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Papers by Aaron Kueck

Research paper thumbnail of On phase transformation models for thermo-mechanically coupled response of Nitinol

Research paper thumbnail of In situ manipulation of cooling rates during planar-flow melt spinning processing

... Through a correlation of cooling rates and SDAS, it is shown that the unmodified ribbon has a... more ... Through a correlation of cooling rates and SDAS, it is shown that the unmodified ribbon has an average cooling rate similar to that measured macroscopically. The cooling rate underneath a laser dimple is estimated to be six times slower near the contact surface. ...

Research paper thumbnail of Atomic-Resolution Imaging of the Nanoscale Origin of Toughness in Rare-Earth Doped SiC

Nano Letters, 2008

Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to i... more Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to investigate the origin of the toughness in rare-earth doped silicon carbide (RE-SiC) by examining the mechanistic nature of the intergranular cracking events which we find to occur precisely along the RE-decorated interface between the SiC grains and the nanoscale grain-boundary phase. We conclude that, for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with judicious choice of rare-earth elements.

Research paper thumbnail of Two-stage sintering inhibits abnormal grain growth during β to α transformation in SiC

Journal of the European Ceramic Society, 2008

ABSTRACT Free sintering of SiC with Al, B, and C additions in two successive stages, first under ... more ABSTRACT Free sintering of SiC with Al, B, and C additions in two successive stages, first under nitrogen and then under argon, produced a near full-density ceramic with equiaxed grain structure. The β to α transformation proceeded to completion; however, the grain shape remained equiaxed due to the action of nitrogen present during the first stage of sintering. It is found that the β to α transformation is necessary but not sufficient for producing the microstructure of interlocking plates found in high-toughness SiC.

Research paper thumbnail of Atomic-scale imaging and the effect of yttrium on the fracture toughness of silicon carbide ceramics

Acta Materialia, 2010

In SiC sintered with Al, B and C additions (ABC-SiC), the presence of Y in the Al-Si-O-C grain-bo... more In SiC sintered with Al, B and C additions (ABC-SiC), the presence of Y in the Al-Si-O-C grain-boundary phase leads to less frequent crack deflection and lower toughness. When Y is absent from the grain-boundary phase and remains in the triple pockets, crack deflection is restored, and higher toughness results from grain-bridging mechanisms. The observations are consistent with elastic modulus changes in the intergranular phase, which depend on their yttria and silica content, and indicate that these can play an important role in determining crack deflection. While high-toughness ceramics such as ABC-SiC and Si 3 N 4 rely on sintering additives forming crack-deflecting intergranular films, the present case is a striking example where the presence of a segregant in the grain boundary promotes transgranular fracture by raising the modulus of the nanoscale intergranular grain-boundary film.

Research paper thumbnail of On phase transformation models for thermo-mechanically coupled response of Nitinol

Research paper thumbnail of In situ manipulation of cooling rates during planar-flow melt spinning processing

... Through a correlation of cooling rates and SDAS, it is shown that the unmodified ribbon has a... more ... Through a correlation of cooling rates and SDAS, it is shown that the unmodified ribbon has an average cooling rate similar to that measured macroscopically. The cooling rate underneath a laser dimple is estimated to be six times slower near the contact surface. ...

Research paper thumbnail of Atomic-Resolution Imaging of the Nanoscale Origin of Toughness in Rare-Earth Doped SiC

Nano Letters, 2008

Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to i... more Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to investigate the origin of the toughness in rare-earth doped silicon carbide (RE-SiC) by examining the mechanistic nature of the intergranular cracking events which we find to occur precisely along the RE-decorated interface between the SiC grains and the nanoscale grain-boundary phase. We conclude that, for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with judicious choice of rare-earth elements.

Research paper thumbnail of Two-stage sintering inhibits abnormal grain growth during β to α transformation in SiC

Journal of the European Ceramic Society, 2008

ABSTRACT Free sintering of SiC with Al, B, and C additions in two successive stages, first under ... more ABSTRACT Free sintering of SiC with Al, B, and C additions in two successive stages, first under nitrogen and then under argon, produced a near full-density ceramic with equiaxed grain structure. The β to α transformation proceeded to completion; however, the grain shape remained equiaxed due to the action of nitrogen present during the first stage of sintering. It is found that the β to α transformation is necessary but not sufficient for producing the microstructure of interlocking plates found in high-toughness SiC.

Research paper thumbnail of Atomic-scale imaging and the effect of yttrium on the fracture toughness of silicon carbide ceramics

Acta Materialia, 2010

In SiC sintered with Al, B and C additions (ABC-SiC), the presence of Y in the Al-Si-O-C grain-bo... more In SiC sintered with Al, B and C additions (ABC-SiC), the presence of Y in the Al-Si-O-C grain-boundary phase leads to less frequent crack deflection and lower toughness. When Y is absent from the grain-boundary phase and remains in the triple pockets, crack deflection is restored, and higher toughness results from grain-bridging mechanisms. The observations are consistent with elastic modulus changes in the intergranular phase, which depend on their yttria and silica content, and indicate that these can play an important role in determining crack deflection. While high-toughness ceramics such as ABC-SiC and Si 3 N 4 rely on sintering additives forming crack-deflecting intergranular films, the present case is a striking example where the presence of a segregant in the grain boundary promotes transgranular fracture by raising the modulus of the nanoscale intergranular grain-boundary film.

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