GB2130250A

GB2130250A - A method for the manufacture of multilayer material having a functional layer applied on to a backing layer and a multilayer material made by the method

Info

Publication number: GB2130250A
Application number: GB08326428A
Authority: GB
Inventors: Dr Erich Hodes; Walter Schneider
Original assignee: GLYCO METALL WERKE
Current assignee: GLYCO METALL WERKE
Priority date: 1982-11-18
Filing date: 1983-10-03
Publication date: 1984-05-31
Also published as: DE3242543A1; DE3242543C2; FR2536309B1; JPS5996945A; GB2130250B; BR8305987A; FR2536309A1; GB8326428D0

Abstract

The functional layer is composed of at least two different substances e.g. aluminium and lead and is applied by plasma spraying of a mixture of the substances, which can be either a mixture of powdered substances or a composite material, e.g. in the form of a wire, containing the substances. The functional layer is supplied in a chronological sequence of several plasma spraying steps with different compositions of the mixture onto a backing layer e.g. steel strip and is used in bearing applications.

Description

SPECIFICATION A method for the manufacturer of multilayer material having a functional layer applied on to a backing layer and a multilayer material made by the method The invention relates to a method for the manufacture of a multilayer material having a functional layer applied on to a backing layer and composed of at least two different substances, the functional layer being applied by plasma spraying of a mixture, in the form of a powder, of substances forming the functional layer. The invention also relates to a multilayer material made by this method.

Numerous methods are known according to which metal heated to a high temperature or other material is sprayed on to a backing material. The sprayed material may even be plastics in the form of a wire or powder for certain purposes, mostly as a protection against corrosion and for repair work.

This is achieved by spraying devices known per se e.g. in the form of flame spraying, plasma arc spraying or electric arc spraying.

It is known from British patent specification 1 083 003 to produce bearing materials, i.e.

multilayer materials, by spraying hot materials forming the functional layer on to a backing body.

When the functional layer is built up of metals having a considerably differing specific weight, e.g. aluminium and lead, these components should be sprayed with separate spraying devices on superimposed or at least overlapping regions of the backing body surfaces. When spraying on to a strip-shaped backing body moving past the spraying devices, the spraying regions for the spraying devices spraying on different metals may be so arranged that in one region, the first one in the direction of movement, is sprayed only a metal with a lower specific weight, e.g. aluminium. In a central surface region, occupying a significant part of the total region, the sprayed regions for the lighter and heavier material, i.e. for aluminium and lead, overlap. In a small surface region, the last one in the direction of movement, only the heavier metal, e.g. lead, is sprayed on.By this is achieved that the functional layer consists in its thickness region, adjacent to the surface of the backing body, substantially of the lighter metal, e.g.

aluminium, whereas in the vicinity of the free surface a significantly increased content of the heavier metal, e.g. lead, is present. At any case no pure lead layer is to be formed.

This known method admits only certain variation of the composition in the two outer thickness regions of the functional layer. Within the functional layer proper is obtained a composition which is practically uniform across the whole thickness.

From US patent specification 2 233 304 is known a spraying device by means of which may be sprayed on to a substrate a mixture of different materials, e.g. a mixture of copper or aluminium and melted lead. This device cannot vary the composition of a functional layer across its thickness.

From a German Offenlegungsschrifft 25 09 109 is known a multilayer material, particularly for composite plain bearings, in which are formed, distributed across the thickness of the functional layer, zones of higher copper contents.

Such a functional layer should be applied by an electrolytic deposition process. However with the electrolytic deposition process the number of metals which could be used for the manufacture of such functional layers is very limited. In addition such electrolytic deposition processes cannot be so well controlled that they could produce exactly defined zonal variations in the layer composition with sufficient reproducibility.

The aim of the invention is to devise a method for the manufacture of a multilayer material of the kind described at the beginning of the specification which enables well controllable and exactly reproducible zonal variations to be obtained in the composition of the layer across its thickness which can be built up practically as desired.

This is achieved according to the invention by the application of the functional layer in a chronological sequence of several plasma spraying steps with a differing composition of the powder mixture of the substances forming the functional layer or of the composite material containing the substances forming the functional layer.

The chronological sequence of a plurality of plasma spraying steps seems at first expensive. It was found, however, that the technical expenses required by the plurality of plasma spraying steps according to the invention are smaller than in known powder metallurgical methods. First of all the danger of separation of the powder combinations is avoided according to the invention, this danger being of particular significance particularly when there are large differences in the specific weights of the substances to be united in the functional layer. By the invention is achieved a layer formation with a particularly high uniformity in the continuous transition between the zones of different composition.

