CA1264993A - Method of producing multicomponent diffusion coatings on metal articles and apparatus for performing same - Google Patents

Abstract

METHOD OF PRODUCING MULTICOMPONENT DIFFUSION
COATINGS ON METAL ARTICLES AND APPARATUS
FOR PERFORMING SAME
A B S T R A C T
A method of producing multicomponent diffusion coatings on metal articles comprises the steps of separately dissolving in a transport melt the alloying elements at temperature T eqalling 0.5 to 0.8 of their respective melting points, and saturating with these alloying elements by diffusion the surface of a metal article at temperature T1 equalling 0.3 to 0.5 of the melting point of the material of this article, with the difference T-T1 being at least 50°C. to perform this method, an apparatus comprises a central chamber for accom-modating the transport melt and the metal article to be coated, and two (in one embodiment) peripheral chambers for accommodating the transport melt and the respective individual alloying elements, commu-nicating via ducts. All the chambers and ducts have heating elements arranged thereon.

Description

~ 3 The invention relate~ to methods of thermal treatme~t of metal~ and their alloy~ and to ap-paratus for per~orming suoh metnods~ and more par-ticularly it relate~ to methods of producing mul-ticomponent diffusion coating~ on metal article~
and to spparatu~ capable of performing the~e me-thod~.
The invention can be utilized to utmost ad-vantage in producing multicomponent coating~ on small articles of intricate shape made of Yarious metal~ and alloys in i~trument-making, e. g9 Oa9es subject to ~riction, contacts, leads and the like7 in watch-making for coating cases, wristband~, part~ of watch and clock moveme~ts9 in chemical engineering for protection of parts against aggressive enviro~ments~ e.g. for enhancing their heat resista~ce.
The invention can be ~urther utilized in the manufacturing o~ fluid-ha~dling valves and fitting~, for their corro~ion protection.
There is known a method of producing multicom-ponent di~fusion coating~ on metal articles made of copper7 Armco iron9 ohrome-nickal and high-mei-ting alloy3 ~nd metals, by isothermal transfer of the diffu~ing element~ (Cr~ Ni, ~o, Fe, Ti) ~;~64~3 onto the surfaces o~ articles to be coated in melt~
o~ Na, Ca9 Li, Bi, Pb (cf. SU Inven-tor's Certifica-te No. 298,701; Int.Cl. C23c 9/08, published MarGh 16, 1971).
~ ccording to this method, the proce~s of dis-sol~ing variou~ element~ to be diffused and ~tura-ting with them by di~fusion the surfa¢a of an ar-ticle i~ conducted at one and the same high tempe-rature, which result~ ln their non-uniform dissol-ving, to say nothing o~ inadequate ~olubility o~
such element~ as Cr or Mo, and in eventuQl oorroding of the sur~aGs o~ the article. Consequently, the production o~ a ooati~g o~ the required composition and densit~ i9 badly hindered~
The~e i9 known an apparatus for producin~ multi-component diifu~ion coating~ o~ metal article~ ca-pable of per~orming the abo~ementioned method, com-pri~in~ means for acoommodating the tr~nsport melt and the alloying elements, received in an electric oven (cf. the abovecited Inventor t ~ Certi~icate)~
In this apparatus the mea~ ~or accommodating the tran~port melt and the allo~ing element~ i9 i~ the ~orm of an ampoule made oi an inert material (i.e.
a material insoluble in the ~aturati~g medium).
The proæ3ss of saturation i~ conducted, a~
follow~: an inert~ eOg. argon atmo~phere i~ e~-tablished, the tran~port melt, e.g~ a sodium or lithium melt is poured into the ampoule, the ~1-loying elements, e.g. ohromium and aluminum ars poured ther~into, and the arti¢le on whic~ the ooati~g i~
