JP2009263797A - Composite amorphous metal object, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an composite amorphous metal object, and to provide a method for producing the composite amorphous metal object. <P>SOLUTION: In the composite metal object, crystalline ductile metal particles exist in an amorphous metal matrix. An alloy is heated above its liquidus temperature. Upon cooling from the high temperature melt, the alloy chemically partitions, forming dendrites in the melt. Upon cooling the remaining liquid below the glass transition temperature, it freezes to the amorphous state, producing a two-phase microstructure containing crystalline particles in an amorphous metal matrix. The ductile metal particles have a size in the range of from 0.1 to 15 μm and spacing in the range of from 0.1 to 20 μm. Preferably, the particle size is in the range of from 0.5 to 8 μm and spacing is in the range of from 1 to 10 μm. The volume proportion of particles is in the range of from 5 to 50% and preferably 15 to 35%. Differential cooling can produce oriented dendrites of ductile metal phase in an amorphous matrix. Examples are given in the Zr-Ti-Cu-Ni-Be alloy bulk glass forming system with added niobium. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an amorphous metal composite and a method for producing the same.

  This application enjoys priority based on US patent application Ser. No. 60 / 131,973.

Metallic glass is deformed by the formation of local shear deformation bands, leading to catastrophic failure.
When a metal glass sample is loaded in a plane stress state, it deforms in a single dominant shear deformation band and exhibits almost no inelastic behavior. When a metallic glass sample is loaded with a constrained shape (plane strain), a large number of shear deformation bands are generated to show elastic / perfect plastic deformation behavior. A large number of shear bands are observed when catastrophic unstable failure is avoided by mechanical constraints such as uniaxial compression, bending, drawing, and local pressing. Many models have been tried to explain the formation of shear bands in metallic glass, but these models currently do not fully explain the experimental facts.

  A new class of ductile metal reinforced bulk metallic glass matrix composites has been made and improved mechanical properties have been found. This newly designed industrial material has improved toughness and a large plastic strain until failure. This new material is designed for structural use (aerospace, automotive, etc.), but is also expected to be used for armor.

  The present invention provides a method for producing a composite material in which crystalline ductile metal particles are contained in an amorphous metal matrix. The alloy is heated to its melting point, ie above the liquidus. Upon cooling from the hot melt, the alloy undergoes concentration partitioning, that is, partial crystallization occurs where the crystalline phase nucleates and grows from the liquid phase. The residual liquid phase is cooled to a temperature lower than the glass transition point (considered as a solidus) and then solidifies into an amorphous state, ie, a glass state, and crystalline particles in an amorphous metal matrix, ie, a bulk metal glass matrix. A two-phase structure in which (ie, dendrite) is present is formed.

  Using this technique, amorphous metal composites with dimensions in any direction greater than 1 mm can be produced. The composite is comprised of a substantially continuous matrix of amorphous alloy and a second phase of ductile metal present in the matrix. For example, the second phase consists of a crystalline metal dendrite with a secondary arm (branch column) having a main column length of 30-150 μm and an adjacent arm spacing of 1-10 μm, more typically about 6-8 μm. .

  In a preferred embodiment, the second phase has an initial composition of zirconium: 52-68 atomic%, titanium: 3-17 atomic%, copper: 2.5-8.5 atomic%, nickel: 2-7 atomic%, beryllium. It is formed by in situ formation from a molten alloy of 5-15 atomic% and niobium: 3-20 atomic%. Other metals that can be included in place of or in addition to niobium are selected from the group consisting of tantalum, tungsten, molybdenum, chromium and vanadium. These elements have the effect of stabilizing the bcc target crystal structures of Ti-based alloys and Zr-based alloys.

FIG. 1 is a schematic binary state diagram. FIG. 2 is a quasi-binary phase diagram of a typical alloy system for producing composites by composition partitioning. FIG. 3 is a quasi-ternary phase diagram of the Zr—Ti—Cu—Ni—Be alloy system. FIG. 4 is a typical SEM micrograph of an in situ generated composite by composition partitioning. FIG. 5 is a typical photomicrograph in a state after applying strain to the composite. FIG. 6 is a stress-strain curve when the composite is compressed. FIG. 7 is a schematic diagram showing a technique for forming a complex having an oriented structure.

DESCRIPTION OF THE INVENTION Bulk metallic glass exhibits significant glass forming ability at low cooling rates (eg, less than about 10 ³ K / sec), so it has a bulk metallic glass matrix and is reinforced with ductile metal by in-situ generation or concentration distribution. Can be produced. The presence of the ductile metal phase in the metallic glass matrix creates a constrained state that can generate a number of shear deformation bands within the metallic glass matrix. This stabilizes crack growth and increases the amount of strain until the composite breaks. That is, by controlling the chemical composition and processing conditions, a stable two-phase composite can be obtained by cooling from the liquid state.

  In order to produce an amorphous metal composite by concentration distribution, a basic composition that does not generate an amorphous metal when cooled from a liquid phase at a practical cooling rate is used. Instead, an element that forms a glass phase upon cooling from the liquid phase is added to the composition as an alloy component.

A particularly noticeable alloy system that forms glass in the bulk state is described in US Pat. No. 5,288,344, the contents of which are referred to in this application. For example, niobium is added to a zirconium-titanium-copper-nickel-beryllium alloy having a glass-forming composition when forming a composite having a crystalline reinforcing phase and an amorphous matrix. An alloy of this composition is melted and made homogeneous. When the molten alloy is cooled to a temperature range between the liquidus and solidus for this composition, the concentration distribution causes a ductile metal dendrite that is a crystalline solid phase and a liquid phase with a different composition. Produces. When the metal concentration in the liquid phase decreases with the growth of the crystalline solid phase, the composition of the liquid phase shifts to a composition that produces bulk metallic glass at a low cooling rate.
When cooling of the remaining liquid phase further proceeds, an amorphous matrix is generated around the crystal phase.

  An alloy suitable for the present invention has a portion where the liquidus and solidus of the phase diagram are both vertical or inclined and the temperature is not constant at least at one location.

