Koji Kakehi - Academia.edu (original) (raw)

Papers by Koji Kakehi

Research paper thumbnail of The role of yttrium micro-alloying on microstructure evolution and high-temperature mechanical properties of additively manufactured Inconel 718

Research paper thumbnail of Effect of test-piece-preparation method on mechanical properties of titanium aluminide alloy additively manufactured by electron beam melting

The Proceedings of Mechanical Engineering Congress, Japan, 2020

Research paper thumbnail of The Effects of Yttrium Addition on Ni-Based Superalloy Fabricated by Hot Isostatic Pressing

Research paper thumbnail of Effects of yttrium and silicon contents in Hastelloy-X built by selective laser melting process

Journal of Alloys and Compounds, 2022

Research paper thumbnail of Effect of build direction on microstructure and mechanical properties of TiAl4822 alloy additively manufactured by electron beam melting

Transactions of the JSME (in Japanese), 2021

Research paper thumbnail of Improvement in Creep Properties of Ni Based Superalloy Fabricated by Selective Laser Melting by Yttrium Addition

The Proceedings of Mechanical Engineering Congress, Japan, 2020

Research paper thumbnail of Effect of Carbide Inoculants Additions in IN718 Fabricated by Selective Laser Melting Process

Research paper thumbnail of Hierarchical microstructure strengthening in a single crystal high entropy superalloy

Scientific Reports, 2020

A hierarchical microstructure strengthened high entropy superalloy (HESA) with superior cost spec... more A hierarchical microstructure strengthened high entropy superalloy (HESA) with superior cost specific yield strength from room temperature up to 1,023 K is presented. By phase transformation pathway through metastability, HESA possesses a hierarchical microstructure containing a dispersion of nano size disordered FCC particles inside ordered L12 precipitates that are within the FCC matrix. The average tensile yield strength of HESA from room temperature to 1,023 K could be 120 MPa higher than that of advanced single crystal superalloy, while HESA could still exhibit an elongation greater than 20%. Furthermore, the cost specific yield strength of HESA can be 8 times that of some superalloys. A template for lighter, stronger, cheaper, and more ductile high temperature alloy is proposed.

Research paper thumbnail of Effects of CoAl2O4 inoculants on microstructure and mechanical properties of IN718 processed by selective laser melting

Additive Manufacturing, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Effect of yttrium addition on creep properties of a Ni-base superalloy built up by selective laser melting

Research paper thumbnail of 20409 Anisotropic creep properties of aluminized Ni-base single crystal superalloy

The Proceedings of Conference of Kanto Branch, 2013

A study on creep behavior of an aluminircd Ni-based single-crystal superalloy was carried out at ... more A study on creep behavior of an aluminircd Ni-based single-crystal superalloy was carried out at intermediate and high ' ' temperatures. In general, the creep rupture lives of aluminizeq specimens were sherter than those of bare specimens, It was also found that the specimens with a (1OO) side-surface showed longer creep rupture life than the specimens with a (110) side-surface. This means that anisotropy of the seconciary orientation, wriich is normal to the primary orientation, occurred. The anisotropic creep behavior of the aluminized specimen was induced by a diffbrent arrangement of {111}<101> sHp systems between the two side-surfaces.

Research paper thumbnail of Influence of Plastic Anisotropy on High Temperature Strength of Single Crystals of a Nickel-Base Superalloy

Journal of the Japan Institute of Metals, 1999

Research paper thumbnail of Effects of build direction and heat treatment on creep properties of Ni-base superalloy built up by additive manufacturing

Research paper thumbnail of High Temperature Properties of Advanced Directionally-Solidified High Entropy Superalloys

Superalloys 2016, 2016

High-Entropy-Superalloys (HESA) with good cost-performance has been proposed. In present work, th... more High-Entropy-Superalloys (HESA) with good cost-performance has been proposed. In present work, the high temperature phase stability, oxidation, hot corrosion and mechanical properties of HESA alloys were studied. The microstructure of HESA is composed of stable FCC γ matrix and L1 2 precipitates, and both and phases are highly alloyed. This / microstructure can remain stable after long term exposure at intermediate to high temperatures. With respect to surface stability, HESAs show high Al and Cr activities to form either protective Al 2 O 3 or Cr 2 O 3 rapidly. With minor additions of refractory elements, the high temperature hardness of HESA can be higher than that of conventional superalloy. HESAs show comparable tensile strength and creep rupture properties comparing to that of commercial superalloys. Furthermore, their densities are below 8.0 g.cm-3 , and the cost of raw materials can be 20 % cheaper than that of CM247LC. Therefore, the potential of HESAs for high temperature applications are revealed in present article.

