2006 25th International Conference on Thermoelectrics, 2006
In analogy to recent demonstrations of enhanced thermoelectric properties in superlattice materia... more In analogy to recent demonstrations of enhanced thermoelectric properties in superlattice materials, composite structures with nanoscale features promise dramatic improvements in the figure of merit of thermoelectric materials. Fabrication of nanostructured thermoelectric materials via bulk synthesis is an attractive route for commercial applications. Nanometer scale lamellae of PbTe and Sb 2 Te 3 form when quenched eutectic PbTe-Sb 2 Te 3 melt is subsequently annealed. The lamellar spacing depends on the temperature and time of the anneal. The mechanism for the development of the nanostructures can be characterized by examining the fraction of material transformed as a function of anneal time. Preliminary analysis of the shape factor exponent reveals that the evolution of the nanostructured lamellae is likened to the thickening of very large plates. The coarsening of the lamellar spacing is also examined as a function of time.
We measured the anisotropic elastic constants of a lotus type porous magnesium, which possesses ... more We measured the anisotropic elastic constants of a lotus type porous magnesium, which possesses cylindrical pores aligned unidirectionally. We used the combination of resonant ultrasound spectroscopy and electromagnetic acoustic resonance methods to determine a complete set of the elastic constants. The acoustic measurements revealed that lotus magnesium shows hexagonal elastic symmetry with the c axis along the longitudinal direction of the pores. Young's modulus E // parallel to the pore direction decreases linearly with porosity, while the normal Young's modulus E ⊥ drops rapidly.
Porous magnesium alloys, Mg 9Al 0.75Zn(AZ91D), Mg 3Al 1Zn(AZ31B), Mg 3Al 0.25Zn(AZ91D dilut... more Porous magnesium alloys, Mg 9Al 0.75Zn(AZ91D), Mg 3Al 1Zn(AZ31B), Mg 3Al 0.25Zn(AZ91D dilution with magnesium), were fabricated by unidirectional solidification under various pressures of hydrogen. Optical micrographic observation of cross sections of the porous magnesium alloys shows that cylindrical pores are aligned in the direction parallel to the solidification direction in the vicinity of bottom of the ingots, while spherical pores are evolved in the region apart from the bottom. The number of the cylindrical pores depends on the concentration of the alloying elements and the solidification velocity. The difference in pore morphology was discussed in the light of the equilibrium phase diagrams.
ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constit... more ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constituent elements in Ni3Ga have been studied by positron annihilation, tracer diffusion and interdiffusion experiments. Thermal vacancies have been detected by positron lifetime measurements for specimens quenched from high temperatures. The vacancy formation energy is in the range between 1.7 and 1.8 eV, and is not dependent strongly on the composition. The tracer diffusion coefficients of Ni and Ga are of the same order of magnitude, and the interdiffusion coefficient is about 10 times larger than the diffusion coefficient of Ni. The diffusion in Ni3Ga has been found to satisfy the Darken-Manning equation, as expected from the model of the self-diffusion in this type of materials, where both the species of atoms are assumed to migrate primarily in the sub-lattice of the major element via the ordinary vacancy mechanism.
2007 26th International Conference on Thermoelectrics, 2007
In the system of PbTe and Sb 2 Te 3 , a metastable compound Pb 2 Sb 6 Te 11 appears by solidifica... more In the system of PbTe and Sb 2 Te 3 , a metastable compound Pb 2 Sb 6 Te 11 appears by solidification processing. It has been reported that heat treatments decomposes this compound into two immiscible thermoelectric materials forming nanosized lamellar structure. The fraction transformed and the interlamellar spacing was systematically investigated. In this work, the thermal conductivities and the electrical resistivities have been measured as functions of annealing time through the transformation and the coarsening processes to clarify the effect of the fraction transformed and the inter-lamellar spacing. The thermal conductivity of Pb 2 Sb 6 Te 11 is lower than that after the decomposition. The lattice part of the thermal conductivity of PbTe/Sb 2 Te 3 lamellar samples decreases with deccreasing inter-lamellar spacing. This is considered to be due to the coarsening of the microstructure.
