GB2182349A - Laser coating with inorganic materials - Google Patents

Abstract

Apparatus for coating a surface has a laser for producing a beam of radiation which is directed onto the surface to be coated, and means for feeding the material of the coating in powder form onto that part of the surface which is illuminated by the laser beam. The powdered coating fuses within the laser beam and may be carbides or ceramics such as chromium or aluminium silicates and oxides, e.g. silica, alumina or zirconia. In a specific embodiment silica powder, 5-10 microns is fed onto steel from an argon gas-controlled powder feed system, a carbon dioxide laser being focused on the surface of the steel. A complete argon blanket is maintained over the surface.

Description

SPECIFICATION Production of Ceramic Coatings This invention relates to the coating of surfaces with layers of high melting point materials, such as carbides or ceramics including for example the oxides of silicon, aluminium and zirconium.

The use of such coatings has been known for some time in providing increased resistance to wear or high temperature corrosion, or as a thermal barrier to insulate the underlying surface from a high temperature environment. Methods of applying these coatings to metal components, such as physical or chemical vapour deposition or plasma spraying, have been expensive however and the structure of coatings so produced are not always entirely effective, particularly in providing resistance to corrosion.

This invention therefore consists of apparatus for coating a surface comprising a laser for producing a beam of radiation, means for directing the beam on to the surface to be coated, and means for feeding the material of the coating in powder form onto that part of the surface which is illuminated by the laser beam.

In some cases it may be possible to illuminate the entire surface which is to be coated, but for the coating of larger areas it may be necessary to provide means for suitable rastering of the surface relative to the laser beam and feeding means, whereby the entire surface is coated in stages by overlapping passes of the feed.

In most applications, particularly when a metallic surface is to be coated, it is essential to ensure that the coating process takes place in an inert environment, such as a vacuum or a gas such as argon or nitrogen. In this way, the surface is prevented from oxidising during the coating process. Although the powdered coating fuses within the laser beam, it is not necessary for the surface to be heated; indeed, for some applications it may be desirable to maintain the substrate at a low temperature. It is found that the coating conditions do not vary with the composition of the surface for most steels and probably not for nickelor cobalt-based materials.

When coating a surface having a high chromium or aluminium content with an oxide, it may be advantageous to permit some oxidation of the surface to take place in order to allow the formation of a complex coating including chromium or aluminium silicates and oxides which for certain applications may exhibit improved properties over a simple oxide coating.

It has been found that coatings of silica, alumina and chromium silicates prnduced by this invention have shown a significant resistance to high temperature oxidation, sulphidation and carburisation attack when exposed respectively to air at temperatures upto 1000"C, a gas mixture simulating the product gas of a coal gasifier at up to 800"C and an environment simulating ethylene production at up to 1050"C.

One example of the use of the present invention is in the coating of the surface of a steel component with silica.

To achieve this, silica powder having a particle diameter in the range 5 to 10 microns is fed onto the surface, for example, Incoloy 800H or a 2 1/4% Cr, 1% Mo steel, from an argon gas-controlled powder feed system at a rate of 0.3 mg per second, a laser beam from a 2 kW carbon dioxide laser being focused onto the surface at the same time. Provision is made to ensure that a complete argon gas blanket is maintained over the surface.

The component is rastered underneath the laser beam and feed system, and a good quality coating has been achieved by this means with a laser power of 1.7 kW within a beam diameter of 10 mm, the velocity of travel of the surface relative to the beam being 10 mm per second with a beam overlap of 8 mm. The coating thickness thus obtained is in the order of 100 microns but coatings having a different thickness may clearly be formed by suitable adjustment of the parameters.

1. Apparatus for coating a surface comprising a laser for producing a beam of radiation, means for directing the beam on to the surface to be coated, and means for feeding the material of the coating in powder form onto that part of the surface which is illuminated by the laser beam.

2. Apparatus as claimed in Claim 1 wherein the beam illuminates the whole surface.

3. Apparatus as claimed in Claim 1 wherein the beam is rastered overthesurface.

4. Apparatus as claimed in any one of Claims 1 to 3 wherein the coating process takes place in an inert environment.

5. Apparatus substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Production of Ceramic Coatings This invention relates to the coating of surfaces with layers of high melting point materials, such as carbides or ceramics including for example the oxides of silicon, aluminium and zirconium. The use of such coatings has been known for some time in providing increased resistance to wear or high temperature corrosion, or as a thermal barrier to insulate the underlying surface from a high temperature environment. Methods of applying these coatings to metal components, such as physical or chemical vapour deposition or plasma spraying, have been expensive however and the structure of coatings so produced are not always entirely effective, particularly in providing resistance to corrosion. This invention therefore consists of apparatus for coating a surface comprising a laser for producing a beam of radiation, means for directing the beam on to the surface to be coated, and means for feeding the material of the coating in powder form onto that part of the surface which is illuminated by the laser beam. In some cases it may be possible to illuminate the entire surface which is to be coated, but for the coating of larger areas it may be necessary to provide means for suitable rastering of the surface relative to the laser beam and feeding means, whereby the entire surface is coated in stages by overlapping passes of the feed. In most applications, particularly when a metallic surface is to be coated, it is essential to ensure that the coating process takes place in an inert environment, such as a vacuum or a gas such as argon or nitrogen. In this way, the surface is prevented from oxidising during the coating process. Although the powdered coating fuses within the laser beam, it is not necessary for the surface to be heated; indeed, for some applications it may be desirable to maintain the substrate at a low temperature. It is found that the coating conditions do not vary with the composition of the surface for most steels and probably not for nickelor cobalt-based materials. When coating a surface having a high chromium or aluminium content with an oxide, it may be advantageous to permit some oxidation of the surface to take place in order to allow the formation of a complex coating including chromium or aluminium silicates and oxides which for certain applications may exhibit improved properties over a simple oxide coating. It has been found that coatings of silica, alumina and chromium silicates prnduced by this invention have shown a significant resistance to high temperature oxidation, sulphidation and carburisation attack when exposed respectively to air at temperatures upto 1000"C, a gas mixture simulating the product gas of a coal gasifier at up to 800"C and an environment simulating ethylene production at up to 1050"C. One example of the use of the present invention is in the coating of the surface of a steel component with silica. To achieve this, silica powder having a particle diameter in the range 5 to 10 microns is fed onto the surface, for example, Incoloy 800H or a 2 1/4% Cr, 1% Mo steel, from an argon gas-controlled powder feed system at a rate of 0.3 mg per second, a laser beam from a 2 kW carbon dioxide laser being focused onto the surface at the same time. Provision is made to ensure that a complete argon gas blanket is maintained over the surface. The component is rastered underneath the laser beam and feed system, and a good quality coating has been achieved by this means with a laser power of 1.7 kW within a beam diameter of 10 mm, the velocity of travel of the surface relative to the beam being 10 mm per second with a beam overlap of 8 mm. The coating thickness thus obtained is in the order of 100 microns but coatings having a different thickness may clearly be formed by suitable adjustment of the parameters. CLAIMS

1. Apparatus for coating a surface comprising a laser for producing a beam of radiation, means for directing the beam on to the surface to be coated, and means for feeding the material of the coating in powder form onto that part of the surface which is illuminated by the laser beam.

2. Apparatus as claimed in Claim 1 wherein the beam illuminates the whole surface.

3. Apparatus as claimed in Claim 1 wherein the beam is rastered overthesurface.

4. Apparatus as claimed in any one of Claims 1 to 3 wherein the coating process takes place in an inert environment.

5. Apparatus substantially as herein described.