  As an example, as shown in FIG. 1, consider a case where there is a eutectic point and one metal A has solubility with respect to the other metal B in the phase diagram of the A-B binary alloy. In such an alloy system, there is a horizontal line at the eutectic temperature in the phase diagram, that is, a solid line at a constant temperature, and this line extends from the B end, and the AB solid solution and B are in equilibrium. Has reached. The solidus is inclined upward from this equilibrium point to reach the melting point of A. The liquidus in this phase diagram reaches from the melting point of A to the eutectic composition point in the horizontal portion of the solidus, and then to the melting point of B. Thus, the solidus has a portion where the temperature is not constant (from the melting point of A to the eutectic point). The perpendicular from the melting point of B to the eutectic temperature can also be considered as a solidus line in which A does not dissolve in B. Similarly, the liquidus has an inclined portion where the temperature is not constant. In the case of a ternary alloy phase diagram, those corresponding to solid phase lines and liquid phase lines are also referred to as solid phase surfaces and liquid phase surfaces.

  Binary and ternary alloys suitable for the present invention are currently unknown. Alloys suitable for the present invention are quaternary, quinary, or more complex multicomponents. Although it is very difficult to visualize such a multi-component phase diagram, there is still a liquid phase surface or a solid phase surface. Multi-component systems can be expressed using quasi-binary phase diagrams and quasi-ternary phase diagrams, but in these state diagrams one side or one corner is not an element by itself but one alloy. Represents.

  Here, the solidus in this application is not exactly the same as the solidus in the conventional crystalline metal phase diagram, for example. As a term in the present application, a line (or plane) that defines a boundary between a metal liquid phase and a metal solid phase may be referred to as a solid phase line. This terminology is suitable to refer to the boundary between the liquid phase and the crystalline solid phase that constitutes the phase embedded in the matrix. For the portion of the molten metal that forms the glass phase, the “solidus” is typically not the temperature that is clearly defined, but the temperature at which the alloy is sufficiently viscous that the alloy is considered rigid or solid. . Knowing the exact temperature itself is not important.

  Before considering the selection of the alloy composition, the distribution phenomenon in the pseudo binary alloy system will be described. FIG. 2 shows a quasi-binary phase diagram of the alloy M and the alloy X having a composition that forms an amorphous metal at a practical cooling rate that has a strong tendency to form a glass phase. In the figure, the left side is 100% M and the right side is 100% X. The upper gentle curve is the liquidus line of M in this alloy, the steep curve near the left side is the solidus line of M, and X has a certain degree of solid solubility in the body-centered cubic M alloy. Yes. The substantially horizontal line located below the liquidus is the substantial solidus of the amorphous alloy. The perpendicular in the middle indicates any alloy containing an excess of M with respect to a composition that has a strong tendency to form bulk glass alloys.

  When this alloy is cooled from the liquid phase, it encounters a liquidus line, and M of the bcc structure (some components of V1, having a composition where the line drawn horizontally from the liquidus line intersects the solidus line, (Titanium and / or zirconium is mainly dissolved) starts to precipitate. When cooling further proceeds, dendrites of M crystals grow and the M concentration in the liquid phase decreases, and the composition of the liquid phase changes along the inclined liquidus line. In this way, concentration distribution occurs, and a bcc crystal phase having a high M concentration and a liquid phase having a low M concentration are generated.

In FIG. 2, at an arbitrary processing temperature T ₁ , the proportion of the solid phase M alloy corresponds to the distance A, and the proportion of the remaining liquid phase corresponds to the distance B. That is, about 1/4 is a solid phase dendrite and 3/4 is a liquid phase. In an equilibrium state at a processing temperature T ₂ slightly lower than T ₁ , approximately 1/3 is a crystalline solid phase and 2/3 is a liquid phase.

When this alloy is cooled to the first higher temperature T ₁ and held there until equilibrium is reached and then rapidly cooled, about 1/4 becomes bcc alloy particles, corresponding to the liquidus at T _1. A composite dispersed in a bulk metallic glass matrix of composition is obtained. By changing the holding temperature above the solidus, the ratio between the crystalline phase and the amorphous phase can be changed. For example, if held at T2, the ratio of the ductile metal particles increases.

  Instead of cooling and holding to reach the equilibrium shown in the phase diagram, it would be common to continuously cool from the melt to the solid state. The form, proportion, size, and spacing of the ductile metal dendrite in the amorphous metal matrix is affected by the cooling rate. In general, the faster the cooling rate, the shorter the time for crystal dendrite nucleation and growth, so the dimensions are smaller and the spacing is larger. The orientation of dendrites is affected by local temperature gradients during solidification. The desired cooling rate to achieve the desired dendrite morphology and proportion for a particular alloy can be found with some experimentation.

For example, in order to produce a composite with excellent mechanical properties in which a crystalline reinforcing phase exists in an amorphous matrix, bulk metal glass formation tendency with M as Nb in the Zr—Ti—M—Cu—Ni—Be system Use a composition with increased FIG. 3 is a quasi-ternary phase diagram, where each vertex represents titanium, zirconium, and X, respectively, and X is B ₉ Cu ₅ Ni ₄ . An example of alloy selection will be described with reference to this figure. The small circles in the figure are near 42% Zr, 13% Ti, 45% X, which is the desired composition of the bulk glass forming alloy.

  In this alloy system, there are two ways to design useful composites in which crystalline metal particles are dispersed in an amorphous matrix. The first method is a method of systematically manipulating the chemical composition of the metallic glass forming composition in the Zr—Ti—Cu—Ni—Be system. The second method is to create a chemical composition that is a mixture of pure metal or alloy added to a good bulk metallic glass forming composition in the Zr-Ti-Cu-Ni-Be system.

First Method: Systematic Operation of Bulk Metal Glass Forming Composition The following chemical composition was found as an excellent bulk metal glass forming composition: (Zr ₇₅ Ti ₂₅ ) ₅₅ X ₄₅ = Zr _41.2 Ti _13.8 Cu _{12 .5} Ni ₁₀ Be _22.5 (unit: atomic%). This composition is denoted as symbol V1. This alloy composition has a ratio of Zr and Ti of 75:25, and is represented by a small circle in a large ellipse in the phase diagram.

  Around the composition V1, there is a large region of chemical composition that forms bulk metallic glass (the dimension in any direction is greater than 1 mm) when cooled from the liquid phase at a practical cooling rate. This bulk glass formation region (GFR) is indicated by GFR in FIG. When a liquid phase having a chemical composition in this region is cooled, it becomes completely amorphous when cooled to a temperature lower than the glass point transfer.