to be produced i9 also placed into the ampoule. The ampoule i9 then ~ealed by weldlng and placed into an ovan, e.g. ele~tric mu~le ~urnace for ~aturation b~ ai~fusion by keeping the ~npoule in the ~urnace for a period and at a temperature 9uf~ici ent ~or producing a coating of the predetermined thickness.
The proce~, a~ it can be seen ~rom the abova-said, is marked b~ a low throughput and im~ossibili-ty of controlling the dissolving o~ the component~9 io e. o~ applying the alloyin~ element~ ~n the requi-red ~equence ~or obtaining coatings o~ required com-position~.
There is also kno~n a method o~ producing mul-ticomponent dif~usio~ coating~ on metal article~, inoluding separately di~olving the a~lo~ing element~
in the tran~port melt a~d ~aturating with them the ~urface of a metal article at ele~ated temperature (cf. SU Inventor'3 Certificate N~. 644,869; Int.Cl.
C23c 9/10, published January 30~ lg79).
~ he tran~port melt in thi~ method i~ molten lead or bi~muth, accommod.ating tha alloying eleJnents -- titanium and nickel. ~eparate dis~olving o~ the alloying ~lement~ in the transport melt and ~aturating with them the ~urfa¢e of an article is conducted ~93 ~u¢ces~ively at a temperature of 1100-1150C, ~or O.5-1.0 hour. ~he number o~ the coating cycle de-pends on the required thickne~3s of the coating.
It can be ~een that this method can~ot be used for obtaining on the surface o~ an article a coating 1~ the form of required interDIetalllc or chemical com-pound.s o~ a predetermined thic:knes~ and densit~
Furthermore9 the high saturation tempera-ture lead.s to stru~tural changes in the matrix o~ the coated articles and to oorro~ion o~ their surface~.
~ here i~ also known an apparatu~ ~or producing multicomponent diffusion ¢oatings on metal article~
by performing the last-de~cribed method, compri~ing means ~or accommodating the tran~port melt and the alloying elements, surround~d by heating element~
(cf the la~t-cited InYentor's Certi~ioate)~
In this apparatu~ the me~n~ ~or accommodating tha transport melt and alloying element~ i3 in the form o~.two bath~ with the transport melt and the.
respective alloying elem~ntæ, each bsth being sur-rounded by heating eleme~tsD
~ he proce~ o~ saturation is conducted ~ucoes~i-vely i~ th~e t~o ~ath~ with the tran~port melt, ~.g.
with the mel-t o~ lead an~ bismuth, by periodically .
tran~erring the article being coated from one bath into the otherO ~ach bath has the respectiv~ one of the alloying element~D e.g, titanium and nickel~ dis-~ol~ed therein.
This process i 8 characte:rized. by low throu~h-put, impo~sibility of ~aturating simultaneousl~ with ~everal alloying elements and non-uniform distribu-tion o~ the alloyi~g element~ through the volume of -the bath.
It i~ an object Oe the present inventlon to create a method of producing multicomponent die:eu-~ion coQtings on metal article, pro~iding for apply-ing multicomponent diffusion coating~ o~ requir;ed composition~ thickne~ and den~ity~
It iæ another object o~ the pre~ent i~vention to lo~er the ~buration temperature~ ~o a~.to avoid ~tructural changes in the matri~ oP the article being coated and corro~ion of the æur~ace o~ this article.
It iæ yet another ob~ect o~ the present in-vention to create a~ apparatu~ ~or producing multi-component diffusion coating~ on metal articles, ca-pable of perf orming the above method and providing for æt~pping up the e~ficiency o~ the proce~s of æa-turation b~ diffusion.
It i3 a further obje~t of the present invention to create an apparatus for producing multicomponent di~fu~io~ coatings on metal articles; capable Oe per~orming the Qbove method and providing for unifo~m di~tribution Oe the ~lloying element~ in the trans-port meltO
-.

