High temperature electric arc furnace and method

An apparatus and process for improving the microstructure of electrically conducting materials is disclosed by the present invention. A revolving heat source applies heat to the surface of the material evenly and quickly. One or more heat sinks quickly cool the material. In the preferred embodiment, the cooling may be done in such a way as to promote as high a degree of directional grain growth as desired or completely nondirectional grain growth.

BACKGROUND OF THE INVENTION 
This invention relates to apparatuses and processes for improving the 
microstructure of electrically conducting materials. More specifically, 
the present invention relates to an apparatus and process for 
substantially improving the grain size of electrically conducting 
materials such as metals and alloys and for forming grain boundaries in a 
directional or nondirectional manner, whichever is desired. 
Electrically conducting materials such as elemental metals, metallic 
alloys, and some ceramics, can be characterized by their microstructure, 
which includes phase morphologies. The particular microstructure of a 
specific sample of material depends on many variables, one of which is how 
it was processed. For example, MAR-M246(HF) (a nickel-based superalloy) 
was melted and solidified with the process described in this patent. The 
microstructure was enhanced by various changes in phase morphology. These 
included eliminating gamma-gamma prime eutectic phase islands from the 
section of rod which was melted and solidified with this process. Also 
carbide morphology was changed from large script-types to extremely small, 
fine, extremely well dispersed carbides. Other rods of MAR-M246(HF) with 
an original small, fine block carbide morphology were processed in this 
same manner. The resulting carbide morphology change after melting and 
solidification was the same; extremely small, fine, and extremely well 
dispersed carbides. 
The microstructure of these materials, and/or relative orientation of the 
boundaries of the grains of these materials, gives them different 
mechanical properties. In some applications nondirectional or equiaxed 
microstructure is preferable to more high directional structure. In other 
applications, the reverse is true, such as when the material may see 
greater stresses and be subjected to greater fatigue in one direction than 
in another. 
The present invention is an apparatus and a process for significantly 
improving the microstructure of electrically conducting materials by 
reducing the size of the material's grains and for determining the 
microstructure of the material which includes establishing the desired 
relative directionality of the grain boundaries. 
It is an object of the present invention to improve the microstructure of 
electrically conducting material. It is another object of the present 
invention to rapidly melt and quickly cool electrically conducting 
materials. It is still further an object of the present invention to 
evenly melt and unevenly cool electrically conducting materials when a 
higher degree of directional grain growth is desired. 
It is yet a further object of the invention to establish very fine carbide 
morphology and the desired microstructure of a particular sample of 
electrically conducting material. 
These and other objects of the invention will become apparent to someone 
skilled in the art of apparatuses and processes for improving the 
microstructure of electrically conducting material upon reviewing the 
following description of the invention. 
SUMMARY OF THE INVENTION 
The present invention is an apparatus and a process for improving the 
microstructure of electrically conducting materials. The apparatus 
comprises a source of intense heat, such as an inert gas tungsten arc, a 
laser welder, focused thermal radiation or an electron beam, that can 
quickly melt the surface of the material to be improved. Specifically, the 
heat source must be capable of melting a 3 mm diameter rod, 10 mm in 
length, within approximately 5 seconds. 
The heat source must be capable of moving rapidly over the surface to heat 
the material both quickly and evenly. The rate of movement and the degree 
of heating must be controllable by standard means so that a wide variety 
of types and shapes of materials can be improved by the instant invention. 
In the preferred embodiment, the heat source revolves about the material 
near to the surface, heating the surface to bring the temperature of the 
material quickly to its melting temperature. It is also desirable in the 
preferred embodiment that the revolving source apply heat to each portion 
of the surface in any single pass so that the heat is evenly applied. 
The material must be quickly cooled to resolidify it within a few seconds. 
A 3 mm diameter rod, 10 mm in length, must be resolidified in 
approximately 10 seconds. In order to cool it that quickly, heat sinks 
capable of establishing a large temperature gradient across the boundary 
of the surface of the material and the surface of the heat sink must be 
provided adjacent to the material. 
