DE2254434A1 - DEVICE FOR PREPOSITING METAL BY DUSTING UP FROM THE LIQUID PHASE - Google Patents

Description

Dr. Hs'mut Späth

8209 Rojanheint / Ofab. 59 P 54

Max-Jo53. ^l $ plate 6

United Aircraft Corporation, 400 Main Street, East Hartford, Conn. 06108 / USA

Device for depositing metal by means of sputtering from the liquid phase

(Addition to patent 2 122 336)

The invention relates generally to a device for sputtering of metals and alloys, in particular for the formation or deposition of alloys or coatings in one with high precipitation speed from a liquid surface =.

The generation of metal precipitates and a device for this can be found, for example, in the USA patents 3,305,473, 3,393,142 and 3,458,426. Sputtering encompasses generally the solid sublimation of a disk material as a result Ions impact on its surface * The sublimated material forms a special, high-energy atom beam, which is ideal for making metal or alloy films and coatings that have excellent adhesiveness on the coating substrate and have a particularly fine structure »The main disadvantage of the known sputtering process lies in the low precipitation rate of nominally about 500 S per minute in a diode circuit. These low speeds do not match the generation of coatings in normally required thicknesses, for example on gas turbine machine parts, to the

309821/1021

_ ρ -

Resistance to oxidation or in the production of alloy deposits with bulky product dimensions. So far, new coatings have been used to achieve significant advances in the service life of components that were exposed to dynamic oxidizing environmental conditions at very high temperatures. These will often applied by thermal evaporation processes. However, these new coating alloys have chemical compositions of relative complexity, with thermal evaporation in all but a few Special traps, a fractionation of an alloy into its basic constituents causes and 'the more volatile constituents are first evaporated so that the precipitates become heterogeneous in composition. To a rainfall To achieve a homogeneous nature over an extended period of time, it is necessary to use the evaporating liquid composition adjust and continuously modify by adding appropriate solid material to correct the fractionation tendency is supplied ..

The sputtering processes significantly reduce the fractionation leotard of alloys because of the sputtering process distant atoms are released unrelated to their natural evaporation tendency and hence the atomized vapor compound primarily on the proportion of alloying elements on the dusted surface and the proportion of the dusted Atoms in the total vapor at any given point in time depends on.

The invention seeks to provide a comparison with the prior art improved sputtering apparatus for generating sufficient energy densities, a is at high temperature impactors having a melting point above to melt around 1100 ⁰ C and a precipitate by using both thermal evaporation and by sputtering, with at a very high rate, reducing fractionation of the alloy during precipitation.

309821/1021

original

2284434

The invention is explained in more detail below with reference to the drawing, which is an embodiment, an inventive Device in a schematic representation for dusting in shows surfaces located in the liquid phase.

A vacuum chamber 1 with suitable valves, pumps and insulated feed tanks is "sucked out via a passage 2 with regard to a controlled argon leakage supply which, through a passage 3, extends to maintain a dynamic pressure of 15 x 10" ^ Torr ", a water-cooled Furnace 4- made of copper, which contains a surface-forming charge 5 made of an alloy and is insulated from the chamber by a 'dielectric sleeve' 6, is on a controlled power supply - and is negatively biased. A shield 8 is symmetrical arranged around the furnace on the inside of the chamber, so that only the liquid surface can be atomized 10 applied * A bias voltage of 60 - 100 V is applied to the filament by e A regulated DC voltage source 11 is transmitted, which causes the build-up of a glow discharge between the filament 9 and all objects on earth potential, including the chamber, provided that the filament is at an operating temperature of about 1371 ⁰ C (2500 ^D K> - is located. A discharge current of about 0.79 - 2.36 A / cm of the hearth. surface area is required, this area being 15-9 cm in the described arrangement.

