Design and Experiments of an In Situ Scratch Tester inside the Scanning Electron Microscope

The in situ scratch test inside the scanning electron microscope (SEM) could provide more detailed information about the dynamic contact process between the indenter and material surface. However, most of the current in situ scratch testers can only perform qualitative tests, and the normal and lateral forces could not be measured. Accordingly, an in situ scratch tester with the ability to observe the scratching region inside the SEM and simultaneously measure the normal and lateral forces, was developed. It mainly consisted of three identical stick -slip piezoelectric actuators, a specially designed two -axis force sensor and a force feedback control system. The z -directional piezoelectric actuator was used to apply the scratch load and the x -directional piezoelectric actuator was used to realize the scratch motion. The normal and lateral forces were measured by the two -axis force sensor, and the force feedback control system was used to control the normal force for achieving the constant load scratching and linear load scratching modes. The compact structure made it easy to integrate with the SEM. By experiments, the main performances and functions of the proposed in situ scratch tester were characterized. The experimental results indicated that the noises of the normal and lateral forces were both less than 0.1 mN, and the minimum single-step displacements in the indentation and scratch directions were about 8 nm and 34 nm, respectively. The in situ scratch test of Ti6Al4V confirmed the ability of the scratch tester to simultaneously observe the scratching region and measure the normal and lateral forces, by which the correlation between the scratch morphology and lateral/normal forces could be established. Accordingly, this study provides a new tool for the investigation of material flow, chip formation and tool adhesion during ultra -precision machining.