DETECTION OF DUCTILE TO BRITTLE TRANSITION IN MICROINDENTATION AND MICROSCRATCHING OF SINGLE CRYSTAL SILICON USING ACOUSTIC EMISSION

Machining of brittle materials entails two modes of material removal: pure plastic deformation and brittle fracture. The mode of material removal is generally identified by surface quality observations in a scanning electron microscope (SEM) or an atomic force microscope (AFM) after machining. Hence, there is a need for the development of in-process monitoring technology in order to detect whether the mode of material removal is ductile or brittle, and thereby predict surface quality. In the present paper, acoustic emission (AE) is proposed as a means of monitoring the ductile to brittle transition. Microindentation and microscratching tests of single crystal silicon were conducted using an ultrafine-motion table with very small motion error. The obtained AE signals were correlated with crack initiation and the ductile to brittle transition. The critical force f_c defined as the force at which AE was induced during the microindentation and microscratching tests was measured to be 40 ～ 50 mN. AFM observations revealed the critical depth of cut d_c to be 0.20 μm in the microscratching test.