Surface texturing of conductive materials can readily be accomplished by means of a moving electric arc which produces a plasma from the environmental gases as well as from the vaporized substrate and arc electrode materials. As the arc is forced to move across the substrate surface, a condensate from the plasma re-deposits an extremely rough surface which is intimately mixed and attached to the substrate material. The arc textured surfaces produce greatly enhanced thermal emittance and hold potential for use as high temperature radiator surfaces in space, as well as in systems which use radiative heat dissipation such as computer assisted tomography (CAT) scan systems. Electrochemical texturing of titanium alloys can be accomplished by using sodium chloride solutions along with ultrasonic agitation to produce a random distribution of craters on the surface. The crater size and density can be controlled to produce surface craters appropriately sized for direct bone in-growth of orthopaedic implants. Electric arc texturing and electrochemical texturing techniques, surface properties and potential applications will be presented

Banks, Bruce A.

Rutledge, Sharon K.

Snyder, Scott A.

English

NASA Technical Reports Server

NASA Technical Memorandum 107508
r
t
Electric Arc and Electrochemical Surface
Texturing Technologies
Bruce A. Banks and Sharon K. Rutledge
Lewis Research Center
Cleveland, Ohio
Scott A. Snyder
Ohio Aerospace Institute
Cleveland, Ohio
Prepared for the
11 th International Conference on Surface Modification Technologies
sponsored by the Society of Metallurgy and Materials
Paris, France, September 8-10, 1997
National Aeronautics and
Space Administration
https://ntrs.nasa.gov/search.jsp?R=19980000589 2020-06-16T01:39:26+00:00Z

