Note: Descriptions are shown in the official language in which they were submitted.
1~761
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P~CESS F0R APPLYING A COA~N~; T~ A ~ STR~TE,
COA~ING AS wE.~L AS P~ O~
~he invention rela~ to a pro~es~ ~or applying a coa~lng on
a substrat~ by means of a ~lasma tor~h, a ~orre~pondingly applied
~oating and a plasma tsrt:h intended and suitable ~o p~form tha
process.
Coatings are app~ied ~or impro~ing the aharact~ristic~ o~
und~rlying mak~rials u~d ~or a ~ariety Or purposes~ one o~ t~e
po~ibilities to apply a co~ting is the ~-aalled C~D-prooe~s,
wh~rein one or two el2ments ~re ~eparated from the ~a~ phase an~
conden3e the instarlt they h~t tho subs~rate. With two el~ment~
it is a~ways the c~ o~ simpl~ aompound~ ~orm~d by ~ lln~ed
reaotlon. As nn example ~or suoh a CVD-coating titan~ um carbide
aan be mention~d, wh~raby the initial gases a~ met~an~ ~nd
tltanium t~t~nchlorid~, th~ ~-3ult o~ ~h2 rea~tLorl bein~ tltanium
~a~bid-t and Hcl. HCl 15~ removed~
Anoth~r wa~ t~ apply coatings to a substrate ~s plasma
6praying, i.e. a thermal 9pray~ng w~e~sby tempe~atures up t~
20,000 ~ are produced in the plAsma torch, tn order to melt a
ma~erial supplied as a powd~r or wire and to let it stxiXe the
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2085~46
subs~r~e~ The plasm~ tor~he~ use~ ~or coating operate primarily
on argon and ~o a 6mall exten~ on hydrogen or helium a~ a ~uel
ga~ for ~he production o~ pla~ma, ~or which purpose a cathode an~
an anode inside the pl~sma korch a direct cur~nt is applied; the
pl~sma can ~lso be produced through an electromagnetic
hi~h-~re~u~nc~ alternating field. An example o~ a plasma torch
is described for instance in the publication "Werkstatt und
Betxieb", Year 1~84, Page 333. The supplied powde~ or wire can
be alloya~ prior to introduction, -~o that the most complicated
compound~, mixture~ and ~tructures can be sprayed onto the
subs~ate, namely metals as well as cexamic mate~ials or mixtur~s
thereof.
In many ca~e~, the coating applied by a plasma torah i~ a
aomposite material, cons~sting ~ a matr~x as an ef~ec~ive la~r
o~ th~ one hand and embedments ~ox impro~ing the mat~i~
chAr~ateristic~ on th2 othex hand. The ma~rix and the embedment~
d~e ~ed to th~ plasma tor~h in powder ~xm. Th~by thro~gh
~arlation~ in th~ p~wder addition it i$ E~cssible to reRch a
grading dur~n~ th~ coating ~uildup, i.e. a modif~cation o~ ~he
embedment density from a point directly on the su~strate ~ur~ace
to a point of th~ ~ur~ace of the uture coating. A typical
material ~or such a matrix is ~or instance a nick~l-c~romium
alloy with embedded ch~omium carbides.
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~ n re~en~ tim~a ~t beaame p~s~ble ~o ~pply pure diamond
coating~ to a substrate, which i~ particularly important ~or the
electranics indu~try. A aorresponding process is descrlbed in
detail in the European Patent Application 90106785Ø ~he carbon
required ~or the diamond partioles ~s ~upplied to the pla~ma ~et
throu~h a ~rbon-con~ainin~ gas or liquid, where~y with the aid
of hydrogen ~nd an inert gas it i~ insured that the carbon
~raction results in a deposition of diamond, respactively
diamond-like mat~r~al an~ not ln ~ graphite deposition.
There~oxs this is a CVD-prooess whereby from a gaseous pha~e
dlamond crystal~ ar~ separated through condensation.
