U.S. patent application number 13/514891 was filed with the patent office on 2012-10-04 for method of fabricating inconel 718 type nickel superalloys.
This patent application is currently assigned to SNECMA. Invention is credited to Jean-Michel Patrick Maurice Franchet, Gilbert Michel Marin Leconte.
Application Number | 20120247626 13/514891 |
Document ID | / |
Family ID | 42313893 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120247626 |
Kind Code |
A1 |
Franchet; Jean-Michel Patrick
Maurice ; et al. |
October 4, 2012 |
METHOD OF FABRICATING INCONEL 718 TYPE NICKEL SUPERALLOYS
Abstract
A method of fabricating Inconel 718 type nickel superalloys. A
last forging operation to which the nickel superalloy is subjected
is such: that it takes place at a temperature lower than the
.delta.-solvus temperature; that at all points of the nickel
superalloy the local deformation ratio is not less than a minimum
value; and that the nickel superalloy is not subjected to any heat
treatment at a temperature higher than a threshold temperature
equal to 750.degree. C. after a quenching.
Inventors: |
Franchet; Jean-Michel Patrick
Maurice; (Paris, FR) ; Leconte; Gilbert Michel
Marin; (Asnieres Sur Seine, FR) |
Assignee: |
SNECMA
Paris
FR
|
Family ID: |
42313893 |
Appl. No.: |
13/514891 |
Filed: |
December 9, 2010 |
PCT Filed: |
December 9, 2010 |
PCT NO: |
PCT/FR2010/052658 |
371 Date: |
June 8, 2012 |
Current U.S.
Class: |
148/676 |
Current CPC
Class: |
C22F 1/10 20130101; C22C
19/056 20130101 |
Class at
Publication: |
148/676 |
International
Class: |
C22F 1/10 20060101
C22F001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2009 |
FR |
0958815 |
Claims
1-6. (canceled)
7. A fabrication method of fabricating an Inconel 718 type nickel
superalloy wherein a last forging operation to which the nickel
superalloy is subjected is such: that it takes place at a
temperature lower than the .delta.-solvus temperature; that at all
points of the nickel superalloy the local deformation ratio is not
less than a minimum value; and the nickel superalloy is not
subjected to any heat treatment at a temperature higher than a
threshold temperature equal to 750.degree. C. after a
quenching.
8. A fabrication method according to claim 7, wherein the minimum
value of the local deformation ratio is equal to 0.7.
9. A fabrication method according to claim 7, wherein the nickel
superalloy is also subjected to tempering directly after the
quenching following the forging operation.
10. A fabrication method according to claim 7, wherein all of
forging operations preceding the last forging operation are
performed at temperatures lower than the .delta.-solvus
temperature.
11. A fabrication method according to claim 7, wherein at an end of
the method, a size of all grains of the superalloy lies in a range
of 5 .mu.m to 30 .mu.m.
12. A fabrication method according to claim 11, wherein at the end
of the method, the size of all the grains of the superalloy lies in
a range of 5 .mu.m to 20 .mu.m.
Description
[0001] The present invention relates to a method of fabricating
Inconel 718 type nickel superalloys.
[0002] The Inconel 718 nickel-based superalloy (NC19FeNb) is in
widespread use for fabricating parts in high-technology
applications, in particular in aviation for rotary parts of turbine
engines, casings, and rings. The mechanical characteristics that
these parts present in use depend both on the intrinsic
characteristics of the alloy (chemical composition) of the part,
and also on the microstructure of the part, in particular on its
grain size. In particular, grain size governs characteristics
concerning low-cycle fatigue, traction strength, and creep. A
microstructure in which the grains are fine (e.g. having grain size
lying substantially in the range 5 micrometers (.mu.m) to 20 .mu.m)
makes it possible to obtain better properties in terms of fatigue
and traction strength, while also guaranteeing good creep
behavior.
[0003] At present, this fine grain size is obtained by applying
heat treatment and forging procedure plans to the part that serve
to produce mechanisms for re-crystallizing the grains.
[0004] Nevertheless, with present procedure plans, zones of coarse
grains are frequently observed on nickel superalloy parts, i.e.
zones having grains of a size that is considerably greater than the
size of fine grains. Such zones are undesirable since they give
rise to a reduction in the mechanical properties of such parts.
[0005] These coarse-grained zones appear even when the procedure
plans comprise forging operations below the .delta.-solvus
temperature (the temperature at which delta precipitates go back
into solution), even though such operations have the reputation of
having no effect on the final microstructure of the alloy, since
theoretically they are assumed to guarantee that there will be no
grain growth.
[0006] The invention seeks to propose a fabrication method that
makes it possible to limit the appearance of coarse grains during
fabrication of the part.
[0007] This object is achieved by the fact that the last stage of
forging to which said nickel superalloy is subjected is such: that
it takes place at a temperature T lower than the .delta.-solvus
temperature; that at all points M in the nickel superalloy the
local deformation ratio D is not less than a minimum value D.sub.m,
where the local deformation ratio D is defined as
D = Ln ( .delta. i .delta. f ) ##EQU00001##
where .delta..sub.i is the initial distance between the point M and
a point M' neighboring the point M, and .delta..sub.f is the
distance between the points M and M' after forging; and that said
nickel superalloy is not subjected to any heat treatment at a
temperature higher than a threshold temperature T.sub.S equal to
750.degree. C. after said quenching.
[0008] By means of these provisions, any coarse grains still
present in the superalloy are transformed back into the fine
grains, and new coarse grains do not form within the
superalloy.
