Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-09-14
2004-01-06
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S246000, C148S274000, C148S708000, C427S156000, C427S435000, C029S611000, C072S041000, C072S042000, C072S046000
Reexamination Certificate
active
06673164
ABSTRACT:
BACKGROUND
Field of the Invention
The present invention is directed to a method to process an aluminide intermetallic alloy. More particularly, the invention is directed to a method of cold forming an aluminide intermetallic alloy in which a viscous medium that provides a moisture resistant barrier is coated on the workpiece.
BACKGROUND OF THE INVENTION
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Aluminides such as iron aluminides based on Fe
3
Al and FeAl as well as aluminides of nickel and titanium are well known to suffer from reduction in ductility, when tested in ambient air as opposed to tested in oxygen. The reduction in ductility is from a hydrogen embrittlement mechanism commonly referred to as “environmental effect” and is considered to result from the following chemical reaction:
2Al+3H
2
O→Al
2
O
3
+6H
The Al from the aluminide, such as in Fe
3
Al or FeAl, reacts with moisture in air and forms Al
2
O
3
with 6 atoms of hydrogen. It is this hydrogen that causes the embrittlement of the alloy. The process of embrittlement is different than in steels in that it is the hydrogen from the surface reaction that causes the embrittlement as opposed to the hydrogen content in steels. One could say that for iron aluminides it is a “dynamic embrittlement” as opposed to “static embrittlement” in steels. Due to the low room temperature ductility of these alloys, processing of an ingot into a thin sheet requires extensive hot working; making powder metallurgy an attractive alternative. However, the deleterious effects of hydrogen embrittlement on ductility can remain even in powder metallurgy processes.
Environmental embrittlement of intermetallic materials is discussed in N. S. Stoloff et al., Eds., “Physical Metallurgy and Processing of Intermetallics Compounds,” New York: Chapman and Hall (1996), Chapters 9 & 12, the entire contents of which are herein incorporated by reference. A further discussion of this phenomenon can be found in C. T. Liu, Materials Research Society Symposium Proceedings, Vol. 288, p. 3-19, 1993, the entire contents of which are herein incorporated by reference. However, while Liu reports on various techniques including formation of protective oxides, refinement of grain structure and microalloying, such techniques may not be practical or economical under a variety of manufacturing conditions.
In forming of sheet metal, it is conventional to use lubricants between a die and metal to be formed. See, for example, Metals Handbook Ninth Edition, Volume 14, entitled “Forming and Hot Forging”, published by ASM International, Metals Park, Ohio, 1988, the contents of which is hereby incorporated by reference. U.S. Pat. No. 3,969,195, the disclosure of which is herein incorporated by reference, discloses improvements to mechanical forming of materials through the use of auxiliary substances including soaps, pastes, and oils and by the use of coatings of electroplated metals.
From the above, there is a need for processing techniques for aluminide intermetallic alloys that can minimize hydrogen embrittlement while maximizing the ductility properties of the alloy. Additionally, such processing techniques should be relatively inexpensive and accommodate workpieces of various shapes and sizes and processing/forming histories.
SUMMARY OF THE INVENTION
A method of cold fabricating an intermetallic alloy composition, comprising steps of coating an article of an intermetallic alloy composition with a viscous medium which provides a moisture resistant barrier on the surface of the article, fabricating the coated article into a desired shape, and optionally removing the coating from the shaped article. The coating step can be carried out by applying oil to the surface of the article or immersing the article in oil. The intermetallic article can be an iron aluminide and the fabrication step can include stamping, bending, forming, cutting, shearing or punching. During the fabrication step a surface oxide film on the article can be cracked and metal surfaces exposed by the cracked oxide film can be protected from exposure to moisture in the air by the viscous medium.
The article can be made by thermomechanical processing of roll compacted or tape cast intermetallic alloy powder, such as an iron aluminide having, in weight %, 4.0 to 32.0% Al and ≦1% Cr. Other suitable intermetallic alloys include an iron aluminide having, in weight %, ≦32% Al, ≦2% Mo, ≦1% Zr, ≦2% Si, ≦30% Ni, ≦10% Cr, ≦0.3% C, ≦0.5% Y, ≦0.1% B, ≦1% Nb and ≦1% Ta, and an iron aluminide having, in weight %, 20-32% Al, 0.3-0.5% Mo, 0.05-0.3% Zr, 0.01-0.5% C, ≦0.1% B, ≦1% oxide particles.
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N.S. Stoloff et al., “Physical Metallurgy and Processing of Intermetallic Compounds” pp. 479-516, 1996, Chapman & Hall, New York, NY, (no month data).
C.G. McKamey, “Iron Aluminides”, Physical Metallurgy and Processing of Intermetallic Compounds pp. 351-391, Chapter 9, 1996, Chapman & Hall, New York, NY., (no month data).
Elliot S. Nachtman, “Selection and Use of Lubricants in Forming of Sheet Metal”, pp. 512-520, Metals Handbook Ninth Edition, vol. 14 Forming and Forging, Metals Park, OH, (no date).
C.T. Liu, “High-Temperature Ordered Intermetallic Alloys V”, Nov. 30-Dec. 3, 1992, Boston, MA, Recent Advances in Ordered Intermetallics, Mat. Res. Soc. Symp. Proc. vol. 288., pp. 3-19, 1993 Materials Research Society., (no month data).
R.E. Mistler et al., “Tape Casting as a Fabrication Process for Iron Aluminide (FeA1) Thin Sheet”, Materials Science and Engineering, vol. A258, Elsevier, New York, NY, 1998, pp. 258-265., (no month data).
F. Rasouli et al., “Tape Casting of Iron Aluminide Powders”, Procd. Internationl Conference on Powder Metallurgy & Particulate Materials, Vol 9, Metal Powder Industries Federation, New York, NY, 2000 pp. 131-140., (no month data).
Written Opinion for PCT/US01/28638 dated Jul. 19, 2002.
Rasouli Firooz
Scorey Clive R.
Burns Doane , Swecker, Mathis LLP
Oltmans Andrew L.
Philip Morris Incorporated
Sheehan John
LandOfFree
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