Background This invention relates to amorphous metallic alloys, commonly referred to metallic glasses, which are formed by solidification of alloy melts by cooling the alloy to a temperature below its glass transition temperature before appreciable nucleation and crystallization has occurred.

There has been appreciable interest in recent years in the formation of metallic alloys that are amorphous or glassy at low temperatures. Ordinary metals and alloys crystallize when cooled from the liquid phase. It has been found, however, that some metals and alloys can be undercooled and remain as an extremely viscous liquid phase or glass at ambient temperatures when cooled sufficiently rapidly. Cooling rates in the order of 10 ⁴ to 10 K/sec are typically required. To achieve such rapid cooling rates, a very thin layer (e.g., less than 100 micrometers) or small droplets of molten metal are brought into contact with a conductive substrate maintained at near ambient temperature. The small dimension of the amorphous material is a consequence of the need to extract heat at a sufficient rate to suppress crystallization. Thus, most previously developed amorphous alloys have only been available as thin ribbons or sheets or as powders.

The resistance of a metallic glass to crystallization can be related to the cooling rate required to form the glass upon cooling from the melt. It is desirable that the cooling rate required to suppress crystallization be in the order of from 1 K/s to 10 ³ K/s or even less. As the critical cooling rate decreases, greater times are available for processing and larger cross sections of parts can be fabricated. Further, such alloys can be heated substantially above the glass transition temperature without crystallizing during time scales suitable for industrial processing.

Recently, alloys of zirconium and/or titanium, copper and/or nickel, other transition metals and beryllium have been found which form amorphous bodies of substantial thickness. It would be desirable to provide amorphous alloys that have a low critical cooling rate and are substantially free of beryllium.

Brief Summary of the Invention

Thus, there is provided in practice of this invention according to a presently preferred embodiment a class of at least quaternary alloys which form metallic glass upon cooling below the glass transition temperature at a rate less than 10 ³ K/s. Two alloy compositions have been found to form amorphous solids with cooling rates that permit formation of objects

with all dimensions being at least one millimeter. In other words, a sheet of such alloy has a thickness of at least one millimeter.

One such group of alloys comprises titanium in the range of from 19 to 41 atomic percent, an early transition metal (ETM) in the range of from 4 to 21 atomic percent and copper plus a late transition metal (LTM) in the range of from 49 to 64 atomic percent. The early transition metal comprises zirconium and/or hafnium. The late transition metal comprises cobalt and/or nickel. The composition is further constrained such that the product of the copper plus LTM times the atomic proportion of LTM relative to the copper is in the range of from 4 to 14. The atomic percentage of ETM is less than 10 when the atomic percentage of titanium is as high as 41, and may be as large as 21 when the atomic percentage of titanium is as low as 24. The atomic percentage of ETM is always less than a line connecting those values.

Stated somewhat more rigorously, the atomic percentage of early transition metal is less than 10 plus (ll/17) ^β (41 - a) where a is the atomic percentage of titanium present in the composition.

In addition, there are upper limits on the amount of LTM when the total of copper and LTM is low. Thus, when copper plus LTM is in the range of from 49 to 50 atomic percent, LTM is less than 8 atomic percent, when copper plus LTM is in the range of from 50 to 52 atomic percent, LTM is less than 9 atomic percent, and when copper plus LTM is more than 52 atomic percent, LTM is no more than 10 atomic percent. This can be stated by the formula

Ti _a (ETM) _b (Cu ₁ . _x (LTM) _x ) _c where ETM is selected from the group consisting of Zr and Hf , LTM is selected from the group consisting of Ni and Co, x is atomic fraction, and a, b, and c are atomic percentages, wherein a is in the range of from 19 to 41 , b is in the range of from 4 to 21 , and c is in the range of from 49 to 64. There are the additional constraints that 2 < x«c < 14 and b < 10 + (11/17)»(41 - a). Other constraints are that when 49 < c < 50, then x < 8; when 50 < c < 52, then x < 9; when 52 ≤ c, then x ≤ 10. Another group of glass forming alloys has the formula (ETM ₁ . _x Ti _x ) _a Cu _b (Ni ₁ . _y Cθ ) _c where ETM is selected from the group consisting of Zr and Hf, x is atomic fraction, and a, b, and c are atomic percentages, wherein x is in the range of from 0.1 to 0.3, y»c is in the range of from 0 to 18, a is in the range of from 47 to 67, b is in the range of from 8 to 42, and c is in the range of from 4 to 37. This definition of the alloys has the additional constraints that (i) when a is in the range of from 60 to 67 and c is in the range of from 13 to 32, b is given by: b ≥ 8 + (12/7) ^» (a - 60); (ii) when a is in the range of from 60 to 67 and c is in the range of from 4 to 13, b is given by: b ≥ 20 + (19/10)«(67 - a); and (iii)

