Effect of heating rate on properties of transparent aluminum oxynitride sintered by spark plasma sintering

Abstract

High heating rates ranging from 50 to 250°C/min are selected to rapidly sinter transparent aluminum oxynitride (AlON) ceramics by spark plasma sintering (SPS) at 1600°C under 60 MPa using a bimodal AlON powder synthesized by the carbothermal reduction and nitridation method. With 1 minute holding time before cooling, all the specimens show high density and high transparence. The maximum transmittance is up to 74.5%-80.6%, where the maximum transmittance is positively correlated with the heating rate. Further analysis reveals that faster heating rates enable the decrease in the amount of the AlON phase decomposed into the α-Al 2 O 3 and AlN phases during heating. These α-Al 2 O 3 and AlN phases have to be converted back to AlON at the final stage of sintering, which indicates that a decrease in the amount of the α-Al 2 O 3 and AlN phases via the boosted heating leads to the higher transmittance of the AlON ceramics. The high heating rates and short holding duration of the SPS utilized in this study result in the fine grain size of the obtained ceramics (1-6 μm) compared to that of the AlON ceramics fabricated by the conventional sintering method. This effect of high heating rates is confirmed by the coupled densification-grain growth modeling. In turn, the obtained AlON specimens exhibit a Vickers hardness of 15.87-16.62 GPa. K E Y W O R D S aluminum oxynitride, phase transformation, rapid rate heating, spark plasma sintering, transparent ceramics

Pressureless sintering of transparent AlON ceramic with assimilable γ‐Al2O3 as sintering promoting additives

“…In Figure 3, the emergence of the diffraction patterns of the Al 2 O 3 phase gives a hint of the decomposition of AlON at 1200°C, which means that the nitrogen‐rich AlON powder we synthesized is not very stable during the sintering. This phenomenon is also be found by other researchers 15,16 . When the temperature is increased to 1400°C, the diffraction patterns of AlN phase also become notable, which again suggests that parts of AlON have decomposed.…”

“…This phenomenon is also be found by other researchers. 15,16 When the temperature is increased to 1400 • C, the diffraction patterns of AlN phase also become notable, which again suggests that parts of AlON According to the AlON phase diagrams of Willems, 17 McCauley and Corbin, 18,19 and McCauley et al, 20 AlON is not stable under 1600 • C, so the decomposition of AlON was found in this work. With the increase of temperature, the solid solution range of AlN-Al 2 O 3 becomes wider, so we found the re-formation of AlON.…”

“…27,28 The mean grain size of all the samples is about 10 μm, which is much smaller than other AlON samples doped with traditional sintering additives. 29,30,26,32 Five valid indentations were made at the same load of 0.3 Kg for each sample, as can be seen in the inserted SEM image of 3,15,31,33 The in-line transmittance parameters of AlON ceramics were determined and the result is shown in Figure 10. Sample0 is translucent and only has an in-line transmit-tance of 47%.…”

“…This phenomenon can be explained by the fact that the doping of Al 2 O 3 makes the properties of AlON approach to Al 2 O 3 . Compared with AlON ceramics fabricated by doping traditional sintering additives, the AlON ceramics in this work are harder 3,15,31,33. The in-line transmittance parameters of AlON ceramics were determined and the result is shown in Figure10.…”

The study on the preparation of AlON transparent ceramic and its ballistic resistance

“…They found that AlON transparent ceramics with high transmittance can be sintered without pressure at 1880 ℃. Shan et al [7] from Dalian Maritime University used SPS to study the heating rate and its effects on the physical characteristics of the transparent ceramic AlON. They found that increasing the heating rate from 50 ℃/min to 250 ℃/min can increase the visible transmittance to 74.6% -80.6%.…”