How do interfaces control local transport properties? Needed: foundational understanding of inter... more How do interfaces control local transport properties? Needed: foundational understanding of interfacial structure and composition in thermoelectric materials Medlin and Snyder, Current Opinion in Colloid and Interface Science, 2009 Microstructural Strategies for Nanostructured Bulk Thermoelectrics Texture Control Grain-size reduction Interfacial Nanocoatings Embedded Nanoinclusions Lamellar Nanostructures
ICT: 2005 24th International Conference on Thermoelectrics, 2005
A solidification processing approach to the refinement of lead-tellurium-antimony alloy microstru... more A solidification processing approach to the refinement of lead-tellurium-antimony alloy microstructure is described. Liquid alloys with eutectic, hyper-eutectic and hypo-eutectic compositions (relative to lead) were cooled to the solid state in three distinct ways, i.e. by water quenching, air cooling and furnace cooling. The structures of the alloys resulting from the three different solidification paths were examined using electron microscopy and the micrographs were quantified. Classical solidification methods were used to interpret the structures in relation to the cooling histories.
A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate the... more A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters.
Lotus-type porous carbon steel (AISI1018) whose long cylindrical pores are aligned in one directi... more Lotus-type porous carbon steel (AISI1018) whose long cylindrical pores are aligned in one direction was fabricated by unidirectional solidification in pressurized nitrogen gas. The ingots with the porosity from 10 to 30% were fabricated under the nitrogen gas pressure of 2.5 MPa at various transference velocities from 40 to 160 mm s Ϫ1. Tensile strength was measured for Lotus-type porous carbon steel. Elongation was improved due to normalizing at 1200K. The yield strength does not change even in lotus steel less than 20% in porosity. This superior property is attributed to nitrogen solid solution hardening and pore existence.
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tenness... more Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.
The effect of pore growth direction on the weld fusion zone profile and the mechanical property o... more The effect of pore growth direction on the weld fusion zone profile and the mechanical property of lotus-type porous magnesium joints were investigated by laser welding through experiments and numerical simulations. The dependencies of the pore growth direction on the weld fusion zone profile were evaluated on the basis of the temperature distribution calculated using the ABAQUS FE code with user subroutines. The calculated weld fusion zone profiles were in good agreement with the experimental results, thereby suggesting that thermal conductivity affects weld fusion zone profiles significantly. Moreover, the effect of pore growth direction on the joint strength of lotus-type porous magnesium was investigated. The anisotropy of the tensile strength of the lotus-type porous magnesium with regard to the pore growth direction was observed. The joints with pores parallel and perpendicular to the tensile direction were fractured at the fusion boundary and the base metal, respectively.
Titanium film was deposited by vapour deposition method on lotus-type porous stainless steel SUS3... more Titanium film was deposited by vapour deposition method on lotus-type porous stainless steel SUS304L fabricated by continuous zone melting technique in hydrogen atmosphere in order to obtain good biocompatibility. Titanium film of several micrometers in thickness was coated on the surface inside pores, while that of 20-30 Am was on the flat surface of the specimen. Tensile tests were carried out to evaluate the adhesive strength between titanium layer and substrate of stainless steel. It was found that the adhesive strength was strong enough for the use for biomedical devices.
Lotus_ type porous Ni 3 Al intermetallics (Ni_ 15 mol÷Al, Ni_ 28 mol÷Al and Ni_ 31 mol÷Al) whose ... more Lotus_ type porous Ni 3 Al intermetallics (Ni_ 15 mol÷Al, Ni_ 28 mol÷Al and Ni_ 31 mol÷Al) whose long cylindrical pores are aligned in one direction have been fabricated by unidirectional solidification of the melt in a pressurized hydrogen gas. The porosity and the pore size are decreased with increasing aluminum content. An increase of solidification velocity from 0.33 to 0.50 mms |1 leads to a decrease of pore diameter and an increase of pore number in lotus_ type porous Ni_ 28 mol÷Al.