when a is in the range of from 47 to 55 and c is in the range of from 11 to 37, b is given by: b < 8 + (34/8)»(55 - a).

Either of these groups of alloys may also comprise up to about 4% other transition metals and a total of no more than 2% of other elements.

Brief Description of the Drawings

These and other features and advantages of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein FIG. 1 is a quasi-ternary composition diagram indicating a glass forming region of alloys provided in practice of this invention; and

FIG. 2 is another quasi-ternary composition diagram indicating a related glass forming alloy region.

Detailed Description

For purposes of this invention, a metallic glass product is defined as a material whic contains at least 50% by volume of the glassy or amorphous phase. Glass forming abilit can be verified by splat quenching where cooling rates are in the order of 10 ⁶ K/s. Mor frequently, materials provided in practice of this invention comprise substantially 100 amorphous phase. For alloys usable for making parts with dimensions larger tha micrometers, cooling rates of less than 10 ³ K/s are desirable. Preferably, cooling rates t avoid crystallization are in the range of from 1 to 100 K/sec or lower. For identifyin preferred glass forming alloys, the ability to cast layers at least one millimeter thick has bee selected. Compositions where cast layers 0.5 mm thick are glassy are also acceptable.

Generally speaking, an order of magnitude difference in thickness represents tw orders of magnitude difference in cooling rate. A sample which is amorphous at a thicknes of about one millimeter represents a cooling rate of about 500 K/s. The alloys provided i practice of this invention are two orders of magnitude thicker than any previously know alloys which are substantially entirely transition metals.

Such cooling rates may be achieved by a broad variety of techniques, such as castin the alloys into cooled copper molds to produce plates, rods, strips or net shape parts o amorphous materials with thicknesses which may be more than one millimeter.

Conventional methods currently in use for casting glass alloys, such as splat quenchin for thin foils, single or twin roller melt-spinning, water melt-spinning, or planar flow castin of sheets may also be used. Because of the slower cooling rates feasible, and the stabilit of the amorphous phase after cooling, other more economical techniques may be used fo making net shape parts or large bodies that can be deformed to make net shape parts, suc as bar or ingot casting, injection molding, powder metal compaction and the like. A rapidly solidified powder form of amorphous alloy may be obtained by an atomization process which divides the liquid into droplets. Spray atomization and ga atomization are exemplary. Granular materials with a particle size of up to 1 mm containin at least 50% amorphous phase can be produced by bringing liquid drops into contact with cold conductive substrate with high thermal conductivity, or introduction into an inert liquid. Fabrication of these materials is preferably done in inert atmosphere or vacuum due to hig chemical reactivity of many of the materials.

A variety of new glass forming alloys have been identified in practice of thi invention. The ranges of alloys suitable for forming glassy or amorphous material can b defined in various ways. Some of the composition ranges are formed into metallic glasse with relatively higher cooling rates, whereas preferred compositions form metallic glasse with appreciably lower cooling rates. Although the alloy composition ranges are defined b reference to quasi-ternary composition diagrams such as illustrated in the drawings, th boundaries of the alloy ranges may vary somewhat as different materials are introduced. Th

boundaries encompass alloys which form a metallic glass when cooled from the melting temperature to a temperature below the glass transition temperature at a rate substantially less than about 10 ⁵ K/s, preferably less than 10 ³ K/s and often at much lower rates, most preferably less than 100 K/s. Previous investigations have been of binary and ternary alloys which form metallic glass at very high cooling rates, generally more than 10 ⁵ K/s. It has been discovered that quaternary, quinary or more complex alloys with copper, titanium, zirconium (or hafnium) and nickel (or in part cobalt) form metallic glasses with much lower critical cooling rates than previously thought possible. Ternary alloys of such materials will not make completely amorphous objects with a smallest dimension of at least one millimeter. Quaternary alloys with critical cooling rates as low as about 50 K/s are found in practice of this invention.

