CA1324166C

CA1324166C - Wear resistant, abrasive laser-engraved ceramic or metallic carbide surfaces for rotary labyrinth seal members

Info

Publication number: CA1324166C
Application number: CA000567100A
Authority: CA
Inventors: John Eric Jackson; Norman Louis Balmer
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1987-05-19
Filing date: 1988-05-18
Publication date: 1993-11-09
Anticipated expiration: 2010-11-09
Also published as: KR880014295A; EP0292250B1; DE3869657D1; EP0292250A1; US4884820A; KR930010259B1

Abstract

ABSTRACT OF THE DISCLOSURE
A rotary gas seal in which a first member, e.g., a tip, cooperates with a second member to inhibit gas flow therebetween, the improvement wherein, the tip is provided with a ceramic or metallic coating bonded thereto, the surface of said coating having a plurality of laser-formed depressions and providing a wear-resistant, cutting surface capable of cutting into said second member. Also, a turbine or compressor blade having a tip surface adapted to cooperate with a sealing surface to form a seal between said blade and said sealing surface and a ceramic or metallic carbide coating bonded to said tip surface, said coating having a plurality of laser-formed depressions and providing a wear-resistant, cutting surface capable of cutting into said sealing surface.

Description

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WEAR ~ESISTANT, ABRASIVE LASER-ENGRAVED C~RAMIC OR
METALLIC CARBIDE SVRFACE~ ~ BERS

BACKGROUND OF THE INVENTION
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¦ Field of the Invention ., .
~hi~ ~nvention relates to ga~ ~eal6 between ~tationary and rotating member6, ~uch a~ rotary ~çal6 in gas turbine ~n~ines. More parkicularly, this inventio~ r~l~tes f ~o blade tip~ or labyrinth type gas 62al~, ~uch a6 kni~e edges, for gas kurbine engines.
' Prior Ar~
,~ :
j A v~riety of rotary seals arç used in ga~ turbine engines. Such r~tary ~eals are generally Df the typ~ :
~ including ro~ating me~ber~ cooperating acro~6 a narrow gap ¦ with another member which ~6 rel~tiv~ly ~tation~ry. 8uch ~eal~ are u~ed, in ~ome ca~ec~ between ~t~tionary me~bers ~nd : a rotatin~ sha~t or drum for the purpose of ~aintaining different pre~ures in chamb~r~ on e~ch ~i~e o~ the se~
, ~or exa~ple, ln one type o~ gas turblne enginer ~ plural~ty ¦ of rows of rotor blade~ exten~ radially outward from ~ rotor h~ft acro~i~ a ~low path ~or the working ~edium gase~
Coll~t~r~lly, a plur~lity ~f row~ of ~tator vane~ ex end !~ radialIy inw~rdly acros~ the flow path from ~ ~a~or c~e or hr~ud. ~n Dme types, the ~tator vane~ are c~nt~l~ver~d lnwardly frofn the stator case. The v~ne6 ~re po6~t~ ed to ,~ direct the work~ng g~6es toward sr ~w~y ~ro~ the ~dj~c¢nt D-156d3 ":

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rotor blades. A 6tator has a ~ealing surface eircumscribing the tips of blade~ in each row of blades and, ~n th~
cantilever 6tator vane types, the rotor is provided with a seal~ng 6urface circumscribing the tip~ of the statQr vane~
~n each stator vane row.
A6 the clearance between the tips of khe blades or nes in each row and the corresponding seallng ~ur~ace iæ
~ncrea~ed, substantial amounts o~ working ~edium gas e60ape rir~umferentially over the tips of the blades and/or ~tators9 reducin~ the aerodynamic efficiency. Furthermore, when the clearance i~ increa~ed, ~dditi~nal amount~ of working ~edium gase~ leak ~xially over the tips rom the d~wnstream end to ~ the upstream end o~ the blade~ or rotor~. There~ore lt i~
l desirable to keep the clearanee to ;~ mini~u~. ~owev~r, it ~6 al~o neces~ary to a~commodate various dimencional change~
which oeour during initial ~tartup, ther~al ex~ur~ion~, high ~:
G turns, et~. ~enerally, there is ~ome we~r-in of the part~
'l under the~e c~ndition~, p~rti~ularly during ~ngine ~tartup.
j It is k~own thaS the ~c~e de~ir~ble condition i~ for ~ he t~p~ or knife edge~ to cut groove~ ~n~o t~e ~orre6ponding I ~aling ~urface rather than ~or the tips or knife e~g~6 to su~t~in w2~rO U. ~. R~tent~ G,238,170 and 4,239,452 provade the ~ealing ~urface of the ~tator or shroud with int~r~r circumferen~ial groove~ clrcumscribing the tip~ of th@
bl~de~, but th~ arrange~ent pr~ent6 ~l~gnment dl~cult~es ' ~ wh~l~ f~ g to ~ccommodate ther~lly-induced ~x~
'. displac2~ent of th@ bliade6 relative to the ~t~tor or Ghroud. :.
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' ~ variety o rotary seal arrangement~ have bee~
di~clo~ed ~n the literature in which rotating mem~er~ :
generat2, cut or abrade a path in a ~ofter, e.g.~ ~bradable, coope~ating member ~uch as filled honeycomb, porou~ ~et~l, fr~able ceramie or the like. In ~me ~f ~hese arrangement~, lt ha6 been ~ound th~t in~dequate s~aling or seiz~ng o the cooperating members can result. ~n other ~uch ~rrang~ment6 , loc~l "hot-6pots" and burning of non-abrading ~ember6 can result~ Example~ of ~eal~ utiliæing an abradable ~e~ber ~re di~clo~ed in U. S. Patent~ 3,068,016; 3~481,715; 3,519,282;