2006 25th International Conference on Thermoelectrics, 2006
In analogy to recent demonstrations of enhanced thermoelectric properties in superlattice materia... more In analogy to recent demonstrations of enhanced thermoelectric properties in superlattice materials, composite structures with nanoscale features promise dramatic improvements in the figure of merit of thermoelectric materials. Fabrication of nanostructured thermoelectric materials via bulk synthesis is an attractive route for commercial applications. Nanometer scale lamellae of PbTe and Sb 2 Te 3 form when quenched eutectic PbTe-Sb 2 Te 3 melt is subsequently annealed. The lamellar spacing depends on the temperature and time of the anneal. The mechanism for the development of the nanostructures can be characterized by examining the fraction of material transformed as a function of anneal time. Preliminary analysis of the shape factor exponent reveals that the evolution of the nanostructured lamellae is likened to the thickening of very large plates. The coarsening of the lamellar spacing is also examined as a function of time.
We measured the anisotropic elastic constants of a lotus type porous magnesium, which possesses ... more We measured the anisotropic elastic constants of a lotus type porous magnesium, which possesses cylindrical pores aligned unidirectionally. We used the combination of resonant ultrasound spectroscopy and electromagnetic acoustic resonance methods to determine a complete set of the elastic constants. The acoustic measurements revealed that lotus magnesium shows hexagonal elastic symmetry with the c axis along the longitudinal direction of the pores. Young's modulus E // parallel to the pore direction decreases linearly with porosity, while the normal Young's modulus E ⊥ drops rapidly.
Porous magnesium alloys, Mg 9Al 0.75Zn(AZ91D), Mg 3Al 1Zn(AZ31B), Mg 3Al 0.25Zn(AZ91D dilut... more Porous magnesium alloys, Mg 9Al 0.75Zn(AZ91D), Mg 3Al 1Zn(AZ31B), Mg 3Al 0.25Zn(AZ91D dilution with magnesium), were fabricated by unidirectional solidification under various pressures of hydrogen. Optical micrographic observation of cross sections of the porous magnesium alloys shows that cylindrical pores are aligned in the direction parallel to the solidification direction in the vicinity of bottom of the ingots, while spherical pores are evolved in the region apart from the bottom. The number of the cylindrical pores depends on the concentration of the alloying elements and the solidification velocity. The difference in pore morphology was discussed in the light of the equilibrium phase diagrams.
ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constit... more ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constituent elements in Ni3Ga have been studied by positron annihilation, tracer diffusion and interdiffusion experiments. Thermal vacancies have been detected by positron lifetime measurements for specimens quenched from high temperatures. The vacancy formation energy is in the range between 1.7 and 1.8 eV, and is not dependent strongly on the composition. The tracer diffusion coefficients of Ni and Ga are of the same order of magnitude, and the interdiffusion coefficient is about 10 times larger than the diffusion coefficient of Ni. The diffusion in Ni3Ga has been found to satisfy the Darken-Manning equation, as expected from the model of the self-diffusion in this type of materials, where both the species of atoms are assumed to migrate primarily in the sub-lattice of the major element via the ordinary vacancy mechanism.
2007 26th International Conference on Thermoelectrics, 2007
In the system of PbTe and Sb 2 Te 3 , a metastable compound Pb 2 Sb 6 Te 11 appears by solidifica... more In the system of PbTe and Sb 2 Te 3 , a metastable compound Pb 2 Sb 6 Te 11 appears by solidification processing. It has been reported that heat treatments decomposes this compound into two immiscible thermoelectric materials forming nanosized lamellar structure. The fraction transformed and the interlamellar spacing was systematically investigated. In this work, the thermal conductivities and the electrical resistivities have been measured as functions of annealing time through the transformation and the coarsening processes to clarify the effect of the fraction transformed and the inter-lamellar spacing. The thermal conductivity of Pb 2 Sb 6 Te 11 is lower than that after the decomposition. The lattice part of the thermal conductivity of PbTe/Sb 2 Te 3 lamellar samples decreases with deccreasing inter-lamellar spacing. This is considered to be due to the coarsening of the microstructure.
