DE102018221823A1 - Welding wire with cubic boron nitride additive, process and component with cubic boron nitride in one layer - Google Patents

Abstract

Due to the use of welding wire with cubic boron nitride, overlay welded layers with boron nitride can be easily created and used in the sealing of layer systems in gas turbines.

Description

The invention relates to a welding wire with cubic boron nitride, which is applied to a component with a welding material and forms an application layer there.

Cubic boron nitride (cBN) is an established high-performance abrasive, which is characterized, among other things, by high thermal stability up to 1573K, and is also considered the second hardest material.
There are already a number of established manufacturing processes for application for cBN. All processes have in common that the construction of contoured geometries containing cBN is only possible very slowly and therefore costly and is subject to a restriction in the selectable grain sizes of the cBN. The idea was developed as an example for turbine blade tips, but is not limited to this.

In the gas turbine, rubbing occurs between rotating turbine blades in the hot gas area and the housing. The blades are ground down, which leads to a loss of performance. It has been experimentally proven that cBN-armored blades do not grind off, but instead deliberately grind into a rub-in layer and thus there are lower losses. The grinding effect depends, among other things, on the grain size.

The challenge now is to enrich the leaf tip contour with cBN.

It is therefore an object of the invention to solve the above-mentioned problem.

Currently, this can only be done using an additive process downstream of the casting.

The object is achieved by a welding wire according to claim 1, a method according to claim 7 and a component according to claim 8.

The subclaims list further advantageous measures which can be combined with one another as desired in order to achieve further advantages.

• 1 eine Anordnung nach dem Stand der Technik,
• 2 eine erfindungsgemäße Auftragschweißung und
• 3 einen Schweißdraht.

Show it:

• 1 an arrangement according to the prior art,
• 2nd a surfacing according to the invention and
• 3rd a welding wire.

The figures and the description represent only exemplary embodiments of the invention.

Inert gas welding processes such as CMT, TIG or MAG are particularly suitable for the efficient application of metal with cBN. For this, the electrode (CMT / MAG) or the filler wire (TIG) must contain the cBN particles. The idea is accordingly to design the welding wires as a multi-material electrode. Grain size and welding base material can be freely selected.

An MCrAlY base material with up to 50% cBN grains is ideal for the exemplary application of a gas turbine blade.
MCrAlY means M = Ni, Co and / or Fe, in particular nickel (Ni) and cobalt (Co) and Y = yttrium, rare earths, tantalum (Ta), iron (Fe) and / or silicon (Si).

A nickel or cobalt-based alloy can also be used 14 for the welding wire 20th be used and / or combined with MCrAlY.

• Niedrigschmelzend: im klassischen Drahtziehverfahren erfolgen (Gussrohling/Faden mit cBN-Körnern 13` wird auf passende Dicke gestreckt/gewalzt).

Depending on the base material of the welding wire 20th the production can vary:

• Low melting: using the classic wire drawing process (cast blank / thread with cBN grains 13` is stretched / rolled to the appropriate thickness).

High-melting: eg base material powder 14 + cBN grains mixed with binder 13 ' , subsequent pressing in the form of welding wire + possibly thermal treatment of the green part.

As mentioned, the use is particularly intended for gas turbines. Here the cBN is used in its thermal limit range, since cBN only oxidizes from 1573K. When applying small cBN particles 13 it means that they oxidize quickly ( 1 ).

Larger particles 13` ( 2nd ) "Survive" longer. The abradable coating is rubbed in in a controlled manner within the first 100 hours of operation.

2nd and 1 are only schematic representations, however, the coarser particles 13` in 2nd larger than the particles 13 in 1 in the state of the art.

The use of larger cBN particles 13` guarantees that these are still present during the first 100 hours in order to be able to use their abrasive properties.

Furthermore, the abrasive effect of large abrasive particles 13` ( 2nd ) with the expected high degree of grinding in much better than with small particles 13 ( 1 ). With small particles 13 ( 1 ) there is simply a strong accumulation of the frictional heat instead of a high material removal. The better abrasive effect of larger abrasive particles is also due to their greater strength.

• - Mit CMT/MAG/WIG-Schweißverfahren kann sehr schnell und sehr kostengünstig eine große Schichtdicke aufgebracht werden;
• - Verwendung von sehr großen cBN-Partikeln, die mindestens 120µm, 150µm oder 200µm groß sind und insbesondere bis zu 500µm Körner bei 2mm Schweißdraht 20 (3) verglichen mit max. 90µm beim Laserpulverschweißen;
• - Schnelligkeit des Prozesses bei großen Schichtdicken;
• - Präziser Konturaufbau über CNC-gesteuerte Schweißroboter;
• - Kombination von großen und kleinen cBN-Partikeln in einem Schichtaufbau möglich;
• - Kein Entmischen wie beim Laserpulver-Auftragschweißen.

In addition, there are the following inherent advantages:

• - With CMT / MAG / TIG welding processes, a large layer thickness can be applied very quickly and very inexpensively;
• - Use of very large cBN particles which are at least 120µm, 150µm or 200µm in size and in particular up to 500µm grains with 2mm welding wire 20th ( 3rd ) compared to max. 90µm for laser powder welding;
• - Speed of the process with large layer thicknesses;
• - Precise contour construction using CNC-controlled welding robots;
• - Combination of large and small cBN particles possible in one layer structure;
• - No segregation as with laser powder cladding.

The cBN particles have an aspect ratio of at least 1.5 and are in particular blocky.

Claims (8)

Metallic welding wire (20) with particles (13 ') made of cubic boron nitride (cBN). Welding wire after Claim 1 , in which the metal (14) of the welding wire (20) has a nickel or cobalt-based superalloy, in particular has only a nickel or cobalt-based superalloy. Welding wire after Claim 1 or 2nd , in which the metal (14) of the welding wire (20) has an MCrAlY alloy, in particular has only one MCrAlY alloy. Welding wire according to one or more of the Claims 1 , 2nd or 3rd which (20) has a diameter of 2mm. Welding wire according to one or more of the Claims 1 , 2nd or 3rd which has at least 10 vol% cubic boron nitride (cBN) and in particular at most 50 vol% cubic boron nitride (cBN). Welding wire according to one or more of the Claims 1 to 5 , whose particles (13 ') made of cubic boron nitride (cBn) are at least 120µm, in particular at least 150µm, very particularly at least 200µm in size and up to 500µm in size and in particular are block-shaped, in particular have an aspect ratio of at least 1.5. Method for producing a surfacing (7), in which a welding wire (20) according to one or more of the Claims 1 to 6 is used. Component (1`) made from a substrate (4), in particular from a nickel or cobalt-based superalloy, on which an overlay weld (7 ') is present, which has cubic boron nitride (cBN) as secondary particles (13'), and in particular by means of a welding wire (20) according to one or more of the Claims 1 to 6 was generated.

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