3,817,719; 3,843,27B; 3tgl8,925; 3,964,877; 3,975,165;

4~377,371 and 4,540,336. The abradabl2 ~eal ~ ad~pt~d t~
ke off or abrade, when there i~ a th~rmal tran~ient or ~.
~hock loading cau~ing thg bl~de tip to ~trike he ~e~l. USP
4,377,371 points out that certain material~ u~ed a~ ~bradable ~e~l~ are ~ulner~ble to larqe ~cAle ~palling propagated by the pr~s~n~e sf sracks in the ~eal 6urface and fli~ se~ the gl~zing ~f the ~eal ~urface by the u~e ~f ~ la~er be~m to produce a ine ~i~r~-~rack network ~n the s~al eurfac~. In a paper "Development oP Improved-Dur~bility ~la~a 8pray~d Ceramic Coatings for Gas Turbine ~ngine~, pre6ented by I. ~.
Sumn~r and ~. Ruokle at th~ AIM /SA~/~SME 16th Joint ~ropulsi~n Con~r~nGer AI~A-80-1193, ~egmented laser 6can~d ting wer~ reported to p~r~orm poDrly.
~ ri~ish Pat~n~ ~53314 ~nd 1008526 di~clo6e turbine or compr~or blade~ formed with rib6 ~n their tlp6 ~or proYidi~g ~ 6eal with a rotor or ~tator ~hroud, the rib6 or -~5683 . .

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~operating 6eal ~urfao~ being removable when worn out. 13SP
4,14B,494 disclose~ a ga6 turbine blade or vane having an ~brasive tip comprising a electrodepo~ited matrix o n~skel or an alloy containing nickel in which are entrapped abrasive p~rti le~, ~.q., ~Grazon particlesg protruding from the tip.
Abra~ve tips oP the ~ype de~crib~d ~n thi~ pat~nt are ~iffi~ult to produce ~nd are extremely expen~ive. USP
3,339,933 di~close~ blade teeth coate~ with bonded alu~ina whlch expand into cooperating honeycomh member~ t~ form a ~eal. USP 3,537~713 disclo~es ~ r~tating ~leev2 having inwardly projecting teeth coated with a hard protective i mater~al, ~uch as a molybdenium or nickel Alu~inide, whi~h di~pl~ce~ a Fub-re~istant ~aterial on a st~tlonary cooperating member to form alternate ridges and grooves~
None of the above-mentioni!d prior art references di~elose or 6ugye~t teeth, ribs or knife edges coated with a wear-re is~ant ceram;c or metal earbide ~oating having laser-formed depressioni6 ~or c~tt:1ng into a se~ling 6ur~ce ~l ~n for~ing ~ labyrinth ~eal.

:, _MMARY OF T~E INVENTION
I Acsording to th~ present inventivn~ the tip~ of -~ turbin~ blades, compr~sor blades, ~n blades, i~peller~, ~' æt~tor van~6, di~u~r~, ~hrouds, ~poiler~, ~paeer~, ~nd the e d~6igned to co~p~ra~e with ~ ~e~ling ~urf~ce ~r~
ovid~d w~th ~ we~r~resi~tant eera~ic or ~etalli~ ~arbide coating hav~ng l~er-~for~ed depre~5i~n~ providing a ' -ls6a3 :~, ' '', la~er-engraved, wear re~istant, cutting ur~ace c~pable o~
cutting into the sealing 6urface. In one ~pecific embodi~ent of the ~nvention the tip is provided with one or ~ore knie edge~L teeth or ribs which are coated wikh the we~r resi~tant, laser-engraved eutting surface of thi~ invention and are designed to cut into the 6ealing ~urface to prov~de ~ :
l~byrinth 6eal. The laser-engraved ~ur~ace~ produced by this invention are wear- and corro~ion-re~istant and are capable o~ cutting $nto the cooperating ~ealing ~urface with ~inimal heat generat.ion thus minimizing the risk of thermal warping ~nd degeneration o~ physical propertie~ of the ~ember to which it i~ applied or ~o the cooperat~n~ ealinq me~ber.
The cutting capabilaty of th~ laser-engraved surf~ce is believed to be due to the elevated land area~ whi~h ~t ~ collection of cutting edg2s. Further, the depre~ion~
between the land areas ~re believed to enhance cutting ~bility by receiving the fine c~tting debri~ dur~ng cutting and r~lea~ing it when the turbine cool~ down and the tip r~tracts fro~ the sealing ~urface.
Dependlng on how the la~er i~ operated, the l~nd ~rea~ can either be part o~ the original coating ~aterial or th~y can be built up ~bov~ the origi~l 6ur~ac~ by ~teri~l be~g ~elted, thrown up ~nd reC~ct ~round the edge6 o~ the depr~ ~ on~ ~ea~t ~a~er~l typically has ~ mioro~tructure ~nd propertie~ whioh dif~r fr~m th~ ~f the bulk c~at~ng.
Re~r~nce i~ ~ade here~nat@r to pho~G~icrogr~ph6 wh~ch ~llu tr~te th~ met~llurgioal and/or topographi~al ch~n9e~