The u~e~uln~g~ oP pur0 diamond coating~ resides primarily in
th~ ~xa~llent electrlc in~ulation ch~ra~teris~ic~ and in th~
axcell~nt hRA~ conducti~i~y o~ th~ diamond. For the~e reason~,
th~ dlamond creates exc~ nt canditions ~or heat sinks whereupon
~lec~ronic component~ sub~eotQd to hi~h thermal loads ar~
appl~Qd. 0~ cours~ th~ h~rdnes~ ~ diamond c~ating~ i~ al~o o~
inter~s~ lndus~xlal a~pliaat~on~, ~or instance a6 w~ar
protection. ~owevor, a 6U~iC~ en~ adh2~ion to the sub~trate
ma~erial i~ no~ easy to aohi~ve.
The Europcan Patent ~ppli~a~ion 90308570.2 describes a
pro~ess and a device for applying di~mond layers accordlng to the
CVD-technique. In order to improve the adhesion of the dlamond
layer~, it is preceded by a bUildup 0~ one or more intermediate
18761
2~8~2'~
layers, whq~eby parti~lar attenti~n is paid ~o the compati~illty
o~ neighboring layers, particu~arly in order to manage ~ erent
e~pansion ~oe~iaients of ~he substrate and the diamond
material. The interme~ e layers are applied ~y the ~ame device
app-lying the diamond layer.
Furthermore, coa~ings are dis~ose~ which con3ist o~
two-phase s~stems with ~h~ incorporation o~ carbon ~or diamond
formation, which are al~o applied by the CVD-techni~ue. Thereby
~he one gaReous el~ments serv~s as a ~arbon carrier, while the
oth~r ~aseous element encourage~ nu¢lei formation, whereby
spe~ifiaally platinum, ni~kel, cobalt, iron, tungsten, silicon,
molybdenum and tltanium are named. ThRse elements are intro~uced
into the pla~ma as fine powder~ and vapo~ized. Based on th~
lndica~ed operation parameters o~ lO to 70 ampere and 50 to 150
volt ~e plasma can be settled in a corona discharge whlch i~ not
wi~hin ~h~ rdnge o~ ~hermal equilibrium, which in fact matahes
the disqlosure ln ~he European Pat~nt Application 9010~7~5,
according to whlch the ~ep~r~tion o~ the diamond modi~iaatiQn ou~
o~ a ~arbon carrier has to t~ place during a "silent"
discharg~. ~her~ore, this is also a ma~er o~ a plasm~ in the
l~wer energ~ l~vels.
It is ~h~ ob~eot o~ the invention to propose a novel
t~chniqu~ ~or tha application o~ a ~oatin~, a nov~l coating a~
well a~ a plasma torch to bs used ~or implementing thia
techniqu~, so that a sprayed-on ~o~ting can be ~c~ieved, who~e
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2~$~2~6
charaak~istlcs can be very easily vari~d within a spectrum
ranging ~rom ~he almo~t pure diamond coa~ ng wl~h a matrix a~ a
~inder to the matrlx ~3 an ef~e~tive layer with diamo~d
embedment~ ~r the improvement of the Characterlstic# o~ th~
~ffective laye~.
The respe~tive invention i6 defined in ~laims 1, 7 and 13, to
which ~p~ci~ic reference is made her~.
qurpri~ingly it has be~n ~ound that even in a ~ery energy
rich, thermally b~lanced plasma which predominates inside a
plasma torch for ~hermal ~p~ying, a reactlon chain ~akes plac~
which al~o leads to a separation o~ diamond particle~, al~hou~h
~o ~ilent dlYcharge or corona disohar~e are present to m~ke
nvalla~l~ the en~y r~lease, but a potential which, with with
respe~t to the ~nergy content i~ higher by an exponent o~ one to
ono and hal~. Obviou~ly also in thes~ ene~gy rich pla~as
radicals ar~ Pormed as ~ result of the mole~ule di~sociation o~
th~ carbon carr~er, th~se radi~als being ex~remely r~aative.
This has a ~ a re~ult the ~a~ that at ~he end of the plasma
flame basi~ally all radiaals wil~ ~orm new compounds, so tha~ the
don~ity of the radicals at ~he end of the ~lame will approach
2~ro, but will be ~onsidera~l~ higher ~t a ~hor~er dista~ae ~rom
th~ plasm~ torch nozzle. ~ ~or ~he deposition o~ ~iamond~ on a
aubstrat~ e.q. methane ~C~4) is used, the radical~ are c~3
atoms and hydro~en a~oms, which obviously play
,:
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2~52a~
~n impor~ant part in determining whether on impact on the
substrat~ a carbon atom depo~i~s a~ a graphite modification or
crystallize~ into a diamon~ modi~ication.
