TY - THES

T1 - Aspects of grain refinement in copper alloys

AU - Cziegler, Andreas

N1 - embargoed until 16-04-2020

PY - 2015

Y1 - 2015

N2 - The purpose of this work was to investigate the grain refinement mechanism of copper alloys. The literature review showed that the grain refinement of copper and copper alloys seems to be a complex mechanism that is strongly dependent on the alloy system, the range of the alloying elements, the impurities and the casting conditions. As grain refinement depends on nucleation and growth restriction the growth restriction factors of the alloying elements of the copper-system were calculated using binary phase diagrams. A comprehensive list containing 63 alloying elements ranked according to their growth restriction factor was given. It was shown that phosphorus is the most powerful segregant in the copper-system, followed by beryllium and lithium. In addition to the growth restriction factor suitable nucleation sites for copper alloys were examined. More than 1000 compounds were observed according to their lattice disregistry to the copper lattice with a focus on binary compounds. Regarding the lattice disregistry and the melting point it was shown that SrO, ZrO2 and BN are the most suitable compounds acting as nucleants in copper alloys. Based on the calculation of the growth restriction factor melting experiments were carried out to validate the influence of the addition of tin, zinc, phosphorus, magnesium and iron on the variation of the grain size of high purity copper. The addition of phosphorus was found to decrease the grain size, whereas the addition of tin, zinc, magnesium and iron was found to increase the grain size. The variation of the grain size is assumed to be of a complex interaction between the growth restriction factor, and its effect on constitutional undercooling and growth restriction by influencing the growth velocity and therefore latent heat release, and the cooling rate. Furthermore, the cooling rate is assumed to be affected to a great extent by the decrease of thermal conductivity of the columnar zone at the mould and by the variation of latent heat release with increasing solute content.

AB - The purpose of this work was to investigate the grain refinement mechanism of copper alloys. The literature review showed that the grain refinement of copper and copper alloys seems to be a complex mechanism that is strongly dependent on the alloy system, the range of the alloying elements, the impurities and the casting conditions. As grain refinement depends on nucleation and growth restriction the growth restriction factors of the alloying elements of the copper-system were calculated using binary phase diagrams. A comprehensive list containing 63 alloying elements ranked according to their growth restriction factor was given. It was shown that phosphorus is the most powerful segregant in the copper-system, followed by beryllium and lithium. In addition to the growth restriction factor suitable nucleation sites for copper alloys were examined. More than 1000 compounds were observed according to their lattice disregistry to the copper lattice with a focus on binary compounds. Regarding the lattice disregistry and the melting point it was shown that SrO, ZrO2 and BN are the most suitable compounds acting as nucleants in copper alloys. Based on the calculation of the growth restriction factor melting experiments were carried out to validate the influence of the addition of tin, zinc, phosphorus, magnesium and iron on the variation of the grain size of high purity copper. The addition of phosphorus was found to decrease the grain size, whereas the addition of tin, zinc, magnesium and iron was found to increase the grain size. The variation of the grain size is assumed to be of a complex interaction between the growth restriction factor, and its effect on constitutional undercooling and growth restriction by influencing the growth velocity and therefore latent heat release, and the cooling rate. Furthermore, the cooling rate is assumed to be affected to a great extent by the decrease of thermal conductivity of the columnar zone at the mould and by the variation of latent heat release with increasing solute content.

KW - copper alloys

KW - grain refinement

KW - growth restriction

KW - nucleation sites

KW - Kupferlegierungen

KW - Kornfeinung

KW - Wachstumsbehinderung

KW - Keimstellen

M3 - Master's Thesis

ER -