TY - THES

T1 - Production and characterization of particle-stabilized nanocrystalline Cu for high temperature applications

AU - Krämer, Lisa

N1 - embargoed until null

PY - 2014

Y1 - 2014

N2 - The goal of this master thesis is to stabilize nanocrystalline Cu for high temperatures applications. This is tried by stabilizing the Cu-grains with different particles. Eight different materials were deformed with high pressure torsion (HPT), their microstructure was investigated with scanning electron microscopy and their mechanical properties with hardness measurement and tensile tests. Four materials were produced by using powder as initial material (Cu-W, Cu-Y2O3, Cu-Fe and pure Cu) and for the other four materials industrial produced bulk materials were used (three WCu samples with different composition and pure Cu). For powders, a two-step HPT-process was used and the bulk materials were deformed in a single HPT-step. The obtained microstructure was in the range of hundreds of nm for higher applied strain and the influence of additional deformation steps at higher temperatures was investigated. To compare the microstructural stability of different materials at higher temperatures, samples were annealed in a vacuum furnace and in air by inductive heating. Materials produced by powder compaction showed after heat treatment, additional to grain growth, a generation of porosity. Emerging of pores was especially strong for pure Cu, Cu-Y2O3 and Cu-W specimens on which little deformation were applied. If the applied strain was high enough, Cu-W samples showed a good stability at higher temperatures and up to 810 ◦C the microstructure did not change. Industrial produced W-Cu samples also got a good temperature stability after little applied strain. In tensile tests, additions of W and Y2O3 decreased the ductility and the particles agglomerate in the samples, which were produced with powders. This caused an early fracture. The surface of W-Cu tensile samples influenced the fracture behavior as a poor surface quality caused an early fracture. Fe was the only element which influenced positively the behavior in tensile testing and after the proper heat treatment fracture strains in the same range as for Cu-bulk samples could be obtained.

AB - The goal of this master thesis is to stabilize nanocrystalline Cu for high temperatures applications. This is tried by stabilizing the Cu-grains with different particles. Eight different materials were deformed with high pressure torsion (HPT), their microstructure was investigated with scanning electron microscopy and their mechanical properties with hardness measurement and tensile tests. Four materials were produced by using powder as initial material (Cu-W, Cu-Y2O3, Cu-Fe and pure Cu) and for the other four materials industrial produced bulk materials were used (three WCu samples with different composition and pure Cu). For powders, a two-step HPT-process was used and the bulk materials were deformed in a single HPT-step. The obtained microstructure was in the range of hundreds of nm for higher applied strain and the influence of additional deformation steps at higher temperatures was investigated. To compare the microstructural stability of different materials at higher temperatures, samples were annealed in a vacuum furnace and in air by inductive heating. Materials produced by powder compaction showed after heat treatment, additional to grain growth, a generation of porosity. Emerging of pores was especially strong for pure Cu, Cu-Y2O3 and Cu-W specimens on which little deformation were applied. If the applied strain was high enough, Cu-W samples showed a good stability at higher temperatures and up to 810 ◦C the microstructure did not change. Industrial produced W-Cu samples also got a good temperature stability after little applied strain. In tensile tests, additions of W and Y2O3 decreased the ductility and the particles agglomerate in the samples, which were produced with powders. This caused an early fracture. The surface of W-Cu tensile samples influenced the fracture behavior as a poor surface quality caused an early fracture. Fe was the only element which influenced positively the behavior in tensile testing and after the proper heat treatment fracture strains in the same range as for Cu-bulk samples could be obtained.

KW - high pressure torsion

KW - HPT

KW - severe plastic deformation

KW - SPD

KW - nanocrystalline

KW - particle-stabilized

KW - Cu

KW - copper

KW - W

KW - tungsten

KW - Fe

KW - iron

KW - yttria

KW - high temperature application

KW - mechanical properties

KW - High Pressure Torsion

KW - HPT

KW - Severe Plastic Deformation

KW - SPD

KW - nanokristallin

KW - teilchenstabilisiert

KW - Cu

KW - Kupfer

KW - W

KW - Wolfram

KW - Yttriumoxid

KW - Fe

KW - Eisen

KW - Hochtemperaturanwendungen

KW - mechanische Eigenschaften

M3 - Diploma Thesis

ER -