A ~urther factor which contribute~ to ~he detexmination oP
the modifioation resulting from ~he crys~allization is ths
compo~ition o~ ~he powder used for ma~rix ~ormati~, i.e. the
effective l~yer, respe~tively the pure binder material, whl~h can
be a ~ommonl~ ~nown pla~ma spray substance. The addition of
carbide producer~, such a~ titanium, chrom~um, ha~nlu~ or
zlrconium leads to bonding into car~ides of the free carbon whic~
doe~ not go into the diamond syn~hesis. ~he carbon which does
not go ln~o the diamond synthesi~ can in addition be dissolved,
~or ins~ance through the additio~ o~ ~oba.~. It has to be
mentioned th~t th~ in~luence on the cr~stalliæ~tion o~ carbo~
~nto the diamond modificati~n is not exerted through a ga6eou~
phase o~ the vaporiz~d powder, but that the reaction taxes pla~
~ol~ly with t~e mel~ed powder.
T2~e ~nvention propo~ or the ~ir~t time to vary by choice
the ratio between the diamond particles and the matrix, whereby
one extreme is represent~d by an almost pure diamond layer with
the matrix acting a~ a binder material and the other ~xtrem~ by a
matr~x wlth a low peroe~tage o~ finely distributed diamond
particles; this with All ~orm~ 0~ mixe~ and appli~ation instance~
in betwee~, wherein the diamond particles as well as the ma~rix
oan b~ a direct u~eful ~omponent. It has been proven that
18761
2Q~2~l~
pure di~mond ooating~ adh~re poorly to the ~ub~trate and o~er in
them~el~ only an insu~fioien~ bonding, so tha~ under flynamic
stre~s it is pra~ti~ally impos~i~le to pu* the diamond hardne~s
to good u~e. There oro the inven~ion compr$6e~ solely diamond
partiales emPedded in a matrix, whe~eby of ~ourse th~ bindl~g
mater$al ~an bo in a very low proportion, as long a~ it i~ finely
di~tributed.
When ~h~ production o~ a ~oating with a high diamond ~ontent
and a low matrix content i~ intende~, then ~he substra~e has to
be brought relativ31y close to the plasma toroh nozzle, ~ecause
at ~hi~ point the radical d~n~ity i6 highest. The high radioal
density insur~s then that the ~arbon atoms are depo~ited on ~he
~ubstrats a~ dlamond m~dification. ~hi~ deposition i~ agaln and
again p~rm~ated by th~ matrix compon~nt~, w~ich ~ix them~lves
~irst to the sub3trate as an adhesL~ bas;e and al90 w~t th~
diamond par~icl~s on all side~. As a re~3ult o~ ~he alo~ene~ o~
tho ~ubstrat~ to the plasma ~orch nozzle,, th~ su~tra~es i~
lnten~ely hea~od, unlQss it i~ int~n~iv~:Ly aooled by an
arrangemant in ~he rear, w~ich aan con~ir~t of ~old gas showers,
spraylng, application o~ cooled plates or ~y a ~low passing
direc~ly through the substrate,
When the propo~tion o~ ~h~ ma~rix with~n th~ coatin~ has to
be increas~d, the su~stra~ is brought to a zone with lower
radi~a~ den~ity in the plasma torch flame, whe~sby then
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~ : .
:
18761 2 ~
increa~ingly carbid~ produaer~ hsve to be admlx~ to the matrixmateri~l in the initial Porm a3 powder. The carbide producers,
e.g. titanium, chrom~um, ha~nium or ~irconium insure that th~
exce B car~on i8 not depo~ited as g~aphite, but fo~ms ~arbides
wi~h th~ ~o-called carbide produ~ers, which in turn ha~e
~xcellen~ wear ~hara~teristics, this way contributin~ togeth~r
with ~he dispersed diamond particles to the w2ar resi~tance o~
~he coa~ing. In individual aas~s it i~ possibl~ to s~lect th~
carbide produaer, whereby this selec~ion depends mainly on its
compatibility with the matrix. ~lternately, besides th~
simultaneouQ diamond synthesis and spray coating, each process
component can also be per~ormed in an alternate time sequence~
i.e. al~ernately be deposited as a ~oating of pur~ matrix
mate~lal or of purq diamond as hard substana~.
