U.S. patent application number 15/693747 was filed with the patent office on 2018-04-19 for self generated protective atmosphere for liquid metals.
The applicant listed for this patent is FEDERAL-MOGUL LLC. Invention is credited to Philippe Beaulieu, Mathieu Boisvert, Denis B. Christopherson, JR., Gilles L'Esperance.
Application Number | 20180104746 15/693747 |
Document ID | / |
Family ID | 61902368 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180104746 |
Kind Code |
A1 |
Boisvert; Mathieu ; et
al. |
April 19, 2018 |
SELF GENERATED PROTECTIVE ATMOSPHERE FOR LIQUID METALS
Abstract
An improved method of manufacturing a cast part by sand casting,
permanent mold casting, investment casting, lost foam casting, die
casting, or centrifugal casting, or a powder metal material by
water, gas, plasma, ultrasonic, or rotating disk atomization is
provided. The method includes adding at least one additive to a
melted metal material before or during the casting or atomization
process. The at least one additive forms a protective gas
atmosphere surrounding the melted metal material which is at least
three times greater than the volume of melt to be treated. The
protective atmosphere prevents introduction or re-introduction of
contaminants, such as sulfur (S) and oxygen (O.sub.2), into the
material. The cast parts or atomized particles produced include at
least one of the following advantages: less internal pores, less
internal oxides, median circularity of at least 0.60, median
roundness of at least 0.60 and increased sphericity of
microstructural phases and/or constituents.
Inventors: |
Boisvert; Mathieu; (Waupun,
WI) ; L'Esperance; Gilles; (Candiac/Quebec, CA)
; Beaulieu; Philippe; (Coventry, GB) ;
Christopherson, JR.; Denis B.; (Waupun, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FEDERAL-MOGUL LLC |
Southfield |
MI |
US |
|
|
Family ID: |
61902368 |
Appl. No.: |
15/693747 |
Filed: |
September 1, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62409192 |
Oct 17, 2016 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 9/082 20130101;
C22C 1/0433 20130101; C22C 1/1042 20130101; C22C 33/02 20130101;
B22F 9/08 20130101; C22C 1/0458 20130101; C22C 37/10 20130101; C22C
1/0416 20130101; B22F 2009/0844 20130101; C22C 1/045 20130101; C21C
7/005 20130101; B22D 27/00 20130101; B22F 9/10 20130101; B22D 1/00
20130101 |
International
Class: |
B22F 9/08 20060101
B22F009/08 |
Claims
1. A method of manufacturing a powder metal material, comprising
the steps of: adding at least one additive to a melted base metal
material, the at least one additive forming a protective gas
atmosphere surrounding the melted base metal material which has a
volume of at least three times greater than the volume of the
melted base metal material to be treated; and atomizing the melted
base metal material after adding at least some of the at least one
additive to produce a plurality of particles.
2. The method of claim 1, wherein the melted base metal material is
iron-based, and the at least one additive includes magnesium.
3. The method of claim 1, wherein the atomizing step includes water
atomizing, gas atomizing, plasma atomizing, ultrasonic atomization
or rotating disk atomizing.
4. The method of claim 1, wherein the melted base metal material
includes at least one of aluminum (Al), copper (Cu), manganese
(Mn), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), and
chromium (Cr); and the melted base metal material optionally
contains at least one alloying element selected from the group
consisting of silver (Ag), boron (B), barium (Ba), beryllium (Be),
carbon (C), calcium (Ca), cerium (Ce), gallium (Ga), germanium (Ge)
potassium (K), lanthanum (La), lithium (Li), magnesium (Mg),
molybdenum (Mo), nitrogen (N), sodium (Na), niobium (Nb),
phosphorus (P), sulfur (S), scandium (Sc), silicon (Si), tin (Sn),
strontium (Sr), tantalum (Ta), vanadium (V), tungsten (W), yttrium
(Y), zinc (Zn), and zirconium (Zr).
5. The method of claim 4, wherein the at least one additive
includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba.
6. The method of claim 4, wherein the melted base metal material is
iron-based, and the at least one additive forming the protective
gas atmosphere includes at least one of K, Na, Zn, Mg, Li, Sr, and
Ca.
7. The method of claim 4, wherein the melted base metal material is
iron-based and includes sulfur present as an impurity; and the at
least one additive includes at least one of Zn, Mg, Li, Sr, Ca, and
Ba.
8. The method of claim 4, wherein the melted base metal material is
iron-based and includes at least one oxide present as an impurity;
and the at least one additive includes at least one of K, Na, Zn,
Mg, Li, Sr, Ca, and Ba.
9. The method of claim 4, wherein the melted base metal material is
iron-based and includes sulfur and at least one oxide present as
impurities; and the at least one additive forming the protective
gas atmosphere includes at least one of Zn, Mg, Li, Sr, and Ca.
10. The method of claim 4, wherein the melted base metal material
is an aluminum alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K and Na; and
the at least one additive includes at least one of K, Na, Mg, Li,
Sr, Ca, and Ba to react with the sulfur, and/or the at least one
additive includes at least one of K, Na, Mg, Li, Ca to react with
the at least one oxide.
11. The method of claim 4, wherein the melted base metal material
is titanium-based and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of Zn, Mg, Li, Ca
and Ba; and the at least one additive includes at least one of K,
Na, Zn, Mg, Li, Sr, Ca, and Ba to react with the sulfur, and/or the
at least one additive includes at least one of Sr, Ca, and Ba to
react with the at least one oxide.
12. The method of claim 4, wherein the melted base metal material
is a cobalt alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K, Na, Li and
Ca; and the at least one additive includes at least one of Na, Mg,
Li, Sr, Ca, and Ba to react with the sulfur, and/or the at least
one additive includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, Ba
to react with the at least one oxide.
13. The method of claim 4, wherein the melted base metal material
is a chromium alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K, Na, Zn, Mg,
Li, Sr, Ca and Ba; and the at least one additive includes at least
one of K, Na, Zn, Mg, Sr, Ca, and Ba to react with the sulfur,
and/or the at least one additive includes at least one of K, Na,
Zn, Mg, Li, Sr, Ca, and Ba to react with the at least one
oxide.
