RU2517057C1 - Cobalt-based alloy for dentures of higher mechanical properties - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed alloy contains the following components in wt %: carbon - 0.36-0.55, silicon - 0.7-2.5, manganese- 0.25-1.00, chromium - 27.5-30.5, molybdenum - 3.5-6.0, tungsten - 0.55-1.55, boron - 0.03-0.10, nickel - not over 0.5 and iron - not over 0.3 Note here that total amount of molybdenum and tungsten does not exceed 4.5-7.0.

EFFECT: higher strength and lower melting point, sufficient linear expansion factor, antirust properties, machinability.

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Description

The invention relates to the field of metallurgy, in particular to cobalt-based alloys for orthopedic dentistry, intended for metal frames of complex clasp prostheses and highly loaded metal-ceramic bridge structures of great length.

These alloys must satisfy the following requirements:

1. In accordance with the international standard ISO 6871-1-94 “Dental casting alloys on a metal basis. Part 1. Alloys based on cobalt ”and the Russian standard GOST R 51389-99“ Procurement of corrosion-resistant alloys based on cobalt for orthopedic dentistry ”for the compositions of denture alloys based on cobalt, the following ratio Cr + Co + Ni≥85% must be fulfilled.

2. Alloys must have high mechanical characteristics, which is especially important for the manufacture of clasp prosthetic frames. Thus, alloys in accordance with the above standards should have a yield strength σ _0.2 ≥500 N / mm. However, based on the experience of dental practice, the yield strength of alloys for highly loaded clasp prostheses is preferably at least 650 MPa, and the elastic modulus (E) is at least 2.0 × 10 ⁵ MPa.

3. Alloys must have improved casting characteristics, ensuring defect-free precision casting of openwork clasp frames and thin-walled metal-ceramic dentures.

4. For the manufacture of cermet structures, the temperature coefficient of linear expansion (TEC) of the alloy must be low, close to that of the applied ceramic mass, and in addition, the alloy must have high adhesion to ceramics.

5. The alloy should be well machined with an abrasive tool and polished.

6. The alloy must be corrosion resistant and non-toxic. Known alloy for casting dentures containing the following components, wt.%:

Carbon ≤0.3 Silicon ≤3 Manganese ≤3 Chromium 20-35 Molybdenum 4-8 Tantalum, Niobium and / or Tungsten 0.05-1.2

each less than 0.5

Iron ≤3 Nitrogen 0.05-0.4 Inevitable impurities ≤1.0 Cobalt Rest

In a particular case, the alloy may contain boron up to 0.1 wt.% (German Patent No.19815091, IPC A61K 6/04, publ. 02/01/2001).

Alloying the alloy with elements such as niobium, tantalum and / or tungsten in combination with nitrogen and carbon leads to the formation of complex carbonitrides of the above elements, which reduce workability and impair polishability of the alloy. The presence of iron in the alloy (up to 3%) reduces the casting characteristics of the alloy, increasing shrinkage, degrades the quality of the oxide film and reduces the strength of the ceramic-metal bond.

Known alloy for ceramic-metal dentures based on cobalt containing the rare-earth element lanthanum and the following components, wt.%:

Chromium 15.0-30.0 Molybdenum 4.0-9.0 Lanthanum 0.03-0.30 Manganese 0-2.0 Silicon 0-3.0 Tungsten 0-10,0 Carbon 0-0.2 Cobalt Rest

(Patent CN 100422367 (C), IPC A61K 6/04, C22C 19/07, publ. 01.10.2008).

From the description of the patent it follows that the alloy has the following strength properties: tensile strength, σ _in = 800 MPa and yield strength, σ _0.2 = 680 MPa, which are quite sufficient for highly loaded metal-ceramic dentures of great length, but to ensure reliability and durability Clasps (fastenings in the form of hooks) of clasp prosthetic frames, it is desirable to have higher strength characteristics of the metal. In addition, the alloy contains a rare, expensive and scarce element lanthanum, which increases the cost of dental prosthetics using this metal.

