Fig. 5. STEM EDS map analysis of Z-phase particle observed in specimen strained under IP-TMF loading conditions. Coloured map documents that particle is rich on Cr, Nb, N. On the contrary, Fe, Ni and Cu are highly depleted within the particle volume.
The STEM EDS analysis of the thin foil extracted from the specimen subjected to IP-TEM cycling in Fig. 5 shows the precipitate rich in Cr, Nb and N and significantly depleted of Fe, Ni and Cu. The composition of the particle corresponds to the Z-phase i.e. complex nitride (Cr,Nb)N2, 10 typically found in as-received condition. Thin foil and EDS map analysis in Fig. 6 shows the typical distribution of nanoparticles in the specimen subjected to IPD-TMF cycling. Larger particles contain copper and smaller particles contain niobium. In agreement with previous studies 11, 26 the particles can be identified as a Cu-rich and NbC nanoparticles which precipitated during TMF cycling.
The STEM image of the thin foil and respective EDS analysis map of the specimens subjected to OPD-TMF cycling shows Fig. 7. A high density of fine particles containing copper and still finer particles containing niobium is apparent. Moreover larger particles containing tungsten having lower density were detected.
Linescan performed on one of the large particles within the grain in Fig. 7 is shown in Fig. 8. While W dominates in the precipitate, a rapid decrease in Cu, Ni and Fe content is clearly documented. According to Zurek et al. 28 two diverse W-rich phases can be identified in the interior of the grains as well as on the grain boundaries after high temperature exposure at 700 °C and 750 °C for 3000 h. Tungsten rich carbide of the type (Cr,W)23C6 and/or (Fe,W)6C can be one of these phases and µ-phase Fe7W6 can be the second one. Both phases were found to be located at the grain boundaries and also in the interior of the grains. The same kind of precipitates was observed in specimens exposed to temperature 700 °C for 10 000h.