A method according to the invention may be used for nearly all combinations of materials. So for instance a substrate may be sprayed with 100% of a substance and after a certain number of spray coats the substrate may be changed in several steps in favour of the proportion of the functional layer to up to 100% functional layer e.g.

an oxide ceramics. This transition from the substrate to the functional layer can be made continuously, or in steps, or in a single step. A particular advantage of the method according to the invention resides in the deposition being made by thermo-kinetic plating which due to its conception enables layers to be made by spraying which are nearly without pores as well as treat materials requiring temperatures above 35000C.

Such temperatures may be reached by plasma arc spraying according to the invention. The high temperatures of the plasma flame allow the use of nearly all metallic as well as non-metallic materials in the form of powder.

In addition to the choice of the plasma gas also the selected spraying parameters, such as the spraying distance, enable the layer quality to be widely varied and exactly adapted to the desired application. The future quality of the layer may be additionally influenced by the kind and amount of powder fed to the plasma flame.

The method according to the invention offers a large scope of variations. So for instance one of the substances or one of the groups of substances forming the functional layer is supplied initially in a high proportion, possibly 100%, and in later plasma spraying steps in smaller proportions, while a second substance or a second group of substances is initially supplied in a smaller proportion and in later plasma spraying steps in larger proportions, possibly of up to 100%. Also a third substance or a third group of substances forming the functional layer may be supplied in all plasma spraying steps in practically the same proportions. One of the substances or groups of substances may be reduced for the last plasma spraying step or steps to have a zero proportion in the mixture.On the other hand the second substance or the second group of substances may be supplied for the first plasma spraying step or steps so as to have an initial zero position.

In a method according to the invention the substances having a lower evaporation temperature are supplied into the powder mixture preferably in a particle size which is larger than that of the substances having a higher evaporation temperature.

One embodiment of the invention which is suitable for the manufacture of a multilayer material for the production of slide or friction elements having a slide or frictional layer of an aluminium-lead suspension alloy provides that pulverised lead is present in the powder mixtures applied by the plasma spraying steps in an initial zero proportion and a final proportion of 1 5 to 40% by weight, preferably 20% by weight.The aluminium powder may be of a particle size smaller than 100 ym, preferably 50 to 100 ym, and the lead powder of a particle size greater than 40 ym, preferably 80 to 1 00 ,um. When using materials which melt at low temperatures, such as aluminium and lead, for the formation according to the invention,the choice of the plasma spraying method is preferable to that of a thermo-kinetic plating method, such as flame spraying or electric arc spraying, because metals melting at low temperatures, such as aluminium and lead, when treated by plasma spraying, produce very dense and nearly poreless layers, and this has positive influence on the strength of the sprayed layer.

The introduction of powdered aluminium and lead into a flame the temperature of which may be greater or equal 1 5000 C, while the evaporation temperature of aluminium is about 20600C and of lead about 1 7400 C, has any sense only if the dwell time is short so that the powder particles are accelerated and, according to the selected spraying distance, impinge on the substrate with a high energy and melted either to a liquid or doughlike state. Fast cooling off takes place on the substrate which, in addition to mechanical clamping, causes tension in the sprayed particles which largely accounts for the adhesion mechanisms.

The build up of layers according to the invention is achieved in that after the substrate surface has been preheated by the plasma flame the layer build up proper takes place. This happens so that after the substrate surface has been preheated first only one substance or one group of substances, e.g. aluminium, is fed in a certain amount per unit of time into the flame. Then after a number of spray coats and on achieving a desired layer thickness the proportion or the amount of the first powdered substance may be reduced or kept constant while simultaneously a second substance, e.g. lead, is supplied in a certain amount per unit of time into the plasma flame.After a desired number of sprav coats the process can be repeated, the proportions of the first substance being supplemented or completed by those of the second substance until the layer has been built up or until the total thickness has been achieved which, e.g. for bearings, contains 80 parts by weight of aluminium and 20 parts by weight of lead. A similar layer build up with a continuous transition to higher proportions of another material component is recommended for use in tribologic conditions and cannot be achieved by any of the hitherto known methods with a continuous transition.

The invention also relates to a multilayer material, made by a method according to the invention the material having a metallic backing layer and a functional layer consisting of a metal alloy. The multilayer material according to the invention is characterised in that at least one of the constituent parts of the alloy in the functional layer increases from a zero proportion in the vicinity of the backing layer with increasing distance from the backing layer practically continuously up-to a preselected maximum proportion.

