Boron carbide is a very special structural ceramic with high hardness and low density. Use it as a bulletproof armor material for vehicles and personnel. However, pure boron carbide has low toughness. It is easy to form long through cracks after being hit by bullets. It is not conducive to resisting the second or third shot. To improve toughness, it is necessary to start from the composition or microstructure.
Professor Wang Zhijiang’s team at Harbin Institute of Technology proposed to introduce a twin structure into boron carbide ceramics to improve its toughness. The relevant results were published in “Ceramics International”.
It notes that the sintering performance of boron carbide ceramics is poor, and it is difficult to obtain dense samples by traditional vacuum sintering. Experimentally, it is generally prepared by the hot pressing sintering process, which takes a long time and has low experimental efficiency. Spark Plasma Sintering is an efficient experimental method. Completes the sample preparation experiment in this article on our CNE-FHP-858 Spark Plasma Sintering furnace.
Experiment process and results
The author selected carbon black and amorphous boron powder as starting materials and obtained boron carbide powder by solid phase synthesis. Then load it into a graphite mold with a diameter of 50mm and sintered in our CNE-FHP-858 Spark Plasma Sintering furnace. The pressure is 50MPa and the sintering temperature is 1750~2050℃. The initial heating rate is 150℃/min, which is reduced to 80℃/min before reaching the sintering temperature. The holding time is 5min. Generally speaking, the entire sintering process does not exceed 30 minutes, and with cooling, it obtains the samples in a maximum of two hours.
SEM photos show that as the sintering temperature increases, the density of the sample continues to increase. At 2000℃ or 2050℃, it can obtain a void-free and high-density boron carbide ceramic sample.
TEM photos show that the sample contains a rich twin structure. This brings about an improvement in the mechanical properties of the sample. Under the optimized process conditions, the boron carbide ceramic sample obtained by the author has a Vickers hardness of 32.2GPa, a bending strength of 486MPa, and a fracture toughness of 4.18MPa m1/2. All of which significantly improved compared with traditional processes.
The results show that spark plasma sintering is very suitable for boron carbide ceramics. Our company has processed boron carbide samples obtained by Spark Plasma Sintering into jewelry such as gem rings and earrings. Boron carbide has a hardness second only to diamond. And sometimes, we call it the black diamond. Combined with the high density obtained by Spark Plasma Sintering, this jewelry shows a unique luster.
