Note: Descriptions are shown in the official language in which they were submitted.
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[Description]
[Title of Invention]
Metal member and manufacturing method thereof
[Technical Field]
[0001]
The present invention is related to metal member using metal
powder as material and manufacturing method thereof.
[Background Art]
[0002]
Metal powder injection molding (or metal injection molding)
is a method of manufacturing a metal powder molded article by
melting a molding material, which results by mixing fine metal
powder and organic binder (for example, a mixture of a plurality
of types of resins; hereinafter called "binder") to perform
injection molding thereof and then performing degreasing and
incinerating thereof.
[0003]
The fine metal powder used in metal powder injection molding
is formed in a fine powder production process by a spray method,
for example. There were cases where production of fine powder for
metal powder injection molding is difficult because a "pouring
blockage", in which a nozzle is blocked in a process of producing
fine powder, occurs when forming a nickel based alloy including
titan with a high strength at high temperatures by the spray
method. Patent literature 1 discloses an invention of setting a
concentration of titan in the nickel based alloy equal to or less
than 0.1 mass % and an invention of performing an adjustment to
decrease a concentration of niobium in a case where the
concentration of titan is more than 1 mass %, in order to prevent
this "pouring blockage".
[Citation List]
[Patent Literature]
[0004]
[Patent Literature 1] Japanese patent publication No. 2005-
350710 A
[Summary of the Invention]
[0005]
A metal manufactured by metal powder injection molding has
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lower strength at high temperatures compared to a metal
manufactured by casting or forging and could not be applied to
members needing strength at high temperatures.
[0006]
In view of the above circumstance, an objective of the
present invention is to manufacture a metal member with high
strength at high temperatures by metal powder injection molding.
[0007]
Other objectives may be understood by following descriptions
and explanation of embodiments.
[0008]
To achieve the above objectives, a metal member related to a
first aspect of the present invention is provided with crystal
grains of a metal and a granular reinforcing substance formed at
boundaries of the crystal grains. The reinforcing substance
includes grains of a shape with a grain area equivalent grain size
larger than 1/100 of a grain area equivalent grain size of the
crystal grains.
[0009]
The above mentioned reinforcing substance preferably
includes grains with a grain area equivalent grain size smaller
than 1/5 of the grain area equivalent grain size of the crystal
grains.
[0010]
The above mentioned reinforcing substance preferably
includes grain of a shape so that a value of a length, in a first
direction in which a length thereof is longest, divided by a
length of a longest part in a direction orthogonal to the first
direction is smaller than 5.
[0011]
It is preferable that 95% or more of the above mentioned
reinforcing substance is formed so that a value of a length, in a
first direction in which a length thereof is longest, divided by a
length of a longest part in a direction orthogonal to the first
direction is smaller than 5.
[0012]
It is preferable that the above mentioned reinforcing
substance includes a plurality of types of substances and is
formed to surround the crystal grains.
[0013]
The above mentioned reinforcing substance preferably
includes any of carbon, nitrogen or oxygen.
[0014]
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A manufacturing method of metal member by injection molding
related to a second target of the present invention includes a
mixing step of mixing metal powder, reinforcing powder and binder,
an injection molding step of forming an injection molded body by
injection molding of mixed powders, a degreasing step of removing
the binder from the injection molded body and forming an
intermediate molded body, and an incinerating step of incinerating
the intermediate molded body. The reinforcing powder includes a
reinforcing substance. A maximal grain size of the reinforcing
powder is larger than 1/100 of a maximal grain size of the metal
powder. The metal powder and the reinforcing powder both are
mixed in a powder state in the mixing step.
[0015]
The maximal grain size of the above mentioned reinforcing
powder is preferably smaller than 1/5 of a maximal grain size of
the metal powder.
[0016]
It is preferable that a step of determining a carbon
concentration of the metal powder in accordance with a mass of the
reinforcing powder to be mixed is further included.
