No abstract

ResumoAs propriedades e caracteristicas do diboreto de titânio (TiB2) e nitreto de alumínio (AlN) tornam esses materiais ideais para aplicações termomecânicas. Entretanto, a dificuldade de sinterizar compósitos cerâmicos à base de TiB2 -AlN tem limitado suas aplicações na indústria contemporânea. Nesse sentido, o presente trabalho tem por objetivo avaliar a técnica de sinterização por plasma pulsado (SPS), como uma alternativa para consolidação de compósito cerâmico em um curto intervalo de tempo. Após a caracterização das matérias primas, as amostras foram sinterizadas utilizando temperaturas entre 1.500°C e 1.900°C, além de 80 MPa de pressão e 10 minutos de permanência na temperatura máxima. A técnica "SPS" mostrou-se eficiente na sinterização desse sistema, alcançando densificações de até 98%. E ainda, como era esperado, a incompatibilidade dos coeficientes de expansão térmica entre o TiB2 e o AlN provocaram um processo de tenacificação nos compósitos. Palavras-chave: Sinterização, Compósitos, Cerâmica, Caracterização. SINTERING CERAMIC COMPOSITES TiB2 -AIN BY WAY OF PULSED PLASM AbstractThe properties and characteristics of titanium diboride (TiB2) and aluminum nitride (AlN) make these ideal materials for thermomechanical applications. However, the difficulty of ceramic composites sintering the based in TiB2 -AlN has limited its applications in th contemporary industry. In this sense, the present study aims to assess the sintering technique pulsed plasm (SPS) as an alternative to ceramic composite consolidation in a short period of time. After the characterization of raw materials, the samples were sintered using temperatures between 1,500°C and 1,900°C, and 80 MPa pressure and 10 minutes permanency at the maximum temperature. The "SPS" technique proved efficient in the sintering of this system, reaching densification up to 98%. And, as expected, the incompatibility of thermal extension coefficient between TiB2 and the AlN in motion a process of toughening of composites.

Aluminum nitride, AlN, and titanium diborite,TiB2, are covalent-based ceramics with wide technological applications. However, sintering of these ceramics using conventional methods of high pressure requires not only elevated temperatures but also long processing time. This causes excessive grain growth, which impairs strength and hardness. In the present work, 70%AlN-30%TiB2 ceramic composites were sintered to relatively higher density and hardness by means of the Spark Plasma Sintering (SPS) at temperatures in the interval from 1500 to 1900°C in order to improve the properties of both compounds and decrease the processing time. The SPS was applied for different sintering temperatures and the effects on density, hardness and surface structure were evaluated. Maximum values obtained for density and hardness were 98.8% of the theoretical value and 13.7 GPa, respectively.

This a preprint and has not been peer reviewed. Data may be preliminary.

The Critical Distances Theory has been used in engineering field as a less expensive method to predict failures. Thus, this research aims to evaluate its methods in other materials, like the aluminum alloy 7075 T6, and notches. Two different notches were machined: a sharp and a blunted, with radius of 0,025 mm and 0,045 mm, respectively. The first in specimens of tests tension and the last in bend tests specimens. The DCT methods analyzed exhibited low percent differences and predictions mutually consistent. However, the Line Method stood out when presented 3% to percent difference. The analysis to stress field around of sharp notch tip, LM achieved a value of 12 MPa√m para K Ic . Although, when these same results were applied in the Traditional Fracture Mechanics equations, a fracture toughness of 34 MPa√m was found. This last result is one of the best predictions achieved until the present moment in this research group. Mainly when compared with other works which determined the same property using the same thermal treatment conditions to this alloy.