Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1114
Jing-Zhi Yu, Qiang Sun, Qian Wang, Utako Onose, Y. Akiyama, Y. Kawazoe
The behavior of hydrogen in Ni was investigated using the first-principles calculations. It was found that there exists only atomic hydrogen in Ni. The hydrogen resides the octabedron, and the lattice constant expands linearly with the concentration of hydrogen. On the basis of a statistical thermodynamic model, the dependency of hydrogen solubility on temperature in Ni was also investigated, and it was found that magnetization does not favor the dissolution of hydrogen, which is in agreement with the experimental results.
{"title":"First-Principles Calculation on Dissociation of Hydrogen Molecule in Nickel","authors":"Jing-Zhi Yu, Qiang Sun, Qian Wang, Utako Onose, Y. Akiyama, Y. Kawazoe","doi":"10.2320/MATERTRANS1989.41.1114","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1114","url":null,"abstract":"The behavior of hydrogen in Ni was investigated using the first-principles calculations. It was found that there exists only atomic hydrogen in Ni. The hydrogen resides the octabedron, and the lattice constant expands linearly with the concentration of hydrogen. On the basis of a statistical thermodynamic model, the dependency of hydrogen solubility on temperature in Ni was also investigated, and it was found that magnetization does not favor the dissolution of hydrogen, which is in agreement with the experimental results.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"30 1","pages":"1114-1117"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79322158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1146
M. Hara, R. Hayakawa, Kuniaki Watanabe
The kinetics of hydrogen-induced disproportionation of Zr 2 Co was studied by the conventional constant volume method in a temperature range of 773 to 873 K. It was found that Zr 2 Co disproportionated as 2Zr 2 Co + 3H 2 → 3ZrH 2 + ZrCo 2 through a two-step mechanism as 1) Zr 2 Co + H 2 → ZrH 2 + ZrCo and 2) 2ZrCo + H 2 → ZrH 2 + ZrCo 2 . The first step was very fast and completed within only 100 s at 773 K. The rate, however, decreased with increases in temperature The apparent rate constant for the first step disproportionation was determined to be k = 2.0 × 10 -2 exp[15.0 × 10 3 (J/mol)/RT], where the kinetics could be explained by nucleation and one-dimensional growth model. The kinetics of the second step disproportionation could be explained by nucleation and three-dimensional growth model.
{"title":"Hydrogen-induced disproportionation of Zr2Co","authors":"M. Hara, R. Hayakawa, Kuniaki Watanabe","doi":"10.2320/MATERTRANS1989.41.1146","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1146","url":null,"abstract":"The kinetics of hydrogen-induced disproportionation of Zr 2 Co was studied by the conventional constant volume method in a temperature range of 773 to 873 K. It was found that Zr 2 Co disproportionated as 2Zr 2 Co + 3H 2 → 3ZrH 2 + ZrCo 2 through a two-step mechanism as 1) Zr 2 Co + H 2 → ZrH 2 + ZrCo and 2) 2ZrCo + H 2 → ZrH 2 + ZrCo 2 . The first step was very fast and completed within only 100 s at 773 K. The rate, however, decreased with increases in temperature The apparent rate constant for the first step disproportionation was determined to be k = 2.0 × 10 -2 exp[15.0 × 10 3 (J/mol)/RT], where the kinetics could be explained by nucleation and one-dimensional growth model. The kinetics of the second step disproportionation could be explained by nucleation and three-dimensional growth model.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"27 1","pages":"1146-1149"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80746869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1154
T. Mohri, T. Nishiwaki, T. Kinoshita, H. Iwasaki, M. Mabuchi, M. Nakamura, T. Asahina, T. Aizawa, K. Higashi
The microstructure and tensile properties of a rolled specimen of Mg-5.5 mass%Zn-0.6 mass%Zr alloy are investigated. A relatively small grain size of 15.9 μm was obtained in the rolled specimen. The rolled magnesium alloy exhibited higher strength than the annealed specimen at room temperature, while the elongation was almost the same as the annealed specimen. Also, a large elongation of 501% was obtained at 573 K for the rolled specimen. A smaller grain size of 9.6 μm was obtained due to dynamic recrystallization during the tensile test at 573 K.
