Abstract
High strength transparent Y2O3 ceramics were fabricated from commercial powders using spark plasma sintering (SPS) technique by optimizing the heating rate. The heating rate significantly influenced the microstructures and the optical/mechanical properties of the Y2O3 ceramics. Grain growth was limited accordingly with increasing the heating rate. The ball milling process of the commercial Y2O3 powders is likely to further enhance the sinterability during the SPS processing. The dense Y2O3 ceramics, which were sintered by SPS with 100 °C/min, showed good transmittance range from visible to near infrared (IR). For a high heating rate of 100 °C/min, the in-line transmittance at a visible wavelength of 700 nm was 66%, whereas for a slow heating rate of 10 °C/min, it reduced to 46%. The hardness Hv tends to increase with increasing the heating rate and rigorously followed the Hall–Petch relationship; that is, it is enhanced with a reduction of the grain size. The toughness KIC, on the other hand, is less sensitive to both the heating rate and the grain size, and takes a similar value. This research highlighted that the high heating rate SPS processing can fabricate fully dense fine-grained Y2O3 ceramics with the excellent optical and mechanical properties.
Highlights
Transparent polycrystalline Y2 O3 ceramics are known as promising optical materials in various applications such as high intensity discharge lamps, missile domes, heat resistive windows, and host material in ceramic lasers and scintillators owing to their significant physical and chemical properties of low thermal expansion, high thermal conductivity, a broad transparency range from violet to infrared light, and high corrosion resistance [1,2,3,4,5,6].the fabrication of transparent Y2 O3 ceramics is quite challenging work because the Y2 O3 ceramics are known to be difficult to sinter, due to the high melting point of Y2 O3(2430 ◦ C)
Yoshida et al [25] have reported the fabrication of the translucent polycrystalline Y2 O3 ceramics at a relatively lower temperature of 950 ◦ C with a slow heating rate of 2 ◦ C/min by spark plasma sintering (SPS)
The grain growth, was limited with increasing the heating rate; it was ~499 nm at a heating rate of 10 ◦ C/min but was reduced to ~164 nm at 100 ◦ C/min. This heating rate dependent grain size conflicts with the results reported by Yoshida et al
Summary
Transparent polycrystalline Y2 O3 ceramics are known as promising optical materials in various applications such as high intensity discharge lamps, missile domes, heat resistive windows, and host material in ceramic lasers and scintillators owing to their significant physical and chemical properties of low thermal expansion, high thermal conductivity, a broad transparency range from violet to infrared light, and high corrosion resistance [1,2,3,4,5,6]. The typical and conventional preparation methods of the transparent polycrystalline Y2 O3 ceramics are hot pressing, hot isostatic pressing, and pressureless sintering at high temperatures [7,8,9] Such high-temperature sintering processes can attain transmittance, those usually cause intense grain growth, and result in the poor mechanical properties, which make it difficult to use in industrial applications. Zhang et al [24] prepared transparent Y2 O3 with an in-line transmission Tin of 68% at a wavelength λ of 700 nm by using high pressure SPS technique at 1050 ◦ C under an uniaxial pressure of 300 MPa. Yoshida et al [25] have reported the fabrication of the translucent polycrystalline Y2 O3 ceramics at a relatively lower temperature of 950 ◦ C with a slow heating rate of 2 ◦ C/min by SPS.
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