Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Alloying occurs during sintering
Reexamination Certificate
1999-09-20
2001-09-04
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Alloying occurs during sintering
C419S036000, C419S037000, C419S019000, C419S054000
Reexamination Certificate
active
06284191
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to iron aluminide and a powder metallurgical technique for preparation of such materials.
BACKGROUND OF THE INVENTION
Iron base alloys containing aluminum can have ordered and disordered body centered crystal structures. For instance, iron aluminide alloys having intermetallic alloy compositions contain iron and aluminum in various atomic proportions such as Fe
3
Al, FeAl, FeAl
2
, FeAl
3
, and Fe
2
Al
5
. Fe
3
Al intermetallic iron aluminides having a body centered cubic ordered crystal structure are disclosed in U.S. Pat. Nos. 5,320,802; 5,158,744, 5,024,109; and 4,961,903. Such ordered crystal structures generally contain 25 to 40 atomic % Al and alloying additions such as Zr, B, Mo, C, Cr, V, Nb, Si and Y.
An iron aluminide alloy having a disordered body centered crystal structure is disclosed in U.S. Pat. No. 5,238,645 wherein the alloy includes, in weight %, 8-9.5 Al, ≦7 Cr, ≦4 Mo, ≦0.05 C, ≦0.5 Zr and ≦0.1 Y, preferably 4.5-5.5 Cr, 1.8-2.2 Mo, 0.02-0.032 C and 0.15-0.25 Zr. Except for three binary alloys having 8.46, 12.04 and 15.90 wt % Al, respectively, all of the specific alloy compositions disclosed in the '645 patent include a minimum of 5 wt % Cr. Further, the '645 patent states that the alloying elements improve strength, room-temperature ductility, high temperature oxidation resistance, aqueous corrosion resistance and resistance to pitting. The '645 patent does not relate to electrical resistance heating elements and does not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
Iron-base alloys containing 3-18 wt % Al, 0.05-0.5 wt % Zr, 0.01-0.1 wt % B and optional Cr, Ti and Mo are disclosed in U.S. Pat. No. 3,026,197 and Canadian Patent No. 648,140. The Zr and B are stated to provide grain refinement, the preferred Al content is 10-18 wt % and the alloys are disclosed as having oxidation resistance and workability. However, like the '645 patent, the '197 and Canadian patents do not relate to electrical resistance heating elements and do not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
U.S. Pat. No. 3,676,109 discloses an iron-base alloy containing 3-10 wt % Al, 4-8 wt % Cr, about 0.5 wt % Cu, less than 0.05 wt % C, 0.5-2 wt % Ti and optional Mn and B. The '109 patent discloses that the Cu improves resistance to rust spotting, the Cr avoids embrittlement and the Ti provides precipitation hardening. The '109 patent states that the alloys are useful for chemical processing equipment. All of the specific examples disclosed in the '109 patent include 0.5 wt % Cu and at least 1 wt % Cr, with the preferred alloys having at least 9 wt % total Al and Cr, a minimum Cr or Al of at least 6 wt % and a difference between the Al and Cr contents of less than 6 wt %. However, like the '645 patent, the '109 patent does not relate to electrical resistance heating elements and does not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
Iron-base aluminum containing alloys for use as electrical resistance heating elements are disclosed in U.S. Pat. Nos. 1,550,508; 1,990,650; and 2,768,915 and in Canadian Patent No. 648,141. The alloys disclosed in the '508 patent include 20 wt % Al, 10 wt % Mn; 12-15 wt % Al, 6-8 wt % Mn; or 12-16 wt % Al, 2-10 wt % Cr. All of the specific examples disclosed in the '508 patent include at least 6 wt % Cr and at least 10 wt % Al. The alloys disclosed in the '650 patent include 16-20 wt % Al, 5-10 wt % Cr, ≦0.05 wt % C, ≦0.25 wt % Si, 0.1-0.5 wt % Ti, ≦1.5 wt % Mo and 0.4-1.5 wt % Mn and the only specific example includes 17.5 wt % Al, 8.5 wt % Cr, 0.44 wt % Mn, 0.36 wt % Ti, 0.02 wt % C and 0.13 wt % Si. The alloys disclosed in the '915 patent include 10-18 wt % Al, 1-5 wt % Mo, Ti, Ta, V, Cb, Cr, Ni, B and W and the only specific example includes 16 wt % Al and 3 wt % Mo. The alloys disclosed in the Canadian patent include 6-11 wt % Al, 3-10 wt % Cr, ≦4 wt % Mn, ≦1 wt % Si, ≦0.4 wt % Ti, ≦0.5 wt % C, 0.2-0.5 wt % Zr and 0.05-0.1 wt % B and the only specific examples include at least 5 wt % Cr.