~3 These and other objects are attained in a method of producing multicomponent diffu3ion ooatin~s on metal articles, including the steps of separately d.issolving the alloying element3 in a tran~port melt and. saturating wi-th them the ~ur~ace of a metal article at ele~ated temperature, in whi¢h method, in accord.ance with the present invention, seperate dis~olving of the alloyi~g element~ i~ the tran~port melt i~ conducted at a tem~erature T whioh ~ 0~5 -to 0.8 of their respective meltin~ points, and sa-turation with them of -the ~urface of the article i~ conducted at a temperature ~l equalling 0.3 -to 0.5 of the melting point of the material of the article, with ~ - Tl being at least 50C.
The aboYementioned upper limit of the ~atura-tion temperature Tl h~s been chosen to accound for higher temper~ture~, in exce~s o~ 0.5T~ (where T2 i9 the melting point of the material of the article3, inducing in the material of the article certQin structural cha~ge39 e.g. recrystallization~ affecting the propertie~ o~ the material.
The lower limit of the ~aturation temperature is e~plained by lower temperature~g below 0 3T29 ~harply af~ec-ting the di~fu~ion mobility of the alloying eleme~t~ in the ~olid melt of the material of the article, ~nd .~hus lowering the r~te of the deposition o~ the coating.

g~

The temperature ~ of di~solvi~g ~he alloying element~, equalling 0~5~0o8 T3 (where T3 is the mel-ting point o~ the respective a:Lloying element) pro-~ides for maintaining an optimiLzed conce~tration o~
the element~ :Ln the tran~port melt for the proce~s o~ appiyin~ the required coati~lgs. The upper limit hs~ been cho~e~ to aocount for the ~act that at . temperature~ in e~cess of 0.8~3 an oxce~ively high concentration of the alloying element~ di~solved i~
the transport melt i9 attainedg yielding non-uniform ~pongy coatingq~ At temperatures below the lo~er limit of 0.5~3, on the other hand9 the oo~ce~tration of the alloying elements in the t~n~port melt become~
insufficient ~or mai~taining an adequately high rate o~ depo3itio~ sf the alloying eleme~ts on the article.
~he temperature of dissolving ~hould be hlgher tha~
the ~aturation temperature by at lesst 50C to pro-vide condition~ for thermal tran3fer ~f the alloying eleme~ts by the tra~spoxt meltO
It i~ e~pedie~t ~or obtaining a multicompo~e~t coating of a comple~ composition to conduot the saturation o~ the ~ur~ace of 8~ article with the alloying elements s1~ultaneou~ly.
Alternatively, it is e~pedient for obtaining a multicomponent coati~g ~ith gradual variation o~ the properties OI the coating acro~ its thlck~ess, to con-duct the saturation o~ the ~ur~aoe o~ an article with ::"

~%~ 3 the alloying element~ 8ucce9si~ely~
The objects o~ the inven-tion are also attained in an appar~tu3 for producing multicomponent diffusio~
coatings on metal articlaa, cornpri~ing me~s ~or accommodating the transport me:Lt and alloying slements, surrounded b~ heati~ elements, in which apparatu~9 in accordance with the invention, the mean~ ~or accommod.aing the tran~port melt and alloying element~
includes a ce~tral chamber ~or acoommodat~on o~
the tran~port meltg adapted to recei~e thsrein the metal ar-ticle to be co~ted, a~d at le~t two peri-pheral chambers ~or accommodatio~ o~ the tran~port melt and o~ the respecti~e indivldual ~lloying ~le-ment~, communicating each with the central chamber adjacent to its end~ via two re3pecti~e duct~, the heating eleme~t~ b~ing arranged on each o~e of the chamber~ and on each one of the communication duct~o It i~ expedient tha~ the apparatus should com~ri~e mean~ for agitati~g the tra~port melt, accommodated i~ the cen~ral ohamber.
Thi~ con~t~uctio~ o~ the disclo~ed apparatu~
~or producing m~lticom~onent dif~usion coating~ on metsl ~rticle~ capable oi per~orming the method according to the in~entio~9 provides ~or applying multicompo~ent dif~usion coating~ of a required compo~itio~ onL metal article~ mad~ OI variou~ mate rial~9 ~or ~peeding up the proce~s OI ~aturatio~

by dlf~u~ion and for lowering the temperatur~ o~
~aturation by diffusion.
These Qnd other objects o~ the present invention will be better understood ~rom the following examples and embodiment3 thereof, with re~erenoe being made to the accomp~nying drawing~9 wherein:
FIGo 1 i~ a lognitudinally ~ectional schematic view o~ the disclo~ed apparQtus for producing multi-component di~usion coating~ on metal artiole~, ca~
pable oi performing the methocL aocording to the inventiono, FIG~ 2 iB a partl~ broken awa~ perspeotive sohematic vie~ of a modi~ication of the disclosed apparatus for producing multicomponent diffusion coating~ on metal article~, cspable of performing the method accord.ing to the invention.
~ he method o~ producing multicomponent diffu~io~
coatings on metal article~9 according to the in~en-tion7 inolude~ the ~tep~ of ~u~ni~hing a metsl article to be coated, e.gO made of a chromium-nickel allo~ or niobium, and also ~uxnishing a -tran~p~rt melt as a melt of low-melting metal~, e.g. 30dium, and allo~ing eleme~ts which ma~ be Mo, Cr~ Tip Ni9 Si, ~f.
Then the Qrtiole to be coat~d i9 placed in the transport melt, ~d the allo~ing elernent~ ~re ~eparately di~3solred in the tran~port melt at a ~L`2~

