Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to corrosion resistant pre-
cision casting alloys particularly suitable for use as dental
alloys.
Metals and metal alloys are used extensively in
r 5 restorative and corrective dentistry for removable restora-
tions, inlays, crowns, and bridges, orthodontic appliances,
; and the like. Dental alloys must meet stringent physical and
chemical requirements. First, the chemical nature of the alloy
must be such that no harmful physiological effects are produced
10 on the patient or the operator. The alloy must be stainless
and resistant to attack by the various acid and alkaline
substances naturally present in the mouth and in foods and
beverages. It must be capable of being fabricated into the
desired dental appliances by dentists and technicians and
~;~ 15 yet must be hard enough and strong enough to resist wear and
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`~ deformation in use, and it must be capable of being cast to
form precision castings free of inclusions, blow holes and
other defects.
Gold alloys were originally the most widely used
and useful of the dental alloys. HoweVer, the high cost and
~ scarcity of gold led to the development of dental alloys
;' comprising predominantly cobalt and chromium with minor amounts
of tungsten, nickel and other metals. These cobalt-chromium
base dental alloys are exemplified by those disclosed in
25 United States patents 1,961,626 and 2,134,423 to Enrique G.
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Touceda. More recent work has led to the development of
dental alloys comprising predominantly nickel and chromium
with minor amounts of molybdenum, iron, copper and other
. metals. These newer nickel-chromium base dental alloys are
exemplified by the alloy disclosed in United States patent
.,
2,597,495 to Jackson and Simmons. Ali of these prior dental
alloys possess to a greater or lesser extent the character-
istics required of such alloys as previously discussed. How-
ever none possesses all of the required characteristics to
the optimum extent, and research and development of new
dental alloys with improved characteristics is constantly
` taking place.
In Canadian Patent No 994,129 we have described an
improved corrosion resistant alloy that comprises essentially,
by weight, 15.0 to 25 per cent chromium, 3.0 to 6.0 per cent
molybdenum, 1.0 to 4.0 per cent tin, 0.5 to 1.5 per cent
- manganese, 0.5 to 5.0 per cent copper, 1.0 to 4.0 per cent
silicon, up to 1.0 per cent aluminum, up to 1.0 per cent
colbalt, up to 0.2 per cent carbon and the balance (52.3 to
, 20 79.0 per cent) nickel. The resulting alloy is capable of
being cast to form precision castings that are free of in-
clusion, blow holes and other defects, and the alloy is
relatively easy to work while possessing adequate strength
` and hardness.
The aforesaid alloy contains a small but significant
-~ amount of tin which greatly improves the fluidity of the
; molten alloy and also~contributes to the strength and hardness
of the cast alloy without unduly reducing the elongation of the
I alloy. As a result of further investigations with respect to
. .. .
' 30 this and related alloys we have found that gallium imparts
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essentially the same characteristics to the molten and cast ~-
alloy as tin and may be included in the alloy along with tin
or in place of tin to obtain an alloy having excellent casting
properties and that is relatively easy to work while possessing
adequate strength and hardness. In addition, we have found
that the amount of tin and/or gallium included in the alloy
may be significantly increased over the amount employed in the
alloy of our copending application and further that the alloy
can optionally contain significant amounts of copper, silicon,
aluminum and cobalt.
The improved corrosion resistant alloy of the in-
vention comprises essentially, by weight, at least 60% nickel,
10 to 25~ chromium, up to 10% molybdenum, 0.50 to 1.50%
. manganese, up to 9.0% tin, 1.0 to 7.5% gallium, up to 5%
copper, up to 4.0% silicon, up to 2.0~ aluminum, up to 5%
cobalt and up to 0.2% carbon, the combined total amount of tin
and gallium not exceeding 10%. The resulting alloy is capable
of being cast to form precision castings that are free of in-
clusions, blow holes and other defects, and the alloy is rel-
atively easy to work while possessing adequate strength and
hardness.
The corrosion resistant alloy of our invention con-
sists predominantly of nickel and chromium with minor but
signifi~cant amounts of other metalc that modify the physical
properties (for example, its fusion point, hardness and work-
. ability) of the basic alloy composition. In general, the
proportion of nickel to chromium in the basic alloy composition
may range from about 2:1 to about 5:1, and in the preferred com-
~ position is about 3.5:1. Nickel is the major component
30 of the alloy and is employed for its inherent resistance to
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corrosion. Chromium, the other predominant component of the
basic alloy composition, enhances the corrosion resistance
of the alloy and also is a solid solution/precipitation
hardener. In addition, a small but significant amount of
manganese act~ as a safeguard against possible sulfur con-
tamination and a small amount of molybdenum is advantageously
employed to enhance the corrosion resistance of the alloy and
as a powerful solid solution/precipitation hardener.
