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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1. Introduction The main technological problems in the synthesis of composite materials containing carbon nanotubes (CNTs) or carbide particles are: the distribution of the hardening phase in the bulk composite; the strength of its adhesion to the matrix; chemical and structural stability of ordered carbon structures in the composite. In addition to the traditional methods for obtaining metal matrix composites, some works present new original methods for mixing matrix and CNT powders, such as: mixing components at the molecular level Hansang (2010), Bakshi (2011), Choi (2011), the method of combining particles Jin-zhi (2010), Singhal (2012). As it has been shown in most papers, these methods can improve the distribution of CNTs in a metal matrix and increase the strength of the interfacial bond, but they are quite time-consuming. Additives of carbon nanotubes and carbide particles can significantly improve the strength properties of aluminum and its alloys Hansang (2010), Bakshi (2011), Choi (2011). To date, to obtain an aluminum composite reinforced with carbon nanotubes (CNTs) and carbide particles, most of the work uses powder metallurgy methods, which consist in obtaining a compact briquette from powder with its subsequent hot deformation. Compacts are obtained by Spark Plasma Sintering (SPS) Jin-zhi (2010), cold pressing and sintering Singhal (2012), explosive compaction Salas (2007), hot isostatic pressing Deng (2007), hot pressing Jafari (2012). Hot extrusion or rolling was used as the final operation Esawi (2008). There are publications in which the production of pressed briquettes from powder has been successfully combined with the extrusion operation by implementing the Spark Plasma Extrusion method (SPE) Morsi (2010). For dispersed reinforced metal matrix materials, the processes occurring at the boundary between the metal matrix and the dispersed hardening phase are particularly critical, since substances with radically different chemical and physical properties are combined in the material. One of such problems is a strong difference in the coefficients of thermal expansion of the metal and the dispersed reinforcing phase (DRP). One of the ways to solve this problem is to select a shell for DRP, which would have an average KTR between the matrix KTR and the DRP KTR. Thus, stress was relieved at the matrix-DRP interface and the strength characteristics of the material would remain constant over wider temperature ranges. As experiments have shown, the creation of a metal matrix material reinforced with CNT or carbide particles without a nickel shell by cold pressing followed by sintering, meets serious difficulties. Composites containing already 3% of the DRP are highly embrittled, which is due to the uneven distribution of the dispersed phase in the volume of the aluminum matrix. This is due to the low wettability of CNTs and carbide particles in the Al matrix, electrification of CNTs during mixing into aluminum powder and aggregation of electrified nanotubes. In this connection, after pressing and sintering the sample, the sample was embrittled to a state that did not allow to study its mechanical properties. Repeated pressing and sintering also did not allow to obtain any durable sample. Nanotubes that are not nickel-plated from the surface, even in small percentages (0.1-1%), are not mixed and are not mixed with aluminum powder into a monolithic sample. The phase of aluminum carbide was detected by the XFA method in such samples, which may mean that the residual amounts of unprotected nanotubes reacted with the matrix material and completely, or almost completely, dissolved in the matrix material, forming the aluminum carbide phase. The formation of aluminum carbide negatively affects the strength of aluminum matrix materials Alekseev (2016), Yufeng (2011). In our work, we introduced a dispersed phase (CNT and carbide particles) protected by a metal shell (Ni) into the aluminum matrix. We obtained composite Al matrix material by repeated cold pressing and alternating pressing by temperature treatments. In the course of work on the creation of Al matrix materials reinforced with CNT with a Ni shell, the necessary conditions were selected for the formation of a metal matrix composite material with stable properties containing CNT in its volume.