but maybe they work because their surface asperities trap
enough lube to keep things sliding along. I don't know the answer, but if
someone else does, then I don't have to to waste a bunch of time trying out
superfinished gears if all it will do is cause lubricant starvation and galling
from what I'm terming the squeegee effect.
>>> have you ever come across any design recommendations
for sizing the lubricant reservoir pockets or grooves that are often seen
in bushings designed for boundary lubricated service (intermittent, slow,
heavily loaded, grease lubricated once at the beginning of life? <<<
> Don't have any answer for this one, other than the
fact that it may be possible to design the bearing so that it could be
actively lubricated without affecting the contact areas.
Ahhh, yes... For my plain bearing problem, you would not believe some of the crazy ideas I have been coming up with along those lines :-) :-) :-)
>>> Finally, do you know of any databases of material combinations (metals, coatings, polymers, etc.) that run well together <<<
> I would contact Bill Jones at NASA, he has worked in this area for years and has written many papers.
Great. Will do.
> also Fred Morales of NASA has done a lot of work
in this area, especially on the decomposition of it.
Thanks. He wrote me an excellent response to my first question last month. I will give him a call.
> For myself, I would not want to use PFPE in vacuum
under boundary conditions.
> The work by Morales shows that it will eventually decompose under boundary conditions.
Understood. Hopefully as the design proceeds and I get some numbers, I'll find that I don't have enough cycles for this to be a problem. We'll see. Right now I'm trying to learn everything I can, plan for the worst, and then back off as need be, but for the right reasons.
> Pennzain grease would be a better choice.
I've been steered away from this in my application because I have been told that my minimum qualification temps are too low for it (-80 °C).
Thanks again for all the help,
Mark Balzer NASA / JPL
I have a ball bearing design that will be used as a zero end-play connection between a flexure and an optical bench. The original design used 440C for the balls and races.
The design is sized to withstand launch loads. On-orbit, it will not see any other loads except for preload, and reactions to spacecraft acceleration and optical bench thermal expansion/contraction.
Here's the dilema - this design is now required to operate at cryogenic temperatures on orbit. The operating temperature is 30K. 440C is brittle at that temperature. However, it will not be seeing high loads. I am looking at other alternatives such as M-50.
Also, lubricants. The extremely low temperatures exclude the use of liquid lubricants. The small clearances to maintain the zero end-play exclude some other solid lubricants. I seem to be limited to sputter-deposited MoS2 or ion-plated lead. However, the contact stress of the design exceeds the maximum that these two lubricants can withstand.
Any suggestions or alternatives for materials and lubricants?
Paul V. Dizon Swales Aerospace
There have been some nice studies of solid-lubricated ball bearings
tested for cryogenic applications done by ESTL. See the following study:
S.G. Gould and E.W. Roberts, "The In-Vacuo Torque Performance of Dry-Lubricated
Ball Bearings at Cryogenic Temperatures," 23rd Aerospace Mech. Symp., Huntsville,
AL, 3-5 May 1989, NASA Conf. Publ. 3032, p. 319.
If you have trouble finding that report, the results are summarized in: E.W. Roberts, "Thin Solid-Lubricant Films in Space," in R.L. Fusaro and J.D. Achenbach, Eds., Flight-Vehicle Materials, Structures, and Dynamics, vol. 4, ASME, New York, 1992, Chap. 5. E. W. Roberts, "Thin Solid Lubricant Films in Space," Tribol. Int. 23, 95 (1990) 95-104.
Briefly, angular contact bearings made of 52100 steel were tested in vacuum from 300K down to 20K. Preloads of 38 N were used. Three lubricating systems were used: 1) PTFE transfer films from a Duroid (glass-filled PTFE/MoS2) cage, 2) ion-plated Pb films on the races with a Pb-impregnated bronze cage, and 3) sputter-deposited MoS2 on the races with several cages (Duroid, MoS2-coated steel, and MoS2/polyimide composite). Pb-coated bearings were noisier than Duroid (with or without sputter-deposited MoS2), but the Pb-coated bearings showed no torque deterioration on reducing the temperature from 300K to 20K, while the Duroid bearings all showed some minor deterioration. All of the bearings tested at 20K survived at least 2 million revolutions. (The ASME article reports additional low-temperature data, showing that using sputter-deposited MoS2 as the only lubricant deposited on the races, balls, and the steel cage was the best performer of all.)
