Focused ion beam (FIB) preparation is a very helpful tool for getting polished cross sections of defined regions in inhomogeneous samples with complicated shape. Examples are deformed samples of metal matrix composites with metastable zirconia particle reinforcement. The local phase composition depends on the local deformation. Thus, local EBSD phase analysis requires a local preparation tool as FIB. Zirconia appears in three structural modifications. All transformations are martensitic and reversible. The high temperature modifications can be stabilized to room temperature by the addition of suitable oxides as CaO, MgO or Y2O3.The tetragonal to monoclinic transformation is of special technical interest. It is connected with a volume change of 5 -8 % and can be used for the realization of the well-known transformation toughening effect. Mg partially stabilized zirconia (Mg-PSZ) with 8-10 Mol-% MgO and Y-tetragonal zirconia polycrystals (Y-TZP) with 2.5-3.5 Mol-% Y2O3 are used within the present investigations. All different aspects of the interaction between the ion beam and the sample are to be considered. In case of metastable Y-TZP and Mg-PSZ phase transformations were observed after FIB preparation with 30 kV, 30 nA and 5° incidence angle while damage was the dominating effect for angles of 72°. The expected local temperature rise is about 700 K for ZrO2 due to the bombardment with 30 kV, 30 nA Ga+ ions. Thus, the observed phase transformations can be explained on the base of the transformation temperature 700 °C in the corresponding Y-TZP phase diagram. In case of Mg-PSZ the transition temperature is 1083 °C. The local temperature rise is obviously smaller. The excitation energy for the observed phase transformation is smaller than expected from phase diagrams of the thermodynamic equilibrium. Using 5 kV, 4,8 nA and 5° incidence angle no phase transformations and no damage were observed. Thus, these conditions are suited for the FIB preparation of metastable zirconia.
In general it can be concluded that the behavior of each new sample material during focused ion beam preparation has to be investigated separately.
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