Thomas Lillo - Academia.edu (original) (raw)

Papers by Thomas Lillo

Generation IV reactors will need to be intrinsically safe, having a proliferation-resistant fuel ... more Generation IV reactors will need to be intrinsically safe, having a proliferation-resistant fuel cycle and several advantages relative to existing light water reactor (LWR). They, however, must still overcome certain technical issues and the cost barrier before it can be built in the U.S. The establishment of a nuclear power cost goal of 3.3 cents/kWh is desirable in order to compete with fossil combined-cycle, gas turbine power generation. This goal requires approximately a 30 percent reduction in power cost for stateof-the-art nuclear plants. It has been demonstrated that this large cost differential can be overcome only by technology improvements that lead to a combination of better efficiency and more compatible reactor materials.

HVOF coating have shown high resistance to corrosion in fossil energy applications and it is gene... more HVOF coating have shown high resistance to corrosion in fossil energy applications and it is generally accepted that mechanical failure, e.g. cracking or spalling, ultimately will determine coating lifetime. The high velocity oxygen-fuel method (HVOF) of applying coatings is one of the most commercially viable and allows the control of various parameters including powder particle velocity and temperature which influence

Equal channel angular extrusion IECAE) offers the potential to introduce \cry large strains into ... more Equal channel angular extrusion IECAE) offers the potential to introduce \cry large strains into a metal workpiece uithout changing its cross-section. Hence. it could be an attractlie technique for developing a tine-grained forging stock uith good forming characteristics. Magnesium alloys are ideal candidates to benetit from the ECAE technique, because of their poor forming characteristics due to a hexagonal close packed crystal structure and a low nielting point, which allows them to be ECAE processed isothermally at temperatures of 300°C and below. An assessment of the technique has been made with the alloys AZ3 I B and ZK60. The mechanical properties of AZ3IB are largely unaffected by the process, however. the ZK60 alloy responds I'a\orably. Relative to the as-receibed material, the ductility is iiiipro\ed by 2 to 3 times over the entire temperature range in\estigated (24 - 450°C). Explanations for the property enhancements are discussed in terms of microstructure ohservatio...

Scripta Materialia, 2004

Equal channel angular processing is shown to induce a strong deformation texture, which persists ... more Equal channel angular processing is shown to induce a strong deformation texture, which persists after recrystallization. The enhancement in the tensile ductility along the extrusion axis originally reported by Mukai et al. [Scripta Mater 45 (2001) 89] is discussed in terms of magnesium's deformation mechanisms, plastic anisotropy, and the texture itself.

Nuclear Engineering and Design, 2012

The Next Generation Nuclear Plant project is considering Alloy 800H and Alloy 617 for steam gener... more The Next Generation Nuclear Plant project is considering Alloy 800H and Alloy 617 for steam generator and intermediate heat exchangers. It is envisioned that a steam generator would operate with reactor outlet temperatures from 750 to 800°C, while an intermediate heat exchanger for primary to secondary helium would operate up to an outlet temperature of 950°C. Although both alloys are

Metallurgical and Materials Transactions A, 2009

Alloy 617, a high temperature creep-resistant, nickel-based alloy, is being considered for the pr... more Alloy 617, a high temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP) which will operate at temperatures exceeding 760 o C. Orientation imaging microscopy (OIM) is used to characterize the grain boundaries in the vicinity of creep voids that develop during high temperature creep tests (800-1000 o C at creep stresses ranging from 20-85 MPa) terminated at creep strains ranging from 5-40%. Observations using optical microscopy indicate creep rate does not significantly influence the creep void fraction at a given creep strain. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular or 45 o to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids while CSL-related grain boundaries did not appear to be consistently associated with void development.

