Effects of Milling Time on Mechanical Properties of Spark Plasma Sintered WC-10wt%Fe3Al cermet

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Abstract
09-063 Luis Antonio Ccopa Ybarra Ybarra, L.C.(Universidade Nove de Julho/Universidade Federal do ABC); Chimanski, A.(Universidade Federal do ABC); Machado, I.F.(Universidade de São Paulo); Yoshimura, H.N.(Universidade Federal do ABC); Cobalt is widely used to produce WC-Co hard metals, but this binder has problems of shortage and unstable price. In this work, cobalt was replaced by an iron aluminide intermetallic binder. WC-10%Fe3Al cermet was prepared by vibration milling of WC, Fe and Al powders and SPSed (spark plasma sintered) at 1150 °C for 8 min under 30 MPa. The milling time was 0.2, 1, 3, 6, 9 and 12 h. The SPS was efficient to consolidate the cermet at low sintering temperature (mostly in solid-state) resulting in relative densities of ~95% or higher. The cermet matrix (binder) was composed of the intermetallic Fe3Al and also by the phase Fe3AlC0.5, as confirmed by X-ray diffraction and scanning electron microscopy. The cermet WC-10 wt% (20 vol%) Fe3Al presented maximum values of hardness and fracture toughness, KIc, in intermediate milling times (in the range of 10 min and 12 h), due to the increase in microstructural homogeneity with elimination of large matrix regions without WC particles. The Vickers hardness values ranged from 9.9 to 14.3 GPa (maximum at 1 h milling time) and the KIc values, determined by indention fracture method, ranged from 18.9 to 25.9 MPa.m1/2 according to the Niihara’s equation and between 14.4 and 18.8 MPa.m1/2 according to Shetty’s equation (maximum at 3 h milling time). The high values of hardness and fracture toughness of the WC-Fe3Al cermet resulted from the good interaction between the intermetallic matrix and the WC grains, since the fracture occurred predominantly in the intergranular mode. Crack deflection and crack bridging were the main toughening mechanisms acting on this cermet.
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