ELECTRIC ARC AND ELECTROCHEMICAL SURFACE
TEXTURING TECHNOLOGIES
Bruce A. Banks and Sharon K. Rutledge
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
Scott A. Snyder
Ohio Aerospace Institute
Brook Park, Ohio 44142
ABSTRACT
Surface texturing of conductive materials can readily be accomplished by means of a moving electric arc which
produces a plasma from the environmental gases as well as from the vaporized substrate and arc electrode materials.
As the arc is forced to move across the substrate surface, a condensate from the plasma redeposits an extremely
rough surface which is intimately mixed and attached to the substrate material. The arc textured surfaces produce
greatly enhanced thermal emittance and hold potential for use as high temperature radiator surfaces in space, as
well as in systems which use radiative heat dissipation such as computer assisted tomography (CAT) scan systems.
Electrochemical texturing of titanium alloys can be accomplished by using sodium chloride solutions along with
ultrasonic agitation to produce a random distribution of craters on the surface. The crater size and density can be
controlled to produce surface craters appropriately sized for direct bone in-growth of orthopaedic implants. Electric
arc texturing and electrochemical texturing techniques, surface properties and potential applications will be
presented.
1.0 INTRODUCTION
1.1 Electric Arc Texturing
Radiative coohng of smooth metal surfaces is minimally effective because such surfaces typically have an unac-
ceptably low thermal emittance. The application of high-emittance metal-oxide coatings can significantly improve
the thermal emittance. However, if the radiator is required to survive wide ranges in operating temperature, the dif-
ferences in coefficient of thermal expansion can cause the coatings to spall. The formation of an electric arc between
the metal surface and a conductive electrode can be used to develop an extremely rough surface in which a conden-
sate of the vaporized substrate metal and the electrode material produces a high emittance surface which is integral
with the substrate metal and thus unlikely to spall. This paper reports an investigation of carbon and silicon carbide
arc texturing of various metals to improve their thermal emittance.
1.2 Electrochemical Surface Texturing
The long-term stability of an orthopaedic implant can be improved if the implant stem is mechanically attached
to the bone by means of direct bone in-growth into pores in the surface as opposed to conventional polymethy-
methacrylate bone cement. Electrochemical texturing of Ti-6% AI-4% V by means of sodium chloride baths with
ultrasonic agitation holds promise to produce the desired geometry post structures on irregularly shaped surfaces at
low cost. The electrochemical bath operating conditions which produce suitable surface textures is reported here.
NASA TM-107508 1
2.0APPARATUSANDPROCEDURE
2.1ElectricArcTexturing
All metalsamplesweresandedwithNumber6003MWetordryTri-M-itePaperpriortoinitialemittancemeas-
urementandbeforesiliconcarbidearctexturingforpurposesof uniformityoftheuntreatedsurfaces.Thecarbonarc
texturedsampleswerenotsandedpriortoarctexturing.Theapparatusedtoarctexturemetalsurfacesi illus-
tratedinfigure1(refs.1and2).Ascanbeseeninfigure l, the arc texturing can be performed by the creation of
either a sine wave or square wave electric arc between the metal surface and a conductive electrode of either carbon
or silicon carbide. Initial tests comparing the performance of textured surfaces produced by both AC as well as DC
arcs indicated that AC arcs produced higher emittances and therefore all texturing was performed using AC arc. The
arc site is moved across the surface by simply manually moving the water-cooled electrically-insulated arc electrode
across the surface. Arc texturing using carbon electrodes was performed at arc currents between 14 and 20 A using
sine wave form arcs at frequencies between 100 and 1000 Hz. All silicon carbide arc texturing was performed at
! 5 A using 60 Hz sine wave arcs. The carbon arc texturing was performed in an inert argon atmosphere and the
silicone carbide arc texturing was performed in an air environment.
Atomic oxygen was used on selected samples to remove carbon which is co-deposited with the substrate metals
during carbon arc texturing by means of an RF plasma asher operated on air. Atomic oxygen exposure tests were
performed to evaluate the thermal emittance which would occur after arc textured surfaces were operated at high
temperatures on radiators exposed to atomic oxygen in low Earth orbit (refs. 1 and 3).
Thermal emittance characterization of arc textured surfaces was performed for room temperature emittance
measurements using a Gier-Dunkle model DB-100 reflectometer which measures thermal emittance at 322 K. High
temperature emittance measurements were calculated by integrating spectral emittance measurements with respect
to the black body curve for the temperature of interest. Spectral emittance measurements were made using both a
Perkin-Elmer Lambda-9 UV-VIS-NIR spectrophotometer for wavelengths ranging from 0.25 to 2.5 lam and a