~-156B3 ., ,, ~ -6-~ 3 ~
wrought on the 6urface of ceramic ~ met~llic carbide coating in thi~ invention where, for example, the appearance of a coated ~urface subsequent to laser treatment san be 6een.
- No prior art has been found ~o disclose the ~oncept oP the present ~nvention which involves fir~t bonding a ceramic or ~etallic carbide ooating to ~he cont~t ~urface of a member de~igned to contact and cut into a coop~rating member in the formation of ~ labyrinth ~eal ~nd Shen l~er-engraving ~ plurality of laser-~or~ed depression~ and re~ultant recast ~ateri~l around each depre~sion to provide ~ uniform cutting ~uraee ~n the contact ~urface.

`/ BRIE~ DESCRIPTION OF 'rHE O~WINt;S
__ _ . _ FigO 1 i a frag~entary, ~ectisnal v$ew ~howing a j turbine blade havin~ knife edge~ in contact w~th ~ 6ealing ~i ~urf~ce diaqrammatically illustrating the ~elative po~ition.
under cold conditions for a new or rebu~lt and unrun engine.
~ Fig~ 2 i~ ~ fragment~ry, di~gram~atic, ect~onal view ~3 illu6trati~g the relative po~itions c~ the blade tip with it~ ~
,~ kni~e ed~e~ and the ~ealing zurf~ce under contact condit~ons the turbine i~ ~celerated tow~rd the ~esign speedO
Fig. 3 ~ ragment~iry, sectional, di~gr~mmatic view ~; lllu8trating the reli~ti~e p~tion o~ t~e turblne blade wath ~t6 kn~fe edg~ in r~l~tion t~ the ~e~ling 6urface under ~, ~e~gn op~r~ting condition~.
.. Fig. 4 i6 a fra~mentary, 6e~t~0nal view 6howing the 1 turb~ne bl~de ~hown in Fig~ 3 d~agra~matic~lly ;i D-1~6~3 ~7~ ~2~

~llustra~ing the relative posit$ons o ~he kni~ edqes and 6eal~ng surface under cold condition~ for an engine which has been run one or more times.
: - Fig. 5 is ~ fragmentary, sectional view sho~ing a turbine blade having ~ tlp in contact wlth ~ ~eal~ng ~urfaee diagrammatically illustrating the relatiYe positions under cold conditions for a new ~r rebuilt and unrun en~ine.
Fig. 6 i~ ~ r~sment~ry, sectional Yl~w ~ the turbine blad~ given in Fig. 5 diagramm~tically illu~trat$ng the relative po~itions of the bl~de tip ~nd the ~ealing ~ur~ace under contact eonditions as the turbine i6 accelerated toward de~ign ~peed.
Fig, 7 i~ a fragmentary, ~ection~l view ~howing the turbane blade of Fig. 5 diagrammatically lllustr~tiny the r~lative positions of the turbine blade with its tip $n rel~t~on to the 6ealing ~urface under d~sign spes~ting : .~
3 conditions.
FigO 8 i5 a fragmentary, ~ie~tional view 6howing the urbine blade of Fig. 5 diagramm~t:ically illustrating the .~ relative pu6ition~ ~f the bl~de t~p ~nd ~eallng ~urf~ce und~r i, eold c~nditi~n~ f~r ~ turbine which ha~ b~eR run one or ~ore ~ tl~e~.
.~ ~ig. 9 ~ M photomicrog~aph at 120x ~gnific~tion ', (Indiu~ ~eplica) ~f a la~e~-eng~av~d knife edge pr~dused pur~u~nt to the pre~ent inv~ntion showing the p~tS~rn af the ~ cells depre6~ion~ for~ed by the la~er.