14. The method of claim 4, wherein the melted base metal material
is iron-based; and the at least one additive includes Mg.
15. A method of manufacturing a cast part, comprising the steps of:
adding at least one additive to a melted base metal material, the
at least one additive forming a protective gas atmosphere
surrounding the melted base metal material which has a volume of at
least three times greater than the volume of the melted base metal
material to be treated; and casting the melted metal material after
adding at least some of the at least one additive.
16. The method of claim 15, wherein the melted base metal material
is iron-based, and the at least one additive includes
magnesium.
17. The method of claim 15, wherein the casting step includes sand
casting, permanent mold casting, investment casting, lost foam
casting, die casting, or centrifugal casting.
18. The method of claim 15, wherein the melted base metal material
includes at least one of aluminum (Al), copper (Cu), manganese
(Mn), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), and
chromium (Cr); and the melted base metal material optionally
contains at least one alloying element selected from the group
consisting of silver (Ag), boron (B), barium (Ba), beryllium (Be),
carbon (C), calcium (Ca), cerium (Ce), gallium (Ga), germanium (Ge)
potassium (K), lanthanum (La), lithium (Li), magnesium (Mg),
molybdenum (Mo), nitrogen (N), sodium (Na), niobium (Nb),
phosphorus (P), sulfur (S), scandium (Sc), silicon (Si), tin (Sn),
strontium (Sr), tantalum (Ta), vanadium (V), tungsten (W), yttrium
(Y), zinc (Zn), and zirconium (Zr).
19. The method of claim 18, wherein the at least one additive
includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba.
20. The method of claim 18, wherein the melted base metal material
is iron-based, and the at least one additive forming the protective
gas atmosphere includes at least one of K, Na, Zn, Mg, Li, Sr, and
Ca.
21. The method of claim 18, wherein the melted base metal material
is iron-based and includes sulfur present as an impurity; and the
at least one additive includes at least one of Zn, Mg, Li, Sr, Ca,
and Ba.
22. The method of claim 18, wherein the melted base metal material
is iron-based and includes at least one oxide present as an
impurity; and the at least one additive includes at least one of K,
Na, Zn, Mg, Li, Sr, Ca, and Ba.
23. The method of claim 18, wherein the melted base metal material
is iron-based and includes sulfur and at least one oxide present as
impurities; and the at least one additive forming the protective
gas atmosphere includes at least one of Zn, Mg, Li, Sr, and Ca.
24. The method of claim 18, wherein the melted base metal material
is an aluminum alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K and Na; and
the at least one additive includes at least one of K, Na, Mg, Li,
Sr, Ca, and Ba to react with the sulfur, and/or the at least one
additive includes at least one of K, Na, Mg, Li, Ca to react with
the at least one oxide.
25. The method of claim 18, wherein the melted base metal material
is titanium-based and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of Zn, Mg, Li, Ca
and Ba; and the at least one additive includes at least one of K,
Na, Zn, Mg, Li, Sr, Ca, and Ba to react with the sulfur, and/or the
at least one additive includes at least one of Sr, Ca, and Ba to
react with the at least one oxide.
26. The method of claim 18, wherein the melted base metal material
is a cobalt alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K, Na, Li and
Ca; and the at least one additive includes at least one of Na, Mg,
Li, Sr, Ca, and Ba to react with the sulfur, and/or the at least
one additive includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, Ba
to react with the at least one oxide.
27. The method of claim 18, wherein the melted base metal material
is a chromium alloy and includes sulfur and/or at least one oxide
present as impurities; the at least one additive forming the
protective gas atmosphere includes at least one of K, Na, Zn, Mg,
Li, Sr, Ca and Ba; and the at least one additive includes at least
one of K, Na, Zn, Mg, Sr, Ca, and Ba to react with the sulfur,
and/or the at least one additive includes at least one of K, Na,
Zn, Mg, Li, Sr, Ca, and Ba to react with the at least one
oxide.
28. The method of claim 18, wherein the melted base metal material
is iron-based; and the at least one additive includes Mg.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This U.S. utility patent application claims priority to U.S.
provisional patent application No. 62/409,192, filed Oct. 17, 2016,
the contents of which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] This invention relates generally to metal materials, and
more particularly to melted metal materials which are either
atomized or solidified to form powder metals or castings, and
methods of forming the same.
2. Related Art
[0003] Powder metal materials can be formed by various processes
such as by water atomization, gas atomization, plasma atomization,
ultrasonic atomization or rotating disk. Powder metal materials are
used in various different technologies such as pressed and
sintered, metal injection molding, and additive manufacturing.
Metal castings are also commonly used in various technologies,
including both automotive and non-automotive parts, and produced by
various processes such as by sand casting, permanent mold casting,
investment casting, lost foam casting, die casting, or centrifugal
casting. Both atomization and casting processes begin with a melted
metal material. Common atomization processes include applying a
fluid (water, gas, oil, ultrasonic, or plasma) to the melted metal
material to form a plurality of particles. The casting process
typically includes pouring the melted metal material into a mold
having a desired shape, and allowing the liquid metal to solidify
before removing the metal part from the mold.
SUMMARY
[0004] One aspect of the invention provides a method of
manufacturing a powder metal material. This method includes adding
at least one additive to a melted base metal material, the at least
one additive forming a protective gas atmosphere surrounding the
melted base metal material which has a volume of at least three
times greater than the volume of the melted base metal material to
be treated; and atomizing the melted base metal material after
adding at least some of the at least one additive to produce a
plurality of particles. Another aspect of the invention provides a
powder metal material formed from the melted metal material with
the self-generated protective atmosphere.
[0005] Another aspect of the invention provides a method of
manufacturing a cast part. The method includes adding at least one
additive to a melted base metal material, the at least one additive
forming a protective gas atmosphere surrounding the melted base
metal material which has a volume of at least three times greater
than the volume of the melted base metal material to be treated;
and casting the melted metal material after adding at least some of
the at least one additive. Another aspect of the invention provides
a casting formed from the melted metal material with the
self-generated protective atmosphere.
