CA1275206C - Production of metal spray deposits - Google Patents

Abstract

ABSTRACT

A method of forming a deposit is provided in which a spray of gas atomised molten metal or metal alloy is generated and directed at a substrate. The substrate is rotated about an axis of rotation and a controlled amount of heat is extracted from the molten metal or metal alloy in flight and/or on deposition?. The spray is oscillated relative to the substrate, preferably along the axis of the substrate?. With continuous production technique involving a single pass? base porosity can be considerably reduced and in the formation of thicker deposits of discrete length base porosity can be minimised and reciprocation lines can be eliminated or reduced in intensity.

Description

~.2~ 6 PRODUCTION OF METAL SPRAY DEPOSITS

This invention relates ~o the production of metal or metal alloy spray deposits using an oscillating spray-for forming products such as tubes of semi-continuous or continuous length or for producing tubulaP, rol~. rin~
cone or other axi-symmetric shaped deposits of discrete length. The invention also relates to the production of coated products.
Methods and apparatus are known (our UK Patent Nos:
137926~, 1472939 and 1599392) for manufacturing spray-deposited sbapes of metal or metal alloy. In these known meth~ds a stream of molten meta1. or metal allo which teems from a hole in the base of a tundisH. is atomised by means of high velocity jets of relatively -cold gas and the resultant spray of atomised particles is directed onto a substrate or collectlng surface to form a coherent deposit. In these prior methods it is al60 disclosed that by extractlng a controlled amount of heat from the atomised particles ln flight and on depositiod, lt ls possible to produce a spray-deposit which is non-particulate in natur~, over 95~ dense and po~se~ses a substantially unlformly distrlbuted, closed to atmosphere pore structure.
At pre~ent product~, such as tubes ~or exampl~, are produced by the ga~ ~to~i~ation of ~ stream of molten metal a~d by directing the reaultant 6pray onto a ~' ~
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rotating tubular shaped substrate. The rotating substrate can either traverse slowly through the spray to produce a long tube in a single pass or may reciprocate under the spray along its axis of rotation (as disclosed in our UK PatPnt No: 1599392) to produce a tubular deposit of a descrete length. By means of the first method (termed the single pass technique~ the metal is deposited in one pass only. In the second method (termed the reciprocation technique) the metal is deposited in a series of layers which relate to the number o~
reciprocations under the spray of atomised metal. In both these prior methods the spray is of fixed shape and is fixed in position (i.e. the mass flux density distribution of particles is e~ectively constant with respect to time) and this can result in problems with respect to both production rate and also metallurgical quality in the resulting spray deposits.
In the drawings:
Figure la is a schematic ~ront view o~ a deposition profile on a tubular shaped substrate;
Figure lb is a schematic front view of a deposition profile o~ another embodiment o~ Figure la;
Figure 2a is a schematic front view of a deposition proPile on the transverse spray depQsit on a tubular substrates; and ~ igure 2b is a schematic ~ront view Q~ a deposition pro~ile o~ another embodiment o~ Fiyure 2a~
These problems with regard to the single pass technique are best understood by re~erring to Figure 1 and Figure 2. The shape o~ a spray o~ a~omised molten metal and the mass distribution o~ metal particles in the spray are mainly a r r~

- 2a -function of the type and specific design of the atomiser used and the gas pressure under which it operates. Typically, however, a spray is conical in shape with a high density of particles in ths centre i.e. towards the mean axis of the spray X and a low density at its periphery. The "deposition profile"

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~.~75.~`6 of the deposit D which is produced on a tubular-shaped substrate 1 which is rotating only under this type of spray is shown iD Figure l(a)~ It can be seen that the thickness of the resultlng deposit D (and consequently the rate of metal depositlon) varies considerably from a position corresponding to the central axis X of the spray to its edge~ Figure 1(b) shows a section through a tubular spray deposit D formed by traversing a rotating tubular-shaped collector 1 through the same spray as in Figure l(a) in a single pass in the direction of the arrow to produce a tube of relatively long length. Such a method has several major dlsadvantages~ For exampl~, the inner and outer surfaca of the spray-deposited tu~e are formed from particles at the edge of the spray which are deposited at relatively low rates of deposition. A low rate of deposition allows the already deposited me~al to cool excessively as the relatlvely col~ atomlsing gas flows over the deposition ~urface~ Consequently, subsequently arriving particles do not "bond" effectively with the already deposlted metal reRulting in porous layers of lnterconnected porosity at the inner and outer surfaces of the depositP. Thls lnterconnected porosity whlch connects to the surface of the deposit can suffer internal oxidation on removal oP the deposlt Prom the pro~ecti~e a~osphere in~ide the ~pray chamber. In total these porous layerfl can account for up to 15~ of .

