Experimental and DFT investigation of (Cr,Ti)₃AlC₂ MAX phases stability

Abstract

Using a synergistic combination of experimental and computational methods, we shed light on the unusual solubility of (Cr,Ti)3AlC2 MAX phase, showing that it may accommodate Cr only at very low concentrations (<2at%) or at the exact Cr/(Cr+Ti) ratio of 2/3, even when the ratio of reactants is far from this stoichiometry (1/2 ≤ Cr/(Cr+Ti) ≤ 5/6). In both phases Cr exclusively occupies the 4f sites, bridging carbide layers with the Al layer. Despite this, the peculiar stability of (Cr2/3Ti1/3)3AlC2 is attributed to the formation of strong, spin-polarised Cr-C bonds, which result in volume reduction and marked increase in c/a ratio. KeywordsQuaternary MAX phase; Synthesis and characterization; DFT simulations; Atomic ordering. Impact statementSolubility of Cr and Ti in (Cr,Ti)3AlC2 was investigated using experimental and DFT techniques. It was also determined that (Cr2/3Ti1/3)3AlC2 owe its remarkable stability to the formation strong Cr-C bonds.

Does aluminum play well with others? Intrinsic Al-A alloying behavior in 211/312 MAX phases

“…Mixing of more than one species in one (or more) sublattices in the MAX phase crystal structure potentially has important consequences from the point of view of phase stability. Sufficiently exothermic interactions may lead to the stabilization of ordered phases, as exemplified by the (Cr 2/3 Ti 1/3 ) 3 AlC 2 system [11][12][13]. These compounds in some cases have functionalities that are dramatically different from the parent compounds [14].…”

Physical properties of predicted MAX phase borides Hf2AB (A = Pb, Bi): A DFT insight

“…One of the limitations of MAX phases is that their diversity regarding X elements is confined within C and N for a long period as compounds [12][13][14][15][16][17][18][19][20][21] or solid solutions [22][23][24][25][26][27][28][29][30][31]. Thus, the extension of X elements beyond C/N can open the platform for a huge number of MAX phase members.…”

First-principle Study and Experiment on Temperature-dependent Substitution Process of Si in Ti3(Si,Al)C2 Solid Solution

“…Solid solution modification method was often used to transform ternary MAX phase to quaternary, or even quinary compounds which at least contain two M, two A or two X elements, such as (Cr,Ti)3AlC2, [19] (Zr,Ti)3AlC2, [20] Ti2(Al,Sn)C, [21] (Ti,Cu)3(Al,Cu)C2, [22] (Zr,Ti)2(Al,Sn)C. [23] Burr [19] summarized the major advantages of quaternary MAX ceramics, indicating that they had new and outstanding mechanical properties compared with common MAX phases. As Si and Al elements have similar atomic radius, Al atoms often dissolved into Ti3SiC2 crystal inevitably, generating Ti3(SixAl1-x)C2 solid solution when Al was added as sintering additive via in-situ synthesis.…”