Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2001-04-24
2003-12-30
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S403000
Reexamination Certificate
active
06669793
ABSTRACT:
BACKGROUND
A glass is a material that when cooled from its heated liquid transforms to the solid state without forming crystals. Such non-crystallized materials are also called amorphous materials. For example, one of the better known amorphous materials is quartz, which can be used to form conventional window glass. Most metals crystallize when they are cooled from the liquid state at reasonable rates, which causes their atoms to be arranged into a highly regular spatial pattern or lattice. A metallic glass is one in which the individual metal atoms have settled into an essentially random arrangement. Metallic glasses are not transparent like quartz glasses and are often less brittle than window glass.
A number of simple metal alloys may also be processed to form a glass-like structure. Binary metal alloys near deep eutectic features of the corresponding binary phase diagrams may be prepared into a glassy structure on cooling from the liquid state at rates greater than 1000 degrees per second. These binary metallic glasses may possess different properties than crystalline metals. These different properties may be useful in certain applications.
Bulk metallic glass forming alloys are a group of multicomponent metallic alloys that exhibit exceptionally high resistance to crystallization in the undercooled liquid state. Compared with the rapidly quenched binary metallic glasses studied prior to 1990, these alloys can be vitrified at lower cooling rates, less than 10 degrees per second.
Many of the recently discovered bulk glass forming alloys can be broadly described as pseudo-ternary alloys of the form ETM
1-x-y
LTM
x
SM
y
. Typically the early transition metal couple, ETM, is a combination of elements from group IVB of the periodic table; e.g., Zr and Ti. The late transition metals, LTM, are typically combinations of the 3d transition metals from groups VIIIB and IB; e.g., Fe, Co, Ni, and Cu. The simple metal element, SM, is normally chosen groups from IIA or IIIA; e.g., Be, Mg or Al. However, the addition of a SM element is not a requirement for the formation of a bulk glass forming alloy. There are also bulk metallic glass forming alloys based on magnesium.
Examples of some of the composition manifolds that contain ideal bulk metallic forming compositions are as follows: Zr—Ti—Cu—Ni—Be, Zr—Nb—Cu—Ni—Al, Ti—Zr—Cu—Ni, and Mg—Y—Cu—Ni—Li. Each of the chemical species and their combinations are chosen for a given alloy composition such that the alloy composition lies in a region with a low-lying liquid surface. Alloy compositions that exhibit a high glass forming ability are generally located in proximity to deep eutectic features in the multicomponent phase diagram. These materials, including the recently developed families of Zr-based bulk metallic glass alloys show great promise as engineering materials. However, as in many metallic glasses, specimens loaded in a state of uniaxial or plane stress fail catastrophically on one dominant shear band, thus limiting their global plasticity. 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. This behavior under deformation has limited the application of bulk metallic glasses as engineering materials.
SUMMARY
The present application teaches a new class of metallic glass materials that employ the previously unknown physical mechanism of shear band pattern formation. The occurrence of shear band pattern formation dramatically increases the plastic strain to failure, impact resistance, and toughness of the material.
To exploit this phenomenon, a metallic glass matrix is combined with a ductile metal or metal alloy phase. The metallic glasses of this type may be glassy matrix composites based on bulk glass forming compositions in any bulk metallic glass forming alloy system. Formation of these objects is carried out using standard powder metallurgy techniques, at temperatures that are below the melting point of the individual constituents. Combinations of powders comprised of bulk metallic glass forming particles and crystalline ductile metal or metal alloy phases are employed. To prepare a ductile metal/bulk metallic glass matrix composite material, mixtures of metal or metal alloy powders are mixed with the bulk metallic glass powders, followed by processing in the super cooled liquid region (“SLR”). The SLR is defined as the difference in temperature between the glass transition and crystallization temperatures of the glass matrix. This temperature interval is defined as &Dgr;T=(T
x
−T
g
), where T
g
and T
x
are the glass transition, and crystallization temperatures, respectively, of the bulk metallic glass constituent which is used to prepare the consolidated powder product or composite, and with the geometry desired. The control of the relative volume fractions of the ductile metal or metal alloy particles and bulk metallic glass matrix is simply controlled by the initial the mixing ratio. The maximum properties allowed by shear band pattern formation upon mechanical deformation are readily controlled in composites prepared in this fashion. This method also allows for bulk metallic glass matrix particles which incorporate crystalline ductile metal phases, formed from the molten state in situ, with a possible further increase in properties. The length scales, or size ranges, associated with the ductile metal or metal alloy phases may be of significantly differing magnitudes. Hence, these differing scales may result in duplex, triplex, or higher order multiplex morphological structures for the added particle sizes; each with a specific purpose. Namely, there will be a preferred size range, of the order of microns in which shear band pattern formation is encouraged. The particles added with larger length scales will further toughen the composite material formed by use of traditional composite toughening mechanisms such as, crack bridging, fiber pull-out, etc. The formation of shear band patterns through the material may cause new effects that had not been previously known in the art.
DETAILED DESCRIPTION
The present invention describes a material formed by a specified combination of ductile metal and bulk metallic glass matrix. More specifically, the system describes crystalline ductile metal particles being existing within a matrix of amorphous bulk metallic glass. Specific materials are described herein, but it should be understood that other materials may be used and other formation techniques. The system operates to toughen bulk metallic glasses using included ductile phases in a composite comprised of a metallic glass matrix.
For introductory purposes only, consider an embodiment for disclosure of the example of shear band pattern forming observed via in situ precipitation from the liquid state in the Zr—Ti—Cu—Ni—Be alloy system. The bulk glass forming compositions in the Zr—Ti—Cu—Ni—Be system are compactly written in terms of a pseudo-ternary Zr—Ti—X phase diagram, where X represents the moiety Be
9
Cu
5
Ni
4
. Results have been obtained for alloys of the form (Zr
100-x-z
Ti
x
M
z
)
100-y
X
y
, where M is an element that stabilizes a crystalline beta-phase in Ti- or Zr-based alloys. The composition of specific interest is (Zr
75
Ti
18.34
Nb
6.66
)
75
X
25
; i.e., an alloy with M=Nb, z=6.66, x=18.34, and y=25. Upon cooling from the high temperature melt, the alloy undergoes partial crystallization by nucleation and subsequent dendritic growth of the beta-phase in the remaining liquid. The remaining liquid subsequently freezes to the glassy state. This produces a two-phase microstructure containing beta-phase dendrites in a glass matrix.
The inherent properties of the final material impose constraints on the glassy matrix. Upon deformation these constraints lead to the generation of highly organized shear band patterns throughout the material. In the deformed regions of the material regularl
California Institute of Technology
Fish & Richardson P.C.
Wyszomierski George
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