Micropillar compression inside zirconia degraded layer

Abstract

In the dental field, Yttria-doped Tetragonal Polycrystalline Zirconia (Y-TZP) plays an important role due to its high mechanical properties, good aesthetics and bio-inert behavior. Surface mechanical properties are crucial for Y-TZP especially when it comes to osseointegration or contact loading, since it may undergo a spontaneous aging phenomenon when exposed to humid environment, creating a thin degraded layer that affects surface integrity. In this work, polished samples of Y-TZP have been artificially aged, and micropillars with diameters in the range 3.3 μm -0.3 μm have been milled by FIB inside the degraded layer and in the reference non-aged surface. Reproducible stress-strain curves were obtained by testing the micropillars in compression, demonstrating that this technique is suitable for assessing the degraded surface properties. Mechanical and failure behavior are significantly different for the degraded micropillars due to the presence of microcracks, while important differences are observed when reducing the micropillar diameter.

Size and plasticity effects in zirconia micropillars compression

“…The observed behavior is completely different for micropillars extracted from the monoclinic surface layer that forms on 3Y-TZP after hydrothermal degradation, which present extensive microcracking, as was reported in a previous work [47]. The slope of the linear part of loading curves in monoclinic degraded micropillars is less than half that of non-cracked tetragonal micropillars, due to the large population of orientated microcracks at the grain boundaries.…”

“…The slope of the linear part of loading curves in monoclinic degraded micropillars is less than half that of non-cracked tetragonal micropillars, due to the large population of orientated microcracks at the grain boundaries. Even though the unloading slope at the peak stress in loadingunloading tests of degraded micropillars also increased slightly with the peak stress, the slope change was associated to the variation in load-transfer area due to the closure of increasing fractions of cracks under the applied stress [47].…”

High temperature deformability of ductile flash-sintered ceramics via in-situ compression

“…The area of the hysteresis loop tends to increase as stress and strain both increase. The appearance of hysteresis loops may be attributed to reverse transformation and reopening of closed pores in the flash-sintered 3YSZ 49 . The pillar after the cyclic loading test experiences 1% plastic strain, but still does not exhibit cracks as can be seen in Fig.…”

Granular shape memory ceramic packings

“…This is a key challenge with these materials. Practical SMCs are therefore most likely to involve small specimen length scales and few grains [6,24,25], so that when the transformation happens it is unconstrained and the transformation mismatch is accommodated at free surfaces. Lai et al [6] first showed that in small zirconia micropillars with very few grains (i.e., oligocrystals or single crystals), the mismatch stresses associated with the transformation could be relieved at the pillar surfaces, permitting recoverable strains as high as ~7-8%.…”