U.S. patent application number 10/574731 was filed with the patent office on 2007-11-29 for method for local alitation, siliconization or chromation of metal components.
This patent application is currently assigned to MTU AERO ENGINES GMBH. Invention is credited to Michael Strasser, Heinrich Walter.
Application Number | 20070272331 10/574731 |
Document ID | / |
Family ID | 34428332 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070272331 |
Kind Code |
A1 |
Strasser; Michael ; et
al. |
November 29, 2007 |
Method for Local Alitation, Siliconization or Chromation of Metal
Components
Abstract
A method for the production of a locally limited diffusion layer
on a metal component is disclosed. In an embodiment, the method
includes the steps of application of a paste containing Cr, Si
and/or Al, and containing activators, to the areas of the metal
component to be coated. The paste is solidified to form a donor
pack. The regions which are not to be coated and are adjacent to
the donor pack are covered with a diffusion-blocking powder pack.
The component is heated to a temperature above 900.degree. C. in
order to carry out the alitation, siliconization and/or chromation.
The method can be used in the production of turbine rotors.
Inventors: |
Strasser; Michael;
(Kleinberghofen, DE) ; Walter; Heinrich;
(Friedberg, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
MTU AERO ENGINES GMBH
DACHAUSER STRASSE 665
80995 MUNICH GERMANY
DE
|
Family ID: |
34428332 |
Appl. No.: |
10/574731 |
Filed: |
September 23, 2004 |
PCT Filed: |
September 23, 2004 |
PCT NO: |
PCT/DE04/02114 |
371 Date: |
February 5, 2007 |
Current U.S.
Class: |
148/279 |
Current CPC
Class: |
C23C 10/04 20130101 |
Class at
Publication: |
148/279 |
International
Class: |
C23C 10/04 20060101
C23C010/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2003 |
DE |
103-47-363.7 |
Claims
1-8. (canceled)
9. A method for production of a locally limited diffusion layer on
a metal: component by alitation, siliconization and/or chromation,
comprising the steps of: applying a paste containing Cr, Si and/or
Al, and containing an activator, to an area of the metal component
to be coated; solidifying the paste to form a donor pack; covering
of a region, which is not to be coated and is adjacent to the donor
pack, with a diffusion-blocking powder pack; and heating to a
temperature above 900.degree. C. in order to carry out the
alitation, siliconization and/or chromation.
10. The method of claim 9, wherein the metal component is covered
before the step of applying the paste, at least in the area to be
coated, with a porous separating layer containing
Al.sub.2O.sub.3.
11. The method of claim 9, wherein the diffusion-blocking powder
pack contains a metal powder having a similar or a same composition
as the metal component to be coated.
12. The method of claim 9, wherein the diffusion-blocking powder
pack consists of Ni or of a Ni alloy.
13. The method of claim 9, wherein the diffusion-blocking powder
pack contains an activator.
14. The method of claim 9, wherein the diffusion-blocking powder
pack, the paste and/or the donor pack contains an activator in an
amount of 0.2 to 5 wt. %.
15. The method of claim 9, wherein the activator is NH.sub.4F,
NH.sub.4Cl and/or AlF.sub.3.
16. The method of claim 9, wherein the metal component is a
component of a turbine rotor.
Description
[0001] This application claims the priority of International
Application No. PCT/DE2004/002114, filed Sep. 23, 2004, and German
Patent Document No. 103 47 363.7, filed Oct. 11, 2003, the
disclosures of which are expressly incorporated by reference
herein.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a method for the production of a
locally limited diffusion layer on the surface of a metal
component, whereby the diffusion layer is formed by the absorption
of Si, Al and/or Cr into the surface of the metal component.
[0003] Mechanically and thermally highly stressed metal components
usually are provided with protective layers which are intended to
improve the wear protection properties or even improve thermal
insulation properties. In order to improve bonding of these
functional layers, it is common to provide a specially adapted
adhesive layer between the component and the functional layer.
Among other things, such adhesive layers must have a suitable
chemical composition, and suitable roughness and surface
topography. In so doing, a rough surface is advantageous in order
to enhance the mechanical meshing of the later-applied cover layer,
for example, a thermal insulation layer.
