Peculiarities of obtaining cutting tool material based on nanodispersed powders by electric sintering

The article is devoted to the production of tool ceramics from nanodispersed powders of Al2O3–WC by hot vacuum pressing and the study of their properties. The cutting material is obtained by hot pressing by direct transmission of electric current. The developed cutting material is characterised by high physical and mechanical properties, the absence of fusible components that could reduce high-temperature strength, and fracture toughness. In addition, it shows high efficiency in the processing of high-hard steels and ceramics, has high hardness, strength of interfacial and intergranular boundaries, high dispersion and uniform distribution of structural components, and a minimum size of defects that could be sources of fracture. Comparative studies of various cutting ceramic materials show that the main reasons for the high wear resistance of oxide-carbide ceramics, in particular the resulting nanocomposite, in steel processing are their fine-grained structure, as well as the substructural and dispersed strengthening mechanism. In white Al2O3 ceramics, the grains contain dislocations, i.e., the grains are not capable to store the deformation energy, which results in microfracture of Al2O3 grains in the surface layers of the tool. It follows that an increase in the resistance to brittle fracture of oxide-carbide ceramics and the stability of its cutting properties could be achieved by reducing the grain size of the matrix, which is observed when using additives in the form of carbides (TiC, WC, SiC). It was found, the optimal sintering temperature of the mixture under pressure is equals to 1600 °C. At a temperature of 1550 °C, the holding time is not sufficient, and at 1650 °C, the temperature of the Al2O3–WC interfacial interaction is exceeded, which could lead to the formation of CO and closed porosity. The pressing pressure is limited by the characteristics of graphite and equals 50 MPa. The maximum pressure is applied only when the maximum pressing temperature is reached to complete degassing of sorbed gases. It has been determined that the grain size of the structural components of ceramics in the range of 2...5 µm is not optimal and is formed not during the sintering process, but during the preparation of the mixture for hot pressing.