Resistance heaters of various materials are disclosed in U.S. Pat. No. 5,249,586 and in U.S. patent application Ser. Nos. 07/943,504, 08/118,665, 08/105,346 and 08/224,848.
U.S. Pat. No. 4,334,923 discloses a cold-rollable oxidation resistant iron-base alloy useful for catalytic converters containing ≦0.05% C, 0.1-2% Si, 2-8% Al, 0.02-1% Y, <0.009% P, <0.006% S and <0.009% 0.
U.S. Pat. No. 4,684,505 discloses a heat resistant iron-base alloy containing 10-22% Al, 2-12% Ti, 2-12% Mo, 0.1-1.2% Hf, ≦1.5% Si, ≦0.3% C, ≦0.2% B, ≦1.0% Ta, ≦0.5% W, ≦0.5% V, ≦0.5% Mn, ≦0.3% Co, ≦0.3% Nb, and ≦0.2% La. The '505 patent discloses a specific alloy having 16% Al, 0.5% Hf, 4% Mo, 3% Si, 4% Ti and 0.2% C
Japanese Laid-open Patent Application No. 53-119721 discloses a wear resistant, high magnetic permeability alloy having good workability and containing 1.5-17% Al, 0.2-15% Cr and 0.01-8% total of optional additions of <4% Si, <8% Mo, <8% W, <8% Ti, <8% Ge, <8% Cu, <8% V, <8% Mn, <8% Nb, <8% Ta, <8% Ni, <8% Co, <3% Sn, <3% Sb, <3% Be, <3% Hf, <3% Zr, <0.5% Pb, and <3% rare earth metal. Except for a 16% Al, balance Fe alloy, all of the specific examples in Japan '721 include at least 1% Cr and except for a 5% Al, 3% Cr, balance Fe alloy, the remaining examples in Japan '721 include ≧10% Al.
A 1990 publication in Advances in Powder Metallurgy, Vol. 2, by J. R. Knibloe et al., entitled “Microstructure And Mechanical Properties of P/M Fe
3
Al Alloys”, pp. 219-231, discloses a powder metallurgical process for preparing Fe
3
Al containing 2 and 5% Cr by using an inert gas atomizer. This publication explains that Fe
3
Al alloys have a DO
3
structure at low temperatures and transform to a B2 structure above about 550° C. To make sheet, the powders were canned in mild steel, evacuated and hot extruded at 1000° C. to an area reduction ratio of 9:1. After removing from the steel can, the alloy extrusion was hot forged at 1000° C. to 0.340 inch thick, rolled at 800° C. to sheet approximately 0.10 inch thick and finish rolled at 650° C. to 0.030 inch. According to this publication, the atomized powders were generally spherical and provided dense extrusions and room temperature ductility approaching 20% was achieved by maximizing the amount of B2 structure.
A 1991 publication in Mat. Res. Soc. Symp. Proc., Vol. 213, by V. K. Sikka entitled “Powder Processing of Fe
3
Al-Based Iron-Aluminide Alloys,” pp. 901-906, discloses a process of preparing 2 and 5% Cr containing Fe
3
Al-based iron-aluminide powders fabricated into sheet. This publication states that the powders were prepared by nitrogen-gas atomization and argon-gas atomization. The nitrogen-gas atomized powders had low levels of oxygen (130 ppm) and nitrogen (30 ppm). To make sheet, the powders were canned in mild steel and hot extruded at 1000° C. to an area reduction ratio of 9:1. The extruded nitrogen-gas atomized powder had a grain size of 30 &mgr;m. The steel can was removed and the bars were forged 50% at 1000° C., rolled 50% at 850° C. and finish rolled 50% at 650° C. to 0.76 mm sheet.
A paper by V. K. Sikka et al., entitled “Powder Production, Processing, and Properties of Fe
3
Al”, pp. 1-11, presented at the 1990 Powder Metallurgy Conference Exhibition in Pittsburgh, Pa., discloses a process of preparing Fe
3
Al powder by melting constituent metals under a protective atmosphere, passing the metal through a metering nozzle and disintegrating the melt by impingement of the melt stream with nitrogen atomizing gas. The powder had low oxygen (130 ppm) and nitrogen (30 ppm) and was spherical. An extruded bar was produced by filling a 76 mm mild steel can with the po
Deevi Seetharama C.
Hajaligol Mohammed R.
Lilly, Jr. A. Clifton
Sikka Vinod K.
Burns Doane , Swecker, Mathis LLP
Chrysalis Technologies Incorporated
Jenkins Daniel J.
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