temperature ~ which i~ 0.5 to 0.8 of their re~peotive meltine point~7 whereafter the alloying elements are diffu~ed into the surface of the metal article at a temperature Tl w~ich i3 0~3 to 0.5 of the melt.lng point of the material o~ the'article, the temperature ~ being higher th~n the temperature T
by at le~st 50C (i.e. T - Tl~ 50C)~
~ he process is conducted .~or a time su~icient for obtaining the required coating~ All the above-mentio~ed operatlon~ are conducted in an i~ert gas atmosphere, i. e . the pouring-in of the transport melt 9 the pouring-in or charging o~ the alloy~ng element~y the d.ipping o~ the article into the tran~port melt and the diffusio~ or saturation~
~ hs surface of the article is saturatcd with the alloying elements simultaneously when a multicom-ponent.coating of a compleg compos~tlon i3 requiredO
Alternativsl~, whe~ a multicomponent coating with' gradual variatio~ o~ its properties acro~s the thickne~ of the coating i~ required, the saturation of the surface of the article with the allo~ing ele-ments is conducted succe~sivelya ~ here i9 hereby di~clo~ed an apparatu~ for produoing multicomponent diffusion coati~g~ on metal article~, capable o~ per~ormi~g the abo~ede3cribed method according to ths ln~e~tio~.
The apparatus ~or prod.ucing multicomponent ~, ~6~9~3 difiu~ion coating~ on ~etal article~, which are two--component coatings in the embodiment being de~c-ribed, in accordance with the invention, comprl~e~
meQn~ IG. 1) for accomrnodatiing the tran~port melt and the alloyin~ elements~ ~he mean~ 1 in-clude~ a oentrsl chamber 2 for accommodating the tr~n~port melt 3, e.g. a sodiun~ melt, into which a holder 4 with an article 5 to be coated i9 placed, and two peripheral chambera 6 and 7 ~or aocommodating the transport melt 3 and the respective individual alloying elements 8 ~nd 9, i.e. the ohamber 6 i9 adapted to accommodate the alloying element 8 - ti-tanium9 ~nd the ch~mber 7 i9 adaptea to accommodate the alloying element g - nickel.
Each one o~ the chamber~ 6 ~nd 7 communiGates with the central chamber 2 adjacent to it9 end~ 10 and 11 via two re~pective duct~ 12~ 13 and 14~ 15.
Arranged on and about each one oi the cham-ber~ 2, 6 ~nd 7 and each o~e o~ the duct3 12, 13, 14 and 15 are heating eleme ts 169 171 189 19~ 20, 21 and 22 in the form o~ re~pec tive electric heat-ing coils~ ~h8 heating eleme~t~ 16, 1~, 20~ 21 and 22 are ~lectri~.ally con trolled with an on-o~
~witch 23S and th~ he~ting element~ 17 and 18 are electricall~ coantrolled nith the re~pectivs on-o~
s~itches 24 ~d 250 The c~ntral chamber 2 addltionally receives .:. .

~ 2~3 ~L

the mean~ 26 ~or agitating the transport melt 3.
Schematically illu~trated in ~IG~ 2 i~ a mo~
di~ication of the herein di~closed apparatu~ ~or producing four-oomponent coating~ on metal article~
by performing a method accordi:ng to the prs~ent in~ention. ~hi~ modificat~on o.f the apparatus ~or performing the claimed method :L~ ba~icall~ ~imilar to the apparatu~ for per~orming a method accordin~
to the prese~t invention, illu~trated in FIG~ 1~
~ he difference i~ in that the mean~ IG. 2) for accom~odating the tran~port melt a~d the allo~ing element~ compri~es not two, but four perlpheral chamber~ 69 73 27, 28 ~or accommodating the tra~
port melt ~ and the re~pective ind.ividual ~lloying element~g the ch~mber.6 accommodaing the alloyi~g element 8 - molybdenum~ the chamber 7 accommodating the allo~i~g eleme~t 9 - chromium~ and the chambers 27 and 28 accommodating~ re~pectivelyD ha~nium ~nd ~ilicon a~ the allo~ing elemant~
S~me a~ the chamber~ 6 a~d 7, the peripheral chamber~ 27 and 28 communi¢ate with the ce~tral chamber 2 ~djace~t to it~ oppo~its end~ 10 and 11 via two re~pe¢tivs duct~ 29, 30 and 31 and 32.
Arranged on and about èa~h one of the chamber~ 27 ~nd 28 and each o~e of the duct~ 29, 30~ 31 and 32 heating elemants 35, 36, 37 and 38 ln the iorm o~
re~pective electric hea$ing coils. ~he ~eating ele , ~ .

