Journal of Alloys and Compounds 505 (2010) 337–342 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Nickel assisted sintering of Ti 3 SiC 2 powder under pressureless conditions Bharat Bhooshan Panigrahi a,∗ , N. Subba Reddy b , Avinash Balakrishnan c , Min-Cheol Chu d , Seong-Jai Cho d , Jose J. Gracio a a Center for Mechanical Technology and Automation, Department of Mechanical Engineering, University of Aveiro, Aveiro 3810-193, Portugal b Division of Materials Science and Engineering, Engineering Research Center, Gyeongsang National University, Chinju 660-701, Republic of Korea c SIMAP, CNRS, Groupe GPM2, Grenoble-INP, 38402 Saint Martin d’Heres Cedex, France d Division of Advanced Technology, Korea Research Institute of Standards and Science, Yuseong, Daejeon 305-340, Republic of Korea article info Article history: Received 11 November 2009 Received in revised form 12 May 2010 Accepted 25 May 2010 Available online 18 June 2010 Keywords: Cold-isostatic pressing Sintering Activation energy Mechanical properties abstract This investigation was aimed to study the effect of nickel addition on the sintering behaviour of Ti 3 SiC 2 powder under pressureless conditions. Nearly pure bulk Ti 3 SiC 2 ceramic with relative density of ∼98.5% was produced at 1500 ◦ C by sintering of Ti 3 SiC 2 powder while using 1 wt.% nickel as a sintering aid. The activation energy of sintering of Ti 3 SiC 2 powder was determined to be 351 ± 5 kJ/mol, which was decreased slightly to 305 ± 10 kJ/mol when nickel (1 wt.%) was added. Sintering of Ti 3 SiC 2 powder was found to be controlled by mixed mode of mechanisms, i.e., the interface reactions and diffusion of Si atoms. The mechanism was changed to liquid phase sintering due to melting of Ni-based compounds in the sample sintered with Ni. The reaction of Ni with Ti 3 SiC 2 helped to decrease the grain growth rate. The hardness (Vickers), flexural strength and fracture toughness of the sintered Ti 3 SiC 2 –1Ni sample were found to be 3.4 GPa, 311 ± 22 MPa and 2.8–6.4 MPa m 1/2 , respectively. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In recent times, the ternary carbides with hexagonal structure, known as MAX phases, have taken a considerable attention from structural ceramists [1,2]. With a good high temperature strength, corrosion resistant, oxidation resistant, good tribological proper- ties, elastic stiffness, good thermal and electrical properties, they exhibit an excellent machinability. Ti 3 SiC 2 (TSC) is the most widely studied compound in this group which is produced using vari- ous combinations of raw materials [3–6] including Ti, Si, C, TiC and SiC. To enhance the purity of TSC phase, excess amount of Si, small amounts of Al and B 2 O 3 powders were used [7–9] and the high purity TSC powder was produced from Ti, Si and TiC powders using 0.10–1.0 mol of extra Si [10–12]. The high density parts of TSC were produced through hot pressing, pulse discharge sinter- ing, spark plasma sintering and self propagating high temperature synthesis processes [3,13–17]. There are some reports on synthesis of TSC by pressureless sintering using Al [18–21] and B 2 O 3 [7] as sintering aids and sintering the ball milled ultra fine powders [22]; however, the final density of over 90% could not be achieved. Pres- sureless sintering of MAX phase powder is difficult due to its easy decomposability at high temperatures, i.e., often subjected to the loss of Si from TSC or Al from Ti 3 AlC 2 and Cr 2 AlC powders. Another ∗ Corresponding author. Tel.: +351 234 370830x23887; fax: +351 234 370953. E-mail addresses: bharat@ua.pt, panigrahi14@yahoo.com (B.B. Panigrahi). important issue during sintering of these compounds is not only the processing atmosphere (i.e., vacuum or inert atmosphere), but the type of furnace used, i.e., graphite heating or non-graphite heating furnaces. High density body was produced by pressing the powder cold-isostatically at a very high pressure of about 380 MPa, followed by the pressureless sintering [23]. A mechanically alloyed powder with about 80 vol.% TSC [24] and the preform prepared by tape cast- ing of TSC powder (∼95 vol.% purity) were sintered to nearly full density [25]. Since the sample was sintered on a graphite heating furnace, the effect of carbon diffusion from atmosphere into the sample was noticed; consequently the titanium carbide content in the sintered body was increased significantly. To reduce the amount of TiC x , large amount (about 10 wt.%) of Si powder was mixed with TSC powder during sintering [25]. Recently, TSC powder with small amounts (1 and 2 wt.%) of Si was sintered under pressureless con- dition on a tungsten heating furnace [26]; the final product had a very low amount of impurities. However, there is no reported study on the sintering kinetic of TSC powder so far. Nickel was used as a sintering aid for the metal and the ceramic powders. Nickel is known as a fast diffuser in the metal, such as titanium, and was found to enhance the sintering rates of titanium [27], tungsten [28] and some ceramic powders [29]. It was also observed that nickel suppressed the grain coarsening process up to some extent during sintering [27]. It would be worth investigating if sintering of TSC powder could be enhanced by nickel addition. The present investigation has been initiated with an aim to pro- duce high purity dense body of TSC powder by sintering under 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.05.177