Research paper thumbnail of Influence of Secondary Precipitates on Strength of Single Crystals of Ni-Based Superalloys

MORRIS:INTERMETALLICS O-BK, 2006

Research paper thumbnail of Magnesium Foam Produced from Bulk AZ31 Magnesium Alloy Sheets

Materials Science Forum, 2005

Using commercial AZ31 magnesium alloy sheets, we produced a foamable preform sheet containing tit... more Using commercial AZ31 magnesium alloy sheets, we produced a foamable preform sheet containing titanium hydride (TiH2) powder through diffusion-bonding and hot-rolling of four cycles. Heating the preform sheets in Ar atmosphere, we obtained closed-cell magnesium alloy foams with various porosities. The foamed specimen at 883 K showed the maximum porosities of 77%.

Research paper thumbnail of Collaborative Research on Thermo-Mechanical and Isothermal Low-Cycle Fatigue Strength of Ni-Base Superalloys and Protective Coatings at Elevated Temperatures in The Society of Materials Science, Japan (JSMS)

Thermomechanical Fatigue Behavior of Materials: 4th Volume

Research paper thumbnail of Influence of heat treatment on anisotropic creep behavior of aluminide coating on a Ni-base single crystal superalloy

Materials & Design (1980-2015), 2013

ABSTRACT The influence of heat treatment on creep behavior of aluminide coating on a Ni-base sing... more ABSTRACT The influence of heat treatment on creep behavior of aluminide coating on a Ni-base single crystal superalloy with different surface orientations was examined. The specimens were coated by pack aluminizing treatment at 1000 °C for 5 h under argon environment. The coated specimens were then tested by the tensile creep test at a temperature of 900 °C and a stress of 320 MPa. To determine the effect of aluminide coating, the bare specimens were also tested. The aluminizing treatment decreased the creep strength of Ni-base single crystal superalloy. The solution heat treatment procedures had a great impact on the creep behavior of Ni-base single crystal superalloy. The combination of solution treatment and subsequent double aging treatment was effective to improve the creep strength of Ni-base single crystal superalloy because of more regular the shape of γ′ precipitates and more homogeneous distribution of γ′ precipitates. In addition, the {1 0 0} specimens showed a better creep lives than those {1 1 0} specimens both in aluminized specimens and bare specimens. The anisotropic creep behavior was primarily induced by the different arrangement of {1 1 1} 〈1 0 1〉 slip systems between the two surface orientations of the specimens. The difference in creep rupture lives between {1 0 0} and {1 1 0} side-surface specimens was more pronounced in the specimens STA than in the specimens A because of homogenization of the γ/γ′ microstructure promoted the deformation by {1 1 1} 〈1 0 1〉 slip system which leads to anisotropy of creep behavior. Moreover, the change in microstructures was also considered as one of factors for the decrease of creep life. Besides, the formation of TCP phase, the depth of TCP phase penetration and the gradient of hardness values in the coating to the substrate regions would be additional factors to clarify the anisotropic creep behavior in aluminized Ni-base single crystal superalloy.

Research paper thumbnail of Effects of Re content and crystallographic orientation on creep behavior of aluminized Ni-base single crystal superalloys

Materials & Design, 2013

ABSTRACT Effects of Re content and crystallographic orientation on creep behavior of aluminized N... more ABSTRACT Effects of Re content and crystallographic orientation on creep behavior of aluminized Ni-base single crystal superalloys have been investigated in the present study. The addition of Re seemed to be effective for the creep strength improvement of Ni-base single crystal superalloys. The creep strength was significantly decreased in aluminized specimens due to the change in microstructure under coating layer by the formation of the interdiffusion zone (IDZ) and substrate diffusion zone (SDZ). The specimens with {100} side-surface showed longer creep rupture lives than the specimens with {110} side-surface which means that the anisotropic creep behavior took place. The anisotropic creep behavior was more evident in aluminized CM186LC than in aluminized PWA 1480. This anisotropic creep behavior was mainly induced by the discrepancy of fracture modes due to the different arrangement of slip systems, the geometry as well as the depth penetration of topologically close-packed (TCP) phases between the two side-surface orientations.

Research paper thumbnail of Influence of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations

Materials & Design (1980-2015), 2014

The effect of thermal exposure on the creep properties of an aluminized Ni-based single crystal s... more The effect of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations has been studied in the present study. The specimens were coated by a pack aluminizing process conducted at 1000°C for 5 h under an argon atmosphere. Long-term exposure was performed at 1100°C for 500 h prior to the creep test. The creep properties were found to deteriorate after the long-term exposure as a result of the coarsening of c 0 precipitates accompanied by the formation of a secondary reaction zone which is known to degrade the strength of aluminide coating on a Ni-based single crystal superalloy. The formation of a topologically close-packed phase is one of the degradation factors that are responsible for the reduction of the creep strength of the aluminide coating on a Ni-base single crystal superalloy both with and without long-term exposure. The anisotropic creep properties between the two side-surfaces are due to the different arrangements of f1 1 1gh1 0 1i slip systems.

