Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C16/00—Alloys based on zirconium
• • 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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/003—Making ferrous alloys making amorphous alloys

Definitions

• Metallic glasses fail by the formation of localized shear bands, which leads to catastrophic failure.
• Metallic glass specimens that are loaded in a state of plane stress fail on one dominant shear band and show little inelastic behavior.
• Metallic glass specimens loaded under constrained geometries (plane strain) fail in an elastic-perfectly -plastic manner by the generation of multiple shear bands. Multiple shear bands are observed when the catastrophic instability is avoided via mechanical constraint; e.g., in uniaxial compression, bending, drawing, and under localized indentation.
• mechanical constraint e.g., in uniaxial compression, bending, drawing, and under localized indentation.
• a new class of ductile metal reinforced bulk metallic glass matrix composite materials has been prepared that demonstrate improved mechanical properties.
• This newly designed engineering material exhibits both improved toughness and a large plastic strain to failure.
• the new material was designed for use in structural applications (aerospace and automotive, for example), and is also a promising material for application as an armor.
• a method for forming a composite metal object comprising ductile crystalline metal particles in an amorphous metal matrix.
• An alloy is heated above the melting point of the alloy, i.e. above its liquidus temperature.
• the alloy chemically partitions; i.e., undergoes partial crystallization by nucleation and subsequent growth of a crystalline phase in the remaining liquid.
• This technique may be used to form a composite amorphous metal object having all of its dimensions greater than one millimeter.
• Such an object comprises an amorphous metal alloy forming a substantially continuous matrix, and a second ductile metal phase embedded in the matrix.
• the second phase may comprise crystalline metal dendrites having a primary length in the range of from 30 to 150 micrometers and secondary arms having a spacing between adjacent arms in the range of from 1 to 10 micrometers, more commonly in the order of about 6 to 8 micrometers.
• the second phase is formed in situ from a molten alloy having an original composition in the range of from 52 to 68 atomic percent zirconium, 3 to 17 atomic percent titanium, 2.5 to 8.5 atomic percent copper, 2 to 7 atomic percent nickel, 5 to 15 atomic percent beryllium, and 3 to 20 atomic percent niobium.
• Other metals that may be present in lieu of or in addition to niobium are selected from the group consisting of tantalum, tungsten, molybdenum, chromium and vanadium. These elements act to stabilize bcc symmetry crystal structure in Ti- and Zr-based alloys.
• Fig. 1 is a schematic binary phase diagram.
• Fig. 2 is a pseudo-binary phase diagram of an exemplary alloy system for forming a composite by chemical partitioning.
• Fig. 3 is a pseudo-ternary phase diagram of a Zr-Ti-Cu-Ni-Be alloy system.
• Fig. 4 is an exemplary SEM photomicrograph of an in situ composite formed by chemical partitioning.
• Fig. 5 is an exemplary photomicrograph of such a composite after straining.
• Fig. 6 is a compressive stress-strain curve for such a composite.
• Fig. 7 is a schematic illustration of a technique for forming a composite with oriented microstructure.
• the remarkable glass forming ability of bulk metallic glasses at low cooling rates allows for the preparation of ductile metal reinforced composites with a bulk metallic glass matrix via in situ processing; i.e., chemical partitioning.
• the incorporation of a ductile metal phase into a metallic glass matrix yields a constraint that allows for the generation of multiple shear bands in the metallic glass matrix. This stabilizes crack growth in the matrix and extends the amount of strain to failure of the composite.
• composition (ductile crystalline metal in a bulk metallic glass matrix) is obtained on cooling from the liquid state.
• ductile crystalline metal in a bulk metallic glass matrix is obtained on cooling from the liquid state.
• the composition includes additional elements or a surplus of some of the components of an alloy that would form a glassy state on cooling from the liquid state.
• a particularly attractive bulk glass forming alloy system is described in U.S. Patent No. 5,288,344, the disclosure of which is hereby incorporated by reference.
