U.S. patent application number 10/529587 was filed with the patent office on 2006-06-15 for nano-crystal austenitic metal bulk material having high hardness, high strength and toughness, and method for production thereof.
Invention is credited to Munehide Katsumura, Harumatsu Miura, Nobuaki Miyao, Masaru Mizutani, Kazuo Oda, Hidenori Ogawa.
Application Number | 20060127266 10/529587 |
Document ID | / |
Family ID | 32040626 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060127266 |
Kind Code |
A1 |
Miura; Harumatsu ; et
al. |
June 15, 2006 |
Nano-crystal austenitic metal bulk material having high hardness,
high strength and toughness, and method for production thereof
Abstract
The invention provides a high hard, strength and tough
nano-crystal metal bulk material and a preparation process thereof.
The metal bulk material comprises an aggregate of metal
nano-crystal grains, wherein an oxide, nitride, carbide, boride or
the like of a metal or semimetal exists as a crystal grain growth
inhibitor between and/or in the nano-crystal grains. The respective
fine powders of nano-metal bulk material-forming components are
mechanically alloyed (MA), using a ball mill or the like, thereby
preparing nano-metal powders. Then, hot forming-by-sintering
treatment such as spark plasma sintering, extrusion and rolling or
explosive forming is applied to the powders to obtain a high hard,
strength and tough nano-crystal metal bulk material.
Inventors: |
Miura; Harumatsu; (Hyogo,
JP) ; Miyao; Nobuaki; (Osaka, JP) ; Ogawa;
Hidenori; (Osaka, JP) ; Oda; Kazuo;
(Yamaguchi, JP) ; Katsumura; Munehide; (Kagawa,
JP) ; Mizutani; Masaru; (Tokyo, JP) |
Correspondence
Address: |
DELLETT & WALTERS
P. O. BOX 82788
PORTLAND
OR
97282-0788
US
|
Family ID: |
32040626 |
Appl. No.: |
10/529587 |
Filed: |
September 30, 2003 |
PCT Filed: |
September 30, 2003 |
PCT NO: |
PCT/JP03/12530 |
371 Date: |
November 28, 2005 |
Current U.S.
Class: |
419/32 ;
148/403 |
Current CPC
Class: |
B22F 2998/00 20130101;
C22C 21/12 20130101; B22F 3/006 20130101; B22F 2003/1032 20130101;
C22C 38/001 20130101; B22F 2998/10 20130101; B22F 2998/00 20130101;
C22C 38/04 20130101; B22F 2998/10 20130101; C22C 38/48 20130101;
C22C 14/00 20130101; C22C 2200/04 20130101; C22C 38/02 20130101;
B22F 2998/00 20130101; C22C 9/01 20130101; C22C 38/18 20130101;
B22F 9/005 20130101; B22F 3/14 20130101; C22C 1/1084 20130101; B22F
3/006 20130101; B22F 3/105 20130101; B22F 1/0018 20130101; B22F
3/08 20130101; B22F 3/20 20130101 |
Class at
Publication: |
419/032 ;
148/403 |
International
Class: |
B22F 3/10 20060101
B22F003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2002 |
JP |
2002-287950 |
Claims
1. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein a metal oxide or a semimetal oxide exists as a crystal
grain growth inhibitor between and/or in said nano-crystal
grains.
2. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein a metal nitride or a semimetal nitride exists as a crystal
grain growth inhibitor between and/or in said nano-crystal
grains.
3. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein a metal carbide or a semimetal carbide exists as a crystal
grain growth inhibitor between and/or in said nano-crystal
grains.
4. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein a metal silicide or a semimetal silicide exists as a
crystal grain growth inhibitor between and/or in said nano-crystal
grains.
5. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein a metal boride or a semimetal boride exists as a crystal
grain growth inhibitor between and/or in said nano-crystal
grains.
6. A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
wherein: at least two compounds selected from the group consisting
of (1) a metal oxide or a semimetal oxide, (2) a metal nitride or a
semimetal nitride, (3) a metal carbide or a semimetal carbide, (4)
a metal silicide or a semimetal silicide and (5) a metal boride or
a semimetal boride exist as a crystal grain grown inhibitor between
and/or in said nano-crystal particles.
7. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claim 1 to 6, wherein the bulk
material comprising an aggregate of metal nano-crystal grains
contains nitrogen in an amount of 0.01 to 5.0% by mass.
8. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 6, wherein the bulk
material comprising an aggregate of metal nano-crystal grains
contains nitrogen in an amount of 0.1 to 2.0% by mass.
9. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 8, wherein the bulk
material comprising an aggregate of metal nano-crystal grains
contains a metal oxide form of oxygen in an amount of 0.01 to 1.0%
by mass.
10. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 9, which further
comprises a metal element having a stronger chemical affinity for
nitrogen than a nano-crystal metal so as to prevent denitrification
of the aggregate comprising metal nano-crystal grains in a
forming-by-sintering process.
11. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 10, wherein a
nano-crystal metal-forming component is at least one element
selected from the group consisting of aluminum, magnesium, zinc,
titanium, calcium, beryllium, antimony, yttrium, scandium, indium,
uranium, gold, silver, chromium, zirconium, tin, tungsten,
tantalum, iron, nickel, cobalt, copper, niobium, platinum,
vanadium, manganese, molybdenum, lanthanum, rhodium, carbon,
silicon, boron, nitrogen and phosphor.
12. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 10, wherein a
nano-crystal metal-forming component is a dental platinum-group
element.
13. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 10, wherein a
nano-crystal material is one or two or more intermetallic compounds
selected from the group consisting of Ni.sub.3Al, Fe.sub.3Al, FeAl,
Ti.sub.3Al, TiAl, TiAl.sub.3, ZrAl.sub.3, NbAl.sub.3, NiAl,
Nb.sub.3Al, Nb.sub.2Al, MoSi.sub.2, Nb.sub.5Si.sub.3,
Ti.sub.5Si.sub.3, Nb.sub.2Be.sub.17, Co.sub.3Ti, Ni.sub.3(Si, Ti),
SiC, Si.sub.3N.sub.4, AlN, TiNi, ZrB.sub.2, HfB.sub.2,
Cr.sub.3C.sub.2, and Ni.sub.3Al--Ni.sub.3Nb.
