Note: Descriptions are shown in the official language in which they were submitted.
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1 PROCESS FOR ENHANCING THE ME(HANICAL PROPERTIES
~F OXIDE DISPERSION STRENGTHENED MATERIALS
ABSTRACT O~ THE DISCLOSURE
A process for producing oxide dispersion strengthened
material having enhanced mechanical properties. The process
S includes the steps of consolidating oxide dispersion strengthened
powder into a solid mass, working said mass into an elongated
body and directionally recrystallizing the body in a direction
transverse to the direction of elongation.
The present invention relates to a process for
enhancing the ~echanical properties of oxide dispersion
strengthened materials.
Oxide dispersion strengthened materials are powder
~etallurgical products characterized by small highly stable
oxide particles dispersed within a metallic matrix. The
dispersed particles block dislocation movement thereby
imparting~high elevated temperature strength to the material.
Numerous processes for producing such materials are disclosed
~ in the prior art. A particular process is disclosed irl United
States Patent No. 4,010,024, issued March lr 1977. ~-~
To attain desirable stress rupture and other high ;
temperature properties, it is necessary to recrystallize oxide
dispersion strengthened materials to a relatively coarse grain
size. Those skilled in the art are aware of the factors which
effect the size of the recrystallized grainsO They include
matrix composition, interparticle spacing and distribution of
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1 the oxide particles, working cemperatures, percent reduction
and recrystallization temperature cycle.
Those skilled in the art are also aware of the fact
that mechanical properties are particularly good in the
direction elongated grains are pointing. For this reason,
they have taken ~easures to recrystallize oxide dispersion
strengthened materials in the direction of working; i.e., the
longitudinal direction. By so doing, they have enhanced the
mechanical properties of the material in the longitudinal
direction, without materially effecting those in the transverse
direction. As longitudinal properties are generally superior
to transverse properties, they have further improved properties
in the better of these two directions through directional
recrystallization in lieu of isothermal recrystallization. A
lS paper describing directional recrystallization is entitled,
"Manufacturing Methods For Directional Recrystalliztion
Process". It was prepared under United States Air Force
Contract No. F33615-72-C-1127. The authors are P. G. Bailey,
R. E. Kutchera and D. B. Arnold.
Prior to the present invention, little thought had
been given to transverse properties. Now through the present
invention, there is provided a process for significantly
i~proving transverse properties, without ~aterially effecting
longitudinal properties. Transverse properties are enhanced
by recrystallizing in a direction transverse to working.
Those skilled in the art did not realize that oxide dispersion
strengthened ~aterials could be directionally recrystallized
in this direction. Hence, the present invention provides a
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;` 1 most significant advance to the state of the art. Many
applications for oxide dispersion strengthened materials;
e.g., turbine vanes, require good mechanical properties in more
than one direction.
; 5 It is accordingly an object of the present invention
to provide oxide dispersion strengthened material having a
desirable combination of mechanical properties in two directions.
In accordance with the present invention oxide
dispersion strengthened material is subjected to the conventional
steps of consolidation and working; and to the improvement of
directionally recrystallizing said material in a direction
transverse to the direction of working. Specific processing
as to the conventional steps is not critical and can be in
accordance with that specified in any number of publications
including heretofore referred to Patent No. 4,010,024.
Directional recrystallization is described in detail in the
heretofore referred to paper entitled, "Manufacturing Methods
For Directional Recrystallization Process". Directional
recrystallization is basically a process wherein a temperature
differential is imposed along the direction grain growth is
desired. Although there is reason to believe that any number
of oxide dispersion strengthened alloys can be treated in
accordance with the teachings of the present invention, nickel
and cobalt base alloys appear to be particularly adaptable
thereto.
The following example is illustrative of the
invention.
1 Oxide dispersion strengthened powder having the
following nominal composition:
Cr Al Y203 Ni
16 5 1 Bal.
. 5 was canned, extruded and hot rolled into stock fro~ which two
stress rupture test specimens (A & B) were prepared. Specimen
A was isothermally annealed in a box furnace. The temperature
was raised from 2200 to 2450F at a rate of 4F per minute and
maintained at 2450F for one hour. Specimen B ~-as fed into a
salt pot at the rate of 2 inches per hour. The salt pot was
' at a temperature of from 2400 to 2450F. The specimen was fed
in a direction transverse to the rolling direction. After the
entire specimen was in the salt pot it was held there for one
hour.
Specimen A was stress rupture tested at a temperature
of 2000F under a stress of 6 ksi. The specimen broke after
15.1 hours. Its elongation was 1.9~ and its reduction in area
was 0.6%.
Specimen B was stress rupture tested at a temperature
of 2000F under the stresses and for the times reported
hereinbelow:
STRESS TIME
(ksi?_ (hours)
~2
5.5 1
6.5 3
7 20*
*specimen broke in threaded portion (that portion which holds
specimen in grips)
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1 No elongation and reduction in area data is available because
' of where specimen broke. In any event, Specimen B lasted for
; a longer period under a higher stress than did Specimen A.
Specimen B was processed in accordance with the subject
invention whereas Specimen A was not. The stress rupture data
for Specimen 3 would have been even more impressive had it not
been for the freak break in its threaded portion.
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 claims they shall not be limited to the specific
examples of the invention described herein.
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