Materials Science and Engineering A 416 (2006) 104–108
Mechanical properties and microstructure of
ZrO
2
–TiN–Al
2
O
3
composite ceramics
Jing Sun
a,b
, Chuanzhen Huang
a,∗
, Jun Wang
c
, Hanlian Liu
a
a
Centre for Advanced Jet Engineering Technologies (CaJET), School of Mechanical Engineering, Shandong University, Jinan 250061, China
b
School of Mechanical and Electrical Engineering, Shandong University of Science and Technology, Qingdao 266510, China
c
School of Mechanical and Manufacturing Engineering, The University of New South Wales, UNSW Sydney, NSW 2052, Australia
Received in revised form 7 September 2005; accepted 5 October 2005
Abstract
20 wt% TiN/3Y-TZP mixed with an amount of less than 15 wt% Al
2
O
3
particles has been fabricated by hot-pressing techniques, and the
mechanical properties and microstructure were investigated. There is a good chemical compatibility among ZrO
2
, TiN and Al
2
O
3
and the addition
of 5 wt% Al
2
O
3
can improve the densification of composites. Al
2
O
3
particles have little effect on improving flexural strength but have a distinct
effect on toughening for 20 wt% TiN/3Y-TZP, which may be due to the residual stresses and microcracks resulting from the mismatch between the
expansion coefficients of Al
2
O
3
and ZrO
2
. An amount of 5 wt% Al
2
O
3
in 20wt% TiN/3Y-TZP can improve the bonding strength among grains
and change the fracture pattern from intergranular to transgranular fracture.
© 2005 Elsevier B.V. All rights reserved.
Keywords: 3Y-TZP; TiN; Al
2
O
3
; Mechanical property; Microstructure
1. Introduction
Yttria stabilized tetragonal zirconia polycrystals (Y-TZP) has
excellent mechanical properties at room temperature, such as
high flexural strength and high fracture toughness, which is due
to the stress-induced transformation from metastable tetragonal
(t-ZrO
2
) to the monoclinic phase (m-ZrO
2
). However, Y-TZP
has a lower hardness and its strength is greatly decreased by
aging at relatively low temperature (100–400
◦
C), especially
in humid environments [1–3]. The composite technology by
dispersing particles is one of the most important means of
improving Y-TZP properties. It is indicated that adding par-
ticles with high elastic modulus such as Al
2
O
3
into Y-TZP
not only greatly enhances the strength [4] but also effectively
inhibits its low-temperature degradation [5,6]. But there are still
conflicting results about Al
2
O
3
toughening of Y-TZP. For exam-
ple, Fukuhara [4] reported that Al
2
O
3
dispersing decreased the
toughness of 2.5Y-TZP at room temperature while other reports
[7,8] showed different results. So, it is necessary to study fur-
ther the effect of Al
2
O
3
particles on mechanical properties of
∗
Corresponding author. Tel.: +86 531 8392539; fax: +86 531 8392328.
E-mail address: huangcz@sdu.edu.cn (C. Huang).
Y-TZP. Recently, it has been indicated that adding TiN particles
to 3 mol% Y
2
O
3
stabilized TZP (TiN/3Y-TZP) can also obvi-
ously improve the flexural strength and fracture toughness of
matrix [9]. In order to develop the new zirconia composites with
higher general mechanical properties, 3Y-TZP codoped by TiN
(thermal expansion coefficient, α ≈ 9.3 × 10
-6
/
◦
C; elastic mod-
ulus, E ≈ 400 GPa) and Al
2
O
3
particles has been fabricated and
the microstructure and mechanical properties of the composites
are studied in this paper.
2. Experimental procedures
The average grain size of starting powder, ZrO
2
doped by
3 mol% Y
2
O
3
(3Y-ZrO
2
), is 1.1 m. Its chemical analysis is
shown in Table 1. TiN and -Al
2
O
3
, whose average grain sizes
are 2.7 m and 0.7 m, respectively, are commercial powders.
Four different composites were prepared by 20wt% TiN/3Y-
TZP added with an amount of 0, 5, 10 and 15 wt% Al
2
O
3
,
respectively. Their compositions are shown in Table 2. The
composite powders measured according to Table 2 were mixed
by a polyester barrel and zirconia balls in ethanol for 20 h.
After drying in vacuum, the mixed powders were screened and
enclosed in a graphite die, then were hot pressed for 30–40 min
at 1500–1550
◦
C under 27 ± 2 MPa pressure. The sintered mate-
0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.msea.2005.10.024