IE41785B1 - Nickel alloy - Google Patents

Abstract

1449788 Nickel-base alloys HOWMEDICA Inc 20 Aug 1975 [26 Sept 1974] 34684/75 Heading C7A Corrosion-resistant, hot workable, dental alloys have a composition in the following range, in per cent by weight:- Ni 60 - Cr 10 - 25 Mn 0À5 - 1À5 Ga 1 - 7À5 Sn 0 - 9 Mo 0 - 10 Cu 0 - 5 Si 0 - 4 Al 0 - 2 Co 0 - 5 C 0 - 0À2 the total of Ga and Sn not exceeding 10.

Description

This invention relates to nickel base alloys, especially corrosion resistant precision casting alloys particularly suitable for use as dental alloys.

Metals and metal alloys are used extensively in 5 restorative and corrective dentistry for removable restorations , inlays, crowns and bridges and orthodontic appliances. Dental alloys must meet stringent physical and chemical requirements. Firstly, the chemical nature of the alloy must be such that no harmful physiological effects are produced 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 yet must be hard enough and strong enough to resist wear and deformation in use, and It must be capable of being cast to form precision 417 8 5 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 United States Patent Specifications Nos. 1,961,626 and 2,134,423. 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 Specification No.2,597,495. All of these prior dental alloys possess to a greater or lesser extent the characteristics required of such alloys as previously discussed. However, 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.

Patent Specification No. describes and claims a corrosion resistant, hot workable and hardenable precision casting alloy comprising, by weight: 15.0 to .0 percent chromium, 3.0 to 6.0 percent molybdenum, 1.0 to 4.0 percent tin, 0.5 to 1.5 percent manganese, 0.5 to 5.0 percent copper, 1.0 to 4.0 percent silicon, 0.0 to 1.0 percent aluminium, 0.0 to 1.0 percent cobalt, 0.0 to 0.2 percent carbon and the balance (52.3 to 79.0 percent) nickel. The resulting alloy is capable of being cast to form precision castings that are free of inclusion, 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 alloy. As a result of further investigations with respect to this and related alloys we have found that gallium imparts 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 Patent Specification No. and further that the alloy optionally may contain significant amounts of copper, silicon, aluminium and cobalt.

Accordingly, the present invention provides a corrosion resistant hot-workable and hardenable precision casting alloy which consists of, by weight, at least 60% nickel, 10 to 25% chromium, 0 to 10% molybdenum, 0.50 to 1.50% manganese, 0 to 9.0% tin, 1.0 to 7.5% gallium, 0 to 5% copper, 0 to 4.0% silicon, 0 to 2.0% aluminium, to 5% cobalt and 0 to 0.2% carbon, the combined total amount of tin and gallium not exceeding 10%, preferably not exceeding 7.5%.

Specific preferred alloy compositions with the amount of each ingredient falling within the quoted ranges 417 8 5 are illustrated in the Examples which appear hereinafter.

The resulting alloy is capable of being cast to form precision castings that are free of inclusions, blow holes and other defects, and the alloy is relatively easy to work while possessing adequate strength and hardness.

The corrosion resistant alloy of the present invention consists predominantly of nickel and chromium with minor but significant amounts of other metals that modify the physical properties (for example, its fusion point, hardness and workability) of the basic alloy composition. The proportion of nickel to chromium in the basic alloy composition is preferably approximately 3.5:1, Nickel is the major component of the alloy and is employed for its inherent resistance to 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 acts as a safeguard against possible sulphur contamination and a small amount of molybdenum optionally may be 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 temperature 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 aluminium, 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 significant 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 reducing the elongation of the alloy.

As previously noted, we have found that gallium 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 and hard15 ness. In addition we have found that the amount of tin and gallium included in the alloy may be significantly increased over the amount employed in the alloy Patent Specification No. Sftfcfc'j and further that the alloy optionally may contain significant amounts of copper, silicon, aluminium, cobalt and molybdenum, as hereinafter described.

The relative proportions of the various elements comprising the new alloy composition have been determined as the result of an intensive investigation to obtain an alloy having optimum chemical and physical properties.

Moreover, it should be noted that molybdenum, tin, copper, silicon, aluminium, cobalt, and carbon are optional constituents of the alloy composition, and further that gallium is an essential constituent thereof. A corrosion resistant alloy which contains the aforementioned components in the amounts 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 presence of gallium and tin in the alloy composition effects a significant improvement in these essential characteristics.

In order to provide a comparison between the alloys described and claimed in Patent Specification No. ϊβίβί»') and the alloys of the present invention the following comparative composition was made employing the procedure exemplified in Patent Specification No. 3 Comparative Composition 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 under an inert atmosphere. 1.5 Parts by weight copper, 2.5 parts by weight silicon and, most important, 2.0 parts by weight tin were than added to the alloy melt. After the molten ingredients were thoroughly mixed to form a homogeneous melt, the molten alloy was poured into a mould of refractory material to obtain a cast metal shape. Several such castings were made. In each case the resulting cast metal Shape conformed precisely to the shape of the mould and was without blow holes, inclusions or other defects. The alloy shape that was allowed to air-cool in its mould had a Rockwell B hardness of 83, and 0.2 percent yield strength of 49,500 psi and a 85 maximum elongation of 13 percent. When cooling was accelerated by the water quenching of the alloy shapemould composite, the alloy had a Rockwell B hardness of 82, and 0.2 percent yield strength of 42,500 psi and a maximum elongation of 17 percent. Further reductions in the Rockwell B hardness and the 0.2 percent yield strength to values of 80 and 42,000 psi respectively, accompanied by an increase in the maximum elongation to 25 percent were accomplished by annealing of the alloy shape at 2000°F. for 30 minutes after which 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 of similar treatments following casting. All of these physical characteristics reflect a substantial improvement over the properties of similar, but tin-free, corrosion resistant precision casting alloys known in the prior art.