14. The high hard, strength and tough nano-crystal metal bulk
material according to any one of claims 1 to 13, wherein the metal
nano-crystal grains have been obtained by mechanical milling (MM)
or mechanical alloying (MA) using a ball mill or the like.
15. A process for preparing a nano-crystal metal bulk material,
which involves steps of: applying mechanical alloying (MA) to
respective fine powders of nano-crystal metal-forming components,
using a ball mill or the like, thereby preparing fine powders of a
nano-crystal metal, and applying to said fine powders of a
nano-crystal metal hot forming-by-sintering treatment such as
sheath rolling, spark plasma sintering or extrusion, or explosive
forming, thereby obtaining a high hard, strength and tough metal
bulk material.
16. A process for preparing a nano-crystal metal bulk material,
which involves steps of: mixing respective fine powders of
nano-crystal metal-forming components together with a substance
that becomes a nitrogen source, applying mechanical alloying (MA)
to the resulting mixture, using a ball mill or the like, thereby
preparing high nitrogen-concentration, nano-crystal metal powders,
and applying to said metal powders hot forming-by-sintering
treatment such as sheath rolling, spark plasma sintering or
extrusion, or explosive forming, thereby obtaining a high hard,
strength and tough metal bulk material.
17. The process for preparing a nano-crystal metal bulk material
according to claim 16, wherein the substance that becomes a
nitrogen source is a metal nitride.
18. The process for preparing a nano-crystal metal bulk material
according to claim 16, wherein the substance that becomes a
nitrogen source is N.sub.2 gas or NH.sub.3 gas.
19. The process for preparing a nano-crystal metal bulk material
according to any one of claims 15 to 18, wherein an atmosphere in
which mechanical milling or mechanical alloying is applied is any
one gas selected from the group consisting of (1) an inert gas such
as argon gas, (2) N.sub.2 gas, and (3) NH.sub.3 gas or (4) a mixed
gas of two or more gases selected from (1) to (3).
20. The process for preparing a nano-crystal metal bulk material
according to claim 19, wherein an atmosphere in which mechanical
milling or mechanical alloying is applied is an atmosphere of a gas
with some reducing substance such as H.sub.2 gas added thereto.
21. The process for preparing a nano-crystal metal bulk material
according to claim 15 or 16, wherein an atmosphere in which
mechanical milling or mechanical alloying is applied is a vacuum, a
vacuum atmosphere with some reducing substance such as H.sub.2 gas
added to a vacuum or a reducing atmosphere.
22. The process for preparing a nano-crystal metal bulk material
according to any one of claims 16 to 21, which involves steps of:
mixing the respective fine powders of nano-crystal metal-forming
components and 1 to 10% by volume of a metal nitride or 0.5,to 10%
by mass of a nitrogen affinity metal having a stronger chemical
affinity for nitrogen than a nano-crystal metal together with a
substance that becomes a nitrogen source, applying mechanical
alloying (MA) to the resulting mixture, using a ball mill or the
like, thereby preparing high-nitrogen nano-crystal metal powders,
and applying to said metal powders hot forming-by-sintering
treatment such as sheath rolling, spark plasma sintering or
extrusion, or explosive forming, wherein said additive nitride is
dispersed or a nitride, carbo-nitride or the like of said metal
element is precipitated or dispersed in a mechanical alloying (AM)
process or a forming-by-sintering process of mechanically alloyed
(MA) powders, thereby obtaining a high hard, strength and tough
metal bulk material.
23. The process for preparing a nano-crystal metal bulk material
according to any one of claims 15 to 22, wherein a nano-crystal
metal has a blending composition containing 0 to 40% by mass of
other element, and the forming-by-sintering is carried out at a
temperature that is at least 10% lower than a melting point or
melting temperature of said nano-crystal metal.
24. A process for preparing a high hard, strength and tough
nano-crystal steel bulk material, which involves steps of: applying
mechanical alloying (MA) to respective powders of nano-crystal
steel-forming components using a ball mill or the like, thereby
preparing nano-crystal steel powders, and applying to said steel
powders forming-by-sintering treatment such as spark plasma
sintering, hot pressing, extrusion or rolling, or explosive forming
at or near a superplasticity-inducing temperature of said steel
powders.
25. A process for preparing a high hard, strength and tough
nano-crystal cast iron bulk material, which involves steps of:
applying mechanical alloying (MA) to respective powders of
nano-crystal cast iron-forming components using a ball mill or the
like, thereby preparing nano-crystal cast iron powders, and
applying to said cast iron powders forming-by-sintering treatment
such as spark plasma sintering, hot pressing, extrusion or rolling,
or explosive forming at or near a superplasticity-inducing
temperature of said cast iron powders.
26. A process for preparing a high hard, strength and tough
nano-crystal steel formed material, which involves steps of:
applying mechanical alloying (MA) to respective powders of
nano-crystal steel-forming components using a ball mill or the
like, thereby preparing nano-crystal steel powders, applying to
said steel powders forming-by-sintering treatment such as spark
plasma sintering, hot pressing, extrusion or rolling, or explosive
forming, thereby obtaining a steel bulk material, and forming said
steel bulk material at or near a super-plasticity-inducing
temperature of said steel bulk material.
27. A process for preparing a high hard, strength and tough
nano-crystal cast iron formed material, which involves involving
steps of: applying mechanical alloying (MA) to respective powders
of nano-crystal cast iron-forming components using a ball mill or
the like, thereby preparing nano-crystal cast iron powders,
applying to said cast iron powders forming-by-sintering treatment
such as spark plasma sintering, hot pressing, extrusion or rolling,
or explosive forming, thereby obtaining a cast iron bulk material,
and forming said cast iron bulk material at or near a
super-plasticity-inducing temperature of said cast iron bulk
material.