Generally speaking, reasonable glass forming alloys are all at least quaternary alloys having titanium, copper, at least one early transition metal selected from the group consisting of zirconium and hafnium and at least one late transition metal selected from the group consisting of nickel and cobalt. A portion of iron, vanadium or zinc may be substituted instead of cobalt although the amount acceptable is believed to be lower. Zinc is less desirable because of its higher vapor pressure. Low critical cooling rates are found with at least quinary alloys having both cobalt and nickel and/or zirconium and hafnium. The glass forming alloys may also comprise up to 4% of other transition metals and a total of no more than 2% of other elements. (Unless indicated otherwise, composition percentages stated herein are atomic percentages.) The additional 2% may include beryllium, which tends to reduce the critical cooling rate.

The glass forming alloys fall into two groups. In one group, the titanium and copper are in a relatively lower proportion, zirconium is in a higher proportion and nickel is in a relatively broader range. In the other group, the titanium and copper are each in a relatively higher proportion, zirconium is in a low range and nickel is in a narrow range. In both groups hafnium is essentially interchangeable with zirconium. Within limits, cobalt can be substituted for nickel.

Broadly stated, the alloys include titanium in the range of from 5 to 41 atomic percent and copper in the range of from 8 to 61 percent. Nickel (and to some extent cobalt) may be in the range of from 2 to 37% In one group the zirconium (and/or hafnium) is in the range of from 4 to 21 % and in the other group it is in the range of from 30 to 57 % . Within these broad ranges, there are alloys that do not have a sufficiently low cooling rate to form amorphous objects at least 1/2 or one millimeter thick as set forth in the various claims. Not all alloys within these ranges are claimed in this invention. The claims are only for an object having a smallest dimension of one millimeter which is at least 50% amorphous phase and having a composition within the recited ranges. If the object is not a metallic glass, it is not claimed.

When the object has a thickness of at least 1 mm in its smallest dimension, i.e., all dimensions of the object have a dimension of at least 1 mm. , the cooling rate that can be achieved from the molten state through the glass transition temperature is no more than about 10 ³ K/s. Higher cooling rates can be achieved only in much thinner sections. If the thickness of the glassy object is appreciably more than 1 mm, the cooling rate is, of course, commensurately lower. Compositions which have lower critical cooling rates and can form glassy alloys in such thicker sections are within the ranges disclosed. For example, alloys have been made completely amorphous in bodies having a smallest dimension of about two millimeters. A number of examples of glass forming alloys are illustrated in the quasi-ternary composition diagrams of the drawings. FIG. 1 is a fraction of a quasi-ternary phase diagram where the lower left apex represents 100 atomic percent of a mixture of zirconium and titanium. In this particular diagram, the proportion is 75 percent zirconium and 25 percent titanium (Zr ₀ 75 Ti ₀ 25)- The lower right apex does not extend to 100% but represents 65 atomic percent copper and 35 percent of the mixture of titanium and zirconium. Similarly, the upper apex represents 65% nickel and 35 percent of the mixture of titanium and zirconium.

A number of alloy compositions within this region are illustrated. The compositions are characterized in two different ways. Compositions represented by open circles are glass forming alloys which form amorphous solids when the smallest dimension of the object, for example a sheet or ribbon, is less than about 1 mm. Closed circles represent alloys which form glass when the smallest dimension of the sample is approximately 1 mm. Some of the alloys represented by closed circles are glassy or amorphous with thicknesses as much as 2 mm or more. Also sketched on FIG. 1 is a hexagonal boundary defining a region within which most of the alloy compositions disclosed can form amorphous alloys in sections at least 1 mm thick. It will be recognized that this is just a single slice in a complex quaternary system and, as pointed out with respect to formulas set forth hereinafter, the boundaries of the good glass forming region are subject to certain constraints which are not fully represented in this drawing.