How do interfaces control local transport properties? Needed: foundational understanding of inter... more How do interfaces control local transport properties? Needed: foundational understanding of interfacial structure and composition in thermoelectric materials Medlin and Snyder, Current Opinion in Colloid and Interface Science, 2009 Microstructural Strategies for Nanostructured Bulk Thermoelectrics Texture Control Grain-size reduction Interfacial Nanocoatings Embedded Nanoinclusions Lamellar Nanostructures
ICT: 2005 24th International Conference on Thermoelectrics, 2005
A solidification processing approach to the refinement of lead-tellurium-antimony alloy microstru... more A solidification processing approach to the refinement of lead-tellurium-antimony alloy microstructure is described. Liquid alloys with eutectic, hyper-eutectic and hypo-eutectic compositions (relative to lead) were cooled to the solid state in three distinct ways, i.e. by water quenching, air cooling and furnace cooling. The structures of the alloys resulting from the three different solidification paths were examined using electron microscopy and the micrographs were quantified. Classical solidification methods were used to interpret the structures in relation to the cooling histories.
A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate the... more A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters.
Lotus-type porous carbon steel (AISI1018) whose long cylindrical pores are aligned in one directi... more Lotus-type porous carbon steel (AISI1018) whose long cylindrical pores are aligned in one direction was fabricated by unidirectional solidification in pressurized nitrogen gas. The ingots with the porosity from 10 to 30% were fabricated under the nitrogen gas pressure of 2.5 MPa at various transference velocities from 40 to 160 mm s Ϫ1. Tensile strength was measured for Lotus-type porous carbon steel. Elongation was improved due to normalizing at 1200K. The yield strength does not change even in lotus steel less than 20% in porosity. This superior property is attributed to nitrogen solid solution hardening and pore existence.
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tenness... more Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.
The effect of pore growth direction on the weld fusion zone profile and the mechanical property o... more The effect of pore growth direction on the weld fusion zone profile and the mechanical property of lotus-type porous magnesium joints were investigated by laser welding through experiments and numerical simulations. The dependencies of the pore growth direction on the weld fusion zone profile were evaluated on the basis of the temperature distribution calculated using the ABAQUS FE code with user subroutines. The calculated weld fusion zone profiles were in good agreement with the experimental results, thereby suggesting that thermal conductivity affects weld fusion zone profiles significantly. Moreover, the effect of pore growth direction on the joint strength of lotus-type porous magnesium was investigated. The anisotropy of the tensile strength of the lotus-type porous magnesium with regard to the pore growth direction was observed. The joints with pores parallel and perpendicular to the tensile direction were fractured at the fusion boundary and the base metal, respectively.
Titanium film was deposited by vapour deposition method on lotus-type porous stainless steel SUS3... more Titanium film was deposited by vapour deposition method on lotus-type porous stainless steel SUS304L fabricated by continuous zone melting technique in hydrogen atmosphere in order to obtain good biocompatibility. Titanium film of several micrometers in thickness was coated on the surface inside pores, while that of 20-30 Am was on the flat surface of the specimen. Tensile tests were carried out to evaluate the adhesive strength between titanium layer and substrate of stainless steel. It was found that the adhesive strength was strong enough for the use for biomedical devices.
Lotus_ type porous Ni 3 Al intermetallics (Ni_ 15 mol÷Al, Ni_ 28 mol÷Al and Ni_ 31 mol÷Al) whose ... more Lotus_ type porous Ni 3 Al intermetallics (Ni_ 15 mol÷Al, Ni_ 28 mol÷Al and Ni_ 31 mol÷Al) whose long cylindrical pores are aligned in one direction have been fabricated by unidirectional solidification of the melt in a pressurized hydrogen gas. The porosity and the pore size are decreased with increasing aluminum content. An increase of solidification velocity from 0.33 to 0.50 mms |1 leads to a decrease of pore diameter and an increase of pore number in lotus_ type porous Ni_ 28 mol÷Al.
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Papers by Teruyuki Ikeda