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Phase evolution of materials in the Ti-Al-C system during hot-pressing

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Some of ternary materials in the Ti-Al-C system are very interesting due to their specific structure. Because of their properties, that are result of their heterodesmic structure, they are called plastic ceramics. In this paper authors would like to present influence of hot pressing on phase evolution in Selfpropagating High-temperture Synthesis (SHS) derived Ti3AlC2. To obtain ternary titani[...]

Synthesis and properties of hot-pressed Ti-Al-C-N materials

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Among many covalent materials such as carbides or nitrides there is a group of ternary compounds referred in literature as H-phases, Hägg-phases, Novotny-phases or thermodynamically stable nanolaminates. These compounds have a Mn+1AXn stoichiometry, where M is an early transition metal, A is an element of A groups (mostly IIIA or IVA) and X is carbon and/or nitrogen. Heterodesmic structures of these phases are hexagonal, P63/mmc, and specifically layered. They consist of alternate near close-packed layers of M6X octahedrons with strong covalent bonds and layers of A atoms located at the centre of trigonal prisms. The M6X octahedra, similar to those forming respective binary carbides, are connected one to another by shared edges. Variability of chemical composition of the nanolaminates is usually labelled by the symbol describing their stoichiometry, e.g. Ti2AlN represents 211 type phase and Ti3AlC2 - 312 typ. Structurally, differences between the respective phases consist in the number of M layers separating the A layers: in the 211’s there are two whereas in the 321’s three M layers [1÷3]. The layered, heterodesmic structure of MAX phases led to an extraordinary set of properties. These materials combine properties of ceramics like high stiffness, moderately low coefficient of thermal expansion and excellent thermal and chemical resistance with low hardness, good compressive strength, high fracture toughness, ductile behavior, good electrical and thermal conductivity characteristic for metals. They can be used to produce ceramic armor based on functionally graded materials (FGM) or as a matrix in ceramic-based composites reinforced by covalent phases [4]. This work was focused on synthesis of three materials in Ti-Al-C-N system, namely Ti3AlC2, Ti2AlN, Ti3Al(C, N)2, by the Self-propagating High-temperature Synthesis (SHS), than obtained powders were hot-pressed and some of their properties were examined. PREPARATI[...]

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