FEATURES OF THE COMPOSITION AND MICROSTRUCTURE OF POROUS SKELETONS OF MAX-PHASES TI3ALC2 AND TI3SIC2 PRODUCED BY SHS METHOD IN AIR AND IN A PROTECTIVE SHELL OF SAND

A simple and inexpensive method for the synthesis of porous skeletons of MAX phases Ti₃SiC₂ and Ti₃AlC₂ by the SHS method in air and in river sand filling, in which the use of a closed reactor with a special atmosphere or vacuum is not required, is considered. The study of the macrostructure of synthesized samples based on the MAX phases of titanium aluminum carbide and titanium silicon carbide showed that the samples have the same porosity of about 50 – 60 %, the open porosity is about 40 %. The average pore size ranges from 10 to 350 microns. The microstructure of the porous Ti₃SiC₂ and Ti₃AlC₂ frameworks consists of characteristic multidirectional blocks of MAX-phase plates, as well as a small number of equiaxed TiC particles surrounded by a single TiSi or TiAl phase, respectively. It is shown that the synthesis of porous frameworks in air leads to the formation of oxide and nitride phases that tightly cover surfaces up to 100 microns thick. The SHS process under a layer of sand makes it possible to reduce the average thickness of oxide and nitride films on the surface of the SHS frame to 20 microns. A subsurface layer consisting of two phases was found on the synthesized samples: TiC – TiSi in the Ti₃SiC₂ frame and TiC – TiAl in the Ti₃AlC₂ frame, the thickness of which is reduced from 50 microns (SHS in air) to 30 microns (SHS under a layer of sand). It was found that oxide and nitride films were absent in closed pores due to the fact that atmospheric gases did not have access to them when the samples cooled

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