Effect of the composition and porosity of sintered titanium nanolaminates on their mechanical properties at high temperatures

Abstract

reaction sintering in compact and porous states. The regularities, specific features, and mechanisms of deformation and fracture processes are established for each material within the temperature range 20-1300°C. The temperature-strain and force boundaries of their existence in the plastic state are determined. The comparative analysis of the mechanical properties of nanolaminates is performed. It is shown that the strength characteristics of nanolaminates and their strain and creep resistance at medium and high temperatures increase in the following sequence: Ti 3 AlC 2 -Ti 4 AlN 3 -Ti 3 SiC 2 . The obtained picture of high-temperature properties of these materials is explained. It is shown that the procedure of prestraining of a porous material by ε = 4-8% may result in a significant increase in its specific high-temperature strength up to values higher than those typical of the compact material.Keywords: sintered titanium nanolaminates, porosity, compression strength, indentation, energy of interatomic bonds, relative testing temperature. Notation θ -porosity of a material H A -Meyer microhardness HV -Vickers macrohardness ΔHV rel -relative decrease in the high-temperature macrohardness on holding under a load P =10 N for t = 60 min ΔHV rel −1 -measure of high-temperature strength in the process high-temperature macroindentation Δh -level of creep in the process of microindentation at room temperature (the depth of penetration of the indentor) h c -level of creep in the process of high-temperature macroindentation (the depth of penetration of the indentor) σ pr -proportionality limit in uniaxial compression 624 0039-2316/06/3806-0624 -specific strength in uniaxial compression σ 5 -strength of the material in uniaxial compression for a level of strain ε = 5% σ ρ 5 -specific strength in uniaxial compression for a level of strain ε = 5% ( ) ( ) σ ρ σ ρ 5 por comp 5 -specific strength of the porous material relative to the specific strength of the compact material in uniaxial compression for a level of strain ε = 5%Introduction. Materials based on titanium are among the most promising structural materials combining low density, low-temperature technological efficiency, and high characteristics of high-temperature strength and heat resistance. In recent years, significant attention of the researchers is given to a new class of materials called nanolaminates (they are also called MAX compounds) [1][2][3][4][5][6][7][8]. The nanolaminates are ternary compounds described by the formula M AX

Mechanical properties of porous Ti3SiC2/TiC, Ti3AlC2/TiC, and Ti4AlN3/TiN nanolaminates at 20 to 1300°C

“…This pattern may be associated with their peculiar crystal lattices. It is shown in [1, 2] and analyzed in [8] that the distance between silicon and titanium atoms is shorter in the Ti 3 SiC 2 lattice (meaning that their interaction is stronger) than that between aluminum and titanium atoms in Ti 3 AlC 2 and Ti 4 AlN 3 . In addition, the binding energy of silicon atoms within a layer in Ti 3 SiC 2 is much higher than that of aluminum atoms in Ti 3 AlC 2 and Ti 4 AlN 3 .…”

“…Compact and porous titanium-silicon carbide Ti 3 SiC 2 undergoes significant work hardening under uniaxial compression above 1000°C [3,8]. It occurs at 5-10% strain, and after that dynamic softening is observed.…”

“…Nanolaminates, a new class of compounds (also called MAX compounds), have been of interest recently [1][2][3][4][5][6][7][8]. They represent ternary compounds M n+1 AX n , where M is a transition metal, A is an element from group IIIA or IVA of the Periodic Table, and X is carbon or nitrogen, n = 1, 2, or 3.…”

“…The structure of layered hexagonal lattices of ternary titanium compounds Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 4 AlN 3 has been analyzed in [8] to reveal four features that determine their mechanical properties.…”

“…It was previously shown [3,[6][7][8] that these features of nanolaminates were influenced by two factors under mechanical loading: porosity and presence of the other phase. Porosity decreases strength but increases plasticity, while particles of the other phase increase strength but decrease plasticity.…”