EP2871257A1 - Method of coating with subsequent remelting method - Google Patents

Abstract

Through the combination of coating processes and remelting processes, known coating processes can be used which have improved properties due to the remelting process.

Description

The invention relates to a coating method in which a first layer is applied and this is converted by remelting.

Cold gas spraying is a coating process in which the coating material is applied to a substrate in powder form at a very high speed of 1000m / s to 2500m / s. To this end, a process gas heated to a few hundred degrees is accelerated to supersonic speed by expansion in a Laval nozzle and then the powder particles are injected into the gas jet. The injected powder material is thereby accelerated to such a high speed that it forms a relatively dense and firmly adhering layer in comparison with other thermal spraying methods, even without a preliminary onset or melting on impact with the substrate. However, the kinetic energy at the time of impact is not sufficient for complete melting of the particles so that there is no metallurgical bond with the base material.

Laser remelting is characterized by exact energy input into a material, so that a desired remelting depth can be set exactly. Due to the large cooling rates and the spatially small melt volume during laser beam remelting, the solidification processes are primarily initiated by a nucleation favored by the melt pool edge. As a result, pores in particular are removed from the remelted areas and, in the case of nickel-base superalloys, the microstructure freezes virtually without pores. In addition, special microstructures can be set by the locally large heat gradients.

It is therefore an object of the invention to provide a method which has improved properties for the bonding of the layers to one another and / or to the substrate.

The object is achieved by a method according to claim 1.

In the dependent claims further advantageous measures are listed, which can be combined with each other in order to achieve further advantages.

The advantage of the invention allows a large-scale coating and local remelting at locations where only certain improved material properties are desired.

Through the combination of coating processes and remelting processes, known coating processes can be used which have improved properties due to the remelting process.

The figure shows schematically the procedure of the method.

It proposes a combination of the methods of thermal spraying / cold gas spraying and remelting. By means of thermal spraying / cold gas spraying, a layer layer is applied to a base material. Subsequently, the layer is remelted by remelting so that either a metallurgical connection to the base material is achieved and / or special microstructural properties are set.

• die Dichte des aufgetragenen Materials wird durch die Reduktion der Poren vergrößert, entsprechend nimmt somit auch die thermischen Leitfähigkeit zu;
• durch das Umschmelzen vergrößert sich die Kornstruktur, wodurch bessere Kriecheigenschaften erzielt werden;
• durch richtungsabhängiges Umschmelzen können die Werkstoffeigenschaften (wie insbesondere Kriechfestigkeit) gezielt in eine Richtung verbessert werden, da die Körner in Verfahrrichtung der Laserstrahlung erstarren.

The following structural properties can thus be changed in a targeted manner:

• the density of the applied material is increased by the reduction of the pores, correspondingly also the thermal conductivity increases;
• the remelting increases the grain structure, resulting in better creep properties;
• By direction-dependent remelting, the material properties (in particular creep resistance) can be purposefully improved in one direction, since the grains solidify in the direction of travel of the laser radiation.

By further applying layers by means of cold gas spraying or other thermal spraying methods and subsequent remelting, gradient layers can also be built up.

In the figure, the sequence of the method is shown schematically.

A component 1 is produced.

The component 1 is preferably a turbine component and has a substrate 4 preferably made of a nickel- or cobalt-based superalloy.

On the surface 5 of the substrate 4, a first layer layer 7 'is applied by means of a material jet 10.

This can be done by cold gas spraying or other thermal spraying methods such as HVOF, LPPS, APS, VPS, PLC, SPPS. Here, in a non-limiting manner, cold gas spraying is mentioned below.

In a further step, by means of a welding beam 13, in particular a laser beam 13, the first applied layer layer 7 'melted around, wherein also at most a part of the substrate 4 is melted with. In this case, a remelted layer 16 is generated.

In a further step, a further cold gas-sprayed layer layer 7 "can be applied to the remelted layer 16, which is then again remelted 7".

In this case, the underlying layer layer 7 'in particular only partially melted in an upper area with.

It is also possible (not shown) to first apply two cold gas-sprayed layer layers 7 ', 7 "and these both remelt, since the remelting depth of the welding beam 13 can often be greater than the coating thicknesses of the layer layers 7 ', 7 ".

The remelting can take place over a large area, i. the complete layer layers 7 ', 7 "are remelted or only a local remelting takes place at locations where certain material properties are desired, such as, in particular, freedom from pores or a certain hardness or a certain grain structure, which have better creep properties.

Likewise, by a direction-dependent remelting the heat-relevant property can be improved in a certain direction.

Through the combination of coating processes and remelting processes, known coating processes can be used which have improved properties due to the remelting process.

Claims (10)

method
for producing a layer (16, 16 ') on a surface (5) of a substrate (4),
in which in a first step at least a first layer layer (7 ') is applied,
wherein the at least one layer layer (7 ') is remelted in a further method step. Method according to claim 1,
in which the first layer layer (7 ') is produced by cold gas spraying. Method according to claim 1,
in which the first layer layer (7 ') is produced by a thermal spraying process. Method according to one or more of the preceding claims,
in which the remelting process is carried out by a laser beam (13). Method according to one or more of the preceding claims,
in which the first layer layer (7 ') is remelted directly before the optional application of further layer layers (7 "). Method according to one or more of the preceding claims 1 to 5,
in which first at least two layer layers (7 ', 7 ") are applied,
which are then remelted together for the first time. Method according to one or more of the preceding claims,
in which the layer layer (7 ') or the layer layers (7', 7 ") are remelted only locally. Method according to one or more of the preceding claims,
in which also the substrate (4) is at most partially remelted. Method according to one or more of the preceding claims,
in which the steps of application of one or more layer layers (7 ', 7 ") and remelting of these once, in particular several times,
is repeated. Method according to one or more of the preceding claims,
in which the remelting is direction-dependent, in particular by tilting a welding beam (13) in a direction opposite to the surface (5).

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