Optionally, the alloy may contain a small amount of silicon
that acts as a deoxidizer and also lowers the fusion temper-
ature of the alloy, and a small amount of copper may be
added to improve the surface finish of the cast alloy. Small
amounts of cobalt and aluminum, the latter as a deoxidizer
and precipitation hardener, and a very small amount of carbon
may also be present in the alloy. Lastly, the alloy of the
invention contains a small but ~ignificant amount of gallium
with or without a small amount of tin which greatly improves
the fluidity of the molten alloy and also contributes to the
,
strength and hardness of the cast alloy without unduly re-
ducing the elongation of the alloy.
As previously noted, we have found that gallium
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, imparts essentially the same characteristics to the molten
and cast alloy as is imparted to the alloy by tin, and
further that gallium may be included in the alloy along with
tin or in place of tin to obtain an alloy having excellent
casting properties and that is relatively easy to work while
possessing adequate strength ahd hardness. In addition we
have found that the amount of tin and gallium included in
the alloy may be significantly i~creasecl over the amount
Canadidn Pa~cnt No 99L;,/19
; 30 employed in the alloy of our oopcnding applioation ~er~
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~7e. 317,591 and further that the alloy can optionally contain
significant amounts of copper, silicon, aluminum, cobalt and
molybdenum, as hereinafter described.
The relative proportions of the various elements com-
prising the new alloy composition have been determined as the
result of an intensive investigation to obtain an alloy having
optimum chemical and physical properties. Specifically, we
have found that the alloy composition of the invention should
contain at least 60 per cent by weight nickel, from 10 to 25
per cent by weight chromium, up to 10 per cent by weight
molybdenum, from 0.50 to 1.5 per cent by weight manganese, from
1.0 to 7.5 per cent by weight gallium, up to~9 per cent by
weight tin, up to 5 per cent by. weight copper, up to 4.0 per
., .
; cent silicon, up to 2.0 per cent by weight aluminum, up to 5
~ 15 per cent by weight cobalt and up to 0.2 per cent by weight
"; carbon. The combined total amount of gallium and tin should
not exceed about 10 per cent by weight of the composition.
Moreover, it should be noted that molybdenum, tin, copper,
~ silicon, aluminum, cobalt, and carbon are optional constituents
~ 20 of the alloy composition, and further that gallium is an
essential constituent thereof. A corrosion resistant alloy
;; which contains the aforementioned components in the amount
specified may be readily cast to produce precision castings that
may be easily finished and that have the necessary strength and
hardness for the applications intended. In particular, the
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~ presence of gallium and tin in the alloy composition effects a
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significant improvement in these essential characteristics.
The following specific examples describe the prep-
aration of the preferred alloy composition of the invention.
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EXAMPLE I
A base alloy composition comprising 68.25 parts
by weight nickel, 20.0 parts by weight chromium, 4.5 parts
by weight molybdenum and 1.25 parts by weight manganese was
prepared by melting the substantially pure components in a
crucible 1.5 parts by weight copper, 2.S parts by weight
silicon and, most important, 2.0 parts by weight tin were
then added to the alloy melt. After the molten ingredients
were thoroughly mixed to form a homogenous melt, the molten
alloy was cast into a mold or investment of refractory
material to obtain a cast metal shape. Several such in-
vestment castings were made. In each case the resulting
cast metal shape conformed precisely to the shape of the
investment mold and was without blow holes, inclusions or
other defects. The alloy shape that was allowed to air-cool
; in lts investment mold had a Rockwell B hardness of 83, and
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0.2 per cent yield strength of 49,500 psi and a maximum
elongation of 13 per cent. When cooling was accelerated by
the water quenching o the alloy shape - investment mold
~; 20 composite, the alloy had a Rockwell B hardness of 82, and
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0.2 per cent yield strength of 42,500 psi and a maximum
elongation of 17 per cent. Further reductions in the Rock-
well B hardness and 0.2 per cent yield strength to values
of 80 and 42,000 psi respectively accompanied by an increase
. 25 in the maximum elongation to 25 per cent were accomplished
' by annea~ing of the alloy shape at 2000F. for 30 minutes after
;:.,
which the alloy was quenched in water. The generally good
working characteristics typical of the alloy when air cooled
can therefore be improved by the two aforementioned techniques
or simi~ar treatments following casting. All of these
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physical characteristics reflect a substantial improvement
over the properties of similar, but tin-free, corrosion
resistant precision casting alloys known in the prior art.
