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  • Note that the so called model of narrow particle binder

    2018-11-03

    Note that the so-called model of “narrow” particle-binder interfaces [7] is used in the calculation presented below. In this model, it is assumed that the width of the raltegravir potassium boundary is much smaller than the size of movable cellular automaton. Moreover, the assumption of ideal adhesion of the composite components (TiC inclusions and NiCr binder) was used. This assumes that the strength characteristics of the interface are equal to the corresponding values for the least durable component of the composite material (in this case Ni–Cr alloy). Use of this approach allows to study the influence of the strength characteristics of carbide inclusions on the mechanical response of the composite in the raw. Fig. 8 shows the dynamic loading of the simulated composite samples with different values of tensile strength of TiC inclusions. The diagram is plotted in terms of normalized stress versus bending angle. Here the stress σ is defined as resistance force of composite applied on mandrel divided by the area of the upper surface of the mandrel,  = 700 MPa is the tensile strength of NiCr binder. It could be seen from Fig. 8 that the strength and deformation characteristics of the composite (Curves 3 and 4) are decreased at tensile strength of TiC inclusions () less than 1100 MPa. In particular, the decrease in to the value of tensile strength of metallic binder leads to a twofold decrease in ultimate strain. As could be seen from Fig. 8, the essential change in the mechanical parameters of the composite occurs in a fairly narrow strength interval of TiC inclusions and has a threshold character. Analysis of the fracture dynamics of the model samples shows that this is due to the active involvement of cracking mechanism of low strength ( < 1100 MPa) TiC particles in the process of composite fracture. Fig. 9 shows the main stages of fracture of the composites with different strength values of TiC inclusions. It could be seen from Fig. 9 that, in the composites with high-strength inclusions, the cracks are nucleated and propagated in the matrix by passing the reinforcing particles along the interphase boundaries ( = 2000 MPa, top row in Fig. 9). For the composites with particles having a tensile strength approaching to the threshold value, the cracks are generated and propagated in the binder, but they “cut” them ( = 1000 MPa, middle row in Fig. 9) when they reach to TiC particles. Further decrease in the particle strength leads to a change in fracture mechanism of the composite. As could be seen from Fig. 9 (bottom row), fracture begins at the bottom part of the sample (in the area of maximum tensile stress) by means of nucleation of cracks in ceramic particles. Then, with the increase in the applied strain, these cracks consequently connect with the cracks passing through the binder into a single main crack. This change in the fracture mechanism is accompanied by the significant decrease in integral deformation characteristics of the composite. Thus, the strength of the reinforcing inclusions is one of the most important factors determining a number of service characteristics of metal–ceramic composites, such as strength, critical deformation, fracture toughness, and others. It should be noted that one of the key elements of the internal structure of the metal–ceramic composites is the interface between the particles of refractory compounds and the metallic binder. The change in the technological peculiarities of metal–ceramic composite fabrication (in particular, applying additional heat treatment of the composite) can vary the geometry (width) of interphase boundaries and, consequently, their mechanical properties [7]. Therefore, the influence of this factor on the mechanical characteristics of MCC was investigated in the paper. The investigation was carried out using a mesoscopic model of “wide” interphase boundary (transition zone). In this model, it is assumed that the width of the interface is comparable to or greater than the size of the movable cellular automaton [7]. Here the particle-binder interface is regarded as an area of variable composition of chemical elements (Ti, Ni, Cr, C) and modeled by several layers of cellular automata. In this area, the volume fractions of TiC and NiCr vary with a distance from the particle surface to the bulk of binder according to a given law. This leads to an appropriate change in the physical and mechanical (including response function and raltegravir potassium strength parameters σc and σt) characteristics of these “transition” automata. This model can be efficiently used in numerical simulation of composites in the case of the width of the transition zone higher than the size of the cellular automaton.