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the total deposit thickness~ The machlning off of these porous layers can adversely affect the economics of the spray deposition process~ The central portion oP the deposit is formed at much higher rates of particle deposition with much smaller time intervals between the deposition of successive particles. Consequently~ the deposition surface is cooled less and the density of the deposit is increased, any porosity that does exist is in the form of isolated pores and is not interconnected.
The maximum overall rate of metal deposition (i~e~.
production rate) that can be achieved (for a given atomiser snd atomising gas consumption) in the single pass techn~que is related to the maximum rate o~
deposition at the centre of the spray. If ehls exceeds a certain critical level insufficient heat is extracted by the atomislng gas from the particles in flight and on depositiod, resulting in an excessively high liquid metal content at the surface of the already depasited metal~ If this occurs the liquid metal is dePormed by the atomislng gas as it impln~es on the deposltion surface and cfln also be e~ected from the surface of the pre~orm by the centrlfugal Porce generated from the rotation of the collector~ Furthermor~, castlng eype detect~ ~e~g. shrinka~e poro~lty~ hot tearln~ etc.) can occur in the deposlt.

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A further problem with the single pass technique of the ptior art ~s that the depos~tion sur~ace has a low angle of incllnation relative to the dlrection of the impinging particles (as shown in Figure l(b)) i.e. the particles ~mpinge the deposition surface at an oblique angle. Such a low i~pingement angle is not desirable and can lead to porosity in the spray deposit~ This is caused by the top parts of the deposition surface acting as a screen or a barrier preventing particles from being deposited lower down. As the deposlt increases in thickness particularly as the angle of impingement becomes less than 45 degree~, the problem becomes progressiv~ely worse. This phenomenon is well known from conventional metallising theory where an angle of impingement of particles relative to the deposition surface of less than 45 degrees is very undesirable and can re6ult in porous zones in the spray deposit~
Consequently~ using the slngle pass technique there ls a llmit on the thickness of deposit that can be successully produced. Typically~ this is approximately 50mm wall thlckness for a tubular ~haped deposlt.
The three major problems associated with the single pass technique; namely, surface poroslty. limited metal deposition rate and llmited wall thickness can be partly overcome ~y using the reciprocation technlque where the m~al 18 dep~it~d in a series a~ layer~ by traverslng the rotating collec~or backwards and orward~ under the ~, .
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spray~ Howeve~, where reciprocation movements are required there is a practical limit to the speed of movement particularly with large tubular ~haped deposits~
(e.g. 500kg) due to the deceleration and acceleration forces generated at the end of each reciprocation stroke. There iB also a limit to the length of tube that can be produced as a result of an increasing time interval (and therefore increased cooling of the deposited metal) between the deposition of each successive layer of metal with increasing tube length~
Moreove~, the microstructure of the spray deposit often exhibits "reciprocation bands or llnes" which correspond to each reclprocatlon pass under the spray~ Depending on the coaditions of deposition the reciprocation bands can consi6t of fine porosity and/or microstructural variations in the sprayed deposit corresponding to the boundary of two successively deposited layers of metal;
i.e. where the already deposited metal hafi cooled excesslvely malnly by the atomising gas flowlng over lts surface prior to returning to the fipray on the next reciprocatlon of the substrate~ Typlcally the reciprocatlon cycle would be of the order of 1-10 ~econds dependin on the slze o~ the 6pray-deposlted artlcle.
~ he proble~ a~ociatad with both the single pa~s technique and the reciprQcation technique can b~