Research paper thumbnail of The role of yttrium micro-alloying on microstructure evolution and high-temperature mechanical properties of additively manufactured Inconel 718

Research paper thumbnail of Effect of test-piece-preparation method on mechanical properties of titanium aluminide alloy additively manufactured by electron beam melting

The Proceedings of Mechanical Engineering Congress, Japan, 2020

Research paper thumbnail of The Effects of Yttrium Addition on Ni-Based Superalloy Fabricated by Hot Isostatic Pressing

Research paper thumbnail of Effects of yttrium and silicon contents in Hastelloy-X built by selective laser melting process

Journal of Alloys and Compounds, 2022

Research paper thumbnail of Effect of build direction on microstructure and mechanical properties of TiAl4822 alloy additively manufactured by electron beam melting

Transactions of the JSME (in Japanese), 2021

Research paper thumbnail of Improvement in Creep Properties of Ni Based Superalloy Fabricated by Selective Laser Melting by Yttrium Addition

The Proceedings of Mechanical Engineering Congress, Japan, 2020

Research paper thumbnail of Effect of Carbide Inoculants Additions in IN718 Fabricated by Selective Laser Melting Process

Research paper thumbnail of Hierarchical microstructure strengthening in a single crystal high entropy superalloy

Scientific Reports, 2020

A hierarchical microstructure strengthened high entropy superalloy (HESA) with superior cost spec... more A hierarchical microstructure strengthened high entropy superalloy (HESA) with superior cost specific yield strength from room temperature up to 1,023 K is presented. By phase transformation pathway through metastability, HESA possesses a hierarchical microstructure containing a dispersion of nano size disordered FCC particles inside ordered L12 precipitates that are within the FCC matrix. The average tensile yield strength of HESA from room temperature to 1,023 K could be 120 MPa higher than that of advanced single crystal superalloy, while HESA could still exhibit an elongation greater than 20%. Furthermore, the cost specific yield strength of HESA can be 8 times that of some superalloys. A template for lighter, stronger, cheaper, and more ductile high temperature alloy is proposed.

Research paper thumbnail of Effects of CoAl2O4 inoculants on microstructure and mechanical properties of IN718 processed by selective laser melting

Additive Manufacturing, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Effect of yttrium addition on creep properties of a Ni-base superalloy built up by selective laser melting

Research paper thumbnail of 20409 Anisotropic creep properties of aluminized Ni-base single crystal superalloy

The Proceedings of Conference of Kanto Branch, 2013

A study on creep behavior of an aluminircd Ni-based single-crystal superalloy was carried out at ... more A study on creep behavior of an aluminircd Ni-based single-crystal superalloy was carried out at intermediate and high ' ' temperatures. In general, the creep rupture lives of aluminizeq specimens were sherter than those of bare specimens, It was also found that the specimens with a (1OO) side-surface showed longer creep rupture life than the specimens with a (110) side-surface. This means that anisotropy of the seconciary orientation, wriich is normal to the primary orientation, occurred. The anisotropic creep behavior of the aluminized specimen was induced by a diffbrent arrangement of {111}<101> sHp systems between the two side-surfaces.

Research paper thumbnail of Influence of Plastic Anisotropy on High Temperature Strength of Single Crystals of a Nickel-Base Superalloy

Journal of the Japan Institute of Metals, 1999

Research paper thumbnail of Effects of build direction and heat treatment on creep properties of Ni-base superalloy built up by additive manufacturing

Research paper thumbnail of High Temperature Properties of Advanced Directionally-Solidified High Entropy Superalloys

Superalloys 2016, 2016

High-Entropy-Superalloys (HESA) with good cost-performance has been proposed. In present work, th... more High-Entropy-Superalloys (HESA) with good cost-performance has been proposed. In present work, the high temperature phase stability, oxidation, hot corrosion and mechanical properties of HESA alloys were studied. The microstructure of HESA is composed of stable FCC γ matrix and L1 2 precipitates, and both and phases are highly alloyed. This / microstructure can remain stable after long term exposure at intermediate to high temperatures. With respect to surface stability, HESAs show high Al and Cr activities to form either protective Al 2 O 3 or Cr 2 O 3 rapidly. With minor additions of refractory elements, the high temperature hardness of HESA can be higher than that of conventional superalloy. HESAs show comparable tensile strength and creep rupture properties comparing to that of commercial superalloys. Furthermore, their densities are below 8.0 g.cm-3 , and the cost of raw materials can be 20 % cheaper than that of CM247LC. Therefore, the potential of HESAs for high temperature applications are revealed in present article.