ments 359 36) 37 and 38 ars electrically a~ociatedwith an on-off control switoh 23, and the heating element~ 33 and 34 are electrically associated with the re~pective on-of~ control ~witchea 39 and 40~
The operating pronciple of the d.isclo~ed ap-paratu~ ~or producing multicomponent diffu~ion coa-ting~ on metal article~ by performing the method. in accordance with the present invention i~9 a~ follow~.
~ he article 5 (FIG. 1) on the holder 4 is placed into the central chamber 2~ ~he alloying element~ 8 and 9 (e6~. titanlum and niokel) in a pul~erized ~orm are pouxed into the two re~pective peripheral chamber~ 6 and 7, and the transport melt 3~ (e.g. a sodium melt) i8 poured into the chambers 2, 6 and. 7. ~hen the on-off ~witches 23, 24 and 25 are operated to turn on the power 8Up-ply o~ the heating coils 16, 17 and 18~ a~d the temperature o~ the trans~ort mslt 3 in the ¢hamber

2 is rai~ed to 0.3-005 o~ the melting point of the material o~ the article 5 being.coated, whil~
the temperature of th~ transport meit 3 in -the chamber~ 6 and 7 i~ ra~sed to 0.5 - 0.8 of the melting point~ of the re~pective alloying eleme~ts 8 and 90 The temperature o~ the transport melt 3 in the ce~tral chamber 2 i9 mainteined by at lea~t .
50C lower than the temperature o~ the transport i~3 melt 3 in the peripheral chambers 6 and 7~ Then the mean~ 26 for agitating the tran~port melt 3 i~
turned on, and the m~ tal artic:le 5 being coated i~ kept in the central chamber 2 ~or a period ~u-ficient for obtaining the requlred coating. In thi~ wa~ the ~urface of the metal article 5 i9 ~i-multaneously ~aturated by dif~u~ion with the alloy-ing element~ 8 and 9.
'rO ~aturate b~ d.i~usion the ~urface o~ th~
metal article 5 with t~e alloying element~ 8 and 9 in ~uccession, oper~t~ons similRr to tho~e descrvibed above are likewise conducted in a ~equence.
~ he difference reside~ in that in thi~ ~a~e the ~itches 23, 24 are operated to ~u~n on t~e po~er ~uppl~ of the heating ooil~ 16 and 17~ and.
the -temperature of the tran~port melt 3 in the centrQl chamber i~ rai~ed to 0.3-0~5 o~ ths melting point of the matsriQl o~ the ~urface 5 to be coatedg while in the peripheral chamber 6 alo~e the tempera-ture i~ rai~ed to 0~5-008 o~ the me~ting point of the alloying element 8, the temperQture of ths tran~port melt 3 in the csntral chamber 2 being m~intained b~ 50C or more lo~er than the tempera~
~ura of the melt 3 in the peripheral chamber 6~
Then the agitating mechani~m 26 i~ aotivated~ and the metal article 5 being co~ted i~ kept in this state for a time ~ufficient for required ~aturation "' of the sur~ace of the part 5 with the alloying elemen-t 89 ~hereafter the power supply of the heating coil 17 is turned off ~ith the ~wit~h 24.
Then the power supply of the heating eleme~t 18 i~
turned on with the ~witch 259 and the surf~ce of the article 5 i~ saturated with t:he allo~ing element 9 under the abovedescribed cond.itions.
The operation of the mod:Lfication of the di~closed apparatu~ illu~trat~d in ~IG. 2 i~ simi-lar to that of the a~paratus illustrated in FIG. 1.
~ or the pr~sent invention t~ be better compre-hended, ther~ are given below e~amples of perfor-mance Qf the method according to the inventi~n in the herei~ di~¢lo~ed apparatu~.

The proces~ is co~ducted in the modification of the apparatu~ ~or producing a two-~omponent coating with simultaneou~ diffu~io~ of two alloying element~g illu~trated in ~IG. 1.
Poured into the peripheral chambers 6 and 79 respectively~ are powder3 ~f the allo~ing element 8 (tita~ium, 5-lG~o b~ weight9 melting point 1668C) and of tha alloying eleme~t 9 (nicXel, 10-2G~o by weight9 melting point 1453C)~ and then the cham-bers 29 6 and 7 are ~illed with the tra~port melt 3 (sodium melt, the rest b~ weitgh)~
~ he~ the switche~ 23~ 24 and 25 are operated to . ..