The heat sinks should have a surface equal to or smaller than the surface 
of the material when a highly directional grain growth pattern is desired. 
The cooling will then take place in the direction of the gradient and 
grain growth will follow the cooling. Thus, by placing heat sinks at 
specific locations the grain growth can be rather precisely controlled. 
Alternatively, the heat sink can be the atmosphere surrounding the material 
when no particular directionality in grain growth is required. It is only 
necessary that the temperature of the heat sink be sufficiently lower than 
the solidifying temperature of the material so that the large temperature 
gradient is established at all points on the surface of the material. 
The present invention is especially advantageous for material to be 
processed in a near zero-gravity environment. The weightlessness allows a 
melted sample to be held in place by its own surface tension rather than a 
support that interferes with the heating and melting of the material. 
Also, the rotation of the heat source is unobstructed in the weightless, 
unsupported condition since it does not have to avoid the material support 
and can heat the entire surface of the material. 
Several examples of the improvements of the present invention are provided. 
To facilitate even heating and cooling, the samples of material were made 
in the form of rods approximately 90 mm long and diameters of 2 to 5 mm. 
Copper, aluminum, tungsten and a nickel-based superalloy were used as 
sample materials. Large aluminum heat sinks were placed at each end of a 
rod. The aluminum heat sinks were in the form of cylinders 13 mm in 
diameter and 25 mm long. The region of the rod that was melted and 
resolidified is called a nugget. 
A commercial inert gas tungsten tube welder capable of 100 amperes DCSP was 
used to melt a portion of each rod. The weld arc revolved around the axis 
of the particular rod in each test. The melting took approximately 5 
seconds; cooling took approximately 10 seconds. 
The experiments were performed in a near weightless environment achieved in 
a single, parabolic climb and dive of a KC-135 aircraft, although the 
present invention does not require a specific aircraft or weightless 
conditions. 
Table A reflects the results of ground test samples verified in 
microgravity flight.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The present invention is an apparatus for improving the microstructure of 
an electrically conducting material. The invention applies heat energy to 
the surface of the material which heat energy is conducted to the interior 
of the material. 
The invention comprises a means for heating the material when the source of 
heat is positioned adjacent to a portion of the surface of the material. 
The heat energy supplied to the surface is of sufficient intensity to 
cause the temperature of the material to rise to or above the melting 
temperature of the material so that the material melts. The source of heat 
must be capable of melting a 3 mm diameter rod of material 10 mm long 
within approximately 5 seconds. 
The apparatus has a means for controlling the heating means which is 
operatively connected to the heating means. In the preferred embodiment, a 
laser, an inert gas tungsten arc, focused thermal radiation or an electron 
beam can be used to apply heat energy to the surface of the material. 
Standard controlling devices for energizing and deenergizing these heat 
sources and for controlling the level of heat energy applied are widely 
available. 
The apparatus also comprises a means for revolving the heat source about 
the surface of the material whereby approximately all portions of the 
surface may be heated in any one revolution. The revolving of the heat 
source assures that the heating is done uniformly over the entire surface 
of the material to be heated and that the material is melted throughout at 
approximately the same time. The rate at which the revolving heat source 
moves is controlled by standard means preferably electrical and its rate 
of movement, path and level of applied heat energy can be programmed for a 
given sample size and shape. For a sample that is rod shaped, 
approximately 3 mm in diameter, the heat source should be capable of 
revolving at least 10 times per minute, and preferably at least sixty 
times per minute. 
Heat sinks positioned adjacent to the material provide a means for cooling 
the material by receiving heat energy from the melted material across the 
boundary between the surface of the material and the surface of the heat 
sink. The heat sinks may be in position before the heating is done or 
moved into position after the heating is done. It is important, however, 
that the cooling be done quickly. If the heat sinks are positioned after 
the heating, a means for controlling the cooling is provided by any 
suitable electrical or electromechanical apparatus. If the cooling means 
is the ambient temperature of the environment, a means must be provided to 
maintain the temperature of that environment sufficiently below the 
solidification temperature of the material so that a large temperature 
gradient will exist across the boundary between the surfaces of the heat 
sinks and the material to assure rapid cooling. 
