U.S. patent application number 13/349047 was filed with the patent office on 2012-09-27 for non-magnetic noble alloy containing ruthenium, cobalt and chromium.
This patent application is currently assigned to The Argen Corporation. Invention is credited to Paul J. Cascone, Arun Prasad.
Application Number | 20120244035 13/349047 |
Document ID | / |
Family ID | 46877508 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120244035 |
Kind Code |
A1 |
Cascone; Paul J. ; et
al. |
September 27, 2012 |
NON-MAGNETIC NOBLE ALLOY CONTAINING RUTHENIUM, COBALT AND
CHROMIUM
Abstract
A noble alloy suitable for dental purposes that contains cobalt
and chromium in addition to ruthenium and optionally gold and/or
platinum group elements, and is non-magnetic is provided. In the
alloy system cobalt-chromium-ruthenium-gallium it was found that
gallium contents above about 10 weight percent may exhibit
ferromagnetism upon slow cooling. Ferromagnetism is an undesirable
feature for dental prosthesis. Reducing the gallium content below
10%, however, lowers the thermal expansion coefficient of the
alloy.
Inventors: |
Cascone; Paul J.; (Del Mar,
CA) ; Prasad; Arun; (Cheshire, CT) |
Assignee: |
The Argen Corporation
San Diego
CA
|
Family ID: |
46877508 |
Appl. No.: |
13/349047 |
Filed: |
January 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61467877 |
Mar 25, 2011 |
|
|
|
Current U.S.
Class: |
420/583 ;
420/587; 420/588 |
Current CPC
Class: |
C22C 30/00 20130101 |
Class at
Publication: |
420/583 ;
420/588; 420/587 |
International
Class: |
C22C 30/00 20060101
C22C030/00; C22C 30/02 20060101 C22C030/02 |
Claims
1. A dental alloy comprising: at least 25 wt. % of Ru; from 15 to
35 wt. % Cr; from 30 to 50 wt. % Co; and at least 5 wt. % Ga;
wherein where the concentration of Ga is from 5 to 10 wt. % the
alloy further contains a sufficient concentration up to 5 wt. % of
at least one modifier selected from the group consisting Ge, Fe, B,
In, Sn and Re such that the liquidus temperature of the alloy is
below 1600 C..degree.; wherein where the concentration of Ga is
greater than 10 wt. %, the concentration of Co is at least 35 wt.
%, the concentration of Cr is less than 25 wt. %, and the alloy
further contains B in a concentration of up to 1 wt. %; and wherein
the alloy is non-magnetic.
2. The dental alloy of claim 1, wherein the concentration of Ga is
between 5 and 10 wt. % and the concentration of Ru is greater than
25 wt. % then the ratio of Co to Ga is 4 to 1 or less.
3. The dental alloy of claim 1, wherein the concentration of Ga is
between 5 and 10 wt. %, and wherein the alloy further contains at
least 1 wt. % Re.
4. The dental alloy of claim 1, wherein the concentration of Ga is
between 5 and 10 wt. %, and wherein the total concentration of Ga
and Re is at least 10 wt. %.
5. The dental alloy of claim 1, wherein the alloy further comprises
less than 5 wt. % of at least one trace additive selected from the
group consisting of copper, nickel and iron.
6. The dental alloy of claim 1, wherein the alloy has a composition
selected from the group consisting of
Co.sub.40Cr.sub.27.5Ru.sub.25Ga.sub.7.5,
Co.sub.38Cr.sub.30Ru.sub.25Ga.sub.7,
Co.sub.41Cr.sub.25Ru.sub.25Ga.sub.8Ge.sub.1,
Co.sub.35Cr.sub.25Ru.sub.30Ga.sub.10,
Co.sub.40Cr.sub.25Ru.sub.25Ga.sub.5Re.sub.5, and
Co.sub.37.5Cr.sub.30Ru.sub.25Ga.sub.7B.sub.0.5.
7. The dental alloy of claim 1, wherein the alloy has a thermal
expansion coefficient within the range of from about 9 to about
18.times.10.sup.-6.
8. The dental alloy of claim 1, wherein the concentration of Ga is
greater than 10 wt. %, and wherein the concentration of B is from
0.15 to 0.55 wt. %.
9. The dental alloy of claim 1, wherein the concentration of Ga is
between 10 and 11.5 wt. %, the concentration of B is between 0.15
and 0.55 wt. %, the concentration of Co is at least 37 wt. %, and
the concentration of Cr is between 22 and 25 wt. %.
10. The dental alloy of claim 1, wherein the alloy has a
composition selected from the group consisting of
Co.sub.40Cr.sub.24.35Ru.sub.25Ga.sub.10.5B.sub.0.15,
Co.sub.40Cr.sub.23.35Ru.sub.25Ga.sub.11.5B.sub.0.15,
Co.sub.40Cr.sub.23.95Ru.sub.25Ga.sub.10.5B.sub.0.55,
Co.sub.37.5Cr.sub.22.95Ru.sub.25Ga.sub.11.5B.sub.0.35, and
Co.sub.40Cr.sub.23.5Ru.sub.25Ga.sub.11B.sub.0.5.