:' - ~15683 -8~ 6 ~

Fig. 10 ir a SEM micrograph at 560x magn~fication (Indium Replica) of an individual cell or depre~s~on in the laser-engraved knife edge.

DETAII,ED DESCRlPT~ON OF THE INVENTION
Fig. 1 illustrates a turhine blade 10 h~ving Icn~:Ee #dge~ 11 on it~ ~ip. The tur~ine blade 10 iB ~ounted on a ~otor 12 and extends towards a sta~or 13. ~rl the cold condition ~or ~ new, or rebuilt, and unrun engine ~e ~hown ln F~g. 1, the knife edg~ 11 ju~t cle~r the stator 13 wherea~, hown in ~ig. 2, as the turbine ~eceler~te~ to desigll -~peed the knif 2dges contact and cut into the ctat~r 13D At design peed, as shown in Fig. 3, ti e knife edge~ rec~de 60mewhat from the grDOVeE; 14 which haY~ been cut ~nto the ~ta~¢or 13, ~ig. 4 lllus~r~tes the relation of ~he knife edges 11 to the ~ealis~ surf~ce 13 i.n a c~ld engine that ha~
b@en run ons or ~nore times.
ig. 5 illu~trates a ~urbine bl~de 20 h~v~ng a tip 21 wherein ~he turbine blade i~ ~ount8cl on a ro~or 12 ~nd ~xtendc toward~ &t~tor 13. ~n e~he ct~ld condi~ion for ~1 ~ew, ;~:
o~ rebul~t, ~nd rerun engine a~ fihown ~n ~iq. 5, th~ 'cip 21 .
ju~t clear~ the ~tator wherea~ hown ~n Fag. 6, ~ the turbine ~ccelera'ce. to de~ign 6peed thc tip 21 cont~t~ ~nd c~ nto tho 6t;~t:0r 13. At de~ign ~p~ed, ~!16 shown in Fig. : .
7, the tip recede~ somewhat f rom qro~ve 22 b~hich h~v~ been - ~;
GUt lnto the ~tator 13 by the tip 21. Fig. 8 Illu6trates the `
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relation of the tip 21 ~o ~he r~ealing 6ur~ac~ 13 ~n a ~old engine that has been run one or ~ore ti~e~.
The ~urface of the knife edge~ 11 and the tlp 21 ~re provided with ceramic or metallic carbide coating~ 15 and 23, respectively, which are applied in th~ ~anner de~cribed ~-hereina~ter and laser-engraved t~ pr~duce a pdttern of la6er f~rmed depressions a~ de~cribed hereinafter. Any ~uitable ~eramic coating or ~etallic carbide ~oating may be ~pplled to ~he knife edge 11 or ~ip 21. ~or exa~ple, tung~ten ~arbide and mixtures and/or alloys of tungsten carbide with coba1t, n$ckel, chr~mium, iron and mixtur~s of ~uch ~et~ls can be empl~yed. In additi~n, titanium carbide, tungsten-titanium c~rbide and chr~mium carbide ~re ~l~o us~ful. ~ho above-~entio~ed carbide~ can b# used æeparat@ly or mixed or alloyed wath cobal~, chromium~ kun~st~7 nickel, $ron or other ~uitable met~ls. The ceramic cDatins~ ~nclude ~lu~ina, mix~ur~s of alumina with titania, ehr~mia, ~ixture~ of chrom$a ~nd ~lumina, zir~n~a mixed with ~3gne~ and the llke. Speci~ally, the ~ollow~ng ~o~ting co~po6itlon6 ~de ~nd ~old by Un~an Carbide C~rp~r~tion can be u~ed to provide ooatings 15 ~nd 23: ~
~ClB a coating c~nt~ining 65 wS. ~ chro~iu~ : :
carbid~ (92 wt. ~ chromium, 8 wt. ~ carbon) ~nd 3S wt. ~ nichr~e ~80 wt. ~ nickel and ::~
20 wS. ~ chromium~

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LC0-17 a coating oont~sing 10 w~ lumin~ d 90 wt~ % o~ ~ cQb~lg alloy contca~n~ng 54 -, w~. % Co, 25~w~. ~ Cr, 10 ~dt. ~ ~a, 7.5 wt.
% ~ wt. 9~ w~ d 2 w~. %
C.