[0017]
According to the present invention, a metal member with a
high strength at high temperatures can be manufactured by metal
powder injection molding.
[Brief Description of Drawings]
[0018]
[Fig. 1] Fig. 1 is a flowchart showing processes of a
manufacturing method related to the present invention.
[Fig. 2] Fig. 2 is structure photography by backscattered
electron imaging in connection with a cross sectional surface of a
metal member related to the present invention.
[Fig. 3] Fig. 3 is a mapping image of titan concentration by
Electron Probe Micro Analyzer (EPMA) analysis in connection with a
cross sectional surface of the metal member related to the present
invention.
[Fig. 4] Fig. 4 is a mapping image of carbon concentration
by EPMA analysis in connection with a cross sectional surface of
the metal member related to the present invention.
[Fig. 5] Fig. 5 is a schematic drawing showing a structure
of the metal member related to the present invention.
[Fig. 6] Fig. 6 is a graph showing tensile strengths of the
metal member related to the present invention and a metal member
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manufactured by conventional injection molding.
[Fig. 7] Fig. 7 is a graph showing elongations of the metal
member related to the present invention and the metal member
manufactured by conventional injection molding.
[Fig. 8] Fig. 8 is structure photography by backscattered
electron imaging in connection with a cross sectional surface of a
metal member manufactured by a conventional injection molding.
[Fig. 9] Fig. 9 is a mapping image of titan concentration by
EPMA analysis in connection with a cross sectional surface of the
metal member manufactured by a conventional injection molding.
[Fig. 10] Fig. 10 is a mapping image of carbon concentration
by EPMA analysis in connection with a cross sectional surface of
the metal member manufactured by a conventional injection molding.
[Fig. 11] Fig. 11 is a schematic drawing showing a structure
of the metal member manufactured by a conventional injection
molding.
[Fig. 12] Fig. 12 is structure photography by secondary
electron imaging in connection with a cross sectional surface of a
metal member manufactured by casting.
[Fig. 13] Fig. 13 is a mapping image of titan concentration
by EPMA analysis in connection with a cross sectional surface of
the metal member manufactured by casting.
[Fig. 14] Fig. 14 is a mapping image of carbon concentration
by EPMA analysis in connection with a cross sectional surface of
the metal member manufactured by casting.
[Fig. 15] Fig. 15 is a schematic drawing showing a structure
of the metal member manufactured by casting.
[Fig. 16] Fig. 16 is a graph showing tensile strengths of
the metal members with different carbon concentrations
manufactured by a conventional injection molding.
[Fig. 17] Fig. 17 is a graph showing elongations of the
metal members with different carbon concentrations manufactured by
a conventional injection molding.
[Description of Embodiments]
[0019]
(Strength of metal)
Causes of lower strength at high temperatures of metal
manufactured by metal powder injection molding compared to metal
manufactured by casting, forging or the like will be explained.
[0020]
Although an influence of crystal grain boundaries on a
tensile strength of a metal is usually limited in a temperature
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range near room temperature, the higher the temperature is, the
stronger the influence of the crystal grain boundaries on the
tensile strength of the metal becomes. In order to improve metal
strength, in general, a metal is manufactured by including
reinforcing substance including a substance such as carbon, oxygen,
nitrogen or the like. This reinforcing substance also reinforces
crystal grains boundaries.
[0021]
In metal powder injection molding, grain surfaces are molten
and grains are bonded to each other to be molded as a member.
That is, in metal powder injection molding, grains are not
entirely molten. For this reason, a metal manufactured by metal
powder injection molding has weaker strength at boundaries of
crystal grains, compared to metals manufactured by casting,
forging or the like. The applicant found out that a cause thereof
is that, not only voids are likely to enter at boundaries of
crystal grains, but substance reinforcing boundaries of crystal
grains is held inside metal grains.