• an alloy in the bulk glass forming zirconium-titanium-copper-nickel-beryllium system with added niobium.
• Such a composition is melted so as to be homogeneous.
• the molten alloy is then cooled to a temperature range between the liquidus and solidus for the composition. This causes chemical partitioning of the composition into solid crystalline ductile metal dendrites and a liquid phase, with different compositions.
• the liquid phase becomes depleted of the metals crystallizing into the crystalline phase and the composition shifts to one that forms a bulk metallic glass at low cooling rate. Further cooling of the remaining liquid results in formation of an amorphous matrix around the crystalline phase.
• Alloys suitable for practice of this invention have a phase diagram with both a liquidus and a solidus that each include at least one portion that is vertical or sloping, i.e. that is not at a constant temperature.
• a binary alloy, AB having a phase diagram with a eutectic and solid solubility of one metal A in the other metal B as shown in Fig. 1.
• the phase diagram has a horizontal or constant temperature solidus line at the eutectic temperature extending from B to a point where B is in equilibrium with a solid solution of B in A. The solidus then slopes upwardly from the equilibrium point to the melting point of A.
• the liquidus line in the phase diagram extends from the melting point of A to the eutectic composition on the horizontal solidus and from there to the melting point of B.
• the solidus has a portion that is not at a constant temperature (between the melting point of A and the equilibrium point).
• the vertical line from the melting point of B to the eutectic temperature could also be considered a solidus line where there is no solid solubility of A in B.
• the liquidus has sloping lines that are not at constant temperature.
• the solidus refers in part to a line (or surface) defining the boundary between liquid metal and a solid phase. This usage is appropriate when referring to the boundary between the melt and a solid crystalline phase precipitated for forming the phase embedded in the matrix.
• the "solidus" is typically not at a well defined temperature, but is where the viscosity of the alloy becomes sufficiently high that the alloy is considered to be rigid or solid. Knowing an exact temperature is not important.
• Fig. 2 is a pseudo-binary phase diagram for alloys of M and X where X is a good glass forming composition, i.e. a composition that forms an amorphous metal at reasonable cooling rates.
• Compositions range from 100% M at the left margin to 100% of the alloy X at the right margin.
• An upper slightly curved line is a liquidus for M in the alloy and a steeply curving line near the left margin is a solidus for M with some solid solution of components of X in a body centered cubic M alloy.
• a horizontal or near horizontal line below the liquidus is, in effect, a solidus for an amorphous alloy.
• a vertical line in mid-diagram is an arbitrary alloy where there is an excess of M above a composition that is a good bulk glass forming alloy.
• the proportion of solid M alloy corresponds to the distance A and the proportion of liquid remaining corresponds to the distance B in Fig. 2.
• about 1/4 of the composition is solid dendrites and the other 3/4 is liquid.
• a composite is achieved having about 114 particles of bcc alloy distributed in a bulk metallic glass matrix having a composition corresponding to the liquidus at T,.
• the morphology, proportion, size and spacing of ductile metal dendrites in the amorphous metal matrix is influenced by the cooling rate. Generally speaking, a faster cooling rate provides less time for nucleation and growth of crystalline dendrites, so they are smaller and more widely spaced than for slower cooling rates.
• the orientation of the dendrites is influenced by the local temperature gradient present during solidification. The preferred cooling rate for a desired dendrite morphology and proportion in a specific alloy composition is found with only a few experiments.
• Strategy 1 is based on systematic manipulations of the chemical composition of bulk metallic glass forming compositions in the Zr-Ti-Cu-Ni-Be system.
• Strategy 2 is based on the preparation of chemical compositions which comprise the mixture of additional pure metal or metal alloys with a good bulk metallic glass forming composition in the Zr-Ti-Cu-Ni-Be system.
• the alloy composition VI lies a large region of chemical compositions which form a bulk metallic glass object (an object having all of its dimensions greater than one millimeter) on cooling from the liquid state at reasonable rates.
