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K. L. Meena and T. S. Srivatsan
Introduction
The composite based on alumina-based ceramics offers an excellent combination of
properties to include the following: (i) overall chemical inertness, (ii) high abrasion
resistance, and (iii) high-hot-hardness against extreme environments [1]. Aluminum
oxide or alumina (Al 2 O 3 ) is often chosen a preferred choice for making cutting
tool inserts in comparison with carbides and the family of high-speed steel. This
is essentially because of its overall inert behavior, or response characteristics, of
alumina (Al 2 O 3 ) upon exposure to both elevated temperatures and hostile or aggressive environments [2]. Alumina-based ceramic cutting inserts are currently being
chosen for use in wear-critical or wear-specific environments, such as (i) mixers, (ii)
grinders, (iii) coal chutes, and (iv) ball mills [3]. Zirconia-toughened alumina (ZTA)
ceramics, classified as a new and emerging generation of ceramics, are noticeably
popular primarily because they are capable of exhibiting remarkably high [4 times]
fracture toughness when compared one-on-one with alumina [4]. During the early
years, the primary objective for the addition of zirconia to alumina (Al 2 O 3 ) was to
improve its density. However, subsequent research studies have found and recorded
zirconia to be a potential reinforcing material capable of improving the fracture
toughness of alumina (Al 2 O 3 ) [5, 6].
Overall, through the years, several experiments have been conducted on the development of ZTA composites having an improved combination of properties. A few
of these studies focused on ZTA as the matrix material while few other studies were
conducted with ZTA as a viable reinforcement to metallic matrices, such as the ironbased composites [7], aluminum [8], and even cast iron [9]. However, like most
other materials, the ceramic-based composites tend to possess certain drawbacks
and often suffer from issues specific to corrosion resistance and oxidation resistance both at room temperature and elevated temperatures. Further, ceramics like
zirconium oxide (ZrO 2 ) and aluminum oxide (Al 2 O 3 ) do not suffer from these drawbacks. However, they tend to become relatively brittle when attempting to improve
their strength and thereby impeding and/or curtaining their selection and use for
several performance-critical applications. Also, the low cost of zirconia and alumina
makes them an attractive choice to both designers and manufacturers for selection
and use in a spectrum of non-performance-critical applications despite their inferior
mechanical properties when compared one-on-one with the other ceramics like the
nitrides and carbides. Also, the important properties of alumina (Al 2 O 3 ) to include
(i) hardness, (ii) fracture toughness, (iii) flexural strength, and (iv) wear resistance
can be noticeably improved by reinforcing it with zirconia [10–12].
The zirconia-based ceramics have in more recent years emerged as a viable alternative to overcome the low fracture toughness of composites by a toughening mechanism [13]. To overcome the intrinsic brittleness of alumina (Al 2 O 3 ), the YSZ is
added to the alumina matrix and the resultant zirconia-toughened alumina (ZTA)
reveals improved fracture toughness for the engineered composites by transforming
the zirconia phase from tetragonal to monoclinic [14]. Pure zirconia can favor the
K. L. Meena and T. S. Srivatsan
Introduction
The composite based on alumina-based ceramics offers an excellent combination of
properties to include the following: (i) overall chemical inertness, (ii) high abrasion
resistance, and (iii) high-hot-hardness against extreme environments [1]. Aluminum
oxide or alumina (Al 2 O 3 ) is often chosen a preferred choice for making cutting
tool inserts in comparison with carbides and the family of high-speed steel. This
is essentially because of its overall inert behavior, or response characteristics, of
alumina (Al 2 O 3 ) upon exposure to both elevated temperatures and hostile or aggressive environments [2]. Alumina-based ceramic cutting inserts are currently being
chosen for use in wear-critical or wear-specific environments, such as (i) mixers, (ii)
grinders, (iii) coal chutes, and (iv) ball mills [3]. Zirconia-toughened alumina (ZTA)
ceramics, classified as a new and emerging generation of ceramics, are noticeably
popular primarily because they are capable of exhibiting remarkably high [4 times]
fracture toughness when compared one-on-one with alumina [4]. During the early
years, the primary objective for the addition of zirconia to alumina (Al 2 O 3 ) was to
improve its density. However, subsequent research studies have found and recorded
zirconia to be a potential reinforcing material capable of improving the fracture
toughness of alumina (Al 2 O 3 ) [5, 6].
Overall, through the years, several experiments have been conducted on the development of ZTA composites having an improved combination of properties. A few
of these studies focused on ZTA as the matrix material while few other studies were
conducted with ZTA as a viable reinforcement to metallic matrices, such as the ironbased composites [7], aluminum [8], and even cast iron [9]. However, like most
other materials, the ceramic-based composites tend to possess certain drawbacks
and often suffer from issues specific to corrosion resistance and oxidation resistance both at room temperature and elevated temperatures. Further, ceramics like
zirconium oxide (ZrO 2 ) and aluminum oxide (Al 2 O 3 ) do not suffer from these drawbacks. However, they tend to become relatively brittle when attempting to improve
their strength and thereby impeding and/or curtaining their selection and use for
several performance-critical applications. Also, the low cost of zirconia and alumina
makes them an attractive choice to both designers and manufacturers for selection
and use in a spectrum of non-performance-critical applications despite their inferior
mechanical properties when compared one-on-one with the other ceramics like the
nitrides and carbides. Also, the important properties of alumina (Al 2 O 3 ) to include
(i) hardness, (ii) fracture toughness, (iii) flexural strength, and (iv) wear resistance
can be noticeably improved by reinforcing it with zirconia [10–12].
The zirconia-based ceramics have in more recent years emerged as a viable alternative to overcome the low fracture toughness of composites by a toughening mechanism [13]. To overcome the intrinsic brittleness of alumina (Al 2 O 3 ), the YSZ is
added to the alumina matrix and the resultant zirconia-toughened alumina (ZTA)
reveals improved fracture toughness for the engineered composites by transforming
the zirconia phase from tetragonal to monoclinic [14]. Pure zirconia can favor the