[0022]
Here, a metal has been manufactured by metal powder
injection molding, by use of reinforcing substance including metal
powder of nickel based alloy including titanium carbide. As shown
in Figs. 8 to 10, it is understood that titanium carbide of a
reinforcing substance is distributed throughout a cross sectional
surface of the metal. That is, the reinforcing substance is held
inside metal grains and is not precipitated from inside metal
grains to boundaries of crystal grains. By showing schematically,
the reinforcing substance 120 is distributed inside crystal grains
110, however is not precipitated at boundaries of crystal grains
110, as shown in Fig. 11. In other words, reinforcing influence
by the reinforcing substance 120 is small at boundaries of crystal
grains 110. For this reason, the crystal grains themselves are
hardly divided due to reinforcing substance and strength of metal
incinerated bodies is high at a low temperature environment. On
the other hand, since the reinforcing substance is not
precipitated at boundaries of crystal grains, the crystal grains
are easily divided at boundaries and strength of the metal member
at high temperatures is low.
[0023]
For comparison, a metal has been manufactured by casting, by
use of reinforcing substance including metal powder of nickel
based alloy including titanium carbide. As shown in Figs. 12 to
14, titanium carbide of the reinforcing substance is precipitated
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at boundaries of crystal grains. That is, it is understood that
since grains are entirely molten in casting, titanium carbide
precipitates from inside crystal grains to boundaries of crystal
grains. By schematically showing, as shown in Fig. 15, since
grains are entirely molten, the reinforcing substance 220 inside
the crystal grains 210 precipitates at boundaries of crystal
grains 210 as reinforcing substance 230. For this reason, there
is a few amount of reinforcing substance 220 inside crystal grains
210. On the other hand, there is a large amount of reinforcing
substance 230 at boundaries of crystal grains 210. As a result,
the strength of metal members manufactured by casting or the like
is high at a high temperature environment. On the other hand,
compared to metal members manufactured by metal powder injection
molding, the strength at a low temperature environment is low.
[0024]
In addition, carbon, nitrogen, oxygens and the like in
reinforcing substance are also brittle materials. For this reason,
the higher the concentration in the reinforcing substance is, the
smaller the elongation of metal member becomes. This is because
reinforcing substance prevents transitions inside metal crystals.
A metal member A has been manufactured by metal powder injection
molding by using metal powder of nickel based alloy with a carbon
concentration of 0.02 mass % with respect to the entire metal
powder.
Similarly, a metal member B has been manufactured by
using metal powder of nickel based alloy with a carbon
concentration of 0.06 mass %. The carbon concentration in the
metal member A after manufacturing was 0.06 mass % with respect to
the entire metal member A. On the other hand, the carbon
concentration in the metal member B was 0.12 mass %.
[0025]
As shown in Fig. 16, the tensile strength of the metal
member A is approximatively 470MPa. On the other hand, the
tensile strength of the metal member B is approximatively 550MPa:
the metal member B with a higher carbon concentration has a higher
tensile strength. In addition, the elongation of the metal member
A is, as shown in Fig. 17, approximatively 5%. On the other hand,
the elongation of the metal member B is approximatively 3%: the
metal member A with a lower carbon concentration has a higher
elongation. That is, in general, the higher the carbon
concentration is, the higher the tensile strength becomes and the
smaller the elongation becomes.
[0026]
From the above, a high strength can be kept at high
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temperature environment by arranging reinforcing substance at
boundaries of crystal grains when manufacturing metal members by
metal powder injection molding. In addition, the elongation of
metal members can be prevented to become smaller by keeping a
concentration of reinforcing substance equal to or lower than a
certain value.
[0027]
(Manufacturing method of metal member)
Based on the above characteristics, a manufacturing method 1
of forming a metal member with a high strength at a high
temperature environment by metal powder injection molding will be
explained. In particular, the manufacturing method 1 manufactures
a metal member in which reinforce substance is arranged at
boundaries of crystal grains even by using metal powder injection
molding.
