Synthesis, microstructure and mechanical properties of Yttria Stabilized Zirconia (3YTZP) – Multi-Walled Nanotube (MWNTs) nanocomposite by direct in-situ growth of MWNTs on Zirconia particles q Amit Datye a , Kuang-Hsi Wu b,⇑ , George Gomes b , Vivana Monroy b , Hua-Tay Lin c , Jozef Vleugels d , Kim Vanmeensel d a Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, United States b Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174, United States c Oak Ridge National Laboratory, Oak Ridge, TN 37831-6068, United States d Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Leuven, Belgium article info Article history: Received 15 April 2010 Received in revised form 20 July 2010 Accepted 5 August 2010 Available online 11 August 2010 Keywords: A. Carbon nanotubes A. Ceramic-matrix composites B. Mechanical properties D. Scanning/transmission electron microscopy (STEM) E. Chemical vapor deposition (CVD) abstract In this research, Yttria Stabilized Zirconia (3YTZP) – carbon nanotube (CNT) composites are fabricated by direct in-situ growth of CNTs on the Zirconia particles, followed by densification via the Spark Plasma Sin- tering (SPS) technique. Scanning electron microscopy analysis of the 3YTZP-CNT powders shows uniform distribution of CNTs without the formation of agglomerates frequently seen with the traditional ex-situ mixing of CNTs in ceramic compositions. The samples were sintered to nearly 100% theoretical density and with a finer grain size microstructure. High Resolution Transmission Electron Microscopy (HRTEM) and Raman Spectroscopy confirm CNT retention in the sintered nanocomposites up to 1600 °C. The flex- ural strength increases from 260 MPa for samples without CNTs sintered at 1600 °C to 312 MPa for samples with 4 wt.% CNTs sintered at the same temperature. A corresponding increase in the indenta- tion fracture toughness is also observed for samples with 4 wt.% CNTs sintered at 1600 °C as compared to samples sintered at the same temperature without CNTs. Published by Elsevier Ltd. 1. Introduction Carbon nanotubes (CNTs) have been an attractive candidate for fundamental research since their discovery by Iijima [1]. Theoreti- cal and experimental results have shown extremely high elastic modulus, greater than 1 TPa (the elastic modulus of diamond is 1.2 TPa) [2–7], and reported strengths 10–100 times higher than the strongest steel at a fraction of its weight [8]. In addition to their extraordinary mechanical properties, carbon nanotubes also pos- sess superior thermal properties. They are thermally stable up to 2800 °C in vacuum, and the thermal conductivity is about twice as high as that of diamond [3,9]. CNTs with their outstanding mechanical properties and extraordinarily high aspect ratios are, therefore, the ideal reinforcing fibers for ceramic matrix compos- ites [4,5,10–14]. The successful incorporation of CNTs in ceramic- based nanocomposites has been greatly hindered by the lack of interface bonding between the CNT and the matrix material and by its difficulty in dispersion in the matrix. Zirconia (ZrO 2 ) is a technologically important material due to its stability at high-temperatures, large energy bandgap, high break- down electric field and low leakage current level. It has been extensively used in applications as a refractory material, in ortho- pedic implants, in common high-temperature applications such as seals, valves, and pump impellers, and as synthetic gemstones. Re- cently, Zirconia has been used in solid oxide fuel cells (SOFC), oxy- gen sensors, ceramic membrane oxygen separation technology, and high-temperature steam electrolysis. Zirconia is one of the most widely investigated structural ceramics and is widely used as a refractory material in metallurgy and structural components for engine applications. Zirconia exhibits high strength, fracture toughness and wear resistance properties compared to other ceramics, but like all other ceramics, it is brittle. CNTs therefore can be used to reinforce Zirconia matrix ceramics to increase their mechanical strength. Several applications have been proposed for CNTs, many of which are concerned with conductive or high strength composites [5,12,15–18]. It is anticipated that the inclu- sion of CNTs in a ceramic matrix would allow one to produce com- posites with high stiffness and improved mechanical properties compared to that of the single phase ceramic material [7,12,15,19]. Xia et al. [20] in their review paper discussed in detail the toughening mechanisms in carbon nanotube reinforced cera- 0266-3538/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.compscitech.2010.08.005 q Presented at the 33rd International Conference and Exposition on Advanced Ceramics and Composites of the American Ceramic Society and the American Ceramic Society’s Engineering Ceramics Division. ⇑ Corresponding author. Tel.: +1 305 348 3146. E-mail address: wu@fiu.edu (K.-H. Wu). Composites Science and Technology 70 (2010) 2086–2092 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech