Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C45/00—Amorphous alloys
  • C22C45/10—Amorphous alloys with molybdenum, tungsten, niobium, tantalum, titanium, or zirconium or Hf as the major constituent

Definitions

• 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.
• 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., 10 6 K/s.
• very high cooling rates e.g. 10 6 K/s.
• most of these alloys cannot be cast into a bulk glassy structure at much lower cooling rates achievable with casting.
• 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 amorphous phase with a cooling rate of 1000 K/s or less, preferably with a cooling rate of 100 K/s or less. Cooling rates in this range are typically experienced in bulk casting operations.
• Bulk metallic glasses generally have mechanical properties that are superior to their crystalline counterparts. Due to the absence of a dislocation mechanism for plastic deformation, they often have a high yield strength and elastic limit. Furthermore, many bulk metallic glasses show good fracture toughness, corro ⁇ sion resistance, and fatigue characteristics. For an overview of the properties and areas of application of such materials see, for example, Johnson WL, MRS Bull. 24, 42 (1999) and L ⁇ ffler JF, lntermetallics 11 , 529 (2003). Reference is made explicitly to the disclosure of these documents and the references cited therein for teaching properties of glass-forming metallic alloys and methods for the determination of such properties. Commercial applications of bulk metallic glasses are described, e.g., in Buchanan O, MRS Bull. 27, 850 (2002).
• the alloy Zr4i.2Tii3.8Cui 2 .sNiioBe 2 2.s which has be- come known under the trade name Vitreloy 1 TM or Vit1 TM, and
• US Patent No. 5,737,975 discloses alloys of the general composition Zr- Cu-Ni-Al-Nb. Specifically, an alloy of composition Zr 57 CUi 54 NiI 2 GAIiONb 5 , which is known under the trade name Vitreloy 106TM or as Vit106TM, is dis ⁇ closed in this document.
• an alloy which contains at least four components A, D, E and G.
• a fifth component Z may be present.
• the alloy preferably has a bulk structure containing at least one amorphous phase, i.e., a volume fraction of at least 10%, preferably at least 50% of the alloy is amorphous.
• a structure is considered to be fully amorphous if the material having this structure does not exhibit significant Bragg peaks in an X-ray diffrac ⁇ tion pattern. Accordingly, the volume fraction of the amorphous phase in a mixed-phase material may be estimated by integrating the intensity of Bragg peaks and comparing with the intensity of non-Bragg features.
• the amorphous phase can be obtained by cooling from a tempera ⁇ ture above the melting point to a temperature below the glass-transition tem- perature of the amorphous phase with a cooling rate of 1000 K/s or less, i.e., preferably the alloy is a bulk metallic glass. More preferably, the amorphous phase can be obtained by cooling with a cooling rate of 100 K/s or less.
• the alloy with at least one amorphous phase can be obtained in a shape with dimensions of at least 0.1 mm, preferably at least 0.5 mm, more preferred at least 1 mm in any spatial direction. This is not possible for alloys which adopt an amorphous structure only at cooling rates as achiev ⁇ able by splat cooling or melt spinning.
• Component A consists of at least one element selected from the group consist ⁇ ing of Zr (zirconium), Hf (hafnium), Ti (titanium), Nb (niobium), La (lanthanum), Pd (palladium) and Pt (platinum).
• the other components D, E, G and, option ⁇ ally, Z are all different from each other and from component A.
• Each of these components may consist of more than one element, as long as all elements of all components are different.
• components D, E and G each consist of a single element.
• the alloy composition follows an "80:20 scheme", i.e., the ratio of the combined atomic content of components A and D to the combined atomic content of components E and G is approximately 80 to 20, within a band of plus or minus 10, preferably a band of plus or minus 5, in particular a band of plus or minus 2.
• the alloy composition is
• each index indicates the number of atoms contributing to a for ⁇ mula unit of the alloy.
• 58 atoms of Zr would be com- bined with 22 atoms of Cu, 8 atoms of Fe and 12 atoms of Al in order to arrive at one formula unit.
• a number is an "atomic percentage" this means that the number, when divided by 100, indicates the stoichiometry in the sense as it is usually understood in chemistry.
• Component A is the main component of the alloy, in the sense that x > 50 .
• x ⁇ 95 and more preferably x ⁇ 90 are not too small, preferably y > 5 , more preferred y > 10.
• the content should not be too large.
• y ⁇ 95 more pre ⁇ ferred y ⁇ 90.
• a fifth component Z is present at all, then it is present in a com ⁇ paratively small proportion only. In numbers, 0 ⁇ b ⁇ 6 , preferably 0 ⁇ b ⁇ 4 , more preferably 0 ⁇ b ⁇ 2.
• the numbers x, y, a and b are generally independent of each other.
• the alloy is substantially free of nickel.
• substantially free of nickel means that the total nickel content of the al- loy is less than 1 atomic percent, preferably less than 0.1 atomic percent. It may even be required that the nickel content is below 10 atomic ppm, e.g., in medi ⁇ cal applications.
• none of the components A, D, E, G or Z should comprise nickel.
• components A and E are miscible in a wide composition and tem ⁇ perature range.
• wide composition and temperature range is to be understood as a range extending over a temperature range of at least 600 K and over a range of compositions spanning at least 60 at.% of either component in the liquid state and below the liquidus temperature in the A-E phase diagram.
• a wide composition range would, e.g., be the range from 20 at.% to 80 at.% of component A in the binary mixture A-E.
• components A and E are capable of forming a deep eutectic composition in the absence of other components.
• the term ..capable of forming a deep eutectic composition is to be understood as meaning that, if A and E are mixed in the melt in the absence of other components, there is a composi ⁇ tion for which A and E are miscible down to the liquidus temperature, and the liquidus temperature of the mixture for that composition has a local minimum as a function of composition. In other words, when varying the composition in a small vicinity of a deep eutectic, the liquidus temperature is higher than at the composition of the deep eutectic itself.
• the liquidus temperature of the binary mixture at the deep eutectic will additionally be lower than the melting point of each of the components taken alone.
• 7 m (Au) 1337 K
• 7 m (Si) 1687 K
• the components are chosen such that a deep eutectic composition of the A-E mixture occurs at a composition A 9 Ei OO a' with 70 ⁇ a' ⁇ 90 , preferably 75 ⁇ a' ⁇ 85.
• the number a is preferably chosen such that the absolute value of the difference between a and a' is smaller or equal to 10 (i.e.,
• components A and D are miscible over a wide temperature and composition range. More preferably, they are capable of forming a deep eutec ⁇ tic composition when mixed in a binary mixture. If components A and D form a deep eutectic composition at A x Di O o-x', then x is preferably chosen such that
• component G is miscible with component E over a wide temperature and composition range, in particular if E is at least one element selected from the group consisting of the transition metals, in particular the group consisting of Fe and Co. It is then preferred that G is capable of forming a deep eutectic composition with component A.
• components G and E are capable of forming a deep eutectic composition at EyG 10 O- V 1 - Tnen y is preferably chosen such that
• a and G are preferably capable of forming a deep eutectic composition.
• the atomic Goldschmidt radius of each element in component A is relatively large, at least 0.137 nm, preferably at least 0.147 nm, more preferred at least 0.159 nm.
• the atomic Goldschmidt radius of each ele ⁇ ment in component A is at least 0.159 nm, then preferably 70 ⁇ a ⁇ 90 , if this radius is at least 0.147 nm, then preferably 75 ⁇ a ⁇ 85 , and if this radius is at least 0.137 nm, then preferably 78 ⁇ a ⁇ 82.
• the components A, D, E and G may have similar atomic radii and atomic prop ⁇ erties. However, it is preferred that the atomic radius of each element in com- ponent E is smaller than the atomic radius of each element in component A.
• the atomic (Goldschmidt) radii of the elements can be found tabulated in stan ⁇ dard textbooks or in the 2004 Goodfellow Catalog, available from Goodfellow Inc., Huntingdon, U.K. In particular, for selected elements, reference is made to Table 1 below.
• component D is preferably at least one element selected from the group consisting of Cu (copper), Be (beryllium), Ag (silver) and Au (gold).
• component A is at least one element selected from the group consisting of La (lanthanum), Pd (palladium) and Pt (platinum)
• component D is preferably Cu (copper).
• A is at least one element selected from the group consisting of Zr (zirconium), Hf (hafnium) and Ti (titanium)
• D is preferably Cu (copper) or Be (beryllium). Both copper and beryllium have deep eutectics with Zr, Hf and Ti.
• component E is preferably at least one metal selected from the group consisting of the transition metals except Ni (nickel); particularly Sc (scandium), Ti (titanium), V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Zn (zinc), Y (yttrium), Mo (molybdenum), Ta (tantalum), and W (tungsten).
• a transition metal is defined as any of the thirty chemical ele ⁇ ments with atomic number 21 through 30, 39 through 48, and 71 through 80. These metals are preferred because of their tendency to form deep eutectics with component A and because of their specific electronic properties.
• component E is preferably at least one metal selected from Fe (iron) and Co (cobalt). These metals have empirically been found to be preferred.
• Component G is preferably at least one element selected from the group con- sisting of Al (aluminum), Zr (zirconium), P (phosphorus), C (carbon), Ga (gal ⁇ lium), In (indium) and the metalloids, particularly B (boron), Si (silicon), and Ge (germanium).
• the known metalloids are B (boron), Si (silicon), Ge (germanium), As (arsenic), Sb (antimony), Te (tellurium), and Po (polonium). It is believed that the specific electronic properties of these elements favorably influence the glass-forming ability.
• the elements B, P, C, and Si have particu- larly small atomic sizes ( ⁇ 0.117 nm), which contributes to a large size differ ⁇ ence between the components A and G.
• component E is Fe (iron)
• component G is preferably selected from the group consisting of Al (aluminum), Zr (zirconium), P (phosphorus), B (boron), Si (silicon) and C (car ⁇ bon). More preferred, if component E is Fe (iron), then component G is Al (alu- minum). Then y is advantageously chosen to be in the range from about 30 to about 50, in particular approximately 40.
• component G is preferably at least one element selected from the group consisting of Zr (zirconium), Al (aluminum), B (boron), Si (silicon), Ge (germanium), Ga (gallium) and In (indium).
• 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 com ⁇ ponent D is Cu (copper). It has been found empirically that this combination leads to alloys with superior glass-forming ability.
• x is chosen be ⁇ tween 62 and 83 (i.e., 62 ⁇ x ⁇ 83 ), preferably 68 ⁇ x ⁇ 77 , in particular that x is approximately 72.5.
• component A is Zr and component D is Cu, it is further preferred that component E is Fe (iron) and component G is Al (aluminum).
• y is advantageously chosen to be in the range from about 30 to about 50, in particular approximately 40. Alloys of this composition, specifically, the alloy compositions in the vicinity of Zr 58 Cu 22 Fe S Ah 2 , have been found by the inven ⁇ tors to belong to the best glass formers known to date.
• component Z is preferably at least one ele ⁇ ment selected from the group consisting of Ti, Nb, Hf.
• component Z may preferably be at least one element selected from the group consisting of the transition metals, or component Z may preferably be at least one element selected from the group consisting of Be (beryllium), Y (yttrium), Pd (palladium), Ag (silver), Pt (platinum), and Sn (tin).
• component Z is pref- erably capable of forming a deep eutectic composition with component A.
• the alloy may have a structure comprising at least one amorphous phase and at least one crystalline phase.
• the volume fraction of the amorphous phase preferably is at least 10%.
• the amorphous and crystalline phases should not be macroscopically separated.
• Such a structure can be generated by different means.
• a composite comprising crystals embedded in an amorphous matrix is produced by subjecting the alloy to heat treatment at a temperature above the glass transition temperature. For details, see the de ⁇ scription of the preferred embodiments below.
• the alloy is subjected to electric currents, as described, e.g., in (Holland TB, L ⁇ ffler JF, Mu- nir ZA, J. Appl. Phys.
• the alloy composition in the melt is chosen to be initially outside the glass-forming region. During cooling, crystals start forming in the melt. This al- ters the composition of the mixture remaining in the melt, which is shifted into the glass-forming region. Upon further cooling, a glassy matrix with embedded crystals is formed. For details, see (Hays CC, Kim CP, Johnson WL, Phys Rev. Lett. 84, 2901 (2000)). In yet another approach, development of crystals in the amorphous matrix is fostered by a suitable choice of the fifth component Z.
• Suitable components Z are preferably at least one element selected from the group consisting of Ti, Nb, Ta, or at least one element selected from the group consisting of the transition metals, or at least one element selected from the group consisting of Be and Pd.
• Suitable components Z are preferably at least one element selected from the group consisting of Ti, Nb, Ta, or at least one element selected from the group consisting of the transition metals, or at least one element selected from the group consisting of Be and Pd.
• A is Zr (zirconium) and D is selected from the group consisting of Cu (copper) and Fe (iron).
• A is Zr (zirconium)
• D is Cu (copper)
• E is selected from the group consisting of Fe (iron) and Co (cobalt).
• G is pref ⁇ erably 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 con ⁇ cept, have favorable glass-forming properties.
• A is Zr (zirconium) and D is Cu (copper)
• D is Cu (copper)
• the ratio of these is chosen according to 62 ⁇ x ⁇ 83
• E j S Fe (iron) and F is Al (aluminum)
• their ratio is chosen according to 30 ⁇ y ⁇ 50 j ne combination of these ranges, together with the general 80:20 concept, defines a region of quaternary compounds with exceptionally good glass-forming properties.
• Zr-Fe-AI-(Pd/Pt) system Another system having excellent glass-forming properties if following the 80:20 concept is the Zr-Fe-AI-(Pd/Pt) system.
• This system has the additional advan ⁇ tage that it is free of copper.
• A is Zr (zirconium)
• D is Fe (iron)
• E is Al (aluminum)
• G is one or both elements selected from Pd (palladium) and Pt (platinum).
• 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.
• Z is preferably at least one element se- lected from the group consisting of Ti, Hf, V, Nb, Y, Cr, Mo, Fe, Co, Sn, Zn, P, Pd, Ag, Au and Pt.
• Excellent glass-forming abilities were achieved in examples where X was Pd, while a slightly improved biocompatibil- ity may be expected by partially or fully replacing Pd by Pt, which has very simi ⁇ lar properties as Pd.
• Preferred ranges are (independently or in combination) ⁇ l ⁇ i ⁇ ll , 19 ⁇ y ⁇ 34 , and ⁇ ⁇ 2.
• ⁇ is substantially zero, i.e., the atomic percentages of Fe and Al are approximately equal.
• ⁇ is substantially zero, 66 ⁇ i ⁇ 70 , 25 ⁇ j ⁇ 29 and 4 ⁇ k ⁇ 7 .
• the best glass formers of this system also conform to the 80:20 concept as described above.
• alloys being substantially represented by one of the following for ⁇ mulas were found to be good glass formers:
• the alloy has a structure comprising at least one amorphous phase and at least one crystalline phase.
• the at least one amorphous phase is pref ⁇ erably obtainable by cooling from a temperature above the melting point of the alloy to a temperature below the glass-transition temperature of the amorphous phase at a cooling rate of 1000 K/s or less, i.e., the alloy is preferably a bulk metallic glass.
• the present invention is further directed at a method of manufacture of the in- ventive alloys.
• the method comprises preparing a melt of aliquots of A, D, E, G, and optionally Z, and cooling the melt from a temperature above the melting point to a tern- perature below the glass-transition temperature of the amorphous phase with a cooling rate of 1000 K/s or less to obtain a solidified material.
• the method comprises casting of the melt into a mold, in particular, a copper mold.
• the inventive alloys may be produced by mechanical alloying, as described, e.g., in (Eckert J, Mater. Sci. Eng. A 226-228, 364 (1997): Mechani ⁇ cal alloying of highly processable glassy alloys).
• Mechanical alloying means mechanical processing of the alloy or its constituents in the solid state, without passing through the liquid state.
• an amorphous metallic alloy may be obtained.
• Suitable me ⁇ chanical alloying methods include, but are not restricted to, ball milling. For de ⁇ tails, explicit reference is made to the teachings of the above-mentioned Eckert paper.
• the method may additionally comprise a step of processing the alloy above the glass transition temperature, e.g., for obtaining a mixed-phase material.
• the method may comprise a step of heat-treating the solidified material for a few minutes up to 15 hours at a temperature below the first crystallization temperature or for a few seconds up to 2 hours at a temperature above the first crystallization temperature.
• the first crystallization temperature is the tempera ⁇ ture of the first exothermic feature in a DTA scan of the amorphous alloy when the temperature is raised from the glass transition temperature. Heat treatment at relatively low temperatures results in slow kinetics, which is believed to lead to the formation of small crystals. For details, see the description of the pre- ferred embodiments below.
• the alloy may be sub ⁇ jected to a microstructuring process as described, e.g., in (Kundig AA, Cucinelli M, Uggowitzer PJ, Dommann A, Microelectr. Eng. 67, 405 (2003): Preparation of high aspect ratio surface microstructures out of a Zr-based bulk metallic glass) or in the patent application PCT/CH 2004/000401.
• Microstructuring may be achieved by casting the liquid alloy into a mold having itself a micro- structured surface.
• Kundig et al. paper and to PCT/CH 2004/000401 are examples of the above- mentioned Kundig et al.
• an already solidified alloy is brought into a superplastic state, i.e, into a state in which it can be easily shaped, by heating the alloy to a temperature above the glass-transition temperature, and is pressed onto a microstructured matrix.
• the microstructured mold resp. matrix is a silicon wafer which has been structured by etching, as it is well known in the art.
• the liquid alloy is drawn into a system of capillaries by the capillary effect and rapidly solidified within the capillaries.
• PCT/CH 2004/000401 the teachings of the application PCT/CH 2004/000401.
• the invention is also directed at the use of an inventive alloy for the manufac- ture of an article destined to be brought into contact with the human or animal body.
• the invention is directed at the use of such an alloy for the manufacture of a surgical instrument, a jewelry item, in particular a watch case, or a prosthesis, in particular an endoprosthesis, specifically, a so-called stent.
• a stent is an endoprosthesis for insertion into a blood vessel, lining the inner sur- face of the vessel. Stents are used in particular for ensuring sufficient blood flow through the vessel, or for stabilizing the blood vessel to prevent aneurisms.
• inventive alloys are in the field of os ⁇ teosynthesis, e.g., hip implants, artificial knees, etc.
• inventive alloys are in the field of os ⁇ teosynthesis, e.g., hip implants, artificial knees, etc.
• the present invention is also directed at an endoprosthesis, in particular a stent, manufactured from an inventive alloy.
• inventive alloys are particularly suited for such biomedical applications due to their good biocompatibility, high strength and high elasticity.
• inventive alloys of general composition Zr-Cu-Fe-Al or Zr-Fe-Al-Pd are well suited for these purposes.
• Fig. 1 shows a strongly simplified, schematic phase diagram of a binary Zr-Fe alloy
• Fig. 2 shows a strongly simplified, schematic phase diagram of a binary
• Fig. 3 shows a strongly simplified, schematic phase diagram of a binary
• FIG. 4 shows XRD patterns of as-cast 1 mm x 1 cm 2 alloys of composi ⁇ tion Zr 5 4. 4 Cu2 5 .6Fe8Ali2, Zr 58 Cu 22 Fe 8 AIi 2 , and Zr 6 I eCUi 84 Fe 8 AIi 2 ;
• Fig. 6 shows DTA scans on samples of composition Zr 544 Cu 25-6 Fe 8 AIi 2 ,
• Fig. 7 shows a DTA scan of Zr 58 Cu 22 Fe 8 AIi 2 , performed with a heating rate of 20 K/min;
• Fig. 8 shows a photograph of cast samples of composition
• Fig. 9 shows XRD patterns of Zr 58 Cu 22 Fe 8 AIi 2 cast to cylindrical rods of diameters 5, 7 and 8 mm, and to a plate of 1 mm thickness (inset);
• Fig. 10 shows DTA scans of Zr 58 Cu 22 Fe 8 AI 12 cast to cylindrical rods of diameters 5, 7 and 8 mm (heating rate 20 K/min);
• Fig. 11 shows XRD patterns of Zr 544 Cu 256 Fe 8 AIi 2 cast to a cone with outer diameter 6 mm
• Fig. 12 shows a DTA scan of Zr 6L eCUi 84 Fe 8 AIi 2 , performed with a heating rate of 20 K/min;
• Fig. 13 shows a SEM image showing the fracture surface of glassy
• Fig. 14 shows a room-temperature tensile stress-strain curve of an as- cast cylindrical Zr 58 Cu 22 Fe 8 AI 12 sample with a diameter of 5 mm;
• Fig. 15 shows XRD patterns of Zr 58 Cu 22 Fe 8 AI 12 in the as-prepared state and after annealing for several hours at different temperatures;
• Fig. 16 shows an XRD pattern (72 hours scan) of Zr 58 Cu 22 Fe 8 AI 12 after annealing at 708 K for 12 h.
• the indexing shows an icosahedral phase with a lattice constant of 4.76 A;
• Fig. 17 shows DTA scans of Zr 58 Cu 22 Fe 8 AI 12 in the as-prepared state and after annealing for several hours at different temperatures, as indi ⁇ cated in the figure (heating rate 20 K/min);
• Fig. 18 shows SANS intensity data of Zr 58 Cu 22 Fe 8 AI 12 obtained from in- situ SANS measurements performed at a temperature of 708 K at different times, as indicated in the figure;
• Fig. 19 shows the time evolution of the particle size, ⁇ , of Zr 58 Cu 22 Fe 8 AI 12 using the Guinier approximation;
• Fig. 20 shows a pseudoternary mixing diagram
• Fig. 21 shows a DTA scan of the alloy Zr 68 ⁇ F ⁇ o.sAlo.sW ⁇ Pd-i. ⁇ cast to a thickness of 1 mm; and Fig. 22 shows an X-ray diffraction pattern of the alloy
• inventive alloys Before describing specific examples of inventive alloys and their characteriza- tion, the concept which led to the development of the inventive alloys shall be described and exemplified.
• nickel improves the glass-forming abilities of an alloy, making nickel an essential component of many quaternary bulk glass- forming alloys, and especially of Zr-based alloys, it has been found by the in ⁇ ventors that nickel can be dispensed with by following the principles of the pre ⁇ sent invention, while still alloys with excellent glass-forming abilities are ob ⁇ tained.
• Zr and Cu have eutectic compositions, one of which occurs at 72.5% Zr, as illustrated in Fig. 2.
• This diagram shows, again in a highly schematic fashion, the liquidus line. At various compositions between 38.2 at.% and 72.5 at.%, several other eutectics are expected.
• the fourth component in the above-mentioned general composition is Al.
• Fig. 3 shows, again in a highly schematic fashion, part of the phase diagram of a bi ⁇ nary Al-Fe alloy. Several solid-solid transitions have been included in this dia ⁇ gram.
• a high-temperature phase the so-called £>-phase 301 , is present around the composition AIeFe 4 .
• This phase prevents a deep eutectic to be present at around 60 at.% in the Al-Fe phase diagram, which would other ⁇ wise be expected by extrapolation, as indicated by the dotted line in Fig. 3.
• the concept is believed to be generally applicable and not to be restricted to the particular Zr-Cu-Fe-Al system described above.
• the same considerations may be applied to alloys which are based on Ti, Hf, Nb, La, Pd or Pt as a main component.
• other elements having a deep eutectic with the main component may be employed.
• Particularly good candidates are Be, Ag and Au.
• the Fe component may be replaced by one or more of the transition metals except Ni, e.g. by Co.
• the Al component may be replaced by, e.g., Zr or one or more of the metalloids.
• Example 1 Preparation and characterization of amorphous (Zr x Cuioo-x)8o(Fe4oAI 6 o)2o samples
• Ingots were prepared by arc melting the constituents (purity > 99.9%) in a titanium-gettered argon atmosphere (99.9999% purity). Using an induction-heating coil, the ingots were remelted in a quartz tube (vacuum « 10 "5 mbar) and injection cast into a copper mold with high-purity argon.
• Samples were cast into plates with a thick ⁇ ness of 0.5 mm, width of 5 mm and length of 10 mm. To determine the critical casting thickness, some samples were additionally or alternatively cast into various rod- and cone-like shapes with diameters ranging up to 10 mm. Fur ⁇ thermore, several samples were made with a thickness of 1 mm and cross sec- tion 1 cm x 4 cm. The samples were then, where appropriate, cut into various pieces of length 1 cm and investigated by X-ray diffraction (XRD), small-angle neutron scattering (SANS), differential thermal analysis (DTA) and/or hardness measurements.
• XRD X-ray diffraction
• SANS small-angle neutron scattering
• DTA differential thermal analysis
• the Ni- bearing alloy Zr 65 AI 75 Ni I oCUi 75 was also investigated by DTA. This result is also shown in Fig. 6 for comparison.
• Table 2 gives the characteristic values extracted from DTA scans like those of Figs. 6 and 7.
• the glass transition temperatures T 9 were extracted from the on ⁇ set of the endothermic events in Fig. 6 (arrows pointing up) and the first crystal ⁇ lization temperatures T x1 were obtained from the onset of the exothermic peaks (arrows pointing down).
• the onset of melting T m and the offset of melting 7 ⁇ were obtained from scans like that in Fig. 7.
• Table 2 lists the ratios of r g /7 m also, since in many publications this ratio has been used as the reduced glass transition temperature.
• the value of T g IT m is 0.59 to 0.62 for the new Ni-free alloys and thus significantly larger than that Of Zr 65 AI 75 Ni 10 Cu 175 .
• undercooled liquid region AT x T x1 - T 9 , liquidus temperature (offset of melting) 7
• Fig. 9 shows X-ray diffraction patterns Of Zr 58 Cu 22 Fe 8 AI 12 cast to cylindrical rods of diameters 5, 7 and 8 mm, and to a plate of 1 mm thickness (inset).
• No Bragg peaks are apparent either in the 5 mm rod sample or in the 1 mm plate, while only very weak Bragg peaks seem to arise in the 7 mm rod sample.
• a clear crystalline component is present in the 8 mm rod sample, as apparent from the strong Bragg peaks from that sample.
• the XRD scans were performed on 0.5 mm thick plates cut perpendicularly to the longitudinal axis of the cone. The average diameter of the corresponding plates is given in the figure.
• the XRD patterns of the plates with diameters of 5 mm or less show typical amorphous structures, while the plate with 6 mm diameter appears to show some Bragg peaks indicat ⁇ ing a small volume fraction of crystals in the amorphous matrix. This is perfectly consistent with the findings for rods with uniform diameter.
• These experimental results agree well with the Turnbull theory (D. Tumbull, Contemp. Phys. 10, 473 (1969), F. Spa- epen and D. Turnbull, Proc. Sec. Int. Conf. on Rapidly Quenched Metals (Cam ⁇ bridge, Mass.: M. IT. Press, 1976), pp. 205-229), which predicts that the best glass-forming ability is obtained for the alloy with the highest ratio of T 9 IT] (see Table 2).
• the composition of the material can be var ⁇ ied within rather broad limits without losing the good glass-forming properties. Specifically, it may be expected that a variation in the composition with respect to the other constituent elements, in particular a moderate variation of the num- bers a and y, will not alter the glass-forming ability dramatically. Furthermore, it is expected that addition of a small amount of an additional component will not negatively affect the glass-forming ability or even possibly improve the glass- forming ability of the inventive materials, while possibly improving certain de ⁇ sired properties.
• Samples with a mixed-phase structure were prepared as follows: Fully amor ⁇ phous samples of Zr 58 Cu 22 Fe 8 AI 12 were prepared as in Example 1. The samples were subjected to heat treatment (annealing) at various temperatures for 12 hours. XRD patterns and DTA scans were recorded for the heat-treated sam ⁇ ples. Fig. 15 shows XRD patterns of the samples in the as-prepared state (bot ⁇ tom trace) and after annealing. The XRD patterns show typical amorphous structures up to an annealing temperature of 683 K. At higher annealing tem ⁇ peratures, however, clear Bragg peaks arising from an icosahedral phase (I. P.) can be observed.
• Fig. 16 shows the XRD pattern of the sample an- nealed at 708 K for 12 hours in more detail. The indexing indicates the pres ⁇ ence of an icosahedral phase with a lattice constant of 0.476 nm.
• Fig. 17 shows DTA scans of the same samples as in Fig. 15, which are consistent with the development of a structure with both glassy and crystalline components.
• the laboratory glass transition temperature is to be understood as the glass transition temperature as determined by DSC (differential scanning calorimetry) with a typical heating rate of 20 K/min. Higher annealing temperatures often lead to the precipitation of larger crystals; for example in the range of 0.1 - 20 ⁇ m.
• Such mixed-phase materials exhibit somewhat different mechanical properties than a fully glassy material.
• ductility is often improved, which can be rationalized by the fact that shear bands which develop as a result of shear forces during forming and which might lead to breaking of the material are dis ⁇ rupted by the crystals. These properties may be particularly beneficial in appli- cations where the material must be shaped or deformed during manufacture of the end product.
• Example 3 Variations of composition Samples in a widely varying range of compositions were prepared andomme ⁇ gated.
• the compositions of the following Tables proved to be at least partially amorphous when cast to a plate with thickness of 1 mm (Table 4), 0.5 mm (ta ⁇ ble 5), or 0.2 mm (Table 6):
• Table 4 Alloys having a partially or fully amorphous structure when cast to a thickness of 1 mm.
• Table 6 Alloys with a partially or fully amorphous structure when cast to a thickness of 0.2 mm.
• alloys in Table 7 While being binary, ternary or Ni- containing alloys, were also investigated and developed an at least partially amo ⁇ hous structure when cast to a thickness of 0.2 mm.
