Effect of mechanical activation of WC-based powder on the properties of sintered alloys

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 1 2021 b) heating from 800 °C to a sintering temperature of 1400 °C at a speed of 5 °C/min; c) exposure at the sintering temperature for 60 minutes; d) furnace cooling from the sintering temperature to room temperature. The sintered samples were polished with diamond pastes of different dispersion. Metallographic analysis was performed using a Labomet-I microscope (Russia). The morphology of the powder particles and the microstructure of the sintered samples were studied by scanning electron microscopy (SEM) using a TESCAN VEGA3 SBH microscope. To determine the structure and phase composition of the studied samples, the methods of X-ray diffraction and X-ray phase analysis were used. X-ray images were obtained using a DRON-3 diffractometer (Russia) with CuK  radiation, the exposure to each point provides a statistical accuracy of at least 0.5 %. The parameters of the crystal lattice were determined using a program for X-ray diffraction calculations. The size of the coherent scattering region (SC R) was calculated using the Scherrer equation [23] for the fi rst line of X-ray spectra, the microdisorsion value [24] was calculated using the Stock-Wilson formula for the last distinguishable line of X-ray spectra. For the calculation, the full width at half the maximum (FWHM) for each phase was determined. The diffraction pro fi les were approximated using the Lorentz function spectra. The hardness of the sintered samples was measured on a Duramin 5 hardness tester (Denmark) at a load of 2 kg. Results and discussion Fig. 1 shows SEM images of powders in the initial state ( a ) and after mechanical activation for 30 s ( b ) and 300 s ( c ). In the initial state of the powder, there are agglomerates with a size of 350 ± 45 μ m, which consist of small particles with a size of 7 μ m. Mechanical activation leads to a decrease in the size of particles and agglomerates. Thus, the powder mechanically activated for 30 s consists of single agglomerates of 40 ± 10 μ m with fi ne particles of 2 μ m in its composition, and the powder after mechanical treatment for 300 s consists of agglomerates with an average size of 15 ± 5 μ m containing fi ne particles of 1.4 μ m. The shape of the particles does not change during mechanical activation and is close to spherical. Figure 2 shows XRD patterns of powders at different times of mechanical activation. The re fl ections of WC and W 2 C phases are seen on all XRD patterns. As the mechanical activation time increases, all the diffraction peaks of the phases widen. Additionally, the treatment for more than 100 s results in a broad component observed in the XRD patterns, which indicates the formation of an X-ray amorphous phase with a relative content up to 15 ± 5 % when treating the powder for 300 s. These results are consistent with [17], where an X-ray amorphous phase is also formed in WC-10Co-0.8VC-0.2Cr 3 C 2 powder after treatment. The a b c Fig. 1. SEM images of the powders: the initial state ( a ); after ball milling for 30 ( b ) and 300 s ( c )