[0028]
At first, as shown in Fig. 1, in the step S10, a powder
manufacturing step of manufacturing metal powder and reinforcing
powder is performed. The method of manufacturing the metal powder
includes a method of melting the metal once and then manufacturing,
a method of mechanically pulverizing and then manufacturing, a
method of chemically manufacturing and the like, and any method
can be chosen. For example, as a method of melting once and then
manufacturing, there is an atomization method. The atomization
method is a method of manufacturing a powder by blowing a gas to
the molten metal which flows out. A maximal grain size of this
metal powder is, for example, 20 Tim (micrometer). This metal
powder is, for example, a fine powder classified by openings of
sieve net compliant to standard of JIS Z8801 or ASTM Ell. In
order to verify maximal grain size, grain size distribution may be
measured by a laser diffraction-scattering method compliant to JIS
Z8825-1 standard. In addition, fine powder classified by
airstream classification may be used.
[0029]
Here, by including a certain amount of reinforcing substance
including carbon or the like to the molten metal, the strength of
the metal member to be manufactured is ensured. For example, 0.12
mass % of carbon is added related to the entire metal to be molten.
Here, in order to mix reinforcing powder and then mold, it is
preferable to determine carbon concentration in metal powder in
accordance with mass of reinforcing powder to mix. In other words,
mass of carbon to add is adjusted in accordance with a mass of the
reinforcing powder to mix. In particular, it is preferable that
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the carbon to add is of an amount larger than 5 mass % and smaller
than 90 mass % related to carbon concentration of the metal member
to manufacture.
In particular, in a case where carbon
concentration of the metal member to manufacture is 0.2 mass %,
then a mass of the carbon to add is preferably larger than 0.01
mass % and smaller than 0.18 mass % related to the entire metal to
melt. For example, in a case where 6 parts by mass of reinforcing
powder is added to 1000 parts by mass of metal powder, an amount
of carbon to add is 0.01 mass % related to the entire metal to
melt. It should be noted that any metal such as nickel based
alloy, cobalt based alloy, titanium alloy, tungsten alloy,
stainless steel, tool steel, aluminum alloy, copper alloy and the
like can be used as the metal.
[0030]
In addition, the reinforcing powder, which includes
reinforcing substance including a plurality of type of substances
such as carbon, nitrogen and the like, is similarly manufactured
as well.
In particular, the reinforcing powder is titanium
carbide powder, silicon carbide powder, titanium nitride powder,
silicon dioxide powder or the like. A maximal grain size of the
reinforcing powder is preferably smaller than 1/5 of a maximal
grain size of the metal powder. Further, the maximal grain size
of the reinforcing powder is preferably smaller than 1/7 of the
maximal grain size of the metal powder. In addition, the maximal
grain size of the reinforcing powder is preferably larger than
1/100 of the maximal grain size of the metal powder. For example,
in a case where the maximal grain size of the metal powder is 20
p.m, the maximal grain size of the reinforcing metal is 3 pm.
Reinforcing powder is, for example, fine powder classified by a
sieve net. In order to verify the maximal grain size, grain size
distribution may be measured by the laser diffraction-scattering
method compliant to JIS Z8825-1 standard. In addition, fine
powder which results of reinforcing powder classified by airstream
classification may be used.
[0031]
Next, in the step S20, a mixing step of mixing the metal
powder, the reinforcing powder and a binder is performed. A
mixing drum or the like is used to mix the metal powder and the
reinforcing powder, both in powder state when mixing. An amount
of the reinforcing powder to mix is preferably larger than 1 part
of mass and smaller than 50 parts of mass related to 1000 parts of
mass of the metal powder. Additives may be mixed as needed. As
the binder, for example, a mixture of one or more types in each of
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organic compounds, such as paraffin wax, carnauba wax, fatty acid
ester and the like, and thermoplastic resins with relatively low
melting point, such as polyethylene (PE), polypropylene (PP),
ethylene vinyl acetate (EVA) copolymer and the like, can be used.
