2018 - Sustainable Industrial Processing Summit & Exhibition
4-7 November 2018, Rio Othon Palace, Rio De Janeiro, Brazil
| Properties of a Lean Silver Alloy After Equal Channel Angular Pressing and Conventional Post-deformation Maciej Krystian1; Bernhard Mingler1; Jelena Horky2; Damien Colas3; Frédéric Diologent3; 1AIT AUSTRIAN INSTITUTE OF TECHNOLOGY GMBH, Wiener Neustadt, Austria; 2AIT AUSTRIAN INSTITUTE OF TECHNOLOGY GMBH, Seibersdorf, Austria; 3VARINOR SA, Delémont, Switzerland; PAPER: 353/SISAM/Invited (Oral) SCHEDULED: 12:10/Tue./Copacabana A (150/1st) ABSTRACT: Silver is a soft, precious metal widely used in electronics, medicine, and in the jewellery sector, due to its exceptional properties such as low electrical resistance, antibacterial behaviour, shiny appearance, and resistance to tarnishing. However, final products are usually made of silver alloys to achieve reasonable hardness and strength needed for these kinds of applications. However, alloying is not always the desirable practice, especially in jewellery, as it can reduce tarnishing and corrosion resistance. Therefore, Severe Plastic Deformation is a promising way to improve the mechanical properties [1]. The copper-free silver alloy of the composition Ag 97.2 wt%, In 1.5 wt%, Ge 1.0 wt%, others 0.3 wt% was developed, cast, and cold-drawn. In order to further improve mechanical properties, room-temperature Equal Channel Angular Pressing (ECAP) along with two-step forging (open-die and impression-die forging) and rolling — as two diverse methods of conventional post-deformation — were performed. In this manner, the original grain size of 130 μm was refined to an ultrafine-grained microstructure with mean grain size of 420 nm. Consequently, the combination of ECAP, two-step forging and rolling resulted in outstanding mechanical properties: tensile yield strength of 491 MPa (+355% compared to the as cold-drawn strength), ultimate tensile strength of 550 MPa (+196%), and Vickers hardness of 167 HV1 (+234%). Furthermore, a much more homogeneous hardness distribution over the whole cross-section of the bars was achieved by ECAP. Contrary to some reports on pure silver [2, 3] both, the microstructure and strength remained thermally stable for at least one year at room temperature as well as for at least 100h and 2h at 100°C and 150°C, respectively. Thus, ECAP is able to effectively increase the mechanical properties of this lean silver alloy which exhibits desirable tarnishing and corrosion resistance. References: [1] M. Zehetbauer and R. Valiev (Eds.), Nanomaterials by Severe Plastic Deformation, Wiley-VCH, 2006, ISBN: 978-3-527-60494-4 [2] H. Matsunaga and Z. Horita, Softening and Microstructural Coarsening without Twin Formation in FCC Metals with Low Stacking Fault Energy after Processing by High-Pressure Torsion, Materials Transactions 50 (2009) 1633-1637. doi:10.2320/matertrans.MF200921 [3] Z. Hegedűs, J. Gubicza, M. Kawasaki, N.Q. Chinh, Z. Fogarassy and Terence G. Langdon, The effect of impurity level on ultrafine-grained microstructures and their stability in low stacking fault energy silver, Materials Science and Engineering A 528 (2011) 8694-8699. doi:10.1016/j.msea.2011.08.034 |