[0006] Both methods include manufacturing a self-generated
protective atmosphere in the melted base metal material. Adding the
at least one additive to the melted base metal material can improve
the quality of the melt. The at least one additive can create the
protective atmosphere which acts as a protective barrier against
oxidation. The protective atmosphere also acts as a barrier to
prevent impurities, such as sulfur (S) and/or oxygen (O.sub.2),
from entering or re-entering into the melted metal material. Thus,
the at least one additive can limit oxidation during the melting
and pouring phases of the process and limit the amount of internal
oxides. Additionally, physical structures of powder particles
and/or microstructural features in the solidified metal material
can be altered to improve or influence the material properties. For
example, the at least one additive can also contribute to the
microstructural engineering of precipitate, such as size and
morphology.
[0007] When the melted metal material is atomized, the at least one
additive can engineer the shape and morphology of the resulting
powder particles. Also in the case of powder atomization, the at
least one additive improves the roundness and sphericity of the
resulting powder particles. The amount of internal porosities in
powders and castings can also be lowered.
[0008] The atomizing step can also include producing a plurality of
particles having a spherical shape. The sphericity of the particles
and that of the shape of microstructural phases or constituents in
the atomized particles or castings in the as-atomized, as-cast or
heat treated state, can be determined by two image analysis
indicators, specifically circularity and roundness, according to
the following formulas:
Circularity (C)=4.pi..times.([Area]/[Perimeter].sup.2)
Roundness (R)=4.pi.([Area]/(.pi..times.[Major
axis].sup.2))=1/AR
wherein AR=[Major axis]/[Minor axis].
[0009] The image analysis indicators can be calculated using open
source software, such as ImageJ (http://imagej.nih.gov/ij/). A
sphericity index value of 1.0 indicates a perfect circle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Other advantages of the present invention will be readily
appreciated, as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0011] FIGS. 1 to 3 present additives (cells marked with an "x")
that will create a protective gas atmosphere, those that will react
with oxides, and those that will react with sulfur respectively for
various chemical systems (Al, Cu, Mn, Ni, Co, Fe, Ti, and Cr);
[0012] FIG. 4 presents a curve of the calculated total volume of
gas that is generated as a function of the amount of additive(s)
for an example composition;
[0013] FIG. 5 is a graph showing EDS spectra that were
experimentally acquired on a polished pure iron surface before and
after it was exposed to the atmosphere on top of the tundish during
an atomization process of the powder that is described in FIG.
4;
[0014] FIG. 6 is a graph showing the calculated volume of gas
generated by sodium (Na) and potassium (K) additives in aluminum at
different temperatures (800 and 900 Celsius), wherein the dashed
line shows the inferior limit of gas;
[0015] FIG. 7 is a graph showing the calculated volume of gas
generated by different additives in titanium at a temperature of
1800 Celsius, wherein the dashed line shows the inferior limit of
gas;
[0016] FIG. 8 is a graph showing the calculated volume of gas
generated by different additives in cobalt at a temperature of 1600
Celsius, wherein the dashed line shows the inferior limit of
gas;
[0017] FIG. 9 is a graph showing the calculated volume of gas
generated by different additives in chromium at a temperature of
2000 Celsius, wherein the dashed line shows the inferior limit of
gas;
[0018] FIG. 10 is a graph showing the calculated volume of gas
generated by different additives in copper at a temperature of 1200
Celsius, wherein the dashed line shows the inferior limit of
gas;
[0019] FIG. 11 is a graph showing the calculated volume of gas
generated by different additives in iron at a temperature of 1650
Celsius, wherein the dashed line shows the inferior limit of
gas;
[0020] FIG. 12 is a graph showing the calculated volume of gas
generated by different additives in manganese at a temperature of
1400 Celsius, wherein the dashed line shows the inferior limit of
gas;
[0021] FIG. 13 is a graph showing the calculated volume of gas
generated by different additives in nickel at a temperature of 1600
Celsius, wherein the dashed line shows the inferior limit of
gas;
[0022] FIG. 14 is a graph showing the calculated total volume of
gas that is obtained per 100 grams of melt of a complex cobalt
alloy at a temperature of 1600 Celsius as a function of the amount
of additive (K and Li);
[0023] FIG. 15 is a backscattered electron micrograph of a water
atomized hypereutectic cast iron powder without added magnesium in
which many irregular primary graphite nodules precipitated on
internal silicon oxides that were introduced in the melt during the
pouring step of the atomization process;
[0024] FIG. 16 is a backscattered electron micrograph of another
water atomized hypereutectic cast iron powder with added magnesium
in which one spherical primary graphite nodule precipitated on a
heterogeneous oxide nuclei that contains Mg during the atomization
process;
[0025] FIG. 17 is a backscattered electron micrograph of a water
atomized hypereutectic cast iron powder that contains about 4.0% C
and 2.3% Si without added magnesium wherein graphite nodules which
grew in the solid state during a post heat treatment process are
present;
[0026] FIG. 18 is a photomicrograph of another water atomized
hypereutectic cast iron powder with added magnesium, according to
an example embodiment, wherein more spherical graphite nodules
compared to those presented in FIG. 17, which grew in the solid
state during a post heat treatment process are present;
[0027] FIG. 19 illustrates the circularity frequency distribution
of the graphite nodules that were observed in the water atomized
hypereutectic cast iron powders presented in FIGS. 17 and 18;
[0028] FIG. 20 illustrates the roundness frequency distribution of
the graphite nodules that were observed in the water atomized
hypereutectic cast iron powders presented in FIGS. 17 and 18;
[0029] FIG. 21 is a table illustrating numerical data for the
circularity of the graphite nodules that grew in the solid state
for two hypereutectic cast iron powders that were observed in FIGS.