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substantially overcome by utilising the present invention.
According to the present invention there i5 provided a method of forming a deposit on the surface of a substrate comprising the steps of;
generating a spray of gas atomised molten meta~, metal alloy or molten ceramic particles which are directed at the substrat~, rotating the sub6trate about an axis of the substrat~.
extracting heat in flight and/or on deposition from the atomlsed particles to produce a coherent deposi~.
and oscillating the spray so that the spray is moved over at least a part of the surface of the substrate~
The atomising gas is typlcally an inert gas such as Nitrogen, Oxygen or Helium~ Other gase~. howeve~. can also be used including mixed gases which may contaln Hydroge~, Carbon Dioxid~. Carbon Monoxide or Oxygenr.
The atomising gas is normally relatlvely cold compared to the stream of liquid metal.
The present invention ls particularly applicable to the continous production of tube~ or coated tubes or coated bar aad in this arrangement the substrate ls in ~he Porm o~ R tube or sQlld bar which is rotated and traver~ed ln an axial direction ln a ~ingle pass under the oscillatlng ~pray~, In this arrangement the ~' ~ ~ 7 ~ j ~d ~ ~ ~

oscillatiod, in the direction of movement of the substrate has several important advantages over the existing method using a fixed spray. These can be explained by ~efe~ence to Figures 2(a) and ~(b). The "deposition profile" of the deposit which is produced on a tubular shaped collector which ls rotating only under the oscillating spray i6 shown in Figure 2(a)~ By comparing with Figure l(a) which is produced from a fixed spray (of the same basic shape as the oscillating spray) it can be seen that the action of oscillatlng the spray has produced a deposit which is more uniform in thickness. 'Flgure 2(b) shows a section through a 'tubular fiprayed deposit formed by traversing in a single pass a rotating tubular shaped collector through the oscillating spra~. The advantages of an o~cillating spray are apparent and are as follows (compare'Figures l and 2):
(i) Assuming that there i8 no varlation in the ~peed o$ movement of the 6pray within each oscillation cycle the majority of metal will be deposited at the same rate of deposition and therefore the conditlons of deposition are relatively uniform. The maxlmum rate of metal deposition is also lower when compared to the fixed spray oE~Fl~ure l~a~ which means that the overall d~po~ieion rate can be increased withou~ the deposltion ~urface becoming exce~ively hot (or cQntalning an excesslvely hlgh liquid content~.

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g (ii) The percentage of metal at the leading and trailing edge~ of the spray which is deposited at a low rate of deposition is markedly reduced and therefore the amount of interconnected poro~ity at the inner and outer surface of the spray deposited tube is markedly reduced or eliminated altogether.
(iii) :Por a given deposit thickness the angle of lmpingement of the depositing partlcles relative to the deposition surface i8 conslderably higher.
Consequently much thicker deposits can be successfully produced using an 06cillating Qpray.
It 6hould be noted that slmply by increaslng the amplltude of oscillatlon of the sprqy (within limits e.gr. included angles of oscillation up to 90 can be used) the angle of impingement of the particles at the deposition surface can be favourably influenced and therefore thicker deposits can be produced~ In additiod, for a given depo6i~, an lncreased amplitude also allows deposltion rates to be increased, ~or gas conHumption to be decreased~ Therefor~, the economics and the production output of the spray depo6iticn process can be increased.
The pre~ent lnvention is also applicable to the production of a 6prayed depoHlt of dlscrete length whe~e there i~ no axlal movement of the subs~rat~, i.e~ the ~ubHtrate ro~ate~ onl~. A "discrqte len~th deposit" 18 typically a slngle product of relatively Qhort ,~
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length~ lae. typically less than 2 metres long, Por a given 6pray height (the distance from the atomising ~one to the deposition surface) ths length of the depo~it formed will be a function of the amplitude of oscillation of the ~pray The discrete deposit may be a tub~, ring, cone or any other axi-symmetric shape~ For exampl~, in the formation of a tubular depoæit the spray is oscillated relative to a rotating tubular shaped collector 80 that by rapidly oscillating the spray along the longltudinal axis of the collector being the axis of rotatio~, a deposit is built up whose micro~tructure snd properties are substantially uniform.
The reasoh'for this is that a spray. because of its low inertl~, can be oscillated very rapidly (typically in excess of 10 cycles per second i_e. at least 10-100 times greater thsn the practical limit for reciprocating the collector) and consequently reciprocation line~
which are formed ln the reciprocatlon technlque using a fixed spray are effectively eliminated or markedly reduced using this new method~.
By controlllng the rate and amplltude of osclllatlon and the instantaneous speed of movement o~
the spray throughout each osclllatlon cycle it 18 possible to form the deposit under whatever condltions are required to ensure uniform depoQitlon cQnditlons and thorcfore a uni~orm micro~ructure and a controlled Qhape. A slmple depo~ltion pro~ile 18 ~hown ln i, , ,~ .