IMlN-40 a coat~ng con~ ny ~2 b~t, ~ ~, 14 wt.
Co, ~nd 4 w O % C.
.
UCAR 24-R a coatisl~ o titarl~u~ nl~r~de~

LZ-4~ a mix'cure c~n~ ing zl rcon~a ~abll~ed J with ~agnesl~ ~o~t~ing ~ wl;. ~ ~gn~a arld ~2 ~. % zir~

,~s-8 ~ coating of LZ~4~ applied ~ver a c~at~Lng o~ LCo-35 ~pplied o~r a c~t~r,g o~ LCo-22.
J~
~h~ ~ezaMic or ~e'callic c~rb~de ~o~ting~ ~re ~ppl~d 1: ~o ~he ~tal ~uY~ac~ o~ t~e l~nlfe ~dge 11 ~nd t~p 21 by a :: . .
h~m~l ~pr~y p~oc~ uch ~ ~h~ d~onatlorl gun proc~i or ::
gh~ pl~c~aa co~t~ng pFOC~ S. The d~tonation glan p~oc~
~11 kn~wn ~nd fully d~c~b~d ~In US~ 2~714~563, 4~173,685 ::-~
and 4, 519, 840 and involv~ feQding G~xygen, acetylane and - ; .
nitrogen into a gun barrel alonq with a charge of ~he material l~eing coated, e.g., ceramic or metallic carbide or : .
"',"

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z~e'c~ o powd~r. ~he g~ ~ixture i6 then ~gnl~c@d ~nd the r~ulting deton~tlon wave ~ooelerate6 ~he powd~r to ~bout 2400 t./6~cond while heating ~t clo6e ~o, o~ ~bov~
aelting point. ~he ~axi~um free-burn~ng te~nperatur~ o oxyg~n-~c~tylen~ ~ixtur~Ei w~der con~t~nt pre~fiure c~ndition~
occurs wlt~l about 45% acetylene anâ i~ ~bou~ 314D~C.
~swev~r, under conditlon~ ~uoh a~ ~ detorlation~ wlh~re combu6~ion occur~ ~66entiially ~t con6tant volu~, the temper~ture probably 2xc~ed~ 4200~C ~;~ th~t llno~t ~t~riDl~
ean b~ ~el~ced by the proce~ .
~ he gun barr~l ic ~ed ~t ths ~ub~trat~ ~nd the powd~r a~ or n~r or ab~ve it~ ~eltin~ p~ c d~po~ d ~n the ~lb~tr~te. A~ter ~h ~ring, the gun ~rrel 1~ purged w~th n~tr~g~n~ Thi cycle is repeal:ed ~bout 4 to 8 t~e~ a ~cond and e~ch pulse of powder resultli ~n the d#po~tion o~
a ~ircle of c~atir~g o~ ~b~u~ 2~ n diametes and a ~ew icron~ thick. The tot~l co~tin~ ~, produc~d by m~ny ove~l~pp~ng c~rcle~ o~ co~tlngs, o~ch o~ which 1~ eompc~o;@d o~
~aa~y o~re~l~pp~Dg~ thltl, lentlcul~r p~r~cl~; or OE~pla~
cor~o~p~ ing to the ~n~vldual pGwder pBrt~cle~. ~rhe os~erlapping circl~ ~re ~lo~gly ~ontrolled to produc~
rel~ti~r~ly ~ooth co~tingO
Th~ pl~ t~hnique or co~t~ng the ~nif~ ~dge~
conv~n~on~lly pr~t~e~d and 1~ dg~cr~ed ~YI US~ 3,016,d~7, 3,914,573, 3,958,097, 4/173,685 and 4,519,840. In the plasma coating techni~ue, a pla6ma torch ' .

