FR2487713A1 - METHOD OF APPLYING A SHEET COATING ON A SUBSTRATE - Google Patents

Abstract

METHOD AVOIDING THE FORMATION OF FRAGILE PHASES. IT INCLUDES THE DEPOSITION OF A LAYER OF BORON ON AT LEAST ONE OF THE COATING SURFACES AND THE SUBSTRATE, THE PLACEMENT OF THE COATING ON THE SUBSTRATE, AND THE EXPOSURE OF THE ASSEMBLY RESULTING TO A TIME CYCLE AND THERMAL SUFFICIENT TO CAUSE THE FORMATION OF A LIQUID ZONE BETWEEN THE SURFACES OF THE COATING AND THE SUBSTRATE. APPLICATION TO TURBINE BLADES.

Description

The superficial superficial stability is a

  important problem with regard to industrial gas turbines

  modern trielles. The combustion of heavy fuel oils gives rise to

  to highly corrosive environments which, together with

  high combustion intervals and at longer intervals between two maintenance operations, lead to

  very strict in the choice of materials. A solution to

  superficial stability depends on the application

  a sheet-coating alloy that is highly resistant to oxidation

  and corrosion on a high-strength substrate. Considerable progress has been made in the development of diffusion bonding methods of a coating to such substrates. For example, U.S. Patent No. 3,928,901 discloses a method in which the sheet coating is

  cold isostatically pressed to produce an adhered film

  rent on the substrate. In US Pat. No. 3,904,101 there is described a method according to which the coating is applied, the vacuum is made in the gap between the coating and the substrate, all the joints are brazed under vacuum and the bonding of the assembly is obtained by diffusion under high pressure and

  high temperature in an autoclave containing a gaseous medium.

  U.S. Patent No. 3,962,939 discloses a process in which a sheet coating and the substrate are pre-assembled and masked at all junctions, surrounded by pieces of glass and then hot-melt bonded, to melt the glass

  and ensure a state of isostatic stress.

  Commonly used coating processes include

  a large number of steps, some of which require many tasks and, as a result, are expensive.

  are also difficult to apply to more com-

  plexes such as the segments of multi-blade diffusers.

  In some coating processes low melting eutectic phases remain after the coating operation

  and are characterized by their fragility at low temperatures.

  res. Inclusions of oxides and other substances can also

  exist at the point of adhesion coating / substrate.

  The subject of the present invention is a novel method of diffusion bonded sheet coating on

  complicated configuration, eliminating several of the main steps

  blades used in the prior art while simultaneously offering

  the possibility of easily and efficiently making a coating on different substrate configurations, and

  provision of objects thus produced. The detailed description

  below will make it obvious to the people of the art that this

  object of the present invention as well as others.

  The invention relates to a method of

  sheet coatings on substrates and parts resulting from such an operation. More particularly, the method comprises the deposition of boron on at least one of the bearing surfaces of the coating and the substrate, the setting up of the

  coating on the object, and the resulting exposure of the assembly

  both at a sufficient time and temperature cycle to cause the formation of a liquid zone between the bearing surfaces

  coating and substrate, and an isostatic pressure cycle

  hot tick (PIC) time-temperature-pressure sufficient for

  completely bond the coating to the substrate.

  The method of the present invention is applicable to

  manufacture of gas turbine blades, diffusion segments

  multiple rotor blades where the configurations are of

  difficult, at certain stages of parts for the passage of hot gas turbine gases at very high temperatures, etc. Such

  parts comprise a substrate with a coating, of appro-

  asked. The substrate is cast metal and, although the present invention is applicable to all types of castings,

  it is particularly useful for castings made

  with the most resistant alloys based on nickel,

  cobalt or iron, called superalloys in industry. The laboratory-

  The casting itself is conventional and does not form part of the present invention. It is possible to use any casting (or coating) whose surface accepts a layer of boron, also capable of accepting welding such as welding

by capacitor discharge.

  Recommended coating materials are alloys

  nickel-chromium solutions such as those marketed by the

  tional Nickel Company under the designation IN-671 and IN.617. These nickel-chromium alloys consist essentially of

  80% by weight of nickel and 20 to 50% by weight of chromium.

  The most complex alloys contain a number of elements, for example IN-617 which comprises 22% by weight of chromium, 1% by weight of aluminum, 2.4% by weight of cobalt, 9% by weight of molybdenum, 0.003% of boron and 0.007% of carbon,

  the rest being nickel. Other coating materials may

  can be used such as the following: Hastelloy-X, FeCrAlY (2541), HS 188, 304 stainless steel, etc. The coating or substrate materials must be able to receive a layer of boron and accept welding with a capacitor discharge welding apparatus. For example, the thickness of a typical coating may range from about 127 mm to 1.27 mm, and preferably 0.254 mm to 0.762 mm; however, other thicknesses may be suitable without departing from the spirit of the

present invention.

