U.S. patent application number 12/800859 was filed with the patent office on 2010-11-18 for device and method for remelting metallic surfaces.
This patent application is currently assigned to MTU Aero Engines GmbH. Invention is credited to Joerg Hoeschele, Dirk Kiesel, Juergen Steinwandel.
Application Number | 20100288399 12/800859 |
Document ID | / |
Family ID | 34684132 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100288399 |
Kind Code |
A1 |
Hoeschele; Joerg ; et
al. |
November 18, 2010 |
Device and method for remelting metallic surfaces
Abstract
A method for remelting metallic surfaces of components using the
effect of a stable high pressure plasma jet, includes melting the
surface in localized areas, the surface having a structure
refinement after solidification. The plasma jet action is generated
by the microwave impact on a carrier gas, the pressure of the high
pressure plasma jet being above the atmospheric pressure. In
addition, a plasma torch for generating a directed high pressure
plasma jet includes a gas supply, a device for generating a plasma,
and an outlet nozzle for a plasma jet. The device for generating
the plasma includes a magnetron and a resonator in which the
supplied pressurized carrier gas is transferred into a plasma under
the effect of microwaves, causing the plasma to exit through the
outlet nozzle at a pressure above 0.1 MPa.
Inventors: |
Hoeschele; Joerg;
(Meckenbeuren-Brochenzell, DE) ; Kiesel; Dirk;
(Immenstaad, DE) ; Steinwandel; Juergen;
(Uhldingen-Muehlhofen, DE) |
Correspondence
Address: |
Davidson, Davidson & Kappel, LLC
485 7th Avenue, 14th Floor
New York
NY
10018
US
|
Assignee: |
MTU Aero Engines GmbH
Muenchen
DE
|
Family ID: |
34684132 |
Appl. No.: |
12/800859 |
Filed: |
May 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11141157 |
May 31, 2005 |
|
|
|
12800859 |
|
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Current U.S.
Class: |
148/512 |
Current CPC
Class: |
C21D 1/09 20130101; H05H
1/30 20130101; C22F 1/02 20130101; C22F 3/00 20130101; C22F 1/04
20130101 |
Class at
Publication: |
148/512 |
International
Class: |
C21D 1/06 20060101
C21D001/06; C22F 1/00 20060101 C22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2004 |
DE |
DE 102004026636.0 |
Claims
1. A method for remelting a metallic surface subjected to
thermal-mechanical stress during use, the method comprising:
generating a plasma jet using microwave impact on a carrier gas so
as to generate a high pressure plasma jet having a pressure higher
than atmospheric pressure; applying the plasma jet to the metallic
surface in a localized area so as to remelt a surface layer; and
allowing the surface layer to solidify, thereby undergoing a
structure refinement, the solidified surface layer being
structurally refined in comparison with the surface layer before
the plasma jet was applied to the metallic surface.
2. The method as recited in claim 1, wherein the pressure of the
plasma jet is from 0.1 MPa to 0.8 MPa.
3. The method as recited in claim 1, wherein the carrier gas
includes at least one of the gases He, Ar, N.sub.2, H.sub.2,
O.sub.2, CO.sub.2, H.sub.2O, CH.sub.4 and C.sub.2H.sub.6.
4. The method as recited in claim 1, wherein the carrier gas is
formed by air.
5. The method as recited in claim 1, wherein the plasma jet has a
length greater than 5 cm.
6. The method as recited in claim 1, wherein the plasma jet is
expanded in a fan-shaped manner.
7. The method as recited in claim 1, further comprising supplying
substances to the plasma jet between a nozzle outlet aperture and
the metallic surface.
8. The method as recited in claim 7, wherein the substances are
solid substances formed by ceramic powders.
9. The method as recited in claim 7, wherein the substances are
liquid substances formed by metal-organic solutions or metal salt
solutions.
10. The method as recited in claim 7, wherein the substances
include at least one of solid and liquid substances and wherein the
substances form solid particles in the remelted surface layer, the
particles being consisting essentially of at least one of
Al.sub.2O.sub.3, AlN, MgO, SiC and Si.sub.3N.sub.4.
11. The method as recited in claim 1, wherein the plasma jet has a
power density from 6 kW/cm.sup.2 to 20 kW/cm.sup.2 and wherein the
applying includes moving the plasma jet over the surface at a speed
of from 2 mm/sec to 4 mm/sec.
12. The method as recited in claim 1, wherein the plasma jet has a
power density from 20 kW/cm.sup.2 to 60 kW/cm.sup.2 range and
wherein the applying includes moving the plasma jet over the
surface at a speed of from 3 mm/sec to 10 mm/sec.
13. The method as recited in claim 1, wherein the metallic surface
is formed by a light metal alloy.