17 and 18;
[0030] FIG. 22 is a table illustrating numerical data for the
roundness of the graphite nodules that grew in the solid state for
two hypereutectic cast iron powders that were observed in FIGS. 17
and 18;
[0031] FIG. 23 is a backscattered electron micrograph of a water
atomized stainless steel powder without added magnesium screened at
-80/+200 mesh (between 177 and 74 microns), wherein the red arrows
point to internal porosities;
[0032] FIG. 24 is a backscattered electron micrograph of a another
water atomized stainless steel powder with added magnesium screened
at -80/+200 mesh (between 177 and 74 microns), wherein one red
arrow points to only one smaller internal porosity compared to
those of FIG. 23;
[0033] FIG. 25 is an optical photomicrograph of a water atomized
high carbon steel alloyed with silicon powder that contains about
1.3% C and 1.1% Si without added magnesium screened at -200 mesh
(74 microns and less) wherein the red arrows point to internal
porosities;
[0034] FIG. 26 is an optical photomicrograph of a comparative water
atomized high carbon steel alloyed with silicon that contains about
1.4% C and 1.1% Si with added magnesium screened at -200 mesh (74
microns and less) according to one example embodiment wherein the
red arrows point to fewer internal porosities than the powder of
FIG. 25; and
[0035] FIG. 27 includes a table listing compositions evaluated.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0036] One aspect of the invention includes an improved method of
manufacturing a powder metal material by water or gas atomization
or any other atomization process that requires that the material to
be atomized goes through the creation of a bath of liquid metal
such as plasma atomization, ultrasonic atomization or rotating disk
atomization, by adding at least one additive to a melted metal
material before and/or during the atomization process. Another
aspect of the invention includes an improved method of
manufacturing a casting by processes such as sand casting,
permanent mold casting, investment casting, lost foam casting, die
casting, or centrifugal casting from a melted metal material by
adding at least one additive to the melted metal material. The at
least one additive forms a protective gas atmosphere surrounding
the melted metal material which is at least three times greater
than the volume of melt to be treated.
[0037] The protective atmosphere created by the at least one
additive that is added to the melted material acts as a barrier to
prevent impurities, such as sulfur (S) and/or oxygen (O.sub.2) or
others, from entering or re-entering into the melted metal material
by pushing them away from the surface of the melted material as the
protective gas is coming out of the melt. The additive(s) that
forms the protective gas atmosphere can also react with the
dissolved sulfur in the melt and/or the oxides that were in
suspension in the melt before the introduction of the additive(s).
Reaction of the additive(s) with the dissolved sulfur in the melt
will increase the sphericity of atomized particles formed from the
melt and/or increase that of the microstructural phases and
constituents in the atomized particles or castings.
[0038] When water atomization is employed, adding the additive(s)
to the melted metal material can increase the sphericity of the
atomized particles to a level approaching the sphericity of
particles formed by gas atomization, but with reduced costs
compared to gas atomization. Adding the additive(s) to the melted
metal material can also produce cleaner particles by limiting the
formation and the entrainment of new oxides from the surface of the
melt and by reacting with those already present in the melt before
the introduction of the additive(s). These oxides can form as
bifilms where films of oxides are folded on themselves leaving a
weak interface in between the oxide films. The additive(s) can also
lower the amount and size of internal porosity, a problem
encountered in atomized powders. The additive(s) can also increase
the sphericity of microstructural constituents and/or phases formed
in the atomized particles and/or during a subsequent heat treatment
process. For example, if the atomized particles are formed from a
cast iron material, at least 50% of the graphite precipitates
formed during the post heat treatment process will have a
circularity of at least 0.6 and a roundness of at least 0.6.
[0039] When casting is employed, adding the additive(s) to the
melted metal material can increase the sphericity of
microstructural constituents and/or phases formed in the castings
and/or during a subsequent heat treatment process. Adding the
additive(s) to the melted metal material can also produce cleaner
castings by limiting the formation and the entrainment of new
oxides from the surface of the melt and by reacting with those
already present in the melt before the introduction of the
additive(s). These oxides can form as bifilms where films of oxides
are folded on themselves leaving a weak interface in between the
oxide films. The additive(s) can also lower the amount and size of
internal porosity, a problem encountered in many castings.
[0040] According to one example embodiment, the method begins by
melting a base metal material. Many different metal compositions
can be used as the base metal material. However, in order to
produce enough gas that will act as a protective atmosphere and
thus obtain either the desired spherical-shape of the powders
and/or more spherical microstructural constituents and/or cleaner
particles and /or having less internal pores, the additive(s) must
have a low solubility in the metal material. The base material and
the additive(s) should be selected such that when the additive(s)
are introduced, the volume of protective gas atmosphere generated
is at least three times the volume of melted metal material to be
treated. For example, if 0.22 weight percent (wt. %) magnesium is
added to an iron-rich melt, the generated volume of gas will be
about 20 times the inferior limit of gas required to provide a
protective atmosphere which is defined as three times the initial
volume of melt to be treated.
[0041] The base metal material typically includes at least one of
aluminum (Al), copper (Cu), manganese (Mn), nickel (Ni), cobalt
(Co), iron (Fe), titanium (Ti), and chromium (Cr). The base metal
material can comprise pure Al, Cu, Mn, Ni, Co, Fe, Ti, or Cr.
Aluminum-rich, copper-rich, manganese-rich, nickel-rich,
cobalt-rich, iron-rich, titanium-rich and chromium-rich alloys, or
an alloy including at least 50 wt. % of Al, Cu, Mn, Ni, Co, Fe, Ti,
and/or Cr are also well suited for use as the starting base metal
material. Mixtures of these base metal materials in different
proportions are also well suited for use as the starting material
such as, but not limited to, Al--Cu, Fe--Ni, Fe--Co, Fe--Ni--Co,
Ni--Cr, Ti--Cu, and Co--Cr alloys. The alloys can also include at
least one of the following as alloying elements, as long as they
will stay in solution in the melt of the alloy of interest: silver
(Ag), boron (B), barium (Ba), beryllium (Be), carbon (C), calcium
(Ca), cerium (Ce), gallium (Ga), germanium (Ge) potassium (K),
lanthanum (La), lithium (Li), magnesium (Mg), molybdenum (Mo),
nitrogen (N), sodium (Na), niobium (Nb), phosphorus (P), sulfur
(S), scandium (Sc), silicon (Si), tin (Sn), strontium (Sr),
tantalum (Ta), vanadium (V), tungsten (W), yttrium (Y), zinc (Zn),
and zirconium (Zr).
