Evidence for the formation of distorted nanodomains involved in the phase transformation of stabilized zirconia by coupling convergent beam electron diffraction and in situ TEM nanoindentation

Abstract

The transformation of zirconia from its tetragonal to its monoclinic phase is an important feature of the zirconia system. First found to be an advantage due to its important toughening effect, it can also be very detrimental when it occurs in the framework of low-temperature degradation, particularly in the case of biomaterial applications. One way to avoid or to control this phase transformation is to understand how it initiates and more particularly the stress states that can trigger it. A new technique available inside a transmission electron microscope (TEM) seems to be particularly well suited for that type of study: Convergent Beam Electron Diffraction (CBED), a well-known technique to reveal stresses, was coupled to in situ TEM mechanical nanoindentation. The experiments reveal the presence of sheared nano-regions at grain boundaries. These could act as embryos for tetragonal-to-monoclinic phase transformations. This is an important first step in the understanding of the earliest stage of zirconia phase transformation.

Transformation toughening in an antiferroelectric ceramic

“…Ceramics are intrinsically prone to fracture [1], and toughening is always desired for structural as well as functional applications [2][3][4][5]. Among the various toughening mechanisms reported in monolithic ceramics, phase-transition toughening demonstrated in ZrO 2 -based ceramics is probably the most effective one [4].…”

A global investigation intoin situnanoindentation experiments on zirconia: from the sample geometry optimization to the stress nanolocalization using convergent beam electron diffraction

“…This splitting may be explained by the presence of nano‐twinned zones premonitory at the zirconia structural transformation. A more specific study of the origin of this splitting is presented elsewhere (Calvié et al , 2012). Nevertheless, from these results, it can be stated that stresses are responsible for the splitting because they introduce a curvature or local modifications of lattice planes.…”

“…Then the beam was focused and the convergence angle gradually increased to get a whole CBED pattern with Bragg lines easily indexed from the SAED pattern. The acquisition and indexation procedure is described elsewhere (Calvié et al , 2012).…”

Mechanical Properties of Nanoparticles: Characterization byIn situNanoindentation Inside a Transmission Electron Microscope

“…Stresses can also be experimentally determined from the convergent beam electron diffraction (CBED) patterns [19]. This technique has recently been used to highlight the nanodomains that can act as embryos during the phase transformation in zirconia [20].…”