Description
ART FIELD
[0001] The present invention relates generally to a metal material,
and more particularly to a high hard, strength and tough
nano-crystal metal bulk material, and its preparation process.
BACKGROUND OF THE INVENTION
[0002] As the Petch relationship teaches, metal material strength
and hardness increase with decreasing crystal grain diameter D, and
such relationships hold as far as D is at or near a few tens of nm.
Thus, reducing crystal grain diameters down to nano-size levels now
becomes one of the most important means ever for the reinforcement
of metal materials.
[0003] On the other hand, as crystal grain diameters are reduced
down to ultra-fine, nano-size levels, most metal materials come to
show a unique phenomenon called super-plasticity in a temperature
region of higher than 0.5 Tm where Tm is a melting point (K).
[0004] Harnessing that phenomenon enables even materials extremely
unsusceptible to plastic processing or the like due to high melting
points or temperatures to be deformed and processed at relatively
low temperatures.
[0005] There are some reports that regarding magnetic elements such
as iron, cobalt and nickel, in nano-order grain diameter ranges
coercive force decreases and soft magnetism improves with
decreasing D, which are not found when the crystal grain diameter D
is in micron-order ranges.
[0006] However, the crystal grain diameter D of most metal
materials produced by melting are usually on the order of a few
microns to a few thousand of microns, and D can hardly be reduced
down to the nano-order even by post-treatments. Even with
controlled rolling that is an important micro-processing of steel
crystal grains, for instance, the lowest possible limit to grain
diameters is of the order of at most 4 to 5 .mu.m. In other words,
with such ordinary processes it is impossible to obtain materials
whose grain diameters are reduced down to the nano-size level.
DISCLOSURE OF THE INVENTION
[0007] The present invention has for its object the provision of
satisfactory solutions to the above problems.
[0008] Basically, the present invention makes use of mechanical
milling (MM) or mechanical alloying (MA) of a powder mixture of
powders of an elementary or semimetal single metal and powders of
other metal additives or the like. The resulting nano-crystal fine
powders are refined by forming-by-sintering or methods using
superplacticity in the forming-by-sintering process down to
nano-size levels, thereby providing a bulk material having strength
(high strength) and hardness (super hardness) close to the limits
achievable with crystal grain diameters reduced down to the
nano-size level, and corrosion resistance as well.
[0009] Thus, the present invention is concerned with nano-crystal
metal bulk materials as recited below, and their preparation
processes.
[0010] (1) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that a metal oxide or a semimetal oxide exists as
a crystal grain growth inhibitor between and/or in said
nano-crystal grains.
[0011] (2) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that a metal nitride or a semimetal nitride exists
as a crystal grain growth inhibitor between and/or in said
nano-crystal grains.
[0012] (3) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that a metal carbide or a semimetal carbide exists
as a crystal grain growth inhibitor between and/or in said
nano-crystal grains.
[0013] (4) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that a metal silicide or a semimetal silicide
exists as a crystal grain growth inhibitor between and/or in said
nano-crystal grains.
[0014] (5) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that a metal boride or a semimetal boride exists
as a crystal grain growth inhibitor between and/or in said
nano-crystal grains.
[0015] (6) A high hard, strength and tough nano-crystal metal bulk
material, comprising an aggregate of metal nano-crystal grains,
characterized in that:
[0016] at least two compounds selected from the group consisting of
(1) a metal oxide or a semimetal oxide, (2) a metal nitride or a
semimetal nitride, (3) a metal carbide or a semimetal carbide, (4)
a metal silicide or a semimetal silicide and (5) a metal boride or
a semimetal boride exist as a crystal grain grown inhibitor between
and/or in said nano-crystal particles.
[0017] (7) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (6) above,
characterized in that the bulk material comprising an aggregate of
metal nano-crystal grains contains nitrogen in an amount of 0.01 to
5.0% by mass.
[0018] (8) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (6) above,
characterized in that the bulk material comprising an aggregate of
metal nano-crystal grains contains nitrogen in an amount of 0.1 to
2.0% by mass.
[0019] (9) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (8) above,
characterized in that the bulk material comprising an aggregate of
metal nano-crystal grains contains a metal oxide form of oxygen in
an amount of 0.01 to 1.0% by mass.
[0020] (10) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (9) above,
characterized by further comprising a metal element having a
stronger chemical affinity for nitrogen than a nano-crystal metal
so as to prevent denitrification of the aggregate comprising metal
nano-crystal grains in a forming-by-sintering process.
[0021] (11) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (10) above,
characterized in that a nano-crystal metal-forming component is at
least one element selected from the group consisting of aluminum,
magnesium, zinc, titanium, calcium, beryllium, antimony, yttrium,
scandium, indium, uranium, gold, silver, chromium, zirconium, tin,
tungsten, tantalum, iron, nickel, cobalt, copper, niobium,
platinum, vanadium, manganese, molybdenum, lanthanum, rhodium,
carbon, silicon, boron, nitrogen and phosphor.
[0022] (12) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (10) above,
characterized in that a nano-crystal metal-forming component is a
dental platinum-group element.
[0023] (13) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (10) above,
characterized in that a nano-crystal material is one or two or more
intermetallic compounds selected from the group consisting of
Ni.sub.3Al, Fe.sub.3Al, FeAl, Ti.sub.3Al, TiAl, TiAl.sub.3,
ZrAl.sub.3, NbAl.sub.3, NiAl, Nb.sub.3Al, Nb.sub.2Al, MoSi.sub.2,
Nb.sub.5Si.sub.3, Ti.sub.5Si.sub.3, Nb.sub.2Be.sub.17, CO.sub.3Ti,
Ni.sub.3(Si, Ti), SiC, Si.sub.3N.sub.4, AlN, TiNi, ZrB.sub.2,
HfB.sub.2, Cr.sub.3C.sub.2, or Ni.sub.3Al--Ni.sub.3Nb.
[0024] (14) The high hard, strength and tough nano-crystal metal
bulk material according to any one of (1) to (13) above,
characterized in that the metal nano-crystal grains have been
obtained by mechanical milling (MM) or mechanical alloying (MA)
using a ball mill or the like.