For oparating the pl~sma tor~h pa~ticularly a direc~current
elea~xic ar is used. Thereb~ the applic:ation spectrum o~ a
sp~ay~d coat;ing according to t~e invention i~ drastiaally
wid~ned. Fox th~ dwellin~ time of the individual aompon~n~s
~n~ide the plasma tor~h it oan ~o suitab~e to u~e a
high-frequency alt~rnating field ~or the p~ductio~ o~ plasma,
inste~d of th~ direct-aur~ent electric arc. A ~urther
possibility to improve ths dwelllng time resides in providing ~he
re~pective plasma torch with an axial ahannel for the supply o~
the carbon-con~a~ninq ~as or liquid , through whi~h these
187 61
2 ~
compon~nt~ ar~ ~ed t~ the center of the ~orch. Beside~ in .hi3
ca~e there i~ no danger Or ohann~l occlu~on, since ~he reaation
wit~ th~ rest o~ the components ~art only af~r the c~annal 1
exite~. As ~ sido e~ec~, th~ ca~hode i~ there~y coolad a~ th~
~ame time.
The coat~nqs a~o~d~ng ~o the in~ntion are prefera~ly
perfoxmed in a pres~ure rang~ below the a~mospheric p~essure.
HOWQVOr, it is ~150 possible to obtain satis~actory re~ults even
above atmo~ph~r~c pr~ssure, whe~by the dlstances have already
been e~plained befor~. In practi~e, distances o~ 6 to ~0 am are
use~ be~wa~n th~ substrate in th~ nozzle o~ the plasma toroh. 0~
course a ~as sh~athing made of an inert gas oould ~e ~uitabls ~or
th~ prot~ction o~ thQ appli~d ooating during its ~ormation and
imm~di~tQly a~t~r itB fo~mation, a ~at ~nown ~e~ ~ and whieh
aan be achiev~d b~ means o~ annular no2z,1es around th~ Laval
nozzle o~ th~ pla$mR torch. For hi~her pressures up to ~ bar and
~vr undaratmospheria pr~s~ures of 50 mbar it is s~ unders~ood
tha~ a chamb~r wi~h oontroll¢d inner pressur~ i~ re~uir~ ~or the
æubstrate. The appl~cation range sp~ci~ically includes an
application undex liguid, e.g. under water.
R~cen~ly the production of so-c~lled fuilerenes, a new
modification Q~ carbon, ha~ been achiev~d, whereby ~ spheri~ally
shap~d oluster o~ 6Q to 70 car~on atoms is availa~le. Thi~
modi~ication can of ~ourse also be used as an effec~ive layer o~
as an embe~men~ in a ma~ri~, wh~n ~orresponding ~haracteristics
ar~ desired.
la7~l 20~2~`6
~ sp~aial f~ature o~ the inventio~ con~i~t~ in the faat that
the thermal pla~ma 6prayin~ can be aombined with the diamond
synthesis, without 105ing the wide ~ariation range mad~ po~sible
by plasma spraying regardin~ the ap~icable coatings. The
parame~ers o~ operating a plasma torch with a direct-current
electric arc lie thereby ~ithin the usual fxamework, at a voltage
o~ approximately l~o V, which can reach up to 500 ~ in individual
cases, a current intensity o$ up ~o 1000 A can be r&ached,
wh~reby powder amounts up to 5 ~g/hour at 50 to 300 l/min of
argon are oonsumed. The typical grain size ~r the suppiied/
optlona~ly prsalloyed powder lies ~ithin the rang~ o~ 5 to loo
/um~
Coatlngs o~ alloys with oxidation stability, or all~ys wlt~
resistance to ho~ gases, or corrosion r~sistant alloys can ~e
sprayed with diamond~ in order ~o improv~ their hardnes~
oha~aote~l~tic~, namely ~or instanoe M-Cx-Al-Y-alloys, whereln
the lett~r M s~ands Eos tha ~lemen~s iron, o~bal~ ~nd~ox nlckel.