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having a copper ~node and tung6ten cathode is usu~lly u~ed~
A ga. ~uch a~ argon or nitrogen or ~ ~ixture of the~e with hydroqen or helium i6 caused to ilow ~round the cathode a~d through the anode which 6erves as ~ constrict~ng nozzle. A
direct current ar~, usually initiat~d with ~ h~gh ~requency d~scharge, iE ~intained between the electrode~. The aro current ~nd volt~ge u~ed vary with the anode/cathode design, gas flow and gas composition. Th~ power used varies from ~bout 5 to 80 killowatts depending on the type o tor~h ~nd the operating parameters.
A gas plasma i~ generated by the arc and ~ontain~
~ree electron~, ionized atoms snd some n~utral atom~ and unas~oci~ted diatomic molecule~ when nitrogen or hydr~gen ~re :~
u~ed. Plasma gas velocitie~ wi~ ~o t conventional torche~
~re subsonic but ~upers~nic velocitie6 can be ge~eratcd u~in~
converging or diverging nozzles with crit~cal ~xit angle~.
~he temperature of the plasma ~ay exceed 50,0005F. A cer~io :-~
oating powdçr or a ~etallic carbide ~G~t~n9 powder ~ntr~duced into ~.he plasma strealm. The co~ting powder ~elt~
ln the pla~a ~nd i~ cau~ed to ~plnge upon the ~ub~tr~te.
The pla~a process of coat~ng ~tilizes ~uch h~gher te~per~ture~ than the d~tonat~on gun (or D ~un) proc~6~ ~nd :~
o ~6 a continuou~ proc~ where~s the D-gun pr~c~s i~
lnter~it~ent ~nd n~n-conti~uou~
The thickne~ o~ the co~ting 15 or 23 appl~e~ by :~
~ithe~ the pla~ma proce~ ~r D-gun proc26~ ~an r~nge fro~ 0.5 l~ 100 111i~ pr01Ferably 2 ~C~ 15 Dlil6.
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Followin~ deposition v~ th~ coating on the knif~ ~dge ~r other cutting 6urface, the resultlng ceramic or ~et~lllc carb~de eoating bonded to the surfa~e of ~he knie edge m~y be ground with a diamond gr~nding wheel to provide a.~ore ~ven surface for application of the laser-engraved pattern~
hereinater described. Other than for di~ension~l control of the coated ~urfaoe, a grinding ~t~p would not usually b~
required ~or the parts d~scribed herein.
The ceramic or metallic carbide coating ~
la6er-engr~ved u~ing a pulsed laser of a gas type ~uch ~s C~2 or ~olid 6tate type ~uch ~s YAG in order to prottuce ~
~uitable pattern a~d depth of laser formed depre66ion~ ~nd l~nd ar~a~ on the co~ting ~urface. The depth~ of the laser~ormed depressions, as measured from the bottom o~ the depres~on to the top o the land ~urrounding it, can v~y from a few microns or l~s to as ~u~h A6 120 or 140 mioron~
or more, e.~. 2 to 200 ~icron~, prefer~bly ~0 to 100 ~icron~.
The avera~e diameter can vary from 1.0 to 12 ~1 , prei~erably -~
from 2.5 to 10 ~ils. The average diameter ~nd depth sf ea~h depres~ion i~ cvntrolled by th~ energy c~ntent ~nd pulse length ~f the la~er pulse. ~he ~pacing betw~en la~erormed depre~ion~ i~ oontrolled by the firing ratç of th~ er ~nd the amount o relative motion betw~en the la~r bea~ ~nd the c~ated ~u~ce, The nu~ber o~ la~er-~or~ed depres6ion per l~neal ~nch ~xtend~ typic~lly ~ro~ 80 t~ 800, preferably 1~0 t~ 40~.

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A wide variety of laser maehine~ are av~ilable for forming depre~6ion~ in the ceramic or metall~c carb~d~
c~ating. ~n general, laser6 a~e available ~at provide an exkremely large ranqe of joules per pul~e, pul~e time~ ~nd operatin~ frequencies. ~hu~, there i~ no proble~ ~n choo~ing ., ~n appropriat~ la~er and operatin~ conditions to produce the ~ur~ace topography herein de~eribed.
As best ~een in Figs. 9 and 19, the ~ur~ace of the cera~i~ or ~et~ c carbide ~oatlng after las~r-engr~ving comprises ~ series of land area~ and depression~ in the form ~:
oP ~icrocavlti~s or cells formed by (a) vap~rization ~ some ~aterial and in 60me cases ~b) the melting, ~oving ~nd reca6ting of additi~nal ~ateri~l when the coating $s hit by ~ ~
the laser pul~e. Where r~cast ~aterl~l i6 pre~ent it ha~ ~-been found to differ con~ider~bly from the original coat~ng.
In general, ~t i~ denser and less porou~ ~han ~he orig~n~l ~
~ateri~l,and ~ay have a different atomic Etructuret ~.9., ~:
alu~ina-ti~ani~ ~ixtures, which ~ co~ted appe~r ~n 6eparate ~.
pha e~ but on reca~ting by la~er treatment for~ a Eingle pha~e fflaterial. ~t i~ believed that the land ~r~a, whether it be the origin~l coating m~terial or r2ca5t mat~ri~
or~ed in ridge~ around eaoh depre~ion pre~enti ~inute ~uttlng ~dgePii which cut into the ~brad~ble ~ateri~l or honeyco~b ~tructure bonded to the ~ur~ce ~ tator 13. ~he thicknes~ ~f the r~ca~t m~terial as ~e~ur~d fr~ the ~urface ~f th~ ~irgin c~ating ca~ ~e 10% to 4$~ D~ tbe tot~l ~epre~sion depthr preferably 20% to 30S.
. .

, . , l D-15683 :~, 4' The depre6sion~ occupy from 10% to 90~ of the ~urg~ce ; area ~nd preferably from 50~ to 90% ~he corr~sponding preferred land area ~ 10% to 50%.
It can al~o be observed from Fig. 9 that the depression~ are provided in a rando~ pattern in the ceramic or metallic carbide co~ting. The average center to center di~tance between depres~ions i~ substantially ~onstant.
~ he following illu~trative Example i8 present~d. ~he follow ng a~breviations and de~ignations ~re used in the Example and elsewhere herein:
D-Gun ~ detonation gun ~ethod of applying a Coating ceramic or metallic carbide coating to a Method ~b~trate ln which the ceramic or metallic carbi.de powder i6 charged to a ;, gun barrel with n~trogen, oxyg~n and ~ acetylene which 1~ detona~d to produce i a te~per~ture of about 6000~r which '~ ~elts the ceramic or ~et~llic carbide powBer ~nd propel~ it ~gain~t She sub~trat~

la~ma a ~chnique Por continuou~ly ~pplying a cer~miç or metallic carbide coating , .
~' M~thod ~o a ~ubs~ra~e by injectang the cera~ic . .
or ~etallic carbide p~wder ~nt3 a pl~ma of ionized ga~ ~or~ed by e6t~blishlng ~n electri~ ~rc ~cro~5 ~ ~trea~ ~f inert ~' .