[0025] (15) A process for preparing a nano-crystal metal bulk
material, characterized by involving steps of:
[0026] applying mechanical alloying (MA) to respective fine powders
of nano-crystal metal-forming components, using a ball mill or the
like, thereby preparing fine powders of a nano-crystal metal,
and
[0027] applying to said fine powders of a nano-crystal metal hot
forming-by-sintering treatment such as sheath rolling, spark plasma
sintering or extrusion, or explosive forming, thereby obtaining a
high hard, strength and tough metal bulk material.
[0028] (16) A process for preparing a nano-crystal metal bulk
material, characterized by involving steps of:
[0029] mixing respective fine powders of nano-crystal metal-forming
components together with a substance that becomes a nitrogen
source, [0030] applying mechanical alloying (MA) to the resulting
mixture, using a ball mill or the like, thereby preparing high
nitrogen-concentration, nano-crystal metal powders, and
[0031] applying to said metal powders hot forming-by-sintering
treatment such as sheath rolling, spark plasma sintering or
extrusion, or explosive forming, thereby obtaining a high hard,
strength and tough metal bulk material.
[0032] (17) The process for preparing a nano-crystal metal bulk
material according to (16) above, characterized in that the
substance that becomes a nitrogen source is a metal nitride.
[0033] (18) The process for preparing a nano-crystal metal bulk
material according to (16) above, characterized in that the
substance that becomes a nitrogen source is N.sub.2 gas or NH.sub.3
gas.
[0034] (19) The process for preparing a nano-crystal metal bulk
material according to any one of (15) to (18) above, characterized
in that an atmosphere in which mechanical milling or mechanical
alloying is applied is any one gas selected from the group
consisting of (1) an inert gas such as argon gas, (2) N.sub.2 gas,
and (3) NH.sub.3 gas or (4) a mixed gas of two or more gases
selected from (1) to (3).
[0035] (20) The process for preparing a nano-crystal metal bulk
material according to (19) above, characterized in that an
atmosphere in which mechanical milling or mechanical alloying is
applied is an atmosphere of a gas with some reducing substance such
as H.sub.2 gas added thereto.
[0036] (21) The process for preparing a nano-crystal metal bulk
material according to (15) or (16) above, characterized in that an
atmosphere in which mechanical milling or mechanical alloying is
applied is a vacuum, a vacuum atmosphere with some reducing
substance such as H.sub.2 gas added to a vacuum or a reducing
atmosphere.
[0037] (22) The process for preparing a nano-crystal metal bulk
material according to any one of (16) to (21) above, characterized
by involving steps of:
[0038] mixing the respective fine powders of nano-crystal
metal-forming components and 1 to 10% by volume of a metal nitride
or 0.5 to 10% by mass of a nitrogen affinity metal having a
stronger chemical affinity for nitrogen than for a nano-crystal
metal together with a substance that becomes a nitrogen source,
[0039] applying mechanical alloying (MA) to the resulting mixture,
using a ball mill or the like, thereby preparing high-nitrogen
nano-crystal metal powders, and
[0040] applying to said metal powders hot forming-by-sintering
treatment such as sheath rolling, spark plasma sintering or
extrusion or explosive forming, wherein said additive nitride is
dispersed or a nitride, carbo-nitride or the like of said metal
element is precipitated or dispersed in a mechanical alloying (AM)
process or a forming-by-sintering process of mechanically alloyed
(MA) powders, thereby obtaining a high hard, strength and tough
metal bulk material.
[0041] (23) The process for preparing a nano-crystal metal bulk
material according to any one of (15) to (22) above, characterized
in that a nano-crystal metal has a blending composition containing
0 to 40% by mass of other element, and the forming-by-sintering is
carried out at a temperature that is at least 10% lower than a
melting point or melting temperature.
[0042] (24) A process for preparing a high hard, strength and tough
nano-crystal steel bulk material, characterized by involving steps
of:
[0043] applying mechanical alloying (MA) to respective powders of
nano-crystal steel-forming components using a ball mill or the
like, thereby preparing nano-crystal steel powders, and
[0044] applying to said steel powders forming-by-sintering
treatment such as spark plasma sintering, hot pressing, extrusion
or rolling or explosive forming at or near a
superplasticity-inducing temperature.
[0045] (25) A process for preparing a high hard, strength and tough
nano-crystal cast iron bulk material, characterized by involving
steps of:
[0046] applying mechanical alloying (MA) to respective powders of
nano-crystal cast iron-forming components using a ball mill or the
like, thereby preparing nano-crystal cast iron powders, and
[0047] applying to said cast iron powders forming-by-sintering
treatment such as spark plasma sintering, hot pressing, extrusion
or rolling or explosive forming at or near a
superplasticity-inducing temperature.
[0048] (26) A process for preparing a high hard, strength and tough
nano-crystal steel formed material, characterized by involving
steps of:
[0049] applying mechanical alloying (MA) to respective powders of
nano-crystal steel-forming components using a ball mill or the
like, thereby preparing nano-crystal steel powders,
[0050] applying to said steel powders forming-by-sintering
treatment such as spark plasma sintering, hot pressing, extrusion
or rolling or explosive forming, thereby obtaining a steel bulk
material, and
[0051] forming said steel bulk material at or near a
super-plasticity-inducing temperature.
[0052] (27) A process for preparing a high hard, strength and tough
nano-crystal cast iron formed material, characterized by involving
steps of:
[0053] applying mechanical alloying (MA) to respective powders of
nano-crystal cast iron-forming components using a ball mill or the
like, thereby preparing nano-crystal cast iron powders,
[0054] applying to said cast iron powders forming-by-sintering
treatment such as spark plasma sintering, hot pressing, extrusion
or rolling or explosive forming, thereby obtaining a cast iron bulk
material, and
[0055] forming said cast iron bulk material at or near a
superplasticity-inducing temperature.
