TY - THES

T1 - An Attempt to Create Amorphous Intergranular Films in Nanocrystalline Cu-Zr Using High-Pressure Torsion

AU - Schaffar, Gerald Josef Kamillo

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - Recently it has been reported that amorphous intergranular films (AIFs) can be generated by segregation of zirconium to the grain boundaries during high temperature annealing of a nanocrystalline Cu-Zr solid solution. These AIFs seem promising to enhance the ductility of the nanocrystalline material. In addition, an outstanding thermal stability beyond a homologous temperature of 0.9 has been reported for the nanocrystalline Cu-Zr alloy. Therefore, the nanocrystalline structure could be retained during the heat treatment. Thus, AIFs could be an interesting concept for materials combining both, high strength, and ductility. However, the feasibility of this approach has so far only been proven on sputter deposited thin films and high energy ball milled powders. This motivated to transfer the idea to bulk samples, introducing a supersaturated solid solution of zirconium in copper by applying high pressure torsion (HPT) directly to arc-molten Cu-Zr samples. Different processing parameters were tested and their effect on the microstructural evolution was evaluated. The most promising route for forcing zirconium into solid solution was found to be a two-step HPT process. The sample is first deformed at 300°C to co-deform copper and the intermetallic phase, followed by further deformation at room temperature. However, the outstanding thermal stability previously reported could not be reproduced with any of the HPT processed samples. Grain coarsening occurred in most of the sample volume before the required temperatures for the generation of AIFs were reached. This could be a consequence of nanoscale intermetallic particles still present in the matrix after deformation, presumably acting as seeds for coarsening of the intermetallic phase during annealing. These seed particles, or the lack of a sufficient amount of growth resistant grain boundary pinning particles, may account for this grain coarsening.

AB - Recently it has been reported that amorphous intergranular films (AIFs) can be generated by segregation of zirconium to the grain boundaries during high temperature annealing of a nanocrystalline Cu-Zr solid solution. These AIFs seem promising to enhance the ductility of the nanocrystalline material. In addition, an outstanding thermal stability beyond a homologous temperature of 0.9 has been reported for the nanocrystalline Cu-Zr alloy. Therefore, the nanocrystalline structure could be retained during the heat treatment. Thus, AIFs could be an interesting concept for materials combining both, high strength, and ductility. However, the feasibility of this approach has so far only been proven on sputter deposited thin films and high energy ball milled powders. This motivated to transfer the idea to bulk samples, introducing a supersaturated solid solution of zirconium in copper by applying high pressure torsion (HPT) directly to arc-molten Cu-Zr samples. Different processing parameters were tested and their effect on the microstructural evolution was evaluated. The most promising route for forcing zirconium into solid solution was found to be a two-step HPT process. The sample is first deformed at 300°C to co-deform copper and the intermetallic phase, followed by further deformation at room temperature. However, the outstanding thermal stability previously reported could not be reproduced with any of the HPT processed samples. Grain coarsening occurred in most of the sample volume before the required temperatures for the generation of AIFs were reached. This could be a consequence of nanoscale intermetallic particles still present in the matrix after deformation, presumably acting as seeds for coarsening of the intermetallic phase during annealing. These seed particles, or the lack of a sufficient amount of growth resistant grain boundary pinning particles, may account for this grain coarsening.

KW - Hochdrucktorsion

KW - HPT

KW - Kupfer

KW - Zirkonium

KW - nanokristallin

KW - intergranulare Filme

KW - high-pressure torsion

KW - HPT

KW - copper

KW - zirconium

KW - nanocrystalline

KW - intergranular films

M3 - Master's Thesis

ER -