[0004] Referring to gas turbine technology, in particular, for
example the production of turbine blades, adhesive layers are
provided between the component and an outer thermal insulation
layer. Suitable thermal insulation layers may be composed of
(partially) stabilized ZrO.sub.2 or even of other refractory
oxides. In addition to being rough, the adhesive layers must be
oxide-free and resistant to hot gas corrosion in order to be able
to cling to the outer protective layers or the thermal insulation
layer. Likewise, the adhesive layers must provide compensation for
various thermal expansion coefficients of metal base materials and
the thermal insulation layer.
[0005] In particular, diffusion layers containing Al and,
optionally, additional transition metals, are well-suited as
adhesive layers. In so doing, the selection of additive elements
added to the diffusion layer, of course, depends significantly on
the base material. Typically, the coating process for the
production of diffusion layers is a powder pack process (Out of
Pack Process). Referring to this, the coated surface is brought
into contact with powders containing additive elements, hereinafter
also referred to as donor pack, and heated to a temperature at
which a diffusion of the powder elements into the surface of the
component can take place. The formation of the diffusion layers,
generally referred to as alitation (diffusion of aluminum),
siliconization (diffusion of silicon), chromation (diffusion of
chromium), etc., corresponds to the absorption of Al, Si or Cr.
[0006] For example, German Patent Document DE 198 24 792 A1
describes a method for the production of a corrosion-resistant and
oxidation-resistant layer, whereby a slurry containing at least one
of the elements Cr, Ni or Ce is applied to a component and dried,
and then alitated at temperatures between 800.degree. C. and
1200.degree. C.
[0007] Referring to German Patent Document DE 3883 857 T2, a method
has been known for the production of a diffusion layer of Al and
other ferrite-stabilizing elements for steel. In so doing, a pack
of Al or an aluminum alloy and other elements, a halide activator
and optionally fillers is produced, and the steel component to be
coated is embedded in this pack. Then diffusion coating takes place
at temperatures above approximately 1000.degree. C.
[0008] The described methods have the disadvantage that the
formation of the diffusion layers cannot be locally limited.
Rather, the entire component is provided with the diffusion layer
in a non-specific manner. A sharp transition between the coated
region and the uncoated component cannot be achieved. However,
frequently a sharp boundary of the coated region is necessary.
Therefore, the diffusion layer should be deposited only at
locations where it is in fact required as the adhesive layer.
Inasmuch as this layer significantly alters the surfaces or
material properties, the layer can create significant disruptions
of functionality in the remaining regions of the component.
[0009] Therefore, the object of the invention is to provide a
method for the formation of diffusion layers on metal components,
the method ensuring a local limitation of coated and uncoated
regions in a simple manner.
[0010] In accordance with the invention, this object is achieved by
a method for the production of a locally limited diffusion layer on
a metal component by alitation, siliconization and/or
chromation.
[0011] Therefore, in accordance with the invention, the diffusion
layer is built up by means of a powder pack process, whereby,
inside the packed bed reactor, at least one diffusion-blocking
powder pack is provided in addition to the donor pack, the
diffusion-blocking powder pack preventing the supply of additive
elements to the uncoated regions of the metal component. In
accordance with the invention, additive elements that are to be
supplied by the donor pack are at least selected from Cr, Si and/or
Al.
[0012] The inventive process comprises at least the following
steps: [0013] a) application of a paste containing Cr, Si and/or
Al--also referred to as a slurry depending on consistency--to the
areas to be coated, in which case the paste also contains
activators; [0014] b) solidification of the paste or slurry to form
a donor pack; [0015] c) covering of the regions, which are not to
be coated, with the diffusion-blocking powder pack; and [0016] d)
heating of the component and the powder packs to a temperature
above 900.degree. C., whereby alitation, siliconization and/or
chromation take place.
[0017] The paste or slurry that is required for the first step is
essentially composed of additive elements, specifically Cr, Si
and/or Al as their pure metals or as their alloys, of activators,
binders and additional ballast substances.
[0018] The additive elements may be pure metals or even alloys.
Frequently, it is advantageous to supply several additive elements
simultaneously in the form of alloys (co-diffusion). Preferably, Al
and Si are supplied simultaneously, with the quantity of Al far
outweighing the quantity of Si.
