Metal treatment – Stock – Copper base
Reexamination Certificate
1997-08-21
2001-02-20
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
C148S432000, C148S683000, C420S494000
Reexamination Certificate
active
06190468
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processing of precipitation hardenable materials and more particularly to a novel method for enhancing properties of beryllium containing alloys.
BACKGROUND OF THE INVENTION
Beryllium-copper alloys are notable for their superior combination of thermal conductivity, strength, toughness, impact energy and resistance to corrosion. This has made them desirable for use in control bearings of aircraft landing gear and a variety of underground and undersea applications. Additional benefits of beryllium-copper alloys such as their relatively high electrical conductivity, ultrasonic inspectability and thermal management has made them suitable for face plates of continuous steel casting molds. Aerospace and compact disc technologies have also benefitted, in particular, from the relatively high polishability of these alloys as well as their magnetic transparency, thermal cycling and anti-galling characteristics. The cost of beryllium-copper being an issue, however, more economical processing is sought. Improvements in alloy properties and enhanced product performance are also desired.
In this connection, conventional processing of beryllium-copper alloys have utilized a series of thermal and mechanical treatment steps. For example, a beryllium-copper alloy is cold rolled to heavy reduction, intermediate annealed at temperatures between about 1000° and 1750° F., solution annealed at temperatures of about 1600° to 1850° F., cold rolled to substantially finished gage, then aged at a temperature within a range of about 600° and 1000° F. for less than 1 hour to about 8 hours. An objective is to enhance strength, ductility, formability, conductivity and stress relaxation. A process of this general description may be found, for example, in U.S. Pat. No. 4,565,586 which issued on Jan. 21, 1986 and in U.S. Pat. No. 4,599,120 which issued on Jul. 8, 1986. The disclosures of both patents are hereby incorporated by reference herein.
Although prior methods of processing have been found useful, further improvements in strength and refinements in grain size are desired. For example, finer grain size with uniform equiaxed structure is sought for increased polishability of guidance system mirrors, i.e., to prevent arcing of lasers, and to improve surface quality of molds for manufacturing compact discs. Superior ductility, formability, ultrasonic inspectability and conductivity would ease product manufacture and reduce costs. Further resistance to heat and corrosion is desired to enhance product life and performance, e.g., of control bearings for aircraft landing gear. Moreover, by increasing the fatigue and creep strength of beryllium-copper face plates, performance of steel casting molds would be enhanced.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention is the metamorphic processing of beryllium-copper alloys known as “gold” alloys. A specific, illustrative process comprises the steps of (i) thermodynamically treating the alloy at a first selected temperature generally within a range of 900° and 150° F., (ii) warm working the alloy of step i at greater than about 30% strain at a strain rate {acute over (&egr;)} greater than or equal to about (2.210×10
7
)/exp[(2.873×10
4
)/(T+459.4°)], where T is in ° F., at the first temperature, (iii) annealing the alloy of step ii at a second selected temperature generally within a range of 1375° and 1500° F., (iv) water quenching the alloy of step iii, and (v) thermal hardening the alloy of step iv at a third selected temperature generally within a range of 480° and 660° F. This produces a generally equiaxed uniform fine grain structure with concomitant improvements in mechanical properties and ultrasonic inspectability.
In accordance with another aspect of the present invention, a “gold” beryllium-copper alloy is (i) thermodynamically treated at a first selected temperature generally within a range of 900° and 1500° F., then (ii) warm worked at greater than about 30% strain at a strain rate {acute over (&egr;)} greater than or equal to about (1.009×10
8
)/exp[(2.873×10
4
)/(T+459.4°)], where T is in ° F., at the first temperature, (iii) annealed at a second selected temperature generally within a range of 1375° and 1500° F., (iv) water quenched, and finally (v) thermal hardened at a third selected temperature generally within a range of about 480° and 660° F.
According to a further aspect of the invention is a metamorphically processed “gold” beryllium-copper alloy where 3.0 times the impact energy of the alloy in foot pounds plus 2.0 times the alloy yield strength in ksi is greater than about 275.
Metamorphic processing of a “red” beryllium-copper alloy, according to yet another aspect of the present invention, produces a generally equiaxed uniform grain structure with concomitant improvements in mechanical properties, electrical conductivity and ultrasonic inspectability. A specific, illustrative process comprises the steps of: (i) thermodynamically treating the alloy at a first selected temperature generally within a range of 900° and 1850° F., (ii) warm working the alloy of step i at greater than about 30% strain at a strain rate {acute over (&egr;)} greater than or equal to about (1.243×10
7
)/exp[(2.873×10
4
)/(T+459.4°)], where T is in ° F., at the first temperature, (iii) annealing the alloy of step ii at a second selected temperature generally within a range of 1400° and 1750° F. for about 15 minutes to about 3 hours, (iv) water quenching the alloy of step iii, and (v) thermal hardening the alloy of step iv at a third selected temperature generally within a range of 800° and 1000° F.
According to still another aspect of the invention, a “red” beryllium-copper alloy is metamorphically processed by the steps of: (i) thermodynamically treating the alloy at a first selected temperature generally within a range of 900° and 1850° F., (ii) warm working the alloy of step i at greater than about 30% strain at a strain rate {acute over (&egr;)} greater than or equal to about (1.243×10
7
) /exp[(2.873×10
4
) /(T+459.4°)], where T is in ° F., at the first temperature, (iii) annealing the alloy of step ii at a second selected temperature generally within a range of 1400° and 1750° F., (iv) water quenching the alloy of step iii, and (v) primary thermal hardening of the alloy of step iv at a third selected temperature generally within a range of 900° and 1000° F. followed by secondary thermal hardening at a fourth selected temperature generally within a range of 700° and 900° F.
In accordance with yet a further aspect of the invention is a metamorphically processed “red” beryllium-copper alloy where 4.5 times the electrical conductivity of the alloy in % IACS plus the alloy yield strength in ksi is greater than about 400.
Although the present invention is shown and described for use with beryllium-copper alloys, it is understood that analogous processes may be practiced on other precipitation hardenable materials such as alloys of aluminum, titanium and iron, giving consideration to the purpose for which the present invention is intended. Also, any alloy containing beryllium, including beryllium-nickel and beryllium-silver alloys, are considered within the spirit and scope of the invention.
It is therefore an object of the present invention to improve strength and toughness of beryllium containing alloys while improving their resistance to heat and corrosion, ductility, formability and conductivity.
Another object of the present invention is to produce beryllium containing alloys with enhanced mechanical properties, simply and efficiently.
Still another object of the present invention is to provide an economical beryllium containing alloy product with enhanced mechanical properties.
A further object of the present invention is to improve fatigue strength, creep strength, and ultrasonic inspectability.
Still a further object of the present invention is to achieve finer polishin
Brush Wellman Inc.
Calfee Halter & Griswold LLP
Ip Sikyin
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