PSI - Issue 20

Fedorov M. V. et al. / Procedia Structural Integrity 20 (2019) 206–211

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Fedorov M. V. et al. / StructuralIntegrity Procedia 00 (2019) 000–000

Fig. 3. The surface of specimens (see. Tab.1) after impact-abrasive wear; magnification is x30.

Macrographs of the fracture surface of the cutting edge of hard-alloy with a magnification of x30 are shown in Fig. 3. The fracture surfaces of all specimens are similar: they have stepped surfaces with different heights (depths) due to the removal of particles. Surface morphologies show differences in the mechanisms of fracture depending on the composition of the specimens studied. Fractographic studies of fracture on a TM3030 microscope have established that the developed structure found consists of fragments of particles of tungsten carbide in cobalt and voids. The voids are traces of tearing up a cluster (agglomerate) of WC particles by chipping. Micrographs of the fracture region of the specimens without additives and with the addition of magnesium spinel and silicon carbide are shown in Fig. 4. Micrographs of fractures of the specimen without additives represent a multi-grain structure consisting of the prevailing large grains, it indicates brittle fracture, see Fig. 4a. Also there are large regions of the surface with clearly defined grain boundaries with large crests of separation and smaller grain sizes. Fractures in specimens with ultrafine additives of magnesium spinel are characterized by quasi-brittle fracture. Ultrafine magnesium spinel additives are inhibitors of the growth of WC grains, which is reflected in Fig. 4b as the presence of grains with small sizes in the structure. Separation ridges were found on the grains, indicating plastic deformation, i.e., an increase in the resistance to fracture. The fracture is quasi-brittle, since radial scars come from the center of the grain, and there are elements on the surfaces of fractures that crystallized at the last moment of crystallization. The pronounced outlines of grains also indicate the existence of an intergranular fracture mechanism.

Fig. 4. Fragments of fractures of the specimens: (a) initial composition No. 0; (b) with the addition of magnesium spinel; (c) with the addition of silicon carbide; magnification is x10000.