11. The dental alloy of claim 1, wherein the concentration of Ga is
between 5 and 10 wt. %, the concentration of Co is at least 35 wt.
%, and the concentration of Cr is between 25 and 30 wt. %.
12. The dental alloy of claim 1, wherein the alloy further
comprises up to 10 wt. % of an additive selected from the group
consisting of Si, W, Ta, Nb, Re, Mo and V.
13. A dental alloy comprising: at least 25 wt. % of Ru; from 15 to
35 wt. % Cr; from 30 to 50 wt. % Co; from 5 to 10 wt. % Ga; further
contains a sufficient concentration of up to 5 wt. % of at least
one modifier selected from the group consisting Ge, Fe, B, In, Sn
and Re such that the liquidus temperature of the alloy is below
1600 C..degree.; wherein the ratio of Co to Ga is greater than 4 to
1; and wherein the alloy is non-magnetic.
14. A dental alloy comprising: at least 25 wt. % of Ru; from 15 to
25 wt. % Cr; from 35 to 50 wt. % Co; at least 10 wt. % Ga; wherein
the alloy further contains B in a concentration of up to 1 wt. %;
and wherein the alloy is non-magnetic.
15. A dental product comprising: a metallic body for dental
application, said body being formed of a dental alloy comprising:
at least 25 wt. % of Ru; from 15 to 35 wt. % Cr; from 30 to 50 wt.
% Co; and at least 5 wt. % Ga; wherein where the concentration of
Ga is from 5 to 10 wt. % the alloy further contains a sufficient
concentration up to 5 wt. % of at least one modifier selected from
the group consisting Ge, Fe, B, In, Sn and Re such that the
liquidus temperature of the alloy is below 1600 C..degree.; wherein
where the concentration of Ga is greater than 10 wt. %, the
concentration of Co is at least 35 wt. %, the concentration of Cr
is less than 25 wt. %, and the alloy further contains B in a
concentration of up to 1 wt. %; and wherein the alloy is
non-magnetic.
16. The dental product of claim 15, wherein the concentration of Ga
is between 5 and 10 wt. % and the concentration of Ru is greater
than 25 wt. % then the ratio of Co to Ga is 4 to 1 or less.
17. The dental product of claim 16, wherein the concentration of Ga
is between 5 and 10 wt. %, and wherein the alloy further contains
at least 1 wt. % Re.
18. The dental product of claim 15, wherein the concentration of Ga
is between 5 and 10 wt. % and wherein the total concentration of Ga
and Re is at least 10 wt. %.
19. The dental product of claim 15, wherein the alloy further
comprises less than 5 wt. % of at least one trace additive selected
from the group consisting of copper, nickel and iron.
20. The dental product of claim 15, wherein the alloy has a
composition selected from the group consisting of
Co.sub.40Cr.sub.27.5Ru.sub.25Ga.sub.7.5,
Co.sub.38Cr.sub.30Ru.sub.25Ga.sub.7,
Co.sub.41Cr.sub.25Ru.sub.25Ga.sub.8Ge.sub.1,
Co.sub.35Cr.sub.25Ru.sub.30Ga.sub.10,
Co.sub.40Cr.sub.25Ru.sub.25Ga.sub.5Re.sub.5, and
Co.sub.37.5Cr.sub.30Ru.sub.25Ga.sub.7B.sub.0.5.
21. The dental product of claim 15, wherein the alloy has a thermal
expansion coefficient within the range of from about 9 to about
18.times.10.sup.-6.
22. The dental product of claim 15, wherein the concentration of Ga
is greater than 10 wt. %, and wherein the concentration of B is
between 0.15 and 0.55 wt. %.
23. The dental product of claim 15, wherein the concentration of Ga
is between 10 and 11.5 wt. %, the concentration of B is between
0.15 and 0.55 wt. %, the concentration of Co is at least 37 wt. %,
and the concentration of Cr is between 22 and 25 wt. %.
24. The dental product of claim 15, wherein the alloy further
comprises up to 10 wt. % of an additive selected from the group
consisting of Si, W, Ta, Nb, Re, Mo and V.
25. The dental product of claim 15, wherein the alloy has a
composition selected from the group consisting of
Co.sub.40Cr.sub.24.35Ru.sub.25Ga.sub.10.5B.sub.0.15,
Co.sub.40Cr.sub.23.35Ru.sub.25Ga.sub.11.5B.sub.0.15,
Co.sub.40Cr.sub.23.95Ru.sub.25Ga.sub.10.5B.sub.0.55,
Co.sub.37.5Cr.sub.22.95Ru.sub.25Ga.sub.11.5B.sub.0.35, and
Co.sub.40Cr.sub.23.5Ru.sub.25Ga.sub.11B.sub.0.5.