In this quasi-ternary phase diagram, there are a large number of crystalline or quasicrystalline coexisting phases that limit the ability to form bulk metallic glass. In the GFR, these phases become unstable and do not prevent vitrification when the liquid phase is cooled from the molten state. However, in the case of compositions outside the GFR, concentration partitioning occurs in the liquid phase when cooling from a hot liquid state. If the alloy composition is appropriate, a good composite industrial material is produced in which a ductile metal crystal phase is present in the amorphous matrix. Outside the GFR, there is an inappropriate alloy composition that results in a composite material in which a brittle crystal phase is present in the amorphous matrix.
The presence of a brittle crystal phase greatly degrades the mechanical properties of the resulting composite material.

For example, in the upper right direction of the large GFR elliptical region, there is a small elliptical region that partially overlaps the edge thereof, and when the alloy in this region is cooled from the liquid phase, brittle Cu ₂ ZrTi can be generated. . This causes embrittlement and is not suitable for the present invention. In the illustrated pseudo-ternary phase diagram, these regions are shown schematically for the purpose of explaining the present invention.

The small circular region shown at the upper left of the large GFR ellipse region is a region where a pseudocrystalline phase that also causes embrittlement is formed. The partially oval region above is the region formed by the NiTiZr Laves phase. In a small triangular region on the side of Zr—X, a TiZrCu ₂ phase and / or a Ti ₂ Cu phase that are intermetallic compounds are formed. In each small region near 70% X, a ZrBe ₂ intermetallic compound phase and / or a TiBe ₂ Laves phase is formed. There may be α-type and β-type Zr or Zr—Ti alloys along the sides of Zr—Ti.

In order to produce a composite material with excellent mechanical properties, a ductile second phase is generated in-situ. Then, the region of the brittle second phase shown in the pseudo ternary phase diagram is avoided. The remaining almost triangular region is located in the upper left direction from the circular shape of Zr ₄₂ Ti ₁₄ X _{44. In} this region, another metal M is used instead of zirconium and / or titanium, and the desired property is obtained. Composite materials can be obtained.
This was investigated using niobium instead of titanium.

In FIG. 3, a dotted line is drawn toward 25% Ti on the side of Zr—Ti. This series of composition on the dotted line _{(Zr 100-x Ti x-} z M z) 100-y ((Ni 45 Cu 55)) 50 Be 50) y, [where M = Nb, X = 25], in, An increase in z means that Ti decreases with respect to the original composition 75:25. The composition on the dotted line within the large elliptical region is a good bulk glass forming alloy. Outside this ellipse, ductile dendrites with a high zirconium concentration are formed in the composite material with an amorphous matrix. This ductile dendrite is generated for a wide range of z and y values by concentration distribution.

  For example, when z = 3 and y = 25, a β phase is generated. It was confirmed that the β phase was generated in the range from z = 13.3 to z = 20 when the y value was about 25. It was found that when M is niobium, excellent mechanical properties can be obtained in the range of z = 5 to z = 10 on the 75:25 dotted line (the optimum composition is z = about 6.66).

  However, on the 75:25 dotted line, beryllium should not be less than about 5%, ie, y should be less than 10. Below this, almost no amorphous phase remains, the alloy is almost composed only of dendrites, and desirable properties as a composite material cannot be obtained.

As a series of _alloys, consider a _{(Zr 100-x Ti x-} z M z) X y. Here, M is an element that stabilizes the crystalline β phase in the Ti-based alloy or Zr-based alloy, and X is the same as described above. To produce in situ generated bulk metallic glass matrix composites with good mechanical properties, the crystalline second phase that preferentially nucleates upon cooling from the hot liquid phase must be a ductile phase. is important. One example that demonstrates excellent mechanical properties in an in situ generated bulk metallic glass matrix composite is (Zr ₇₅ Ti _18.34 Nb _6.66 ) ₇₅ X ₂₅ , ie M = Nb, z = 6.66, x = 18.34, y = 25 alloy. This is the composition on the dotted line in FIG.

  From the peak on the X-ray diffraction pattern of this composition (shown in the SEM micrograph in FIG. 4), the second phase present has a body-centered cubic (bcc) phase or β phase crystal symmetry, X-ray It can be seen that the pattern is due to the β phase only. The β-phase lattice constant determined by the Nelson-Riley extrapolation method is a = 3.496 angstroms. Thus, upon cooling from the high temperature liquid phase, the alloy is partially crystallized by nucleation and growth of the crystalline ductile metal phase. Thereafter, the remaining liquid phase is solidified to form a glassy phase. As a result, a two-phase structure in which a β-phase dendrite is present in the amorphous matrix is formed. FIG. 4 shows an SEM image of the microstructure obtained by chemically etching the finally obtained sample.

According to EPMA analysis in SEM, the average composition of β-phase dendrites (bright phase in FIG. 4) was Zr ₇₁ Ti _16.3 Nb ₁₀ Cu _1.8 Ni _0.9 .

Assuming that all of the beryllium in the alloy is distributed into the matrix, the average composition of the amorphous matrix (the phase that appears dark) is Zr ₄₇ Ti _12.9 Nb _2.8 Cu ₁₁ Be _16.7 . As a result of EPMA analysis, there was no composition variation in the two phases within the range of experimental error (about ± 1 atomic%).

Comparing the amount of heat of crystallization of the residual amorphous matrix by scanning differential thermal analysis with a completely amorphous sample, the molar fraction (and volume fraction) of the two phases is directly determined. According to this, the β phase was about 25% by volume and the amorphous phase was about 75% by volume. This result was in good agreement with the result of area measurement on the SEM image.
It can be seen from the SEM image in FIG. 4 that the β-phase dendrite structure is well developed. The dendrite structure has a primary dendrite column length of 50 to 150 μm and a radius of about 1.5 to 2 μm. Secondary dendrite arms slightly thinner than the primary crystal dendrite are regularly arranged at intervals of about 6 to 7 μm. This dendrite “tree” is a very uniform and regular organization. As expected from dendrite growth in the direction of the local temperature gradient during solidification, the dendritic column has a texture throughout the sample.