• This bulk glass forming region is a large region of chemical compositions which form a bulk metallic glass object (an object having all of its dimensions greater than one millimeter) on cooling from the liquid state at reasonable rates.
• GFR is defined by the oval labeled as GFR in Fig. 3.
• chemical compositions that lie within this region are fully amorphous when cooled below the glass transition temperature.
• the pseudo-ternary diagram shows a number of competing crystalline or quasi- crystalline phases which limit the bulk metallic glass forming ability. Within the GFR these competing crystalline phases are destabilized, and hence do not prevent the vitrification of the liquid on cooling from the molten state. However, for compositions outside the GFR, on cooling from the high temperature liquid state the molten liquid chemically partitions. If the composition is alloyed properly, it forms a good composite engineering material with a ductile crystalline metal phase in an amorphous matrix. There are compositions outside GFR where alloying is inappropriate and the partitioned composite may have a mixture of brittle crystalline phases embedded in an amorphous matrix. The presence of these brittle crystalline phases seriously degrades the mechanical properties of the composite material formed.
• FIG. 3 Above the left part of large GFR oval as illustrated in Fig. 3 there is a smaller circle representing a region where a quasi-crystalline phase forms, another embrittling phenomenon.
• An upper partial oval represents another region where a NiTiZr Laves phase forms.
• a small triangular region along the Zr-X margin represents formation of intermetallic TiZrCu 2 and/or Ti 2 Cu phases.
• Small regions near 70% X are compositions where a ZrBe 2 intermetallic or a
• a ductile second phase is formed in situ.
• the brittle second phases identified in the pseudo-ternary diagram are to be avoided. This leaves a generally triangular region toward the upper left from the Zr 42 Ti 14 X 44 circle where another metal M may be substituted for some of the zirconium and/or titanium to provide a composite with desirable properties. This is reviewed for a substitution of niobium for some of the titanium.
• a dashed line is drawn on Fig. 3 toward the 25% titanium composition on the Zr-Ti margin. In the series of compositions along the dashed line,
• Peaks on an x-ray diffraction pattern (inset in SEM photomicrograph of Fig. 4) for this composition show that the secondary phase present has a body-centered-cubic (bcc) or ⁇ phase crystalline symmetry, and that the x-ray pattern peaks are due to the ⁇ phase only.
• In situ composites in the Zr-Ti-M-Cu- Ni-Be system have been prepared for alloy series other than the series along the dashed line. These additional alloy series sweep out a region of the quinary composition phase space shown in Fig. 3.
• the region sweeps in a clockwise direction from a line (not shown) from the V 1 alloy composition to the Zr apex of the pseudo-ternary diagram through the dashed line, and extending through to a line (not shown) from the VI alloy to the Ti apex of the pseudo-ternary diagram, but excluding those regions where a brittle crystalline, quasi-crystalline or Laves phase is stable.
• in situ composite alloys of this form are prepared by first melting the metal or metallic alloy with the early transition metal constituents of the BMG composition. Thus, pure Nb metal is mixed via arc melting with the Zr and Ti of the VI alloy. This mixture is then arc melted with the remaining constituents; i.e., Cu, Ni, and Be, of the VI
• ductile niobium alloy crystals are formed in an amorphous matrix upon cooling a melt through the region between the liquidus and solidus.
• the composition of the dendrites is about 82% (atomic %) niobium, about 8% titanium, about 8.5% zirconium, and about 1.5% copper plus nickel. This is the composition found when the proportion of dendrites is about 1/4 bcc ⁇ phase and 3/4 amorphous matrix. Similar behaviors are observed when tantalum is the additional metal added to what would otherwise be a VI alloy.
• suitable additional metals which may be in the composition for in situ formation of a composite may include molybdenum, chromium, tungsten and vanadium.
• the proportion of ductile bcc forming elements in the composition can vary widely.
• Composites of crystalline bcc alloy particles distributed in a nominally VI matrix have been prepared with about 75% VI plus 25% Nb, 67% VI plus 33% Nb (all percentages being atomic).