FIG. 2 is a portion of another quasi-ternary phase diagram where the lower left apex represents 60 atomic percent of titanium, 40 percent copper plus nickel and no zirconium. The scale on the opposite side of the triangle is the percentage of copper plus nickel. The upper apex of the diagram is at a composition of 10 percent titanium and 90 percent copper plus nickel. The lower right apex also does not extend to 100% but a composition with 50 percent zirconium, 10 percent titanium and 40 percent copper plus nickel.

A hexagonal boundary on FIG. 2 defines a region within which most of the alloy compositions disclosed can form amorphous alloys in sections at least 1 mm thick.

Compositions represented by open circles are glass forming alloys which form amorphous solids when the smallest dimension of the object is less than about 1 mm. Closed circles represent alloys which form glass when the smallest dimension of the sample is approximately 1 mm. The preferred alloy compositions within the glass forming region have a critical cooling rate for glass formation less than about 10^ K/s and some appear to have critical cooling rates lower than 100 K/s. The cooling rate is not well measured and may be, for example, 3X10 ³ or below 10 . A cooling rate of 10 ³ is considered to be the order of magnitude of samples about 0.5 to 1 mm thick. For purposes of this specification an early transition metal (ETM) includes Groups 3,

4, 5, and 6 of the periodic table, including the lanthanide and actinide series. The previous IUPAC notation for these groups was IIIA, IVA, VA and VIA. For purposes of this specification, late transition metals (LTM) include Groups 7, 8, 9, 10 and 11 of the periodic table. The previous IUPAC notation was VIIA, VIIIA and IB. The smaller hexagonal area illustrated in the FIG. 1 represents a glass forming region of alloys bounded by the composition ranges for alloys having a formula In this formula x and y are atomic fractions, and a, b, and c are atomic percentages. The early transition metal is selected from the group consisting of zirconium and hafnium. In this composition a is in the range of from 47 to 67, b is in the range of from 8 to 42, and c is in the range of from 4 to 37, subject to certain constraints. The atomic fraction of titanium, x, is in the range of from 0.1 to 0.3. The product of the atomic fraction of cobalt, y, and the atomic percentage, c, of the late transition metal (Ni plus Co), y«c, is in the range of from 0 to 18. In other words, there may be no cobalt present, and if there is, it is a maximum of 18 percent of the composition. In other words, nickel and cobalt are completely interchangeable up to 18 percent. If the total LTM is more than 18 atomic percent, up to

18 percent can be cobalt and any balance of late transition metal is nickel. This can be contrasted with the zirconium and hafnium which are apparently completely interchangeable.

The composition can also be defined approximately as comprising least four elements including titanium in the range of from 5 to 20 atomic percent, copper in the range of from 8 to 42 atomic percent, an early transition metal selected from the group consisting of zirconium and hafnium in the range of from 30 to 57 atomic percent and a late transition metal selected from the group consisting of nickel and cobalt in the range of from 4 to 37 atomic percent. As mentioned, there are certain constraints on this formula definition of the good glass forming alloys. In other words, there are excluded areas within the region bounded by this formula. A first constraint is that when the ETM and titanium content, a, is in the range of

from 60 to 67 and the LTM content, c, is in the range of from 13 to 32, the amount o copper, b, is given by the formula: b ≥ 8 + (12/7)»(a - 60). Secondly, when a is in the range of from 60 to 67 and c is in the range of from 4 to 13, is given by the formula: b > 20 + (19/10)«(67 - a). Finally, when a is in the range of from 47 to 55 and c is in the range of from 11 to 37, is given by the formula: b < 8 + (34/8)«(55 - a). These constraints have been determined empirically. In the FIG. 1 there is a boundar illustrated by a solid line bounding a hexagonal region. This region illustrates the boundarie defined by the formula without the constraints on the value of b. A smaller hexagonal are is also illustrated with a "fuzzy" boundary represented by a shaded band. The constraint were determined by selecting points on the boundary represented by the solid lines an connecting the points by straight lines that included alloys that formed glassy alloys whe cast with a section about one millimeter thick and excluded alloys that were not amorphou when cast about one millimeter thick. The constraints stated in the formulas above indicat the slopes of the lines so selected.

