Synthesis, microstructure evolution, and mechanical properties of (Cr 1-x V x ) 2 AlC ceramics by in situ hot-pressing m
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arly dense and almost single-phase bulk (Cr1–xVx)2AlC (x 5 0, 0.25, 0.5, 0.75, and 1.0) ceramics were successfully fabricated by in situ hot-pressing method using Cr, V, Al, and C powders as raw materials. A possible synthesis mechanism was proposed to explain the formation of (Cr1–xVx)2AlC solid solutions. The lattice parameters, microstructure, and mechanical properties of the (Cr1–xVx)2AlC ceramics were investigated in detail. The results indicated that the lattice parameters increased with the substitution of Cr by V and the aspect ratio of the grain changed from 1.4 to 3.2. The dependence of the mechanical properties on the V content was a single-peak type. The (Cr0.5V0.5)2AlC ceramic possessed the optimal mechanical performance and its Vickers hardness, flexural strength, and fracture toughness reached the maximum values of 5.18 GPa, 402 MPa, 5.91 MPa m1/2, respectively, due to the solid solution effect. The energy-consuming mechanisms of the material were also discussed.
I. INTRODUCTION
The Mn11AXn compounds, where M is an early transition metal, A is an element of IIIA or IVA, X is either C or N, and n 5 1–6, are a class of hexagonalstructure ternary carbides and nitrides which have attracted extensive attention owing to the combination of the excellent properties of both metals and ceramics.1–3 Like metals, they have high thermal and electrical conductivity,4 excellent thermal shock resistance and good machinability; like ceramics, they possess high strength,5 high melting point, excellent high-temperature oxidation resistance,6,7 and good thermal stability.8,9 Moreover, the solid solution based on the MAX phases can be formed by the substitution of elements on M, A, or X site. Such as (Cr1–xVx)2AlC,10 (Ti1–xNbx)2AlC,11 (Ti1–xVx)2AlC12 and Ti2Al(C0.5N0.5)13 in the so-called 211 phase, and Ti3SixAl1–xC2,14 Ti3AlxSn1–xC2,15 Ti3GexSi1–xC216 and Ti3Al(C0.5N0.5)217 in 312 phase. Solid solution treatment is considered as an effective way to optimize the properties of Mn11AXn compounds. For example, Wang and Zhou18 investigated the elastic stiffness and electronic band structure of MxM92–xAlC (M and M9 5 Ti, V, Cr) phases by the ab initio pseudopotential total energy method. They found that the second-order elastic constant c44, a hardness predictor, reached a maximum value as the valence electron concentration (VEC) was in the range 8.4–8.6. So it was predicted that the mechanical properties of MxM92–xAlC a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.91 1168
J. Mater. Res., Vol. 29, No. 10, May 28, 2014
http://journals.cambridge.org
Downloaded: 06 Nov 2014
would be improved by forming solid solutions. As a member of MxM92–xAlC, (Cr1–xVx)2AlC is of great interest to us. For this system, both experimental and theoretical studies had been conducted in the past. Schuster et al.2 first synthesized (Cr0.75,V0.25)2AlC, (Cr0.5,V0.5)2AlC, and (Cr0.25,V0.75)2AlC solid solutions by annealing a series of Cr2AlC and V2AlC powder mixtures in appropriate proportions at 1000 °
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