• Table 7 Comparative listing of other alloys with a partially or fully amorphous structure when cast to a thickness of 0.2 mm.
• this list shows that also ternary, nickel-free alloys can be reasona ⁇ bly good glass-formers, especially if composed according to the "80:20 scheme".
• the list shows that ternary alloys of composition (Zr x D 100-x )aFe 100-a , where the number a is in the range from about 70 to about 90, in particular approximately 80, are good glass formers.
• D is advanta ⁇ geously Cu, Nb, Al or Sn.
• the alloys in Table 8 have also been prepared and were found to be fully amor- phous when subjected to splat cooling to a thickness of 20 micrometers at high cooling rates of approximately 10 6 K/s. These alloys may be regarded as candi ⁇ date materials for bulk metallic glasses, while casting experiments will be nec ⁇ essary to verify which of these are indeed bulk metallic glasses.
• Table 8 Alloys having a fully amorphous structure when splat-cooled. All num ⁇ bers are atomic percentages.
• Table 9 Ternary and binary alloys having a fully amorphous structure when splat-cooled.
• the cytotoxicity of the al ⁇ loy Zr 58 Cu22Fe8Ali2 was determined.
• the effect of surface modification by pas- sivation in diluted nitric acid was also investigated.
• the thickness of the zirconia layer is only slightly increased by passivation with nitric acid. However, this treatment clearly improves the quality of the surface layer, which leads to increased corrosion resistance and lower diffusion of bulk elements into the medium, and thus to improved biocompatibility.
• the alloy shows cell growth comparable to that on polysty- rene, which is used here as a negative control.
• Table 10 Cu-free Zr-Fe-Al-Pd alloys having a partially or fully amorphous struc ⁇ ture when cast to a thickness of 3 mm
• Table 11 Cu-free Zr-Fe-Al-Pd alloys having a partially or fully amorphous struc ⁇ ture when cast to a thickness of 1 mm
• Table 12 Cu-free Zr-Fe-Al-Pd alloys having a partially or fully amorphous struc- ture when cast to a thickness of 0.5 mm
• Tables 10, 11 and 12 are indicated by black squares in the pseudoternary mixing diagram of Fig. 20. From this diagram, it may be appreci ⁇ ated that alloys containing at least 50 at.-% Zr, at least 0.5 at.-% Pd and at least 19 at.-% of a mixture of Fe and Al in approximately equal atomic proportions are expected to be good glass formers. This is even more true for alloys of this type containing at least approximately 59 at.-% of Zr, up to approximately 36 at.-% of the Fe-Al mixture and/or at least approximately 4 at.-% Pd. In particular, all al ⁇ loys in the trapezoidal area indicated in Fig. 20 may reasonably be expected to be good glass formers. Small variations of the relative proportions between Fe and Al within a few percent, say, between 60:40 and 40:60 or better between 55:45 and 45:55, are not expected to strongly affect the glass-forming ability.
• the ratio of the atomic percentage of Zr to the atomic percentage of Fe is in the range between approximately 76:24 and approxi ⁇ mately 89:11. It appears that this is a preferred range. In particular, in the ex ⁇ amples of Table 10, this ratio varies between approximately 81 :19 and ap ⁇ proximately 85:15. In contrast, the ratio between Al and Pd may apparently vary in a wider range without detrimental effects on the glass-forming ability of the alloy.
• the ratio of the atomic percentage of Al to the atomic percentage of Pd varies between approximately 40:60 and ap ⁇ proximately 82:18. In particular, in the examples of Table 10, this ratio varies between approximately 65:35 and approximately 78:22.
• Pt platinum
• Pt (platinum) has very similar properties as Pd, such as outer electronic structure, in consequence, similar chemical properties, and almost the same Goldschmidt radius. Therefore, a par ⁇ tial or full replacement of Pd by Pt will not strongly alter the mechanical proper- ties of the alloy or its glass-forming ability.
• Fig. 21 shows a DTA scan
• Fig. 22 shows an X-ray diffraction pattern, using a Co- K 0 X-ray source, of the alloy cast to a thickness of 1 mm.
• the DTA scan exhibits a clear glass transition and a second crystallization event, while the X-ray diffraction pattern exhibits the broad hump indicative of an amorphous material.
• a further example of an alloy found to be at least partially amorphous when cast to a thickness to 0.2 mm is Zr 70 Fe 28 NbiSni .

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