Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2001-08-03
2003-04-01
Sheehan, John P. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S565000, C148S668000, C148S422000
Reexamination Certificate
active
06540851
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to metal alloys, processes of making the same, and products made from or containing the alloy. More particularly, the present invention relates to alloys containing at least tantalum.
Tantalum has many uses in industry, such as use in capacitor-grade wires, deep-draw quality strips for making crucibles and the like, thin gauge strips, and other conventional uses. In forming products to be used in industry, the tantalum is obtained from tantalum bearing ore and converted to a salt which is then reduced to form a powder. The powder can be processed into an ingot by melting or the powder can be pressed and sintered to form the desired product. While the currently available commercial grades of tantalum has been acceptable to industry, there has been a desire to improve the tantalum properties since a powder metallurgy tantalum bar can have a wide range of different tensile strengths throughout the product and/or the ingot metallurgy tantalum can have large grain sizes which cause unwanted embrittlement of the tantalum, especially when formed into small diameters, as in the case of wire gauges.
Accordingly, there is a desire to improve the consistency of properties of tantalum to overcome the above-described disadvantages.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, the present invention relates to a metal alloy containing at least tantalum and silicon, wherein the tantalum is the highest weight percent metal present in the metal alloy. The alloy preferably has a uniformity of tensile strength when formed into a wire, such that the maximum population standard deviation of tensile strength for the wire is about 3 KSI for an unannealed wire at finish diameter and about 2 KSI for an annealed wire at finish diameter.
The present invention further relates to various products made from the alloy such as bars, tubes, sheets, wire, capacitors, and the like.
The present invention also relates to a process of making a metal alloy containing at least tantalum and silicon, wherein the tantalum is the highest weight percent metal present in the metal alloy. The method includes the steps of blending a first powder containing tantalum or an oxide thereof with a second powder containing at least silicon, an oxide thereof, or a silicon-containing compound to form a blend. This blend is then reduced to a liquid state, such as by melting the blend, and a solid alloy is then formed from the liquid state.
The present invention also relates to another process of making the alloy which includes reducing into a liquid state, either separately or together, a silicon-containing solid and a tantalum-containing solid to form a silicon-containing liquid and tantalum-containing liquid. The two liquids are then mixed together to form a liquid blend and then the liquid blend is formed into a solid alloy.
The present invention, in addition, relates to a method of increasing the uniformity of tensile strength in tantalum metal by silicon doping or introducing silicon to the tantalum metal in a sufficient amount to increase the uniformity of the tensile strength in the tantalum metal.
The present invention further relates to a method of reducing embrittlement of tantalum metal which includes the steps of doping the tantalum metal with silicon or introducing silicon to the tantalum metal in a sufficient amount to reduce the embrittlement of the tantalum metal.
Finally, the present invention relates to a method of imparting a controlled mechanical tensile strength level in tantalum metal by doping the tantalum metal with silicon or introducing silicon to the tantalum metal and then annealing the tantalum metal to impart a controlled or desired mechanical tensile strength in the tantalum metal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention relates, in part, to a metal alloy ingot comprising at least tantalum and silicon. The tantalum that is part of the metal alloy is the primary metal present. Thus, amongst any metal that may optionally be present, the highest weight percent of any metals present will be tantalum. Preferably, the weight percent of tantalum present in the alloy is at least about 50%, more preferably at least about 75%, even more preferably at least about 85% or at least about 95%, and most preferably at least about 97% or from about 97% to about 99.5% or higher tantalum. In the preferred embodiment, the alloy can be also considered tantalum microalloyed with silicon. The silicon is present in low amounts. Preferably, the tantalum-silicon alloy (or Ta—Si alloy) comprises from about 50 ppm by weight to about 5% by weight elemental silicon, more preferably from about 50 ppm to about 1,000 ppm elemental silicon, and most preferably from about 50 ppm to about 300 ppm elemental silicon, based on the weight of the alloy. The alloy preferably has less than 1% by weight elemental silicon present. The amount of silicon present in the alloy is generally a sufficient amount to increase the uniformity of the tensile strength of the resulting alloy compared to a tantalum metal containing no silicon.
The alloy of the present invention can contain other additional ingredients such as other metals or ingredients typically added to tantalum metal, such as yttrium, zirconium, titanium, or mixtures thereof. The types and amounts of these additional ingredients can be the same as those used with conventional tantalum and would be known to those skilled in the art. In one embodiment, the yttrium present in the alloy is less than 400 ppm or less than 100 ppm or less than 50 ppm. Metals other than tantalun can be present and preferably comprise less than 10% by weight in the alloy, more preferably less than 4% by weight in the alloy, and even more preferably less than 3%, or less than 2% by weight of alloy. Also, preferably, no or substantially no tungsten or molybdenum are present in the alloy.
Also, the alloy preferably has low levels of nitrogen present, such as less than 200 ppm and preferably less than 50 ppm, and even more preferably less than 25 ppm and most preferably less than 10 ppm. The alloy can also have low levels of oxygen present in the alloy, such as less than 150 ppm, and preferably less than 100 ppm, and more preferably less than about 75 ppm and even more preferably less than about 50 ppm.
The alloys of the present invention generally can have any grain size including the grain size typically found in pure or substantially pure tantalum metal. Preferably, the alloy has a grain size of from about 75 mircons to about 210 microns and more preferably from about 75 microns to about 125 microns when heated at 1800° C. for 30 minutes. Also, preferably, the alloy can have a grain size of from about 19 microns to about 27 microns when heated at 1530° C. for 2 hours.
The alloy preferably has a uniformity of tensile strength when formed into a wire, such that the maximum population standard deviation of tensile strength for the wire is about 3 KSI, more preferably about 2.5 KSI, even more preferably about 2.0 KSI, and most preferably about 1.5 KSI or 1.0 KSI for an unannealed wire at finish diameter. The alloy also preferably has a maximum population standard deviation of tensile strength for the wire of about 2 KSI, more preferably about 1.5 KSI, and even more preferably about 1.0 KSI, and most preferably about 0.5 KSI for an annealed wire at finish diameter.
The alloys of the present invention can be made in a number of ways. In a preferred method, a first powder comprising tantalum or an oxide thereof (e.g., tantalum containing solid) is blended with a second powder comprising silicon or a silicon-containing compound.
For purposes of the present invention, a silicon-containing solid is any solid which can subsequently be reduced to a liquid state to impart elemental silicon
Huber, Jr. Louis E.
Michaluk Christopher A.
Cabot Corporation
Oltmans Andrew L.
Sheehan John P.
LandOfFree
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