The relative volume fraction of β phase present in this in-situ composite can be varied greatly by controlling the chemical composition and processing conditions. For example, by changing the y value group of alloys that are on the dotted line of FIG. 3 [For M = Nb] _{(Zr 75 Ti 18.34 Nb 6.66)} 100-y X y, i.e., the period of the transition metal By changing the relative proportions of the first element (first transition metal) and the second element (second transition metal) in the table, the microstructure and mechanical behavior under load changes dramatically.
Zr—Ti—M—Cu—Ni—Be based in-situ composites were prepared for alloy groups other than the alloy group on the dotted line. These additional alloy groups cover the quaternary composition phase region in FIG. This region passes clockwise from a line drawn from the V1 alloy composition (not shown), through a dotted line through the Zr corner of the pseudo-ternary phase diagram, and through a line drawn from the V1 alloy composition (not shown). This leads to the Ti corner of the quasi-ternary phase diagram, but excludes each region where the brittle crystal phase, pseudocrystal phase, and Laves phase are stable.

  Second method: Creation of a chemical composition that is a mixture of a good bulk metallic glass forming composition plus a pure metal or alloy in the Zr-Ti-Cu-Ni-Be system Designing in situ composites by concentration distribution As an example, the following material group will be described. These alloys are produced by a mixing rule of a composition that easily forms bulk metallic glass (BMG) and a metal or an alloy. The mixing formula is BMG (100−x) + M (x), and when M = Nb, BMG (100−x) + Nb (x). Desirably, to make this form of an in situ generated composite alloy, the metal or alloy is first dissolved with the first transition metal of BMG composition. Thereby, pure metal Nb is alloyed with Zr and Ti of V1 alloy by arc melting. This alloy is arc melted with the remaining components of the V1BMG alloy: Cu, Ni, Be. When this alloy is cooled from a hot molten state, partial crystallization occurs in which almost pure Nb dendrites with β phase symmetry are nucleated and grown from the liquid phase. Thereafter, the residual liquid phase is solidified to become a glass phase, and a two-phase structure in which a β-phase dendrite having a high Nb concentration exists in the amorphous matrix is formed.

When an alloy composition with an excess of about 25 atomic% Nb is used in _comparison with a composition that easily forms a bulk metallic glass (Zr _41.2 Ti _13.8 Cu _12.4 Ni _10.1 Be _22.5 ), Crystalline ductile niobium alloy forms upon cooling through the region between the phase and solidus lines. The composition of this dendrite is about 83% (atomic%) niobium, about 8% titanium, about 8.5% zirconium, and about 1.5% (copper + nickel). This composition is obtained when the bcc phase dendrite is about 1/4 and the amorphous matrix is 3/4. Similar behavior is observed when only tantalum is added to the V1 alloy. In addition to niobium and tantalum, additional metal elements in the composition that forms the composite in situ include molybdenum, chromium, tungsten, and vanadium.

  If the distribution phenomenon is used, a dendrite ratio is small and an amorphous matrix ratio is large, and a dendrite ratio is large and an amorphous matrix ratio is small. This ratio can be easily changed by changing the amount of metal that stabilizes the crystalline phase. For example, the ratio of crystalline particles in the glass matrix can be increased by increasing the ratio of niobium and decreasing the total amount of other elements in the alloy that can easily form bulk metallic glass.

  It is important to form a two-phase complex and avoid the formation of a third phase. Obviously, it is important to avoid the formation of these as a third phase because the intermetallic phase, Laves phase, and pseudocrystalline phase greatly degrade the mechanical properties of the composite.

  It is possible to obtain a good composite of the present invention by setting the particle size of the third phase, ie, the brittle phase, to less than 0.1 μm. Such a small particle can minimize the influence on the formation of the shear deformation band and can almost eliminate the influence on the mechanical properties.

  In the Zr—Ti—Cu—Ni—Be system having a high niobium concentration, the structure obtained by the formation of dendrite from the molten metal is a stable crystalline Zr—Ti—Nb alloy having a β-phase (bcc) structure. It is a structure existing in the Ti—Nb—Cu—Ni—Be amorphous metal matrix. The ductile crystalline metal particles are dispersed in an amorphous metal matrix, and have inherent geometric constraints on the matrix and generate a number of shear deformation bands when loaded.

Sub-size Charpy specimens were made from the in-situ produced composite material of the present invention having an overall average composition of Zr _56.25 Nb ₅ Ti _13.76 Cu _6.875 Ni _5.625 Be _12.5 . The Charpy impact value was 250% larger than that of the bulk metal glass matrix alone, with the former being 15 ft-lb and the latter being 6 ft-lb. As a result of the bending test, the plastic strain until the fracture was as large as about 4%. A number of shear deformation bands generated during the bending test had a periodic interval of about 8 μm, and this cycle was determined by the form and interval of β-phase dendrites. In the case of a plate cast at a high cooling rate, the plastic strain until bending fracture was about 25%. The sample could be bent 180 °.

  As shown in FIG. 5, a shear deformation band crossing both the amorphous metal matrix phase and the ductile metal dendrite phase was observed in the test piece after applying strain. The direction of the shear band is slightly different between the two phases, which is due to the difference in mechanical properties and possibly the crystal orientation of the dendrite phase.

The above shear band pattern occurs over a wide range of strain rates. The test piece formed with the shear deformation band crossing the matrix and the dendrite was tested under a quasi-static load with a strain rate of about 10 ⁻⁴ to 10 ⁻³ / sec. Since the Charpy impact value is dramatically improved, it can be seen that the same mechanism works even at a strain rate of 10 ³ / sec or more.

  The test piece tested with the compressive load had a large value on the order of 8% in strain until breakage. As shown in FIG. 6, in a typical stress-strain curve, an elastic-perfect plastic type compression behavior appears, plastic deformation starts at an elastic strain of about 1%, and the Young's modulus is about 106 GPa. It was. In the region exceeding the elastic limit, the slope m = dσ / dε of the stress-strain curve is about 106 GPa / unit strain> 0 and dσ / dε> 0, so that considerable work hardening has occurred. I understand. In the case of bulk metallic glass, this behavior is not observed, and it is common that the work softens in a region exceeding the elastic limit. This test was not limited to a test piece in which an amorphous metal single phase was devastatingly broken. In this compression test, fracture occurred on a plane inclined by about 45 ° with respect to the load axis. This behavior is similar to the fracture mode of a bulk metallic glass matrix. A plate material produced with a high cooling rate and a small dendrite size was broken at a strain of about 20% in a tensile test.