turn on the power supplY of the heating coil~ 16, 17 and 18, Qnd the temperature of the tran~port 90-dium melt 3 in -the ch~ber 2 is rai~ed to the tem-pera-ture Tl=477C (0~3 of the melting point of the material of the article 5, equalling 1590C), the temperature of the ~odium melt 3 is rai~ed in the chamber 6 to the temperature T=834C ~0v5 of the melting point of titanium, equalling 1668C), a~d in the chamber 7 to the tempe:rature T=726C (0.5 of ~he melting point o~ nickel, equalling 1453C~.
In this way the di~eren~e betNeen the respqctl~e temperatures of the ~odium melt 3 i~ the chamber 2 and in the chamber~ 6 and 7 i9 maintained at a value in excess of 50C.
Then the article 5 of chromium-nick~l alloy ~teelg.o~ the following compo~ition (% by weight): .
C=0.08; r~n=1-2; Cr=17-19; Ni=9~ i=0.7; Fe - the re~t (the melti~g poi~t of thi~ material o~
the article 5 i9 15gOC) ~ 0~ a 5~10xl mm 3ize i lowerad into the chamber 2. The agi~ation meohani~m 26 i3 actuated, a~d th~ article 5 i9 kept in the chamber 2 for 4 hours. Then the article 5 i~ removed and wa~hed i~ run~ing water.
All the operations are performed in a~ inert argon atmo~phere~
~ he pro~adure yields uni~orm~ pore-~ree tita-nium-nickel d~u~ion coating of about 40~um thick-nes~a 16 -~ ~3 The structure o~ the coating thu~ obtained i9 Ni3Ti intermetallic compound i.n a ~olid nickel-base 301ution.
The coating ha~ proved to have high corrosion resistance in both acid and alkali media. ~hus, the rate of corrosion in 5% aqueou~ solution o~ HN03 and 10% aqueous ~olution of NaOH i~9 re~pecti~ely, 0.01 mm/year and 0.003 mm/year.
Eæample 2 As compared with E~mple 1, the proce~s di~fers in that the temperature of the melt 3 of ~odium in the chamber 2 i~ mainta~ned at Tl=636C (0.4 of the melting point of the material of tha artiole 5, equalling 1590C)~ the temperature of the melt 3 in the chamber ~ i~ mai~tained at T=834C (0.5 of the melting point o~ titanium), and the temperature in the chamber 7 i~ maihtained at T=726C (0.5 of the melting point o~ nickel~. Thus, the di~ference between the temperature~ of the melt 3 in the chamber 2 Qnd i~ the chambers 6 Rnd 7 is maintained at a value in sæoes~ of 50C.
The process yields a uniform pore-~ree tita-nium-nicke~ diffusion coating of a 50~um thicknes~.
The propertie~ o~ the coating are ~imilar to th~ e described in ConneGtio~ ~ith Ex~mple 1.

As compared with Example 1, the proce~s differs ~L2~i~33 in that the temperature o~ the ~odium melt 3 in thechamber 2 i~ Tl=795C tOo5 of the melting point of the material of the article 5, equalling 1590C), the tempera-ture of the melt 3 in the chambe~ 6 i~
~=834C (0~5 of the melting point of titanium~ and the temperature o~ the melt 3 in the chamber 7 i~
T=871C (0.6 of the melting po:int of nickel). Thu~9 -the d.i~Perenoe between the temperature~ of the sodium melt 3 in the chamber 2 and in the chamber 6 i~ substantially equal to 50C, and in the chamber~ 2 and 7 e~ceeds 50C.
The procedure yeilds a coating o~ a 55Jum thick-nes~, of properties identical to tho~e described in co~nection with Bxample 1.

.
Unlike Example 2, the proces~ accordi~g to the invention is conducted ~o that the ~aturation o~ the sur~ace oi the metal article 5 with the alloying elements 8 and 9 is e~eeted in succes~ion~ ~he sequence of the operations invol~ed i~ i~ other respects similar to that des¢ribed in E~ample 1.
The proces~ di~fers in that, fir3t, the power supply o~ the heating eoil~ 16 and 17 is turned on ~ith the switche~ 23 and 24, and the temperature o~
the sodium melt 3 is rai~ed in the chamber 2 to Tl=795C (0.5 of the melti~g poi~t of the material of the article 57 equalling 1590C) ~nd in the chamber ~: .

