Microtribological/mechanical testing in 0, 1 and 2 dimensions: A comparative study on different materials

Nanomechanical testing can be classified by dimensions of lateral movement of the tip: starting with nanoindentation (0D), followed by scratching and linear oscillating wear (1D) and finally scanning/area wear (2D). In this paper a comparison of theses four techniques is made for three types of materials: AF45 glass (amorphous), silicon (hard, crystalline) and aluminium (soft, crystalline). The morphology of craters, the wear depth and the pile-up characteristic of all types of testing is evaluated as a function of load. While 0D- and 1D testing often result in linear dependence of wear depth as a function of load, 2D testing shows different behaviour: at low loads a low or zero wear rate is found while above a certain threshold wear increases significantly. The analysis of pile-up created at the crater edges shows that the transport of piled-up material out of the crater seems to be the dominant factor for this effect. While below a threshold pile-up is redistributed within the crater (ploughing wear), above the threshold it is moved out of the crater and deposited outside of the scanned area (cutting wear). A critical attack angle is believed to be the decisive factor for the change of wear mode. It has been determined to be 19 ± 2° for all materials. Additionally, for scanning wear (2D) the effect of density of scan lines on the wear depth is compared with multiple scanning the same area. It is found that doubling or quadruplicating the number of scan lines has not the same effect as scanning the same area twice or four times. Again the transport of piled-up material seems to be responsible for this effect.