26. The dental product of claim 15, wherein the concentration of Ga
is between 5 and 10 wt. %, the concentration of Co is at least 35
wt. %, and the concentration of Cr is between 25 and 30 wt. %.
27. The dental product of claim 15, wherein where the concentration
of Ga is from 5 to 10 wt. % then the ratio of Co to Ga is greater
than 4 to 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/467,877, filed Mar. 25, 2011, the disclosure of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention concerns a noble alloy suitable for dental
purposes that contains cobalt and chromium in addition to
ruthenium, and is non-magnetic.
BACKGROUND OF THE INVENTION
[0003] Dental alloys employed in the porcelain-fused-to-metal
processing technique may be classified into several groups: gold
based; palladium based; cobalt based and nickel based. Typically,
preferred alloy compositions have been tied to the cost of the
alloy components. To this end, the economic advantage of the
cheaper base metals such as cobalt and nickel is obvious, but the
functional characteristics of the base metal alloys do not compare
with those of the gold or palladium based dental products. In
general, the base metal alloys are more difficult to cast, grind
and bond to porcelain.
[0004] There have been numerous attempts to improve the functional
characteristics of cobalt and nickel alloys through the addition of
gold and the platinum group metals (the platinum group metals
comprise platinum, palladium, rhodium, iridium, osmium and
ruthenium). Exemplary US patents describing such dental alloys
include:
TABLE-US-00001 U.S. Patentee Pat. No. Comments Prosen 4,253,869
Describes a cobalt chromium alloy that may contain 7 to 15 wt. %
ruthenium Prosen 4,255,190 Describes a cobalt chromium alloy that
may contain 1 to 5 wt. % ruthenium with gallium plus tungsten
Zwingmann 4,382,909 Describes a cobalt chromium alloy that may
contain 1 to 70 wt. % palladium Prasad 4,459,263 Describes a cobalt
chromium alloy that may contain 5 to 15 wt. % ruthenium Vuilleme
6,613,275 Describes a cobalt chromium alloy that may contain 0.5 to
4 wt. % gold Prasad 6,656,420 Describes an alloy that may contain
25 to 60 wt. % gold and up to 2 wt. % ruthenium, the balance
cobalt. Prasad 6,756,012 Describes a cobalt chromium alloy that may
contain up to 20 wt. % platinum or palladium, up to 10 wt. % gold
and up to 6 wt. % ruthenium Cascone 7,794,652 Describes a cobalt
chromium alloys that contains at least 15 wt. % ruthenium, at least
40 wt. % cobalt and from 5 to 15 wt. % gallium
[0005] In each case, some improvement in the functional
characteristics of the base metal alloy is achieved through the
addition of gold and the platinum group metals. However, recently
it has been discovered that many of these alloys have magnetic
properties. In the past, such magnetic properties have not posed a
significant problem. However, the growing importance of
magnetically based imaging techniques has put the issue of dental
appliances made from strongly ferromagnetic materials in the
spotlight, because the presence of such strongly ferromagnetic
materials in a patient can interfere with obtaining clear images
from such techniques.
[0006] One of the first attempts to describe a true "non-magnetic'"
dental alloy family was recently submitted by the assignee of the
present application, The Argen Corporation (U.S. Pat. Pub. No.
2008/0232998). Unfortunately, the alloys disclosed in this
publication require the use of palladium, which is a relatively
expensive noble metal. Accordingly, it would be desirable to find a
similarly non-magnetic family of noble dental alloys comprising the
less expensive noble materials, such as, for example,
ruthenium.
SUMMARY OF THE INVENTION
[0007] Thus, there is provided in the practice of this invention
according to a presently preferred embodiment, a workable noble
alloy that is non-magnetic and can be used in dental applications.
The noble alloy according to the invention comprises: (i) at least
25 wt. % ruthenium; (ii) between 15-35% chromium; (iii) thermal and
mechanical property modifiers selected from the group of Ga, Ge,
Si, B, In, Sn, Al and Rare Earths metals in amounts sufficient to
result in an alloy that is non-magnetic and having a lower,
processable liquidus temperature (preferably below 1600 C..degree.,
and more preferably below 1450 C..degree.; (iv) and the balance
cobalt.
[0008] In one such embodiment, the non-magnetic cobalt based dental
alloy includes: [0009] at least 25 wt. % of Ru; [0010] from 15 to
35 wt. % Cr; [0011] from 30 to 50 wt. % Co; and [0012] at least 5
wt. % Ga; [0013] wherein where the concentration of Ga is from 5 to
10 wt. %, the alloy further contains a sufficient concentration of
up to 5 wt. % of at least one modifier selected from the group
consisting Ge, Fe, B, In, Sn and Re such that the liquidus
temperature of the alloy is below 1600 C..degree.; [0014] wherein
where the concentration of Ga is greater than 10 wt. %, the
concentration of Co is at least 35 wt. %, the concentration of Cr
is less than 25 wt. %, and the alloy further contains B in a
concentration of up to 1 wt. %; and [0015] wherein the alloy is
non-magnetic.
