Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas

Definitions

• the present invention relates to a method for producing a hot gas corrosion-resistant protective layer on metal parts by thermal spraying using a powdered ceramic material, and a hot gas corrosion-resistant protective layer produced by thermal spraying on metal parts, which consists of metallic and ceramic material.
• Diesel engines and gas turbines that work with heavy oil are exposed to high levels of hot gas corrosion.
• At the high combustion temperatures that occur or are striven for, for example, in marine diesel engines there is a particularly high level of corrosion as a result of the contamination of the heavy oil, which leads, for example, to the formation of sulfur and alkali compounds and vanadium pentoxide.
• the various parts subject to corrosion such as exhaust valves, pistons, combustion chambers, injection nozzles, turbine blades, cause high replacement or repair costs, which could not be significantly reduced by the previously known methods of protective coating.
• the invention has for its object to provide a method for producing a protective layer of ceramic materials with which layer thicknesses of more than 0.5 mm and a very good corrosion resistance at high temperatures up to 1200 ° C can be achieved.
• the ceramic material used is only partially stabilized in such a way that 10-20% by volume of unstabilized phase occurs in the layer formed, or it comprises at least two different grain areas, the maximum grain size of the finer grain area being substantially smaller than the average grain size of the coarser grain area is.
• the aforementioned procedural measures and the type of materials used in a controlled manner, cause microcracks in the layer produced, by means of which the stress states in the layer are reduced and therefore no larger ones which impair the density and durability of the layer Cracks occur.
• the protective layer according to the invention consists of a plurality of layers sprayed on top of one another, each of which has a decreasing metallic portion and an increasing ceramic portion from the inside to the outside, the outermost layer being purely ceramic.
• the layer has 10-20% by volume of unstabilized phases in which microcracks are present, the length of which is at most equal to three times the largest dimension of the storage of unstabilized phase resulting from a spray particle, or it has microcracks, the length of which is at most is two thirds of the largest dimension of the deposited spray particle in which the crack occurs.
• microcracks are caused, in particular, by a strong, shock-like cooling during the spraying process, either localization and control of either the inventive presence of unstabilized phases in the application or the even coexistence of larger and smaller lamellar deposits due to the selected grain distribution in the ceramic spray material Size of the cracking occurs.
• the tensions between the base material or a metallic intermediate layer and the ceramic cover layer are reduced by a graduated structure of the protective layer.
• Ni-Cr-Al-Y, Co-Cr-Al-Y, Ni-Al-Ni-Cr-Al or Ni-Cr alloys are used as the adhesive or intermediate layer, and a Cr intermediate layer is also preferably used as a diffusion barrier in the event of corrosion attack by vanadium pentoxide .
• An exhaust valve of a marine diesel engine showed strong corrosion after a long period of operation due to hot gas corrosion due to the sulfur and vanadium content (up to 0.5% S and up to 50 ppm V) of the heavy oil used.
• a new exhaust valve intended for replacement was coated in a plasma spraying system prior to installation.
• a Ni - Cr - Al powder was used for the adhesive layer and a partially stabilized zirconium oxide powder made of 80% ZrO 2 + 20% Y 2 O 3 was used for the cover layer.
• the application was graded from 100% metal to 100% ceramic by spraying intermediate layers with the proportions 80/20, 60/40, 40/60, 20/80, the total layer thickness being 2 mm.
• An argon-hydrogen mixture was used as the plasma gas and argon as the powder carrier gas.
• the electrical power was 52 kW.
• For cooling liquid CO 2 was used.
• a sample coated simultaneously for control purposes was examined microscopically in order to determine the length of the microcracks formed in the layer. The measurements showed a microcrack length of at most 2.5 times the length of the embedded particles of the unstabilized phase. In the present case, the mentioned particle length was 5 ⁇ m and the maximum micro-crack length was 12 ⁇ m.
• the percentage of the non-stabilized phase was checked by the known cathode luminescence method and gave a percentage of 11.5% by volume.
• the coated exhaust valve was installed in the engine and put into operation. No corrosion was found on this valve after 2000 hours of operation. A further check after 5000 operating hours showed only a slight corrosion attack. The running time of the coated part could therefore be increased by at least two and a half times.
• the piston surface of a diesel engine which was operated with heavy oil with a contamination of more than 50 ppm vanadium, showed a strong attack by hot gas corrosion.
• the piston was coated with a plasma spraying system according to the following scheme:
• the sample was examined by the cathode luminescence method and a portion of 13 percent by volume was measured.
• the running time of the piston could be extended considerably by the applied coating.
• the surface to be coated was prepared by mechanical processing and subsequent blasting with corundum.
• the autogenous flame spraying process was used for coating.