14. The method as recited in claim 1 wherein the surface refinement
enhances a surface hardness, a surface strength or a surface
ductility of the surface layer in comparison with the surface
hardness, the surface strength or the surface ductility of the
surface layer before the plasma jet was applied to the metallic
surface.
Description
[0001] Priority is claimed to German Patent Application No. DE 10
2004 026 636.0, filed on Jun. 1, 2005, the entire disclosure of
which is incorporated by reference herein.
[0002] The present invention relates to a method for remelting
metallic surfaces using the effect of a high pressure plasma jet,
the surface being melted in localized areas and having a structure
refinement after solidification, the plasma jet action being
generated by the microwave impact on a carrier gas and the pressure
of the high pressure plasma jet being above the atmospheric
pressure.
BACKGROUND
[0003] For metallic materials, alloy remelting represents a known
method for enhancing the surface hardness, the surface strength, or
the surface ductility. The change in the material properties is
based on structure transformation which is caused by melting and
quenching processes. The quick solidification of the melted surface
layer is accompanied by structure transformation, a grain
refinement for example, or the formation of metastable phases. It
is frequently only necessary to treat the surface layer in
localized areas of the material and to leave the base material
outside these function surfaces unchanged.
[0004] It is known from CH 664 579 A5 to use a plasma welding
apparatus in a method for remelting metallic surfaces using a
plasma jet.
[0005] Different high-performance jet methods, such as laser
remelting, are known for treating the surface layer of a work
piece. The laser remelting method is associated with high
investment and operating costs.
[0006] Plasma jet methods are also known as additional methods. The
plasma jet methods are typically high-performance micro jet methods
having the disadvantage of low jet quality and low power density.
It is also disadvantageous that the choice of the type of plasma
gas is very limited. Gases or gas mixtures of Ar, H.sub.2, and
N.sub.2 are the only common choices. Due to the system inertia,
regulation of the gas supply and the power may only take place in a
delayed manner--the delay in plasma jet methods is several seconds
at best.
[0007] In the laser remelting method as well as in the plasma jet
method, a local area of the work piece surface, only a few .mu.m to
mm thick, is melted.
[0008] However, such alloy remelting methods do not conform to the
increasing demands placed on the mass production of components with
larger dimensions. In the automotive industry in particular, alloy
remelting methods, directed in particular to increasing the
strength and ductility of work pieces or components which are
subjected to thermal-mechanical stress (TMF thermal-mechanical
fatigue), are becoming increasingly important in order to replace
the expensive coating methods. This is true, for example, for valve
bars and/or valve seats of a light metal cylinder head.
[0009] A method for manufacturing a cylinder head for an internal
combustion engine using an Al casting alloy is known from DE
3605519 A1, for example, in which, by directing energy of high
power density such as a tungsten inert gas arc or laser energy, the
surface of the aluminum alloy is melted and quickly cooled down
again to solidify. Laser energy, plasma arcs, and electron beams
are cited as further energy sources.
[0010] The described methods have the disadvantage that the energy
sources used allow only low power densities, i.e., achieving high
power densities involves substantial complexity with regard to
equipment. This represents a disadvantage for the mass production
of components to be remelted since this is associated in particular
with long processing times and high processing costs. In addition,
the focusing and stabilizing of conventional plasma jets are
problematic at high plasma energy densities. Current plasma jet
methods are pure surface methods and are not suitable for the
remelting of deeper-lying areas of the surface.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a method
for remelting metallic surfaces of components having energy
densities on the metal surface in order to make shorter processing
times possible in particular. A further or alternate object of the
present invention is to provide a suitable plasma torch.
[0012] The present invention provides a method for remelting
metallic surfaces of components using the effect of a stable high
pressure plasma jet, the surface being melted in localized areas
and having a structure refinement after solidification, wherein the
plasma jet (9) is generated by the microwave impact on a carrier
gas, the pressure of the high pressure plasma jet being above the
atmospheric pressure. In addition, the present invention provides a
plasma torch for generating a directed high pressure plasma jet
including a gas supply, a device for generating a plasma, and an
outlet nozzle for a plasma jet, wherein the device for generating
the plasma includes a magnetron (13) and a resonator (5) in which
the supplied pressurized carrier gas is transferred into a plasma
under the effect of microwaves, causing the plasma to exit through
the outlet nozzle (3) at a pressure above 0.1 MPa.
[0013] The method according to the present invention provides that,
for remelting metallic surfaces, a stable high pressure plasma jet
is directed over the surface of the component, the surface being
melted in localized areas due to the impact of this stable high
pressure plasma jet and having a structure refinement after
solidification. The plasma jet action is generated by the microwave
impact on a carrier gas, the pressure of the high pressure plasma
jet being above the atmospheric pressure.