A known alloy for dental ceramic-metal prostheses based on cobalt, with a low coefficient of thermal expansion, containing the following components, wt.%:

Carbon 0.1-0.3 Silicon 1-3 Manganese 0.3-0.8 Chromium 22-27 Molybdenum + Tungsten 10-15 Boron 0-1 Nickel <1 Iron <2 Cobalt Rest,

the temperature coefficient of linear expansion corresponds to 14.4 × 10 ^-6 deg ^-1 in the temperature range from 20 ° C to 600 ° C, and the tungsten content does not exceed 5%.

(European patent No. 0509910 B1, IPC С22С 19/07, А61К 6/04, published on July 6, 1994 - prototype).

The alloy has the following properties: tensile strength, σ _in = 890 MPa, yield strength, σ _0.2 = 700 MPa, elongation, δ = 4%.

Despite the fact that the prototype has higher values of tensile strength, σ _in , compared with the previous analogue, its yield strength remains at the same level, and the high content of molybdenum and tungsten in the composition of the alloy increases its melting point, and therefore for casting prostheses require more powerful melting plants, which may limit its use due to the lack of such melting equipment, for example, in small clinics or in rural areas. In addition, increased energy consumption and time of molten metal, which leads to an increase in the cost of prosthetics.

The problem to which the invention is directed is to create an alloy based on cobalt with improved mechanical characteristics for metal frames of complex clasp prostheses and for highly loaded metal-ceramic bridge structures of great length, combining the following set of properties: high mechanical (strength, ductility, elasticity, etc.) e.) and casting characteristics (with a reduced melting point), as well as corrosion resistance and non-toxicity, good machinability, according to lability and low values of thermal expansion coefficient, close to thermal expansion coefficient of ceramic mass, providing reliable ceramic-metal bonding.

The technical result of the invention is to increase the mechanical characteristics of the alloy (σ _in , σ _0.2 , δ) and lower the melting temperature while maintaining the level of thermal expansion coefficient, casting characteristics, corrosion resistance and non-toxicity, machinability and polishability.

The specified technical result is achieved in that the cobalt-based alloy for dentures with improved mechanical characteristics for highly loaded arch prostheses and for long-length metal-ceramic bridges containing carbon, silicon, manganese, chromium, molybdenum, tungsten, boron, nickel and iron, according to the invention contains components in the following ratio, wt.%:

Carbon 0.36-0.55 Silicon 0.7-2.5 Manganese 0.25-1.00 Chromium 27.5-30.5 Molybdenum 3,5-6,0 Tungsten 0.55-1.55 Boron 0.03-0.10 Nickel no more than 0.5 Iron no more than 0.3 Cobalt and inevitable impurities Rest,

the total content of molybdenum and tungsten is due to the following relationship:

[% Mo] + [% W] = 4.5-7.0.

When the carbon content in the alloy is less than 0.36%, high mechanical and casting characteristics are not provided, and when the carbon content is above 0.55%, the ductility of the alloy and workability are reduced.

If the alloy has a silicon content of less than 0.7%, corrosion resistance and casting characteristics are not ensured; doping with silicon over 2.5% is impractical, since the ductility of the alloy is reduced.

When the content of manganese alloy is less than 0.25%, sufficient fluidity of the alloy during casting is not provided, and more than 1.00% - ductility is reduced.

The chromium content in the alloy less than 27.5% reduces the strength of the alloy and corrosion resistance, and an increase in its content over 30.5% increases the hardness and worsens the polishability.

Alloying with molybdenum in an amount of less than 3.5% is inefficient, since corrosion resistance, strength and low level of thermal expansion coefficient are not ensured, and when its content is above 6.0%, ductility and workability are reduced, and the melting temperature also increases.

The content in the alloy of tungsten in an amount of less than 0.55% is ineffective, alloying up to 1.55% increases the strength and elasticity (E) of the alloy, and above 1.55% increases the melting temperature.

Alloying the alloy with boron in an amount of less than 0.03% is not effective, but in the range of 0.03-0.10% it increases the strength and ductility of the alloy due to the uniform distribution of excess phases in the alloy structure and contributes to a more dense an oxide film that enhances adhesion to ceramics.

The use of dentures made of alloys with a nickel content of more than 0.5% can lead to allergic reactions in the body of patients who are “sensitive” to nickel.