[0056] According to the invention as defined above, as either
mechanical milling (MM) or mechanical alloying (MA) is applied to a
powdery material of a single metal with other element added
thereto, it is formed into powders having an ultra-fine crystal
grain structure. By the forming-by-sintering of those powders at a
temperature that is at most 10% lower than the melting point or
melting temperature of those powders, the metal bulk material can
be easily prepared.
[0057] As mechanical alloying (MA) is applied to a powdery mixture
of powders of a practical single metal such as iron, cobalt,
nickel, and aluminum with carbon, niobium, titanium or the like
added thereto, there is obtained a more ultra-fine crystal grain
structure. Such forming-by-sintering as mentioned above readily
gives a bulk material having a nano-crystal grain structure, which
is much higher than that obtained by melting in terms of strength
and hardness.
[0058] By suitable selection of crystal grain size, composition, or
the like, superplasticity is induced in the nano-crystal material,
and this phenomenon can be effectively applied to the
forming-by-sintering process of MA powders.
BRIEF EXPLANATION OF THE DRAWINGS
[0059] FIG. 1 is illustrative of the mean crystal grain diameters
of each element upon 50-hour mechanical alloying (MA) of powders of
iron, cobalt and nickel with other element (A) added thereto in an
amount of 15 at %, as used in one specific example of the
invention.
[0060] FIG. 2 is illustrative in graph of the relationships between
the crystal grain diameter D.sub.Fe of iron used in one specific
example of the invention and the logarithm log .beta. of grain
boundary segregation factor .beta. of the solute element added.
[0061] FIG. 3 is illustrative in graph of the relationships between
the crystal grain diameter D.sub.Co of cobalt used in one specific
example of the invention and the logarithm log .beta. of grain
boundary segregation factor .beta. of the solute element added.
[0062] FIG. 4 is illustrative in graph of the relationships between
the crystal grain diameter D of the sample as used in one specific
example of the invention and the amount of tantalum added (at
%).
BEST MODE FOR CARRYING OUT THE INVENTION
[0063] Some embodiments of the invention are now explained. In one
embodiment of the invention, mechanical milling (MM) or mechanical
alloying (MA) is applied to elementary powders of single metals
such as iron, cobalt, nickel, aluminum and copper with or without
other elements added thereto, using a ball mill or the like at room
temperature in an argon gas or other atmosphere.
[0064] The mechanically milled or mechanically alloyed powders are
easily reduced down to a crystal grain diameter of about 10 to 20
nm by mechanical energy applied by ball milling. For instance, iron
reduced down to a grain diameter of about 25 nm has a Vickers
hardness of about 1,000.
[0065] Then, the thus mechanically milled or mechanically alloyed
powders are vacuum charged in a stainless steel tube (sheath) of
about 7 mm in inside diameter, for forming-by-sintering by means of
sheath rolling using a rolling machine at a temperature that is at
most 10% lower than the melting point or melting temperature. In
this way, for instance, an iron sheet of at least 1.5 GPa in offset
yield strength and about 1.5 mm in thickness can be easily
prepared.
[0066] Further, if mechanical alloying (MA) is applied to a powdery
mixture comprising elementary powders of iron, cobalt, nickel,
aluminum, copper and so on with other elements such as carbon,
niobium and titanium added thereto in an amount of about 0.5 to 15%
by mass, using a ball mill or the like, the powders are much
further reduced in the MA process down to more ultra-fine levels,
i.e., crystal grains of a few nano-order level.
[0067] If the amount of a metal or semimetal oxide form of oxygen
inevitably entrapped in the powders that are undergoing mechanical
alloying (MA) is usually regulated to up to about 0.5% by mass, it
is then possible to prevent coarsening of crystal grains in the
forming-by-sintering process. To enhance such coarsening-prevention
effects, it is desirable to add 1 to 10% by volume, especially 3 to
5% by volume of a crystal grain dispersant such as AlN, and NbN to
the mechanically alloyed (MA) powders.
[0068] In the invention, mechanical milling (MM) or mechanical
alloying (MA) is applied to powders of single metals such as iron,
cobalt, nickel, aluminum, coppers with or without other elements
added thereto to prepare powders having a nano-size crystal grain
structure. Then, as the metal powders are formed by
forming-by-sintering such as sheath rolling or extrusion, the
amount of a metal oxide form of oxygen that is inevitably formed
during the mechanical milling (MM) or mechanical alloying (MA)
process is regulated to up to about 0.5% (by mass), so that any
coarsening of crystal grains is held back by the pinning effect of
that oxide on crystal grain boundaries. It is thus possible to
achieve effective preparation of nano-crystal materials.
EXAMPLES
[0069] Examples of the invention are now explained with reference
to the accompanying drawings.
Example 1
[0070] FIG. 1 is illustrative of changes in the mean crystal grain
diameter of each mechanically alloyed element, that is, iron,
cobalt and nickel when a 50-hour mechanical alloying (MA) was
applied to an elementary powder mixture having an M.sub.85A.sub.15
(at %) (M is iron, cobalt or nickel), which comprised powders of
the elements iron, cobalt and nickel with the addition thereto of
15 at % of carbon (C), niobium (Nb), tantalum (Ta), titanium (Ti)
and so on as other elements (A).
[0071] In FIG. 1, D.sub.Fe, D.sub.Co and D.sub.Ni are the mean
crystal grain diameter (nm) of the mechanically alloyed iron,
cobalt, and nickel, respectively. From FIG. 1, it has been found
that the reduction of crystal grain diameters of each of the
elements iron, cobalt and nickel can be more effectively promoted
by mechanical alloying with the addition thereto of carbon,
niobium, tantalum, titanium and so on, all the three elements being
refined down to grain diameters of a few nano-orders.
[0072] It has also been found that the reduction of crystal grains
of copper, aluminum, and titanium, too, is promoted by the addition
thereto of other elements, and that carbon, phosphor and boron are
particularly effective as such elements. It is here noted that the
other elements used include carbon (C), niobium (Nb), tantalum
(Ta), phosphor (P), boron (B) or the like, and that the data about
nitrogen N are directed to iron alone.