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`Figure 2(a) but this can be varied to suit the alloy and the product~. In Figure 2(a) most of the metal ha~ been deposited at the same rate of deposition.
The invention can also be applied to the production of spray-coated tube or bar for either single pass or discrete length production~ In this case the ~ubstrate (a bar or tube) ls not removed after the deposition operation but remains part of the final product~ It should be noted that the bar need not necessarily be cylindrical ln section and could for example be squar~
rectangula~, or oval etc, The inventlon will now be further described by way of examplé'with reference to the ~ccompanying diagrammatic drawings in Figures 3-~;
Figure 3 illustrates the continuous formation of a tubular deposit in accordance with the present lnventlon;
'Figure 4 is a photomlcrograph of the mlcrostructure of a nlckel-based superalloy IN625 spray deposited in conventional manner wlth a fixed spray on to a mild steel collector;
~ F~gure 5 18 a photomicrograph of the microstructure of IN625 spray deposited by a slngle pass tec~nique in accordance with the invention onto a mild steel collqct~ r ;
'Figure fi illu~trate~ dia~rammatically the ~ormation of a discrete tubular depos1t.

- -Figure 7 illustrates the formation of a dlscrete tubular deposit of ~ubstantially frusto-conical shape;
'Figure 8 lllustrates diagrammatically a method for osclllating the spray; and Figure 9 is a diagrammatic view of the deposit formed in accordance with the example discussed later.
In the apparatus ~hown in Figure 3 a collector 1 is rotated about an axis of rotation 2 and is withdrawn in a direction indicated by arrow A beneath a gas atomised spray 4 of molten metal or metal allo~. The spray 4 is oscilliated to either side of a mean spray axis S in the direction of the axis of rotation of the substrate 1 -which in fact coincideæ with the direction of withdrawal.
:Figures 4 and 5 contrast the microstructures of an IN625 deposit formed on a mild steel collector in the conventlonal manner (Figure 4) and in accordance with the invention (Figure S) on a s~ngle continuous pass under an oscillating spray. The darker portion at the bottom of each photomicrograph is the mild steel collecto~, and the lighter portion towards the top of each photomicrograph i~ the spray deposlted IN62S~ In Figure 4 there are ~ub~tantial areas in the spray deposited IN625 which are black and wbich are areas of poro~ity. In Flgure S using the o~cillating spray . i .

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technique of the invention the porosity i6 6ubstantially eliminated~.
In Figure 6 a ~pray of ato~ised metal or metal alloy droplets 11 is directed onto a collector 12 which-is ~otatable about an axis of rotation 13. The spray deposit 14 builds up on the collector 12 and uniformity is achieved by oscillating the spray 11 in the direction of the axis of rotation 1~. The speed of oscillation ~hould be sufficiently rapid and the heat extraction controlled so that a thin layer of semi-solid/semi-liquid metal i8 malntained at the surface of the deposit over its complete length~ ~or exampl~, the 06cillation is typically 5 to 30 cycles per 6econd.
As seen from Figure 7 the shape of the depos~t may be altered by varying the speed of movement of the spray within each cycle of oscillatiod~ Accordingly, where the deposit is thicker at 15 the ~peed of movement of the spray at that point may be slowed 80 that more ~etal is depo6ited a8 opposed to the thinner end where the speed of movement is increased~. In a simllar manner 6hapes can also be generated by spraying onto a collector surface that itself is conc1cal in shape-.
More complicated shapes can also be generated by careful control of the osclllating amplltude and in~tantaneous Qpecd o~ mov~ment within each cycle o~ oscillation~ I~
18 also po~sible to ~ary the ~a~ to metal ratio during each cycle o~ oscillatlQn in order to accurately control / ~. b.

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the cooling conditions of the atomlsed particles deposited on di~ferent part of the collector.
Furthermore the axis of rotation of the substrate need not necessarlly be at right angles to the mean axis of ---the oscillating spray and can be tilted relative to the spray~
In one method of the invention the oscillation of the spray is su1tably achieved by the use of apparatus disclosed diagrammatically in Figure 8~ In Figure 8 a liquid stream 21 of molten metal or metal alloy is teemed through an atomising device 22~ The devlce 22 is generally annular in shape and is supported by diametrica~}ly prajecting supports 23~. The supports 23 also serve to supply atomising gas to the atomising device in order to atomise ehe stream 2l into a spray 24~ In order to lmpart movement to the spray 24 the pro~ecting supports 23 are ~ounted in bearlngs (not shown) so that the whole atomisln~ device 22 ls able to tilt about the axis defined by the prajecting supports 23~. The control of the tilting of the atomlsing devlce 22 comprises an eccentric cam 25 and a cam follower 26 connected to one of the supports 23~ ~y altering the speed of rotatlon of the cam 25 the rate of oscillat10n of the atomising device 22 can be varled~. In additio~, by changing the surPace profile of the cam 29, the speed o~ moveMent of th~ ~pray at any ln6tant du~ing the cyle oP o~cillaton can be varled~ In a prePerred method oP