[0016] In one such embodiment, the concentration of Ga is less than
10 wt. % and the concentration of Ru is from 25 to 45 wt. %, and
the ratio of Co to Ga is 4 to 1 or less.
[0017] In another such embodiment, the concentration of Ga is less
than 10 wt. %, and the alloy further contains at least 1 wt. %
Re.
[0018] In still another such embodiment, the concentration of Ga is
less than 10 wt. % and the total concentration of Ga and Re is at
least 10 wt. %.
[0019] In yet another such embodiment, the at least one modifier
material is selected from the group consisting of up to 3 wt. %
silicon, up to 1 wt. % boron, up to 3 wt. % aluminum, up to 3 wt. %
germanium, and up to 1 wt. % cerium.
[0020] In still yet another such embodiment, the alloy further
comprises less than 5 wt. % of at least one trace additive selected
from the group consisting of copper, nickel and iron.
[0021] In still yet another such embodiment, where the
concentration of Ga is from 5 to 10 wt. %, the ratio of Co to Ga is
greater than 4 to 1.
[0022] In still yet another such embodiment, the alloy is a
composition selected from the group consisting of
Co.sub.40Cr.sub.27.5Ru.sub.25Ga.sub.7.5,
Co.sub.38Cr.sub.30Ru.sub.25Ga.sub.7,
Co.sub.41Cr.sub.25Ru.sub.25Ga.sub.8Ge.sub.1,
Co.sub.35Cr.sub.25Ru.sub.30Ga.sub.10,
Co.sub.40Cr.sub.25Ru.sub.25Ga.sub.5Re.sub.5, and
Co.sub.37.5Cr.sub.30Ru.sub.25Ga.sub.7B.sub.0.5. The suffixes
represent weight % of the elements in the alloys and not atomic
fractions.
[0023] In still yet another such embodiment, the alloy has a
thermal expansion coefficient within the range of from about 9 to
about 18.times.10.sup.-6.
[0024] In another embodiment of the present invention, the
concentration of Ga is greater than 10 wt. %, and the concentration
of B is from 0.15 to 0.55 wt. %.
[0025] In still yet another embodiment, the concentration of Ga is
from 10 to 11.5 wt. %, the concentration of B is from 0.15 to 0.55
wt. %, the concentration of Co is at least 37 wt. %, and the
concentration of Cr is from 22 to 25 wt. %.
[0026] In still yet another such embodiment, the alloy composition
is selected from the group consisting of
Co.sub.40Cr.sub.24.35Ru.sub.25Ga.sub.10.5B.sub.0.15,
Co.sub.40Cr.sub.23.35Ru.sub.25Ga.sub.11.5B.sub.0.15,
Co.sub.40Cr.sub.23.95Ru.sub.25Ga.sub.10.5B.sub.0.55,
Co.sub.37.5Cr.sub.22.95Ru.sub.25Ga.sub.11.5B.sub.0.35, and
Co.sub.40Cr.sub.23.5Ru.sub.25Ga.sub.11B.sub.0.5. The suffixes in
these alloys represent weight % of the elements in the alloys and
not the atomic fractions.
[0027] In still yet another embodiment of the present invention,
the concentration of Ga is from 5 to 10 wt. %, the concentration of
Co is at least 35 wt. %, and the concentration of Cr is from 25 to
30 wt. %.
[0028] In still yet another embodiment, the alloy composition
further comprises up to 10 wt. % of an additive selected from the
group consisting of W, Ta, Nb, Re, Mo and V.
[0029] In another aspect, the invention is directed to a dental
product formed using the alloys described above.
[0030] In yet another aspect, the invention is directed to a method
of manufacturing a dental product formed using the alloys described
above and using a technique selected from casting, molding, milling
or laser sintering.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
exemplary embodiments of the invention and should not be construed
as a complete recitation of the scope of the invention,
wherein:
[0032] FIG. 1 provides a data graph showing the magnetic properties
of an exemplary alloy in accordance with an embodiment of the
invention;
[0033] FIG. 2 provides a data graph showing the magnetic properties
of other exemplary alloys in accordance with an embodiment of the
invention;
[0034] FIG. 3 provides a data graph showing the magnetic properties
of other exemplary alloys in accordance with an embodiment of the
invention; and
[0035] FIG. 4 provides a data graph showing the magnetic properties
of other exemplary alloys in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] A noble alloy (as defined by the American Dental
Association) is considered to be one with at least 25 wt. % noble
metal content, the noble metals consisting of ruthenium, platinum,
palladium, iridium, osmium, rhodium and gold. The alloy provided
herein is noble, but is considered to be a cobalt-chromium based
alloy since a high proportion of these base metals are in the
alloy. It should be noted that unless otherwise indicated all
percentages herein are by weight.