(We reviewed this along with some non-cryogenic studies in a chapter
on solid lubricants for spacecraft applications; see: J. R. Lince
and P. D. Fleischauer, "Solid Lubricants," Chap. 7, in Space Vehicle Mechanisms:
Elements of Successful Design, P. Conley, ed. , Wiley-Interscience, 1998.)
Jeffrey R. Lince, PhD Research Scientist
Space Materials Laboratory, The Aerospace Corporation
To my esteemed space mechanism and tribology colleagues:
A cryogenic (35-50 deg K) instrument under consideration is proposing a 10 year life with 300,000 bearing output cycles to precisely position filter wheel(s) and grating/grism wheel(s) - perhaps to the "arc-second" class positioning. I originally suggested sputtered MoS2 for a long life solid lubricant with the provision that it must be kept out of a humid environment. Eventually it was explained to me that the mechanisms and instrument is passively cooled and would be ground tested in ambient conditions. Not wanting to complicate the GSE required to perform these tests (ie., a dewar or GN2 purging), tungsten disulfide (WS2) appears to have the desirable low hygroscopicity.
My problem is two fold:
1. Referring to Bob Fusaro's Space Mechanisms Handbook, table 15.4 (pg 236), I find a reference to unbonded MoS2 and WS2 which treats the two lubricants identically. In the table's 7th column, sputter coated MoS2 properties are listed with no mention anywhere of sputter or ion deposited WS2. Can WS2 be sputter coated? Are the properties of sputtered MoS2 the same as sputtered WS2? Does anyone know of a reference document where I can find this readily?
2. If it exists, does sputtered WS2 have any flight heritage? If so,
what missions/instruments and what operating temperatures, life time and
output cycles?
Joseph P. Schepis, NASA/Goddard Space Flight Center, Electromechanical Systems Branch
Here's my thoughts on the WS2 vs. MoS2 question. WS2 is often thought to be less-oxidation sensitive than MoS2. Thermodynamic calculations and experimental data show this is true at elevated temperatures. However, at lower temperatures, the thermodynamics indicate that MoS2 is actually _more_ stable than WS2 with respect to oxidation. You can see a more graphic description of this "curve-crossing" behavior on the Dicronite website at http://www.dicronite.com/chart.htm; the chart in the center indicates that the oxidation rate of MoS2 actually becomes lower than that for WS2 at about 350C (higher oxidation half life = lower oxidation rate).
Occasionally someone will perform research on sputter-deposited WS2, but it does not seem to have achieved general usage.
Oxidation stability issues aside, MoS2 is generally thought to be superior to WS2 tribologically. Here's some references on that comparison. (Note: I've only read the abstracts of these papers, so caveat emptor.)
FC Higgs III, CA Heshmat, H Heshmat, "Comparative evaluation of MoS2 and WS2 as powder lubricants in high-speed, multi-pad journal bearings," Journal of tribology , 121(3) (1999) 625-630.
H Waghray, TS Lee, BJ Tatarchuk, "A study of the tribological and electrical properties of sputtered and burnished transition metal dichalcogenide films," Surf. Coat. Technol., 77(1-3) (1995) 415-20.
E Bergmann, G Melet, C Muller, A Simon-Vermot, "Friction properties of sputtered dichalcogenide layers," Tribology International , 14(6) (1981) 329-32.
