U.S. patent application number 10/933340 was filed with the patent office on 2005-05-05 for copper-niobium alloy and method for the production thereof.
This patent application is currently assigned to LEIBNIZ-INSTITUT FUR FESTKORPER-UND. Invention is credited to Botcharova, Ekaterina, Heilmaier, Martin, Schultz, Ludwig.
Application Number | 20050092400 10/933340 |
Document ID | / |
Family ID | 34553240 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092400 |
Kind Code |
A1 |
Botcharova, Ekaterina ; et
al. |
May 5, 2005 |
Copper-niobium alloy and method for the production thereof
Abstract
The invention relates to the field of materials engineering and
relates to copper-niobium alloys which can be used for producing
powder metallurgical products by known shaping methods, e.g., after
having been processed into semi-finished products or shaped bodies,
and a method for the production thereof. The object of the
invention is to disclose copper-niobium alloys and a method for the
production thereof in which a homogenous metastable Cu mixed
crystal is present and a method for its implementation. The object
is attained through a copper-niobium alloy in which, in addition to
a copper-niobium mixed crystal, niobium deposits with particle
diameters of 5-100 nm are also present in a copper matrix. The
object is further attained through a method for producing
copper-niobium alloys in which copper powder as matrix material and
0.1 to 50 at. % niobium powder are jointly ground and mechanically
alloyed and then subjected to at least one thermal treatment.
Inventors: |
Botcharova, Ekaterina;
(Dresden, DE) ; Heilmaier, Martin; (Magdeburg,
DE) ; Schultz, Ludwig; (Dresden, DE) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
LEIBNIZ-INSTITUT FUR
FESTKORPER-UND
Dresden
DE
|
Family ID: |
34553240 |
Appl. No.: |
10/933340 |
Filed: |
September 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10933340 |
Sep 3, 2004 |
|
|
|
PCT/DE03/00764 |
Mar 3, 2003 |
|
|
|
Current U.S.
Class: |
148/432 ;
419/66 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 2998/10 20130101; C22C 1/0425 20130101; C22C 9/00 20130101;
B22F 3/14 20130101; B22F 1/0085 20130101; B22F 1/0003 20130101;
B22F 9/04 20130101; B22F 2998/10 20130101; B22F 2009/041
20130101 |
Class at
Publication: |
148/432 ;
419/066 |
International
Class: |
C22C 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2002 |
DE |
102 10 423.9 |
Claims
1. Copper-niobium alloy comprising in a copper matrix, in addition
to a copper-niobium mixed crystal, niobium deposits with particle
diameters of 5-100 nm.
2. Copper-niobium alloy according to claim 1, wherein the niobium
is present partially dissolved in the copper lattice.
3. Copper-niobium alloy according to claim 1, wherein the niobium
deposits are present in a form of fine particles or fibers.
4. Copper-niobium alloy according to claim 3, wherein the niobium
deposits are present in a form of fibers, and the fibers have an
aspect ratio of greater than 4:1.
5. Copper-niobium alloy according to claim 1, with a conductivity
of 50 to 80% IACS.
6. Copper-niobium alloy according to claim 1, with a strength of
1200 to 2000 MPa.
7. Method for producing a copper-niobium alloy according to claim
1, wherein copper powder as matrix material and 0.1 to 50 at. %
niobium powder are jointly ground and mechanically alloyed and
subsequently subjected to at least one thermal treatment.
8. Method according to claim 7, wherein 0.5 to 20 at. % niobium
powder is added.
9. Method according to claim 7, wherein the grinding is carried out
at temperatures of -196.degree. C. to -10 C.
10. Method according to claim 7, wherein the grinding is performed
in a grinding vessel, and cooling of the grinding vessel is carried
out at least one of during grinding and between grinding
stages.
11. Method according to claim 7, wherein the grinding is performed
in a grinding vessel, and the grinding vessel is cooled with liquid
nitrogen or with ethanol.
12. Method according to claim 7, wherein a complete forcible
solution of the niobium in the copper lattice is carried out during
grinding.
13. Method according to claim 7, wherein the at least one thermal
treatment is carried out at temperatures .gtoreq.500.degree. C.
14. Method according to claim 7, wherein the at least one thermal
treatment includes a thermal treatment carried out at a same time
as a shaping process.
15. Method according to claim 14, wherein the shaping process
includes forming a fiber-shaped structure of the copper-niobium
alloy.
16. Method according to claim 15, wherein a fiber aspect ratio of
greater than 4:1, is established during shaping.
17. Method according to claim 7, wherein grinding is performed for
between 20 and 30 hours.
18. Copper-niobium alloy according to claim 4, wherein the fibers
have an aspect ratio of greater than 10:1.
19. Method according to claim 16, wherein a fiber aspect ratio of
greater than 10:1 is established during shaping.