{"title":"Microstructure and tensile properties of rolled Mg-5.5 mass%Zn-0.6 mass%Zr alloy","authors":"T. Mohri, T. Nishiwaki, T. Kinoshita, H. Iwasaki, M. Mabuchi, M. Nakamura, T. Asahina, T. Aizawa, K. Higashi","doi":"10.2320/MATERTRANS1989.41.1154","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1154","url":null,"abstract":"The microstructure and tensile properties of a rolled specimen of Mg-5.5 mass%Zn-0.6 mass%Zr alloy are investigated. A relatively small grain size of 15.9 μm was obtained in the rolled specimen. The rolled magnesium alloy exhibited higher strength than the annealed specimen at room temperature, while the elongation was almost the same as the annealed specimen. Also, a large elongation of 501% was obtained at 573 K for the rolled specimen. A smaller grain size of 9.6 μm was obtained due to dynamic recrystallization during the tensile test at 573 K.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"24 4 1","pages":"1154-1156"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87244339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1129
Chang-Woo Lee, Y. Ikematsu, D. Shindo
The accuracy of electron energy-loss spectroscopy (EELS) and electron holography on thickness measurement of amorphous SiO 2 was discussed. Since the SiO 2 particles investigated in this work have a spherical shape, local thickness along the incident electron beam can easily be evaluated. Thus, from EELS, the mean free path of inelastic scattering was determined to be 178 ± 4nm at 200kV. It is considered that thickness measurement is limited to amorphous SiO 2 film thicker than about 20 nm with EELS. On the other hand, from phase shift in the electron hologram, the mean inner potential was evaluated to be 11.5 ± 0.3 V. It is suggested that the thickness measurement is possible up to a few nanometers with electron holography. Thus, it is pointed out that the accurate thickness measurement is possible for a thinner region wilt electron holography than EELS.
{"title":"Thickness measurement of amorphous SiO2 by EELS and electron holography","authors":"Chang-Woo Lee, Y. Ikematsu, D. Shindo","doi":"10.2320/MATERTRANS1989.41.1129","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1129","url":null,"abstract":"The accuracy of electron energy-loss spectroscopy (EELS) and electron holography on thickness measurement of amorphous SiO 2 was discussed. Since the SiO 2 particles investigated in this work have a spherical shape, local thickness along the incident electron beam can easily be evaluated. Thus, from EELS, the mean free path of inelastic scattering was determined to be 178 ± 4nm at 200kV. It is considered that thickness measurement is limited to amorphous SiO 2 film thicker than about 20 nm with EELS. On the other hand, from phase shift in the electron hologram, the mean inner potential was evaluated to be 11.5 ± 0.3 V. It is suggested that the thickness measurement is possible up to a few nanometers with electron holography. Thus, it is pointed out that the accurate thickness measurement is possible for a thinner region wilt electron holography than EELS.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"14 1","pages":"1129-1131"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90205279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1132
Young-Gil Park, D. Shindo, M. Okada
Magnetic domain structures of Nd 2 Fe 14 B based permanent magnets were studied by using electron holography and Lorentz microscopy. In a sintered Nd 2 Fe 14 B permanent magnet, a domain wall width of a 180° magnetic domain was evaluated to be 5.1 nm by Lorentz microscopy, while the magnetization distribution in the 90° magnetic domain was clarified by electron holography. In overquenched Nd 2 Fe 14 B permanent magnets, the sharp difference in the magnetization distribution due to the heat treatment was clarified by electron holography. The different magnetic properties of the magnets was directly attributed to the difference of the magnetization distribution.
{"title":"Magnetic Domain Structures of Nd-Fe-B based Permanent Magnets Studied by Electron Holography and Lorentz Microscopy","authors":"Young-Gil Park, D. Shindo, M. Okada","doi":"10.2320/MATERTRANS1989.41.1132","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1132","url":null,"abstract":"Magnetic domain structures of Nd 2 Fe 14 B based permanent magnets were studied by using electron holography and Lorentz microscopy. In a sintered Nd 2 Fe 14 B permanent magnet, a domain wall width of a 180° magnetic domain was evaluated to be 5.1 nm by Lorentz microscopy, while the magnetization distribution in the 90° magnetic domain was clarified by electron holography. In overquenched Nd 2 Fe 14 B permanent magnets, the sharp difference in the magnetization distribution due to the heat treatment was clarified by electron holography. The different magnetic properties of the magnets was directly attributed to the difference of the magnetization distribution.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"72 1","pages":"1132-1135"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75815725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1168
R. Nishiguchi, Y. Shimomura
Computer simulations of molecular dynamics (MD) were used to study the clustering of vacancies in nickel. This was carried out in order to investigate the atomistic processes of vacancy agglomeration in irradiated metals. Simulations were carried out using DYNAMO ver. 8.5 code, by implementing the potential of the embedded atom method (EAM). Firstly, a perfect crystal was thermalized at 1300, 1500, 1700 and 1800 K. Next, four triangular vacancy clusters whose sizes were 10 were introduced on the (111) planes at randomly selected positions. MD simulations were performed using a very small time step of outputs to observe the atomistic processes of the movement of each vacancy. It was found that the vacancy clusters moved and agglomerated whilst maintaining the individual clusters. Thus, a vacancy did not evaporate from a cluster to be absorbed into a larger cluster. There were three different processes in the agglomeration of the vacancy clusters. One was an atom caged in a tetrahedral structure of vacancies moved to another lattice site. Another was an atom caged in a octahedral structure of vacancies moved to another lattice site. The other was an atom moved along a (110) row.