~3 6 to T=1008C (o~6 0~ the melting point of titanium).
'~hus, there i~ maintained a difference between the temperature~ of ths sodium me].t 3 in the centr~l chamber 2 and the pe.ripheral charnber 6 in e~ce of 50C~
Then the agitating mechaD.ism 26 i~ actuated, and the article 5 being coated. i~ kept i~ the oham-ber 2 ~or 4 ~lour~ for the surfaoe of the article 5 to become saturated with titanium. Then the power ~upply of the heatin~ coll 17 i~ turned o~f with the switch 24, and the power ~upply of the heating coil 18 i~ turned on with the switch 25 to raise the temperature of the melt 3 in the chambex 7 to T=1160C
(0.8 o~ the melting poi~t o~ nickel). Thus, there i~
maintained a d.ifference between the temperature~
of the sodium melt 3 in the central chamber 2 and peripheral chamber 7 in excos~ o~ 50~C. Under the~e condition~ the article 5 i~ kept for 4 hour~e, for the surfa¢e of the~article 5 to become saturated with nickel. The~ the ~rticle 5 i~ removed and wa~hed in running wa-t er .
The pro~eduxa yield~ a uniform pore-free titani-um-nickel dif~u~ion coati~g of about 60~um thicknes~.
~he coating i9 a double~layer one, the fir~t layer being a ~olid ~olu-tion o~ tit~nium in iron. The ~e cond layer i~ ~i3Ti intermetallic compound i~
~olid 301ution of iron and titanium. The propertie~

o.~ the coating are 1.5 times higher than those o~
the coating ob-tained in Example 1.
Example 5 Thi~ example i9 as~ociated with ~IG~ 2 of -the appended drawings where a modification of -the di~-closed apparatu~ ~or producing a four component coating in simultaneous ~a-turation with four alloy-ing element~ chematicall~ i.llu~trated.
Powder~ o~ the alloying eleme~t~: mol~bdenum (10% by weight; melting point 2~20C~9 chromium (10% by weight; melting point 1875C)~ hafnium (10%
by ~eight; melting point 2222C) and ~ilicon (10% by weight; melting point 1415C3 are poured, respecti-vely, into the peripheral chamber~ 6, 7, 27 and 28 which are ~ub~equently filled with the tran~port 30dium solution 3 (the re~t by weight).
Then the power ~uppl~ of the heating coils 16, 179 18, 3~ ~nd 34 is turned on with the switches 23, 24, 259 39 ~nd 40 to r~ise the temperature o~ the tran~port ~odium melt 3 i~ the ~hamber Z to tempera-ture Tl=987C (0.4 of the melting point of the materi-al of the article 5~ equalling 2468C3~ in the chamber 6 to temperature ~=1310C (0.5 of the meltin~
point of molybdenum, equalling 2620C) 9 in the chamber 7 to -temperature ~z1125C ~o.6 of the.melting point o~ chrornium9 equalling 1875C), in the oham-ber 27 to temperature T=1111C ~0.5 o~ the melting point o~ hafnium, equalling 2222C) 9 in the chamber 28 to temperature T-1132C(0~8 o~ the melting point of ~i licon, equalling 1415C)~ ~hus, the di~ference bet-ween the temperature~ of the tran~port ~odium so-lution 3 in the chamber 2, on the one hand~ and 1~
the chambers 6, 7, 27 and 28~ -on the other9 i~ main-tained ~t value~ in e~ce~s of 50C.
Then the metal article 5 of niobium (melting point 2468C) of a 5xlO~l mm ~ize i~ lowered into the chamber 2. The agita-ting mechani~m 26 i~ actu-atedS and the article 5 i~ kept i~ the chamber 2 for 8 hour~. Then the article 5 i~ removed and washed in running wate~.
The procedure yield~ a ~olid coating, uniform over the entire periphery of the article 5~ oP a 60~um thickness. '~he coating contain~ the ~ollowing phage3- ~bSi3,. 1~0S~9 Cr5Si3~ CrHfi ~ he coating render~ the high-melting ba~e metal oxidation-proof~ ~h~ article with the coating produced in the abo~ede~cribed procedure wa~ heated in open air at 1000C for 25 hour~ th no sig-nificant trace~ of o~idation and penetration of o~y-gen ob~erYed.

