Influence of Sintering on the Development of Alumina-Toughened …
169
‘Image J’ software having a linear intercept approach program was used to calculate
the average grain size of the engineered composite materials using the corresponding
microstructure. To evaluate the mechanical properties, both microhardness and fracture tests were conducted. The microhardness was measured using a computerized
Vickers hardness tester having a 300-g indenter load and a dwell time of 10 s. For
each sample, ten indentations were systematically made across an area of the sample
and subsequently measured for both accuracy and precision. The calculated c/a ratio
in the present study was higher than 2.5. Hence, it comes under the radial-median
crack system [32, 33]. Also, for this condition, the Anstis equation is favorable for
calculating the fracture toughness of the composite sample. The Anstis equation is
given by Eq. 1 [34] and was used to calculate the fracture toughness (K IC ) of the
composite sample.
K IC = 0.016
E
H V
1
2 P
C
3
2
(1)
In this expression or equation, p is the indenter load, ‘c’ is the radial crack length,
E is the elastic modulus, which is calculated using the mixture rule; ‘a’ is half of the
indentation diagonal, and H v is Vickers hardness.
Results and Discussion
X-Ray Diffraction (XRD) Analysis
An evaluation of the phases formed in the developed composites was done using
X-ray diffraction (XRD) analysis and the corresponding XRD patterns are shown
in Fig. 2. From Fig. 2a and b show peaks of the ATZ composites sintered using the
techniques of conventional sintering (CS) and microwave (MW) sintering. It is easily
noticed that the major peaks indicate tetragonal zirconia (t-ZrO 2 ) [designated as t,
ICDD files No. 072-7115] and alumina (α-Al 2 O 3 ) [designated as α, ICDD files No.
ICDD 089-7717], while the minor peaks of monoclinic zirconia (m-ZrO 2 ) [designated as m, ICDD files No. 037-1484] and cubic zirconia (c-ZrO 2 ) [designated as m,
ICDD files No. 027-0997] were easily observed. There was no distinct for the presence of secondary phases. The highest peak intensity for the tetragonal t-ZrO 2 phase
was detected at an angle of 30°. The formation and presence of secondary phases does
affect both the microstructure and resultant properties of the developed composites.
The metastable transformation of zirconia from t-ZrO 2 to m-ZrO 2 can essentially
be attributed to the ‘local’ stress that is induced in the field around a propagating
crack and that which contributes to enhancing the toughness of zirconia ceramics.
The m-ZrO 2 phase in the microwave (MW) sintered sample did transform to t-ZrO 2.
Also, it was observed that the microwave (MW) sintered sample did exhibit a lower
amount of the monoclinic zirconia phase. In the present study, despite selection of
169
‘Image J’ software having a linear intercept approach program was used to calculate
the average grain size of the engineered composite materials using the corresponding
microstructure. To evaluate the mechanical properties, both microhardness and fracture tests were conducted. The microhardness was measured using a computerized
Vickers hardness tester having a 300-g indenter load and a dwell time of 10 s. For
each sample, ten indentations were systematically made across an area of the sample
and subsequently measured for both accuracy and precision. The calculated c/a ratio
in the present study was higher than 2.5. Hence, it comes under the radial-median
crack system [32, 33]. Also, for this condition, the Anstis equation is favorable for
calculating the fracture toughness of the composite sample. The Anstis equation is
given by Eq. 1 [34] and was used to calculate the fracture toughness (K IC ) of the
composite sample.
K IC = 0.016
E
H V
1
2 P
C
3
2
(1)
In this expression or equation, p is the indenter load, ‘c’ is the radial crack length,
E is the elastic modulus, which is calculated using the mixture rule; ‘a’ is half of the
indentation diagonal, and H v is Vickers hardness.
Results and Discussion
X-Ray Diffraction (XRD) Analysis
An evaluation of the phases formed in the developed composites was done using
X-ray diffraction (XRD) analysis and the corresponding XRD patterns are shown
in Fig. 2. From Fig. 2a and b show peaks of the ATZ composites sintered using the
techniques of conventional sintering (CS) and microwave (MW) sintering. It is easily
noticed that the major peaks indicate tetragonal zirconia (t-ZrO 2 ) [designated as t,
ICDD files No. 072-7115] and alumina (α-Al 2 O 3 ) [designated as α, ICDD files No.
ICDD 089-7717], while the minor peaks of monoclinic zirconia (m-ZrO 2 ) [designated as m, ICDD files No. 037-1484] and cubic zirconia (c-ZrO 2 ) [designated as m,
ICDD files No. 027-0997] were easily observed. There was no distinct for the presence of secondary phases. The highest peak intensity for the tetragonal t-ZrO 2 phase
was detected at an angle of 30°. The formation and presence of secondary phases does
affect both the microstructure and resultant properties of the developed composites.
The metastable transformation of zirconia from t-ZrO 2 to m-ZrO 2 can essentially
be attributed to the ‘local’ stress that is induced in the field around a propagating
crack and that which contributes to enhancing the toughness of zirconia ceramics.
The m-ZrO 2 phase in the microwave (MW) sintered sample did transform to t-ZrO 2.
Also, it was observed that the microwave (MW) sintered sample did exhibit a lower
amount of the monoclinic zirconia phase. In the present study, despite selection of