| Summary: | The present thesis provides thorough investigations on the industrial fabrication of hot-rolled ZnCuTi sheets regarding the continuous casting process, the subsequent thermal treatment and the final hot rolling process. As an additional, more fundamentally aimed investigation along with a possible application in the field of bioabsorbable stents, the same bulk ZnCuTi alloy was highly deformed by high-pressure torsion in order to provoke the formation of an ultra-fine grained microstructure exhibiting extraordinary strength.
The key outcome of the investigations on the commercial production of hot-rolled ZnCuTi was the determination and semi-empirical quantitative description of the predominant microstructure forming mechanism during hot working. The coarse grained solidification structure issued from the continuous casting process is not significantly influenced by the applied industrial thermal treatment, but strongly modified by continuous dynamic recrystallization during hot rolling. The initiation and saturation state of recrystallization were empirically determined by flow curve analysis of laboratory compression tests as a function of the deformation parameters. The analytically predicted re-crystallization behaviour was successfully validated by microstructure analysis of samples processed both in the laboratory and in the industrial line covering a wide range of hot working parameters. Additional measurements of the development of the recrystallized grain size have completed the observations on the hot working behaviour of ZnCuTi. Microstructure properties of the hot-rolled end product can now be adjusted by making use of the developed predictions.
The prospective application of low-alloyed Zn as bioabsorbable implant was driven ahead through investigations on severe plastic deformation of ZnCuTi. The comparison of HPT deformed ZnCu and ZnCuTi demonstrated that the TiZn16 intermetallic phase particles present in ZnCuTi enable the development of an UFG structure, which exhibits twice the hardness of the CG state. This approach could be used to process strengthened stents composed of Zn alloyed with small amounts of Ti. Indeed, further questions like ductility and workability of the UFG structured alloy have to be clarified, but the results open a new avenue for processing extraordinary strong, low-alloyed zinc alloys.
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