These selections are somewhat arbitrary. The data points in the composition diagra are at increments of five atomic percent. Thus, there is an uncertainty of the location of th boundary of about ±2%. The slopes indicated by the formulas are selected as a bes approximation of the boundary. Alloys that apparently fall outside the boundaries so define may be quite equivalent to compositions that are well within the boundaries insofar as th ability to form relatively thick glassy objects. The smaller polygon formed by this formula and constraints in a quasi-ternar composition diagram of copper, nickel and a single apex for titanium plus zirconiu (Zr ₀ 75T-0 25) ^as illustrated by the shaded boundaries in FIG. 1 has as its six approximat corners:

Corner #

1 57 39 4

2 54 42 4

3 47 42 11

4 55 8 37

5 60 8 32

6 67 20 13

Preferably, the early transition metal is entirely zirconium since it is economical an provides the alloy with exceptional corrosion resistance and light weight. Preferably, the lat

transition metal is nickel since cobalt is somewhat more costly and lower critical cooling rates appear feasible with nickel than with cobalt.

Generally speaking, up to 4 atomic percent of other transition metals is acceptable in the glass alloy. It can also be noted that the glass alloy can tolerate appreciable amounts of what could be considered incidental or contaminant materials. For example, an appreciable amount of oxygen may dissolve in the metallic glass without significantly shifting the crystallization curve. Other incidental elements, such as germanium, phosphorus, carbon, nitrogen or oxygen may be present in total amounts less than about 2 atomic percent, and preferably in total amounts less than about one atomic percent. The following is an expression of the formula for glass-forming compositions of differing scope. Such alloys can be formed into a metallic glass having at least 50% amorphous phase by cooling the alloy from above its melting point through the glass transition temperature at a sufficient rate to prevent formation of more than 50% crystalline phase. Objects with a smallest dimension of at least 1 mm can be formed with such alloys. In the following formula of a good glass forming alloy, x is an atomic fraction and the subscripts a, b and c are atomic percentages:

Ti _a (ETM) _b (C _Ul . _χ (LTM) _x ) _c The early transition metal, ETM, is selected from the group consisting of zirconium and hafnium. The late transition metal, LTM, is selected from the group consisting of nickel and cobalt. In this alloy range, the titanium content, a, is in the range of from 19 to 41, the proportion of early transition metal, b is in the range of from 4 to 21, and the amount of copper plus other late transition metal, c is in the range of from 49 to 64. Again, there are certain constraints on the region bounded by this formula. The product, x»c, of the LTM content, x, and the total of copper plus LTM, c, is between 2 and 14. That is, 2 < x«c < 14. Furthermore, the amount of ETM is limited by the titanium content of the alloy so that b < 10 + (11/17)»(41 - a).

It has been found that there are additional constraints on the boundary of good glass forming alloys. When the total of copper plus nickel or cobalt is at the low end of the range, the proportion of LTM cannot be too high or crystallization is promoted and good glass forming is not obtained. Thus, when copper plus LTM is in the range of from 49 to 50 atomic percent, LTM is less than 8 atomic percent, when copper plus LTM is in the range of from 50 to 52 atomic percent, LTM is less than 9 atomic percent, when copper plus LTM is more than 52 atomic percent, LTM is no more than 10 atomic percent.

Stated differently by formula, the constraints are when 49 < c < 50, then x < 8; when 50 < c < 52, then x < 9; when 52 ≤ c, then x ≤ 10.

The polygon formed with this formula and the constraints on the triangular composition diagram of titanium, zirconium and a third apex representing combined copper plus nickel as illustrated in FIG. 2 has as its six approximate corners:

Corner ft

1 41 10 49 2 24 21 55 3 19 21 60 4 19 17 64 5 32 4 64 6 41 4 55

With the variety of material combinations encompassed by the ranges described, ther may be unusual mixtures of metals that do not form at least 50% glassy phase at coolin rates less than about 10 ⁵ K/s. Suitable combinations may be readily identified by the simpl expedient of melting the alloy composition, splat quenching and verifying the amorphou nature of the sample. Preferred compositions are readily identified with lower critica cooling rates.