[0009] Advantageously the nickel superalloy is also subjected to
tempering directly after the quenching following the last forging
step.
[0010] Thus, the toughness properties of the superalloy are
improved, while its other mechanical properties are not
significantly diminished. The tempering operation takes place at a
temperature that is low enough to avoid recreating coarse grains
within the superalloy.
[0011] The invention can be better understood, and its advantages
appear more clearly on reading the following detailed description
of an implementation shown by way of non-limiting example. The
description refers to the accompanying drawings, in which:
[0012] FIG. 1 is a diagram showing the fabrication method of the
invention; and
[0013] FIG. 2 is a diagram showing an example of the fabrication
method of the invention.
[0014] In the present invention, consideration is given to nickel
superalloys of the Inconel 718 type.
[0015] In the method of the invention, the starting billet has
already been subjected to thermomechanical treatments for the
purpose of giving the billet a structure and a shape that comply
with specifications.
[0016] On examining prior art nickel superalloys in which the
microstructure presents coarse grains, the inventors have observed
that those coarse grains are of two different kinds.
[0017] Thus, a distinction is made between firstly coarse equiaxed
grains that result from static enlargement of fine grains, e.g.
because the alloy is maintained at a temperature higher than the
.delta.-solvus temperature. Such enlargement may be avoided by
performing the forging operations of the alloy treatment procedure
plan at temperatures lower than the .delta.-solvus temperature.
[0018] Unexpectedly, within the alloy, the inventors have also
observed "exploded" or "burst" coarse grains with outlines that are
very irregular. It is thought that these grains generally form at
temperatures lower than the .delta.-solvus temperature, and that,
when the deformation is performed at temperatures lower than the
.delta.-solvus temperature (e.g. lower than 1000.degree. C.) it is
the energy stored as a result of the work hardening during the
preceding forging operation, that gives rise to this bursting of
the grains. This stored energy is then "released" in the form of
early and uncontrolled migration of the grain boundaries, thereby
generating these "burst" grains.
[0019] According to the invention, and as shown in FIG. 1, it is
ensured that in the forging procedure plan to which the superalloy
is subjected, the last forging step (referenced 1 in FIG. 1) takes
place at a temperature T that is lower than the .delta.-solvus
temperature, and also that at all points M of the nickel
superalloy, the local deformation ratio D is not less than a
minimum value D.sub.m.
[0020] The local deformation ratio D characterizes the local
deformation at a point M of a material. It is defined by the
equation
D = Ln ( .delta. i .delta. f ) ##EQU00002##
where .delta..sub.i is the initial distance between the point M and
a point M' neighboring the point M, and .delta..sub.f is the
distance between the points M and M' after forging.
[0021] Performing this last forging step at a temperature T lower
than the .delta.-solvus temperature makes it possible to avoid
forming coarse equiaxed grains.
[0022] Furthermore, the condition that the local deformation ratio
D is not less than a minimum value D.sub.m in a region of the
superalloy enables the "burst" grains to be re-crystallized as fine
grains in this region. During the forging step, and depending on
the final shape given to the part, certain regions of the part may
be subjected to greater amounts of deformation than other regions.
The fact that the above condition concerning the local deformation
ratio D is valid at all points M in the superalloy makes it
possible to ensure that the "burst" grains are re-crystallized as
fine grains throughout the volume of the superalloy.
[0023] For example, the minimum value D.sub.m may be equal to
0.7.
[0024] Alternatively, the minimum value D.sub.m may be equal to 0.8
or 0.9.
[0025] After this forging, the superalloy is subjected to quenching
from the forging temperature T to ambient temperature T.sub.A.
[0026] Advantageously, quenching is performed at a rate of about 15
degrees Celsius per minute (.degree. C./min), since tests performed
by the inventors have shown that mechanical characteristics are
best optimized when quenching at that rate. Quenching is preferably
performed with water.
[0027] Furthermore, after this quenching following the final
forging step, the superalloy is not subjected to any heat treatment
at a temperature higher than a threshold temperature T.sub.S equal
to 750.degree. C.
[0028] Heat treatment at a temperature higher than the threshold
temperature T.sub.S would be likely to give rise to "burst" grains
within the superalloy.
[0029] In particular, the superalloy it is not subjected to
solution annealing since that takes place at a temperature higher
than the threshold temperature T.sub.S.
[0030] In contrast, the superalloy may be subjected directly to
tempering (step referenced 2 in FIG. 1) after the quenching
following the last forging.
[0031] For example, the superalloy may be heated to a temperature
of 720.degree. C. for 8 hours, and then cooled to a temperature of
620.degree. C. for 8 hours, prior to being cooled down to ambient
temperature. This situation is shown in FIG. 2.
[0032] Prior to the last forging step of the invention, the
superalloy may have been subjected to no other, to one other, or to
several other forging steps, with each, several, one, or none of
these steps taking place at a forging temperature higher than the
.delta.-solvus temperature.
[0033] Advantageously, all of the forging steps preceding the last
forging step are performed at temperatures lower than the
.delta.-solvus temperature.
[0034] Digital simulations have been performed by the inventors and
they show that at the end of the method of the invention, the size
of the grains is indeed reduced.
[0035] For example, at the end of a method of the invention, the
size of all of the grains of the superalloy may lie in the range 5
.mu.m to 30 .mu.m.
[0036] Advantageously, at the end of a method of the invention, the
size of all of the grains of the superalloy may lie in the range 5
.mu.m to 20 .mu.m. This fine mean grain size gives rise to a
superalloy having a fatigue lifetime and an elastic limit that are
further improved.
* * * * *