It is also possible to design an alloy that has a high Ti compared to the above-described high-Zr alloy and that is easy to form bulk glass. For example, in the Zr—Ti—M—Ni—Cu—Be alloy system, the composition suitable for glass formation is (Zr _100-x Ti _x M _z ) _100-y ((Ni ₄₅ Cu ₅₅ )) ₅₀ Be ₅₀ ). _{In y} , x = 5 to 95, y = 10 to 30, and z = 3 to 20, and M is selected from the group consisting of niobium, tantalum, tungsten, molybdenum, chromium, and vanadium. It is also possible to form a structure in which the ductile second phase is embedded in the amorphous matrix by adding other elements or adding a larger amount of the above elements and partitioning from the molten metal.

  According to experimental results, the morphology and spacing of the β phase can be controlled by chemical composition and / or processing conditions. Thereby, for example, properties such as fracture toughness and high cycle fatigue can be significantly improved. As a result, a material superior to conventional bulk metallic glass materials can be obtained.

  Conventional ductile metal reinforced bulk metallic glass matrix composites have not been able to significantly improve Charpy values and strain to break. At least in part, the size and distribution of the second phase particles mechanically introduced into the bulk metallic glass matrix. The significant improvements found in the in situ generated composites of the present invention are exerted by dendrite morphology, particle size, particle spacing, periodicity and ductile β phase volume fraction. This geometric constraint based on the dendrite distribution increases the density of the shear deformation zone, thereby increasing the plastic strain.

  Another factor of improvement is the quality of the interface between the ductile metal beta phase and the bulk metal glass matrix. In the composite material of the present invention, this interface is chemically homogeneous, automatically sharpened, and does not include the third phase. That is, the materials on both sides of the interface are in chemical equilibrium because they are generated from the molten metal by concentration distribution. Since the interface is clean in this way, the particle / matrix interface is in an equistrained state, thereby stabilizing the deformation and allowing the shear deformation band to propagate through the β-phase particles. Conventional composites have been made by embedding ductile refractory metal wires or particles in a glass-forming alloy matrix. The interface was inhomogeneous and the shear deformation zone could not pass.

  The mechanical properties of in-situ composites are most improved with respect to amorphous metals because of the natural nature of the ductile crystalline phase dispersed in the amorphous matrix, which requires large stresses to further increase the strain. This is the case with a strain limit. This is seen in compositions that produce stress-induced martensitic transformation or compositions that produce work twins. In the case of martensite, the particles undergo transformation-induced plasticity, and shear deformation has a strain limit where no further transformation occurs. Once the twinning occurs when the shear deformation zone of the amorphous phase meets the ductile particles, the strained material does not deform easily and the stress needs to be increased to further impart strain.

  Thus, it is desirable that the ductile metal phase present in the glass matrix has the property of undergoing stress-induced martensitic transformation. The stress level for causing the ductile metal particles to undergo transformation-induced plasticity is equal to or less than the shear strength of the amorphous metal phase in both the martensitic transformation and twinning.

  The ductile particles desirably have a crystal structure of any one of fcc, bcc, and hcp. In any of these crystal structures, not all fcc, all bcc, and all hcp, but a composition that exhibits stress-induced plasticity. Exists. Other crystal structures are brittle or are transformed into brittle structures and are not suitable for strengthening amorphous metal matrix composites.

The new concept of concentration partitioning is thought to be a universal phenomenon in many bulk metallic glass forming systems, ie composites formed by in situ generation methods in which a ductile metallic phase is present in the bulk metallic glass matrix. For example, a similar mechanical behavior improvement is observed for the (Zr100 _- xTix _{- zMz} ) _100-x (X) _y material, where X is a late transition metal that causes the formation of bulk metallic glass. In this alloy, X does not contain Be.

  It is important that the crystalline phase is a ductile phase and the shear deformation zone can pass through. If the second phase in the amorphous matrix is an ordered intermetallic compound or Laves phase that is inherently brittle, the composite material hardly exhibits ductility. The ductile deformation of the particles is important for the generation and propagation of shear deformation zones. Here, the ductile material in the particles is work-hardened, and this work-hardening can be relaxed by annealing, but must not exceed the glass transition temperature at which the amorphous phase disappears.

  The grain size of the crystalline phase dendrites can also be controlled during distribution. When the region between the liquidus and the solidus is cooled slowly, few nucleation sites are generated in the melt and relatively large particles are generated. On the other hand, if the processing temperature is rapidly cooled from the completely melted state at a temperature higher than the liquidus to the vicinity of the equilibrium state, a large number of nucleation sites are generated and the particle size is reduced.

  Control of the particle size and particle spacing in the solid phase can be controlled by the cooling rate in the region between the liquidus and the solidus and / or the holding time at the processing temperature in this region. This can be done in a short time to prevent excessive crystal growth. Addition of elements distributed to the crystal phase also helps control the grain size of the crystal phase. For example, when the amount of niobium added is increased, the number of nucleation sites clearly increases and the generated particles become finer. As a result, the volume fraction of the amorphous phase does not change substantially, and the particle size and particle spacing simply change. On the other hand, the volume fraction of the crystal and the amorphous phase can be controlled by changing the temperature between the liquidus / solidus which becomes the rapid cooling start temperature of the alloy. The volume fraction of the ductile crystal phase is optimally about 25%.

  As an example, the composition of the solid phase generated from the molten metal is: zirconium: 67 to 74 atomic%, titanium: 15 to 17 atomic%, copper: 1 to 3 atomic%, nickel: 0 to 2 atomic%, niobium: 8 to 12 Atomic%. This composition is crystalline and does not form an amorphous alloy at a practical cooling rate.

  The composition of the liquid phase as the remaining part is: zirconium: 35 to 43 atomic%, titanium: 9 to 12 atomic%, copper: 7 to 11 atomic%, nickel: 6 to 9 atomic%, beryllium: 28 to 38 atomic%, Niobium: 2 to 4 atomic%. This composition is within a range where an amorphous alloy is formed with sufficient quenching.

  When the region between the liquidus and solidus is cooled at an estimated rate of less than 50 K / sec, ductile dendrites with primary column lengths of about 50-150 μm are produced. (Cooling was performed in a water-cooled copper crucible with a 1 mm thick sample from one side.) This dendrite has a well-developed secondary arm with a width of about 4-6 μm and an arm spacing of about 6-8 μm. When this material was compression tested, shear deformation bands arranged at equal intervals of about 7 μm were observed. Thus, the shear deformation band interval corresponds to the dendrite secondary arm interval.