• the dendritic particles of bcc alloy form by chemical partitioning from the melt, leaving a good glass forming alloy for forming a bulk metallic glass matrix.
• Partitioning may be used to obtain a small proportion of dendrites in a large proportion of amorphous matrix all the way to a large proportion of dendrites in a small proportion of amorphous matrix.
• the proportions are readily obtained by varying the amount of metal added to stabilize a crystalline phase.
• niobium for example, and reducing the sum of other elements that make a good bulk metallic glass forming alloy, a large proportion of crystalline particles can be formed in a glassy matrix.
• a good composite as described herein with a third phase or brittle phase having a particle size significantly less than 0.1 micrometers. Such small particles may have minimal effect on formation of shear bands and little effect on mechanical properties.
• the microstructure resulting from dendrite formation from a melt comprises a stable crystalline Zr-Ti-Nb alloy, with ⁇ phase (body centered cubic) structure, in a Zr-Ti-Nb-Cu-Ni-Be amorphous metal matrix.
• ⁇ phase body centered cubic
• Sub-standard size Charpy specimens were prepared from a new in situ formed composite material having a total nominal alloy composition of Zr 5625 Nb 5 Ti 13 76 Cu 6 875 Ni 5 625 Be 125 These have demonstrated Charpy impact toughness numbers that are 250%) greater than that of the bulk metallic glass matrix alone; 15 ft-lb. vs. 6 ft-lb. Bend tests have shown large plastic strain to failure values of about 4%. The multiple shear band structures generated during these bend tests have a periodicity of spacing equal to about 8 micrometers, and this periodicity is determined by the ⁇ phase dendrite morphology and spacing. In some cast plates with a faster cooling rate, plastic strain to failure in bending has been found to be about 25%. Samples have been found that will sustain a 180° bend.
• shear bands can be seen traversing both the amorphous metal matrix phase and the ductile metal dendrite phase .
• the directions of the shear bands differ slightly in the two phases due to different mechanical properties and probably because of crystal orientation in the dendritic phase.
• Shear band patterns as described occur over a wide range of strain rates.
• a specimen showing shear bands crossing the matrix and dendrites was tested under quasi-static loading with strain rates of about 10 "4 to 10 "3 per second.
• Dramatically improved Charpy impact toughness values show that this mechanism is operating at strain rates of 10 3 per second, or higher.
• Specimens tested under compressive loading exhibit large plastic strains to failure on the order of 8%.
• a suitable glass forming composition comprises (Zr 100 . x Ti x . z M z ) 100 .
• x is in the range of from 5 to 95
• y is in the range of from 10 to 30
• z is in the range of from 3 to 20
• M is selected from the group consisting of niobium, tantalum, tungsten, molybdenum, chromium and vanadium. Amounts of other elements or excesses of these elements may be added for partitioning from the melt to form a ductile second phase embedded in an amorphous matrix.
• Another factor in the improved behavior is the quality of the interface between the ductile metal ⁇ phase and the bulk metallic glass matrix.
• this interface is chemically homogeneous, atomically sharp and free of any third phases.
• the materials on each side of the boundary are in chemical equilibrium due to formation of dendrites by chemical partitioning from a melt.
• This clean interface allows for an iso-strain boundary condition at the particle-matrix interface; this allows for stable deformation and for the propagation of shear bands through the ⁇ phase particles.
• Previous composites have been made by embedding ductile refractory metal wires or particles in a matrix of glass forming alloy. The interfaces are chemically dissimilar and shear band propagation across the boundaries is inhibited.
• the ductile metal phase included in the glassy matrix has a stress induced martensite transformation.
• the stress level for transformation induced plasticity, either martensite transformation or twinning, of the ductile metal particles is at or below the shear strength of the amorphous metal phase.
• the ductile particles preferably have fee, bcc or hep crystal structures, and in any of these crystal structures there are compositions that exhibit stress induced plasticity, although not all fee, bcc or hep structures exhibit this phenomenon.