Hohlraum reflectometer for wavelengths from 1.5 to 15 I.tm (ref. 4).
2.2 Electrochemical Surface Texturing
Electrochemical texturing was performed by immersing cylindrical samples of Ti-6% A1-4% V, in a water
solution which was saturated with sodium chloride. Sodium chloride was selected as the means to make the water
sufficiently conductive to perform electrochemical texturing because of its biocompatibility. After electrochemical
texturing for durations between 1 and 16 min, the samples were washed, dried and photographed by fight micros-
copy. The samples ranged in size from 1 to 2 cm in diameter x 1 to 3 cm long. Evaluation of the resulting surface
texture was made on either an end face surface or the cylindrical side surface of the samples. The samples were
immersed in an 800 ml saturated salt water solution in a stainless steel ultrasonic bath 15.2 cm wide by 30.5 cm long
which also served as the negative electrode in the electrochemical cell. The titanium alloy to be textured was electri-
cally connected to the positive output of a current controlled DC power supply. Currents ranging from 0.3 to 3.0 A
were used with voltages ranging from 5 to 29 V. Ultrasonic agitation was conducted during the electrochemical
texturing to assist in removal of oxides forming on the titanium surface.
3.0 RESULTS AND DISCUSSION
3.1 Electric Arc Texturing
A comparison of the total hemispherical emittance of untreated as-received W, 304 stainless steel, Ti 6%
A1-4% V, Ti, Cu, and Nb-1% Zr with carbon arc textured samples of these same materials as a function of tempera-
ture is shown in figure 2. As can be seen, for every metal a significant thermal emittance increase is achieved
through carbon arc texturing of the surfaces.
Table I shows the thermal emittance at 322 K of various metals sanded, prior to and after carbon arc texturing
and silicon carbide arc texturing.
NASA TM-107508 2
Inaddition,thethermalemittanceofcopperandNb-l%Zrwasmeasuredaftercarbonarctexturingandsubse-
quentexposuretoatomicoxygeni anRFplasmashertoremovecarbonfromthesurfaceofthesample.The
removalofcarbonthroughatomicoxygenoxidationof carbonarctexturedNb-1%Zrreducedthethermalemit-
tanceofthesurfaceslightly.However,atomicoxygenexposureofcarbonarctexturedCuincreasedthethermal
emittance,venthoughthecarbonhadlargelybeenremovedfromthesurface.Thisisaconsequenceof thedevel-
opmentofasubstantialcopperoxideonthesurfacebecauseCudoesnotformaprotectiveoxideinanatomicoxy-
genenvironmentasit doesinatmosphericdiatomicoxygen.Slidingtheatomicoxygentreatedcoppersampleona
sheetofpaperresultedinareddishbrownstreakbecauseofasoftcopperoxide.
Ascanbeseenin tableI,siliconcarbidearctexturingwasfoundtoproducehigherthermalemittancesthan
thecarbonarctexturedsurfaces.Anotheradvantageofsiliconcarbideisthatitappearstobeunaffectedbyatomic
oxygen,becauseathinsilicondioxidefilmprobablyformswhenit is exposedtoatomicoxygen,whichwould
resultinanegligiblechangein thermalemittance.
3.2ElectrochemicalSurfaceTexturing
Operationoftheelectrochemicaltexturingsystemwithsimultaneousultrasonicagitationofthesaturated
sodiumchloridesolutionbathwasfoundtoproduceahighlypock-markedsurfaceif thesamplebiaswasashighas
24VDCwithrespecttothestainlesssteeltankholdingthebathandoperatedatacurrentof3A foradurationof
24sec.Thesamplewasacylindricalrodof9.52mmdiameterwithonlyitsendface xposed.Thus,thesamplewas
exposedtoacurrentdensityof4.2A/cm2.Ascanbeseenfromfigure3whichshowsopticalphotomicrographsof
theelectrochemicallytexturedsurfaces,theerosionappearsasnearlyhemisphericaletchedpocketsof -50 _tm
diameter randomly separated by unetched Ti-6% Al-4%V. The key advantage of this type of electrochemical etch-
ing is that the initial overall outside dimension of the metal is unaffected. Thus, if this technique is used for stems of
orthopaedic prostheses for direct bone in-growth, the tools necessary to achieve a reliably tight fit for direct
in-growth are simply the original size of the implant stem. This is quite independent of the pit texturing which is
placed into the surface.
4.0 CONCLUSION
Electric arc texturing using silicon carbide electrodes can produce surfaces with higher thermal emittance than
carbon arc texturing electrodes can produce. In addition, radiator surfaces made from silicon carbide arc texturing
electrodes are less prone to emittance degradation from atomic oxygen exposure which may be critical for radiator
surfaces operating in low Earth orbit. Terrestrial applications of arc textured surfaces include high temperature
radiator surfaces which are under high mechanical stress such as rotating anodes for CAT scan systems.
Electrochemical texturing of Ti-6% AI-4% V can be achieved using several saturated sodium chloride water
solution baths in conjunction with ultrasonic agitation to produce surfaces which have randomly distributed nearly
hemispherical pits which are separated by regions completely unaffected by the etching. Such surfaces may be suit-
able for use on stems of orthopaedic implants for direct in-growth fixation.
5.0 REFERENCES
