Note: Descriptions are shown in the official language in which they were submitted.
CA 022476~4 l998-09-l8
TITLE OF THE INVENTION
HIGH-STRENGTH, HIGH-DAMPING METAL MATERIAL
AND METHOD OF MAKING THE SAME
FIELD OF THE INVENTION
The invention relates to a material, and particularly a metal
based composite material, having a high damping capacity and a
high tensile strength, comprising an essentially metallic base
material or matrix and a second phase in the matrix. The inven-
tion further relates to a method of making such a material.
15 BACKGROUND INFORMATION
In various fields of industry, the presently typical high accel-
erations of mechanically moving parts cause undesirable vibra-
tions in those parts over a wide frequency spectrum. The high
vibration loading in the vibrating systems leads to long dead or
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idle times, for example due to long run-up transient processes,
and also limits the operating lifetime of the vibrationally
loaded parts. Another significant problem is the noise generated
by the vibrations.
5 In order to overcome or avoid these problems of vibrations, it
is generally known to use materials having a high damping capac-
ity to damp out the vibrations as much and as quickly as possi-
ble. However, present structural materials do not possess a
sufficient damping capacity in and of themselves, and present
10 damping materials do not possess a sufficient strength to perform
as structural materials themselves.
Metals and metal alloys are predominantly used as structural
materials in a broad field of applications, due to their high
strength, low weight or density, and good corrosion resistance.
15 However, such metals and metal alloys typically have a rather low
damping capacity, so that it becomes necessary to use additional
damping materials purely for the purpose of achieving the desired
damping in structures comprising metal and metal alloy structural
parts. Such damping materials are generally synthetic polymers
20 or plastics, but such materials suffer limitations in their
applicability, for example in applications at temperatures above
the respective melting points of the materials or in situations
of limited space. Gray cast iron and pure magnesium are charac-
terized by a higher damping capacity, but on the other hand these
25 materials possess a rather limited strength.
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U. S. Patent 4,946,647 (Rohatgi et al.) discloses metallic com-
posite materials of an aluminum matrix with graphite particles
dispersed therein as a second phase, as well as a method for
making the same. While the known composite materials are said
5 to have an improved damping capacity relative to aluminum or
aluminum alloys per se, the disclosed composites have a signifi-
cantly reduced strength compared to aluminum or aluminum alloys
per se. Particularly, the disclosed materials have a tensile
strength of at most 190 MPa, which is far below that of the
10 ma-trix, and an elongation of at most 4~, even when pure aluminum
is used as the matrix material. These mechanical properties
demonstrate that the disclosed composite materials achieve the
desired damping characteristics only at the expense of a drastic
reduction in strength, and the materials are thus not suitable
15 for use as structural materials. The reference even admits this
deficiency in the strength, and suggests that the graphite con-
tent must be controlled or limited to achieve the required
strength values. Of course, such limitations on the graphite
content will in turn reduce the desired damping characteristics.
U. S. Patent 4,236,925 (Onuki et al.) discloses a method of
producing a sintered material having an increased damping capac-
ity and comprising a second phase of graphite, lead or magnesium.
The disclosed method includes steps of mixing the second phase
material in powder form with the remainder of a powdery iron,
copper, or aluminum metal, compression-molding the mixture,
sealing or canning the compression-molded mixture in a deformable
vessel, subjecting the vessel and the mixture therein to a plas-
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tic deformation treatment, and then sintering the plastically
deformed vessel and mixture therein. The heating temperature in
the sintering step must be above the recrystallization tempera-
ture of the matrix metal, so that the matrix metal becomes re-
5 crystallized, and the second phase material is aggregated in theform of spindles on the crystal surface or in the crystals of the
matrix metal. These steps are complicated and costly, and the
method necessarily limits the second phase material to have a
spindle shape.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention
to provide a material that comprises an essentially metallic base
material or matrix and a second phase in the matrix, which has
both an increased damping capacity already at low vibration
5 amplitudes, as well as a sufficiently high tensile strength and
elongation so that it may be used as a structural material. A
further object of the invention is to provide a method for pro-
ducing a material having a high damping capacity and a high
strength, without requiring additional complicated method steps
20 such as high temperature sintering or the like, and without
limitation of the form of the second phase material. The inven-
tion further aims to avoid or overcome the additional disadvan-
tages of the prior art, and to achieve additional advantages, as
apparent from the present description.
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The above objects have been achieved in a metallic material
according to the invention, having a high damping capacity and
a high tensile strength, comprising a metallic base material or
matrix and a second phase in the matrix, wherein the second phase
s is metallic and at least partially comprises a martensitic grain
structure. It has been discovered that the inventive combination
of a metallic second phase at least partially comprising a mar-
tensitic grain structure in a metallic matrix achieves high
damping characteristics, even at low vibration amplitudes. A
10 further advantage is that the partially martensitic second phase
does not negatively influence the mechanical properties of the
matrix, so that the overall material maintains its strength
characteristics and therefore can be used as a structural mate-
rial in the same manner and the same applications as the matrix
15 material could be used by itself.