VK Prokudina, VL Kalikhman, AA Golubnichaya, IP Borovinskaya, AG Merzhanov,
"Synthetic molybdenum and tungsten disulfides," Poroshkovaya Metallurgiya,
vol.17, no.6 , Page: 48-52 , June 1978, Translated in: Soviet Powder Metallurgy
and Metal Ceramics , vol.17, no.6 , Page: 450-4 , June 1978.
Jeffrey R. Lince, PhD Research Scientist
Space Materials Laboratory, The Aerospace Corporation
1.... Can WS2 be sputter coated? Are the properties
of sputtered MoS2 the same as sputtered WS2? Does anyone know of
a reference document where I can find this readily?
2. If it exists, does sputtered WS2 have any flight
heritage? If so, what missions/instruments and what operating temperatures,
life time and output cycles?
I have no real answers for you, but here are some leads to chase down:
This page lists vendors that might be able to answer some of your questions:
http://www.dicronite.com/
I have read that this coating technology was originally developed by
NASA. I believe it is applied by high velocity compressed air spraying
(no binder). We use it on many of our threaded fasteners and often
on sliding parts.
Mark Balzer NASA / JPL
Hi all,
I just heard an interesting sales pitch from a couple guys with "a solution looking for a problem". They have a bi-stable, buckled thin metal tab-like device that can be actuated from one state to the other via shape memory alloy wires. This works a little like a "clicker" toy except it is stable in both states.
One proposed application is for 1-rev control tabs for active blade tracking on helicopter rotors. In this case, the SMA wires are activated by electric current. An advantage is that current is needed only for actuation, not for holding position between transitions.
They are now trying to find interest in developing a satellite application for their device. In particular, they submitted an SBIR proposal last year but were not selected. They would like to find interest before writing another proposal this year. They can talk to interested NASA parties through June 5 before a "blackout" period starts on the 6th.
If anyone has an interest (whether for SBIR or otherwise), contact Robert McKillip at Continuum Dynamics, 609-538-0444x112 or bob@continuum-dynamics.com
Disclaimer: I have no financial interest in this company nor other personal interest other than as described above.
--- Fred
Fred Oswald, PE
NASA Glenn Research Center, MS 23-3
Dear colleagues:
Did anyone ever apply the IBAD MoS2 from the Naval Research Center in a real mechanism?
If so, did you inspect it after flight?
Thank you in advance
Elena Forlerer
Departamento de Materiales (CAC)
Elena & Space Drives Folk -
We have only a little experience with IBD films, so I thought I'd ask an expert from NRL. Her response follows. In summary, the IBD films have some very attractive properties, but they have not been used on any actual spacecraft mechanisms. Please contact Dr. Wahl if you have any further questions.
Jeff Lince
---------------------------------------------------------------------
Jeffrey R. Lince, PhD
Space Materials Laboratory
The Aerospace Corporation
---------------------------------------------------------------------
Jeff,
I know of only one "official" bearing test done on IBD films. NRL submitted three IBAD films for Aerospace/SDI round-robin to tests (thrust washer tests in dry N2) circa summer 1991. Three "experimental" compositions, viz. sulfur-modulated MoS2, were sent. Two of the films were outstanding, running close to 5 million cycles; the third -- actually first to be made -- failed instantly. By the time we heard the results, we'd moved on to other compositions (mainly metal-doped IBD MoS2 coatings). These tests were completed and published by the Aerospace group. (see Aerospace Report # TOR-92(2064)-1, "Thrust bearing wear life and torque tests of sputter-deposited MoS2 films", by Didziulis, Hilton, Bauer and Fleischauer).
In retrospect, the NRL Ion Beam Deposited films developed after those (ca 1992-1997) showed significantly better performance (sliding life and wear). Unfortunately, they were never tested in bearing tests.
Kathy
Dr. Kathryn J. Wahl
Tribology Section, Code 6176
Naval Research Laboratory
| Space Drives List | Space Mechanisms Project Page | Mechanical Components Branch |
Curator & responsible official:
Fred.B.Oswald_AT_nasa.gov.
NASA Web Privacy Policy and Important Notices
Last modified 20 Dec 2007