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the invention the movement of the atomlser is controlled by electro-mechanical means such as a programme controlled stepper mo~o~. or hydraulic means 6uch as a programme controlled electro-hydraulic servo mechanism.
In the atomisation of metal`in accordance with the inventlon the collector or the atomiser could be tilted.
The important aspect of the invention is that the spray is moved over at least a part of the length of the collector so that the hlgh density part of the spray is moved too and fro across the deposition surfa~e.
Preferably~ the oscillation is such that the spray actually moves along the length of the collecto~. which (as shown~'is preferably perpendicular to the spray at the centre of its cycle of osclllatlonr. The spray need not oscillate about the central axis of the atomise~, -thls will depend upon the nature and shape of the deposit being formed.
Full detallGof the preferred apparatus may be obtalned from our co-pendlng application filing herewith to which rePerence is directed.
The speed of rotation of the substrate and the rate of oscillation of the spray are important parameters and lt 1~ essentlal that they are selected 80 that the metal i0 deposited uni~ormly during each revolution of the collector. Knowing the mass flu~ den~lty di~tribu~ion o~ the ~pray tran~verse to the direction of o~cillatioa it is po~ible to calculate the num~er of ' .

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- l6 spray oscillation per revolutlon of the substrate which are required for uniformity~
One example of a discrete length tubular product is now disclosed by ~ay of example: -EXAMPLE OF DISCRETE LENGTH: TUBULAR PRODUCT

DEPOSITED MATERIAL - 2~5% Carbod. 4~3%
Chromlu~, 6~3%
Molybdenu~ 7~3%
Vanadiu~. 3~3X TuDgste~.
0~.75% Cobal~. a~8%
., Silico~ a~35% Nanganes~.
~alance IroD plus trace elements POURING TEMP~ - 1450 degrees C
METAL POURING NOZZLE - 4~8mm diameter orifice SPRAY HEIGHT - 480mm (Dlstance from the underslde of the atomiser to the top surface of the collector) OSCILLATING ANGLE - ~/- 9 de8rees about a vertical axls QSCILLATING SPEED - 12 cycles/sec A~OMISTNG GAS - Nitr~gen at ambient temperature ,~

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COLLECTOR - 70mm outslde diameter by lmm wall thickness 6tainless steel tube (at.
ambient temperature) COLLECTOR ROTATION - 95 r.pX.m.
LIQUID METAL:FLOW RATE
INTO ATOMISER - 18kg/min GAS/METAL RATIO - Q~5-Q~7 kg/kg Note that this was deliberately varied throughout the deposition cycle to compensate for excessive cooling by the cold collector of the first metal to be deposited and to maintain uniform deposition conditions as the deposlt in~reases in th~ckness.
DEPOSIT SIZE - 90mm ID 170mm OD llOmm long The averaga density of the deposit in the above example was 9~o8% wlth essentially a uniPQrm microstructure and uniform distribution of porosity throughout the thickness of the deposlt. A simi1ar tube made under the same conditionfi except that the collector was oscillated under a flxed spray at a rate of 1 cycle per 2 seconds, showed an flverage den~ity of ga~7~. In additlo~ the porosity Wfl8 mainly present of the reclprocation line~ aad not un$formly dlstributed~ The grain ~tructure flnd ~ize of carbide precipitate~ were ~ fllso varlable being condiderably finer in the .~

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reciprocation zones~ This was not the case wlth the above example where the microstructure was uniform throughout. `
There is now disclosed a second example of a deposit made by the single pass technique and with reference to Figures 4 and 5 discussed above:
EXAMPLE OF DEPOSIT MADE BY THE SINGLE PASS TECHNIQUE
'FIXED SPRAY OSCILLATING SPRAY

