Characterization of the mechanical behavior of wear surfaces on single crystal nickel by nanomechanical techniques
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N.R. Moodyb) Sandia National Laboratories, Livermore, California 94551-0969
S.V. Prasad and J.R. Michael Sandia National Laboratories, Albuquerque, New Mexico 18185
W.W. Gerberich University of Minnesota, Chemical Engineering and Materials Science, Minneapolis, Minnesota 55455 (Received 29 July 2008; accepted 13 October 2008)
In ductile metals, sliding contact induces plastic deformation resulting in subsurfaces, the mechanical properties of which are different from those of the bulk. This article describes a novel combination of nanomechanical test methods and analysis techniques to evaluate the mechanical behavior of the subsurfaces generated underneath a wear surface. In this methodology, nanoscratch techniques were first used to generate wear patterns as a function of load and number of cycles using a Hysitron TriboIndenter. Measurements were made on a (001) single crystal plane along two crystallographic directions, and . Nanoindentation was then used to measure mechanical properties in each wear pattern. The results on the (001) single crystal nickel plane showed that there was a strong increase in hardness with increasing applied load that was accompanied by a change in surface deformation. The amount of deformation underneath the wear patterns was examined from focused ion beam cross-sections of the wear patterns. I. INTRODUCTION
Wear-induced subsurface deformation has been the subject of numerous investigations.1–5 Typically, in work-hardening alloys the high surface strain under sliding contacts leads to the formation of a layered subsurface structure. A hard surface layer is composed of small subgrains and surface dislocation cells and grains that increase in size as the distance increases from the surface.1,5 With the evolution in microstructure and deformation substructures comes a positive hardness gradient moving from the bulk material to the sliding interface.3,4 Previous authors have mostly used metallographic and conventional transmission electron microscope (TEM) specimen preparation techniques to prepare cross-sections of wear surfaces and evaluate the wear-induced deformation and microstructural changes1,4,6–8 or surface-analysis
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Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr_policy DOI: 10.1557/JMR.2009.0075 844
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J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 19 Mar 2015
techniques.9 More recently, focused ion beam (FIB) microscopy and electron backscatter diffraction (EBSD) techniques were used to understand these phenomena in microscale wear tests.2 Although TEM techniques are excellent for examining the grains and dislocation cell structure that are formed by the sliding contact, mechanical properties of the different cell structures and work-hardening regions cannot be easily probed this way. Previous indentatio
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