US 3887667 A
A method for producing pre-alloyed metallic powder which utilizes a pair of electrodes and a reservoir to accomplish its objectives. An arc is struck between a consumable electrode and a second electrode to produce molten metal which is collected, held and homogenized in a reservoir and subsequently atomized.
Description (OCR text may contain errors)
0 United States Patent 11 1 1111 3,887,667 Clark June 3, 1975  METHOD FOR POWDER METAL 2,304,130 12/1942 Truthe 264/8 4 P 2,816,826 12/1957 Byennan 264/12 RODUCTIOI? 3,556,780 1/1971 Holtz, Jr. 264/12 Inventor: Irvm g t Clark, New ord, 3,586,747 6/1971 Radtke et a1. 264/8  Assignee: Special Metals Corporation, New Primary ExaminerR0bert F. White Hartford, Assistant Examiner-J. R. Hall  Filed: Aug 6, 1973 Attorney, Agent, or FirmVincent C. Gioia; Robert F.
Dropkm  Appl. No.: 386,127
I Related US. Application Data ABSTRACT  Continuation of Ser. No. 55,123, July 15, 1970,
abandoned. A method for producing pre-alloyed metallic powder which utilizes a pair of electrodes and a reservoir  US. Cl 264/8; 264/10 to a omplish its objectives, An arc is struck between  Int. Cl 1322f 9/00 a consumable electrode and a second electrode to Field 0f Search 8 produce molten metal which is collected, held and homogenized in a reservoir and subsequently atomized.  References Cited UNITED STATES PATENTS 2/1940 Wissler 264/25 5 Claims, 1 Drawing Figure METHOD FOR PQWDER METAL'PRODUCTION This 'is a continuation of application Ser. No. 55:123. filed July, 15, l970,'n'ow abandoned. I
The present invention relates toa method of producing powder and'more" particularly to a'method of producing pre-alloyedmetallic powder. i
Design applications frequently require alloys which will not fail at elevated temperaturesregt, l,70()F, under relatively high stresses; e.g., l5 ksi.'Alloys which meet the requirements are referred to as superalloys."
An exemplary superalloy consists essentially of, in weight percent, up to 0.18%carbon, from l4.2 to cobalt, froml3.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.7 5 to 3.75% titanium, from3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium,'balance essentially nickel with incidental impurities. Many'other superalloys are described in'various technical publicatlons.
Superalloys are often desired in,small and/or complex shapes. These shapes are most economically produced by powder metallurgy techniques. To produce optimum mechanical properties in powder metallurgy manufactured products it is often desirable to use pre alloyed powder, i.e., powder that has each element present in each particle in substantially equal amounts.
Metallic powder has been produced from consumable electrodes. Certain prior practices comprised the striking of an are between a metallic consumable spinning electrode and a tungsten electrode and others comprised the striking of an are between a metallic consumable electrode and a spinning wheel. A particular prior art process is disclosed in US. Pat. No. 2,897,539 issued on Aug. 4, 1959. The process disclosed therein is disadvantageous insofar as it requires a starter body to protect the rotating table from damage caused by the arc and to preclude contamination of the powder being produced. In addition, it is plagued by a troublesome sliding electrical contact to the rotating table.
I have determined that the prior art consumable electrode melting processes for producing metallic powder, such as the process disclosed in U.S. Pat. No. 2,897,539, are not suitable for the production of prealloyed Superalloy metallic powder as superalloy consumable electrodes have a segregated; i.e., heterogeneous, makeup. Superalloy consumable electrodes have a concentration of low melting point impurities, elements and compounds in their center and form metal droplets of varying composition when melted. The grains of consumable electrodes grow inward during their solidification and drive the low melting point impurities, elements and compounds along with them. thereby setting up a degree of segregation within the electrodes. This degree of segregation is more prominent in superalloys than in other alloys as superalloys have a greater difference between their liquidus and solidus temperatures and since superalloys are statically cast.
The present invention provides a method for producing pre-alloyed metallic powder and utilizes a pair of consumable electrodes and a reservoir; e.g., a tundish, to accomplish its objectives. Use of a pair of electrodes removes the need for an electrical connection to the rotating table which obviates the troublesome sliding electrical contact and eliminates the requirement of a starter body to protect the rotating table from damage caused by the arc and to preclude contamination of the powder being produced. In addition, the double electrodes improve melting efficiency when both are consumablel'The reservoir provides a means for holding a homogenizing molten metal prior to atomization.
It is accordingly an object of this invention to provide a methodfor producing pre-alloyed metallic powder.
