Papers by Keyword: hBN

Abstract: We present a performance assessment of graphene/hexagonal Boron Nitride heterojunctions based transistors able to provide large current modulation. The study is performed by means of a multi-scale approach leveraging ab-initio simulations to capture the physics at the atomic scale, and tight-binding simulations to compute transport. In particular, we focus on two technological solutions, a vertical and a planar structure both able to provide large Ion/Ioff ratios. As we will show, due to reduced capacitative coupling, the planar structure outperforms the vertical device as far as digital applications are concerned.

Abstract: Tungsten carbide (WC) and WCCo powders added with 30 vol.% cubic boron nitride (cBN) and 5 and 12 wt% of Ti were sintered by the pulse plasma sintering (PPS) technique. The sintering process was conducted under a load of 75 MPa at a pressure of 5.10- 5 mbar and a temperature of 1100-1500°C for 5min. The phase composition, density, hardness and microstructure of the sintered material thus obtained were examined. In the cBN-WCTi5wt% composite with an addition of 6wt% Co, the cBN particles are well bound with the matrix. The transcrystalline fractures of the cBN particles also indicate that the binding forces between these particles and the WCCoTi matrix exceed the matrix cohesion. The interfaces between the cBN grains and the surrounding matrix are almost straight lines, and no reactions between the cBN grains and the matrix were revealed in SEM observations.

Abstract: In order to produce Si3N4/hBN composite with low cost, it seems necessary to use nitrided Si3N4 powders since the cost of Si powder is much cheaper than that of Si3N4 powder. The purpose of the present work is to investigate the nitride conditions, and in particular, we focused on the relationship between microstructures and mechanical properties of hot-pressed Si3N4/hBN ceramic composite using nitrided Si3N4 powders. The mixed powders of Si3N4 and hBN were prepared by nitriding Si powders at 1380oC for 24 h, and subsequently sintered by hot-pressing at 1800oC for 2 h in N2 atmosphere. The microstructure and mechanical properties of the Si3N4/hBN composites were investigated. Flexural strength, Young’s modulus, and hardness decreased by the addition of 20 vol% hBN. The addition of BN resulted in a decrease in the modulus as well as an increase in the size of fracture source, both contribute to the observed decrease in mechanical properties. The Si3N4/BN based ceramic composites revealed enhanced crack deflection. The Vickers indentation crack paths in specimens are sinusoidal due to pull-out of grains during crack propagation.

Abstract: In this study, powder blasting techniques are applied for micro groove forming on the developed AlN/hBN composites. First, material properties of the composites are evaluated according to the variation of h-BN contents. And, a series of required experimental works are performed to determine optimum powder blasting conditions for micro groove forming. The experiments are performed for the prepared samples with masked patterns. As the results, it can be observed that the machiniability of the developed AlN/hBN composites increases as h-BN contents in the composites. Also, from the experimental results, it is possible to determine the optimum blasting conditions for micro groove forming on the developed AlN/hBN composites.

Abstract: The effects of hBN content on microstructure, mechanical properties, and machinability of the pressureless-sintered Si3N4 ceramics were investigated. Flexural strength, Young’s modulus, and hardness decreased with increasing h-BN content. The mechanical properties are decreased mainly because of increased porosity of composite, and the much lower Young's modulus of BN compared to that of Si3N4. Pressureless-sintered Si3N4/hBN composites exhibit strong texture of BN grains oriented with the c-axis parallel to the cold-pressing direction. Cutting resistance of Si3N4 ceramic composites with more than 10 vol% hBN decreased with increasing hBN content, demonstrating a good machinability of the composites. The residual pores can be attributed to improved machinability of pessureless-sintered Si3N4-BN composite.