[0042] There is a distinction to be made between the elements
described as "alloying elements" and those described as
"additives." Alloying elements will stay in solution in the base
metal material and/or form different phases/constituents in the
final parts/powders.
[0043] Alloying elements will impact the microstructure and the
properties of the parts. For instance, C in Fe will form cementite,
which increases strength. Additives are defined as elements added
to the melt to either create a protective gas atmosphere, react
with S and/or with oxides. FIGS. 1 to 3 include a complete list of
additives in different base metal materials. One particular element
can be an alloying element in one base material but be an additive
in a different base material. For instance, Mg is an alloying
element in Al-rich alloys but is an additive in Fe-rich alloys.
According to one example embodiment, to create a gaseous protective
atmosphere in an Al-Mg alloy, K and/or Na should be used as an
additive and the melt temperature should be selected according to
the selected additive(s). For example, since Mg is used as an
alloying element in aluminum alloys (the Al-5000 series) it will
not generate a protective gas atmosphere.
[0044] However, the starting metal material is not limited to the
above mentioned compositions. Other metal compositions can be used,
as long as the additive has a low solubility in the selected
material and generates a sufficient amount of protective gas
atmosphere. Some additives that are used to create the gaseous
protective atmosphere will naturally react with the dissolved
sulfur in the melt to create more stable compounds and thus
increase the surface tension. This is the case for Mg in Fe-rich
systems in which solid MgS will precipitate. However, some
additives will create a protective atmosphere but will not react
with the dissolved sulfur, as is the case with Na in Fe-rich
systems. In these situations, a combination of different additives
must be used to increase surface tension and create a protective
atmosphere.
[0045] As mentioned above, various different additives could be
added to the melted metal material to achieve the increased
protective atmosphere and the other advantages mentioned above. The
additive(s) selected depends on the composition of the base metal
material. For example the at least one additive can include at
least one of K, Na, Zn, Mg, Li, Ca, Sr, and Ba. The protective gas
atmosphere generated by the additive(s) prevents impurities from
entering or re-entering into the melted metal material.
[0046] The additives listed above generate different amounts of
protective gas atmosphere, depending on the chemical system in
which they are used. Some additives are more suited for some
systems than others. For example, in aluminum alloys, K and Na are
oftentimes preferred. In copper alloys, K and Na are oftentimes
preferred. In manganese alloys, K, Na, Zn, Mg, and Li are
oftentimes preferred. In nickel alloys, K and Na are oftentimes
preferred. In cobalt alloys, K, Na, Li, and Ca are oftentimes
preferred. In iron alloys, K, Na, Zn, Mg, Li, Sr, and Ca are
oftentimes preferred. In titanium alloys, Zn, Mg, Li, Ca, and Ba
are oftentimes preferred. In chromium alloys, K, Na, Zn, Mg, Li,
Sr, Ca, and Ba are oftentimes preferred. Examples are provided in
FIG. 1, wherein the preferred additives are marked.
[0047] According to one specific example embodiment, the metal base
material is iron-rich and includes Mg which generates the
protective gas and also reacts with the sulfur impurity.
Alternatively, the base metal material is pure iron and the
additive is Mg. According to another specific example, the metal
base material is iron-rich and the additives include a mixture of K
and Ba. The potassium (K) will generate the protective gas
atmosphere, and the barium (Ba) will react with the sulfur.
[0048] The protective atmosphere limits the amount of oxides in the
atomized particles and castings and will also limit the size and
amount of internal porosities in the atomized particles and
castings. Some additives that are used to create the gaseous
protective atmosphere will naturally react with oxides that are in
suspension in the melt to create more stable compounds and will
also change their morphology during the chemical reaction process,
for example a Mg additive in Fe-rich systems that contain Si as an
alloying element. In these materials, oxides of SiO.sub.2 that
could be in the form of bifilms (overlapping films of oxides that
are poorly bounded) are in suspension in the melt. One of the
reason explaining that a smaller amount of porosities is observed
is that Mg helps to bound the interfaces between the overlapping
films, a result of a chemical reaction between Mg and the oxides,
creating a stronger interface that cannot be subsequently separated
to form pores. The self-generated Mg gaseous atmosphere will limit
further oxidation of the surface of the melt, which will limit the
amount of internal oxides in the particles. However, some additives
will create a protective atmosphere but will not react with the
oxides in suspension in the melt, as is the case of Zn in Ti-rich
systems. In these situations, a combination of different additives
must be used to limit the amount and size of internal porosities.
For example, at least one additive could be added to generate the
protective gas atmosphere that will prevent impurities from
entering or re-entering into the melted metal material, and at
least one additive could be added to react with the oxides already
in the melt but would not necessarily create a protective gas
atmosphere. An example of such a combination of additives in a
Ti-rich alloy to create more spherical particle and/or phases and
constituents having less internal porosities could be a mixture of
Zn to create a protective atmosphere and Sr to react with S and
with TiO.sub.2 but without participating in the generation of the
protective atmosphere.