~ 15683 .
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f ~ ~ 3 f~f ~f : , :' gas~ speci~ically argon. A çeramiz or metallic carbid~ powde~ ts continuou~ly fed ~o the plasma which ~ay be operating 'f _ a~ a temperature as high i~ff~ 50~400 The p~wder iff; he~ted and ~eceler~ted wi th the expanding gaffii~eff; in the pl~lffSma Z and is direc'ced a~ain~t the ffsub6trate where the powder ooolz, congez~ls and ~:
bonds to the substrat~, ~reen Si zeaverage nwnber of depreffiff;ion~ per lineal ~ ~
inch. : .
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LWlN-40 a coatins cont~lin~ng ~f2 Wt. ~S W, 14 Wt. ~ - `
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: EXAMPL~ 1 Eight ~nife ~dge ~eal ~pecimRn~ representing the rotary ~ember of ~ rotary labyrinth seal were prepared ~or coati~g by grit-blasting the knife edges with 60 ~h A1203 fed at 2.1 pounds per minute unde~ a pressure of 15 p i through a pressure bl~st unit utillzing ~ 1/4 1nch ~.d. ~1203 nozzle aimed at the beveled edg~ of the kni~e edge ~t a 5 inch standoff ~or a total o about 32 geconB~. Th2 grit~bla~ted ~urface of the knife edge had a rouqhne~s of 105 Ra. ~h~ knife edge ~pecimens were coated with ~W-lN40 by the use of a detonation gun operating with a gas oompo ition of 28% acetylene, 2B% oxygen and 44% n~trogen, a ga~ ~low r~te o 11 cubîc ft. per ~inute and a powder feed rate of 54 grams ! per ~inute to provide a coating thickne~s o~ 0.005" to ~ û . ûO~ " O
;~ Six of the coated knife ed~3e ~eal ~pecimen6 were ~ ~urth~r proce~ed by 1a~er-enqraving ~n both ~ide~ ~uch th~t I

the la~er be~m w~5 perpendicular to the ~nife edge ~ur~ace on which lt w~s op~r~tiny under ~uch condit~on~ D~ would prsvide a dia~t~r o~ the la6er formed depre6~i~n~ tanging between 0.010 ~nd 0.096" which i~ the equivalent o~ ~ ~creen siæ~ of 100 to 140, re~peetively. In ~ddition, the l~er-~n~raving ; w~s c~rried out under 6uch conditaon~ de~igned to provide a d@pre~sio~ depth ~f 50 t~ 70 ~icron~. The l~ser W~6 operated ~t ~ p~wer o~ ~9 watts, ~ pul~e duration of 145 ~cr~cond6 ~t a ~equency oP 1400 Bertz. The ~nergy cont~nt per pul~e w~ ~pproxi~ately 0.059 Joule~. The depre~si~ ormed were .

-156B~

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-10- ~32~
50 micrometers deep and had ~ 6c~een which averaged 130 depres6ions per lineal inch. ~ence, the average diameter of the depressions ~s 0.0077 inch (l/130)~ Thu~, ~n this c~e the depressions occupy approximately 79~ of the ~urf~ce are~
and the land area occupies the remaining 21%.
After ensraving, the knife edges were ~u~j~cted to macr~ ~nd micro 6tructural analysi~, ~etallographically and on the scanning electron microscope (SEM), ~n order to determine the ~ctual depression depth and di~meter the presence or absence o~ recast ma~erial ~nd the over~
condition of the engraving. The average depre~6ion depth from the Yirgin co~ting surface to th~ bottom o~ the depression was f~und to be 45.6 ~icro~eter~ while the averaye depth of the depressions from the t.op ~ the reca~t ~ateri~1 to the bottom of the depression was found t~ be 73.6 ~isrometer~. The average thicknesE; of the rec~st ~aterial w~s mea~ured ~ 23.8 micrometers. A metallograph microscope was used in making the depth and thickness measurements.
Fig. 9 i~ a photomicro~r~ph o~ the r~6ulting laser-engraYed knife edge ~pe~i~en o~ thic ~xa~ple at a ~agni~ication ~f 120x (indiu~ ~eplica). Fig. 9 ~how~ the ~ub~tanti~l~y unifor~ di~trabution o l~er-for~ed d~pre~ions ~nd the presence ~f rec~t ~aterial a~ound each ~epre~isn. Sn ~ddition, ~ig. 9 ~h~ws the v~rgin co~ting between the ~ndividu~l r~ws o~ depre~6i~n~. Fig. 10 6how..
the ~orph~l~gy ~f an individual depre~iDn at ~ ~agni~ic~ti~n of 560x (~ndium r~plica) ~howing ~ecast ~eriol ~r~und the 3 2 ~