20. Copper-niobium alloy according to claim 1, comprising a
homogeneous single-phase alloy of copper and niobium.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of International
Application No. PCT/DE03/00764, filed Mar. 3, 2003, and claims
priority under 35 U.S.C. .sctn. 119 of German Patent Application
No. 102 10 423.9 filed on Mar. 4, 2002. Moreover, the disclosure of
the International Patent Application No. PCT/DE03/00764 is
expressly incorporated by reference.
FIELD OF ART
[0002] The invention relates to the field of materials engineering
and relates to copper-niobium alloys which can be used for
producing powder metallurgical products by known shaping methods,
e.g., after having been processed into semi-finished products or
shaped bodies, and a method for the production thereof.
PRIOR ART
[0003] In order to produce a metallic material with the highest
possible mechanical strength and electrical and thermal
conductivity, in addition to silver, which has the highest
electrical conductivity of all metals, copper is mainly used as a
matrix metal because of its much lower cost. In order to increase
the strength of the ductile copper matrix effectively, without its
thermal and electrical properties being substantially impaired, a
strengthening through largely insoluble secondary phases in
thermodynamic equilibrium suggests itself. In the case of cubic
face-centered copper matrix these can be hard ceramic particles
(e.g., oxides, nitrides, carbides), but also a number of
high-melting cubic space-centered refractory metals (e.g., Cr, W,
Ta, Nb, Mo). Due to their insolubility in the matrix, the
above-mentioned alloy additives thereby all meet the requirement
for the best possible microstructural stability at high stress
temperatures. However, due to the difference in density and melting
point present, a homogenous distribution of the respective
secondary phase and the particle size distribution in the nanometer
range necessary for an efficient increase in strength cannot be
achieved through metallurgical fusion methods. The use of the
mechanical alloying method overcomes these problems and renders
possible, e.g., the production of Ag-oxide composite materials with
the finest oxide distribution (diameter <50 nm) and the greatest
hardness and strength (B. J. Joshi et al., Proceedings Vol. 3,
Powder Metallurgy World Congress, Granada/Spain, 1998; JP 07173555
A; DE 199 53 780 C1).
[0004] With mechanical alloying the grinding progress results from
repeated fracturing and cold-welding of the powder particles.
However, in the case of hard ceramic particles in a soft metallic
matrix of copper, when the oxide content is reduced below 10% by
volume, the tendency increases that the oxides are only encased by
the soft matrix, which means their further fracturing is prevented
(DE 44 18 600 C2). The grinding progress is advantageously
influenced by a "soft/soft" material combination, i.e., by the
selection of a secondary phase best matched to the elastic
properties of the copper (C. C. Koch, Nanostructured Materials 2,
1993, 109-129). Of the suitable alloy elements listed above,
niobium is the most suitable (L. G. Fritzemeier, Nanostructured
Materials 1, 1992, 257-262). The mechanical alloying of
concentrated Cu--Nb alloys at room temperature has already been
reported (A. Benthalem et al., Scripta Metallurgica et Materialia
27, 1992, 739-744 and Materials Science and Engineering A161, 1993,
255-266). Through the grinding at high energy, the mixed crystal
range is expanded and a high homogeneity of the microstructure is
achieved. It was likewise shown that part of the added niobium is
forcibly dissolved in the copper lattice by the grinding.
[0005] However, due to the increase in temperature during grinding,
with such alloy systems in general there is a danger of the powders
adhering to the wall of the vessel and to the balls, which leads to
a low powder yield. Although organic auxiliary agents can reduce
the weld tendency, they are fractured by the energy input into
CO.sub.2 and H.sub.2 and ground into the powders (U.S. Pat. No.
5,322,666). If this gas is not removed by degassing annealing at
high temperatures, a consolidation of the powders into dense
compact semi-finished products is not possible or leads to shape
instability ("swelling") during later use at high temperatures. On
the other hand, the nanocrystalline grain structure intentionally
established in the powder is destroyed through an upstream
degassing annealing.
DISCLOSURE OF THE INVENTION
[0006] The object of the invention is to disclose copper-niobium
alloys and a method for the production thereof in which a
homogenous metastable Cu mixed crystal is present and a method for
the implementation thereof.
[0007] The object is attained through the invention disclosed in
the claims. Further developments are the subject of the subordinate
claims.
[0008] With the copper-niobium alloy according to the invention, in
addition to a copper-niobium mixed crystal, niobium deposits with
particle diameters of 5-100 nm are present in a copper matrix.
[0009] The niobium is thereby advantageously present partially
dissolved in the copper lattice.
[0010] The niobium deposits are likewise advantageously present in
the form of fine particles or fibers.
[0011] It is also advantageous if the fibers are present with an
aspect ratio of greater than 4:1, advantageously greater than
10:1.
[0012] Furthermore, the copper-niobium alloy according to the
invention advantageously features a conductivity of 50 to 80% IACS
and/or strengths of 1200 to 2000 MPa.
