Abstract
The densification and mechanical properties of alumina ceramics were investigated via two-step sintering (TSS) with different holding time. The alumina ceramics were sintered at 1450 °C for 1 min during the first stage, followed by sintering at 1350 °C with different holding times (2-24h). Conventional sintering (CS) was also performed on the alumina ceramics at 1450 °C for 2 h for comparison purpose. It was found that dense alumina with a relative density above 98% could be attained when TSS with a holding time of more than 12 h. The samples exhibited Vickers hardness between 5-8 GPa and fracture toughness of about 6 MPa.m1/2. In contrast, conventional sintered alumina yielded low relative density (85%), large grain size (2 μm), low Vickers hardness (4.23 GPa) and fracture toughness (4.73 MPa.m1/2). This study revealed that TSS is a viable approach in aiding densification, suppressing grain growth, and improving the mechanical properties of alumina ceramics.
Highlights
Alumina (Al2O3) is one of the widely used engineering ceramics in biomedical and aerospace industries owing to its excellent biocompatibility, strength, hardness, and stability in physiological environment [1,2]
The results showed that there were two grain size-densification trajectory which represents the densification rate as depicted by the slope of the linear line in Figure 3 could be observed for the alumina ceramic
Li & Ye [11] reported similar findings, where fast grain growth was noticeable when relative density of alumina exceeded 90%. They found that two-step sintered alumina ceramics (1450 °C/1 h → 1350 °C/34 h and 1380 °C/1 h → 1330 °C/50 h) resulted in better densification and smaller grain size
Summary
Alumina (Al2O3) is one of the widely used engineering ceramics in biomedical and aerospace industries owing to its excellent biocompatibility, strength, hardness, and stability in physiological environment [1,2]. Since high sintering temperatures (>1450 °C) were generally required to produce high-density alumina ceramics using pressureless sintering [7], two-step sintering has been experimented to lower the densification temperatures and suppressing abnormal grain growth in order to retain a fine microstructure [8]. The green sample is heated to a high temperature of T1 and holding at this temperature for a very short period This is followed by the second stage, where the temperature is lowered to T2 and holding at this temperature for a longer holding time to allow densification to proceed without grain coarsening. Densification and Mechanical Properties of Alumina Ceramics via Two-Step Sintering with Different Holding Times. International Journal of Engineering Materials and Manufacture, 6(4), 209-304
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