• Other crystal structures may be too brittle or transform to brittle structures that are not suitable for reinforcing an amorphous metal matrix composite.
• This new concept of chemical partitioning is believed to be a global phenomenon in a number of bulk metallic glass forming systems; i.e., in composites that contain a ductile metal phase within a bulk metallic glass matrix, that are formed by in situ processing.
• similar improvements in mechanical behavior may be observed in (Zr 100.x Ti x . z M z ) ]00.x (X) y materials, where X is a combination of late transition metal elements that leads to the formation of a bulk metallic glass; in these alloys X does not include Be.
• the crystalline phase be a ductile phase to support shear band deformation through the crystalline phase.
• the second phase in the amorphous matrix is an intrinsically brittle ordered intermetallic compound or a Laves phase, for example, there is little ductility produced in the composite material.
• Ductile deformation of the particles is important for initiating and propagating shear bands. It may be noted that ductile materials in the particles may work harden, and such work hardening can be mitigated by annealing, although it is important not to exceed a glass transition temperature that would lose the amorphous phase.
• the particle size of the dendrites of crystalline phase can also be controlled during the partitioning.
• the particle size and spacing between particles in the solid phase may be controlled by cooling rate between the liquidus and solidus, and/or time of holding at a processing temperature in this region. This may be a short interval to inhibit excessive crystalline growth.
• addition of elements that are partitioned into the crystalline phase may also assist in controlling particle size of the crystalline phase.
• addition of more niobium apparently creates additional nucleation sites and produces finer grain size. This can leave the volume fraction of the amorphous phase substantially unchanged and simply change the particle size and spacing.
• a change in temperature between the liquidus and solidus from which the alloy is quenched can control the volume fraction of crystalline and amorphous phases.
• the solid phase formed from the melt may have a composition in the range of from 67 to 74 atomic percent zirconium, 15 to 17 atomic percent titanium, 1 to 3 atomic percent copper, 0 to 2 atomic percent nickel, and 8 to 12 atomic percent niobium.
• a composition is crystalline, and would not form an amorphous alloy at reasonable cooling rates.
• the remaining liquid phase has a composition in the range of from 35 to 43 atomic percent zirconium, 9 to 12 atomic percent titanium, 7 to 11 atomic percent copper, 6 to 9 atomic percent nickel, 28 to 38 atomic percent beryllium, and 2 to 4 atomic percent niobium. Such a composition falls within a range that forms amorphous alloys upon sufficiently rapid cooling.
• ductile dendrites are formed with primary lengths of about 50 to 150 micrometers. (Cooling was from one face of a one centimeter thick body in a water cooled copper crucible.)
• the dendrites have well developed secondary arms in the order of four to six micrometers wide, with the secondary arm spacing being about six to eight micrometers. It has been observed in compression tests of such material that shear bands are equally spaced at about seven micrometers. Thus, the shear band spacing is coherent with the secondary arm spacing of the dendrites.
• the dendrites are appreciably smaller, about five micrometers along the principal direction and with secondary arms spaced about one to two micrometers apart.
• the dendrites have more of a snowflake-like appearance than the more usual tree-like appearance.
• Dendrites seem less uniformly distributed and occupy less of the total volume of the composite (about 20%) than in the more slowly cooled composite. (Cooling was from both faces of a body 3.3 mm thick.) In such a composite, the shear bands are more dense than in the composite with larger and more widely spaced dendrites.
• the direction of a primary dendrite is determined by the local temperature gradient present during solidification.
• the principal dendrite axes extend in the direction of the temperature gradient, nucleating at the cooler regions and propagating toward the warmer regions as cooling progresses. Secondary arms form transverse to the principal axis and generally are skewed away from the cooler regions. In other words, the dendrite is somewhat like the fletching on an arrow and the pointed end is toward the direction from which heat is extracted.
• the individual shear bands that form upon mechanical loading tend to propagate along the principal direction of the dendrites and across the secondary dendrite arms.