EXAMPLE II
The alloy composition of Example I was modified
by the substitution of 1% by weight of gallium for 1% by
weight of tin (one half of the tin) in the composition to
obtain a corrosion resistant dental alloy having the compo-
sition listed below. The molten alloy was cast into in-
, 10 vestment cast shapes to provide test specimens free from
; defects and having the physical characteristics also listed
below
Composition (% by weight) and properties
Ni 68.25 Si 2.5Q
v 15 Cr 20.00 Cu 1.50
Mo 4.S0 Sn 1.00
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? Mn 1.25 Ga 1.00
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Proportional limit (pBi) 31,600
~` 0.2% Yield Strength (psi) 42,600
Ultimate Tensile Strength (psi) 66,300
Elongation (%) 11
Rockwell "B" Hardness 82
Y,.~
~^ EXAMPLE III
The alloy composition of Example I was modified
; 2S by the substitution of 2% by weight of gallium for the 2%
, by weight of tin present in the alloy to obtain a corrosion
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' resistant dental alloy having the composition listed below.
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~he molten alloy was cast into investment cast shapes to
~' provide test specimens free from defects and having the
;,~ 30 physical characteristics also listed below.
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Composition (% by weight) and properties
Ni 68.25 Si 2.50
Cr 20.00 Cu 1.50
Mo 4.50 Ga 2.00
Mn 1.25
~, Proportional limit ~psi) 44,700
0.2% Yield Strength ~psi) 51,S00
Ultimate Tensile Strength ~psi) 79,000
Elongation ~%) 14
: 10 Rockwell "~" Hardness 81
EXAMPLE IV
; An alloy having the composition listed below was pre-
:~ pared in accordance with the procedure described in
Example I, and test specimen~ were prepared by investment
casting of the alloy to obtain defect-free cast alloy shapes
having the physical characteristics also listed below.
Composition ~5~ by weight) and properties -
Ni 66.25 Si 2.5
~r 20.00 Cu 1.5
Mo 4.50 Sn 3.0
Mn 1.25 Ga 1.0
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. - Proportional Limit ~psi) 38~600
0.2~ Yield Strength ~psi) 47,50n
Ultimate Tensile Strength ~psi) 69~800
~5 Elongation ~%) 6
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Rockwell "B'; Hardness 87
EXAMPLE V
,
; An alloy having the composition listed below ~as
~ prepared in accordance with the ~rocedure described in
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1047284 `:
Example I, and test specimens were prepared by investment
casting of the alloy to obtain defect-free cast alloy shapes
having the physical characteristics also listed below.
Composition (% by weight) and properties
Ni 66.25 Si 2.5
Cr 20.00 Cu 1.5
Mo 4.50 Sn 2.0
:- Mn 1.25 Ga 2.0
Proportional Limit (psi) 37,000
~` 10 0.2% Yield Strength (psi) 47,400
.- ~ Ultimate Tensile Strength (psi) 73,600
Elongation (%) 11
Rockwell "B" Hardness 86
,
EXAMPLE VI
. 15 An alloy having the composition listed below was
. prepared in accordance with the procedure described in
, .,
; Example I, and test specimens were prepared by investment
casting o the alloy to obtain defect-free cast alloy shapes
having the physical characteristics also listed below.
Composition (% by weight) and properties
: Ni 66.25 Si 2.5
.~. Cr 20.00 Cu 1.5
:~ Mo 4.50 Sn 1.0
; .
.. Mn .1.25 Ga 3.0
.
Proportional Limit (psi) 37,200
0.2% Yield Strength (psi) 46,700
- Ultimate Tensile Strength (psi) 68,700
Elongation (%) 9
Rockwell "B' Hardness 86
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EXAMPLE VII
An alloy having the composition listed below was
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prepared in accordance with the procedure described in Example
I, and test specimens were prepared by investment casting of
the alloy to obtain defect-free cast alloy shapes having the
physical characteristics also listed below.
, Composition (% by weight) and properties
; Ni 75.5
Cr 15.0 Cu 1.5
. 10 Mn 0.5 Ga 7.5
Proportional Limit (psi) 35,000
0.2% Yield Strength (psi) 42,500
Ultimate Tensile Strength (psi) 69,000
. Elongation (%) 16
; 15 Rockwell "B" Hardness 72 :
The foregoing alloy compositions were modified by
the inclusion of up to 10% by weight molybdenum, up to 9% by
i, weight of tin and 7.5% by weight of gallium, up to 5% by
weight copper, up to 4.0% by weight silicon, up to 2.0% by
weight aluminum and up to 5% by weight cobalt. All possessed
the improved physical properties characteristic of the alloy
composition of the invention.
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