Influence of Sintering on the Development of Alumina-Toughened …
173
Fig. 4 a Relative density of the conventional sintered and microwave sintered sample b Porosities
of the conventional sintered and microwave sintered sample
1 and shown in Fig. 4a. Porosity is a factor that exerts an influence on density of the
as-synthesized composite materials and the following formula was used to calculate
porosity of the developed or synthesized composites.
Porosity (% ) =
ρ t − ρ s
ρ t
(2)
In this expression, ρ t is the theoretical density and ρ s is the sintered density.
The microwave (MW) sintered sample which experienced rapid heating and resultant higher densification led to a noticeable reduction in level or amount of porosity.
The porosity of the microwave (MW) sintered sample was marginally lower than
that of the conventional sintered (CS) sample. The percentage of porosity in the
conventional sintered (CS) sample was 0.84 ± 0.07% and microwave (MW) sintered
sample was 0.71 ± 0.05%. This is shown in Fig. 4b.
Microhardness and Surface Roughness
The variation in microhardness of the composite samples developed using the techniques of both microwave (MW) sintering and conventional sintering (CS) is shown
in Fig. 5a.
The ATZ composite samples developed using microwave (MW) sintering possess
higher values of the microhardness when compared to the conventional sintered (CS)
composite sample. However, the hardness slightly decreased due to the presence
of ZrO 2 , while hardness was expected to enhance with the presence of alumina
(Al 2 O 3 ) particulate reinforcements in the metal matrix. The observed improvement
in hardness can be attributed to both an improvement in the suppression of grain
growth and a near uniform dispersion of the ZrO 2 in the alumina (Al 2 O 3 ) matrix.
Moreover, the 3 mol.% Yttria-doped zirconia ceramic has reduced the monoclinic
phase during transformation toughening mechanism of the ZrO 2 matrix and increased
173
Fig. 4 a Relative density of the conventional sintered and microwave sintered sample b Porosities
of the conventional sintered and microwave sintered sample
1 and shown in Fig. 4a. Porosity is a factor that exerts an influence on density of the
as-synthesized composite materials and the following formula was used to calculate
porosity of the developed or synthesized composites.
Porosity (% ) =
ρ t − ρ s
ρ t
(2)
In this expression, ρ t is the theoretical density and ρ s is the sintered density.
The microwave (MW) sintered sample which experienced rapid heating and resultant higher densification led to a noticeable reduction in level or amount of porosity.
The porosity of the microwave (MW) sintered sample was marginally lower than
that of the conventional sintered (CS) sample. The percentage of porosity in the
conventional sintered (CS) sample was 0.84 ± 0.07% and microwave (MW) sintered
sample was 0.71 ± 0.05%. This is shown in Fig. 4b.
Microhardness and Surface Roughness
The variation in microhardness of the composite samples developed using the techniques of both microwave (MW) sintering and conventional sintering (CS) is shown
in Fig. 5a.
The ATZ composite samples developed using microwave (MW) sintering possess
higher values of the microhardness when compared to the conventional sintered (CS)
composite sample. However, the hardness slightly decreased due to the presence
of ZrO 2 , while hardness was expected to enhance with the presence of alumina
(Al 2 O 3 ) particulate reinforcements in the metal matrix. The observed improvement
in hardness can be attributed to both an improvement in the suppression of grain
growth and a near uniform dispersion of the ZrO 2 in the alumina (Al 2 O 3 ) matrix.
Moreover, the 3 mol.% Yttria-doped zirconia ceramic has reduced the monoclinic
phase during transformation toughening mechanism of the ZrO 2 matrix and increased