It is further significant that the inventive material does not
place any particular limitations on the selection of the outer
shape, form or configuration of the second phase. Namely, the
second phase can be in the form of granular or globular parti-
20 cles, fibers, strands, whiskers, wires, or the like. By appro-
priately selecting the form of the second phase, it is possible
in a simple manner to adapt the respective characteristics of the
overall material to the requirements at hand in any particular
application. It should be noted that the second phase is prefer-
25 ably dispersed throughout the matrix in an unmixed and un-alloyed
condition relative to the matrix, such that distinct particles
of the second phase remain embedded in the matrix, thus providing
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an overall composite structure for the inventive material. In
other words, the overall material according to the invention is
especially not a homogenous alloy, but rather a composite of un-
mixed materials.
5 Preferably, the second phase itself is an alloy. An advantageous
material damping capacity can be achieved if an alloy of nickel
and titanium is used as the second phase, and particularly when
each of these alloying components is present and intermixed in
the range of 48 to 52 atom %. The most preferred alloy composi-
10 tion of nickel and titanium for the second phase is 49.9 atomic% nickel, and 50.1 atomic % titanium. These components and
compositions of the alloy are only preferred values, and are not
necessary limitations on the broadest scope of the invention.
The material damping capacity can be even further increased if
15 the second phase includes additives in a positive amount up to
25 atomic %, for stabilizing the martensitic phase and for adapt-
ing the material properties to the operating requirements in a
particular application. Both the number of additives as well as
the compositional content limits thereof are not absolute limita-
20 tions on the broadest scope of the invention, but representpreferred values. The additives may advantageously be selected
from among zirconium, hafnium, copper, niobium, manganese, palla-
dium, platinum and iron. Stabilization of the martensitic phase
can be further reinforced by a pretreatment of the ~econd phase
Z5 material, for example by plastically deforming the second phase
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or carrying out a homogenizing treatment of the alloy components
of the second phase.
As mentioned above, the second phase can be in the form of granu-
lar or globular particles, grains, short fibers, long fibers,
s whiskers, spheroids, or the like. Throughout this disclosure,
the general term "particles~ will be used to cover all different
configurations or forms of the particles, grains, fibers, etc.,
unless the particle shape is particularly specified. The second
phase particles can be uniformly dispersed throughout the matrix,
10 or may be present or concentrated in one or more layers extending
through the matrix material. Particles having an anisotropic
shape, such as fibers or whiskers, may be randomly oriented or
oriented in a uniform direction. By properly selecting the
particle form, dispersion pattern through the matrix, and parti-
15 cle orientation, the overall properties of the resulting compos-
ite material can be m~;m~lly adapted to the externally specified
requirements.
This can further be achieved in that the proportional content of
the second phase in the total material is varied or selected,
20 preferably in the range from 5 to 60 vol. %, depending on the
desired overall properties of the material. A higher proportion
of the second phase will generally achieve a higher damping
capacity. Therefore, in applications where damping is particu-
larly important, the invention provides for greater than 30 vol.
25 % and particularly greater than 35 vol. % of the second phase.
Once again, these ranges are preferred proportional ranges pro-
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.
viding improved characteristics, but are not strict limitations
on the broadest scope of the invention.
In order to improve the bonding of the second phase with the
matrix material, and thereby to better ensure the necessary load
5 transfer from the matrix material to the second phase for achiev-
ing the desired damping, it is advantageous if an outer boundary
layer of each particle of the second phase material forms a
compound or a mixed phase with the matrix material. Such a
structure can be achieved by carrying out the method according
10 to the invention as discussed below.
By providing a metallic second phase that has an at least par-
tially martensitic grain structure within the matrix material,
it is possible to achieve the required damping characteristics
of the overall composite material by the function or action of
15 the second phase by itself, while the tensile strength and elon-
gation of the overall material are predominantly provided or
determined by the matrix. Namely, the overall composite material
preferably has a minimum tensile strength and minimum elongation
of 10%, or preferably only 5%, below the corresponding values of
20 the matrix material by itself. More preferably, the tensile
strength and elongation of the overall composite are equal to or
even better than those of the matrix material by itself. For
this reason, the matrix material can be selected accordingly to
achieve all requirements as a structural material in different
25 applications, while the second phase can be selected to achieve
the desired damping characteristics. The overall composite
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material preferably has a minimum tensile strength of at least
, more preferably at least , and even more preferably
at least ; an elongation of at least , more preferably
at least , and even more preferably at least ; and
5 a damping capacity of at least ; more preferably at least
, and even more preferably at least
In view of the mechanical properties, the base material is advan-
tageously a light metal or a light metal alloy, such as
10for example. In this context, it is particularly
preferred to use the aluminum alloy designated as EN AW-6061
according to the German Industrial Standard DIN EN 573, which has
the following composition: 0.40 to 0.8 wt.% of silicon, up to
0.7 wt.% of iron, 0.15 to 0.40 wt.% of copper, up to 0.15 wt.%
15of manganese, 0.8 to 1.2 wt.% of magnesium, 0.04 to 0.35 wt.% of
chromium, up to 0.25 wt.% of zinc, up to 0.15 wt.% of titanium,
up to 0.15 wt.% total of other additives, and the remainder of
aluminum. However, applications that require an even higher
strength may exist or arise, in which case it is possible to use
20 a matrix material that has different or various grain structures
or that is a composite material in itself including a matrix and
a third phase dispersed in the matrix for reinforcement. A
thermomechanical treatment properly adapted for the particular
matrix material can similarly lead to an advantageous increase
25 of the strength of the matrix material.