[0019] Activators that are suitable in accordance with the
invention include compounds which, under reaction conditions, may
form volatile, specifically molecular, halides with the additive
elements. Preferred activators are NH.sub.4F, NH.sub.4Cl or
AlF.sub.3. It is also possible that at least part of the fluorides
or chlorides are formed due to the decomposition of fluoridated or
chlorinated organic binders or ballast substances.
[0020] Considering activators, ammonium halides are of particular
interest, because the ammonia formed as a by-product occurs as
reducing agent for metals. The undesirable oxidation of metals is
thus suppressed.
[0021] Essentially, the usual organic binders used in the
preparation of pastes or slurries are used as the binders.
[0022] Following are examples of solids compositions of the
slurries or pastes in accordance with the invention. These
compositions are intended to simply explain the subject matter of
the invention in detail and are by no means to be understood as
being restrictive. The stated numerical values are to be understood
as being approximate.
[0023] Solids for Paste for Alitation: TABLE-US-00001 Powder of Al,
AlSi, AlTi, AlCo and/or AlCr: 5-50 wt. % Powder of Al.sub.2O.sub.3:
5-50 wt. % Organic binder: 1-15 wt. % Activator of NH.sub.4F and/or
NH.sub.4Cl: 0.5-2 wt. %
[0024] Solids for Pastes for Siliconization: TABLE-US-00002 Powder
of Si: 5-50 wt. % Powder of Al.sub.2O.sub.3: 5-50 wt. % Organic
binder: 1-15 wt. % Activator of NH.sub.4F and/or NH.sub.4Cl: 0.5-2
wt. %
[0025] Solids for Paste for Chromation: TABLE-US-00003 Powder of
Cr: 5-50 wt. % Powder of Al.sub.2O.sub.3: 5-50 wt. % Organic
binder: 1-15 wt. % Activator of NH.sub.4F and/or NH.sub.4Cl: 0.5-2
wt. %
[0026] Typically, the solids are mixed with water and/or alcohols
and worked to result in a paste or a slurry. In conjunction with
this, preferably a paste having the consistency of a plastically
moldable material is prepared.
[0027] The organic binders may also be liquid compounds, of
course.
[0028] During the continued process the paste or slurry is applied
to the coated regions and solidified. Typically, solidification is
achieved by drying in an oven or the like. As a result of this, a
firm donor pack adhering to the surface of the metal component is
formed.
[0029] Referring to an advantageous embodiment of the inventive
method, at least the surfaces of the metal component, which later
will be in contact with the powder pack or extend into the packed
bed reactor, are provided with a separating layer. The separating
layer is to facilitate the subsequent detachment of the powder
packs after the formation of the diffusion layer. The separating
layer is formed by a porous material which is largely inert to the
base metal and the additive elements. Preferably, the separating
layer is a thin layer of refractory oxides, specifically
Al.sub.2O.sub.3. Generally, the layer thickness is at approximately
0.02 mm to 3 mm.
[0030] The separating layer may be applied by conventional coating
processes in order to form thick layers. Considering a preferred
variant, a slurry is applied, for example, by spreading, immersion
or spray-depositing. The slurry essentially consists of
Al.sub.2O.sub.3 and binder.
[0031] During the subsequent method step (c), the component
provided with the packed bed is introduced at least partially in a
packed bed reactor.
BRIEF DESCRIPTION OF THE DRAWING
[0032] The inventive arrangement of the packed bed reactor will be
explained in detail with reference to FIG. 1, in which case the
illustration represents only one of any number of potentially
inventive variants.
DETAILED DESCRIPTION OF THE DRAWING
[0033] FIG. 1 shows the alitation of damper pockets of a turbine
rotor in a packed bed reactor (1) with the turbine rotor end (2),
whereby its blade footing (3) extends into the packed bed reactor
and is coated with a separating layer (4) of Al.sub.2O.sub.3, and
further shows the donor pack (5) arranged around the damper
pockets, and the diffusion-blocking powder pack (6).