[0049] In other words, some additives are more effective in some
systems than in others, depending on the type of oxides that are
formed. As indicated above, if less internal porosities with
smaller sizes are desired, the additive(s) must react with the
oxides in suspension in the melt. These oxides are also considered
impurities in the melted base metal material, for example,
Al.sub.2O.sub.3 in an aluminum-based material, or Fe.sub.2O.sub.3
in an iron-based material. When the melted base metal material is
an aluminum alloy or aluminum-based, the preferred additives to
react with the oxides include K, Na, Mg, Li, and Ca. When the
melted base metal material is an iron alloy or iron-based, the
preferred additives to react with the oxides include K, Na, Zn, Mg,
Li, Sr, Ca, and Ba. When the melted base metal material is a
titanium alloy or titanium-based, the preferred additives to react
with the oxides include Sr, Ca, and Ba. When the melted base metal
material is a chromium alloy or chromium-based, the preferred
additives to react with the oxides include K, Na, Zn, Mg, Li, Sr,
Ca, and Ba. When the melted base metal material is a cobalt alloy
or cobalt-based, the preferred additives to react with the oxides
include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the melted base
metal material is a copper alloy or copper-based, the preferred
additives to react with the oxides include K, Na, Zn, Mg, Li, Sr,
Ca, and Ba. When the melted base metal material is a manganese
alloy or manganese-based, the preferred additives to react with the
oxides include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the melted
base metal material is a nickel alloy or nickel-based, the
preferred additives to react with the oxides include K, Na, Zn, Mg,
Li, Sr, Ca, and Ba. Examples are provided in FIG. 2.
[0050] When the melted base material is iron-based and includes
sulfur as an impurity, Zn, Mg, Li, Sr, Ca, and Ba are preferred to
react with the sulfur. An example of such a combination of
additives in an iron-based material or Fe-rich alloy to create more
spherical particle and/or phases and constituents could be a
mixture of Na and Ba. Na will create a protective atmosphere and Ba
to will react with S. When the melted base metal material is a
titanium alloy or titanium-based and includes sulfur as an
impurity, K, Na, Zn, Mg, Li, Sr, Ca, and Ba are preferred to react
with the sulfur. When the melted base metal material is a cobalt
alloy or cobalt-based and includes sulfur as an impurity, Na, Mg,
Li, Sr, Ca, and Ba are preferred to react with the sulfur. When the
melted base metal material is a chromium alloy or chromium based
and includes sulfur as an impurity, K, Na, Zn, Mg, Sr, Ca, and Ba
are preferred to react with the sulfur. When the melted base metal
material is an aluminum alloy or aluminum-based and includes sulfur
as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba are preferred to
react with the sulfur. When the melted base metal material is a
nickel alloy or nickel-based and includes sulfur as an impurity,
Mg, Li, Sr, Ca, and Ba are preferred to react with the sulfur. When
the melted base metal material is a copper alloy or copper-based
and includes sulfur as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba
are preferred to react with the sulfur. When the melted base metal
material is a manganese alloy or manganese-based and includes
sulfur as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba are preferred
to react with the sulfur. Examples are provided in FIG. 3.
[0051] In addition, certain additives will successfully generate
the protective gas atmosphere, and also react with the sulfur and
oxides present as impurities in the melted base metal material. For
example, when the melted base metal material is an iron-alloy or
iron-based, additives that will generate the protective gas
atmosphere and react with the sulfur and oxide impurities include
Zn, Mg, Li, Sr, and Ca. When the melted base metal material is a
titanium alloy or titanium-based, additives that will generate the
protective gas atmosphere and react with the sulfur and oxide
impurities include Ca and Ba. When the melted base metal material
is a chromium alloy or chromium-based, additives that will generate
the protective gas atmosphere and react with the sulfur and oxide
impurities include K, Na, Zn, Mg, Sr, Ca, and Ba. When the melted
base metal material is a cobalt alloy or cobalt-based, additives
that will generate the protective gas atmosphere and react with the
sulfur and oxide impurities include Na, Li, and Ca. When the melted
base metal material is an aluminum alloy or aluminum-based,
additives that will generate the protective gas atmosphere and
react with the sulfur and oxide impurities include K and Na. When
the melted base metal material is a copper alloy or copper-based,
additives that will generate the protective gas atmosphere and
react with the sulfur and oxide impurities include K and Na. When
the melted base metal material is a manganese alloy or
manganese-based, additives that will generate the protective gas
atmosphere and react with the sulfur and oxide impurities include
K, Na, Mg, and Li.
[0052] As stated above, the melted metal material can be atomized,
for example by water or gas atomization, to form powder metal.
Alternatively, the melted metal material can be formed into a
casting.
[0053] As alluded to above, the starting base metal material
selected oftentimes includes iron in an amount of at least 50.0 wt.
%, based on the total weight of the metal material before adding
the additive(s). For example, cast irons, highly alloyed cast
irons, stainless steels, unalloyed and alloyed steels, tool steels,
Maraging steels, or Hadfield steels could be used. According to one
example embodiment, the metal material is a steel powder including
1.3 wt. % carbon and 1.1 wt. % silicon. According to another
example embodiment, the metal material is a cast iron powder
including 4.0 wt. % carbon and 2.3 wt. % silicon. According to
another example embodiment, the metal material is a stainless steel
powder including 1.2% Mn, 0.30% Si, 0.44% Cu, 0.23% Mo, 17.3% Cr,
9.5% Ni, and other trace elements. As stated above, aluminum alloys
(for instance the alloys designated as 2024, 3003, 3004, 6061,
7075, 7475, 5080 and 5082), copper alloys (such as aluminum
bronzes, silicon bronzes, and brass), manganese alloys, nickel
alloys (for instance the alloy designated as 625), cobalt alloys
(such as tribaloy and Haynes188), cobalt-chromium alloys (such as
CoCrMo alloys and stellite), titanium alloys (for instance the
alloys designated as Ti-6Al-4V or as Ti-6Al), chromium alloys (such
as the Kh65NVFT alloy) and any hybrid alloys made from these
chemical systems can also be used as the starting powder metal
material (for instance, alloys designated as Invar, Monel, Chromel,
Alnico, and Nitinol60). These examples are not exhaustive and other
metal compositions can be used, as long as the at least one
additive (potassium (K), sodium (Na), zinc (Zn), magnesium (Mg),
lithium (Li), strontium (Sr), calcium (Ca), and barium (Ba)) has
low solubility in the selected material, such that a protective gas
atmosphere is formed on top of the melted material to form a total
amount of at least three times the initial volume of melt to be
treated. FIGS. 4-14 represent the results of calculations and
experiments conducted which show the increased volume of protective
gas atmosphere generated when the additive(s) are added to the
melted metal material according to example embodiments of the
invention. FIG. 4 presents a curve of the total volume of gas that
is obtained as a function of the amount of additive(s) for an
example composition. The additive (here, the additive was a mixture
of 90 wt.% Mg and 10 wt.% Na). The alloy is a cast iron powder
material (Fe-rich) that contains 4.0% C, 1.5% Si, 0.02% S and 2.0%
Cu. This curve was calculated using the chemical composition of one
powder that was water atomized, the amount of additive used in this
experiment was 0.11 wt. %, which resulted in about 0.40 liter of
protective gas (Mg and Na) for each 100 grams of melt. The dashed
line represents the inferior limit of gas that should be obtained
to provide a protective atmosphere which is a volume that is three
times the initial volume of melt to be treated. In this specific
example, the calculated amount of gas is about five times the
inferior limit.