[0037] The choice of ruthenium as a major additive has both
metallurgical and economic benefits. For example, consider the
approximate price/troy ounce of gold and the platinum group metals
as of December 2011:
TABLE-US-00002 Rhodium $1500 Platinum $1430 Gold $1600 Iridium
$1050 Ruthenium $120 Palladium $660
Ruthenium is one of the lower cost metals relative to the other
platinum group metals so there is an economic advantage to maximize
the content of ruthenium in place of gold and the other platinum
group elements.
[0038] From a metallurgical perspective, ruthenium may substitute
for other materials in cobalt, nickel and iron based alloys, such
as for example molybdenum, tungsten, and, to a certain extent,
chromium. Ruthenium acts as an alloy strengthener, is a thermal
expansion adjuster for the alloys (to better match thermal
expansion of dental porcelains), and reduces the alloy's oxidation
rate. Both ruthenium and chromium protect the alloy from corrosion
and oxidation. The ruthenium enobles the alloy, due to its
non-reactive nature as opposed to the chromium that forms an oxide
to protect the alloy from adverse reactions.
[0039] As discussed in the background, alloys incorporating
elevated ruthenium concentrations have been proposed in the past,
such as, for example, U.S. Pat. No. 7,794,652, which describes a
family of highly processable cobalt-chromium based ruthenium
containing noble dental alloys. While this patent focuses on
maximizing the processability of these ruthenium containing
cobalt-chromium alloys, no guidance is provided on how to ensure
that the alloys are not strongly-ferromagnetic. Table 1, below,
provides a number of exemplary alloys meeting the requirements of
the prior art that were found to have strong magnetic
properties.
TABLE-US-00003 TABLE 1 Prior Art Co--Cr--Ru Alloys Alloy No.
Formulation PA1 Co40Cr25Ru25Ga10 PA2 Co37Cr25Ru25Ga13 PA3
Co38Cr25Ru25Ga12 PA4 Co39Cr25Ru25Ga11
[0040] The current invention addresses the issue of minimizing the
magnetic properties of ruthenium-containing cobalt-chromium alloys
by carefully balancing the concentrations of the base metals and
through the judicious use of select additives. It should be
understood that though truly non-magnetic, or paramagnetic alloys
are preferred, in the following description of this invention the
term "non-magnetic alloy" refers to an alloy that is either
paramagnetic or only weakly ferromagnetic, as shown in the attached
data graphs.
[0041] The current invention is based upon the discovery that by
carefully balancing the relative proportions of cobalt, gallium and
modifiers, it is possible to control the magnetic properties of
ruthenium containing noble cobalt chromium alloys and obtain
processable alloys with non-magnetic properties. The challenge to
the metallurgist in composing such an alloy is in finding the
balance between processability on the one hand and non-magnetism on
the other. As described above in the Background, previously it was
thought that ruthenium containing cobalt-chromium alloys required a
minimum concentration of gallium and cobalt to ensure that the
processing characteristics of the alloys (such as liquidus
temperature) would be such as to allow them to be used in the
construction of dental appliances. However, it has now been
discovered that when such alloys have a gallium content above about
10 wt. % they may exhibit strong ferromagnetism upon slow cooling.
As discussed above, such strong ferromagnetism is an undesirable
feature for dental prostheses and appliances. Reducing the gallium
content below 10 wt. % eliminates this problem, but also lowers the
thermal expansion coefficient of the alloy. This may restrict the
alloy's thermal compatibility with some popular dental porcelain
brands.
[0042] The alloys of the current invention address both
factors--processability and magnetic properties--by judiciously
manipulating the content of cobalt, chromium, gallium, and certain
additives. In particular, there are two relevant compositional
regimes for such ruthenium containing cobalt-chromium alloys: high
gallium content alloys (greater than 10 wt. %); and low gallium
content alloys (from 5 to 10 wt. % gallium). In the high gallium
content alloys, it is necessary to include boron and carefully
control the content of cobalt in the alloy to ensure that the alloy
retains its non-magnetic properties. In the low gallium alloys, the
cobalt content may be reduced and boron eliminated, but in turn it
is important to monitor the ratio of cobalt to gallium, and, in
some alloys to include sufficient concentrations of certain
specific additives to ensure that the processability of these
alloys is maintained.