Metallurgical and Materials Transactions A, 2005

Elevated temperature tensile and creep-rupture tests were performed on INCONEL alloy MA754 in an ... more Elevated temperature tensile and creep-rupture tests were performed on INCONEL alloy MA754 in an as-rolled, fine-grained condition. Tensile tests were performed at 25 C, 800 C, 900 C, and 1000 C; creep-rupture tests were performed at 800 C, 900 C, and 1000 C. the elevated temperature strength in the fine-grained condition was approximately 25 pct of that the coarse-grained, annealed

Metallurgical and Materials Transactions A, 2009

Nickel-based superalloys are being considered for applications within advanced nuclear power gene... more Nickel-based superalloys are being considered for applications within advanced nuclear power generation systems due to their high temperature strength and corrosion resistance. Alloy 617, a candidate for use in heat exchangers, derives its strength from both solid solution strengthening and the precipitation of carbide particles. However, during creep, carbides that are supposed to retard grain boundary motion are found to dissolve and re-precipitate on boundaries in tension. To quantify the redistribution, we have used electron backscatter diffraction and energy dispersive spectroscopy to analyze the microstructure of 617 after creep testing at 900 and 1000°C. The data were analyzed with respect to location of the carbides (e.g., intergranular vs. intragranular), grain boundary character, and precipitate type (i.e., Cr-rich or Mo-rich). We find that grain boundary character is the most important factor in carbide distribution; some evidence of preferential distribution to boundaries in tension is also observed at higher applied stresses. Finally, the results suggest that the observed redistribution is due to the migration of carbides to the boundaries and not the migration of boundaries to the precipitates.

Materials Science and Engineering: A, 2004

A previous investigation produced evidence that twin boundaries in annealed copper were a signifi... more A previous investigation produced evidence that twin boundaries in annealed copper were a significant source of dislocations during the initial stages of plastic flow. The character of the dislocation source was unknown, but it was hypothesized that twin boundaries could be non-regenerative dislocation sources that would cause migration of the boundary during plastic deformation. Channel die deformation and intermittent orientation imaging were performed on split specimens of pure copper in an attempt to observe twin boundary migration. Approximately 15% of the twin boundaries were observed to migrate beyond that expected from the imposed strain. The data support the hypothesis that twin boundaries can serve as dislocation sources.

Materials Science and Engineering: A, 2005

Texture strongly impacts the plasticity of metals and the equal channel angular extrusion (ECAE) ... more Texture strongly impacts the plasticity of metals and the equal channel angular extrusion (ECAE) process has been demonstrated to induce unusual textures and enhance the room temperature ductility of magnesium alloys. This paper documents a wide range of textures that may be generated by ECAE of magnesium alloys. Considered broadly, the ECAE processing of magnesium alloys tends to produce 0 0 0 1 fiber textures. Unlike conventional rolling, which tends to produce 0 0 0 1 || normal direction textures, the orientation of the 0 0 0 1 fiber texture (as well as its strength) is strongly affected by alloying additions and processing history. For example, route B-processing of Mg-Al-Zn (AZ) alloys tends to produce textures with 0 0 0 1 highly inclined (∼55 • ) from the extrusion axis. This texture appears to promote excellent ductilities along the axis of the ECAE billets. End effects, which influence the distribution of strain and texture, are modeled.

Journal of the American Ceramic Society, 2014

The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering ... more The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering is determined as a function of temperature using laser-based modulated thermoreflectance. The films exhibit significantly reduced conductivity compared with stoichiometric bulk CeO 2 . A variety of microstructure imaging techniques including X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron analysis, and electron energy loss spectroscopy indicate that the thermal conductivity is influenced by grain boundaries, dislocations, and oxygen vacancies. The temperature dependence of the thermal conductivity is analyzed using an analytical solution of the Boltzmann transport equation. The conclusion of this study is that oxygen vacancies pose a smaller impediment to thermal transport when they segregate along grain boundaries. D. Clarke-contributing editor Manuscript No. 32233.