  In the method of the present invention, one of the

  the face surfaces of the sheet and the substrate (or possibly both) may be provided with a

  boron layer by any suitable conventional method. Borura-

  may be performed before or after the shaping of the cladding sheet in the case where the bearing surface of this

  coating must receive the deposit. Then, the cover sheet

  and the substrate are assembled in the conventional manner, that is,

  to say that the pre-shaped sheet, of composition and form

  appropriate, is prepared by a suitable means such as

  chemical page, degreasing, abrasion or nickel plating and placed on the substrate; the junctions are then spot welded or

  welded continuously in such a way that the

  valle between junctions be as weak as possible. In general

  ral, an interval of less than 0.0254 mm can be obtained. Boron acts as a melting point-lowering product for the surface of the deposited material, so that the borured object has a higher overall melting temperature than the boride surface. When the assembly is subjected to an appropriate combination of high temperature and long vacuum time, the surface melts to form a liquid zone; this is followed by rapid isothermal solidification of the liquid phase due to the extremely rapid diffusion rate of boron due to its small atomic dimension (atomic radius: 0.80 Angstrom) compared with other temperature-lowering products. fusion such as silicon or phosphorus. The heat treatment and diffusion provide a gastight seal around the junctions of the coating. This gas-tight seal allows the establishment of pressure

  differential between the outer and inner surfaces of the coating

  during the hot isostatic pressure cycle (PIC) sub-

  sequent. Then the diffusion bonded substrate is

  subject to a PIC cycle, usually at pre-selected

  (up to 1232aC) and under selected pressures

  up to 2068 bars over a period of

  cation of about 0.5 to 16 hours, such that there is no significant degradation of the mechanical properties of the substrate after the treatment, but sufficiently to cause the deformation of the coating around the substrate and its total adhesion to him. The PIC cycle is usually performed at a

  temperature of about 9820C-12320C.

  The present invention is characterized by a precise control of the liquid phase, the elimination of low melting eutectic phases which are characterized by their low temperature brittleness and by decomposition or dissolution.

  oxides and other inclusions at the bonding point

substrate.

  The control of the liquid phase is obtained by the

  determining the amount of boron deposited on the coating and / or the substrate. Determining the amount of boron controls the amount of liquid phase present during the specific chemical phase processes entering the diffusion bonded coating. Sufficient boron is used to create enough liquid to form an effective gas-tight seal between the coating and the substrate but no more than necessary

  because excessive amounts of boron could be

  for the substrate and the properties of the coating. In general, boron is used in sufficient amounts to obtain a nominal liquid phase of about 0.005 mm to 0.1 mm

  thickness and, preferably, between 0.015 mm and 0.05 mm

  thick. The amount of boron required depends on the composition

  chemical composition of the particular boride material. For example, the amount of boron chosen should be sufficient to form a liquid seal between the joints of the coatings while minimizing the time and temperature required

  the diffusion elimination of the boron-rich phases.

  Elimination of eutectic phases at low point

  fusion is achieved by the use of boron as the sole

  melting point depressant and time-cycle

  temperature and pressure that diffuse boron into the coating

  and the substrate. As mentioned above, the exclusive use of boron makes possible the isothermal solidification of the liquid phase during the diffusion heat treatment and the PIC cycle since the boron diffusion rate is extremely fast because of its small atomic dimension.

  compared to other products that

  if we. In general, diffusion heat treatment uses

  temperatures in the range 10380C-12600C, preferably at least

  turn of 1121aC-1176aC, for a duration of about 0.05 to 20

  hours, preferably around 0.1 to 4 hours.

  The decomposition of oxides and other inclusions at the surface coating interface is achieved by the presence of

  the liquid phase containing boron throughout the region of the in-

  surface coating-substrate. In other processes of coating

  there is no liquid phase covering the entire region. It is believed that the presence of the liquid phase at the interface breaks down the inclusions that may be present either on the surface of the coating or on that of the substrate

  by melting the metal in the immediate environment of the inclusions.

  In addition, the liquid film prevents the oxidation of the surfaces due to the covering of the substrate by this film in the elements.

low oxidation stability.

  To further illustrate the present invention, hereinafter are examples of the method and products which make it

  the object. It will be seen that in specification and claims

  all parts and percentages are given in

  weight and all temperatures in degrees Celsius unless indicated

contrary cation.

EXAMPLE 1

  A sheet of IN-671 (50% nickel, 50% chromium) coating material 0.254 mm + 0.025 mm is cut to the approximate dimensions required for cold forming

  on a profiled form of first-stage turbine blade

  available in the trade. The pre-shaped IN-671 piece is then cold-formed in a series of progressive dies until it closely matches the envelope (generally 0.254 to 0.508 mm) of the desired shaped shape. The

  formed coating is then welded to obtain a shape advantage

  It can be slid over the dawn of the trade.

