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Kalathur Narasimhan - One of the best experts on this subject based on the ideXlab platform.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels. Part I. Microstructure characterization
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels have been widely employed due to the cost-savings associated with near-net shape manufacturing. The microstructure of P/M steels, especially the porosity, has a significant effect on the mechanical behavior. In this paper, the microstructure of hybrid and Prealloy Ni–Mo P/M steels was studied. Porosity, pore size, shape, interpore spacing, as well as phase fraction of steel matrix have been quantified. The quantification of pore clustering was also investigated. The mechanical behavior of each phase in steel matrix was investigated using Vickers microhardness. Significant difference in pore morphology and steel matrix microstructure between hybrid and Prealloy steels, at the similar densities, were observed. The microstructure characterization presented in this paper is linked to the companion paper on fatigue crack growth behavior of these steels.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels: Part II. Fatigue behavior
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels will encounter fatigue loading in service. A fundamental understanding of porosity and steel matrix microstructure on fatigue behavior is important. In this paper, the fatigue crack growth behavior of hybrid and Prealloy Ni–Mo P/M steels was investigated. The density of P/M steels was varied from 7.0 to 7.6 g/cm 3 . The relationship between microstructure and fatigue crack growth was investigated in detail. The density, matrix microstructure, and the degree of pore clustering had a significant effect on the crack growth behavior. The crack closure and two parameters (static: K max and cyclic: Δ K ) were employed to describe and explain the fatigue behavior of the steels.
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Fatigue-crack growth of Fe.0.85Mo-2Ni.0.6C steels with a heterogeneous microstructure
International Journal of Powder Metallurgy, 2005Co-Authors: George B. Piotrowski, Xin Deng, Nikhilesh Chawla, Kalathur Narasimhan, Michael L. MarucciAbstract:Powder metallurgy (P/M) processing of steels typically results in a material with a heterogeneous microstructure and residual porosity. The fatigue-crack-growth behavior of these materials is strongly affected by the nature of the porosity and the heterogeneous microstructure. Notched fatigue specimens were prepared from a Fe-0.85 w/o Mo Prealloy mixed and binder treated with 2 w/o Ni and 0.6 w/o C. The steels were tested at three different sintered densities: 6.98 g/cm 3 , 7.36 g/cm 3 , and 7.53 g/cm 3 . The microstructure was characterized at each density to determine the porosity, microconstituents, and phase fractions. Fatigue testing was performed at various R-ratios, ranging from -2 to 0.8. Increasing porosity and increasing R-ratio resulted in a decrease in D K th . In situ observations of crack growth showed that the cracks propagated through the Ni-rich regions. It appears that the pearlite regions, and to some extent the bainite regions, contributed to toughening and crack deflection. These findings are supported by quantitative measurements of crack-growth rates through the various microconstituents.
Xin Deng - One of the best experts on this subject based on the ideXlab platform.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels. Part I. Microstructure characterization
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels have been widely employed due to the cost-savings associated with near-net shape manufacturing. The microstructure of P/M steels, especially the porosity, has a significant effect on the mechanical behavior. In this paper, the microstructure of hybrid and Prealloy Ni–Mo P/M steels was studied. Porosity, pore size, shape, interpore spacing, as well as phase fraction of steel matrix have been quantified. The quantification of pore clustering was also investigated. The mechanical behavior of each phase in steel matrix was investigated using Vickers microhardness. Significant difference in pore morphology and steel matrix microstructure between hybrid and Prealloy steels, at the similar densities, were observed. The microstructure characterization presented in this paper is linked to the companion paper on fatigue crack growth behavior of these steels.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels: Part II. Fatigue behavior
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels will encounter fatigue loading in service. A fundamental understanding of porosity and steel matrix microstructure on fatigue behavior is important. In this paper, the fatigue crack growth behavior of hybrid and Prealloy Ni–Mo P/M steels was investigated. The density of P/M steels was varied from 7.0 to 7.6 g/cm 3 . The relationship between microstructure and fatigue crack growth was investigated in detail. The density, matrix microstructure, and the degree of pore clustering had a significant effect on the crack growth behavior. The crack closure and two parameters (static: K max and cyclic: Δ K ) were employed to describe and explain the fatigue behavior of the steels.