[0073] FIG. 2 is illustrative in graph of the relationships between
the crystal grain diameter D.sub.Fe of iron and the common
logarithm log .beta. of grain boundary segregation factor .beta. of
the additive element A in iron.
[0074] The additive element A, for instance, includes carbon (C),
nitrogen (N), tantalum (Ta), and vanadium (V).
[0075] From FIG. 2, it has been found that the larger the value of
log .beta., the more enhanced the effect on the refinement of
crystal grains in the MA process is.
[0076] FIG. 3 is illustrative in graph of the relationships between
the crystal grain diameter D.sub.co of cobalt and the common
logarithm log .beta. of grain boundary segregation factor .beta. of
the additive element A in cobalt.
[0077] The additive element A, for instance, includes carbon (C),
niobium (Nb), and tantalum (Ta).
[0078] From FIG. 3, it has been found that the larger the value of
log .beta., the more enhanced the effect on the refinement of
crystal grains in the MA process is.
Example 2
[0079] FIG. 4 is illustrative in graph of the relationships between
the mean crystal grain diameter D (nm) of an
Fe.sub.64-yCr.sub.18Ni.sub.8Ta.sub.YN.sub.10 (at %) where y=0 to
15, obtained by a 100-hour MA treatment of a powder mixture of
elements iron, nickel and tantalum with the addition thereto of
iron nitride, and the amount of tantalum added y (at %).
[0080] From FIG. 4, it has been found that the marked grain
refinement effect of the additions elements A having the large
value of the grain boundary segregation factor .beta. in the binary
Fe and A materials is similarly seen in the multicomponent
materials based on component Fe as well.
Example 3
[0081] A powder sample of Fe.sub.99.8C.sub.0.2 (% by mass) was
obtained by the mechanical alloying (MA) of a powder mixture of
elements iron and carbon for 200 hours. Then, the sample was vacuum
charged in a stainless steel tube (sheath). Consolidation (i.e.,
sintering) of the vacuum charged powder sample was performed by
sheath rolling (SR) at a temperature of 900.degree. C., obtaining
an SR formed product (bulk material) as shown in Table 1.
TABLE-US-00001 TABLE 1 Mean crystal grain diameter D, Vickers
hardness Hv and the value of oxygen upon analysis of
Fe.sub.99.8C.sub.0.2 (% by mass) bulk material obtained by
900.degree. C.-sheath rolling (SR) of powder material mechanically
alloyed from a power mixture of elements iron and carbon Sample D
(nm) Hv Oxygen % by mass SR formed material* 23 980 0.485 The value
of D was calculated from Scherrer's equation, and * indicates that
the material thickness was about 1.4 mm.
[0082] From Example 3 and Table 1, it has been found that according
to the invention, the Vickers hardness Hv of the formed material is
enhanced by the reduction of crystal grains down to the nano-order,
exceeding that of a hardened material having a high-carbon steel's
martensite structure.
Example 4
[0083] Alloy powders of (a) Fe.sub.86Cr.sub.13N.sub.1 (% by mass)
and (b) Fe.sub.69.25Cr.sub.20Ni.sub.8Ta.sub.2N.sub.0.75 (% by mass)
were prepared by mechanical alloying (MA) of powder mixtures
comprising powders of elements iron, chromium, nickel and tantalum
and iron nitride (containing 8.51% by mass of nitrogen), using a
ball mill in an argon atmosphere.
[0084] Then, these alloy powders were charged in a graphite die of
40 mm in inside diameter, and the die was placed in a vacuum for
spark plasma sintering (SPS) at 900.degree. C., after which hot
rolling was further applied to the sintered product at the same
temperature, annealed at 1,150.degree. C. for 15 minutes, and
finally cooled with water. Table 2 shows the mean crystal grain
diameter d, hardness Hv, tensile strength .sigma.B, elongation
.delta. and the value of oxygen and nitrogen upon analysis of the
rolled/annealed products. TABLE-US-00002 TABLE 2 Mean crystal grain
diameter d, hardness Hv, tensile strength .sigma. B, elongation
.delta. and the value of oxygen and nitrogen upon analysis of the
formed materials (spark plasma sintering (vacuum, 900.degree. C.)
plus rolling (vacuum, 900.degree. C.) plus annealing (1,150.degree.
C. .times. 15 minutes/water cooling)), obtained from mechanically
alloyed (MA) powder samples of (a) Fe.sub.86Cr.sub.13N.sub.1 (% by
mass) and (b) Fe.sub.69.25Cr.sub.20Ni.sub.8Ta.sub.2N.sub.0.75(% by
mass) .sigma.B .delta. Oxygen* Nitrogen Sample d (nm) Hv MPa % % by
mass % by mass a A B 20 200 770 2,200 15 0.502 1.02 b 17 150 680
2,050 20 0.544 0.746 A MA powder sample B formed material sample
*the value of oxygen of the feed powders used for MA upon analysis
was 0.23 to 0.28% by mass.
[0085] From Table 2, it has been found that although there is some
considerable growth of crystal grains during both the hot
forming-by-sintering process and the annealing process, yet both
the formed samples keep their nano-size level crystal grain
structure. This could be due to the pinning of crystal grain
boundaries by metal or semimetal oxides of oxygen contained in the
mechanically alloyed (MA) alloy powders.
[0086] It has also been found that through both the effects of
nitrogen solid solution and ultra-fined crystal grains, both the
alloys are much more improved in terms of hardness Hv and tensile
strength .sigma.B.
[0087] For making use of superplasticity induced by
forming-by-sintering in powder materials, it is of the most
importance that crystal grains therein be reduced down to a
ultra-fine level, and that growth of crystal grains during the
deformation process due to super-plasticity be reduced as much as
possible.
[0088] According to the invention, forming-by-sintering processes
harnessing superplasticity are easily achievable, because powders
of nano-size ultra-fine crystal grains are easily obtainable by
mechanical alloying (MA) of feed powders, and because metal oxides
resulting inevitably from that mechanical alloying (MA) prevent
growth of grains during forming-by-sintering processes.
