Metal treatment – Process of modifying or maintaining internal physical... – With measuring – testing – or sensing
Reexamination Certificate
2001-11-14
2004-02-24
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With measuring, testing, or sensing
C148S403000, C148S539000, C075S375000, C075S384000, C075S386000
Reexamination Certificate
active
06695936
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for the identification and processing of bulk metallic glass forming alloys, and the manufacture of components fabricated from these alloys.
2. Description of the Related Art
During the past decade, numerous university and industrial research groups have invested significant efforts to discover metal alloy formulations which form glass when cooled from the molten state at relatively slow rates of cooling. Vitrification or glass formation in metal alloys was first discovered in about 1960 by P. Duwez and coworkers at the California Institute of Technology (“Caltech”). They used “rapid solidification” techniques to produce glassy alloys by cooling the liquid alloy at rates of about 1 million degrees per second. A variety of such rapidly quenched metallic glasses were produced over the following three decades.
Beginning in about 1990, the research groups of Prof. A. Inoue in Japan and Prof. W. L. Johnson at Caltech developed complex alloys containing 3, 4, 5 or more components which formed glasses at far lower cooling rates, typically 1-100 degrees per second when solidified from the equilibrium liquid state. During the past several years, these “bulk” glass forming alloys have attracted substantial commercial interest as engineering materials. The bulk metallic glasses have high strength, high hardness, high specific strength, and a variety of other useful engineering properties. Furthermore, the liquid alloys are highly processable and can be cast into complex three dimensional very near net shapes. Interest in utilizing these materials in engineering applications has led to widespread interest in developing and discovering new bulk glass forming alloys, in processing these alloys from the melt, and utilizing these alloys to produce commercially useful materials such as rods, plates, sheets, tubes, and other more complex shapes.
A key parameter which distinguishes alloys with exceptional glass forming ability is their relatively low melting point. Alloys which form bulk metallic glass undergo equilibrium melting of the initial alloy over a range of temperatures which are relatively low compared with the compositionally averaged melting point of the pure metals which comprise the alloy. Very often, the optimum glass forming alloy lies near a minimum in the melting surface (liquidus surface) of the alloy taken as a function of the alloy composition. This liquidus surface is conventionally represented in alloy phase diagrams as a “liquidus projection.” For example, in a two component alloy, the liquidus curve can be represented as a curve in the composition/temperature plane.
A simple example is shown in the Au—Si phase diagram of FIG.
1
. This phase diagram of binary Au—Si alloy shows a eutectic composition
10
with a eutectic temperature
12
of 363° C. The liquidus line
14
represents the line above which a single liquid phase is present. The solidus line
16
represents the line below which the system has completely solidified. Note that the melting point of Au is about 1064° C. and that of Si is about 1414° C. Also illustrated is the compositional partitioning of a slowly cooled liquid at an off-eutectic composition
18
during solidification where x
L
is the composition of the remaining liquid.
In this simple binary case, the eutectic composition is precisely the compositional range where Duwez and coworkers produced the first metallic glass by rapid quenching. More generally, low lying liquidus temperatures (e.g. near alloy eutectic compositions) locate the optimum glass forming regions in higher order ternary, quaternary, quinary, etc. glass forming alloys. See W. L. Johnson, 24
Materials Research Society Bulletin
42-56 (October 1999). Generally speaking, the ability to form metallic glass is optimized at or near eutectic compositions, or more generally near the lowest lying temperatures of the liquidus surface in ternary, quaternary and higher order alloys. As such, the search for easy glass forming alloys is very frequently found to be equivalent to finding those alloy compositions corresponding to the lowest lying melting temperatures (or lowest lying liquidus surface). Most often, the best glass forming alloys lie within about ±5 at. % of a minimum in the liquidus surface. The search for easy glass forming alloys is thus dramatically simplified when the lowest melting alloys can be identified.
To locate glass forming compositions, it is critical to be able to identify or “discover” alloys with chemical compositions located near the lowest lying regions of the melting curves in the higher order alloys. Thus, it is of interest to develop an efficient means of both discovering and isolating the lowest melting alloys in a complex multicomponent alloys system containing two, preferably three or more metals. In the case of alloys with more than three components, the phase diagrams are generally not available and little or no information exists to guide the researcher to the optimum low melting compositions.
It has actually been proposed to develop materials combinatory methods whereby one searches for low melting alloys by literally making thousands of alloy compositions (using for example thin film processing methods) and screening their melting points in a rapid and parallel manner. See 159 Chem. Week 57 (1997). This approach requires carrying out literally thousands or tens of thousands of screening experiments. Thus, what is needed is a method of identifying the lowest melting alloy in a single or small number of experiments on a bulk liquid.
The production of bulk metallic glass, in addition to developing low melting point alloys, also requires that the low melting liquid alloy be substantially free of contaminants, oxides, and debris which induce crystallization. For metals, the most frequently encountered contamination of the liquid is in the form of crystalline oxide particles, carbide particles, and a variety of other types of nascent foreign substances. These contaminants are ubiquitous and ever present in the processing of nearly all commercial metals used in casting of metallic components. In most common cases (e.g., casting of aluminum, iron, and titanium alloys), they are inevitable inclusions in the liquid. It is well known that this nascent contamination frequently induces crystallization of the liquid alloy when it is undercooled below its melting point. Metallurgists refer to this as heterogeneous crystal nucleation. Practically speaking, heterogeneous nucleation is extremely harmful to the glass forming ability of metal alloys. As such, it would be extremely desirable to develop methods to reduce or eliminate nascent oxide, carbide, and other debris from metallic melts when attempting to produce metallic glass. Thus, what is needed is a direct and efficient means of removing most or nearly all of this nascent contamination and debris from a molten alloy.
Finally, it is of importance to produce bulk metallic glass in useful shapes. What is needed is a natural means of efficiently cooling and solidifying or casting a “decontaminated” alloy with an optimized composition (having the lowest melting point) into plates, rods, tubes, or other very near net shape castings.
SUMMARY OF THE INVENTION
The preferred embodiments of the present invention address these and other needs by providing a rapid and efficient method to identify and physically isolate alloy compositions of low melting alloys which readily form bulk metallic glass. Certain preferred embodiments also process these materials in a manner which removes unwanted and harmful impurities and debris (such as crystalline oxide, carbide or nitride particles) in the molten alloy to improve the glass forming ability of the liquid alloy. Preferred embodiments also describe the production and manufacture of large net shape castings, plates, rods, and other useful shapes from the purified and compositionally optimized liquid alloy.
In one aspect of the present invention, a method of identifying the
California Institute of Technology
Kastler Scott
Knobbe Martens Olson & Bear LLP
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