The metal powder and the binder may be mixed when manufacturing
the powder in the step S10. In particular, the binder is kneaded
in a molten state together with the molten metal to be granulated
into metal powder which is then used.
[0032]
In the step S30, an injection molding step of molding an
injection molded body by injection molding of the mixed powder.
In particular, the mixed powder is provided to an injection
molding apparatus. The provided powder is heated and molten, then
pumped into a metal mold to be injection molded. Later, the metal
mold is cooled down and opened to take the injection molded body
therefrom.
[0033]
In the step S40, a degreasing step of degreasing the
injection molded body that has been taken out and removing the
binder from the injection molded body is performed. For example,
the injection molded body is heated to 500 C to remove the binder
therefrom. As a result, an intermediate molded body, from which
the binder is removed, is formed. In addition to this, various
methods can be used, such as degreasing by irradiating a light
beam, degreasing by immersing in a solvent such as water or
organic solvent, or the like, in accordance with characteristics
of the binder.
[0034]
In the step S50, an incinerating step of incinerating the
intermediate molded body from which the binder has been removed to
form an incinerated body is performed. In particular, bonding of
metal powder is grown by heating in vacuum or inert gas.
Incineration temperature is, for example, 1200 C or more and
1300 C or less.
[0035]
In the step S60, a pressurizing step of pressurizing the
incinerated body to remove voids in the incinerated body is
performed. By this pressurization, a metal member with an
incinerated density of 90% or more and 100% or less is molded.
The incinerated density may be 95% or more. In
addition, the
incinerated density may be 97% or less.
[0036]
As described above, by using a powder in which the metal
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powder is added with a reinforcing powder, a metal member with a
reinforcing substance arranged at boundaries of crystal grains can
be manufactured.
[0037]
(Example)
A nickel based alloy member has been manufactured by the
manufacturing method 1. In
particular, a nickel based alloy
powder has been prepared. This nickel based alloy powder has a
maximal grain size of 20um and a carbon concentration of 0.01
mass %. This carbon concentration is a value in accordance with
an amount of reinforcing powder to be mixed, because the carbon
concentration of the metal member after manufacturing is
controlled to 0.2 mass %. In addition, a titanium carbide powder
has been prepared as reinforcing powder. The maximal grain size
of this titanium carbide powder is 3p.m. An amount of the titanium
carbide is 0.66 mass % related to the nickel based alloy powder.
[0038]
As a result of using above powder, carbon concentration of
manufactured metal member has been 0.22 mass %. As shown in Figs.
2 to 4, in the manufactured metal member, the titanium carbide of
the reinforcing powder is formed in granular state so as to
surround crystal grains of the nickel based alloy. This is a
characteristic obtained by mixing reinforcing powder to a powder
for injection molding. Actually, as shown in Figs. 8 to 10, no
reinforcing substance is precipitated at boundaries of crystal
grains of an injection molded metal member in general.
[0039]
As shown in Figs 2 to 4, it is understood that the titanium
carbide precipitated at boundaries of those crystal grains is
greater than the maximal grain size of the reinforcing powder. It
is understood by this as well that the titanium carbide at
boundaries of crystal grains results of the mixed reinforcing
powder which has melted and precipitated. That is, the grain area
equivalent grain size of the reinforcing substance precipitated at
boundaries of crystal grains is larger than 1/100 of the grain
area equivalent grain size of crystal grains. In addition, in a
case where the maximal grain size of the reinforcing powder is
smaller than 1/5 of the maximal grain size of the metal powder,
the reinforcing powder includes a one with a size smaller than 1/5
of the grain area equivalent grain size of the crystal grains. In
a case where the maximal grain size of the reinforcing powder is
smaller than 1/8 of the maximal grain size of the metal powder,
the reinforcing powder includes a one with a size smaller than 1/8
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of the grain area equivalent grain size of the crystal grains. In
addition, most of titanium carbide have a shape so that a value of
a length, in a direction in which the length thereof is the
longest, divided by a length of a longest part in a direction
orthogonal to this direction, is smaller than 5. In particular,
90% or more of granular titanium carbide has a shape in which this
value is smaller than 5. Further, this value may be smaller than
3.