[0089] Examples of forming-by-sintering making use of
superplasticity according to the invention are now explained with
reference to Tables 3, 4 and 5.
Example 5
[0090] According to the invention, a superplasticity-harnessing
forming-by-sintering process was effectively achieved with powders
obtained by mechanical alloying (MA) of a carbon steel material
having a hyper-eutectoid steel composition with a carbon content of
0.765 to 2.14% by mass in particular. One example is given
below.
[0091] Alloy powders having a hyper-eutectoid steel composition of
Fe.sub.96.1-xC.sub.1.5Cr.sub.1.7Mn.sub.0.5N.sub.0.2Si.sub.x (% by
mass) where x=1 to 3 were prepared by ball mill mechanical alloying
(MA, an argon gas atmosphere) of a powder mixture of powdery
elements iron, carbon, chromium, manganese and silicon with iron
nitride having a nitrogen content of 8.51% by mass. The powders
were charged in a graphite die of 40 mm in inside diameter for a
15-minute hot pressing in a vacuum and at 750.degree. C. and a
pressure of 60 MPa, thereby obtaining a pre-sintered mass of 40 mm
in diameter and about 5 mm in thickness.
[0092] Then, a given compression load was applied to the
pre-sintered mass at 800.degree. C. and a strain rate of
10.sup.-4/sec. for 30 minutes in its thickness direction to obtain
a formed-by-sintering product. Set out in Table 3 are the mean
crystal grain diameter d, hardness Hv, tensile strength .sigma.B,
elongation .delta. and the values of oxygen and nitrogen upon
analysis of the formed product at different Si concentrations (x, %
by mass).
[0093] It is here noted that nitrogen was incorporated in the
present alloy sample for the purpose of enhancing its strength.
[0094] From Table 3 and the value of ordinary-temperature hardness
Hv, it has been found that the sintering process of these samples
at 800.degree. C. comes to be more effective from the Si
concentration of 2% by mass or higher.
[0095] The concentration of Si should preferably be from 2.0 to
3.5% by mass. TABLE-US-00003 TABLE 3 Relationships between the
concentration of Si of Fe.sub.96.1-x
C.sub.1.5Cr.sub.1.7Mn.sub.0.5N.sub.0.2Si.sub.x (% by mass, x = 1 to
3) samples obtained by mechanical alloying (MA) and forming-by-
sintering, densification during the forming-by-sintering process
and the mechanical properties of the formed samples Si con-
centration (x) (% by mass) 1.0 1.5 2.0 2.5 3.0 d* (nm) 4,400 3,200
290 240 210 Hv 200 230 570 610 650 .sigma. B (MPa) -- -- 1,220
1,350 1,430 .delta.(%) -- -- 24 15 12 Oxygen 0.445 0.506 0.496
0.431 0.543 (% by mass) Nitrogen 0.202 0.198 0.207 0.210 0.204 (%
by mass) *indicates that the MA powders at each concentration x
have a mean crystal grain diameter of 7 to 20 nm.
Example 6
[0096] According to the invention, a superplasticity-harnessing
forming-by-sintering process was effectively achieved with powders
obtained by mechanical alloying (MA) of a material having a plain
cast iron composition, and a white cast iron composition with a
carbon content of 2.2 to 4.3% by mass. One example is given
below.
[0097] As in Example 5, alloy powders having a cast iron
composition of Fe.sub.94.3C.sub.3.5Cr.sub.2N.sub.0.2 (% by mass)
were prepared by mechanical alloying (MA) of a powder mixture of
powdery elements iron, carbon and chromium with iron nitride having
a nitrogen content of 8.51% by mass. The powders were charged in a
graphite die of 40 mm in inside diameter for a 15-minute hot
pressing in a vacuum and at 700.degree. C. and a pressure of 60
MPa, thereby obtaining a pre-sintered mass of 40 mm in diameter and
5 mm in thickness.
[0098] Then, a given compression load was applied to the
pre-sintered mass at a strain rate of 10.sup.-4/sec. for 30 minutes
in its thickness direction at temperatures of 550.degree. C.,
600.degree. C., 650.degree. C., 700.degree. C. and 750.degree. C.
to obtain a formed-by-sintering product. Set out in Table 4 are the
mean crystal grain diameter d, hardness Hv, tensile strength
.sigma.B, elongation .delta. and values of oxygen and nitrogen upon
analysis of the formed product at different forming temperatures T.
TABLE-US-00004 TABLE 4 Forming-by-sintering temperatures of
mechanically alloyed (MA) powder alloy
Fe.sub.94.3C.sub.3.5Cr.sub.2N.sub.0.2 (% by mass) and mechanical
properties of the formed products T (.degree. C.) 550 600 650 700
750 d (nm) 2,080 2,510 150 230 270 Hv 145 210 810 740 690 .sigma.B
(MPa) -- -- 1,610 1,530 1,380 .delta.(%) -- -- 10 17 23 Oxygen
0.503 0.469 0.457 0.432 0.425 (% by mass) Nitrogen 0.205 0.208
0.201 0.204 0.207 (% by mass)
[0099] From Table 4 and the ordinary-temperature hardness, it has
been found that the sintering process of each sample comes to be
more effective from the temperature of 650.degree. C. or
higher.
Example 7
[0100] As in Example 6, alloy powders of (a)
Ti.sub.88Ta.sub.6Nb.sub.4Fe.sub.2 (% by mass), (b)
Ti.sub.88Nb.sub.6Zr.sub.4Fe.sub.2 (% by mass) and (c)
Ti.sub.88Zr.sub.6Ta.sub.4Fe.sub.2 (% by mass) were prepared by
mechanical alloying (MA) of powder mixture of elementary powders
titanium, tantalum, niobium and zirconium, and iron. The powders
were charged in a graphite die of 40 mm in inside diameter for a
15-minute hot pressing in a vacuum and at 850.degree. C. and a
pressure of 60 MPa, thereby obtaining a pre-sintered mass of 40 mm
in diameter and 5 mm in thickness.