[0034] Preferably, the reactor (1) is a simple device for holding
the component and for accommodating the powder fill or the
diffusion-blocking powder pack. For example, the reactor may be
designed as a metal capsule, into which extends the coated region
of the component. Thereafter, the component (3) having coated and
adjacent uncoated regions, as well as the donor pack (5), are
covered with the diffusion-blocking powder pack (6).
[0035] The diffusion-blocking powder pack has the inventive effect
of retaining or bonding the volatile compounds of the additive
elements, so that a coating of the surfaces of the metal component
not directly in contact with the donor pack is suppressed or
completely avoided. The material responsible for the
diffusion-blocking effect of this powder pack is metals which are
capable of chemically bonding the additive elements. Typically, Ni,
Co and/or Fe alloys are used in conjunction with this. Preferably,
the diffusion-blocking powder pack contains metal powders having a
similar or the same composition as the metal component to be
coated. As a result of this, the contamination of the metal
component with elements of the diffusion-blocking powder pack is
avoided. Ni or Ni alloys are particularly preferred.
[0036] In accordance with the invention, additional components of
the diffusion-blocking powder pack are activators. In so doing, the
same or even different activators than those used in the donor pack
may be selected. Due to the presence of the activators in the outer
powder pack, the activator loss occurring during the diffusion
reaction is advantageously reduced in the region of the donor
pack.
[0037] A preferred composition of the diffusion-blocking powder
pack consists of a minimum of 50% of metal powder and of an
activator content within the range of 0.2 and 5 wt. %. Additional
components may be inert substances, such as, for example
Al.sub.2O.sub.3.
[0038] Finally, the actual diffusion coating takes place in the
packed bed reactor. To do so, the reactor is heated to a
temperature above 900.degree. C. Preferably, the reactor is run
with inert or protective gas, whereby Ar and/or H.sub.2 are
particularly preferred. As a result of the reducing conditions
under H.sub.2, specifically the oxide formation is prevented, or at
least partially reversed.
[0039] In this method step, preferably an alitation, siliconization
and/or chromation is performed.
[0040] The selection of process temperatures and process times are
a function of the selected components, the donor packs and the
desired layer consistency. Considering Cr base alloys, Ni base
alloys or Co base alloys, the process temperatures used for
alitation are typically in the range of 750.degree. C. to
1200.degree. C. with holding times of 1 h to 20 hrs; for
chromation, this is typically between 900.degree. C. and
1200.degree. C. with the same holding time.
[0041] Optionally, the metal components may already have metal
coatings. As a result of this, optionally, a minimal adaptation to
the process parameters--compared with those of uncoated
components--may be necessary. However, the essential features of
the inventive method basically remain unchanged.
[0042] The chemical components required for the surface treatment
are formed inside the reactor, i.e., in situ. In so doing, the
formation or decomposition of gaseous metal halides plays a
substantial part in transporting the metals determined for
diffusion from the packed bed to the surface of the metal
component.
[0043] The metal halides are formed in situ by halide-containing
activators. The metal halides which reach the areas of the
diffusion-blocking powder pack are bound by metal powder and
prevented from diffusing into the uncoated regions.
EXAMPLE
[0044] Following is a description of an example of the alitation of
a rotor blade for gas turbines that is locally restricted to the
region of the damper pockets:
[0045] In order to prepare an alitation paste, 10 g of
Al.sub.2O.sub.3 powder (wettable powder), 10 g of Al powder and 0.2
g of NH.sub.4F were mixed, and then a paste was formed by admixing
a binder-containing alcoholic water solution.
[0046] As a result, the paste had a kneadable consistency. The
paste was pressed on the damper pockets and dried at approximately
50.degree. C. in a forced air oven. Referring to FIG. 1, the thusly
conditioned rotor blade was fitted into a metal box, with only the
blade end projecting into the packed bed reactor formed in this
manner. The penetration site of the blade was sealed with some
paste. Thereafter, the reactor was filled with diffusion-blocking
cover powder (powder pack) to approximately double the height of
the damper pockets. This powder pack was composed of Ni base
material powder and 1 wt. % of NH.sub.4F.
[0047] Alitation took place at a starting temperature of
1080.degree. C. and at a holding step at 1050.degree. C. and a
duration of 4 hrs. The protective gases used for rinsing were Ar
and H.sub.2.
* * * * *