2018 - Sustainable Industrial Processing Summit & Exhibition
4-7 November 2018, Rio Othon Palace, Rio De Janeiro, Brazil
| Optimization of Mechanical and Corrosion Properties of Biodegradable Mg-Zn-Ca Alloys by SPD-Processing and Additional Heat Treatment Michael J. Zehetbauer1; Andrea Ojdanic1; Erhard Schafler1; Jelena Horky2; Bernhard Mingler3; Dmytro Orlov4; 1UNIVERSITY OF VIENNA, Wien, Austria; 2AIT AUSTRIAN INSTITUTE OF TECHNOLOGY GMBH, Seibersdorf, Austria; 3AIT AUSTRIAN INSTITUTE OF TECHNOLOGY GMBH, Wiener Neustadt, Austria; 4LUND UNIVERSITY, Lund, Sweden; PAPER: 424/SISAM/Regular (Oral) SCHEDULED: 17:40/Wed./Copacabana A (150/1st) ABSTRACT: This lecture reports the changes in hardening and corrosion of biodegradable Mg-Zn-Ca alloys caused by HPT-processing and long-term heat treatments, which have been applied in order to strengthen the alloy and to adapt the Younga's modulus of the alloy to that of the human bone, for suitable application as an biodegradable implant material. The structural changes are represented by the evolution of precipitates as well as of deformation induced defects like dislocations and vacancy clusters. The studies aimed to quantify the individual effects of the structural modifications to strength and to corrosion rate, with the final goal to optimize the alloy for the use as biodegradable implants with respect to mechanical properties as well as corrosion rate [1]. The thermomechanical procedure used in this work follows that of Orlov et al. [2] applied to Mg-Zn-Zr alloy ZK60. Both the precipitates as well as the vacancy clusters achieve strength increases; in case of the latter, the Zn atoms act as trapping sites not only for HPT-induced dislocations but also for vacancies. So far, overall increases of strength of up to 250% were reached. Quantitative estimations show that the vacancy clusters contribute far more to the total strength increase than the precipitates. Furthermore, vacancy concentrations of at most 10-5 cause the hardness increase measured [3]; the experimental results, however, exhibited vacancy concentrations till to even 10-3 which means that a significant part of the HPT-induced vacancies stays single and thus does not contribute to hardening. The corrosion rate as well as the Younga's modulus remained unchanged during the processing history consisting of both HPT deformation as well as heat treatments, thus making these alloys a very attractive biodegradable material. This work has been supported by projects J2-7157 of the Slovenian Research Agency ARRS, and I2815-N36 of the Austrian Science Fund FWF. References: [1] Hofstetter J., Becker M., Martinelli E., Weinberg A.M., Mingler B., Kilian H., Pogatscher S., Uggowitzer P.J., Loeffler J.F. (2014) JOM, 66, 566-572 [2] Orlov D., Pelliccia X., Fang L., Bourgeois L., Kirby N., Nikulin A.Y., Ameyama K., Estrin Y. (2014) Acta Mater. 72, 110-124 [3] Kirchner H.O.K. (1976) Z.Metallk. 67, 525-532 |