{"title":"An MD Simulation of the Atomistic Processes of Movement and Agglomeration of Vacancy Clusters in Nickel at 1300 K","authors":"R. Nishiguchi, Y. Shimomura","doi":"10.2320/MATERTRANS1989.41.1168","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1168","url":null,"abstract":"Computer simulations of molecular dynamics (MD) were used to study the clustering of vacancies in nickel. This was carried out in order to investigate the atomistic processes of vacancy agglomeration in irradiated metals. Simulations were carried out using DYNAMO ver. 8.5 code, by implementing the potential of the embedded atom method (EAM). Firstly, a perfect crystal was thermalized at 1300, 1500, 1700 and 1800 K. Next, four triangular vacancy clusters whose sizes were 10 were introduced on the (111) planes at randomly selected positions. MD simulations were performed using a very small time step of outputs to observe the atomistic processes of the movement of each vacancy. It was found that the vacancy clusters moved and agglomerated whilst maintaining the individual clusters. Thus, a vacancy did not evaporate from a cluster to be absorbed into a larger cluster. There were three different processes in the agglomeration of the vacancy clusters. One was an atom caged in a tetrahedral structure of vacancies moved to another lattice site. Another was an atom caged in a octahedral structure of vacancies moved to another lattice site. The other was an atom moved along a (110) row.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"46 1","pages":"1168-1171"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79310853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1232
M. Lee, S. Yi, D. Kim
Liquidus projections in the Ni-rich comer of the Ni-Nb-P ternary system have been studied through the analysis of as-cast microstructures. A peritectic reaction involving Ni 9 Nb 2 P and Ni 2 NbP is proposed: L + Ni 9 Nb 2 P → Ni 2 NbP, The slopes of liquidus surface boundaries between Ni solid solution (Ni ss ), Ni 3 P, Ni 9 Nb 2 P and Ni 2 NbP along with two invariant reactions are proposed: L + Ni ss → Ni 3 P + Ni 9 Nb 2 P and L → Ni 3 P + Ni 9 Nb 2 P + Ni 2 NbP. A ternary amorphous alloy with a large undercooled region before crystallization (ΔT x = 15°C) is developed demonstrating the importance of phase equilibria in designing the alloy with high glass forming ability.
通过铸态显微组织分析，研究了Ni-Nb-P三元体系富镍角的液相投影。包晶反应涉及倪9注2 P和倪2提出了平衡:L +倪9注2 P→倪2平衡,山坡上的液相线表面界限镍固溶体(Ni ss),倪3 P,倪9注2 P和倪2平衡两个不变的反应提出了:L +倪党卫军→倪3 P +倪9注2 P和L→倪3 P +倪9注2 P +倪2平衡。制备了一种具有较大过冷区(ΔT x = 15℃)的三元非晶合金，证明了相平衡在设计高玻璃化能力合金中的重要性。
{"title":"Phase equilibria and amorphous phase formation in the Ni-Nb-P ternary alloy system","authors":"M. Lee, S. Yi, D. Kim","doi":"10.2320/MATERTRANS1989.41.1232","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1232","url":null,"abstract":"Liquidus projections in the Ni-rich comer of the Ni-Nb-P ternary system have been studied through the analysis of as-cast microstructures. A peritectic reaction involving Ni 9 Nb 2 P and Ni 2 NbP is proposed: L + Ni 9 Nb 2 P → Ni 2 NbP, The slopes of liquidus surface boundaries between Ni solid solution (Ni ss ), Ni 3 P, Ni 9 Nb 2 P and Ni 2 NbP along with two invariant reactions are proposed: L + Ni ss → Ni 3 P + Ni 9 Nb 2 P and L → Ni 3 P + Ni 9 Nb 2 P + Ni 2 NbP. A ternary amorphous alloy with a large undercooled region before crystallization (ΔT x = 15°C) is developed demonstrating the importance of phase equilibria in designing the alloy with high glass forming ability.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"130 1","pages":"1232-1236"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88351396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1172
T. Maeda, S. Sugimoto, T. Kagotani, D. Book, M. Homma, H. Ota, Y. Houjou
