Impact of aluminum concentration on the synthesis of highly pure Cr2 AlC MAX phase

O P Pandey

This fascinating class of materials are layered ternary carbides and nitrides having hexagonal crystal structure. MAX phases exhibit a unique combination of properties of both metals and ceramics such as high thermal and electrical conductivity, excellent machinability, good damage tolerability and superb thermal shock resistance, as compared to binary carbides and nitrides. However, the wide applicability of MAX phases restricts due to cost effective synthesis and their phase stability. In this study, we have successfully synthesized Cr2 AlC MAX phase through pressure less sintering route. The impact of aluminum content (10 – 50 mol%) on the phase formation and structural properties of Cr2 AlC has been investigated. It is observed that the purity of Cr2 AlC MAX phase can be enhanced by varying the aluminum content, even at lower temperatures (1200–1300o C), as compared to previously reported Cr2 AlC MAX phase (> 1300o C). The highly pure Cr2 AlC is obtained at 1300o C, when the aluminum content in 40 mol%. Furthermore, the crystallite size is discovered greatest (28.14 nm) and cross section strain (4.03 × 10-3) is least for profoundly unadulterated Cr2 AlC. Additionally, oxidation active investigation is performed to gauge initiation vitality (Eg) by following Kissinger-Akahira-Sunose (KAS) technique. The MAX phase demonstrated high oxidation resistance and no mass gain is observed in the TGA curve below 700o C. In addition, two exothermic peaks are observed at ~ 700o C and ~ 1050o C. The previous pinnacle is related the oxidation of abundance aluminum present on the outside of MAX stage. While later pinnacle speaks to the arrangement of Al2 O3 layer over the surface MAX stage. MAX phases have attracted a lot of interest in the last years due to their unique combination of properties, bridging the gap between ceramics and metals. Among this large family of materials, with more than 70 different compositions and a huge number of solid solutions, Al‐based MAX phases show the best performance to operate under high temperature (>1000°C) and aggressive environments. They combine the good properties of conventional MAX phases such as high elastic modulus, low density, high thermal and electrical conductivities, excellent thermal shock resistance and damage tolerance, with an outstanding oxidation resistance through the in situ formation of protective alumina scales up to 1300°C‐1400°C. Furthermore, they show self‐healing mechanisms at high temperatures under oxidizing environments. Among Al‐based MAX phases, Cr2AlC, Ti2AlC, Ti3AlC2, Ti2AlN, and Ti3AlN2 are the most well‐studied and oxidation‐resistant compositions.