[0043] More particularly, alloys within the scope of this invention
comprise: [0044] at least 25 wt. % of ruthenium with only minor
substitutions of the other noble alloys--platinum, palladium,
iridium, osmium, rhodium and gold; [0045] between 15-35 wt. %
chromium; [0046] from above 30 to 50 wt. % cobalt; [0047] at least
5 wt. % gallium; [0048] wherein where the concentration of Ga is
from 5 to 10 wt. %, preferably a ratio of Co to Ga of at least 4 to
1, and the alloy further contains up to 5 wt. % of at least one
modifier selected from the group consisting Ge, Fe, B, In, Sn and
Re where the concentration of the modifier is selected such that
the liquidus temperature of the alloy is below 1600 C..degree.;
[0049] wherein where the concentration of Ga is greater than 10 wt.
%, the concentration of Co is at least 35 wt. %, the concentration
of Cr is less than 25 wt. %, and the alloy further contains B in a
concentration of up to 1 wt. %; and [0050] wherein where the
concentration of Ru is greater than 25 wt. % then the Co to Ga
ratio is less than 4 to 1.
Low Gallium Content Non-Magnetic Alloys
[0051] In some embodiments of the invention, the ruthenium
containing cobalt-chromium dental alloy has a gallium content of
between 5 and 10 wt. %. In such embodiments, the alloy is a
cobalt-chromium based alloy comprising at least 25 wt. % ruthenium;
a sufficient amount of a modifier selected from Ge, Fe, B, In, Sn
and Re to ensure the material is sufficiently processable; chromium
in the range of 15 to 35 wt. %, and preferably 25 to 35 wt. % and
more preferably at least 30 wt. % cobalt. Preferably the ratio of
cobalt to gallium is greater than 4 to 1.
[0052] As discussed above, in some of these embodiments of the
invention the addition of a sufficient amount of the modifier's
selected from the group of Ge, Fe, B, In, Sn and Re is necessary to
obtain thermal expansion properties suitable for the construction
of dental appliances. In particular, the combination of high noble
content and low gallium concentration in alloys of this type can
make it difficult for the alloys to be melted and shaped in the
absence of very high temperatures. The addition of appropriate
additives in accordance with the present invention lowers the
melting temperature of the alloys so that they can be melted with a
natural gas- or propane-oxygen torch commonly used in dental
laboratories. Accordingly, in such embodiments sufficient modifier
is added to reduce the liquidus temperature sufficiently low to
allow for the use of inductive heating to shape the material (less
than 1600 C..degree.), and preferably below 1450 C..degree..
[0053] Accordingly, in these embodiments of the invention (between
5 and 10 wt. %, gallium), the total amount of such additives is at
least 5 wt. %, and preferably between 5 to 15 wt. %, with least 5
wt. % of the additive being gallium. In such alloys, as discussed,
other substitutions may be made and other additives may be included
in amounts sufficient to lower the liquidus temperature preferably
below at least 1600 C..degree.. Examples of such substitutions
and/or modifier additions include increasing the ruthenium content
in place of cobalt, or adding one of the modifiers listed from the
group of Ge, Fe, B, In, Sn and Re as a substitute in place of or in
addition to gallium to ensure a suitable thermal expansion
coefficient.
[0054] Table 2, below, provides a listing of non-magnetic
chromium-cobalt-ruthenium-gallium alloys according to the invention
having between 5 and 10 wt. % gallium, and preferably with cobalt
to gallium ratios of greater than 4 to 1, that also demonstrate a
liquidus temperature sufficiently low to ensure that the material
is workable in dental applications (less than 1600 C..degree., and
preferably less than 1450 C..degree.). As is shown, a lower thermal
expansion may be obtained by the judicious use of the additives
listed. In particular, as shown in Table 1, by adding additives
such as rhenium, germanium, iron or boron (Alloys 17 to 27, Table 2
below). (The magnetic behavior of alloy 22 is shown as an example
of the non-magnetic behavior of this group of compositions in FIG.
1.) The linear relationship between B and H in the data plot
demonstrates that the material has no magnetic response. The
suffixes represent weight % of the elements in the alloys and not
atomic fraction.
TABLE-US-00004 TABLE 2 Low Gallium Content Non-Magnetic Alloys
Alloy No. Formulation 1 Co50Cr15Ru25Ga10 2 Co40Cr20Ru30Ga10 3
Co41Cr25Ru25Ga9 4 Co42Cr25Ru25Ga8 5 Co41Cr26Ru25Ga8 6
Co39Cr28Ru25Ga8 7 Co37Cr30Ru25Ga8 8 Co40Cr27.5Ru25Ga7.5 9
Co43Cr25Ru25Ga7 10 Co42Cr26Ru25Ga7 11 Co40Cr28Ru25Ga7 12
Co38Cr30Ru25Ga7 13 Co42.5Cr26Ru25Ga6.5 14 Co43Cr26Ru25Ga6 15
Co45Cr25Ru25Ga5 16 Co40Cr30Ru25Ga5 17 Co40Cr25Ru25Ga5Re5 18
Co40Cr24.5Ru25Ga10B0.5 19 Co40Cr25.5Ru25Ga9B0.5 20
Co40Cr26.5Ru25Ga8B0.5 21 Co40Cr27Ru25Ga7.5B0.5 22
Co37.5Cr30Ru25Ga7B0.5 23 Co40Cr29.5Ru25Ga5B0.5 24
Co44.75Cr25Ru25Ga5B0.25 25 Co41Cr25Ru25Ga7Fe2 26 Co41Cr25Ru25Ga8Ge1
27 Co40Cr28Ru25Ga6.5Ge0.5
[0055] To demonstrate the criticality of the compositional
limitations, other experiments were conducted to show the loss of
non-magnetic properties if these compositional limitations are
violated. As discussed with regard to Tables 1 and 2, above, the
importance of the cobalt and gallium ratio was demonstrated by
studying the prior art alloys, however, it was also discovered that
there are important lower (30 wt. %) and upper (50 wt. %) limits to
the amount of cobalt in the material and a lower limit on the
amount of gallium (greater than 5 wt. %) in the alloy, as shown in
alloys 28 to 34, below, all of which showed strongly ferromagnetic
properties during testing.