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Fatigue-crack growth of Fe.0.85Mo-2Ni.0.6C steels with a heterogeneous microstructure
International Journal of Powder Metallurgy, 2005Co-Authors: George B. Piotrowski, Xin Deng, Nikhilesh Chawla, Kalathur Narasimhan, Michael L. MarucciAbstract:Powder metallurgy (P/M) processing of steels typically results in a material with a heterogeneous microstructure and residual porosity. The fatigue-crack-growth behavior of these materials is strongly affected by the nature of the porosity and the heterogeneous microstructure. Notched fatigue specimens were prepared from a Fe-0.85 w/o Mo Prealloy mixed and binder treated with 2 w/o Ni and 0.6 w/o C. The steels were tested at three different sintered densities: 6.98 g/cm 3 , 7.36 g/cm 3 , and 7.53 g/cm 3 . The microstructure was characterized at each density to determine the porosity, microconstituents, and phase fractions. Fatigue testing was performed at various R-ratios, ranging from -2 to 0.8. Increasing porosity and increasing R-ratio resulted in a decrease in D K th . In situ observations of crack growth showed that the cracks propagated through the Ni-rich regions. It appears that the pearlite regions, and to some extent the bainite regions, contributed to toughening and crack deflection. These findings are supported by quantitative measurements of crack-growth rates through the various microconstituents.
Hidemi Kato - One of the best experts on this subject based on the ideXlab platform.
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3D morphological evolution of porous titanium by x-ray micro- and nano-tomography
Journal of Materials Research, 2013Co-Authors: Yu-chen Karen Chen-wiegart, Takeshi Wada, Hidemi Kato, Nikita Butakov, Xianghui Xiao, Francesco De Carlo, Jun Wang, David C. Dunand, Eric MaireAbstract:The 3D morphological evolution of titanium foams as they undergo a two-step fabrication process is quantitatively characterized through x-ray micro- and nano-tomography. In the first process step, a Cu–Ti–Cr–Zr Prealloy is immersed in liquid Mg, where Cu is alloyed with Mg while a skeleton of crystalline Ti–Cr–Zr is created. In the second step, the Mg–Cu phase is etched in acid, leaving a Ti–Cr–Zr foam with submicron struts. 3D images of these solidified Ti–Cr–Zr/Mg–Cu composites and leached Ti–Cr–Zr foams are acquired after 5, 10, and 30 min exposure to liquid Mg. As the Mg exposure time increases, the Ti–Cr–Zr ligaments grow in size. The tortuosity loosely follows the Bruggeman relation. The interfacial surface distribution of these Ti-foams is qualitatively similar to other nano-porous metal prepared by one-step dealloying. The characteristic length of the Mg–Cu phase and pores are also reported.
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Mg-based metallic glass matrix composite with in situ porous titanium dispersoids by dealloying in metallic melt
Materials Science and Engineering: A, 2013Co-Authors: Hideki Oka, Wei Guo, Takeshi Wada, Hidemi KatoAbstract:Abstract A Mg3Cu3Gd bulk metallic glass matrix composite with porous α -Ti dispersoids was prepared by dealloying in a metallic melt. The in situ formed α -Ti dispersoids had a pore-size of ∼500 nm, which was imparted from the Ti 2 Cu precipitate in the Prealloy. Pore size was therefore controllable through the cooling rate of the Prealloy preparation. Plasticity was not improved apparently, however the maximum fracture stress under four point bending mode increased from 217 MPa for the monolithic counterpart to 387 MPa. This was due to the optimal relationship where dispersoid size ( L )≈dispersoid interval distance ( S )≈process zone size ( R p ). This was achieved locally within and around the porous Ti dispersoids, and helped improve the toughness and ductility.
Juwon Fayomi - One of the best experts on this subject based on the ideXlab platform.
