Effect of Grain Orientation on Scratch Testing

Machining is complex, high strain-rate and high strain deformation/fracture process. It is also a strong function of the crystal structure of the work piece and its orientation with respect to cutting direction. The effect of crystallographic orientation on cutting forces for single crystal material has been studied by many researchers in the past. However, a study of the same in polycrystal grains and effect of grain boundary (GB) is limited. Hence this work focuses on the effect of grain orientation on forces during scratch experiments on commercially pure aluminum. Heat treatment cycles were applied to grow coarse grains (100-500 um) in the aluminum alloy. The crystallographic structure was determined by Electron Backscatter Diffraction and was used as a basis for scratch experiments. The forces required to perform scratch were measured for different grain orientations and grain boundaries. The measured forces were rationalized based on the underlining grain crystallography and scratch direction.