[0013] With the method according to the invention for producing
copper-niobium alloys, copper powder as matrix material and 0.1 to
50 at. % niobium powder are jointly ground and mechanically alloyed
and then subjected to at least one thermal treatment.
[0014] Advantageously 0.5 to 20 at. % niobium powder is added.
[0015] The grinding process is also advantageously carried out at
temperatures of -196.degree. C. to -10.degree. C.
[0016] It is also advantageous if the cooling of the grinding
vessel is carried out during grinding and/or between the grinding
stages.
[0017] Furthermore it is advantageous if the grinding vessel is
cooled with liquid nitrogen or with ethanol.
[0018] It is furthermore advantageous if a complete forcible
solution of the niobium in the copper lattice is carried out during
grinding.
[0019] It is likewise advantageous if the thermal treatment is
carried out at temperatures >500.degree. C.
[0020] Advantageously the thermal treatment is also carried out at
the same time as a shaping process.
[0021] Likewise advantageously through the shaping process a
fiber-shaped structure of the copper-niobium alloy is produced in
which again advantageously a fiber aspect ratio of greater than
4:1, advantageously greater than 10:1 is established during
shaping.
[0022] It is also advantageous that a high powder yield of the
copper-niobium alloy is produced.
[0023] It is also advantageous if grinding is carried out for
between 20 and 30 hours.
[0024] In the method according to the invention at the start an
intentional embrittlement of the copper powder is created. In
contrast to the materials produced in a known manner by means of
mechanical alloying, it is thus possible to obtain a homogenous
single-phase alloy of copper with niobium. Since the grinding
process is advantageously carried out at low temperatures, it is
possible to achieve a partial or complete forcible solution of the
niobium atoms in the copper mixed crystal with a relatively low
energy input. The degree of solution of the niobium atoms in the
copper mixed crystal depends, i.a., on the duration of grinding and
the oxygen content of the powders used.
[0025] The gas content virtually does not change at all thereby
during the grinding process so that an additional degassing step
can be omitted during further processing.
[0026] After the niobium atoms have been dissolved in the copper
mixed crystal, fine niobium particles are deposited during the
subsequent thermal treatment. These niobium deposits substantially
contribute to increasing the strength and ensuring a high
conductivity of the alloy.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] The invention is described below in more detail on the basis
of an exemplary embodiment.
[0028] A grinding cup charged with steel balls, copper powder and
10 at. % niobium powder is cooled in liquid nitrogen to a
temperature on the lid of the grinding cup of -196.degree. C.
Subsequently the cooled grinding cup is covered with polystyrene to
insulate it from the ambient air. The subsequent grinding process
is regularly interrupted every 30 min. in order to cool the
grinding cup again to -196.degree. C. The grinding process takes
place at a rotational speed of 200 rpm and with a powder/ball ratio
of 1:14. In 35 h the added niobium powder has been completely
forcibly dissolved in the copper lattice. This can be seen from
x-ray and transmission electron microscope (TEM) tests in which
niobium reflections no longer occur (FIGS. 1 and 2). The
mechanically alloyed powder features a nanocrystalline structure
with crystallite sizes of 7 nm. The powder microhardness thereby
reaches 500 HV 0.025.
[0029] The powder obtained is compacted at 500.degree. C. in a hot
press under vacuum and a pressure of 650 MPa to a relative density
of 98-99% to form cylindrical shaped bodies with a diameter of 10
mm.
[0030] Shaped bodies produced in this way have a hardness of 400 HV
2 with an electrical conductivity of 20 MS/m (corresponding to 35%
IACS).
[0031] A subsequent thermal treatment during which the niobium is
deposited from the copper matrix leads to an increase in electrical
conductivity up to 45-50 MS/m (corresponding to 70-80% IACS) with a
slight reduction in hardness to 380 HV 2. Through the formation of
a fiber structure a final cold shaping increases the hardness to
550 HV 2 again with continued high electrical conductivity.
[0032] With a reduction of the Nb content in the starting powder
mixture to 5 at. %, mechanically alloyed powder can be produced
with a crystallite size of 11 nm and a powder microhardness which
reaches 450 HV 0.025. At 30 MS/m (50% IACS) the electrical
conductivity of the shaped bodies is then somewhat higher and at
350 HV 2 the hardness somewhat lower than with the shaped bodies
with 10 at. % Nb. By carrying out a thermal treatment a higher
electrical conductivity of approx. 50 MS/m (80% IACS) is achieved,
but also a lower hardness of approx. 300 HV 2, which can be
increased to 500 HV 2 again through the final shaping.
[0033] Reference Numbers:
[0034] FIG. 1 a Diffraction image of the Cu/20 at. % Nb powder, 17
h grinding time
[0035] FIG. 1b: Diffraction image of the Cu/10 at. % Nb powder, 35
h grinding time
[0036] FIG. 2 X-ray analysis of the mechanically alloyed powders
according to the different grinding times.
* * * * *