When casting was performed at an estimated cooling rate of 100 K / second or higher, the dendrite was clearly small, the main column length was about 5 μm, and the secondary arm spacing was 1-2 μm. This dendrite was not a typical dendritic shape, but rather a flaky shape.
Compared to a composite with a slow cooling rate, dendrites are less uniform and have a small volume fraction (about 20%) in the composite. (Cooling was performed from both sides of a 3.3 mm thick sample.) This composite has a higher density of shear deformation bands than a composite material with a large dendrite and a wide spacing. About 4-5% of the volume in the aforementioned composite was a shear deformation zone, whereas this “fine-grained” composite was 2-5 times in density. That is, in the latter composite, the amount of deformed metal is large, which is also indicated by a large amount of strain until breakage.

  The direction of primary dendrites is determined by the local temperature gradient during solidification. As the cooling progresses, the dendritic main column nucleates along the temperature gradient, that is, in the low temperature portion and extends toward the high temperature portion. The secondary arm is generated laterally with respect to the main column, and is generally inclined in a direction away from the low temperature portion. In other words, this dendrite is arrow-shaped and its tip is directed to the heat removal direction.

  Each of the shear deformation bands formed when a load is applied propagates in the direction of the main column of the dendrite and crosses the secondary dendrite arm. Each plane formed by these deformation bands is along the dendrite main pillar. Thus, the orientation of the dendrite affects the direction of strain and the direction of fracture in the composite. Accordingly, the direction of strain and fracture can be controlled by controlling the orientation of the dendrite.

  The direction of the external load also affects the direction of the shear deformation zone, and may have priority over the propensity to propagate toward the dendrite main column. Knowing how the shear deformation zone propagates, it can be designed to improve the properties of the composite in critical stress regions by appropriately controlling not only the dendrite morphology, ie its orientation, but also its dimensions. .

  When describing the particle size or particle interval as a term in the present application, it refers to the width and interval of the dendrite secondary arm. For the case where no dendrite structure is present, the particle size has the usual meaning and refers to the average diameter of spherical or nearly spherical particles. It is also possible to form an acicular or lamellar structure of ductile metal in the amorphous matrix. The width of these structures is also considered as the particle size. Here, the widths of the dendrite secondary arms are not uniform, and extend from the wide end portion closest to the main column toward the dotted or slightly rounded free end portion. Therefore, the “width” is a value in a region through which a shear deformation band between both ends passes. Similarly, since the base of the arm is wide, the arm interval is narrow at the base and widens toward the tip. Shear deformation bands appear to propagate preferentially through regions of similar width and spacing. Of course, the dendrite has a three-dimensional structure and the shear deformation band is flat to some extent, so the above description is only approximate.

  The particle spacing means the distance between the centers, and the same applies to the portion that can be read as the distance between the ends in the context of the present specification.

  Another means of particle size control is to disperse artificial nucleation sites in the melt. Therefore, a substance that does not dissolve in the molten metal, such as fine ceramic particles having an appropriate crystal structure, can be used. Agitation can also affect nucleation and dendrite growth. Cooling rate control is desirable because it is reproducible and easy.

  When the ductile metal second phase in the amorphous metal matrix has a particle size of about 0.1 to 15 μm, it is considered that the mechanical properties of the composite material are improved. If the particles are less than 100 nm, there is little or no effect on the mechanical properties, as the shear deformation zone can substantially avoid the particles. If the particles are too large, the ductile metal is the main component and the desired properties of the amorphous matrix cannot be substantially exhibited. The particle size is preferably 0.5 to 8 μm, and the best mechanical properties can be obtained in this range. If the crystal phase particles are too small to be smaller than the width of the shear deformation band, the effect is reduced. It is desirable that the particles be slightly larger than the spacing between the shear deformation bands.

The interval between adjacent particles is 0.1 to 20 μm. With this range of spacing for the ductile metal reinforcement phase in the continuous amorphous matrix, the shear deformation band over the entire deformed volume in the composite at a strain rate of about 10 ⁻⁴ to 10 ⁻³ / sec. Are evenly distributed. In order to obtain the best mechanical properties as a composite, the particle spacing is preferably 1 to 10 μm.

  The volume fraction of ductile metal particles in the amorphous matrix is also important. In order to improve the mechanical properties most, the ductile particles are desirably 5 to 50% by volume, and most desirably 15 to 35% by volume. If the ratio of the ductile crystalline metal phase is too small, the effect on the properties is reduced, and the properties of the amorphous metal phase are hardly improved. On the other hand, if the proportion of the second phase is too large, the property becomes dominant and the useful property of the amorphous phase cannot be utilized.

  However, in some cases, the volume ratio of the amorphous metal phase may be less than 50%, and the matrix may be a discontinuous phase. Although the volume ratio of the crystalline metal generated in situ is larger, the amorphous metal having the smaller volume ratio adjusts the stress-induced transformation, and desirable mechanical properties as a composite can be obtained.

  Desirably, the size and spacing of the ductile metallic crystalline phase is such that a shear deformation band having a width of about 100 to 500 μm is uniformly distributed. Typically, at least about 4 volume percent shear deformation bands are formed before the composite is strained and breaks. Since the ductility is related to the volume% of the material in the shear deformation band, it is desirable that the interval between the shear deformation bands is small. Therefore, it is desirable that the shear deformation band interval when the strain is applied until the material breaks is about 1 to 10 μm. When the shear deformation band interval is less than about 1/2 or exceeds about 20 μm, the effect of improving toughness by the particles is hardly obtained. The interval between the shear deformation bands is preferably about 2 to 5 times the width of the shear deformation band. When the shear deformation band interval is increased up to 20 times the shear deformation band width, an industrial material having sufficient ductility and toughness for many applications can be obtained.

As an example, when the density of the shear deformation band is about 4% of the material volume, the energy of deformation until fracture is estimated to be 23 Joules in a Charpy type test with a strain rate of about 10 ² to 10 ³ / sec. Based on this estimate, increasing the shear deformation band density to 30% by volume of the material volume increases the deformation energy to about 120 joules.

It is also desirable that the crystalline phase has approximately the same elastic modulus as the amorphous metal.
Thereby, the distribution of the shear deformation band becomes practically uniform. It is desirable that the elastic modulus of the crystalline metal phase is in the range of 50 to 150% of the elastic modulus of the amorphous metal alloy.
If the elastic modulus of the particles is too large, a large stress difference occurs at the interface between the particles and the amorphous matrix, and the particles break when applied with strain. Particles with a large elastic modulus may fall out of the matrix when the composite is strained.

