Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
  • F01D5/284—Selection of ceramic materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
  • F01D5/288—Protective coatings for blades

Definitions

• the invention relates to a method for producing a thin ceramic deposit on a metal substrate. It applies in particular to the production of ceramic coatings of the thermal barrier type such as those used on certain components of aeronautical or aerospace engines subjected to high thermal gradients. For many applications, it is known to produce ceramic coatings to protect a metal substrate and thus increase its performance.
• the structure of the ceramic deposit made by PVD or EBPVD is very good, however these deposit techniques have the disadvantage of a prohibitive price for most applications. In addition, these techniques are extremely difficult to master in order to produce large parts with complex shapes and they require the use of high vacuum chambers.
• the technique of depositing ceramic by plasma spraying does not make it possible to obtain a dense structure and does not make it possible to produce deposits of small thickness less than 50 ⁇ m. In addition, these different methods do not allow the structure of the deposited crystals to be modulated: the vacuum deposition techniques give a columnar structure, the plasma spray deposition techniques give a structure in successive layers.
• the object of the invention is to overcome the drawbacks known methods and to determine a new method of deposit of a ceramic on a metal substrate allowing to make thin ceramic deposits less than 100 ⁇ m, or even less than 50 ⁇ m, with good adhesion, at a reduced cost, allowing to control the porosity of the deposit and the structure of the ceramic such as grain size and crystal orientation, and for covering complex shaped parts with a control of the desired thicknesses.
• the deposition of ceramic on a substrate metallic is done using a deposition method electrochemical combined with an oxidation method electrochemical or thermal.
• This type of deposit can be produced on all metallic substrates, the melting temperature is higher than the bath temperature electrolysis.
• the process for producing the ceramic coating comprises two steps.
• the first step consists in carrying out a dense electrolytic deposition of a metal on a metallic substrate, the metal being able, in an oxidized form, to form a ceramic and being chosen from zirconium, titanium, aluminum, magnesium.
• the substrate is immersed in an electrolytic deposition bath of the chosen metal and an anode system is arranged around the substrate to be coated.
• the metal can be deposited in an aqueous solution or in a bath of molten salts.
• zirconium which is a very reactive metal of the titanium family and whose oxide, zirconia, is commonly used as thermal barrier.
• the deposition of zirconium is carried out in a bath of molten salts, for example a fluoride bath brought to a temperature between 400 ° C. and 900 ° C.
• a voltage is applied to the terminals of the electrolyser; this voltage can be continuous, crenellated or pulse.
• By adjusting the cathodic current density applied and / or adding a crystallization inhibitor it is possible to orient the crystals formed during electrolytic deposition.
• the crystals can be oriented in the direction of the applied electric field so as to obtain a columnar structure; the crystals formed can also be oriented parallel to the substrate, or not have a preferred orientation.
• the second step consists in oxidizing the deposited metal so as to obtain a ceramic adhering to the substrate.
• This oxidation operation can be carried out in different ways.
• the oxidation can be carried out in an oven under a controlled atmosphere, that is to say at temperatures between 300 ° C. and 900 ° C. in an atmosphere in which the oxygen composition is controlled.
• Oxidation can also be carried out by a method electrochemical, called anodization, in an aqueous medium or in bath of molten salts.
• Anodizing is suitable for oxidation of metals such as aluminum, titanium, zirconium and magnesium.
• the achievable oxide thicknesses are a function of the conductivity of the film formed. As example, the oxide thickness achievable on zirconium in aqueous medium is of the order of 13 to 15 nm per volt applied across the electrolyser. On titanium, in the middle aqueous, the achievable oxide thickness is of the order of 5 to 10 nm per volt applied to the terminals of the electrolyser.
• Additions may be introduced into the ceramic coating to improve some characteristics of this coating.
• the yttrium is an addition element in zirconia which allows stabilize the high temperature phase of the zirconia and prevent dimensional changes of the mesh crystalline during thermal cycles. This element increases therefore very considerably the lifetime of the barriers zirconia thermal.
• the amount of yttrium added is typically between 6 and 20% by weight.
• the electrolysis was carried out at a temperature of between 700 and 800 ° C., with a crenellated cyclic current comprising a slot for ionic redissolution and two slots for depositing metal at potentials of -2040mV and -2250mV.
• the current densities applied are of the order of 165mA / cm 2 and 400mA / cm 2 .
• the cycle time is 2 seconds, so it takes 30 minutes to deposit 300 ⁇ m of a Zr-Y mixture.
• the zirconium coating thus produced comprises 2 to 15% of yttrium.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Ceramic Engineering (AREA)
• Electrolytic Production Of Metals (AREA)

Priority Applications (2)

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Publications (2)

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Citations (3)

• 1998
  • 1998-10-26 EP EP19980203600 patent/EP0997555B1/de not_active Expired - Lifetime
  • 1998-10-26 DE DE69821942T patent/DE69821942D1/de not_active Expired - Lifetime

Patent Citations (3)

Non-Patent Citations (2)

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