The electromagnetic wave absorption properties of a magnetic powder with a fine α-Fe structure, produced by the disproportionation of Sm 2 Fe 17 , were investigated in the GHz frequency range. A fine, sub-micrometre α-Fe/SmH 2 structure was formed from the Sm 2 Fe 17 compound after disproportionation in a hydrogen atmosphere. The grain size of the α-Fe phase was calculated by X-ray diffraction line broadening analysis, to he about 30nm. In this way, a magnetic powder with a line structure of α-Fe was obtained. This powder was then heated in air in order to oxidize the SmH 2 , with the result that an α-Fe/SmO two-phase microstructure was obtained. Toroidally shaped epoxyresin composites were made from this powder, and the microwave absorption properties of these samples were measured. As a result, the disproportionated samples (heated in hydrogen at 873 K for 1 hour, milled for 30 minutes and oxidized at 473 K for 2 hours in the air) exhibited electromagnetic wave absorption (R.L. < -20 dB) in the frequency range 0.75 to 1.3 GHz, for absorber thicknesses ranging from 12.5 to 7.5 mm, respectively. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range.
{"title":"Electromagnetic Microwave Absorption of α-Fe Microstructure Produced by Disproportionation Reaction of Sm 2 Fe 7 Compound","authors":"T. Maeda, S. Sugimoto, T. Kagotani, D. Book, M. Homma, H. Ota, Y. Houjou","doi":"10.2320/MATERTRANS1989.41.1172","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1172","url":null,"abstract":"The electromagnetic wave absorption properties of a magnetic powder with a fine α-Fe structure, produced by the disproportionation of Sm 2 Fe 17 , were investigated in the GHz frequency range. A fine, sub-micrometre α-Fe/SmH 2 structure was formed from the Sm 2 Fe 17 compound after disproportionation in a hydrogen atmosphere. The grain size of the α-Fe phase was calculated by X-ray diffraction line broadening analysis, to he about 30nm. In this way, a magnetic powder with a line structure of α-Fe was obtained. This powder was then heated in air in order to oxidize the SmH 2 , with the result that an α-Fe/SmO two-phase microstructure was obtained. Toroidally shaped epoxyresin composites were made from this powder, and the microwave absorption properties of these samples were measured. As a result, the disproportionated samples (heated in hydrogen at 873 K for 1 hour, milled for 30 minutes and oxidized at 473 K for 2 hours in the air) exhibited electromagnetic wave absorption (R.L. < -20 dB) in the frequency range 0.75 to 1.3 GHz, for absorber thicknesses ranging from 12.5 to 7.5 mm, respectively. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"33 1","pages":"1172-1175"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78461089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1268
Y. Park, H. Hashimoto, Y. Hahn
MoSi 2 is one of the most promising candidates for high-temperature structural materials because of its high melting point and excellent oxidation resistance. However, the low room temperature fracture toughness and ductility, etc., still remain as major disadvantages to potential high temperature structural applications. MoSi 2 composites containing Nb have shown a great improvement in mechanical properties, especially in fracture toughness, over the monolithic MoSi 2 . However, the addition of refractory metals such as Nb or W has not been that acceptable because of the high reactivity of these additions with the MoSi 2 matrix, and the deleterious effect of reducing oxidation resistance and increasing density. Also, Nb reinforced MoSi 2 composites resulted in a penalty with decreasing strength, both at room and elevated temperatures. In the present study, MoSi 2 and MoSi 2 -Nb powders with a fine grain size were prepared by mechanical alloying. In order to retain the fine microstructure in the consolidated samples, pulse discharge sintering was used to consolidate these powders at a lower sintering temperature compared to that of the conventional hot pressing or HIP. The grain size of the consolidated MoSi 2 -10Nb composite was 0.18 to 1.2 μm, which was finer than that of monolithic MoSi 2 , 1.5 to 3.0 μm. The formation of the (MoNb) 5 Si 3 phase was pronounced in the Nb added composites, and this phase seemed to be formed during the sintering process. Both monolithic MoSi 2 and MoSi 2 -10Nb composites from the mechanically alloyed powders showed a significant amount of plastic deformation in a bending test at 1073 K. The yield stress of the Nb added alloy was higher than that of the monolithic MoSi 2 , which may be caused by the refinement of the microstructure.