Iron in an amount of more than 0.3% increases the shrinkage of the alloy and affects the quality of the oxide film, which is responsible for the strength of the ceramic-metal compound.

If the sum of molybdenum and tungsten in the alloy is less than 4.5%, the strength and elasticity of the alloy are not provided, and if this amount is more than 7.0%, its melting point increases.

The invention is illustrated by the following example.

The alloy was smelted in a PIVK vacuum induction furnace on a clean charge with vacuum casting into a rectangular split mold in order to obtain cast rods with a diameter of 12 mm and a length of 200 mm. After cooling in air, the obtained rods were cut into cylindrical billets weighing ~ 15 g each, of which samples were cast by centrifugal casting according to the technology adopted in dental prosthetics laboratories of dental clinics, in accordance with ISO 6871-1-94 and GOST R 51389-99 which were then tested according to the techniques recommended in the above standards.

The strength of the ceramic-metal compound was investigated by the 3-point bending method according to GOST R 51736-2001 “Dental metal-ceramics for dental prosthetics”.

The chemical compositions of the proposed alloy and prototype alloy are shown in table 1, the properties in table 2.

From the above data it follows that the mechanical characteristics of the proposed alloy: strength (σ _in , σ _0.2 ) and ductility (δ) is higher, the melting temperature is lower at the same level of thermal expansion coefficient, providing a strong cermet bond. The elastic modulus of the proposed alloy is sufficiently high E≈2.26 · 10 ⁵ MPa, which is especially important for clasps clasp dentures that provide strength and reliability of fastening clasp prostheses.

The study of the strength of the ceramic-metal compound, fluidity, technological characteristics and corrosion resistance, as well as toxicological tests of the proposed alloy showed that the proposed alloy is corrosion-resistant and non-toxic, provides a strong ceramic-metal bond, is well cast, processed and polished, i.e. Meets all modern requirements for alloys for orthopedic dentistry; at the same time, the new alloy has higher strength characteristics that make it possible to cast thinner loaded denture frames from it at lower energy consumption (due to the lower melting temperature).

Table 1 The chemical composition of the proposed and known alloys based on cobalt No. Alloy Mass fraction,%; Co - the rest Dependence FROM Si Mn Cr Mo Ni Fe W AT Mo + W one Proposed 0.42 0.77 0.91 28.0 5.9 0.02 0.25 0.93 0.032 6.83 2 Proposed 0.51 1.20 0.51 29.2 3.9 0.23 0.18 0.61 0.088 4.51 3 Proposed 0.37 2.1 0.32 30.1 4.8 0.31 0.11 1.49 0.059 6.29 four Famous (prototype) 0.15 2.0 0.6 25.0 10.0 <0.6 <1.0 - - 10

table 2 Properties of the proposed and known cobalt-based alloys Alloys Mechanical characteristics Physical properties σ _in σ _0.2 5, % Ex10 ⁵ MPa TKLR, αx10 ^-6 deg ^-1 ΔT of melting, ° С MPa in the range 20-500 ° C 20-600 ° C one Proposed 930 770 6.0 2.25 14.19 14.28 1215- 2 Proposed 900 764 6.2 2,30 14.23 14.32 1340 3 Proposed 940 778 5.9 2.22 14.21 14.29 four Famous (prototype) 890 700 four - 14.2 1250-1370

Claims (1)

A cobalt-based alloy for highly loaded frameworks of clasp and metal-ceramic dentures containing carbon, silicon, manganese, chromium, molybdenum, tungsten, boron, nickel and iron, characterized in that it contains components in the following ratio, wt.%, To increase mechanical characteristics :
Carbon 0.36-0.55 Silicon 0.7-2.5 Manganese 0.25-1.00 Chromium 27.5-30.5 Molybdenum 3,5-6,0 Tungsten 0.55-1.55 Boron 0.03-0.10 Nickel no more than 0.5 Iron no more than 0,3 Cobalt and Inevitable Impurities Rest,
the total content of molybdenum and tungsten is due to the following relationship:
[% Mo] + [% W] = 4.5-7.0.