METAL POURING NOZZLE
(ORIFICE DIAMETER) 6.8mm ~6mm SPRAY HEIG~T 380mm 380mm OSCILLATING ANGLE 0 3 about vertical axis OSCILLATING SPEED O 25 cycles per fiecond ATOMISIMG GAS Nltrogen Nitrogan COLLECTOR 80mm dlameter stainless steel by lmm wall thlckness COLLECTOR ROTATION 3 r.p.s. 3 r~p.s.
TRAVERSE SPEED OF
CQLLECTOR a:39 m/mln 0~51 m/mln LI~UID METAL FLOW
RATE INTO ATOMISER 32 kg/min 42 kg/mln GAS/METAL RATIO ~S k&tkg 0~38 kg/kg SIZE QF DEPOSIT 80mm ID by 130mm OD

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POROSITY See Fi~. 4 See Fig~ 5 It will be noted from Figure 5 that there is reduced porosity for the Oscillating Spray~. Also a higher flo~ rate of metal and a lower gas/metal ratio has been achieYed.
In the method of the invention it i~ essential tha~, on averag~ a controlled amount of heat is extracted from the atomised particles in flight and on deposition including the superheat and a signlficant proportion of th0 latent heat.
The heat extraction from the atomised droplets before and after deposition occurs ln 3 main stages:-(i) ~n-flight coollng malnly by convectlve heat transfer to the atomisfng gas~. Cooling will typically be in the range 10-3 - 10-6 degC/sec depending mainly on the size of the atomised particles. (Typically atomised particles sizes are in the ~lze range 1-500 mlcrons);
(ii) on depositiod. cooling both by convection to the atomislng gas as lt flows over the surface of the spray deposlt and also by conductlon to the already deposited metal and (lii) after deposition coollng by conductlon to the already deposited metal~
~ t la e~sential to carefully control the heat e~traction in ~ach of the three abo~e stages~ It 15 al00 i~portant to enfiure that the ~urface oE the already deposlted metal confilsts of a layer of seml-solld~aeml-7~

liquid metal into which newly arriving Atomised particles are deposited. This is achieved by extracting heat from the atomised particles by supplying gas to the atomis~ng device under carefully controlled conditions -of flo~, pressur~. temperature and gas to metal mass ratio and also by controlling the further extraction o$
heat after deposition~. By using this technique deposits can be produced which have a non-particulate microstructure (i.e~ the boundarle~ of atomised particles do not show in the microstructure) and which are free from macro-segregation.
If desired the rate of the conduction of heat on and after deposition may be increased by applylng cold injected particles as disclosed in our European Patent published under No: 0198613 As indicated above the invention is not only applicable to the formation of new product~ on a substrate but the invention may be u~ed to form coated product~ In such a case it is preferable that a substrat~, ~hlch 18 to be coated is preheated in order to promote a metallurglcal bond at the substrate~deposlt interface. Moreove~. when forming discrete deposits, the lnvention has the advantage that the atomising conditions can be varied to give substantially unlform depositlon canditlons as the deposit increases in thickn~ss~ `For exampl~, any coollng of the flrst metal particle8 to be deposited on the collector can be s.
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reduced by depositing the initial particles with a low gas to metal mass ratio. Subseguent particles are deposited with an increased gas to metal mass ratio to maintain constant deposition conditions and therefo~, -uniform solidification conditions with uniform microstructure throughout the thickness of the deposit.
It will be understood thae, whilst the invention has been described wlth reference to metal and metal 8110y depositio~. metal matrix composites can also be produced by incorporating metallic and/or non-metallic particles and/or fibres into the atomised spray~ In the discrete method of production it is also possible to produce graded microstructures by varying the amount of particles and/or fibres injected throughout the deposition cycle~ The alloy composition can also be varled throughout the deposition cycle to produce a graded mlcro~tructure~ This is particularly useful for products where different propertles are required on the outer surface of the deposit compared to the lnterior (e.g~. an abraslon reslstant outer layer with a ductile main body)~ In addltio~. the lnvention can also be applied to the spray-deposition of non-metal~ e.g.
molten ceramics or refractQry materials~

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Claims (20)

1. A method of forming a deposit on the surface of a substrate comprising the steps of:
generating a spray of gas atomized molten metal, metal alloy or molten ceramic particles, said spray having a mean axis directed at the substrate, rotating the substrate about an axis of the substrate, and extracting heat in flight and/or on deposition from the atomized particles to produce a coherent deposit;
the improvement comprising oscillating the spray in the direction of the axis of the substrate whereby the angle of the mean axis of the spray to the substrate is varied, and oscillating the spray at a speed of oscillation sufficiently rapid that a thin layer of semi-solid/semi-liquid metal or ceramic is substantially maintained at the surface of the deposit over the amplitude of oscillation to maintain a substantially uniform microstructure through the thickness of the deposit.