{"title":"Microstructure and Mechanical Properties of MoSi2/Nb Composites Made by MA-Pulse Discharge Sintering","authors":"Y. Park, H. Hashimoto, Y. Hahn","doi":"10.2320/MATERTRANS1989.41.1268","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1268","url":null,"abstract":"MoSi 2 is one of the most promising candidates for high-temperature structural materials because of its high melting point and excellent oxidation resistance. However, the low room temperature fracture toughness and ductility, etc., still remain as major disadvantages to potential high temperature structural applications. MoSi 2 composites containing Nb have shown a great improvement in mechanical properties, especially in fracture toughness, over the monolithic MoSi 2 . However, the addition of refractory metals such as Nb or W has not been that acceptable because of the high reactivity of these additions with the MoSi 2 matrix, and the deleterious effect of reducing oxidation resistance and increasing density. Also, Nb reinforced MoSi 2 composites resulted in a penalty with decreasing strength, both at room and elevated temperatures. In the present study, MoSi 2 and MoSi 2 -Nb powders with a fine grain size were prepared by mechanical alloying. In order to retain the fine microstructure in the consolidated samples, pulse discharge sintering was used to consolidate these powders at a lower sintering temperature compared to that of the conventional hot pressing or HIP. The grain size of the consolidated MoSi 2 -10Nb composite was 0.18 to 1.2 μm, which was finer than that of monolithic MoSi 2 , 1.5 to 3.0 μm. The formation of the (MoNb) 5 Si 3 phase was pronounced in the Nb added composites, and this phase seemed to be formed during the sintering process. Both monolithic MoSi 2 and MoSi 2 -10Nb composites from the mechanically alloyed powders showed a significant amount of plastic deformation in a bending test at 1073 K. The yield stress of the Nb added alloy was higher than that of the monolithic MoSi 2 , which may be caused by the refinement of the microstructure.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"5 1","pages":"1268-1273"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85752940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-09-20DOI: 10.2320/MATERTRANS1989.41.1221
Kaichi Saito, S. Sugawara, Tomonori Sato, J. Guo, A. Tsai
The shapes of micro-pits formed in an Al-Pd-Mn icosahedral quasicrystal have been examined by alternating sequence of electrochemical etching and scanning electron microscopy (SEM) observations. Anodic etching was executed on fivefold and twofold surfaces of the single-quasicrystal. Prolonged anodic etching in a solution of CH 3 OH + HNO 3 (volume ratio 3 : 1) followed by SEM observations has revealed that two different types of micro-pits, i.e. pre-existing micro-voids and electrochemical etch-pits, develop into the same regular shape. The micro-pits develop into a pentagonal pyramid on the fivefold surface, and a flat-bottomed rhombic pyramid on the twofold surface. It is shown that these two polyhedral etch-figures correspond to two different sections of a regular rhombic triacontahedron.
{"title":"Unique Shapes of Micro-Pits Formed in an Al-Pd-Mn Icosahedral Quasicrystal by Anodic Etching","authors":"Kaichi Saito, S. Sugawara, Tomonori Sato, J. Guo, A. Tsai","doi":"10.2320/MATERTRANS1989.41.1221","DOIUrl":"https://doi.org/10.2320/MATERTRANS1989.41.1221","url":null,"abstract":"The shapes of micro-pits formed in an Al-Pd-Mn icosahedral quasicrystal have been examined by alternating sequence of electrochemical etching and scanning electron microscopy (SEM) observations. Anodic etching was executed on fivefold and twofold surfaces of the single-quasicrystal. Prolonged anodic etching in a solution of CH 3 OH + HNO 3 (volume ratio 3 : 1) followed by SEM observations has revealed that two different types of micro-pits, i.e. pre-existing micro-voids and electrochemical etch-pits, develop into the same regular shape. The micro-pits develop into a pentagonal pyramid on the fivefold surface, and a flat-bottomed rhombic pyramid on the twofold surface. It is shown that these two polyhedral etch-figures correspond to two different sections of a regular rhombic triacontahedron.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"69 1","pages":"1221-1225"},"PeriodicalIF":0.0,"publicationDate":"2000-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83597645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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