[0054] FIG. 5 presents Energy-dispersive X-ray spectroscopy (EDS)
spectra that were acquired on a polished pure iron surface before
and after it was exposed to the gaseous atmosphere on top of the
tundish during the atomization process of the powder that is
described in FIG. 4. This confirms that the additives (in this case
Mg and Na) formed a gaseous protective atmosphere that was
generated on top of the melt and that these elements deposited on
the exposed polished iron surface;
[0055] FIG. 6 presents examples of different amounts of gas that
can be generated in aluminum alloys for different additives at
different temperatures. The base system for calculations is
Al+0.02% S+0.02% Al2O3. The dashed line represents the inferior
limit of the amount of gas that should be obtained to provide a
protective atmosphere which is defined as three times the initial
volume of melt to be treated. In these examples, the minimum amount
of additive to be added varies according to the nature of the
additive and the temperature of the melt. For instance, Na cannot
generate enough gas if the melt is at a temperature of about 800
Celsius, regardless of the amount that is added. However, if the
temperature of the melt is increased to about 900 Celsius, the
minimum amount of Na is about 0.32 wt. % to generate at least three
times the initial volume of melt to be treated. For K, the minimum
amount is 0.36 wt. % if the melt is at 800 Celsius, and 0.26 wt. %
if the melt is at about 900 Celsius. If a mixture of half Na and
half K is used in an aluminum melt at 900 Celsius, the minimum
amount of Na+K will be about 0.29 wt. % (0.16 wt. % Na and 0.13 wt.
% K). FIG. 7 presents examples of the minimum amount of different
additives to be added to a titanium melt at 1800 Celsius. For
instance, an addition of 0.11 wt. % Ca will provide about the same
minimum amount of gas protection as an addition of 0.48 wt. % Zn.
Similarly, FIGS. 8 to 13 present other examples of the minimum
amount of different additives in different systems (Co, Cr, Cu, Fe,
Mn, and Ni). FIG. 14 presents the calculated minimum amount of
additive (K+Li) in a complex cobalt alloy.
[0056] After adding the at least one additive to the melted base
metal material, the melt can be either atomized or cast. Water
atomization is oftentimes preferred to gas atomization because it
is three to nine times less expensive and is even less expensive
than the other atomization processes. However, for some alloys that
are readily oxidized, gas atomization is preferred. An additive
treatment before gas atomization could allow improved conditions
for atomization such as larger gas pressures and still achieve
round particles and could also limit the amount of internal oxides
and porosities. In addition, the added additive(s) can increase the
sphericity of the water atomized particles, such that the
sphericity approaches the sphericity of gas atomized particles.
[0057] As discussed above, the additive(s) is added in an amount
such that the total volume of gas after the introduction of the
additive(s) is at least three times the initial volume of the melt
to be treated. In one example embodiment, the additive, in this
case, Mg, is added in a single operation as lumps of pure Mg in an
amount ranging from 0.05 to 1.0 wt. %, for example 0.18 wt. %,
based on the total weight of the melted base metal material (an
iron-rich alloy) and the added magnesium. Thus, the resulting
atomized powder metal material or casting includes a very low
amount of residual magnesium and a total sulfur content similar to
the material without the additive but for which S is now chemically
bounded with the additive (as solid precipitates of MgS) and not
dissolved in the melt, which leads to a larger surface tension and
thus more spherical particles, and/or more spherical
microstructural phases and constituents, and/or a lower amount of
internal porosities. Thermodynamical calculations showed that the
free sulfur content in the Mg-treated iron-rich material was more
than 10 times lower than that of the non-treated material, even if
the total sulfur content for both material was similar.
[0058] The additive(s) can be added in a single continuous step,
for example up to 1.0 wt. % in a single continuous step, or
multiple steps spaced from one another by a period of time, for
example three or four steps each including up to 0.2 wt. % of the
additive(s). The additive(s) can also or alternatively be added in
the furnace or in a ladle and they can be in the form of pure
metal, or as an alloy or compound including the additive(s).
Different techniques that are already available can be used to
introduce the additive(s) to the melted metal materials such as,
but not limited to, lumps/chunks of the material that contain the
additive(s) can be directly deposited on top of the melt or at the
bottom of the furnace/crucible, or in the mold, or introduced in
the melt by the usage of the cored wire technique or the usage of
the plunger process. For instance, the cored wire technique uses a
steel sheath filled with the Mg-rich alloy and is introduced in the
melt at a rate dependent on the process parameters. The plunger
technique uses a container in which the Mg containing master alloy
is located, this container is plunged into the liquid cast iron.
Therefore, magnesium makes contact with the liquid cast iron deeper
into the melt, away from the surface.
[0059] As stated above, by adding the additive(s) to the melted
metal material (in the case of Mg in Fe-rich alloys), the number of
water atomized particles that have a circularity and a roundness
value of 0.6 and larger increased by at least 8%, compared to the
same water atomized material without the additive(s). The
additive(s), for example magnesium, also results in fewer internal
oxides, and could close the interface of residual oxide bifilms
present in the melted metal material. This, in turn, produces
cleaner atomized particles and cleaner castings having less and
smaller internal porosities.
[0060] After the atomization or casting step, the method can
include a post heat treatment process. The heat treating step can
include annealing or another heating process typically applied to
powder metal materials. The heat treatment can be conducted in an
inert or reducing atmosphere, such as but not limited to an
atmosphere including nitrogen, argon, and/or hydrogen or vacuum.