  On the IN-671 welded coating, a layer of 0.0007 to 0.0009 grams / cm 2 of diffused boron was deposited on the inner side only. After ultrasonic cleaning and degreasing in

  Freon of the boron layer coating and dawn, the coating

  is assembled on the first stage turbine blade and welded to this dawn by capacitor discharge at points

very close together.

  The dawn and its coating are placed in a vacuum oven under a pressure of 10-4 Torr and heated at 11350C + 40C for ten minutes. The cycle produces a 0.005 mm to 0.05 mm liquid zone on the surface of the boron coating and seals

the coating at dawn.

  After cooling the oven, the dawn is removed and inspected visually for any discontinuity around

  joints of the coating on the dawn. The piece is then inserted

  pectée under a pressure of 20,68 bars in a pressure vessel of helium; it is quickly decompressed and the part removed from the pressure vessel to be immersed in methanol. The absence of bubbles indicates a tight seal

between the coating and the dawn.

  The blade is then placed in a hot isostatic pressure vessel, heated to 109 ° C. under argon pressure of 55 kgf / mm 2, and maintained under these conditions for 1 to 3 hours. The PIC cycle closes any porosity

  between the coating and the dawn and to complete the diffusion

  boron by removing it from the coating-dawn interface

  which increases the melting temperature of the region of inter-

  face. The dawn is then taken out of the autoclave and ultrasonically inspected for defects in the blade-to-blade connection. Finally, the dawn with coating undergoes aging for 24 hours at 843,330C in order to develop the properties

  mechanical special alloy substrate; it is also light

  treated on a sanding belt machine for

  the solder of the coating and polish the asperities

in place.

EXAMPLE 2

  A sheet of S-57 coating material (25% Cr, 3% Al, 5% Ta, 10% Ni, 0.2% Y, the remainder Co) of 0.762 mm + 0.050 mm thickness is cut to size. approximativres

  required for cold forming on a simple bladed diffuser

  first floor of commerce. Three parties are required

  res: one for the profiled section and one for each of the two end walls of the diffuser. The three pre-shaped parts

  are then cold-formed on a series of progressive matrices

  until they agree closely with the enve-

  the section of the profiled section and the shapes of the end walls.

  desired. Enough material is left on each part so that a lap joint can be achieved between

  parts of the profiled section of the end walls

moth.

  The coating parts formed are then covered

  A layer of about 0.0007 to 0.0009 grams / cm2 of boron scattered on the inner side only. After ultrasonic cleaning and degreasing in freon of the boron coating parts and the diffuser, the coating parts are assembled and soldered by capacitor discharge at points

  very close on the diffuser and one to the other.

  The diffuser and the coating are then placed in a vacuum oven for vacuum heat treatment of 10-4 Torr at a temperature of 114 ° C. ± 3.8 ° C. for one hour. The cycle produces a liquid zone of 0.005 mm to 0.05 mm on the surface

  boron coating which seals the coating parts

  together and on the broadcaster.

  The diffuser is visually inspected for any gaps around all joints in the coating

  then by immersion according to the process described in Example 1.

  The broadcaster is then subjected to a PIC cycle at

  temperature of 112 ° C., under argon at a pressure of 10.55 kgf / m 2,

for 1 to 3 hours.

Claims (9)

  1. Method of applying a coating to a substance   characterized in that it comprises the deposition of a cou-   boron on at least one of the bearing surfaces of the coating and the substrate, placing the coating on the substrate, and exposing the resulting assembly to a   sufficient time and temperature cycle to provoke   a liquid zone between the bearing surfaces of the coating and the substrate.   2. Method according to claim 1, characterized in that the amount of deposited boron is sufficient to create a   Nominal liquid area of about 0.0046 to 0.0936 mm thick.   3. Method according to claim 2, characterized in that the boron is the only product melting point depressant   for the surfaces of the coating and the substrate in question.   4. Method according to claim 3, characterized in that the entire region of the coating-substrate interface is   covered with a deposit at the assembly.   5. Method according to claim 4, characterized in that the time of the thermal and temporal cycle is from about 0.05 to 20 hours and the temperature of this time cycle and   Thermal is around 10370C-12600C.   6. Method according to claim 5, characterized in that the time is about 0.1 to 4 hours and the temperature around 11210C-11760C.   7. The method according to claims 1 or 6, characterized   in that the assembly, after the cycle in ques-   is subjected to hot isostatic pressure.   8. Method according to claim 7, characterized in that the coating and the substrate are each of special alloy. 9. Method according to claim 8, characterized in   what the coating is nickel-chromium alloy.