• the planes formed by these bands tend to run along the primary dendrite axes.
• the orientation of the dendrites influences the direction of strain in the composite and the direction of failure.
• the intent is to refer to the width and spacing of the secondary arms of the dendrites, when present.
• particle size would have its usual meaning, i.e. for round or nearly round particles, an average diameter.
• acicular or lamellar ductile metal structures may be formed in an amorphous matrix. Width of such structures is considered as particle size.
• the secondary arms in a dendritic are not uniform width; they taper from a wider end adj acent the principal axis toward a pointed or slightly rounded free end. Thus, the "width" is some value between the ends in a region where shear bands propagate.
• the center-to-center spacing is intended, even if the text may inadvertently refer to the spacing in a context that suggests edge-to-edge spacing.
• the improved mechanical properties can be obtained from such a composite material where the second ductile metal phase embedded in the amorphous metal matrix, has a particle size in the range of from about 0.1 to 15 micrometers. If the particles are smaller than 100 nanometers, shear bands may effectively avoid the particles and there is little if any effect on the mechanical properties. If the particles are too large, the ductile phase effectively predominates and the desirable properties of the amorphous matrix are diluted.
• the particle size is in the range of from 0.5 to 8 micrometers since the best mechanical properties are obtained in that size range.
• the particles of crystalline phase should not be too small or they are smaller than the width of the shear bands and become relatively ineffective. Preferably, the particles are slightly larger than the shear band spacing.
• the spacing between adjacent particles should be in the range of from 0.1 to 20 micrometers. Such spacing of a ductile metal reinforcement in the continuous amorphous matrix induces a uniform distribution of shear bands throughout a deformed volume of the composite, with strain rates in the range of from about 10 "4 to 10 3 per second. Preferably, the spacing between particles is in the range of from 1 to 10 micrometers for the best mechanical properties in the composite.
• the volumetric proportion of the ductile metal particles in the amorphous matrix is also significant.
• the ductile particles are preferably in the range of from 5 to 50 volume percent of the composite, and most preferably in the range of from 15 to 35% for the best improvements in mechanical properties.
• the proportion of ductile crystalline metal phase is low, the effects on properties are minimal and little improvement over the properties of the amorphous metal phase may be found.
• the proportion of the second phase is large, its properties dominate and the valuable assets of the amorphous phase are unduly diminished.
• volumetric proportion of amorphous metal phase may be less than 50% and the matrix may become a discontinuous phase.
• Stress induced transformation of a large proportion of in situ formed crystalline metal modulated by presence of a smaller proportion of amorphous metal may provide desirable mechanical properties in a composite.
• the size of and spacing between the particles of ductile crystalline metal phase preferably produces a uniform distribution of shear bands having a width of the shear bands in the range of from about 100 to 500 nanometers.
• the shear bands involve at least about four volume percent of the composite material before the composite fails in strain. Small spacing is desirable between shear bands since ductility correlates to the volume of material within the shear bands.
• the spacing between bands is preferably about two to five times the width of the bands. Spacings of as much as 20 times the width of the shear bands can produce engineering materials with adequate ductility and toughness for many applications.
• the energy of deformation before failure is estimated to be in the order of 23 joules (with a strain rate of about 10 2 to 10 3 /sec in a Charpy -type test. Based on such estimates, if the shear band density were increased to 30 volume percent of the material, the energy of deformation rises to about 120 joules.
• the crystalline phase have a modulus of elasticity approximately the same as the modulus of elasticity of the amorphous metal. This assures a reasonably uniform distribution of the shear bands.
• the modulus of elasticity of the crystalline metal phase is in the range of from 50 to 150 percent of the modulus of elasticity of the amorphous metal alloy. If the modulus of the particles is too high, the interface between the particles and amorphous matrix has a high stress differential and may fail in shear. Some high modulus particles can break out of the matrix when the composite is strained. For alloys usable for making objects with dimensions larger than micrometers, cooling rates from the region between the liquidus and solidus of less than 1000 K/sec are desirable.