[0014] This method has the advantage that a high energy density,
i.e., power density of the jet, may be achieved on the component's
surface.
[0015] The high power density depends in particular on the high
pressure, i.e. the high density of the plasma gas. Due to the
density, the number of energy-transferring gas atoms or molecules
per volume unit is increased. According to the present invention,
the pressure of the plasma jet, at least at the outlet aperture, is
above 0.1 MPa, preferably in the 0.1 MPa to 0.8 MPa range,
particularly preferably in a 0.15 MPa to 0.4 MPa range. Too high a
pressure is difficult to achieve by the equipment. And also, too
high a pressure of the plasma jet results in an undesirable blowing
of the melted surface.
[0016] A further advantageous effect of the high pressure method is
the fact that the microwave source enters the carrier gas with a
high thermal degree of efficiency. The pressure in the microwave
device, generated by a microwave resonator in particular, is
preferably in the 0.1 MPa to 0.8 MPa range.
[0017] Another advantage of the present invention is the fact that
the selection of carrier gases, which form the plasma jet, is
hardly limited. When choosing, a distinction should be made between
inert gases and reactive gases in particular, which, depending on
the application, may also be used combined in a suitable manner.
The carrier gases preferred according to the present invention are
the gases Ar, He, N.sub.2, H.sub.2, O.sub.2, CO.sub.2, H.sub.2O,
CH.sub.4, and/or C.sub.2H.sub.6, which may be found in pure form or
in different gas mixtures with each other.
[0018] Air is used as the carrier gas in a preferred embodiment of
the present invention.
[0019] If only a pure remelting process is intended, then inert
gases, Ar in particular, are preferred carrier gases.
[0020] If reactive gases, such as O.sub.2, N.sub.2, or H.sub.2O,
are used, a partial reaction of the superficial light metal with
the reactive gas takes place. This causes light metal oxides in
particular, or nitrides, e.g., Al.sub.2O.sub.3 or AlN, to be
formed. These ceramic reaction products are incorporated into the
remelted surface layer, causing an advantageous dispersion
gain.
[0021] A further advantage of the method according to the present
invention is the fact that a comparatively stable plasma jet is
used which is able to be accurately directed onto the surface of
the component to be treated. Furthermore, it is possible to
geometrically modify the gas dynamics of the plasma jet, i.e., to
fan out, for example, or to focus it.
[0022] In a preferred variant, a filament-shaped plasma jet having
a length above 5 cm is used. In a particularly preferred variant,
the plasma jet has a diameter in the 0.5 cm to 5 cm range and a
length in the 10 cm to 40 cm range.
[0023] By varying the plasma jet diameter and the speed with which
the plasma jet is guided over the surface, different remelting
temperatures and/or different cooling temperatures of the melt may
be achieved for a given output of the plasma torch.
[0024] The method according to the present invention for remelting
metallic surfaces is advantageous in particular when components
made of light metal alloys are used. This includes the current
aluminum alloys.
[0025] The components which are able to be handled particularly
advantageously using the method according to the present invention
include cylinder heads in particular.
[0026] If the usual aluminum alloys are used, the energy, entered
via the plasma jet, is preferably set in such a way that a cooling
rate in the 20 K/sec to 110 K/sec range is achieved.
[0027] In cylinder heads made of aluminum alloy, the remelting is
preferably set in such a way that a structure in the T7 state is
formed. The remaining cylinder head typically has a T6
structure.
[0028] The remelted surface layer preferably has a thickness, i.e.
depth, in the range of a few 100 .mu.m to a few mm. A thickness is
preferably set which is in the 0.5 mm to 1.5 mm range. However, due
to the method according to the present invention using a high
pressure plasma jet, it is also possible to set considerably
thicker layers, in the range of several mm for example, without
great additional costs. This may be an advantage if, for example
after remelting, targeted areas of the surface should be remachined
to remove chips without the remelted material layer becoming
completely lost.
[0029] According to the present invention, the plasma jet has a
comparatively high power density in order to be able to implement
short processing times.
[0030] The surface is preferably treated using a plasma jet having
a power density in the 6 kW/cm.sup.2 to 20 kW/cm.sup.2 range, the
jet being moved over the surface at a speed of 2 mm/sec to 4
mm/sec.
[0031] In a further preferred variant, the plasma jet has a power
density in the 20 kW/cm.sup.2 to 60 kW/cm.sup.2 range and is moved
over the surface at a speed of 2 mm/sec to 10 mm/sec.
[0032] In a further advantageous embodiment of the present
invention, solid or liquid substances are supplied to the plasma
jet close to the nozzle outlet aperture. This may take place either
prior or subsequent to opening the nozzle. In terms of design, it
must be borne in mind that remixing of the supplied substances into
the gas chamber of the resonator is largely impossible.