The constituent part of the alloy, the proportion of which changes with increasing distance from the backing layer, changes to a maximum proportion of practically 100% on the side of the functional layer remote from the backing layer.

This would mean, in the example of a suspension alloy containing aluminium and lead, that its composition from initial 100% aluminium ends up with 00% lead as a covering layer. Such a formation would be less suitable for use as a structural element, e.g. plain bearing. For this is preferred to build up the functional layer as a slide layer substantially of an aluminium-lead suspension alloy in such a way that it consists in the neighbourhood of the backing layer of pure aluminium and on the side remote from the backing layer contains 1 5 to 40% by weight, preferably 20% by weight, of lead.Functional layers which change in their free surface in a -overing layer containing 100% lead are, however, of a particular interest for the manufacture of corrosion-resistant structural parts, which is a technical problem often to be solved in chemical industry.

To obtain formation of a layer according to the invention a powder conveyor which operates as follows is particularly advantageous: powder is mechanically conveyed, e.g. by a bucket wheel, through a connection to a plasma flame the mechanical process being assisted by a carrier gas. This carrier gas carries, at a predetermined pressure and volume flow rate of gas, powder particles to the flame. One such device is needed for every powder used so that the number of powders to be simultaneousiy treated by plasma spraying depends on the number of available conveyors, a further variant of the method according to the invention being to mix a powder or all powders to be used additionally with others before their use, i.e. before their feeding into the conveyor. It is naturally also possible to use not only powder mixtures but also powdered alloys.So for instance aluminium may be provided with alloying components typical for aluminium.

The same applies to lead which can also be alloyed.

The shape of particles of the mixture to be used within the framework of the invention for thermokinetic plating, or of the alloy or powder should be preferably spherical. Such a spherical shape of particles is preferred to an irregular or club-shaped particle shape.

Both nitrogen and argon may be used as a plasma gas for the thermic spraying process, hydrogen being used in both cases as a secondary gas.

The spraying distance between the nozzle and the substrate to be provided with said layer should be 100 to 1 50 mm, preferably 125 + 5 mm. Even small deviations in the distance -- with otherwise constant parameters -- influence the quality of the layer to a great extent. The method according to the invention achieves an optimum bond between the sprayed layer and the selected backing material with a continuous transition up to the desired composition of the final layer, i.e.

the surface layer of the functional layer.

Continuous coating of the substrate with layers is achieved in that the plasma flame is supplied with the predetermined amount of each powder and the preheated substrate to be coated is coated by the plasma flame moving past the substrate. In addition it is also possible to apply the plasma flame so that it is stationary and to move the substrate past the plasma flame.

The movement takes place in such a way that the entire surface of the substrate which is to be coated is traversed by the plasma flame at a constant vertical and horizontal speed of 500mmis. As many spray coats, i.e. cycles, may be made until the desired thickness of the sprayed layer has been achieved. After every coating the composition of the layer to be sprayed may be varied by the change of the amount of powder fed into the plasma flame. After the coating process has been completed the layer material made in this manner must not be subjected to additional compacting because the layer produced by the plasma flame spraying method is nearly porefree (less than 5% pore volume).

The method according to the invention can be modified in that, after having been mixed, the powders to be introduced into the plasma flame are pressed to form a solid body and are introduced into the plasma flame as a composite material in the form of a pressed solid body e.g. in the form of a wire.

An example of a multilayer material made by a method according to the invention will now be explained in greater detail with reference to the drawing.

The drawing is an enlarged section through a multilayer material according to the invention which has a backing layer in the form of a steel body and a functional layer from an Al-Pb suspension alloy, the transition from aluminium to the Al-Pb suspension alloy of desired composition being made continuously.

A steel strip 1 is on its surface 2 to be coated pre-treated by jets to have a clean surface for the functional layer which surface offers due to its form partly the possibility of mechanical clamping.

A coating 3 is produced by a plurality of plasma spraying steps, the coating being formed substantially by an aluminium constituent part 4 and a lead constituent part 5. As a base material was used steel according to DIN 1 623 which was 1.5 mm thick. The base sprayed layer 6 contains Al 99.5. The further layer 7 sprayed thereon has a continuously increasing proportion of lead up to a ratio of 80% by weight of aluminium and 20% by weight of lead.

Example 1 The used aluminium powder was in the form of mostly spherical particles of a grain size of 1 00%: > 40Xam. The region of the grain size of the used lead was 100%50nm, the powder particles being also preferably of spherical shape.

