Tribo-induced melting transitions and internal friction at magnetic and nonmagnetic asperity contacts

We report a study of tribo-induced nanoscale surface melting mechanisms that employs a combined QCM-STM technique [1] for a range of Au and Au-Ni alloys with varying compositional percentages and phases [2]. A transition from solid-solid to solid-``liquid like'' contact was observed for most samples at sufficiently high asperity sliding speeds. Pure gold, solid-solution and two-phase Au-Ni (20 at.{\%} Ni) alloys were compared [3]. Samples with 5-20{\%} nickel alloyed with gold were deposited as a homogenous solid-solution or as a two-phase FCC solid through the modification of annealing procedures. The solid solution is known to be paramagnetic for concentrations below 35{\%} Ni while the two phase solid maintains domains of ferromagnetism within bulk gold. A ``flexing'' effect associated with the application of an external magnetic field on the two-phase alloy samples illuminates physical mechanisms that correlate with the observed tribo-induced melting temperatures [4].\\[4pt] [1] B. D. Dawson, S. M. Lee, and J. Krim, Phys. Rev. Lett. 103, 205502 (2009).\\[0pt] [2] L. Pan, Ph.D. Thesis, North Carolina State University (2011).\\[0pt] [3] Zhenyin Yang; Lichtenwalner, D.J.; Morris, A.S.; Krim, J.; Kingon, A.I, Journal of Microelectromechanical Systems, April 2009, Volume: 18 Issue:2, 287-295.\\[0pt] [4] K. Stevens, L. Pan and J. Krim, (2014) submitted