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MAGNESIUM (Mg) has emerged as a potential material for use in the aerospace and automotive industries, being a lightweight metal with a density of 1.74 g/cc, low specific weight, and high specific strength.[1] Generally, pure Mg has low compressive strength, wears easily, and also oxidizes rapidly. As-cast Mg alloys[2–4] offer attractive applications owing to their moderate strength-to-weight ratio. The next-generation materials for aerospace applications are expected to provide high strength-to-weight ratios. In addition, these advanced lightweight materials are expected to provide improved wear resistance and also damping properties without compromising their strength properties. In this context, substantial research work is being carried out globally to improve the performance of Mg and its alloys with the reinforcement of ceramic

L. RANGARAJ, R.V. SAGAR, M. STALIN, K. RAGHAVENDRA, and K. VENKATESWARLU are with the Materials Science Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India. Contact-email: [email protected] Manuscript submitted December 19, 2018. Article published online May 30, 2019 3714—VOLUME 50A, AUGUST 2019

particulates, such as Al2O3, SiC, TiC, and B4C.[5–17] In general, Mg-metal matrix composites (Mg-MMCs) are produced by melt infiltration (MI), pressure infiltration, mechanical alloying (MA), powder metallurgy (PM), stir casting and extrusion, and hot pressing (HP) methods. However, the ceramic particulates used as reinforcement for the fabrication of Mg-MMCs are brittle and hard, making machining difficult. Also, these composites exhibit low ductility compared to their base alloys. In recent years, materials with a combination of properties for both metals and ceramics have been invented;[18] one such general material is the MAX phase, having a chemical formula Mn+1AXn (n = 1, 2, or 3), where ‘‘M’’ is an early transition metal (Sc, Ti, V, Cr, Zr, Hf, Ta, Nb, Mo, etc.), ‘‘A’’ is an A group element (Al, Si, Ga, Ge, Cd, In, etc.), and ‘‘X’’ is either C or N. The crystal structure of the MAX phase is a layered ceramic wherein close-packed ‘‘MX’’ layers are interspersed with A layers, with n as the deciding factor. When n = 1, every 2 MX layer is interspersed with an A layer, and when n = 2, every 3-MX layer is interspersed with an A layer, etc.[19–21] Like metals, MAX phase materials have moderate hardness, have good electrical and thermal conductivity, and are machinable using conventional high-speed steel tools. Comparable to

METALLURGICAL AND MATERIALS TRANSACTIONS A

ceramics, MAX phase materials have a high melting temperature, high modulus, high compressive strength, and excellent oxidation resistance. It is well known that the MAX phase powders are produced by reactive synthesis of a Ti-Al(Si)-C powder mixture to yield Ti2AlC, Ti3AlC2, or Ti3SiC2 at 1573 K to 1873 K (1300 C to 1600 C) under argon atmosphere.[22,23] Owing to the excellent physical, mechanical, and thermal properties of MAX phases, fabrication of an electrofriction composite by introducing Ti3SiC2 as a re