[0101] Then, a given compression load was applied to the
pre-sintered mass at a strain rate of 10.sup.-4/sec. for 15 minutes
in its thickness direction at varying temperatures to find a
superplasticity start temperature T.sub.sp at which the
normal-temperature hardness of the pre-sintered mass started to
rise sharply. The results are reported in Table 5. TABLE-US-00005
TABLE 5 Mechanical properties of formed products obtained from
mechanically alloyed (MA) (a) Ti.sub.88Ta.sub.6Nb.sub.4Fe.sub.2 (%
by mass), (b) Ti.sub.88Nb.sub.6Zr.sub.4Fe.sub.2 (% by mass) and (c)
Ti.sub.88Zr.sub.6Ta.sub.4Fe.sub.2 (% by mass) alloy powders and
softening (superplasticity) start temperatures thereof during the
forming process d* .sigma. B .delta. T.sub.sp Oxygen Sample nm Hv
MPa % .degree. C. % by mass a 150 720 1,700 10 910 0.551 b 190 650
1,610 14 890 0.603 c 240 590 1,540 22 850 0.675 *indicates that the
mean crystal grain diameter in the MA powders was 14 to 20 nm.
[0102] Specifically, Table 5 shows the mean crystal grain diameter
d, hardness Hv, tensile strength .sigma.B, elongation .delta. and
the value of oxygen upon analysis of the formed product obtained by
the application of a given compression load at a temperature
50.degree. C. higher than T.sub.sp and a strain rate of
10.sup.-4/sec. for 30 minutes.
[0103] From Example 5 (Table 3), Example 6 (Table 4) and Example 7
(Table 5), it has been found that with the formed-by-sintering
product comprised of nano-crystals, there is a specific temperature
at which super-plasticity occurs depending on the size,
composition, etc. of crystal grains, and superplasticity induced at
or near that temperature allows crystal grains to be more
effectively bonded together at nano-size levels during the
forming-by-sintering process, contributing to an extremely high
hardness of the bulk material at ordinary temperature.
[0104] Referring now to Example 5 (Table 3), the more effective
sintering process at the Si concentration of more than 2% could be
due to the effect. of Si on noticeable prevention of grain growth
under the compression load.
[0105] From Example 7 (Table 5), it has been found that according
to the invention, even alloys having a high melting temperature,
like Ti alloys, can be refined by MA to powders composed of
nano-size crystal grains, and that bulk materials can be prepared
from such alloys by way of a forming-by-sintering process at
relatively low temperatures.
Example 8
[0106] Alloy powders of mechanically alloyed (MA) (a)
Al.sub.93.5Cu.sub.6Zr.sub.0.5 (% by mass), (b)
Cu.sub.87Al.sub.10Fe.sub.3 (% by mass) and (c)
Ni.sub.48.25Cr.sub.39Fe.sub.10Ti.sub.1.75Al.sub.1 (% by mass)
exhibit super-plasticity at or near 430.degree. C., 750.degree. C.
and 770.degree. C., respectively, and each temperature was about
50.degree. C. lower than the super-plasticity start temperature of
an alloy prepared by melting.
[0107] Chief reasons for that could be that the crystal grains in
the nano-crystal material of the invention are reduced down to
ultra-fine levels, and the metal oxide or the like present between
and/or in nano-crystal grains behaves as an effective crystal grain
growth inhibitor.
[0108] In accordance with the invention, for instance,
hard-to-process materials such as cast iron, high-melting point
materials or titanium alloys that have only limited applications
because of their brittleness, too, can be converted into high hard,
strength and tough materials that are never achievable by the prior
art by way of the preparation of nano-crystal powders by mechanical
alloying (MA) and the application thereto of a forming-by-sintering
process harnessing superplasticity. Thus, the present invention can
successfully provide an unheard-of, high hard, strength and tough
material (a bulk material comprising an aggregate of nano-crystal
grains), as explained with reference to Examples 6 and 7.
Possible Applications of the Invention to the Industry
[0109] The nano-crystal metal bulk materials obtained according to
the inventions are well fit for such applications as given
below.
(1) Bearings
[0110] When the nano-crystal metal bulk material of the invention
is used for the rotary parts of bearings, the amount of that
material used can be much reduced because of its strength
properties, so that not only can the material used be greatly
saved, but it is also possible to achieve great power savings
during bearing operation through a large lowering of centrifugal
force of the moving part of the bearing.
(2) Gears
[0111] Metal materials used for most of gears must meet
contradictory requirements of giving wear resistance to the surface
(tooth face) portion of, and strong toughness to the interior of,
one single gear, resulting in the need of surface hardening
treatment that relies on a sophisticatedly combined technique and
skill comprising carburizing to the tooth face portion, etc. and
hardening and tempering. When the super hard and tough nano-crystal
metal bulk prepared by extrusion according to the invention is used
for this purpose, however, such surface hardening treatment can be
dispensed with.
(3) Tools for Hot Processing and Extrusion
[0112] Hardened and tempered materials often used as
high-temperature cutting tools, for instance, molybdenum based
high-speed steel materials, have the nature of softening rapidly at
a temperature higher than near 400.degree. C. owing to the fact
that the matrix is composed of a tempered martensite phase that
becomes instable upon temperature rises. However, the nano-crystal
metal bulk material of the invention, because its matrix is
composed in itself of a stable phase and so free from rapid
softening at such a temperature region, could be used as more
favorable materials for tools dedicated to hot processing.
[0113] The nano-crystal metal bulk material of the invention, also
because its matrix is relatively thermally stable, could be more
effectively used for extrusion tools exposed to vigorous thermal
changes during use.
(4) Medical Tools or the Like
[0114] Unlike nickel-containing chromium-nickel based austenite
stainless steels, titanium based bulk materials or high-nitrogen
chromium-manganese based austenite steels cause no inflammation to
the skin or skin diseases, and so they are potentially promising as
surgeon's knives, medical low-temperature tools, sharp-edged tools
like general-purpose knives, tools so on.
* * * * *