Unlike E~ample 5~ the method according to the invention i3 conductde ~or succe~ive ~aturation of the ~urface of the artiole 5 (FIG. 2~ with the ~3 alloying elements7 'rhe sequence ~ the oper~tion~ i~gener~lly similar to E~mple 5.
The difference i9 in that~ first, the poYr~r 9uppl~ of the heating coil~ 16 and 17 i9 turned o~
with the ~witohes 2~ and 24, to raise the temperatu-res of the sodium me~t 3 in the chamber 2 to Tl=987C, and in the chamber 6 to T=1310C. In thi~ way the d.if-ference b~t~een the temperature~ oP the ~odium melt 3 in the central chamber 2 and in the peripheral cham-ber 6 i~ malntained higher than 50C.
Then the agitation meohani~m 26 i~ actuated~
the metal article 5 oP niobium is lowared into the chamber 2 and kept there under the~e conditions for

3 hour~. This e~po~ure results in saturation o~ the ~urface of the article 5 with molybdenumg ~ hen the power supply of the h~ating coil 17 is turned off with the 3~itch 24. ~he power supply of the heatin~ coil 18 i~ turned on with the 3witch 25, to raise the temperature of the melt 3 i~ the cham ber 7 to T=1125C 9 and the article 5 is kept undar these condition~ for 3 hours. Thi~ e~posure yield~
saturation of the ~urface of the ~rticle 5 with chromiumO
~ he~ the power supply of the heating coil 18 is turned off with the switch 25~ and the power ~upply of the heating coil 33 i9 turned on ~ith the ~witch 39, -to raise the temperature of th~ m~lt 3 _ 22 -iæ6~3 in the chamber 27 to 1111C, and the article 5 i~kep-t under the~e conditions ~or 3 hour~, which yield~ ~a-turation o~ the sur~aoe o~ -the article 5 with ha~nium.
Then the power supply of the heating coil 33 is turned o~ with the ~witch 39, and the power suppl~
of the heating coil 34 i9 turn~ed on with the swi-~ch 40, to rai~e the temperature o;~ ths melt 3 i~ the chamber 28 to ~_1132C, and thle article 5 i~ kept under theæe conditio~s for 3 houræ~
~ hus, the di~erence between the temperatures of the sodium melt 3 in the central chamber 2 and in the peripheral chamberæ 7, 27 a~d 28 i~ main-tained at values in e~ce~ of 50C, ~ he procedure yeild~ a four-layer d.if~usion coating containing complex pha~es based on Nb7 Mo, Cr, Hf and Si. ~he properties o~ the coati~ are similar to tho~e of the coating produced in E~ample 5.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of producing multicomponent diffusion coatings on metal articles, including the steps of separately dissolving alloying elements in a transport melt at temperature T
equalling 0.5 to 0.8 of their respective molting points; and sat-urating with said alloying elements by diffusion the surface of said metal article at temperature T1 equalling 0.3 to 0.5 of the melting point of the material of said article, with the differ-ence T-T1 being at least 50°C.

2. A method of producing multicomponent diffusion coatings on a metal article in a melt, including the steps of separately dissolving alloying elements in a transport melt at temperature T1 equalling 0.5 to 0.8 of their respective melting point by selectively heating each element in a peripheral chamber connected by a duct to a central chamber containing the metal article and maintaining the surface of said metal article at a temperature T1 equalling 0.3 to 0.5 of the melting point of the material of said article and saturating with said alloying ele-ments by diffusion the surface of said metal article at tempera-ture T1 equalling 0.3 to 0.5 of the melting point of the material of said article, with the difference T-T1 being at least 50°C
thereby diffusing said elements in said metal article.

3. A method as set forth in claim 1 o 2, wherein said saturating with said alloying elements of the surface of said article is conducted simultaneously.

4. A method as set forth in claim 1 or 2, wherein said saturating with said alloying elements of the surface of said article is conducted successively.

5. An apparatus for producing multicomponent diffusion coatings on a metal article, comprising a central chamber for accommodating a transport melt, adapted for lowering thereinto said metal article to be coated, said central chamber having the first end and the second end; at least two peripheral chambers for accommodating said transport melt and individual respective alloying elements, communicating each with said central chamber adjacent to said first end and said second end thereof a first duct and a second duct through which said central chamber and each said respective peripheral chamber communicate, respec-tively, adjacent to said first end of said central chamber and said second end of said central chamber and a plurality of heat-ing elements surrounding all said chambers and all said ducts and arranged on each one of said chambers and on each one of said ducts.

6. A method as set forth in claim 1 or 2, wherein said saturating with said alloying elements of the surface of said article is conducted successively and means to selectively heat each of the alloying elements and the metal article.

7. An apparatus as set forth in claim 5 , compris-ing means for agitating said transport melt, accommodated in said central chamber.