Amorphous Alloys on the Base of Zr and their Use

Abstract

An alloy is disclosed which contains at least four components. The alloy has a bulk structure containing at least one amorphous phase. The alloy composition follows an “80:20 scheme”, i.e., the alloy composition is [(AxD100−x)a(EyG100−y)100−a]100−bZb with the number “a” being approximately 80. Preferably, component A is Zr. The other components D, E, G and, optionally, Z are all different from each other and different from component A. A preferred system is Zr—Cu—Fe—Al. Further disclosed are Cu-free systems of the type Zr—Fe—AI-Pd / Pt. Importantly, the alloy is substantially free of nickel. This makes the alloy especially suitable for medical applications. Methods of preparing such an alloy, uses of the alloy and articles manufactured from the alloy are also disclosed.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an alloy with the features of the preamble of claim 1 or 19, to the use of such an alloy, and to articles manufactured from such an alloy, in particular implants such as endoprostheses.BACKGROUND OF THE INVENTION[0002]A number of alloys may be brought into a glassy state, i.e., an amorphous, non-crystalline structure, by splat cooling at very high cooling rates, e.g., 106 K / s. However, most of these alloys cannot be cast into a bulk glassy structure at much lower cooling rates achievable with casting.[0003]In recent years, many bulk metallic glass-forming liquids have been discovered for which cooling rates of less than 1000 K / s are sufficient for vitrification. For the purposes of this document, a “bulk metallic glass” is to be understood as an alloy which develops an at least partially amorphous structure when cooled from a temperature above the melting point to a temperature below the glass-transition temperature of the...

AI Technical Summary

Benefits of technology

[0023]It is therefore an object of the present invention to provide an alloy which has good glass-forming ability and an improved biocompatibility, in particular, an alloy which does not release nickel in contact with body liquids.

[0025]It is another object of the present invention to provide an alloy which has good glass-forming ability and an improved biocompatibility, in particular, an alloy which is essentially free of both copper and nickel.

[0045]In a preferred embodiment, component A is Zr (zirconium) or a mixture of Zr (zirconium) with either Hf (hafnium) or Ti (titanium) or both wherein at least 80 atomic percent of component A is Zr (zirconium). It is then preferred that component D is Cu (copper). It has been found empirically that this combination leads to alloys with superior glass-forming ability.

[0050]Specifically, it is preferred that A is Zr (zirconium), D is Cu (copper), and E is selected from the group consisting of Fe (iron) and Co (cobalt). Then G is preferably at least one element selected from the group consisting of Al (aluminum) and the metalloids. A particularly preferred system is the Zr—Cu—Fe—Al system, i.e., A is Zr (zirconium), D is Cu (copper), E is Fe (iron) and G is Al (aluminum). It has been found that alloys of this composition, when following the 80:20 concept, have favorable glass-forming properties.

[0053]Another system having excellent glass-forming properties if following the 80:20 concept is the Zr—Fe—Al—(Pd / Pt) system. This system has the additional advantage that it is free of copper. In other words, preferably A is Zr (zirconium), D is Fe (iron), E is Al (aluminum), and G is one or both elements selected from Pd (palladium) and Pt (platinum). Specifically, excellent glass formers have been found if G is palladium, while a slightly improved biocompatibility may result by partially or fully replacing Pd by Pt. In this connection, it is to be noted that Pd and Pt are known to occupy the same group of the periodic system of elements, and have a similar (outer-shell) electronic structure, almost the same Goldschmidt radius and a similar chemical behaviour. It is therefore to be expected that Pd may be replaced by Pt without dramatic changes in the glass-forming properties of the alloys. In these systems, it has been found to be advantageous if the atomic percentages of Fe and Al are substantially equal. A range of good glass formers was found for 68≦x≦89 and 73≦a≦87. Particularly good results were achieved for 81≦x≦85, 80≦a≦83, and 65≦y≦80, in particular if G was Pd. The ratio of Al to Pd / Pt is favourably chosen according to 40≦y≦82.

Problems solved by technology

However, most of these alloys cannot be cast into a bulk glassy structure at much lower cooling rates achievable with casting.

Due to the absence of a dislocation mechanism for plastic deformation, they often have a high yield strength and elastic limit.

Exposure to nickel is known to possibly cause allergies.

Therefore these alloys are not well suited for medical applications, in which the alloy can come into contact with body fluids, with the skin, with tissue or other body parts.

Specifically, these alloys may cause allergic reactions because they tend to release small amounts of nickel when they come into a prolonged contact with the body.

Copper (Cu) may also be problematic, albeit to a lesser extent.

However, these alloys are not bulk metallic glasses; they are only amorphous when using melt spinning or splat quenching.

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