International Journal of Hydrogen Energy, 2011

Cold rolling a b s t r a c t There are few adequate materials available for severe corrosion cond... more Cold rolling a b s t r a c t There are few adequate materials available for severe corrosion conditions, like those of the SeI thermochemical cycle. High Si, Ni-alloys have excellent corrosion resistance, especially in mineral acids, but have typically been limited by poor mechanical properties or difficult fabrication issues. The ductility of nickel silicide, Ni 3 Si, can be improved through a combination of micro-and macro-alloying. Nb and other minor alloying elements yield a cast alloy with excellent corrosion resistance to sulfuric acid and good mechanical properties. In this paper, efforts to optimize the alloys performance are presented along with progress toward the development of a wrought version of the material. It was found that an appropriate heat treatment provides the largest improvement in the cast NieSi alloy microstructure. Trials have resulted in more than a 50% reduction by the cold rolling process. This process not only increases homogenization but also results in a more uniform distribution of G-phase particles, which is beneficial for the improvements in ductility and corrosion resistance. These alloys have great potential for use in future hydrogen production as well as fossil energy combustion. (J.W. Newkirk).

Acta Materialia, 2005

Equal channel angular extrusion (ECAE) has been demonstrated to induce unusual deformation textur... more Equal channel angular extrusion (ECAE) has been demonstrated to induce unusual deformation textures and resulting properties in magnesium alloys, such as the remarkably enhanced room temperature ductility first reported by Mukai et al. [Mukai T, Yamanoi M, Watanabe H, Higashi K. Scr Mater 2001;45:89]. This paper documents a wide range of textures which evolve during ECAE of magnesium alloys. The fact that different alloys exhibit different texture evolutions is an indication of distinctions in the balance of deformation mechanisms which operate within the different alloys. Polycrystal plasticity modeling is used to develop explanations for these texture distinctions in terms of the relative activities of non-basal secondary slip modes, involving AEaae and AEc + aae type dislocations. AZ alloys appear to exhibit balanced secondary slip of non-basal AEaae and AEc + aae dislocations, while ZK60 and WE43 appear to favor non-basal AEc + aae slip. A binary Mg-Li alloy exhibits a radically distinct texture evolution, which is associated with large-scale strain accommodation by non-basal AEaae slip.

Acta Materialia, 2001

The flow stress behavior of OFHC polycrystalline copper was evaluated using cold-rolled and equal... more The flow stress behavior of OFHC polycrystalline copper was evaluated using cold-rolled and equal channel angular extruded materials. Prior to tensile testing at room temperature, the specimens were heat treated to obtain grain sizes ranging from 3 to 60 µm. The flow stress, when correlated with the square root of true strain, is associated with four stages of hardening. These stages, in terms of increasing strain, are attributed to: (1) dislocation source activation, possibly at annealing twin boundaries during the onset of plastic flow, (2) dislocation slip and cross slip, (3) constriction of the screw dislocation partials for cross slip continuation, and (4) dislocation annihilation and saturation as interpreted through dynamic recovery. The tensile properties and analyses are supported by observations and measurements from orientation imaging and transmission electron microscopy. 

Acta Materialia, 2007

The texture and grain boundary structure of recrystallized materials are dependent upon the chara... more The texture and grain boundary structure of recrystallized materials are dependent upon the character of the deformed matrix and the selective nucleation and growth of crystallites from the deformation structure. Annealing twin boundary formation in materials of low to medium stacking fault energy is not only a product of the recrystallized structure, but also plays an important role in the recrystallization process itself. In situ and ex situ recrystallization experiments were performed on pure copper (99.99% pure) previously deformed by equal channel angular extrusion. Intermittent characterization of the structure on the surface of bulk specimens was accomplished using electron backscatter diffraction. The character of the structure where nucleation preferentially occurs is presumed to be in heavily deformed regions as nuclei were first observed in such microstructures as viewed from the specimen surface. Grain growth is observed to be heavily dependent upon twinning processes at the low temperatures used for in situ experiments, with twinning occurring to aid the recrystallization process. It is shown at these temperatures that the slowest growing grains obtain the highest fraction of twin boundaries as the new twin orientations presumably increase the boundary energy at positions where there is insufficient driving force to continue growth.

