Journal of Advanced Ceramics (Jun 2024)
Grain growth behavior and properties of high-entropy pseudobrookite (Mg,Co,Ni,Zn)Ti2O5 ceramics
Abstract
It is well known that the grain size of high-entropy ceramics is quite small owing to the sluggish diffusion effect. However, abnormal grain growth often occurs in high-entropy pseudobrookite ceramics, ultimately resulting in the formation of many abnormally grown grains with a grain size as large as 50 μm. To study this phenomenon, the grain growth behavior of high-entropy pseudobrookite ceramics was systematically investigated in this paper. The results demonstrate that the starting material powders first react with each other to form a high-entropy intermediate phase and calcined TiO2 powders (TiO2-1100 °C), and then as the sintering temperature increases, the formed high-entropy intermediate phase further reacts with TiO2-1100 °C to form high-entropy pseudobrookite ceramics. Thus, in this system, in addition to the sluggish diffusion effect, the grain sizes of the high-entropy intermediate phase and TiO2-1100 °C also affect the morphology of high-entropy pseudobrookite. Compared to nanosized TiO2, micron-sized TiO2 has a lower sintering activity. Therefore, the high-entropy intermediate phases (Mg,Co,Ni,Zn)TiO3 and TiO2-1100 °C prepared with micron-sized starting materials exhibit lower grain sizes, finally resulting in the formation of high-entropy (Mg,Co,Ni,Zn)Ti2O5 with small grain sizes. Moreover, nano-indentation and thermal conductivity tests were carried out on high-entropy (Mg,Co,Ni,Zn)Ti2O5 with different morphologies. The results show that the hardness of high-entropy (Mg,Co,Ni,Zn)Ti2O5 increases from 6.05 to 9.95 GPa as the grain size increases, whereas the thermal conductivity decreases from 2.091±0.006 to 1.583±0.006 W·m−1·K−1. All these results indicate that high-entropy (Mg,Co,Ni,Zn)Ti2O5 with a small grain size is a potential material for thermal protection.
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