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 g enerally 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 i n order to detect whether the mode of material removal is ductile or brittl e, and thereby predict surface quality. In the present paper, acoustic emis sion (AE) is proposed as a means of monitoring the ductile to brittle trans ition. Microindentation and microscratching tests of single crystal silicon were conducted using an ultrafine-motion table with very small motion erro r. The obtained AE signals were correlated with crack initiation and the du ctile to brittle transition. The critical force f(c) defined as the force a t which AE was induced during the microindentation and microscratching test s was measured to be 40 similar to 50 mN. AFM observations revealed the cri tical depth of cut d(c) to be 0.20 mum in the microscratching test.