Experimental Investigation and Modelling of Laser Machining of Sapphire for High Temperature Pressure Transducers

摘要

Sensing of pressure at high temperatures is currently limited by melting temperature and the plastic deformation undergone by silicon based technologies due to brittle to ductile transition.1 Sapphire has been proposed as an alternative sensing material that can overcome these temperature limitations using photonic methods. In order to manufacture the sensors, an ultra-short pulsed laser is utilized to machine sapphire as opposed to plasma etching methods used in silicon-based microelectromechanical systems (MEMS) technology. Here we quantify the change in mechanical properties of sapphire due to laser machining. Vicker's indentations were applied to both pristine and laser machined specimens showing that there is a toughening effect due to the machining process. The underlying mechanisms associated with toughening were quantified using transmission electron microscopy (TEM) and a single crystal plasticity model using finite element analysis. The TEM cross-sections illustrated dense sub-surface regions of dislocations only in laser machined specimens. To further understand the toughening, finite element modeling of nanoindentations were conducted and compared with data illustrating complex evolution of the single crystal sapphire material underneath the nanoindent. The modeling and data comparison suggest hardening occurs locally that can be associated with an increase in the elastic properties as well as local damage.