Wear and corrosion r~si6tant alloys, as well as pure hard alloy~ :
on an iron-cobalt- or nic~cal basis can also be sprayed with the
admixture o$ diamon~s, in the same way as pure cobalt-hard
mate~ial allc)ys c:ommerc:ially lcnown as stellite. E~ard nickel
~lloys containing ni~kel, chromium, boron and silicon, are use~
~or simil~r purpo~es. Fur~hermore, it is o~ course posslble ta
spray hard metals on a tungsten ~arbide-cobalt b~sis, on a
tungs~en-titaniu~ carbide/tantalum carbide-cobalt ~asis or o~ a
niokel-ohromlum carbida ba is. Diamond modi~cations can al~o be
~dmixed to ~hese hard metals in order to improve their
~haraoteri~tics.
--10--
1876~
2 4 6
Th~ afoxemanticned sprayable coatings are named ~olely as
examples in the ~i~ld o~ prote¢tion agains~ corro~ion and wea~.
Du~ to the v~ry high en~r~y during pl~sma spraying, o~ide c~ramio
and nonox~ ceram~ ~aterl~ls ~ix~d wit~ moly~denum, also ~nown
unde~ th~ name ce~met, can be ~prayed. Sprayable axe ~l~o all
pure oxides and mixed oxi~e~, a~ well as mul~i~omponen~ oxide~,
eaoh being mod~la~le according to the invention with the diamond
material. ~60 ~ilicate known under the designation cordleri~
ha~e to be men~ioned her~.
Even in biocompa~ible ¢oatings,when phosphates, al~o known
under the name o~ hydroxyl~apatite, axe ~pxa~ed, it can be u~eful
in ~rtain case~ to introdu~e diamond embedments in various
di~tributions and density, again in order to improve the wear
ahara~eristi~. This applieo Rlso to the qpraying o~
lntermetallia phase~ o~ b~nary, ternar~ or even hl~h~r ~y~t~m~
e.g. on a ni~sl-Rluminum-, tltanium ha~is and more ~ the 3ame.
Finally, durln~ ~he spra~in~ o~ haavy metals ~n~ con~c~
ma~rial~ it can be advantageau~ in ~erta~n indlvidual cas~ to
imbed wear-reduciny diamond hard material, which can ea~ily be
done with th~ aid o~ the inven~ion.
The afor~mentioned examples chow what a wide application
ran~e i5 o~fered by the~mal pl~sma spraying, whereby based on the
invention it be~mes poss~bl~ ~or ~he ~irst time to bring dtamond
1~761
2 ~
embedm~nts, re~ea~ively almost pure diamond la~er~ i~ conn~ction
wlth these m~trice~ i8 alway~ l~portan~ to Xeep su~iciently
~avorable paramete~s for ~h~ separation of diamond modifiaation
~ro~ carbon, which however i~ no problem within the ~ramewor~ of
the pre~e~t invention.
Fur~her, an embodimen~ example o~ a plasma torch accordin~ to
the inventi~n and ~or ~he implementation o~ the pro~ess o~ ~he
invention is alosex des¢ribed as shown in the drawing: the ~ole
~iguxe of the drawing showss
a aross slection through a schematically represen~d
plasma torah aaaording to the invention ~or producing a
~oat~ng accordin~ to the ~nventi.on.
The illustrated pl~ma torah consist~ of a ~asic body 1, to
whiall an anode 2 and a ¢athode 3, electr~ally insulated with
xespect to ea~h othe~, are moun~ed. Between both eleatrode~
there is an elec~ric ara zone 4, wherein electric discharges take
place, whiah are a preaondition for plasma ~ormation. Beca~se of
th~ hiqh thermal load, the torc~ is ~ooled b~ a travereing flow
with th2 aid of a coolin~ wate~ inlet 5 and a coolin~ water
outlet 6, where~y at the same time the anode ~ and the c~thode 3
are also reached. via a sepa~ate fuel gas connection 7 ar~on or
a mixture o~ ar~on and hydrQgen is upplied. At the ~rontal ~nd
-12 -
la7Bl 2~$~2~
oP anode 2 thflxe ia a powd~r ~let 8 ~or the supply ~ the matrix
material, as well as o~ the materials o~ the embedments to ~he
pl~sma flam~ ~2.