[0033] In a first variant of this embodiment, the solid substances
are formed by ceramic powders. These particles preferably have a
nano structure and have particle sizes essentially below
approximately 1.mu., in particular below approximately 500 nm. The
ceramic particles are inserted into the melted surface layer via
the plasma jet and are dispersed in the melt layer, causing a
dispersion gain of the metal layer. An increase in particular in
vibrostability under thermo mechanical stress of the local surface
area is achieved via the nano-structured particles. The increase in
vibrostability is based on the dispersion gain of the local area of
the surface layer due to the finely distributed nano-structured
particles as well as on the dependency of the yield point from the
grain refinement (Hall-Petch relationship) which is brought about
by the remelting process.
[0034] The preferred ceramic particles include oxides such as
Al.sub.2O.sub.3, or nitrides such as AlN, Si.sub.3N.sub.4 and/or
carbides such as SiC.
[0035] The solid or liquid substances are preferably supplied to
the plasma jet via a ring nozzle. The use of a ring nozzle results
in a homogenization of the nano-structured particles in the plasma
jet as well as in the melted surface layer of the metallic work
piece.
[0036] The liquid substances may be supplied in an analogous
manner. The preferred liquid substances include solutions of metal
salts, e.g., metal hydroxides or metal carboxylic acid salts, or
solutions of metal-organic compounds, e.g., silanes, carbosilanes,
or metal chelate compounds. The liquid substances decompose under
the plasma jet's conditions into the corresponding metal oxides,
metal nitrides, or metal carbides. These act in an analogous manner
as the supplied ceramic particles. The particles supplied via the
decomposition of the liquid substances are generally distinctly
finer than those obtainable via the supply of the solid
substances.
[0037] Another aspect relates to the application of the remelting
method via high pressure plasma jet on components made of light
metal alloy. A preferred application is the remelting of surface
layers of cylinder heads, preferably in the valve bar and/or valve
seat area(s).
[0038] Another aspect of the present invention relates to a device
for generating a high pressure plasma jet, hereinafter referred to
as a plasma torch, using microwave energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The configuration of the method and the plasma torch
according to the present invention is subsequently explained in
greater detail with reference to the drawings, in which:
[0040] FIG. 1 shows a schematic representation of a plasma torch
including short-circuiting plunger (1), aperture (2), nozzle (3),
observation window (4), resonator (5), inspection glass (6), gas
feeder (7), glass holder (8), plasma jet (9), water load (10),
circulator (11), frequency tuner (12), and magnetron (13); and
[0041] FIG. 2 shows the remelting process including melted surface
layer (11), metallic surface of a component (21), supply device
(31), supplied particles (41), and plasma jet (9).
DETAILED DESCRIPTION
[0042] The carrier gas is supplied to the plasma torch via a gas
feeder (7) for generating a directed high pressure plasma jet. At
least during the feeding of microwave energy, the gas is
pressurized with an overpressure. A pressure above 0.1 MPa is
preferably set, particularly preferred in the 0.2 MPa to 0.8 MPa
range. The microwave energy is generated in a magnetron (13) and
acts on the carrier gas in resonator (5). Common frequencies are
around 0.95 GHz to 12 GHz. A frequency of 2.45 GHz is particularly
preferred. The output of the magnetron depends in particular on the
intended power density of the plasma jet. Typical values are in the
1 kW to 20 kW range.
[0043] The microwaves are conducted to resonator (5) via a hollow
conductor system and generate the plasma by resonant coupling.
[0044] The generated plasma exits under pressure to the outside via
nozzle (3) and aperture (2) and forms a stable plasma jet (9). For
the fan-shaped expansion of the jet, the nozzle may have an
expansion device in the direction of the jet.
[0045] The plasma jet is preferably further stabilized via a swirl
stabilization of the working gas. This makes very exact jet
geometries possible, e.g., filament-shaped high pressure plasma
jets.
[0046] A further embodiment of the plasma torch according to the
present invention provides devices which magnetohydrodynamically
stabilize the highly ionized plasma. Electromagnetic apertures in
the outlet area of the plasma jet are provided for this purpose,
for example.
[0047] In contrast to the known torches for remelting surfaces
which use laser energy or arcs, the torch according to the present
invention is characterized by a long service life and high
operating reliability due to its microwave energy source.
[0048] Another embodiment of the plasma torch according to the
present invention provides supply devices (31) with which liquid or
solid substances may be fed into the plasma jet (9). The supply of
solid particles (41) to plasma jet (9) close to the plasma cone on
the surface (21) to be remelted is schematically shown in FIG.
2.
[0049] A ring nozzle around plasma jet (9) is provided in a further
advantageous embodiment of the supply device. Plasma jet (9) and
the particle or liquid jet preferably run concentrically to one
another.
* * * * *