TABLE-US-00005 TABLE 3 Magnetic Co--Cr--Ru Alloys 28
Co51Cr15Ru25Ga9 29 Co55Cr15Ru25Ga5 30 Co50Cr20Ru25Ga5 31
Co60Cr15Ru25 32 Co55Cr20Ru25 33 Co42.5Cr30Ru25B0.5 34
Co30Cr25Ru25Ga10Fe10
High Gallium Content Non-Magnetic Alloys
[0056] As discussed above, in other embodiments of the invention,
ruthenium containing cobalt-chromium alloys with high gallium
concentrations (in excess of 10 wt. %) that show low ferromagnetism
may be obtained. As can be appreciated with reference to FIGS. 2 to
4, by adding boron, and by judiciously controlling the relative
concentrations of cobalt, it is possible to obtain compositions
that are either paramagnetic, or that show only weak or no
ferromagnetism.
[0057] FIG. 2 provides data in connection with a range of alloys
that were tested showing a full range of magnetic behavior--from
strongly ferromagnetic to paramagnetic. FIG. 3 shows those alloys
(those with low cobalt concentrations) that exhibited a strong
magnetic response (note the typical curve in these data plots, and
for a few samples, a hysteresis effect that are indicative of a
strong ferromagnetic behavior.) However, note that as the cobalt
concentration increases and the boron is added the compositions
lose their ferromagnetic behavior and become more paramagnetic
(i.e. the relation between B and H in the data plots is linear).
Finally, FIG. 4 shows those alloys, according to the invention,
that were weakly ferromagnetic or paramagnetic. (The change in the
y-axis scale should be noted.) These alloys are of particular value
since the materials also exhibit the required thermal properties to
bond to popular porcelains, yet show little or no ferromagnetic
behavior.
[0058] Of importance in these embodiments of the invention is the
inclusion of sufficient cobalt, the judicious use of boron, and the
careful titration of chromium to render the alloy non-magnetic.
With decreasing gallium, as shown in the embodiments above, it is
possible to decrease the cobalt concentration and increase the
concentration of chromium. As the gallium concentration increases,
however, it is necessary to add boron, decrease the concentration
of chromium and increase the concentration of cobalt. Thus, by
adjusting the compositional contributions of chromium, cobalt and
boron, the alloys of the invention can be made paramagnetic or
ferromagnetic, even at high gallium content, which has never before
been demonstrated.
[0059] Thus, in these embodiments, the alloys of the present
invention include cobalt-chromium based alloys comprising at least
25 wt. % of ruthenium; greater than 10 wt. % gallium, and
preferably from between 10.5 to 11.5 wt. % gallium; a non-zero
concentration of up to 1 wt. % boron, and preferably from 0.15 to
0.55 wt. % boron; chromium in the range of 20 to 25 wt. %, and
preferably 22 to 25 wt. %; and a balance of Co, where the cobalt
content is above 35 wt. %.
[0060] Table 4, below, provides a summary listing of the
chromium-cobalt-ruthenium-gallium alloys studied. In these alloys,
non-magnetic properties were obtained by the judicious use of boron
and chromium. In particular, as shown in Table 2 by including a
small amount of boron, and decreasing the chromium concentration,
it is possible to obtain alloys with high gallium concentrations
(greater than 10 wt. %) that consistently demonstrate non-magnetic
properties. The suffixes represent weight % of the elements in the
alloys and not atomic fractions.