Generation IV reactors will need to be intrinsically safe, having a proliferation-resistant fuel ... more Generation IV reactors will need to be intrinsically safe, having a proliferation-resistant fuel cycle and several advantages relative to existing light water reactor (LWR). They, however, must still overcome certain technical issues and the cost barrier before it can be built in the U.S. The establishment of a nuclear power cost goal of 3.3 cents/kWh is desirable in order to compete with fossil combined-cycle, gas turbine power generation. This goal requires approximately a 30 percent reduction in power cost for stateof-the-art nuclear plants. It has been demonstrated that this large cost differential can be overcome only by technology improvements that lead to a combination of better efficiency and more compatible reactor materials.

HVOF coating have shown high resistance to corrosion in fossil energy applications and it is gene... more HVOF coating have shown high resistance to corrosion in fossil energy applications and it is generally accepted that mechanical failure, e.g. cracking or spalling, ultimately will determine coating lifetime. The high velocity oxygen-fuel method (HVOF) of applying coatings is one of the most commercially viable and allows the control of various parameters including powder particle velocity and temperature which influence

Equal channel angular extrusion IECAE) offers the potential to introduce \cry large strains into ... more Equal channel angular extrusion IECAE) offers the potential to introduce \cry large strains into a metal workpiece uithout changing its cross-section. Hence. it could be an attractlie technique for developing a tine-grained forging stock uith good forming characteristics. Magnesium alloys are ideal candidates to benetit from the ECAE technique, because of their poor forming characteristics due to a hexagonal close packed crystal structure and a low nielting point, which allows them to be ECAE processed isothermally at temperatures of 300°C and below. An assessment of the technique has been made with the alloys AZ3 I B and ZK60. The mechanical properties of AZ3IB are largely unaffected by the process, however. the ZK60 alloy responds I'a\orably. Relative to the as-receibed material, the ductility is iiiipro\ed by 2 to 3 times over the entire temperature range in\estigated (24 - 450°C). Explanations for the property enhancements are discussed in terms of microstructure ohservatio...

Scripta Materialia, 2004

Equal channel angular processing is shown to induce a strong deformation texture, which persists ... more Equal channel angular processing is shown to induce a strong deformation texture, which persists after recrystallization. The enhancement in the tensile ductility along the extrusion axis originally reported by Mukai et al. [Scripta Mater 45 (2001) 89] is discussed in terms of magnesium's deformation mechanisms, plastic anisotropy, and the texture itself.

Nuclear Engineering and Design, 2012

The Next Generation Nuclear Plant project is considering Alloy 800H and Alloy 617 for steam gener... more The Next Generation Nuclear Plant project is considering Alloy 800H and Alloy 617 for steam generator and intermediate heat exchangers. It is envisioned that a steam generator would operate with reactor outlet temperatures from 750 to 800°C, while an intermediate heat exchanger for primary to secondary helium would operate up to an outlet temperature of 950°C. Although both alloys are

Metallurgical and Materials Transactions A, 2009

Alloy 617, a high temperature creep-resistant, nickel-based alloy, is being considered for the pr... more Alloy 617, a high temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP) which will operate at temperatures exceeding 760 o C. Orientation imaging microscopy (OIM) is used to characterize the grain boundaries in the vicinity of creep voids that develop during high temperature creep tests (800-1000 o C at creep stresses ranging from 20-85 MPa) terminated at creep strains ranging from 5-40%. Observations using optical microscopy indicate creep rate does not significantly influence the creep void fraction at a given creep strain. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular or 45 o to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids while CSL-related grain boundaries did not appear to be consistently associated with void development.