• cooling rates to avoid crystallization of the glass forming alloy are in the range of from 1 to 100 K/sec or lower.
• the ability to form layers at least 1 millimeter thick has been selected.
• an object having an amorphous metal matrix has a thickness of at least one millimeter in its smallest dimension.
• Fig. 7 illustrates schematically a technique for controlling orientation of the dendritic structure formed during chemical partitioning of a ductile metal phase in an amorphous matrix.
• a controlled temperature gradient is established by directional solidification from one end of an elongated member so that subsequently formed dendrites tend to be oriented similarly to previously formed dendrites.
• the process is conducted in a vacuum chamber 11 to protect the reactive materials from oxidation or other contamination.
• An elongated vessel 12, such as a quartz tube extends vertically in the vacuum chamber and is mounted on a feed mechanism 13 for gradual lowering through the chamber.
• the tube descends through an RF induction coil 14 which is used to heat an alloy contained in the tube to a temperature above its melting point.
• the tube then descends through one or more cooling sleeves 15 which extract heat from the tube and alloy to initially cause partitioning and precipitation of dendrites of crystalline metal alloy from the melt. Upon further cooling the remaining melt solidifies to form an amorphous matrix surrounding the particles of ductile refractory metal.
• the resulting composite has dendrites oriented preferentially due to the directional solidification along the length of the metal contained in the tube. The dendrites are more or less coherent in that the principal directions of the dendrites are roughly aligned.
• an additional induction heating zone may be included before the cooling sleeve for holding the alloy at a processing temperature where formation of dendrites proceeds at a controlled rate.
• particle size, spacing, periodicity and orientation can be controlled by both the rate of descent from the molten zone to the cooling zone and also by holding at an intermediate elevated temperature between the liquidus and solidus of the alloy.
• Other techniques may be used for assuring or controlling a temperature gradient in the alloy as it cools form the melt. For example, an entire volume of metal may be melted and a temperature gradient applied by differential cooling in different portions of the melt, particularly as the alloy passes through the temperature region between the liquidus and solidus. This could take the form of cooling from only a selected surface area, for example, or by extracting heat from different areas of the surface at different rates.
• a plate- or sheetlike casting may be cooled preferentially from one face for selectively orienting dendrites in the composite structure, for example, or an elongated article may be cooled from an end face for axial orientation.
• the composite reinforcement was added to the bulk metallic glass alloy by melting the glass-forming metal and introducing pieces of reinforcement into the molten alloy, which is then solidified at a rate sufficiently high that the metal matrix is amorphous.
• a mass of pieces of the reinforcement material are infiltrated under positive gas pressure by the molten glass-forming alloy and then cooled. Both of these methods lack sufficient control of the secondary reinforcing particle size and spacing needed to adequately constrain the bulk metallic glass matrix such that multiple shear bands are formed during mechanical loading.
• the interfaces between the particles and matrix are not chemically homogeneous, leading to higher internal energy and less effective strain transfer.
• the in situ formed two-phase microstructure, interface homogeneity, dendritic morphology, particle size, and/or particle spacing of the new composites is responsible for the improved mechanical behavior.
• the principles of in situ formation of a composite by partitioning of the metals in a melt as it is cooled may be used to form a dual composite.
• a bundle of tungsten wires may be infiltrated with a molten alloy selected from those described above.
• the combination is then cooled to a processing temperature below the liquidus of the molten alloy and above the glass transition temperature.
• a crystalline metal phase forms from this melt, depleting the melt of some of its elements.
• the combination is then cooled sufficiently rapidly to form an amorphous metal matrix around the metal phases.
• a composite formed in situ serves as a matrix for the embedded tungsten wires.
• the same principles may be used for infiltrating other arrays or materials.
• a reinforcing phase may be stirred into a melt that is cooled to form a precipitated phase by partitioning and further cooled to form an amorphous matrix. Either way, one may form a three-phase composite of a reinforcing metal in a matrix that is a composite itself.

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