Metal Matrix Composites (MMCs) consisting of an austenitic steel with the TRIP effect as the metallic component and PSZ as the ceramic component are designed as new construction materials for special applications, in which a high energy absorption is necessary. [1][2] Zirconia can be partially stabilized (PSZ) at room temperature by the addition of e.g. MgO, CaO, Y 2 O 3 to form tetragonal stabilized zirconia (t-ZrO 2 ) and cubic stabilized zirconia (c-ZrO 2 ). [3] Analytical transmission electron microscopy (TEM) has been effectively used in many investigations of bulk PSZ [3][4] and PSZ thin films on different substrates such as Si wafers, glass, stainless steel. [5][6][7][8] McComb compared t-ZrO 2 and c-ZrO 2 with monoclinic ZrO 2 using analytical TEM in his study. [3] Information about the metastable phases of ZrO 2 can be obtained from the shape of the electron energy-loss spectra. [3] Backhaus-Ricoult studied (La,Sr)MnO 3 -3YSZ (yttrium oxide stabilised zirconia) interface in composite cathode using analytical TEM. [4] Cavallaro et al. investigated multilayers containing YSZ [6] and Chraska et al. [7] analysed plasma sprayed YSZ layers on stainless steel substrate using analytical TEM, too. In a previous study, [8] it was shown using the transmission electron microscopy with high resolution (HRTEM) that the cubic form of ZrO 2 can be stabilized by the local heteroepitaxy between the austenitic steel and the intrinsically non-stabilized zirconia. Later on, this finding was supported by the ab initio calculation based on the density functional theory, which verified a possible chemical bonding at a doped Fe/ZrO 2 interface. [9] In this study we summarise the results of TEM investigations of phenomena on the interface between PSZ and TRIP steel in PSZ thin films deposited on TRIP steel substrates (model system) and in bulk sample prepared via Spark Plasma Sintering (SPS). The zirconia in the samples was partially stabilized with Y 2 O 3 in the thin films and with MgO in the SPS sample. The microstructure of the thin films was investigated in the as-deposited state (sample #1) and after deformation with the aid of a four-point bending device (sample #2). In more details, the microstructure of three samples was investigated on the micro-and nanoscale using TEM with HRTEM and STEM. EDX and EELS in STEM were executed for the local analysis of chemical composition and the phase analysis on the interface between PSZ and TRIP steel at the nanoscale.
ExperimentalFor the investigation of interfaces between TRIP steel and PSZ using TEM, three samples were prepared. Two samples were deposited as thin films of (Zr,Y)O 2 on TRIP steel substrates by magnetron sputtering. The first sample (sample #1) was used to prove, whether the stabilised phase c-ZrO 2 can be deposited on the steel substrate by magnetron sputtering. The second sample (sample #2) was prepared for a bending test and subsequent microstructure characterization in order to investigate defect microstructures near the interfaces and possible phase transformatio...