Study of the influence of Si₃N₄ and AlN additives on production and properties of hot-pressed materials based on BN

Graphite-like hexagonal boron nitride (h-BN) is a promising material for the metallurgical industry due to its high melting point and heat resistance, low wettability and ability not to react with other substances. The main disadvantage of this material is its low mechanical properties, which prevent the use of this material for practical purposes. The solution to this problem can be the addition of various additives to boron nitride, increasing its mechanical properties. Currently, to obtain products from boron nitride the method of sintering turbostratic powders of boron nitride, the method of sintering under gas pressure and hot pressing are used. In this paper, the influence of Si₃N₄ and AlN additives on the physical and mechanical properties, structure of boron nitride-based materials depending on the sintering temperature and the content of additives was investigated. The investigated materials were obtained by hot pressing at temperatures ranging from 1360 to 1700°C. To intensify the sintering process, silicon nitrides (Si₃N₄) and aluminum nitrides (AlN) were added to the powder mixture in varying amounts in addition to hexagonal boron nitride. X-ray diffraction studies, porosity, density, modulus of elasticity and compression tests were carried out. The obtained hot-pressed composite materials based on BN have a high degree of crystallinity, containing both crystal structures corresponding to hexagonal boron nitride, silicon and aluminum nitrides, and phases of aluminum oxide, aluminum oxynitride and silicon. Using the example of BN+ 10% Si₃N₄ sample, it was found that the highest density of materials obtained at 1500°C is 3,02 g/cm3 with porosity 0,29. The materials obtained at 1700°C have the highest elastic modulus and sound velocity: E = 52,6 GPa, hzv = 4389 m/s. It was found that the increase in the mass content of Si₃N₄ and AlN additives contributes to a significant increase in the density of the material. Increasing the hot pressing temperature from 1360 to 1500°C also contributes to a significant increase in density. Values of elastic modulus and speed of sound do not change significantly with increasing the content of Si₃N₄ + AlN additives complex, but increase with increasing the hot pressing temperature and with increasing the mass content of Si₃N₄ in the composition from 20% to 50%. Mechanical characteristics with increasing the content of Si₃N₄ + AlN additive complex decreases, while with increasing the temperature of hot pressing strength increases. When increasing the mass content of Si₃N₄ in the composition from 20% to 30%, the tensile strength increases significantly, at the same time, decreases with the subsequent increase in the mass content of Si₃N₄. The authors declare no conflicts of interests.

Keywords

Authors

References