PSI - Issue 50

N.F. Morozov et al. / Procedia Structural Integrity 50 (2023) 192–199 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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As can be seen from the data obtained during mechanical tests by uniaxial loading, with an increase in the content of the mass fraction of CNT in the sample of the material, its strength decreases and embrittlement of the material occurs. The most promising of the above samples is one containing 0.1% CNT. The ultimate strength of the sample reaches 85 MPa (74 MPa for pure Al), while maintaining the plasticity characteristic of pure aluminum. The increase in mechanical strength for materials containing 0.1 and 1% CNT is explained by the redistribution of loads applied to the material along the pseudo-dimensional defect formed by the nanotube, which significantly reduces the loads at the shear boundary and redistributes energy along the defect, contributing to the relaxation of the material in the zone of the incipient shear, without significant destruction of the existing micrograin structure. For a sample containing 0.1% nanotubes, plasticity equal to that of pure Al is observed, as well as a slight increase in the tensile strength. At the same time, for a sample containing 1% CNT, a decrease in plasticity is observed, against the background of a slight decrease in the tensile strength (compared to 0.1% CNT), this indicates the formation of agglomerates by nanotubes and numerous intersections in the matrix array, which leads to the sample embrittlement, due to the formation of fatigue defects along the intersecting nanotubes grid. A further increase in the CNT content in the aluminum matrix only intensifies these processes by additional formation of nanotube aggregates, the growth of aggregates and a decrease in the effective cross sections of the metal matrix in the zones of CNT aggregates Tolochko (2019). The characteristics of the mechanical properties of Al matrix composites samples with different composition of DRP containing different amounts of CNTs are given in Table 1 For a sample containing 0.1% CNT, plasticity equal to that of pure Al is observed, and an increase in tensile strength is also observed. At the same time, for a sample containing 1% CNT, a decrease in plasticity is observed, against the background of a slight increase in the tensile strength (compared to 0.1% CNT), this indicates the formation of agglomerates from nanotubes and numerous intersections in the matrix array, which leads to embrittlement of the sample. Reinforcement with the micron phase of TiC slightly increases the tensile strength of the Al matrix composite, but at the same time, significantly reduces its plasticity, compared with the original Al. The nanoscale TiC phase significantly increases the tensile strength of the aluminum matrix composite, although it reduces its plasticity, but significantly lower than the micron phase does. Thus, the phase with nanoscale structures is the most promising for inclusion in metal matrix composites. 4. Conclusion As a result of the research, a pressing and sintering technique was developed, including two stages of compaction with subsequent sintering and one stage of pressing followed by annealing, which made it possible to form a monolithic metal matrix with CNTs included in it. The modes of pressing and sintering chosen by us, as well as the stage of nickel plating of nanotubes, helped to avoid the formation of aluminum carbide in the volume of the matrix and, as a consequence, the deterioration of the mechanical properties of the samples. Studies have shown that the introduction of a dispersed CNT phase into an Al matrix in quantities of more than 1% and the bulk composite formation by powder metallurgy methods leads to the formation of microcracks and extensive areas in the form of CNT agglomerates in the bulk sample, and consequently to a significant drop in the mechanical properties of the material. Thus, the creation of reinforced material with more than 1% CNT by powder metallurgy methods is an unpromising direction for the creation of structural materials. Table 1. Mechanical properties of aluminum matrix composites. CNT content Ϭ V , MPa Ɛ , % 43.5 31.9 16.0 Al +0.1 % CNT Al +1 % CNT 85.4 87.6 93.8 83.7 Al +1% TiC (150 nm) Al + 1% TiC (1.5 microns) 7.7 ASP-50 Al 74 47.2