Nitrogen was used as a primary gas at a pressure of 3.5 bar and a volume flow rate of 1 50 1/mien. Hydrogen was used as secondary gas at a pressure of 3.5 bar and a volume flow rate of 1 0/l min. The power of the plasma device was kept constantly at 30kW. At the beginning of the spraying process 40 gamin of aluminium was used. Up to the last spraying coat this amount of powder was not changed. After the third spray coat lead was separately fed, in addition to aluminium, to the plasma flame until, after the desired thickness has been achieved, the proportion of lead increased to 20% by weight.

Example 2 The method was performed as in Example 1.

except that argon was used as plasma gas, i.e. as primary gas. The pressure of the primary gas was 6.9 bar. The volume flow rate 1 50 I/min.

Hydrogen was used as secondary gas at a pressure of 3.5 bar and a volume flow rate of 5 I/min.

Claims

1. A method for the manufacture of a multilayer material having a functional layer applied on to a backing layer and composed of at least two different substances, the functional layer being applied by plasma spraying of a mixture, in the form of a powder, of substances forming the functional layer, or a composite material, e.g. in the form of a wire, containing the substances forming the functional layer, wherein the functional layer is applied in a chronological sequence of several plasma spraying steps with a differing composition of the powder mixture of the substances forming the functional layer or of the composite material containing the substances forming the functional layer.

2. A method according to Claim 1, wherein a first one of the substances or a first group of the substances forming the functional layer is supplied initially in a high proportion and in later plasma spraying steps in smaller proportions while a second one of the substances or a second group of the substances is initially supplied in a smaller proportion and in later plasma spraying steps in larger proportions.

3. A method according to Claim 2, wherein a third one of the substances or a third group of the substances forming the functional layer is supplied in all plasma spraying steps in practically the same proportions.

4. A method according to Claim 2 or 3, wherein the first substance or first group of substances is reduced for the last plasma spraying step or steps to have a zero proportion in the mixture.

5. A method according to any one of Claims 2 to 4, wherein the second substance or the second group of substances is supplied for the first plasma spraying step or steps so as to have an initial zero proportion.

6. A method according to any one of Claims 1 to 5, wherein that one or those of the substances having a lower evaporation temperature is or are supplied into the powder mixture in a particle size which is larger than that of that one or those of the substances having a higher evaporation temperature.

7. A method according to any one of Claims 1 to 6 for the manufacture of a multilayer material for the production of slide or friction elements having a slide or friction layer of an aluminiumlead suspension alloy, wherein lead is provided in the powder mixture applied by the plasma spraying steps in an initial zero proportion and a final proportion of 1 5 to 40% by weight.

8. A method according to Claim 7, wherein the lead powder is present in the mixture in a final proportion of 20% by weight.

9. A method according to Claim 6, 7 or 8, wherein an aluminium powder of a particle size of < 1 0Qtm and the lead powder of a particle size > 40,um are used.

10. A method according to Claim 9 wherein the aluminium powder is of a particle size between 50 and 100,us.

1 A method according to Claim 9 or 10 wherein the lead powder is of a particle size between 80 and 100 yam.

12. A method for the manufacture of a multilayer material having a functional layer applied on to a backing layer substantially as herein described.

13. A multilayer material made by a method according to any one of Claims 1 to 12 having a metallic backing layer and a functional layer consisting of a metal alloy, wherein the proportion of at least one of the constituent parts of the alloy in the functional layer increases from a zero proportion in the vicinity of the backing layer with increasing distance from the backing layer practically continuously up to a preselected maximum proportion.

14. A material according to Claim 13, wherein the constituent part of the alloy, the proportion of which changes with increasing distance from the backing layer changes to a maximum proportion of substantially 100% on the side of the functional layer remote from the backing layer.

1 5. A material according to Claim 13, wherein the functional layer is a slide layer substantially of an aluminium-lead suspension alloy which in the vicinity of the backing layer consists of pure aluminium and on the side remote from the backing layer contains 15 to 40% by weight of lead.

1 6. A material according to Claim 15, wherein on the side remote from the backing layer the functional layer contains 20% by weight of lead.

1 7. A material according to Claim 13 or 14, wherein the functional layer is a layer protecting against corrosion which in the vicinity of the backing layer is formed only of pure aluminium and on the side remote from the backing layer changes into a surface layer formed only of lead.

1 8. A multilayer material according to Claim 1 3 substantiaally as herein described.

1 9. A plain bearing made of a material according to any one of Claims 13 to 18.