2. A method of forming a deposit on the surface of an elongated substrate comprising the steps of:
generating a spray of gas atomized molten metal, metal alloy or ceramic particles by means of an atomizing device, the spray having a mean axis directed at the substrate with a relatively cold atomizing gas and the substrate being positioned with its longitudinal axis transverse to the spray, supporting the atomizing device for angular movement about an axis transverse to the mean axis of the spray, rotating the substrate about its longitudinal axis, effecting angular movement of the atomizing device whereby the spray is oscillated and the angle of the mean axis of the spray relative to the substrate is varied so that the spray is moved over at least part of the surface of the substrate, and extracting a controlled amount of heat in flight and on deposition from the atomize particles by the relatively cold atomizing gas to produce and maintain a thin layer of semi-solid/semi-liquid metal or ceramic at the deposition surface over the amplitude of the oscillation throughout the deposition operation to produce a deposit which has a non-particulate microstructure and is free from macro-segregation.

3. A method according to Claim 1 wherein the substrate is additionally moved in its axial direction relative to the spray,

4. A method according to Claim 1 wherein the axis of the substrate is substantially perpendicular to the direction of the mean axis of the spray during a part of its oscillation.

5. A method according to Claim 2 wherein the spray is oscillating along at least a part of the length of the substrate.

6. A method according to Claim 1 wherein the speed of movement of the spray is varied during each cycle of oscillation.

7. A method according to Claim 1 wherein the gas to metal mass ratio is varied from cycle to cycle or during each cycle of oscillation in order to accurately control the deposition conditions of the atomized particles deposited on different parts the substrate.

8. A method according to Claim 1 wherein the substrate is a collector and the deposit formed is a hollow body generated about the axis of rotation.

9. A method according to Claim 1 wherein the substrate is a hollow or solid body and the deposit formed is a coating on the body.

10. A method according to Claim 1 wherein the deposit is a discrete deposit and a variable amount of heat is extracted in flight during the formation of the deposit to maintain said thin layer.

11. A method according to Claim 10 wherein less heat is extracted in flight on initial deposition to reduce porosity.

12. A method according to Claim 10 wherein the extraction of heat is varied during each cycle of oscillation as well as from cycle to cycle.

13. A method according to Claim 1 comprising the additional step of introducing ceramic or metal particles or fibres into the deposit.

14. A method according to Claim 1 wherein the speed of rotation of the substrate is varied.

15. A method according to Claim 1 wherein the sped of rotation of the substrate and the speed of oscillation are inter-related to form a predetermined pattern of deposition.

16. A method according to Claim 1 wherein metallic or non-metallic particles and/or fibres are introduced into the atomized spray to form a composite deposit.

17. A method according to Claim 16 wherein a graded microstructure is produced by varying the amount of particles and/or fibres throughout the deposition cycle.

18. A method according to Claim 1 comprising generating a spray of gas atomized molten metal alloy particles and varying the alloy composition throughout the deposition cycle to produce a graded microstructure.

19. A method of forming a deposit on the surface of a substrate comprising the steps of:
generating a spray of gas atomized molten metal, metal alloy or molten ceramic particles, said spray having a mean axis directed at the substrate, rotating the substrate about an axis of the substrate, extracting heat in flight and/or on deposition from the atomized particles to produce a deposit, and moving the substrate relative to the spray in a single pass, the improvement comprising oscillating the spray in the direction of the axis of the substrate whereby the angle of the mean axis of the spray to the substrate is varied so that the spray is moved over at least a part of the surface of the substrate, controlling the rate of speed of the oscillation so that it is sufficiently fast to maintain a thin layer of semi-solid/semi-liquid metal or ceramic at the surface of the deposit over the amplitude of oscillation, and controlling the rate and amplitude of the oscillation of the spray to favourably influence the angle of impingement of the atomized particles on the forming deposit.

20. A method according to Claim 1 wherein the speed of oscillation is between 5 and 30 cycles per second.