The amorphous nature of the metallic glasses can be verified by a number of wel known methods. X-ray diffraction patterns of completely amorphous samples show broa diffuse scattering maxima. When crystallized material is present together with the glas phase, one observes relatively sharper Bragg diffraction peaks of the crystalline material.

The fraction of amorphous phase present can also be estimated by differential therma analysis. One compares the enthalpy released upon heating the sample to induce crystalliza tion of the amorphous phase to the enthalpy released when a completely glassy sampl crystallizes. The ratio of these heats gives the molar fraction of glassy material in th original sample. Transmission electron microscopy analysis can also be used to determin the fraction of glassy material. Transmission electron diffraction can be used to confirm th phase identification. The volume fraction of amorphous material in a sample can b estimated by analysis of the transmission electron microscopy images. The alloys provided in practice of this invention are particularly useful for formin composite materials where fibers or particles of other materials are embedded in a matrix o amorphous metal alloy. A great variety of particles and fibers are suitable for making suc composites, including, for example, diamond, refractory metal carbides, nitrides carbonitrides, oxides and suicides, silicon and other semiconductors, refractory metals an intermetallic compounds, pyrolytic carbon, graphite, boron, glass, and natural or syntheti minerals.

It is found that the metallic glass alloys readily wet many materials and a composit material can be made by pressing particles at high pressure to form a self supporting bod and infiltrating liquid alloy into the pores of the body. One may also make a felt or wove fabric of fibers and infiltrate liquid alloy into the felt or fabric. Alternatively, particle and/or fibers may be mixed with liquid alloy which is then cast into a desired shape.

With some of the particles or fibers, the thermal conductivity of the composite i greater than the thermal conductivity of the alloy alone. With such composites, the thicknes

of the body which can be amorphous is greater than the thickness of a body of the same alloy which can be amorphous with a given cooling rate.

Examples Following is a table of alloys which can be cast in a strip at least one millimeter thick with more than 50% by volume amorphous phase. The alloys listed fall within the boundaries of an region defined by the formula

Ti^ETM^Cu^LTM)^ where ETM is selected from the group consisting of Zr and Hf and LTM is selected from the group consisting of Ni and Co where a is in the range of from 19 to 41 , b is in the range of from 4 to 21, and c is in the range of from 49 to 64. Furthermore, the boundaries are constrained such that 2 < x»c < 14 and b < 10 + (11/17) ^» (41 - a).

It will be noted that at least one of the alloy compositions can be cast into an object with a minimum thickness of at least three or four millimeters, such a composition has about 34 percent titanium, about 11 percent zirconium and about 55 total percentage of copper and nickel, either 45 or 47 percent copper and 8 or 10 percent nickel. Another good glass forming alloy has a formula Cu ₅ 2Ni Zr ₁₀ Ti3o- It can be cast in objects having a smallest dimension of at least 3 mm.

Following is a table of alloys which can be cast in a strip at least one millimeter thick with more than 50% by volume amorphous phase. The alloys listed fall within the boundaries of an region defined by the formula

( ^Zr l-x ^Ti χ)a ^Cu b( ^Ni l-y ^Co y)c wherein x is in the range of from 0.1 to 0.3, a is in the range of from 47 to 67, b is in the range of from 8 to 42, and c is in the range of from 4 to 37. In these examples y is zero.

In addition there are the following constraints: (i) When a is in the range of from 60 to 67 and c is in the range of from 13 to 32, b is given by: b ≥ 8 + (12/7)«(a - 60); (ii) when a is in the range of from 60 to 67 and c is in the range of from 4 to 13, b is given by: b ≥ 20 + (19/10)»(67 - a); and (iii) when a is in the range of from 47 to 55 and c is in the range of from 11 to 37, b is given by: b ≤ 8 + (34/8)»(55 - a).

A number of categories and specific examples of glass-forming alloy compositions having low critical cooling rates are described herein. It will apparent to those skilled in the art that the boundaries of the glass-forming regions described are approximate and that compositions slightly outside these precise boundaries may be good glass-forming materials and compositions slightly inside these boundaries may not be glass-forming materials at cooling rates less than 1000 K/s. Thus, within the scope of the following claims, this invention may be practiced with some variation from the precise compositions described.