TABLE-US-00006 TABLE 4 High Gallium Content Non-Magnetic Alloys
Alloy No. Formulation Magnetic Property 35
Co35Cr29.35Ru25Ga10.5B0.15 Ferromagnetic 36 Co40Cr23.5Ru25Ga11B0.15
Paramagnetic 37 Co40Cr24.35Ru25Ga10.5B0.15 Paramagnetic 38
Co35Cr28.35Ru25Ga11.5B0.15 Ferromagnetic 39
Co40Cr23.35Ru25Ga11.5B0.15 Paramagnetic 40 Co40Cr24Ru25Ga10.85B0.15
Paramagnetic 41 Co37.5Cr22.95Ru25Ga11.5B0.35 Paramagnetic 42
Co33.5Cr30Ru25Ga11B0.5 Ferromagnetic 43 Co40Cr23.5Ru25Ga11B0.5
Paramagnetic 44 Co35Cr28.95Ru25Ga10.5B0.55 Ferromagnetic 45
Co40Cr23.95Ru25Ga10.5B0.55 Paramagnetic 46
Co35Cr27.95Ru25Ga11.5B0.55 Ferromagnetic 47
Co40Cr22.95Ru25Ga11.5B0.55 Ferromagnetic
General Compositional Considerations
[0061] It should be noted that in the above embodiments the amount
of noble metal in the alloy may be greater than 25 wt. %, up to as
much as 45 wt. % (as shown in Table 5, below) and still maintain
the non-magnetic properties described herein, but there is no
economic advantage to using these higher concentrations of the
costly material. In addition, although the alloys of the invention
comprise at least 25 wt. % ruthenium, it will be understood that
additions or substitutions of other noble metals selected from the
list of ruthenium, platinum, palladium, iridium, osmium, rhodium
and gold may be made without fundamentally changing the nature of
the material.
TABLE-US-00007 TABLE 5 High Ru Content Alloys 48 Co35Cr25Ru30Ga10
49 Co40Cr20Ru30Ga10 50 Co25Cr20Ru40Ga15 51 Co25Cr20Ru45Ga10
[0062] In addition to the main components as described above, the
alloys of the present invention may also contain trace
concentrations of other additives to improve specific properties.
For example, up to about 10% of molybdenum, silicon, vanadium,
tungsten, niobium, tantalum and/or the Rare Earths (or appropriate
combinations of these elements) to further adjust coefficient of
thermal expansion (CTE), to enhance the casting characteristics of
the alloy and for grain refinement. Finer grain castings are more
readily ground to a smooth finish suitable for covering with dental
ceramics. However, it should be understood that these additives are
not essential to the practice of the current invention.
[0063] It is appreciated that the above compositions are suitable
for use with dental appliances, but are not to be considered
exclusive. Those of skill in the art will be aware that some of the
materials can be substituted or additional materials may be added
without altering the key properties of the alloys of the current
invention. For example, small concentrations (less than 5 wt. %) of
other materials may also be added or be found in the alloy as
impurities without affecting the properties of the overall
composition, some of these include, for example, Al, Si, V, W, Ta,
Nb, Re, Mo and the Rare Earths.
[0064] Although the above description has focused on a range of
compositions for alloys of the current invention suitable for use
in, for example, dental applications, the invention is also
directed to dental products made from the alloys and to methods of
manufacturing dental products from the alloys. In general, such
methods will include the steps of providing an alloy having a
composition in accordance with the above description and then
shaping the dental product with that alloy using any suitable
means. In this regard, the alloys of the present invention allow
for the use of a number of conventional shaping techniques, such
as, casting and molding. Moreover, the alloys of the invention also
allow for the use of more recent advances in shaping technologies,
such as, for example, CAD/CAM milling and selective laser
sintering. It should be understood that any of these techniques or
a combination thereof may be used with the alloys of the present
invention.
[0065] Specifically, despite their high hardness value, the alloys
may be ground using traditional dental laboratory grinding media
making them especially suited for use with newer CAD/CAM and powder
metallurgical applications where no casting is required. In one
such technique, substrates or final restorations can be milled from
blocks made from these alloys. As powders, these alloys can be used
either to create three dimensional performs utilizing appropriate
binders and then be sintered, or can be directly sintered/melted
such as for example, with a laser, to create substrate or final
restoratives. Exemplary disclosures of such processes can be found,
for example, in U.S. Pat. Nos. 7,084,370 and 6,994,549, the
disclosures of which are incorporated herein by reference. It
should be understood that while some prior art laser sintering
techniques specify a specific range of useable alloy particulate
sizes, the alloys of the current invention are contemplated for use
in laser sintering techniques over all possible particulate size
ranges.
DOCTRINE OF EQUIVALENTS
[0066] Those skilled in the art will appreciate that the foregoing
examples and descriptions of various preferred embodiments of the
present invention are merely illustrative of the invention as a
whole, and that variations in the relative composition of the
various components of the present invention may be made within the
spirit and scope of the invention. For example, it will be clear to
one skilled in the art that typical impurities and/or additives may
be included in the compositions discussed above that would not
affect the improved properties of the alloys of the current
invention nor render the alloys unsuitable for their intended
purpose. Accordingly, the present invention is not limited to the
specific embodiments described herein but, rather, is defined by
the scope of the appended claims.
* * * * *