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Influence of sintering temperature on the corrosion and wear behaviour of spark plasma–sintered Inconel 738LC alloy
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Olagunju Ogunbiyi, Lodewyk Beneke, Oluwagbenga Adesina, Rotimi Sadiku, Tamba Jamiru, Juwon FayomiAbstract:Inconel 738 low carbon is a nickel-based superalloy that is widely used in the marine and petroleum industries, where it is subjected to an aggressive erosive and/or corrosive environment. Degradation due to erosion and corrosion often has a negative impact on the material’s long-term performance. This study aims to improve the mechanical properties and wear resistance of the material. This was achieved by using spark plasma sintering (SPS) technique to fabricate IN738LC superalloy. The elemental powders were Prealloy in a tubular mixer for a period of 12 h. The samples were sintered at four different temperatures of 900, 1000, 1100 and 1200 °C under a pressure of 50 MPa, heating rate of 100 °C/min and holding time of 5 min. Wear test was conducted on the sintered alloys at 15, 25 and 35 N loads. Potentiodynamic polarization tests were performed in 3.65% NaCl and 0.5 M H2SO4 solutions. Worn surfaces and microstructural analyses of the sintered alloys were conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and polarized optical microscopy (POM). Microstructural evaluation of the alloys revealed that there was a homogenous dispersion of elemental composition, with less morphological defects. Wear results showed that the sample sintered at 1200 °C has the highest resistance to wear and corrosion attack. It also possesses superior hardness property. Therefore, the new material is suitable for application in a highly corrosive environment and also for high strength applications.
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Influence of sintering temperature on the corrosion and wear behaviour of spark plasma–sintered Inconel 738LC alloy
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Olagunju Ogunbiyi, Lodewyk Beneke, Oluwagbenga Adesina, Rotimi Sadiku, Tamba Jamiru, Juwon FayomiAbstract:Inconel 738 low carbon is a nickel-based superalloy that is widely used in the marine and petroleum industries, where it is subjected to an aggressive erosive and/or corrosive environment. Degradation due to erosion and corrosion often has a negative impact on the material’s long-term performance. This study aims to improve the mechanical properties and wear resistance of the material. This was achieved by using spark plasma sintering (SPS) technique to fabricate IN738LC superalloy. The elemental powders were Prealloy in a tubular mixer for a period of 12 h. The samples were sintered at four different temperatures of 900, 1000, 1100 and 1200 °C under a pressure of 50 MPa, heating rate of 100 °C/min and holding time of 5 min. Wear test was conducted on the sintered alloys at 15, 25 and 35 N loads. Potentiodynamic polarization tests were performed in 3.65% NaCl and 0.5 M H2SO4 solutions. Worn surfaces and microstructural analyses of the sintered alloys were conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and polarized optical microscopy (POM). Microstructural evaluation of the alloys revealed that there was a homogenous dispersion of elemental composition, with less morphological defects. Wear results showed that the sample sintered at 1200 °C has the highest resistance to wear and corrosion attack. It also possesses superior hardness property. Therefore, the new material is suitable for application in a highly corrosive environment and also for high strength applications.
G. Piotrowski - One of the best experts on this subject based on the ideXlab platform.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels. Part I. Microstructure characterization
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels have been widely employed due to the cost-savings associated with near-net shape manufacturing. The microstructure of P/M steels, especially the porosity, has a significant effect on the mechanical behavior. In this paper, the microstructure of hybrid and Prealloy Ni–Mo P/M steels was studied. Porosity, pore size, shape, interpore spacing, as well as phase fraction of steel matrix have been quantified. The quantification of pore clustering was also investigated. The mechanical behavior of each phase in steel matrix was investigated using Vickers microhardness. Significant difference in pore morphology and steel matrix microstructure between hybrid and Prealloy steels, at the similar densities, were observed. The microstructure characterization presented in this paper is linked to the companion paper on fatigue crack growth behavior of these steels.
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Fatigue crack growth behavior of hybrid and Prealloyed sintered steels: Part II. Fatigue behavior
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Xin Deng, G. Piotrowski, Nikhilesh Chawla, Kalathur NarasimhanAbstract:Abstract Powder metallurgy (P/M) steels will encounter fatigue loading in service. A fundamental understanding of porosity and steel matrix microstructure on fatigue behavior is important. In this paper, the fatigue crack growth behavior of hybrid and Prealloy Ni–Mo P/M steels was investigated. The density of P/M steels was varied from 7.0 to 7.6 g/cm 3 . The relationship between microstructure and fatigue crack growth was investigated in detail. The density, matrix microstructure, and the degree of pore clustering had a significant effect on the crack growth behavior. The crack closure and two parameters (static: K max and cyclic: Δ K ) were employed to describe and explain the fatigue behavior of the steels.