For example, annealing in a reducing atmosphere after water
atomization can reduce surface oxides. The heat treatment step can
also be used to form new microstructural phases and/or constituents
in the atomized particles or castings, for example graphite
precipitates or nodules, carbides, or nitrides. Other
microstructural phases and/or constituents could be present,
depending on the composition of the metal material. In one example
embodiment, the metal material is a hypereutectic cast iron alloy,
and the cementite present in the cast iron alloy transforms into
ferrite and spheroidal graphite nodules during the heat treatment
step, see FIGS. 17 and 18. Spherical carbides should also be formed
during the heat treatment of highly alloyed steel. An external
protective atmosphere or vacuum system can also be used together
with the self-generated protective atmosphere described herein such
as, but not limited to: the projection of a flow of nitrogen (N2),
or the projection of an argon (Ar) stream on top of the melt. The
melt could also be enclosed in a chamber with a protective inert
atmosphere or a vacuum system. These systems can increase the
effectiveness of the process.
[0061] The additive(s) can also increase the sphericity of the
microstructural constituents and/or phases formed in the atomized
particles or castings during post heat treatment. However, rounder
phases and/or constituents could be present in the powder metal
material directly after atomization or in the as-cast materials and
not only after heat treatments. The microstructural phases can
include graphite precipitates, carbides, and/or nitrides. Other
microstructural phases and/or constituents could be present,
depending on the composition of the metal material. Typically, the
microstructural constituents and/or phases have a median of the
circularity and a median of the roundness of at least 0.6. Also,
there is at least 10% more, and preferably at least 15% more
constituents and/or phases formed in the magnesium-treated
iron-based material that have a circularity and a roundness value
larger than 0.6 compared to those of the same alloy but without the
additive treatment.
[0062] According to one example embodiment, the powder metal
material includes iron, such as cast iron, in an amount of at least
50 wt. %, and the atomized particles include graphite precipitates,
wherein at least 50% of the graphite precipitates have a
circularity and a roundness value of 0.6 and greater. In another
embodiment, wherein the metal material is iron-based and was
treated with Mg, the annealing step includes producing graphite
precipitates or nodules, and the graphite precipitates or nodules
have a median of the circularity and a median of the roundness of
at least 0.6. In one example embodiment, the metal material is a
hypereutectic cast iron alloy treated with Mg, and spheroidal
graphite nodules are formed during the heat treatment process.
[0063] As stated above, the self-generated protective atmosphere
created after the introduction of the additive(s) will inhibit the
oxidation of the surface of the melt and will limit the amount of
internal oxides in powders after atomization and in castings after
solidification. FIG. 15 shows primary graphite nodules in a
hypereutectic cast iron powder that precipitated on silicon oxides
in suspension in the melt that were formed during pouring from the
crucible to the tundish; this alloy was not treated with any
additives. In Fe-rich systems that contain a high carbon content,
carbon provides a protection against oxidation of the melt in the
crucible (because of the high temperature), which prevents the
formation of oxides in the crucible. Numerous graphite nodules that
grew on these different oxides can be observed in the powder
without an additive. By comparison, FIG. 16 presents one of the
relatively few primary graphite nodules that can be observed in the
hypereutectic cast iron powder that was treated with an additive
(Mg). Since the protective atmosphere made of Mg gas limited the
oxidation of the melt directly from the crucible and throughout
pouring, the amount of oxides that were present in the melt before
the introduction of the additive was significantly less than in the
melt without the additive. Thus, very few substrates were available
for graphite precipitation during solidification and fewer graphite
nodules are present.
[0064] As stated above, the melted metal material can be atomized
to form a powder metal material or cast to form a solidified part.
The powder metal material is typically formed by water or gas
atomization, however another atomization process can be used.
Powders and castings obtained with the disclosed method can be used
in various different automotive or non-automotive applications. For
example, the atomized particles can be used in typical press and
sinter processes. The atomized particles can also be used for metal
injection molding, thermal spraying, and additive manufacturing
applications such as three-dimensional printing, electron beam
melting, binder jetting and selective laser sintering.
[0065] When the melted metal material is cast, the method includes
melting the base metal material, and then adding the at least one
additive to the base metal material. The method then includes
pouring the melted metal material into a mold having a desired
shape, and allowing the liquid metal to solidify before removing
the solidified metal part from the mold.
[0066] Experiment
[0067] FIGS. 17 and 18 are photomicrographs illustrating the
improved sphericity of the microstructural phases and/or
constituents, specifically graphite nodules, achieved by adding an
additive (in this case magnesium) before or during the water
atomization process and after heat treatment. Each material is a
cast iron powder including about 4.0 wt. % carbon and 2.3 wt. %
silicon. However, the material of FIG. 17 was atomized without the
added magnesium, while the material of FIG. 18 was atomized with
the added magnesium. The median of the roundness of the graphite
nodule shown in FIG. 17, without the added magnesium, was
calculated to be 0.56. The median of the roundness of the graphite
nodule with magnesium shown in FIG. 18, was calculated to be 0.73.
Other results that show the improved sphericity of the nodules by
the additive treatment are presented in FIGS. 19 to 22.
[0068] FIGS. 23 and 24 illustrate the lower internal porosities
content according to an example embodiment of the invention. In
this example 304 stainless steels were water atomized. The powder
presented in FIG. 24 was treated with Mg and showed a lower amount
of internal porosities.
[0069] FIGS. 25 and 26 illustrate the lower internal porosities
content according to an example embodiment of the invention. In
this example high carbon steels alloyed with silicon were water
atomized. The powder presented in FIG. 26 was treated with Mg and
showed a lower amount of internal porosities.
[0070] FIG. 27 presents the chemical composition of the example
embodiments of the invention.
[0071] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings and may be
practiced otherwise than as specifically described while within the
scope of the following claims. In particular, all features of all
claims and of all embodiments can be combined with each other, as
long as they do not contradict each other.
* * * * *
References