~ he ~a~ic body 1 a~ well a~ the cathode 3 are provided with
an axial channel lo through whioh a ~arbon-containin~ ~a~, ~u¢h
a~ methane or a ~ar~on-containin~ liquid such as alcohol i~
~n~roduaed in the r~action zone o~ the plasma to~h. Thi~
component conta~ns the oarbon ~rom whiah la~er the di~per~e~
diamond hard material will re6ult. Instead o~ pas~ing throug~
chann~l 10, ~hQ msthane can also be introduced in the plasma
~hrough thæ powder inje~t~on pipe, i.e. the powder inlet 8. All
componen~s par~icipating in the coatlng deposition leave the
plasma torch a~ 5pray jet 13 and strike a ~ubstrate 14, whereupon
th~ ~oating 15 i9 ~ormed.
~ he plasma torch to~ether with the stlbstrate 1~ aan be
accommodat~d ~n an unde~pre~uro ahamb~r, which i8 not clo~er
sh~wn in the drawin~. This i~ continuou,31y kept at a preselec~d
pressur~, ~or ins~ance at a pre~ure o~ 50 m~ar. Be~au9~ o~ the
~ontinuou ly ~lowing pl~sma this underpressure chamber has to be
mai~a~ned at the same pressure by continuous evacuation through
pumping. The introduction o~ the plasma torch and th~ substrate
14 in ~n underpres~ur2 chamber is not a requirement, sinae t~
oaating acc~rdin~ ~o the ~nvention can be produce~ al~o a~
atmospheric pr~ssur~ or even at a hi~her pre~sure.
-~3-
~ .,.
187~1
2~2~
The ~uel ya~ ~equir~d ~or th~ op~r~t:Lon o~ the pla~ma torch
i~ argon or any othRr noble gas wi~h a certain proportion o~
hydrogen. ~he hydrogen has the propexty of eroding the gr~phit~
already formed during deposition, so that the presence o~
hydrogen also contributes ~o graphit~ reductio~. These phenomena
howe~er are ~ow~ e.
The coating according to the inve~tion succeeds of course
even then when carbon carrior i6 ~ad to the plasma flame 12 in
the form o~ ~as or in ~he ~orm of a li~uid su~h a~ alcoho~, for
instance in or opposite the powder inlet 8. Then it is lnsured
$n any case that in the ~aval nozz~e inside the anode 2 no
depo~its ~an ~orm.
The special element of the invention consists in the large
va~iation possibilitie~ of the coating due to the chan~ o~
paran~eters. On the one hand, the substra.te is brou~ht more or
le6~ alo5e to the zone o~ h~h radical dqlnsity, on the othe~
hand, ~n th~ area ~ low radical ~ensitie~s a car~ide producer i~
introduo~d in the matrix material, which in addition to the
hydrogen, takes aar~ of the separation of ca~bon ~hi~h does n~
o~ndense into the diamond modt~ication. When the substrate i~
plaoed in an area wi~h high density of radic~ls, as a rule the
su~strate ha~ t~ be cooled, whic~ howe~er i~ not a serious
ob~tacle. ~he ~imples~ possibili~y of ~u~strate coolln~ is
plasma spraying under water.
-14-
1~7~1
2 ~ ~
0~ cour~e, wlth the process o~ th~ l:nvenkion it is po3~bl~
~o aohiQv~ a ~radua~ion, ~.e. a ohange in the ra~io ~e~ween
matrix and hard material embsdm~nt~, measuxed ov~r ~he lay~r
thickn~s, In addition o~ a gxaduation between ~atrix ~n~
em~dment, it is o~ course al~o po6sible ~o achleve a multiple
graduatio~, 50 ~or instance a tun~sten, tunysten-molybdenum or
v~nadium layer ~an be spra~ed, which clowly change~ ovex lnto
titanium o~ tantalum, which a~ain form th~ matri~ for the diamond
parti~les. In a variant thareo~, in addition to the titanium or
tantalum, ~t i5 po~si~le to ~orm a tran~i~ion to ~nother ~atrix
ma~rial, e.g. a highl~ active caxbi~e producer, wha~eby then the
aforemention~d layer s~rves as a barrier layer. Gen~rally, the
invent~ on can be u~ed ev~ry~here a matrix has to be suacess~ully
applied to a subs~at~, so that adhesion, porosity, tear
re~istance and th~ like axe satisfa~tory.
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