• the injection nozzles and corresponding control samples were provided with a metallic adhesive layer made of Ni-Al powder, the thickness of which was 0.15 mm. Then an additional powder was added Conveyor a mixture of 20% Ca 2 SiO 4 in the grain size range of 5-45 microns, 77.5% Ca 2 SiO 4 in the grain size range of 63-150 microns and 2.5% B 2 O 3 in a grain size range of 5-45 microns fed.
• the powder feed was regulated in such a way that a transition from layer to layer between the metallic component corresponding to the adhesive layer and the ceramic component was achieved from the mixture mentioned.
• the cooling was increased with the aid of ring-shaped cooling nozzles so that a cooling rate of when the outer, purely ceramic cover layer was reached 10 ° C / sec was reached on the surface of the spray layer.
• the combustion chamber was coated with a protective coating of calcium disilicate, which was stabilized with 3.0% phosphorus pentoxide was provided.
• a Ni - Cr alloy of 80% Ni and 20% Cr was applied as the adhesive layer.
• the coating was carried out by autogenous flame spraying in a system with two external powder conveyors.
• the course of the coating process was as follows:
• the surface to be coated was degreased by washing with carbon tetrachloride and then dried. The surface was then cleaned by blasting with silicon carbide with a grain size of 0.5-1.0 mm and roughened.
• the combustion chamber part was preheated to 150 ° C and the metallic adhesive layer sprayed on from a first powder conveyor.
• the layer thickness was 0.2 mm.
• a mixture of 30% Ca 2 SiO 4 with a grain size of 5-37 ⁇ m, 67% Ca 2 SiO 4 with a grain size of 53-95 ⁇ m and 3.0% P 2 O 5 was introduced into the second powder conveying device. After the 0.2 mm adhesive layer had been applied, the setting of the two powder conveying devices was changed so that the proportion of the metallic to ceramic powder per layer was graded in the ratios of 80/20, 60/40, 40/60, 20/80 % occurred. Then a layer of 100% ceramic was sprayed on. The total layer thickness was 2.5 mm.
• the surface of the layer was cooled with CO 2 by means of several nozzles directed towards the surface in such a way that a cooling rate of 5 ° C./sec in the surface of the layer was achieved when the ceramic cover layer (100% ceramic) was reached has been.
• a plasma spraying system was used. The preparation was carried out by blasting with corundum with a grain size of 0.25-0.75 mm. After blasting, the surface had a roughness of 35-40 ⁇ m.
• the Ni - Al powder for the intermediate layer was then sprayed onto the blade surface prepared in this way. During the spraying, the surface was cooled with two air jets. The layer thickness was 0.15 mm. Subsequently, the protective layer made of 88% ZrO 2 + 12% CaO was applied in stages from the metal layer. For cooling, three CO 2 nozzles were used, which were attached at a distance of 5 cm from the center of the flame. The cooling rate at the surface was 8 ° C / sec. The total thickness of the coating was 0.9 mm. Together with the turbine blades, two test samples were coated in order to determine the necessary investigations for determining the formation of microcracks, for checking the absence of voltage and the proportion of non-stabilized phases. As expected, it was found on these samples that the microcracks were triggered by the unstabilized phases and their length corresponded to 1.5 times the length of the intercalation resulting from a corresponding particle.
• the coated turbine blades were installed in the turbine during the next overhaul. After 5000 hours of operation, the turbine blades were inspected and it was found that there was no significant hot gas corrosion attack on the edges and surfaces of the blades.
• Turbine blades for a hot gas turbine that is operated with heavy oil with a contamination of 0.3% sulfur should be provided with a protective coating against the corrosion of the hot combustion gases.
• the coating was carried out by the plasma spraying process using two powder feed units, one powder feed device being the Material of the adhesive layer (Ni-Cr-Al-Y) and the other that promoted the top layer (Al 2 O 3 + ZrO 2 ).
• the coating process was as follows:
• the turbine blades were prepared by blasting with corundum with a grain size of 0.25-0.50 mm. After blasting, a Ni - Cr - Al - Y powder was sprayed with an argon / hydrogen plasma, in which the electrical power was 48 kW, without cooling. After this metallic adhesive primer had been sprayed on in a layer thickness of 0.1 mm, the transition to the ceramic cover layer was produced as in Example 4. The plasma gases and the electrical power corresponded to the spraying of the metallic adhesive layer. A cooling rate of 6 ° C./sec was maintained on the surface by cooling nozzles arranged around the plasma torch in order to relieve the internal stresses generated during the application. The layer thickness of the entire layer was 0.8 mm.
• test samples sprayed with the turbine blades were examined for the formation of microcracks and it was found that the length of the microcracks in the embedded ZrO 2 particles corresponded to half the particle diameter and that the ZrO 2 was homogeneously distributed. The examination was again carried out using the known cathode luminescence method.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coating By Spraying Or Casting (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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Citations (2)

• 1980
  • 1980-12-05 CH CH900180A patent/CH645925A5/de not_active IP Right Cessation
• 1981
  • 1981-11-24 FR FR8121984A patent/FR2495503A1/fr active Granted
  • 1981-12-04 WO PCT/EP1981/000189 patent/WO1982001898A1/de not_active Ceased

Patent Citations (2)

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