1. B. Banks, S. Rutledge, T. Barton, D. Hotes, M. Kussmaul, J. Berry, and F. Difilippo: 'Arc Textured Metal
Surfaces for High Thermal Emittance Space Radiators,' NASA TM-100894, presented at the International
Conference on Metallurgical Coatings, San Diego, California, April 11-15, 1988.
2. B. Banks, S. Rutledge and D. Hotes: 'High Emittance Surfaces for High Temperature Space Radiator Applica-
tions,' Proceedings of the SPIE International Symposium on Optical and Opto-electronic Applied Science and
Engineering, San Diego, California, July 8-13, 1990.
3. S. Rutledge, D. Hotes and P. Paulsen: 'The Effects of Atomic Oxygen on the Thermal Emittance of High
Temperature Radiator Surfaces,' NASA TM-103224, paper presented at the Spring meeting of the Materials
Research Society, San Diego, California, April 24-29, 1989.
NASA TM-107508 3
4. S. Rutledge, M. Forkapa and J. Cooper: 'Thermal Emittance Enhancement of Graphite-Copper Composites for High Temperature
Space-based Radiators,' NASA TM-105178, AIAA Paper 91-3527, presented at the Conference on Advanced Space Exploration
Initiative Technologies, Cleveland, Ohio, September 4-6, 1991.
TABLE I.--THERMAL EMITTANCE AT 322 K OF SANDED METALS PRIOR TO
AND AFTER CARBON AND SILICON CARBIDE ARC TEXTURING
Metal Sanded and
untreated
Carbon_
texm_d
Carbon arc textured
and exposed to
atomic ox_,[en
Silicon
carbide arc
textured
606 l-T6 AI 0.086 0.822
Cu 0.050 0.657 0.870 0.839
Ni 0.044 0.763
Nb-l% Zr 0.112 0.676 0.505 0.812
Type 304 stainless steel 0.146 0.511 --- 0.600
Ti-6% AI-4% V 0.144 0.534 0.670
W O.145 0.347 - - - 0.689
Water cooling
and insulation
Carbon
electrode _,, \_
Sample _\\_
_- Vacuum based
/_ sample holder
and electrode
60 Hz variable
power supply
Vadable frequency
and vadable waveform
power supply
Figure 1 ._Schematic diagram of a texturing apparatus.
NASA TM-107508 4
1.0
0.9
0.8
0.7
0.6
E 0.5
_6 0.4
I--
0.3
_ -- Nb-1%Zr
....... Cu
.... Ti
.... Ti-6%AI-4%V Arc-textured
-t
..... 304 SS _ _" |
__ ° ,'*
.. _.. , _..--_
O_b_ D
o
...- Untreated
_*'-- .....0 ..,.." / "..-*J'--_,_.__.....,' '_''_" ."--_'_'*/*"_'" "--" ._" "_-*_'.._.. -.."''*_" "-'* ..0......0 _ ...0..0. _ *-" }
0.2
0.1
0.0
300 700 1100 1500 1900 2300 2700
Temperature, K
Figure 2.--Total hemishperical emittance vs. temperature for untreated and carbon arc textured surfaces.
1000 t_m
Figure 3._Optical microscope photographs of electrochemical textured titanium-6% AI-4% V.
NASA TM-107508 5
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 1 3. REPORT TYPE AND DATES COVERED
August 1997 Technical Memorandum
4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Electric Arc and Electrochemical Surface Texturing Technologies
6. AUTHOR(S)
Bruce A. Banks, Sharon K. Rutledge, and Scott A. Snyder
7. PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)
National Aeronautics and Space Administration
Washington, DC 20546-0001
WU-505-23-2C
8. PERFORMING ORGANIZATION
REPORT NUMBER
E-10810
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA TM- 107508
11. SUPPLEMENTARY NOTES
Prepared for the i lth International Conference on Surface Modification Technologies sponsored by the Society of Metallurgy and
Materials, Paris, France, September 8-10, 1997. Bruce A. Banks and Sharon K. Rutledge, NASA Lewis Research Center; Scott A.
Snyder, Ohio Aerospace Institute, 22800 Cedar Point Road, Cleveland, Ohio 44142. Responsible person, Bruce A. Banks, organization
code 5480, (216) 433-2308.
1211. DISTRIBUTION/AVAILABIUTY STATEMENT
Unclassified - Unlimited
Subject Category 26
This publication is available from the NASA Center for AeroSpace Information, (301) 621-0390.
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words)
Surface texturing of conductive materials can readily be accomplished by means of a moving electric arc which produces
a plasma from the environmental gases as well as from the vaporized substrate and arc electrode materials. As the arc is
forced to move across the substrate surface, a condensate from the plasma re-deposits an extremely rough surface which is
intimately mixed and attached to the substrate material. The arc textured surfaces produce greatly enhanced thermal
emittance and hold potential for use as high temperature radiator surfaces in space, as well as in systems which use
radiative heat dissipation such as computer assisted tomography (CAT) scan systems. Electrochemical texturing of
titanium alloys can be accomplished by using sodium chloride solutions along with ultrasonic agitation to produce a
random distribution of craters on the surface. The crater size and density can be controlled to produce surface craters
appropriately sized for direct bone in-growth of orthopaedic implants. Electric arc texturing and electrochemical texturing
techniques, surface properties and potential applications will be presented.
14. SUBJECT TERMS
Texturing; Arc; Titanium; Electrochemical; Orthopaedic
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OF REPORT
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18. SECURITY CLASSIFICATION
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19. SECURITY CLASSlRCATION
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