An adjustable magnetic field of 1 - 200 Gauss in such an orientation that its field axis is perpendicular to the liquid surface level is aligned by a magnetic coil 12 generated, which is fed by a direct current source 13 «Das Magnetic field increases the degree of ionization in the discharge. If the negative bias of the furnace is increased, the charge is melted by intensive ion bombardment. When the alloy surface into the liquid phase

309821/102 1

is transferred, a substantial and unexpected increase in current occurs from the energy source 7, which is a Rapid atomization of the liquid surface conditions and enables the temperature of the filament to be reduced or in In some cases it is possible to switch off the filament flow. Thermal or other unknown electron emission mechanisms result in the electrons required to maintain the glow discharge, as it was passed through the filament were delivered. Therefore, under the diode-type operating condition, sputtering occurs when the surface has melted and is at a temperature sufficient for thermal emission.

The method has been studied as applied to elemental tin, which has a suitably low melting point and very low vapor pressure so that in fact no thermally introduced vapor would be obtained from the liquid surface. A comparison of the corresponding sputtering speed of liquid and solid tin surfaces at specific bombardment energies showed that the liquid surface gave a yield up to 15% higher than the surface in the solid state.

In another case, an alloy with a nominal weight composition of 25 % chromium, 6% aluminum, 0.1 % yttrium, the remainder iron, was liquefied and deposited on a base by condensation. The precipitate gave an analysis by weight of 31% chromium, 4% aluminum, 0.1 % yttrium, the remainder being iron. In this particular case, a

Energy density of 130 watts / cm of the liquid surface at a furnace potential of 2600 V used. The entire Energieeinspeisuiig was 9j9 KW over 180 minutes, during which Time 120 g of a total batch of 250 g removed from the surface ., A coating deposition rate of 254-, U per hour was determined at a distance of 8.9 cm.

In the case of an alloy of iron and 30 % vanadium, which

309821/1021

BATH ORIGINAL

-5 - 225U34

would give a theoretical precipitate with a calculated analysis of 0.02% vanadium by thermal evaporation a precipitate of 10.3% vanadium, the remainder iron, which is "a value better than the predicted value by a factor of 500" Wait for vanadium on thermal evaporation alone is equivalent to. The iron / vanadium area was at 105 watts / cm of the molten surface is atomized with a total system power of 6.3 KW over a period of 225 minutes, with in during this time 93 g of a "batch containing a total of 315 g" were removed became. The rate of precipitation was 68.5 / «. Per Hour at a distance of 8.9 cm between the surface «

As is understood, occur in the method according to the invention two effects in combination, namely the atomization of the liquid surface and the thermal evaporation. However, the procedure was carried out so that the atomization one has a considerably beneficial effect on the composition of the steam; in systems where the essential vapor pressures are low are, the atomization prevails over the process of generating steam ago * The process resulted in exceptionally high sputtering speeds and also the ability, to a large extent, to maintain the chemical integrity of the surface composition to keep up with the precipitated material.

The very high atomization speeds that occur with liquid Surfaces that are achievable are likely to occur for the following reasons:

1. Atoms are more easily released from the surface of a plate, when the temperature is raised «,

2. The electron emission from that subject to ion bombardment Area increases during liquefaction and contributes to a higher ion density in the gas phase compared to the liquid Metal, which helps to maintain the plasma. This is perhaps the main reason why the use of the filament becomes unnecessary if a high temperature

3 0.9821 / 1021

2 2 S / 1 i. ° ί ·,

sensitive liquid is applied.

3. The higher metal atom content in the vapor than in the liquid itself provides an ion source for self-sputtering by the atoms of the constituent part of the liquid surface Materials themselves »Self-dusting is an effective Process because the same mass of the bombarding ion and the surface atom of the material to be sputtered represents the ideal case for a transfer of the carrying mass. It was found that the system pressure can be reduced after start-up and that the sputtering mechanism itself helps Operating conditions can be maintained with ultra high vacuum.