  For an alloy suitable for producing an object having a size larger than a micron unit, the cooling rate from the liquidus / solidus region is desirably less than 1000 K / second. The cooling rate for avoiding crystallization of the glass-forming alloy is desirably 1 to 100 K / second. In order to identify applicable glass forming alloys, those with the ability to form layers of 1 mm or more were selected. In other words, the dimension of the object having an amorphous metal matrix is 1 mm or more at the minimum part.

  FIG. 7 schematically shows a technique for controlling the orientation of the dendrite structure when the ductile metal phase in the amorphous matrix is formed by concentration distribution. In this embodiment, temperature gradient control is performed so as to cause unidirectional solidification from one end of the elongated member, and a new dendrite is generated in the same direction as the already generated dendrite. This process is performed in the vacuum chamber 11 to protect the active material from contamination such as oxidation. The elongate container 12 is, for example, a quartz tube, is arranged in the vertical direction in the vacuum chamber, and is attached to a supply mechanism 13 for gradually lowering the inside of the vacuum chamber. The tube descends through a radio frequency induction coil 14 that heats the alloy in the tube above the melting point.

  Thereafter, the tube descends through one or more cooling sleeves 15, which remove heat from the tube and the alloy within the tube, and first deposit dendrites of crystalline alloy from the melt by distribution. Further, the remaining molten metal is cooled and solidified to form an amorphous matrix surrounding the ductile refractory metal particles. In the obtained composite, dendrite preferentially oriented is formed by unidirectional solidification along the length direction of the metal in the tube. This dendrite has almost the same direction of the dendrite main pillars, although the degree is different.

  If necessary, an additional heating zone may be provided in front of the cooling sleeve to keep the alloy at a processing temperature at which dendrite formation proceeds at a controlled rate. In this way, control of particle size, particle spacing, periodicity, orientation, both the descent rate from the melting zone to the cooling zone, and the holding at the intermediate temperature between the liquidus and solidus of the alloy Can be done.

  Other techniques can also be used to ensure and control the temperature gradient in the alloy during cooling from the melt. For example, the entire metal is melted, and the temperature gradient is obtained by performing one-way cooling in different parts of the obtained molten metal, particularly in the part where the alloy passes through the temperature region between the liquidus and solidus. Form. This can be done by cooling only from selected surface areas, for example by removing heat at different speeds in different surface areas. In the case of a plate-like or sheet-like casting, heat is preferentially removed from one side to selectively orient the dendrites in the composite structure. Can be oriented.

  As a result, the dendrite form of a complex-shaped member is controlled not only by controlling the chemical composition of the alloy, but also by the cooling rate and cooling direction in the temperature range between the liquidus and solidus. be able to. When the cooling rate is increased, the strain until breakage can be increased by controlling the cooling direction, and the orientation of the dendrite can be deflected in a direction that enhances the properties of the composite. The composite can also be cold worked, eg, cold rolled, to provide the desired texture.

  Even if wires, whiskers, and particles are mechanically added to the bulk metallic glass forming alloy, the mechanical properties obtained with the material of the present invention cannot be improved. Conventionally, the introduction of the reinforcing material into the bulk metallic glass alloy has been performed by melting the glass-forming metal and then introducing the particles of the reinforcing material into the molten alloy. Alternatively, the molded article of reinforcing material particle pieces was impregnated with a molten glass-forming alloy under gas pressure, and then cooled.

  Both of these methods reliably control the size and particle spacing of the second phase strengthening particles necessary to sufficiently constrain the bulk metallic glass matrix so that multiple shear deformation zones are formed when loaded. I couldn't. Since the interface between the reinforcing particles and the matrix is not chemically homogeneous, the internal energy is high and the strain transmission action is low. The composite material of the present invention has improved mechanical properties due to the in situ generated two-phase structure, interface homogeneity, dendrite morphology, particle size and particle spacing.

  Double complexes can be formed using the principle of in situ formation of complexes by metal concentration distribution during the cooling of the melt. For example, a bundle of tungsten wires is impregnated with a molten alloy selected from the alloys of the present invention. The resulting impregnated body is cooled to a processing temperature below the liquidus of the alloy and above the glass transition temperature. A crystalline metal phase is generated from the molten metal, and accordingly, the molten metal has several concentrations of component elements lowered. Next, sufficient quenching is performed to form an amorphous metal matrix surrounding the metal phase. The composite formed thereby becomes a matrix and embeds tungsten wires. The same principle can be used to impregnate other material bundles. Similarly, after the reinforcing phase is stirred and introduced into the molten metal, it is cooled to form a precipitated phase by distribution, and further cooled to form an amorphous matrix. By either method, a three-phase composite in which a reinforcing metal is embedded in a composite matrix can be formed.

Claims (42)

