Materials Chemistry and Physics 113 (2009) 596–601
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Y2 O3 –Nd2 O3 double stabilized ZrO2 –TiCN nanocomposites S. Salehi, B. Yüksel, K. Vanmeensel, O. Van der Biest, J. Vleugels ∗ Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium
a r t i c l e
i n f o
Article history: Received 29 May 2008 Received in revised form 28 July 2008 Accepted 3 August 2008 Keywords: Nanocomposites Sintering Microstructure Mechanical properties
a b s t r a c t Yttria-neodymia double stabilized ZrO2 -based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 ◦ C range. The Y2 O3 stabilizer content was fixed at 1 mol% whereas the Nd2 O3 co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 ◦ C was assessed. The nanocomposites with 1–1.75 mol% Nd2 O3 , PECS at 1400 or 1450 ◦ C, have an excellent fracture toughness of 8 MPa m1/2 , although the grain size of both ZrO2 and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10−5 m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO2 -based composites with the same overall stabilizer content. © 2008 Elsevier B.V. All rights reserved.
1. Introduction ZrO2 -based composites with electrically conductive secondary phase additions are under investigation for electrical discharge machining (EDM) applications [1–5]. TiCN is an electrical conductive phase (resistivity = 2.28 × 10−6 m) [6], but the brittleness and high sintering temperature of pure titaniumcarbonitride are the two most important factors preventing its widespread use [7]. Nonconductive ZrO2 (resistivity = 109 m) [8] on the other hand is well known for its high toughness, due to transformation toughening [9,10], and excellent strength. Degradation in humid environments in the 20–400 ◦ C temperature range is one of the main concerns of yttria-stabilized ZrO2 ceramics [11,12]. Preliminary work however revealed that the hydrothermal stability and at the same time the fracture toughness of 1 mol% Y2 O3 + 1 or 2 mol% Nd2 O3 co-stabilized ZrO2 is higher than for 2 and 3 mol% Y2 O3 stabilized ZrO2 [13]. In the present study, 40 vol% TiCN is added to a Y2 O3 + Nd2 O3 costabilized zirconia matrix in order to try to make a composite that combines hydrothermal stability, a high toughness and strength with electro-conductivity allowing EDM. The aim of EDM is to avoid the expensive grinding operation for final shaping and surface finishing of components with a complex geometry, therefore
∗ Corresponding author at: MTM, Kasteelpark Arenberg 44 - bus 2450, 3001 Heverlee, Belgium. Tel.: +32 16 321244. E-mail address:
[email protected] (J. Vleugels). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.08.014
increasing the possibility of mass production and manufacturing cost reduction. 2. Experimental procedures 2.1. Ceramic preparation Commercial zirconia nanopowder (grade TZ-0, Tosoh, Japan) was stabilized with neodymia and yttria by means of a coating method. For this purpose, the proper amount of neodymia (99.9%, Chempur, Germany) and yttria (99.9%, Acros, Belgium) was dissolved in nitric acid (65%, Sigma–Aldrich, Belgium) at 90 ◦ C. The resulting nitrate solution was applied to the monoclinic zirconia powder via a suspension drying process [14]. The stabilizer coated powder was calcined at 800 ◦ C in air for 20 min. The yttria stabilizer content was fixed at 1 mol% whereas the neodymia stabilizer content was varied between 0.75 and 2 mol%. 40 vol% TiC0.5 N0.5 nanopowder (
