Materials Science and Engineering A 449–451 (2007) 1045–1048 Redistribution of SnO 2 particles in Ag/SnO 2 materials during rapid solidification Qibin Ye a , Yaping Wang a,b,∗ a Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China b Xi’an Jiaotong University, Xi’an 710049, China Received 21 August 2005; received in revised form 9 January 2006; accepted 24 February 2006 Abstract Melt spinning experiments were performed on Ag–12 wt.% SnO 2 contact materials with and without CuO addition for the purpose of simulating the rapid solidification process of an instantaneously remelted thin surface layer during arcing. The microstructure of the rapidly solidified ribbons was investigated using optical and scanning electron microscopy, and compared with that of the samples subjected to arcing tests. The results evidenced a redistribution of the reinforcement SnO 2 particles during rapid solidification as well as a strong dependence of it on the addition of a small amount of CuO to the starting materials. In CuO-free ribbons, much more of the SnO 2 particles were confined at grain boundaries rather than engulfed in Ag matrix grains. In CuO-doped ribbons, however, the SnO 2 particles were uniformly distributed both inside Ag-matrix grains and at grain boundaries. Additionally, short SnO 2 rods were formed on the surfaces of the CuO-doped ribbons. Similar effects of the addition of CuO were noted for arc-tested samples. The results were discussed with respect to several models dealing with the particle–dendrite interaction during solidification. © 2006 Elsevier B.V. All rights reserved. Keywords: Contact materials; Rapid solidification; Particle redistribution; Arc erosion 1. Introduction The contact material Ag/SnO 2 has shown a promising prospect in applications of low-voltage switches because of its remarkable resistance to arc-erosion and welding during arcing tests [1–3] and its environmentally friendly character- istic. Despite a uniform microstructure in the starting material, a SnO 2 -rich layer is always formed on the arcing surface of Ag/SnO 2 contacts, which increases the contact resistance dra- matically and in turn causes an unfavorable rapid temperature rise. It is therefore of great technical interest to understand the formation of the SnO 2 -rich layer during arcing. Because of high arc energy, the electrode surface is heated instantaneously to the boiling point of the contact material, leading to the occurrence of a remelted thin layer. Upon the quenching of arcs, the remelted layer will be subjected to rapid solidification due to a rapid heat extraction through the unmelted ∗ Correspondence at: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China. Tel.: +86 24 23971872; fax: +86 24 23891320. E-mail address: ypwang@imr.ac.cn (Y. Wang). contact matrix. The SnO 2 -rich layer on the Ag/SnO 2 contacts is believed to form during rapid solidification. However, it has proven difficult to in situ study this instantaneous solidifica- tion process because of extremely short time. Hence, ex situ experiments under simulated experimental conditions have to be considered. In present work, the melt spinning technique was used to simulate rapid solidification of a remelted surface layer of Ag/SnO 2 contact materials. Our choice of the technique was because rapid solidification of the melt-spun material is also sus- tained by highly efficient heat extraction to a chill substrate as is in the post-arcing rapid solidification process. In addition, it has been reported by different researchers [4–7] that the addition of a small amount of CuO to the Ag/SnO 2 contact material can upgrade the performance of the Ag/SnO 2 contact material signif- icantly. Hence, CuO-doped materials were also rapidly solidified using the melt spinning technique. 2. Experimental Pure SnO 2 particles and those doped with 6 wt.% CuO were prepared by using chemical precipitation technique. Then they were mixed with pure Ag powders of a mean size of 6 m 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.02.359