Nanoscratching - 4 Nanoscratching 4.1 Introduction Scratch...

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4 Nanoscratching 4.1 Introduction Scratch tests are of enormous practical importance. They used to be ap- plied on a macroscopic, microscopic, and nanoscopic scale, the latter with the atomic force microscope (AFM). The most recently emerging development is nanoscratching, using nanoindenters equipped with a two-dimensional (2D) or three-dimensional (3D) transducer. Scratching of surfaces is closely related to the field of tribology, but greasing is to be avoided for original materials characterization. Scratching experiments lead to abrasive wear in the majority of cases. Applications were primarily in macroscratching with foundations in micro- scratching. The industrial importance of macro- and microscratching has been widespread and various different approaches exist for the definition of scratch hardness in the various fields. Thus, the Mohs hardness is a nonlinear scratch hardness still in extended use (DIN EN 101 and DIN EN ISO 1518) and scle- rometers provide relative macroscopic scratch hardness values (DIN EN 438). Architects use grated scratch devices for probing the quality of cement floor- ing. The macroscopic applications compare either the depth of a scratch at a predefined load on varied scratching tools or the limiting load that is needed for a scratch to emerge. But there are also sound emission analyses (upon fail- ure after linear increase of the normal load or during plowing with constant load) in scratch tests. More recently two different definitions of scratch hard- ness H s have been put forward: H s = F L /A N [1] and H s = F N /A L [2] where A N and A L are the projected normal and lateral areas, respectively. The scratch resistance Erichsen, which is used to judge long-term stability, is prescribed in DIN 53799/10. Instrumentation for the study of microscratching wear of metallic materials at high temperatures (room temperature to 1 , 000 C) has also been developed [3]. Several mechanisms have been distinguished primar- ily on the basis of microscratching. Thus, grooving wear is subdivided into various factors that depend both on the materials properties and on the in- denter tip geometry (attack angle). The term plowing has been coined for
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230 4 Nanoscratching largely plastic formation of a permanent ditch with abrasion, pileup to both sides and eventually slip lines away from the scratch direction. The volume of pileup does normally not correspond with the ditch volume as microchipping or brittle removal of dust loses material and these processes may strongly prevail. Additionally, adhesional loss of material (removal of scales from the surface) may be discussed as well as microfatigue upon repeated plowing and cross plowing. The mechanism may change at phase boundaries. In composites with different hardness of the components the softer partner might be abraded while the harder partner may crack out and produce fissures due to pressure enhancement that builds up around it. Also fissuring or microcracking with detachment of larger particles can be very important. These distinctions are
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