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The above objects have further been achieved by a method of
making a material having high damping capacity and high strength,
according to the invention, comprising steps of mixing a powdery
matrix material and a powdery second phase material, and then
s heat treating the mixture in a temperature range from 400 to
700~C and consolidating the same at a pressure of 100 to 300 MPa.
In this context, the holding time can be between one hour and six
hours. However, carrying out the consolidation at 540~C and 200
MPa ~or a two hour holding time has been shown to achieve the
10 best results.
With regard to the selection of the characteristics of the start-
ing or initial states of the matrix material and of the second
phase, the best results have been obtained when the matrix mate-
rial is in the form of a particulate or powder material that has
15 been rapidly solidified by atomizing it into an inert gas envi-
ronment. Insofar as the selected outer configuration of the
second phase particles allows it, the second phase material is
also provided in the form of particles that have been processed
in this manner. An advantageous additional method step involves
20 de-gassing the mixture of matrix material and second phase mate-
rial before carrying out the consolidation. The consolidation
itself can be carried out by means of hot isostatic pressing,
sintering, extrusion pressing, or forging.
As a further variation of the method according to the invention,
25 the matrix material may first be melted, and the second phase
material may then be mixed into the molten matrix material. In
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this case, it is advantageous to protect the second phase parti-
cles in order to prevent an excessive reaction between the two
materials when the second phase particles are mixed into the
molten matrix material. This can be achieved by providing a
5 coating on the outside surface of the respective second phase
particles before introducing the particles into the molten matrix
material.
In both variants of the inventive manufacturing method, i.e.
either using a powdery matrix material or using a molten matrix
10 material as a starting point, the second phase particles can be
provided in various external configurations. Advantageously, the
second phase is provided in the form of globular or granular
particles, wires, short fibers, or one or more layers. In a
further preferred step, the second phase is pre-treated in order
15 to stabilize the martensitic phase before carrying out the con-
solidation. This martensite stabilizing treatment can involve
deforming the second phase material, or homogenizing the compo-
nents of the second phase therein.
The methods for manufacturing the material according to the
20 invention do not necessarily include any critical method steps
in which the second phase material must be brought into a partic-
ular external form or configuration. Moreover, the present
methods do not require an additional step of heating the material
to a temperature above the recrystallization point of the matrix
25 material in order to achieve a high damping capacity.
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DETAILED DESCRIPTION OF A PREFERRED EXAMPLE EMBODIMENT OF THE
INVENTION
An example embodiment of the method for producing a material
according to the invention was carried out as follows. An alumi-
s num alloy material designated as EN AW-6061 according to the
German Industrial Standard DIN EN 573 was atomized into an argon
environment to form a corresponding aluminum alloy powder having
a particle size smaller than 45 ~m. A nickel-titanium powder
having a particle size smaller than 180 ~m and a composition of
49.9 atomic % nickel and 50.1 atomic % titanium was formed in a
similar manner, i.e. by atomization into an argon atmosphere.
The two powders were mixed together to provide a mixture contain-
ing 10 vol. % of Ni-Ti powder and 90 vol. % of Al alloy powder.
The powder mixture was filled into capsules, whereby the mixture
15 was degassed at room temperature and then the capsules were
sealed in a gas-tight manner to avoid the formation of gas-filled
pores. The consolidation of the material was then carried out
by hot isostatic pressing for two hours at a pressure 200 MPa and
a temperature of 540~C.
20 The resulting composite material produced in the above manner was
examined, to find that the Ni-Ti particles were homogeneously
dispersed and distributed throughout the Al alloy matrix. The
tensile strength of the composite material corresponds to that
of the Al alloy EN AW-6061 itself, manufactured by hot isostatic
25 pressing. Furthermore, the resulting composite material com-
prises an elongation of greater than 10%. With these properties,
it is apparent that the composite material is suitable for use
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as a structural material in all the same applications as the
matrix alloy would have been useful by itself.
Another recommended alloy composition of the second phase parti-
cles is 60 atomic % copper, 21 atomic % zinc, and 19 atomic %
5 aluminum, having a martensitic grain structure. This second
phase alloy can be substituted for the Ni-Ti alloy described
above, according to the same method for forming an advantageous
composite material. It is expected that substantially any metal-
lic second phase material having a martensitic grain structure
10 and being compatible with the respective selected matrix material
would be suitable and would achieve the desired improvement in
the damping capacity.
Although the invention has been described with reference to
specific example embodiments, it will be appreciated that it is
15 intended to cover all modifications and equivalents within the
scope of the appended claims. It should also be understood that
the present disclosure includes all possible combinations of any
individual features recited in any of the appended claims.
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