Metallurgical and Materials Transactions A, 2005

Elevated temperature tensile and creep-rupture tests were performed on INCONEL alloy MA754 in an ... more Elevated temperature tensile and creep-rupture tests were performed on INCONEL alloy MA754 in an as-rolled, fine-grained condition. Tensile tests were performed at 25 C, 800 C, 900 C, and 1000 C; creep-rupture tests were performed at 800 C, 900 C, and 1000 C. the elevated temperature strength in the fine-grained condition was approximately 25 pct of that the coarse-grained, annealed

Metallurgical and Materials Transactions A, 2009

Nickel-based superalloys are being considered for applications within advanced nuclear power gene... more Nickel-based superalloys are being considered for applications within advanced nuclear power generation systems due to their high temperature strength and corrosion resistance. Alloy 617, a candidate for use in heat exchangers, derives its strength from both solid solution strengthening and the precipitation of carbide particles. However, during creep, carbides that are supposed to retard grain boundary motion are found to dissolve and re-precipitate on boundaries in tension. To quantify the redistribution, we have used electron backscatter diffraction and energy dispersive spectroscopy to analyze the microstructure of 617 after creep testing at 900 and 1000°C. The data were analyzed with respect to location of the carbides (e.g., intergranular vs. intragranular), grain boundary character, and precipitate type (i.e., Cr-rich or Mo-rich). We find that grain boundary character is the most important factor in carbide distribution; some evidence of preferential distribution to boundaries in tension is also observed at higher applied stresses. Finally, the results suggest that the observed redistribution is due to the migration of carbides to the boundaries and not the migration of boundaries to the precipitates.

Materials Science and Engineering: A, 2004

A previous investigation produced evidence that twin boundaries in annealed copper were a signifi... more A previous investigation produced evidence that twin boundaries in annealed copper were a significant source of dislocations during the initial stages of plastic flow. The character of the dislocation source was unknown, but it was hypothesized that twin boundaries could be non-regenerative dislocation sources that would cause migration of the boundary during plastic deformation. Channel die deformation and intermittent orientation imaging were performed on split specimens of pure copper in an attempt to observe twin boundary migration. Approximately 15% of the twin boundaries were observed to migrate beyond that expected from the imposed strain. The data support the hypothesis that twin boundaries can serve as dislocation sources.

Materials Science and Engineering: A, 2005

Texture strongly impacts the plasticity of metals and the equal channel angular extrusion (ECAE) ... more Texture strongly impacts the plasticity of metals and the equal channel angular extrusion (ECAE) process has been demonstrated to induce unusual textures and enhance the room temperature ductility of magnesium alloys. This paper documents a wide range of textures that may be generated by ECAE of magnesium alloys. Considered broadly, the ECAE processing of magnesium alloys tends to produce 0 0 0 1 fiber textures. Unlike conventional rolling, which tends to produce 0 0 0 1 || normal direction textures, the orientation of the 0 0 0 1 fiber texture (as well as its strength) is strongly affected by alloying additions and processing history. For example, route B-processing of Mg-Al-Zn (AZ) alloys tends to produce textures with 0 0 0 1 highly inclined (∼55 • ) from the extrusion axis. This texture appears to promote excellent ductilities along the axis of the ECAE billets. End effects, which influence the distribution of strain and texture, are modeled.

Journal of the American Ceramic Society, 2014

The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering ... more The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering is determined as a function of temperature using laser-based modulated thermoreflectance. The films exhibit significantly reduced conductivity compared with stoichiometric bulk CeO 2 . A variety of microstructure imaging techniques including X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron analysis, and electron energy loss spectroscopy indicate that the thermal conductivity is influenced by grain boundaries, dislocations, and oxygen vacancies. The temperature dependence of the thermal conductivity is analyzed using an analytical solution of the Boltzmann transport equation. The conclusion of this study is that oxygen vacancies pose a smaller impediment to thermal transport when they segregate along grain boundaries. D. Clarke-contributing editor Manuscript No. 32233.