[0040]
On the other hand, in a metal member manufactured by casting,
as shown in Fig. 15, reinforcing substance 230 is precipitated
along boundaries of crystal grains 10. This is because, since a
metal completely melts in casting, reinforcing substance inside
crystal grains 10 precipitates at boundaries of crystal grains.
As a result, the reinforcing substance 230 precipitating at
boundaries of the crystal grains 10 precipitates along the
boundaries.
In addition, in the metal member manufactured by
casting, most of the reinforcing substance 230 precipitated at
boundaries have a shape so that a value of a length in a direction
in which the length thereof is the longest, divided by a length of
a longest part in a direction orthogonal to this direction, is
greater than 5.
[0041]
The manufacturing method 1 manufactures by injection molding.
For this reason, it is understood that the entire grain is not
molten and that titanium carbide of reinforcing substance is
distributed inside the crystal grains too. By schematically
showing, as shown in Fig. 5, since reinforcing powder is mixed,
the reinforcing substance 30 is formed in granular state so as to
surround crystal grains 10. In addition, the reinforcing
substance 20 is included inside crystal grains 10 too. On the
other hand, as shown in Figs. 12 to 14, reinforcing substance is
hardly verified inside crystal grains of metal members
manufactured by casting.
[0042]
As described above, metal members manufactured by the
manufacturing method 1 has a structure different from ones
manufactured by conventional metal powder injection molding,
casting or the like.
[0043]
Next, tensile strengths and elongations will be compared
between a metal member manufactured by the manufacturing method 1
and a metal member manufactured by a general metal powder
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injection molding. For comparison, a metal member C has been
manufactured by use of metal powder of nickel based alloy with a
carbon concentration of 0.12 mass %, by metal powder injection
molding. A maximal grain size of this powder is 20pm. The carbon
concentration of the manufactured metal member was 0.20 mass %.
That is, the carbon concentration is of a same level than the one
of the metal member manufactured by manufacturing method 1.
[0044]
As shown in Fig. 6, the tensile strength of this metal
member C was approximatively 585MPa. On the other hand, the
tensile strength of the metal member manufactured by the
manufacturing method 1 was approximatively 620MPa, which is a
higher strength compared to the metal member C. Further, by
comparing their elongations, while the one of the metal member C
is approximatively 2%, the one of the metal member by the
manufacturing method 1 is approximatively 6% which is larger.
That is, it is understood that the tensile strength and the
elongation of a metal member manufactured by the manufacturing
method 1 are higher than ones of metal member having a carbon
concentration of a same level.
[0045]
Further, as shown in Fig. 17, the elongation of the metal
member A, of which the carbon concentration after manufacturing is
0.06%, is approximatively 5%. The elongation of the metal member
by the manufacturing method 1 is approximatively 6%: although the
carbon concentration thereof after manufacturing is higher, this
is larger than the elongation of the metal member A. That is, the
metal member manufactured by the manufacturing method 1 has both
larger tensile strength and larger elongation. Thus, the metal
member manufactured by the manufacturing method 1 has an
advantageous effect on both tensile strength and elongation
compared to a metal member manufactured by conventional metal
powder injection molding.
[0046]
The present invention has been explained above by use of
embodiments. However, various modifications can be made to the
embodiments. The above described embodiments can be arbitrary
combined unless technical contradiction occurs. Such
modifications and combinations are included in the present
invention.
[0047]
The present application claims priority based on Japanese
patent application No. 2017-085858 filed on April 25, 2017 and the
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entire disclosure thereof is incorporated by reference herein.