A substantially continuous matrix composed of an amorphous alloy, and a second phase consisting of ductile metal particles embedded in the matrix, the spacing between adjacent particles being 0.1-20 μm;
Comprising
Formed of at least two materials selected from the group consisting of Zr, Ti, Ni, Cu, Be, Nb, Ta, W, Mo, Cr, V and late transition metals,
Amorphous metal composite.   The amorphous metal composite according to claim 1, wherein the ductile metal particles of the second phase have a particle size of 0.1 to 15 μm.   The amorphous metal composite according to claim 1, wherein the ductile metal particles of the second phase have a particle size of 0.5 to 8 µm and an interval between adjacent particles of 1 to 10 µm.   The composition before crystallization of the molten alloy constituting the second phase is as follows: zirconium: 52-68 atomic%, titanium: 3-17 atomic%, copper: 2.5-8.5 atomic%, nickel: 2 The reinforced amorphous metal composite according to claim 1, which has 7 atom%, beryllium: 5 to 15 atom%, and niobium: 3 to 20 atom%.   The amorphous metal composite according to claim 1, wherein a residual molten portion after crystallization of the molten alloy has the same composition as the matrix.   The amorphous metal composite according to claim 1, wherein the second phase is dendritic.   The amorphous metal composite according to claim 1, wherein the second phase has an elastic modulus from 50% of the amorphous metal alloy to a value approximately equal to the amorphous metal alloy.   The amorphous metal composite according to claim 1, wherein the second phase is strengthened.   2. The amorphous metal composite according to claim 1, wherein the amorphous metal alloy constitutes a substantially continuous matrix, and the second phase is in a dendrite state having a secondary arm interval of more than 0.1 μm.   The amorphous metal composite according to claim 9, wherein the second phase comprises dendrite having a secondary arm width of 0.1 to 15 µm and an adjacent arm interval of 0.1 to 20 µm.   The amorphous metal composite according to claim 9, wherein the second phase comprises dendrites having a secondary arm interval of 0.5 to 8 µm and an adjacent arm interval of 1 to 10 µm.   The amorphous metal composite according to claim 11, wherein the orientation of each dendrite is uniform.   The amorphous metal composite according to claim 1, wherein the second phase comprises a plurality of ductile metal particles dispersed in the matrix, and the particles cause deformation-induced plasticity and are dissolved in the matrix alloy.   The amorphous metal composite according to claim 13, wherein the transformation-induced plasticity is due to martensitic transformation or twin deformation.   The reinforced amorphous metal composite according to claim 13, wherein the ductile metal particles cause a stress-induced martensitic transformation.   The reinforced amorphous metal composite according to claim 13, wherein a stress level at which the ductile metal particles cause transformation-induced plasticity is equal to or less than a shear strength of the amorphous alloy matrix.   The amorphous metal composite according to claim 13, wherein the particles have a particle size of 0.5 to 15 μm.   The ductile metal particles are discrete with sufficient spacing to produce a uniformly distributed shear zone across both the amorphous metal phase and the second phase, the shear zone having an individual width of 100 The amorphous metal composite according to claim 13, which is ˜500 nm.   The ductile metal particles are discrete with sufficient spacing so as to generate a shear deformation band that is uniformly distributed over the entire deformation region of the composite, and the shear deformation band is broken up to fracture under strain. The amorphous metal composite according to claim 13, which is 4% by volume or more of the composite and crosses both the amorphous metal phase and the second phase.   The amorphous metal composite according to claim 1, wherein the second phase is formed from a molten alloy by in situ generation.   The amorphous metal composite according to claim 1, wherein the dimension in any direction is larger than 1 mm.   The amorphous metal composite according to claim 1, wherein the second phase constitutes 5 to 50% by volume of the composite.   The amorphous metal composite according to claim 1, wherein the second phase constitutes 15 to 35% by volume of the composite.   The amorphous metal composite according to claim 1, wherein the second ductile metal phase is formed in the matrix by chemical partitioning from the same molten alloy as the amorphous metal alloy is formed.   2. The amorphous metal according to claim 1, wherein the second phase is a state of particles precipitated by in-situ generation from nucleation sites distributed in the metal substantially composed of the amorphous metal alloy and the second phase alloy. Complex.   The second phase of the ductile crystalline metal is embedded in the matrix, most elements of the crystalline phase are common with elements of the matrix, and most elements of the matrix are elements of the crystalline phase The amorphous metal composite according to claim 1, which is in common.   27. The amorphous metal according to claim 26, wherein the second phase is a state of particles precipitated by in-situ formation from nucleation sites distributed in the metal comprising the amorphous metal alloy and the second phase alloy. Complex.   27. The amorphous metal composite according to claim 26, wherein the second phase is dendritic.   27. The amorphous metal composite of claim 26, wherein the second phase of ductile metal comprises dendrites embedded in the matrix and the amorphous metal volume fraction is less than 50%. The following steps:
Heating an alloy formed of at least two materials selected from the group consisting of Zr, Ti, Cu, Be, Nb, Ta, W, Mo, Cr, V and a late transition metal to a temperature higher than the melting point;
Cooling the alloy for a sufficient time between the liquidus and solidus to produce a ductile crystalline phase having a particle size of 0.1 to 15 μm dispersed in the liquid phase; and A method for producing an amorphous metal composite, comprising the step of sufficiently rapidly cooling to a temperature lower than the glass transition point of forming an amorphous metal matrix surrounding the crystalline phase.   31. The method of claim 30, wherein the alloy is held between a liquidus and a solidus before cooling to a temperature below the glass transition point.   31. The method of claim 30, wherein the composition of the alloy is a composition outside the range that generates amorphous metal during slow cooling, and the composition of the liquid phase is a composition within the range that generates amorphous metal during slow cooling. .   The composition of the alloy is: zirconium: 52-68 atomic%, titanium: 3-17 atomic%, copper: 2.5-8.5 atomic%, nickel: 2-7 atomic%, beryllium: 5-15 atomic%, 31. The method of claim 30, wherein niobium is from 3 to 20 atomic%. The composition of the alloy is _{(Zr 100-x Ti x-} z M z) 100-y (Ni 45 Cu 55)) 50 Be 50) y, M is niobium, tantalum, tungsten, molybdenum, chromium and vanadium 31. The method of claim 30, wherein the method is selected from the group, x = 5-95, y = 10-30, z = 3-20. The process of forming the ductile crystalline phase is the following process:
A step of producing a dendrite having a secondary arm spacing of 0.1 to 20 μm from the molten alloy, and an amorphous metal matrix surrounding the dendrite by cooling the molten alloy remaining after the dendrite is sufficiently rapidly The method of claim 30, comprising the step of forming.   The alloy is cooled to a temperature between the liquidus and the solidus and the alloy is retained in the liquidus for a sufficient time between the liquidus and the solidus to disperse in the liquid phase 36. The method of claim 35, wherein a dendrite phase of is formed.   The composition of the dendrite is Zr: 67 to 74 atomic%, Ti: 15 to 17 atomic%, Cu: 1 to 3 atomic%, Ni: 0 to 2 atomic%, and Nb: 8 to 12, and the liquid phase The composition of Zr: 35 to 43 atom%, Ti: 9 to 12 atom%, Cu: 7 to 11 atom%, Ni: 6 to 9 atom%, Be: 28 to 38 atom%, and Nb: 2 to 4 atom 31. The method of claim 30, wherein the method is%.   32. The method of claim 30, wherein the composition of the crystalline phase is different from the liquid phase. The method according to claim 30, wherein the composition of the alloy is a composition that does not produce an amorphous phase when cooled at a rate of less than 10 ³ K / sec.   The alloy is cooled between the liquidus and solidus for a sufficient time to cause partial crystallization by nucleation and subsequent growth of the ductile crystalline phase in the residual liquid phase, 32. The method of claim 30, wherein the composition of the phase is different from the liquid phase.   36. The method of claim 35, wherein the dendrite is heat treated at about a nucleation temperature to render the dendrite particle size distribution uniform.   42. The method of claim 41, wherein the dendrite microstructure coarsens during the heat treatment.

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