International Journal of Hydrogen Energy, 2011

Cold rolling a b s t r a c t There are few adequate materials available for severe corrosion cond... more Cold rolling a b s t r a c t There are few adequate materials available for severe corrosion conditions, like those of the SeI thermochemical cycle. High Si, Ni-alloys have excellent corrosion resistance, especially in mineral acids, but have typically been limited by poor mechanical properties or difficult fabrication issues. The ductility of nickel silicide, Ni 3 Si, can be improved through a combination of micro-and macro-alloying. Nb and other minor alloying elements yield a cast alloy with excellent corrosion resistance to sulfuric acid and good mechanical properties. In this paper, efforts to optimize the alloys performance are presented along with progress toward the development of a wrought version of the material. It was found that an appropriate heat treatment provides the largest improvement in the cast NieSi alloy microstructure. Trials have resulted in more than a 50% reduction by the cold rolling process. This process not only increases homogenization but also results in a more uniform distribution of G-phase particles, which is beneficial for the improvements in ductility and corrosion resistance. These alloys have great potential for use in future hydrogen production as well as fossil energy combustion. (J.W. Newkirk).

Acta Materialia, 2005

Equal channel angular extrusion (ECAE) has been demonstrated to induce unusual deformation textur... more Equal channel angular extrusion (ECAE) has been demonstrated to induce unusual deformation textures and resulting properties in magnesium alloys, such as the remarkably enhanced room temperature ductility first reported by Mukai et al. [Mukai T, Yamanoi M, Watanabe H, Higashi K. Scr Mater 2001;45:89]. This paper documents a wide range of textures which evolve during ECAE of magnesium alloys. The fact that different alloys exhibit different texture evolutions is an indication of distinctions in the balance of deformation mechanisms which operate within the different alloys. Polycrystal plasticity modeling is used to develop explanations for these texture distinctions in terms of the relative activities of non-basal secondary slip modes, involving AEaae and AEc + aae type dislocations. AZ alloys appear to exhibit balanced secondary slip of non-basal AEaae and AEc + aae dislocations, while ZK60 and WE43 appear to favor non-basal AEc + aae slip. A binary Mg-Li alloy exhibits a radically distinct texture evolution, which is associated with large-scale strain accommodation by non-basal AEaae slip.

Acta Materialia, 2001

The flow stress behavior of OFHC polycrystalline copper was evaluated using cold-rolled and equal... more The flow stress behavior of OFHC polycrystalline copper was evaluated using cold-rolled and equal channel angular extruded materials. Prior to tensile testing at room temperature, the specimens were heat treated to obtain grain sizes ranging from 3 to 60 µm. The flow stress, when correlated with the square root of true strain, is associated with four stages of hardening. These stages, in terms of increasing strain, are attributed to: (1) dislocation source activation, possibly at annealing twin boundaries during the onset of plastic flow, (2) dislocation slip and cross slip, (3) constriction of the screw dislocation partials for cross slip continuation, and (4) dislocation annihilation and saturation as interpreted through dynamic recovery. The tensile properties and analyses are supported by observations and measurements from orientation imaging and transmission electron microscopy. 

Acta Materialia, 2007

The texture and grain boundary structure of recrystallized materials are dependent upon the chara... more The texture and grain boundary structure of recrystallized materials are dependent upon the character of the deformed matrix and the selective nucleation and growth of crystallites from the deformation structure. Annealing twin boundary formation in materials of low to medium stacking fault energy is not only a product of the recrystallized structure, but also plays an important role in the recrystallization process itself. In situ and ex situ recrystallization experiments were performed on pure copper (99.99% pure) previously deformed by equal channel angular extrusion. Intermittent characterization of the structure on the surface of bulk specimens was accomplished using electron backscatter diffraction. The character of the structure where nucleation preferentially occurs is presumed to be in heavily deformed regions as nuclei were first observed in such microstructures as viewed from the specimen surface. Grain growth is observed to be heavily dependent upon twinning processes at the low temperatures used for in situ experiments, with twinning occurring to aid the recrystallization process. It is shown at these temperatures that the slowest growing grains obtain the highest fraction of twin boundaries as the new twin orientations presumably increase the boundary energy at positions where there is insufficient driving force to continue growth.