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  • The existing experimental data on the structure of

    2018-10-22

    The existing experimental data on the structure of particle-binder interfaces show that these areas contain a significant amount of secondary dispersed particles of titanium carbide (with the size of 50 ÷ 100 nm) [1,7,38]. The volume content of this particles decreases with the increase in distance from particle surface to the bulk of binder. In the paper, this factor is considered using so-called multiscale approach. In the framework of this approach, the elements of the internal structure of the composite at the mesoscopic scale (binder, primary particles TiC and wide interphase boundaries) are taken into account explicitly. Taking into account structural elements of lower scales (in particular, the presence of secondary titanium carbide nanoparticles in the interphase boundaries) is carried out by considering the structural models of lower scales (in this case the submicron scale) with explicit prestoring concentrations, sizes and spatial distribution of nanoscale elements. On the met inhibitor of analysis of simulation results of mechanical tests of submicron-sized samples their integral mechanical (including rheological) properties are determined. In the subsequent, they are used as input data for cellular automata modeling composite response at the mesoscopic scale. Thus, using of the multiscale approach allows to obtain the dependence of mechanical properties of the interphase boundaries on local concentration of the nanoparticles of the carbide phase. The influence of the width of interphase boundaries on the integral mechanical characteristics of metal–ceramic composite is investigated hereafter. Fig. 10 shows the loading diagrams of the composite samples with different width of particle-binder interfaces. It could be seen from Figs. 10 and 11 that the increase in the width of the interphase boundaries leads to the increase in the strength of the composite, as well as the increase in the value of the ultimate strain (critical value of bending angle in the considered test). As follows from the analysis of dependencies presented in Fig. 11, the main effect of increasing the width of the interphase boundaries up to 1.6 microns is manifested in the increase in the critical strain of the material (up to 2 times). Analysis of the results of computer simulation show that the increase in strength and value of ultimate strain of the composite material with the increase in width of the interphase boundaries is due to the significant expansion of the region of the stress reducing from the high value in the reinforcing particles (which are the stress concentrators in the composite) to the significantly lower value in the plastic binder. Von Mises stress distributions for the samples which are characterized by different widths of interphase boundaries are shown in Fig. 12. It can be seen from Fig. 12 that the formation of wide transition zones around the reinforcing particles, which are characterized by a smooth change of the mechanical characteristics with the distance from the surface of the ceramic inclusion to the bulk of the binder, leads to “smearing” the stress field and, consequently, to reducing the stress gradient at the interface. This means that the formation of wide interphase boundaries among reinforcing particles and metallic binder interfaces in metal–ceramic composites provides a relatively low level of stress in the transition zones. This leads to increasing the deformation ability and strength of the modified surface layers. It is necessary to note that the results obtained herein by simulation are in good agreement with the existing experimental data. As pointed out in Ref. [40], the constraint imposed on matrix plastic deformation by the ceramic reinforcements induces large tensile hydrostatic stresses in the matrix. This enhances the load carried by the reinforcements and hence the composite flow stress, and also triggers the early development of internal damage in the form of particle fracture, interface decohesion, and/or matrix void growth. New experimental techniques, such as automated serial section and X-ray computed microtomography (XCT), provide detailed information on the relationship between the damage nucleation or growth and specific features of the three-dimensional microstructure [40,42]. The experiments with model materials, presented in Ref. [40], show that the damage of the model composite material made of a soft matrix is mainly attributed to decohesion along the particle/matrix interface, while for the material with the same structure but with a harder matrix, the damage mechanism changes to particle fracture. In Ref. [42], for a notched glass fiber/epoxy cross-ply laminate subjected to three-point bending, the onset and evolution of the damage in three dimensions were studied by XCT. It was found that the damage began by formation of intra-ply cracks in the 90° plies followed by intra-ply cracking in the 0° plies.