Certain other features and advantages of the invention will emerge when coating objects with complex alloys, especially turbine parts. The intense electron emission of the melt, which is subjected to ion bombardment, provides a convenient source of heat for those to be coated Parts, and preheating these parts often improves the adhesion as well as the integrity of the coating. In fact, the ballistic electrons that result from this intense electron emission are not only used to Carrying out a preheating function in the usual sense but also as a means of controlling the substrate temperature during the used throughout the entire coating process. Above an ion

The process produces a bombardment limit density of about 60 mA / cm with regard to the precipitation flow itself a substantial insensitivity with regard to the potential of the impact body, Taking into account this insensitivity as well as the fact that the heating effect of the ballistic electrons of depends on the potential of the target, it turned out to be possible by simply changing the potential of the target, generally within the range of about 1000-1700 V to precisely regulate the substrate temperature.

These ballistic electrons also result in another special one, however favorable, effect in terms of the obtained

21/10 2 1 _{0R | Q | NAL}

2264434

Coating itself, although they play no part in the precipitation itself. Their energy creates an actual effect on the coating or an electron impact during the entire deposition process or during the growth and not afterwards. The result is a coating of a particularly favorable morphology compared to coatings obtained by other coating methods, even if these coatings are based on the same chemical conditions _β ·

The pressure range over which the sputtering is carried out requires only mechanical pumps to achieve the desired vacuum conditions. The ion bombardment density is uniform over any desired surface area, so that complicated furnace shapes correspond generally to the shape of the object to be coated to maintain the surface material can be used «, therefore collection efficiencies of 25 - 50% were achieved on supports that were similar in their dimensions to the dimensions of the furnace of 6.35 ^χ 6j35 cm, as it was used in the program » ■ Since the dimensions of the melt compared the dimensions of the part to be coated can be large, shadow effects on geometrically complex parts, for example turbine blades, are reduced «,

Other suitable elements may be used under appropriate circumstances can be used to liquefy the batch, e.g. * induction heating or electron beam melting o The sputtering ■ off the liquid phase can take place as long as the bias requirements "Any suitable gas, for example argon, or combinations of gases for the Sputtering can be used which has the required discharge density maintained close to the melt «when there is sufficient energy density on the liquid surface is present, there can obviously be an ionization of the vapor atoms the necessary ion bombardment in the sputtering process in order to maintain the precipitation process, which in particular eliminates the need to use a discharge gas

309821/1 0 2Ί

■ '. ■ ORIGINAL INSPECTED

would exclude altogether.

In the device according to the invention, the bias in In accordance with normal practice, the pad may be either positive or negative to the plasma as long as the pad is opposite the impact body is held positively, i.e. as long as the base is more positive than the impact body »Typically at the beginning of the coating process, the underlay biased negatively with respect to the plasma in order to achieve a cleaning of their surface by the sputtering process. The base tension is then made positive, generally at about -100 to +100 V for a potential of the impact body from -1000 to -1700 V, so that the effect of the precipitation exceeds the effect resulting from the dust loss results, provided that such an effect exists at all.

The emitter current for a 10 cm diameter batch is typically set to around 100 A at 12 V *

Therefore, during the precipitation process, the substrate is also dusted up Atoms and ions, thermal atoms and ions, and ballistic electrons are all related contribute to the special character of the coating. In order for this to occur there is a sputtering of the liquid surface This does not imply that all matter to be deposited is the result of both being dusted up as well as thermal atoms. For example, eating can be cheap, both liquid and side-by-side to dust solid surfaces, especially if a Species either has a very high melting point or is incompatible with the melt for other reasons. Hence, actual Types like carbon, aluminum oxide or maybe some of the refractory metals evaporated from the solid state will. However, the main species with the greater part of the layering build-up will necessarily become a liquid one Dusted surface.

3 0 9 8 21/10 2 1 ^, _NSPECT EO

Claims (1)

Claims vij / Vorrichtxing for carrying out an alloy coating process on a metallic substrate according to the patent
2 22 336t characterized by a device for negative pre-tensioning of the impact body against the Pietall charge (5) for the purpose of cleaning its surface and a device for the subsequent positive pre-tensioning of the impact body against the metal eye for the purpose of causing the vapor deposition 2 »Application of the device according to claim Λ on alloys to be sputtered with melting points above about ^ Üt82t / 1itt ORIGINAL -INSPECTED Blank page