If directional grain growth is desired, the surfaces of the heat sinks will 
be equal to or smaller than the surface of the material so that there is a 
preferential flow of heat energy from the melted material through the 
material in the direction of the heat gradient established at the heat 
sink boundary. 
The present invention is also a process for improving the microstructure of 
an electrically conducting material. The process comprises the rapid and 
even application of heat to the surface of the material until the 
temperature of the material is above the melting temperature so as to melt 
the material being processed all at approximately the same time at which 
time the heating is halted and followed by the rapid cooling of the 
material below the solidification temperature of the material so that the 
material solidifies. 
The heating is most evenly accomplished by moving a heat source rapidly 
over the entire surface of the material, energizing the heat source so 
that heat is applied at sufficient intensity to melt the material. 
The heat sinks may be placed at any part of the surface of the material 
where heat flow out of the material and into the heat sink is desired. The 
arrangement can be as simple or as complex as desired based on the 
ultimate purpose to be served by the material. 
In the configuration selected for experimentation, shown in FIG. 1, a rod 
10 is positioned between heat sinks 11. The heat sinks 11 will produce a 
gradient across the heat sink/rod boundary 12 and its counterpart at the 
other end of the rod. Thus, grain growth will take place in direction 
shown by the arrows. 
In FIG. 2, rod 10 is being heated by heat source 13 such as an Automatic 
Tube Welder Model PA-100STW manufactured by Weldlogic, Inc., of 
Chatsworth, Calif. or NIKA-BTW Model 9121 ST International. This heat 
source 13, having a power cable 14, a handle 15, and a weld head 16 
surrounds the rod 10. An inert gas tungsten arc within the weld head 16 
orbits rod 10. 
While a preferred embodiment of the invention has been described using 
specific terms, such description is for illustrative purposes only, and it 
is to be understood that changes and variations may be made without 
departing from the spirit or scope of the following claims. 
__________________________________________________________________________ 
Sample Arc Nugget 
No. Material 
Length 
Current 
RPM Position 
Size Remarks 
__________________________________________________________________________ 
1 Aluminum 
0.635 
mm 30 amp. 
24 Hor. 
4.76 .times. 5.33 
mm 
2 Aluminum 
1.24 
mm 30 amp. 
24 Hor. 
4.76 .times. 6.2 
mm 
3 Aluminum 
1.24 
mm 30 amp. 
8 Hor. 
4.76 .times. 7.1 
mm Nugget is longer 
on top, arc 
started on side 
and moved under 
4 Aluminum 
1.24 
mm 50 amp. 
24 Vert. 
4.76 .times. 18.4 
mm 
5 Aluminum 
1.24 
mm 50 amp. 
24 Hor. 
6.2 .times. 5.7 
mm 
6 Aluminum 
1.24 
mm 75 amp. 
24 Vert. 
6.2 .times. 13.9 
mm 
7 Copper 
1.24 
mm 75 amp. 
24 Vert. 
4.1 .times. 3.2 
mm 
8 Copper 
1.24 
mm 75 amp. 
24 Hor. 
4.1 .times. 4.3 
mm Nugget sagged 
about 1.5 mm 
9 Tungsten 
1.24 
mm 90 amp. 
24 Vert. 
3.2 .times. 2.8 
mm 
10 Tungsten 
1.24 
mm 100 
amp. 
24 Vert. 
3.2 mm Gravity opened 
melt zone 
__________________________________________________________________________ 
NOTES: 
Arc lengths resulted in voltages of 9 and 14 volts (Argon Shielding Gas) 
(DCSP). Nugget sizes are sample diameter .times. nugget length in 
millimeters. All samples were made at Merrick Engineering, Nashville on a 
orbital tube welder. RPM is the rate the arc moved around the sample 
(revolutions per minute).