laser-engraved depre~sion and ~he v~rgin coatiny ~round the reca6t material.
The ~ix laser en~raved knife edge speci~en6 were te~ted ~t ambient temperature condition6. In th~ t~Bt the knife edge ~s r~ta~ed with ~n edge veloci~y of 950 ft./æec.
and ~nove~ in~o an arcuate oeealing ~urface a~ ~ rate o~ 0.002n per ~econd thereby cutting ~ 0.06" groove in the arcuate ~ealin~ sur~ace ~pecimen during a thir~y oeecond te~t or a 0.030" groove during a fi teen ~econd te~t.

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Claims

1. A rotary gas seal comprising a first member, and a second member, in which the first member is adapted to move in relation to the second member and has a tip surface cooperating with a sealing surface of the second member to inhibit gas flow between the tip surface and sealing surface, said tip surface coating with a coating selected from the group consisting of ceramic coatings and metallic carbide coatings; a plurality of substantially circular laser-formed depressions defined by land areas formed in the coated surface of said tip surface and said land areas providing a wear-resistant, roughened cutting area adapted for cutting into the sealing surface of the second member.

2. The rotary gas seal of claim 1 wherein said tip surface is in the form of at least one knife edge extending in the direction of movement of the first member relative to the second member.

3. The rotary gas seal of claim 1 or 2 wherein the thickness of said coating before formation of said laser-formed depression is from about 0.5 to about 100 mils.

4. The rotary gas seal of claim 1 or 2 wherein the thickness of said coating before formation of said laser-formed depressions is from about 2 to about 15 mils.

5. The rotary gas seal of claim 1 or 2 wherein the depth of said laser-formed depressions is in the range between about 2 and about 200 microns.

6. The rotary gas seal of claim 1 or 2 wherein said depressions are formed in a random pattern having substantially uniform spacings between adjacent depressions.

7. The rotary gas seal of claim 1 or 2 wherein said depressions are spaced from about 80 to about 800 depressions per lineal inch.

8. The rotary gas seal of claim 1 or 2 wherein said laser-formed depressions occupy 50 percent to 90 percent of the surface and the land areas between the depressions occupy the remaining 50 percent to 100 percent of the surface.

9. The rotary gas seal of claim 1 or 2 wherein the coating is selected from the group comprising tungsten carbide, titanium carbide, chromium carbide, alumina, titania, chromia, zirconia, magnesia, and titanium nitride.

10. The rotary gas seal of claim 9 wherein the coating additionally comprises at least one member from the group comprising cobalt, nickel, chromium, iron, tantalum, aluminum, yttrium, and silicon.

11. A blade comprising a tip surface adapted to cooperate with a sealing surface moving relative to the tip surface to inhibit gas flow between the sealing surface and the tip surface, said tip surface coated with a coating selected from the group comprising ceramic coatings and metallic carbide coatings; a plurality of substantially circular laser-formed depressions defined by land areas formed in the coated surface of said tip surface and said land areas providing a wear-resistant, roughened cutting area adapted for cutting into the sealing surface.

12. The blade of claim 11 wherein said tip surface is in the form of at least one knife edge extending in the direction of movement of the tip surface relative to the sealing surface.

13. The blade of claim 11 or 12 wherein the coating is a ceramic coating.

14. The blade of claim 11 or 12 wherein the coating is a metallic carbide coating.

15. The blade of claim 11 wherein the thickness of said coating before formation of said laser-formed depressions is from about 0.5 to about 100 mils.

16. The blade of claim 11 wherein the thickness of said coating before formation of said laser-formed depressions is from about 2 to about 15 mils.

17. The blade of claim 11 wherein the depth of said laser-formed depressions is in the range between about 2 and about 200 microns.

18. The blade of claim 11 wherein the depth of said laser-formed depressions is in the range between about 20 and about 100 microns.

19. The blade of claim 11 wherein said depressions are formed in a random pattern having substantially uniform spacings between adjacent depressions.

20. The blade of claim 11 wherein said depressions are spaced between 80 to 800 depressions per lineal inch.

21. The blade of claim 11 wherein said depressions are spaced between 100 to 400 depressions per lineal inch.

22. The blade of claim 11 wherein the coating is selected from the group comprising tungsten carbide, titanium carbide, chromium carbide, alumina, titania, chromia, zirconia, magnesia, and titanium nitride.

23. The blade of claim 22 wherein the coating additionally comprises at least one member from the group comprising cobalt, nickel, chromium, iron, tantalum, aluminum, yttrium, and silicon.