The foregoing and other objects of the invention will be best understood from the following description, reference being had to the accompanying drawing wherein:
The Figure is a schematic view of an embodiment of the apparatus for producing pre-alloyed powder from consumable electrodes.
The method of the present invention comprises the steps of melting a metallic consumable electrode by striking an arc between it and a second electrode (the second electrode can be consumable or nonconsumpassing the homogenized molten metal from the reservoir, atomizing the homogenized molten metal into powder and collecting the powder. Atomization can be performed in the air but is preferably performed in a non-reactive atmosphere such as an inert atmosphere; e.g., argon, or a vacuum. Illustrative methods of atomization comprise the steps of passing the homogenized .molten metal onto a moving disintegrator or into an inert gas stream.
The apparatus used to perform the method of the present invention is best seen from the Figure which is a schematic view of a particular embodiment of the invention. It comprises reservoir or tundish 10, having an inlet 10 and outlet valve 10'', which holds and homogenizes molten metal 20, supplied from consumable electrodes 11 and 12 (either electrode could have been nonconsumable), electrical connections 13 and 14 for striking an are between electrodes 11 and 12, hydraulic pressure cylinders 15 and 16 for moving electrodes 11 and 12 together. sight port 17 for viewing the are between electrodes 11 and 12, resistance heater 18 for supplying heat to molten metal 20 in tundish l0, atomization chamber 30, disintegrating wheel 31 for atomizing the molten metal (an inert gas stream or a vibrating disintegrator could have been used), shaft 33 for imparting motion to disintegrating wheel 31 through motor 35 and speed increaser 37, vacuum pump 39 and inert gas source 41 for producing a nonreactive atmosphere in atomization chamber 30 through conduits 40 and 42, hopper 43 for collecting metallic powder 50, moving belt 45 for carrying metallic powder 50 into hopper 43, shield 47 for directing metallic powder 50 onto belt 45, cooling coils 49 to dissipate heat from powder 50 and atomization chamber 30 so as to keep particles from adhering to each other, container chamber 60, containers 62 for receiving powder from hopper 43 and turntable 64 for holding and placing empty containers below hopper 43.
In operation the relative position of consumable electrodes 11 and 12 is adjusted, through hydraulic pressure cylinders 15 and 16, to obtain proper spacing for the passing of an electrical arc. Current is passed through electrical connections 13 and 14 in order to strike an arc and melt the electrodes. Proper spacing of consumable electrodes 11 and 12 is maintained through hydraulic pressure cylinders and 16 as the electrodes are consumed. The character of the arc is observed through sight port 17. Molten metal from the electrodes is collected through inlet 10 and held in tundish 10 for a period of time sufficient to homogenize it. A nonreactive atmosphere is created in atomization chamber 30 through conventional means utilizing vacuum pump 39 and conduit 40 or vacuum pump 39, conduit 40, inert gas source 41 and conduit 42. Motion is imparted to disintegrating wheel 31 from motor 35 through speed increaser 37 and shaft 33. Molten metal is atomized into metallic powder by being passed from tundish 10, through outlet valve 10-", onto disintegrating wheel 31 (outlet valve 10" is positioned at mid radius with respect to wheel 31 so as to give the powder particles proper directional motion, as depicted in the Figure). Metallic powder is carried to hopper 43 by moving belt 45 and passed through hopper 43 into collecting containers 62.
From the above paragraphs it will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended I claims they should not be limited to the specific examples described herein.
1. A method of producing metallic powder of a superalloy wherein each element in the alloy is present in each particle of powder in substantially equal amounts,
4 which comprises the steps of: arranging a statically cast superalloy consumable electrode having a heterogeneous make-up in a substantially horizontal position; arranging a second electrode in a substantially horizontal position; melting said consumable electrode by striking an electric are between it and said second elec-.
trode; collecting molten metal droplets from said consumable electrode in a heated reservoir. said droplets having varying compositions; holding said molten metal in said reservoir for a period of time sufficient to homogenize it; passing said homogenized molten metal from said reservoir; atomizing said homogenized molten metal and cooling it to a temperature below its melting point as it passes from said reservoir, thereby forming metallic superalloy powder, each particle of powder containing each element in said alloy in substantially equal amounts; and collecting said powder, said powder being processable into parts having excellent high temperature strength.
2. A method according to claim 1 wherein said atomizing comprises the step of passing said homogenized molten metal onto a moving disintegrator.
3. A method according to claim 1 wherein said atomizing is performed in a nonreactive atmosphere.
4. A method according to claim 1 wherein said second electrode is a metallic consumable electrode.
5. A method according to claim 2 wherein said moving disintegrator is a wheel and wherein said molten metal contacts said wheel off-center thereof.