Research paper thumbnail of Influence of Secondary Precipitates on Strength of Single Crystals of Ni-Based Superalloys

MORRIS:INTERMETALLICS O-BK, 2006

Research paper thumbnail of Magnesium Foam Produced from Bulk AZ31 Magnesium Alloy Sheets

Materials Science Forum, 2005

Using commercial AZ31 magnesium alloy sheets, we produced a foamable preform sheet containing tit... more Using commercial AZ31 magnesium alloy sheets, we produced a foamable preform sheet containing titanium hydride (TiH2) powder through diffusion-bonding and hot-rolling of four cycles. Heating the preform sheets in Ar atmosphere, we obtained closed-cell magnesium alloy foams with various porosities. The foamed specimen at 883 K showed the maximum porosities of 77%.

Research paper thumbnail of Collaborative Research on Thermo-Mechanical and Isothermal Low-Cycle Fatigue Strength of Ni-Base Superalloys and Protective Coatings at Elevated Temperatures in The Society of Materials Science, Japan (JSMS)

Thermomechanical Fatigue Behavior of Materials: 4th Volume

Research paper thumbnail of Influence of heat treatment on anisotropic creep behavior of aluminide coating on a Ni-base single crystal superalloy

Materials & Design (1980-2015), 2013

ABSTRACT The influence of heat treatment on creep behavior of aluminide coating on a Ni-base sing... more ABSTRACT The influence of heat treatment on creep behavior of aluminide coating on a Ni-base single crystal superalloy with different surface orientations was examined. The specimens were coated by pack aluminizing treatment at 1000 °C for 5 h under argon environment. The coated specimens were then tested by the tensile creep test at a temperature of 900 °C and a stress of 320 MPa. To determine the effect of aluminide coating, the bare specimens were also tested. The aluminizing treatment decreased the creep strength of Ni-base single crystal superalloy. The solution heat treatment procedures had a great impact on the creep behavior of Ni-base single crystal superalloy. The combination of solution treatment and subsequent double aging treatment was effective to improve the creep strength of Ni-base single crystal superalloy because of more regular the shape of γ′ precipitates and more homogeneous distribution of γ′ precipitates. In addition, the {1 0 0} specimens showed a better creep lives than those {1 1 0} specimens both in aluminized specimens and bare specimens. The anisotropic creep behavior was primarily induced by the different arrangement of {1 1 1} 〈1 0 1〉 slip systems between the two surface orientations of the specimens. The difference in creep rupture lives between {1 0 0} and {1 1 0} side-surface specimens was more pronounced in the specimens STA than in the specimens A because of homogenization of the γ/γ′ microstructure promoted the deformation by {1 1 1} 〈1 0 1〉 slip system which leads to anisotropy of creep behavior. Moreover, the change in microstructures was also considered as one of factors for the decrease of creep life. Besides, the formation of TCP phase, the depth of TCP phase penetration and the gradient of hardness values in the coating to the substrate regions would be additional factors to clarify the anisotropic creep behavior in aluminized Ni-base single crystal superalloy.

Research paper thumbnail of Effects of Re content and crystallographic orientation on creep behavior of aluminized Ni-base single crystal superalloys

Materials & Design, 2013

ABSTRACT Effects of Re content and crystallographic orientation on creep behavior of aluminized N... more ABSTRACT Effects of Re content and crystallographic orientation on creep behavior of aluminized Ni-base single crystal superalloys have been investigated in the present study. The addition of Re seemed to be effective for the creep strength improvement of Ni-base single crystal superalloys. The creep strength was significantly decreased in aluminized specimens due to the change in microstructure under coating layer by the formation of the interdiffusion zone (IDZ) and substrate diffusion zone (SDZ). The specimens with {100} side-surface showed longer creep rupture lives than the specimens with {110} side-surface which means that the anisotropic creep behavior took place. The anisotropic creep behavior was more evident in aluminized CM186LC than in aluminized PWA 1480. This anisotropic creep behavior was mainly induced by the discrepancy of fracture modes due to the different arrangement of slip systems, the geometry as well as the depth penetration of topologically close-packed (TCP) phases between the two side-surface orientations.

Research paper thumbnail of Influence of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations

Materials & Design (1980-2015), 2014

The effect of thermal exposure on the creep properties of an aluminized Ni-based single crystal s... more The effect of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations has been studied in the present study. The specimens were coated by a pack aluminizing process conducted at 1000°C for 5 h under an argon atmosphere. Long-term exposure was performed at 1100°C for 500 h prior to the creep test. The creep properties were found to deteriorate after the long-term exposure as a result of the coarsening of c 0 precipitates accompanied by the formation of a secondary reaction zone which is known to degrade the strength of aluminide coating on a Ni-based single crystal superalloy. The formation of a topologically close-packed phase is one of the degradation factors that are responsible for the reduction of the creep strength of the aluminide coating on a Ni-base single crystal superalloy both with and without long-term exposure. The anisotropic creep properties between the two side-surfaces are due to the different arrangements of f1 1 1gh1 0 1i slip systems.