Machining induced defects in Relaxor ferroelectric PMN-PT crystals

Deng, Cheng
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Aerospace Engineering
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The superior piezoelectric and dielectric properties of the relaxor based piezoelectric single crystals (PMN-PT) render them as prime candidates for Navy sonar detectors as well as broad band medical ultrasonic imaging devices. Production of phased array probes utilizing these types of high performance ceramics requires dicing these crystals to arrays with pitches of less than the desired wavelength, ranging from tens to hundreds of micrometers. However, the relaxor based single crystals are very brittle with fracture toughness of about a third to a half that of typical PZT ceramics ( ). Excessive chipping and cracking, either during the cutting or poling process, have been reported as major hurdles in processing, leading to spurious resonance and degradation of the distance resolution. In addition, residual stress from the cutting process could be major reliability degradation if it is not well quantified and minimized.

In this work, we experimentally analyzed the machining induced damage in a group of Lead Magnesium Niobate-Lead Titanate solid solution single crystal {(1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT)} under simulated process parameters for cutting speeds and down feeds. The machined surfaces are examined by non-contact optical profilometer for planarity and roughness, scanning electron microscopy for subsurface damage, and by micro-raman spectroscopic analysis and X-ray diffraction analysis to uncover machining induced phase transformations. The analysis reveals the preferred process parameters for minimal machining induced damages.