Characterization of Reinforced Metal Composites

A technique with several steps was applied to produce the reinforced specimens. This technique is schematically presented in Figure 1 and Figure 2. Commercial powders of WC powders (99.0 wt.% purity) and Fe (99.0 wt.% purity), from Alfa Aesar, ThermoFisher (Kandel, Germany) GmbH were used to produce green compacts to be inserted in the mold cavity. First, the morphology and granulometric distribution of the powders were characterized by scanning electron microscopy (SEM), using a FEI QUANTA 400 FEG (FEI Company, Hillsboro, OR, USA) with an energy-dispersive detector (EDS) and dynamic light scattering (DLS, Laser Coulter LS230 granulometer, Beckman Coulter, Inc., Brea, CA, USA). In the second step, the WC and Fe powders were mixed in a volume fraction of 40:60, which, according to the literature, is within the range that it is expected to guarantee the best wear performance. The mixture was homogenized in Turbula shaker-mixer (Willy A. Bachofen AG, Muttenz, Switzerland) for 7 h, and bound with sodium silicate (1.5 mL). Then, the mixture was uniaxially cold-pressed at approximately 70 MPa in a metallic mold to produce green compacts with dimensions of 31 mm × 12 mm × 7 mm. SEM analysis was performed to study the characteristics of both the powder mixtures and the green compacts. The composition of the mixture was selected from data the literature.
In the final step, the green compacts were inserted in the mold cavity, and the high-chromium white cast iron, melted in a medium frequency induction furnace with a capacity of up to 1000 kg, was poured at a temperature of 1460 °C. The nominal chemical composition of the base metal (see Table 1) was analyzed by optical emission spectrometry (MAXx LMM05, Spectro, Germany).
A cross-section of the specimen was cut by wire electrical discharge for visual control of the inner zones of the composite and the bonding between the composite and the base metal. Metallographic samples were prepared and etched with Beraha-Martensite reagent. The microstructure was characterized by optical microscopy (OM) using a Leica DM 4000M with a DFC 420 camera (Leica Microsystems, Wetzlar, Germany) and SEM secondary electron (SE) and backscattered electron (BSE) image. Electron backscatter diffraction (EBSD) analysis has been used to assist with phase identification. The data obtained from EBSD were submitted to a dilation clean-up procedure, using a grain tolerance angle of 15° and the minimum grain size of 10 points, to avoid inaccurate predictions.
A detailed characterization of the phases formed was performed in transmission electron microscopy (TEM) using a JEOL 2100 (JEOL Ltd., Akishima, Tokyo) operated at 200 keV. For that, thin foils were prepared in a dual-beam focused ion beam (FIB) FEI Helios NanoLab 450S (FEI Company, Hillsboro, OR, USA). On TEM, the phases were fully identified through selected area electron diffraction (SAED). X-ray diffraction (XRD, Cu Kα radiation, Bruker D8 Discover), with a scanning range (2θ) of 20° to 100°, was used to complement the characterization of the phases.