The following Examples illustrate the preparation of preferred alloy compositions according to the present invention.

EXAMPLE I The alloy of the comparative composition 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 composition listed below. The molten alloy was cast into cast shapes to provide test specimens free from defects and having the physical characteristics also listed below:8 41785 Composition (% by weight) and properties Nickel 68.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 1.00 Gallium 1.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01 Proportional limit (psi) 31,600 0.2% Yield Strength (psi) 42,600 Ultimate Tensile St: rength (psi) 66,300 Elongation (%) 11 Rockwell B Hardne: ss 82 EXAMPLE II The alloy of the comparative composition was modified by the substitution of 2% by weight of gallium for the 2% by weight of tin present in the alloy to obtain a corrosion resistant dental alloy having the composition listed below. The molten alloy was oast into cast shapes to provide test specimens free from defects and having the physical characteristics also listed below.

Composition (% by weight) and properties Nickel 68.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 - 9 41785 Composition (% by weight) and properties (contd.) Gallium 2.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01 Proportional limit (psi) 44,700 0.2% Yield Strength (psi) 51,500 Ultimate Tensile Strength (psi) 79,000 Elongation (%) 14 Rockwell B Hardness 91 EXAMPLE III An alloy having the composition listed below was prepared in accordance with the procedure described in the comparative composition and test specimens were prepared by casting of the alloy to obtain defect-free cast alloy shapes having the physical characteristics also listed below.

Composition (% by weight) and properties Nickel 66.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 3.00 Gallium 1.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01 Proportional limit (psi) 38,600 0.2% Yield Strength (psi) 47,500 Ultimate Tensile Strength (psi) 69,800 - 10 41785 Elongation {%) Rockwell B Hardness EXAMPLE IV An alloy having the composition listed below was prepared in accordance with the procedure described in the comparative composition, and test specimens were prepared by casting of the alloy to obtain defectfree cast alloy shapes having the physical characteristics also listed below.

Composition (% by weight) and properties Nickel 66.25 Chromium 20,00 Molybdenum 4.50 Manganese 1.25 Tin 2.00 Gallium 2.00 Copper 1.50 Silicon 2.50 Carbon less than 0,01 Proportional Limit (psi) 37,000 0.2% Yield Strength (psi) 47,400 Ultimate Tensile Strength (psi) 73,600 Elongation (%) 11 Rockwell B Hardness 86 EXAMPLE V An alloy having the composition listed below was prepared in accordance with the procedure described in the comparative composition, and test specimens were prepared by casting of the alloy to obtain defect-free cast alloy shapes having the physical characteristics also listed below.

Composition (% by weight) and properties Nickel 66.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 1.00 Gallium 3.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01 Proportional Limit (psi) 37,200 0.2% Yield Strength (psi) 46,700 Ultimate Tensile Strength (psi) 68,700 Elongation {%) 9 Rockwell B Hardness 86 EXAMPLE VI An alloy having the composition listed below was prepared in accordance with the procedure described in the comparative composition, and test specimens were prepared by casting of the alloy to obtain defect-free cast alloy shapes having the physical characteristics also listed below.

Composition (% by weight) and properties Nickel 75.50 Chromium 15.00 Manganese 0.50 Gallium 7.50 Copper 1.50 Carbon less than 0.01 Proportional Limit (psi) 35,000 0.2% Yield Strength (psi) 42,500 Ultimate Tensile Strength (psi) 69,000 Elongation (%) 16 Rockwell B Hardness 72

Claims (8)

1. CLAIMSi1. A corrosion resistant hot-workable and hardenable precision casting alloy consisting of, in percentage by weight: Nickel at least 60 Chromium 10.00 to 25.00 Molybdenum 0.00 to 10.00 Manganese 0.50 to 1.50 Tin 0.00 to 9.00 Gallium 1.00 to 7.50 Copper 0.00 to 5.00 Silicon 0.00 to 4.00 Aluminium 0.00 to 2.00 Cobalt 0.00 to 5.00 Carbon 0.00 to 0.20 the combined total amount of tin and gallium not exceeding 10.00.

2. An alloy according to claim 1, in which the combined total amount of tin and gallium does not exceed 7,5% by weight.

3. A corrosion resistant alloy according to claim 2, comprising, in percentage by weight: Nickel 68.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Gallium 2.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01

4. A corrosion resistant alloy according to claim 2, comprising, in percentage by weight: Nickel 75.50 Chromium 15.00 Manganese 0.50 Gallium 7.50 Copper 1.50 Carbon less than 0.01

5. A corrosion resistant alloy according to claim 2, comprising, in percentage by weight: Nickel 66.25 20 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin. 3.00 Gallium 1.00 25 Copper 1.50 Silicon 2.50 Carbon less than 0.01

6. A corrosion resistant alloy according to claim 2, comprising in percentage by weight:14 Nickel 68.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 1.00 Gallium 1.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01

7. A corrosion resistant alloy according to claim 2, comprising, in percentage by weight: Nickel 66.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 2.00 Gallium 2.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01

8. A corrosion resistant alloy according to claim 2, comprising, in percentage by weight: Nickel 66.25 Chromium 20.00 Molybdenum 4.50 Manganese 1.25 Tin 1.00 Gallium 3.00 Copper 1.50 Silicon 2.50 Carbon less than 0.01