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Ti3SiC2 powder of about 96 wt% purity was produced using TiCx and Si powders. The synthesis process was characterized by an exothermic reaction at
985  C and low activation energy (
27 kJ/mol) of conversion. Almost complete conversion to Ti3SiC2 phase was observed during sintering. The onset temperature of sintering was found to be at about 1060  C using dilatometer. The density of nearly 99% (theoretical) was achieved through the pressureless sintering of Ti3SiC2 powder by 1 and 2 wt% Si powder additions. The sample (without sintering aid) sintered at 1500  C for 4 h showed uniformly distributed angular grains, whereas the bimodal nature of the microstructure was observed when Si was added as a sintering aid. I. INTRODUCTION

Ti3SiC2 belongs to a MAX phase group, which has emerged as a new class of material having a unique combination of properties of both metals and ceramics.1 To produce Ti3SiC2, various combinations of raw materials such as Ti, Si, C, TiC, and SiC powders are used and various production methods have been reported.2–6 The products obtained by most of the processes often contain the hard phases of TiC, SiC, and intermetallics. The excess amount of Si and small quantities of Al and B2O3 have been used to enhance the purity of the Ti3SiC2 phase.7–9 Depending on the starting materials, various synthesis mechanisms have been proposed,3,4,10 including the formation of intermediate compounds, melting of silicides, nonstoichiometric titanium carbides (TiCx), Ti5Si3Cx, and so forth. Formation of unusually shaped particles, i.e., whiskers or needlelike particles of Ti3SiC2, has also been observed11 during mechanically activated sintering of ball-milled Ti–Si–C mixed powders, which has been attributed to the appearance of the eutectic liquid phase during heating. The high-density parts of Ti3SiC2 could be produced through hot isostatic pressing or sintering under applied pressure including hot pressing, pulse discharge sintering, spark plasma sintering, and self-propagating hightemperature synthesis processes.6,12–16 If the high-density part with high purity could be produced through the pressureless sintering method, this would be a great economical and technological advantage and it would broaden the application area of this material. There have

Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0063 J. Mater. Res., Vol. 24, No. 2, Feb 2009

been some reports of producing Ti3SiC2 by pressureless sintering using Al17–20 and B2O37 as sintering aids and the sintering of ultrafine reactive powder prepared by the ball milling21; however, the sintered density could not reach more than 90%. Relatively high-density material has been produced from Ti3SiC2 powder through the ink-jet threedimensional (3D) printing technique, followed by coldisostatic pressing of the preform at a high pressure of
380 MPa, and sintered under a pressureless condition.22,23 A mechanically alloyed powder with 80 vol% Ti3SiC2 has been sintered to nearly fu