Spark plasma sintering is used to consolidate a WC-Co powder produced from milled discharged hard metal cutting inserts. The powder was mixed to 10%wt Co powder and spark plasma sintered (SPS) under 80Mpa pressure, at 1200ºC with heating rate of 160ºC/min. A reference alloy was prepared with a commercial WC powder and 10%wt. Co under the same conditions. The structures of both alloys were investigated by means of scanning electron microscopy and Vickers hardness. The results show structures with densities and hardness at the same level. SPS can be used to produce hard metal pieces directly from scrap powder without any prior chemical and thermal treatment.

RESUMO O diboreto de titânio (TiB2) é um material cerâmico que se destaca por sua elevada resistência mecânica, estabilidade química e dureza a altas temperaturas, entretanto, características como baixa sinterabilidade e tenacidade a fratura limitam a atuação deste material em aplicações termomecânicas. Técnicas de sinterização não convencionais como SPS e aditivo de sinterização como AlN e Si3N4 podem reduzir a temperatura de sinterização e aumentar a tenacidade à fratura do TiB2. Neste sentido, o presente trabalho teve como objetivo avaliar a eficiência da técnica de sinterização por plasma pulsado (Spark Plasma Sintering - SPS) no processamento do diboreto de titânio. O nitreto de alumínio foi utilizado como aditivo para reduzir temperatura e tempo de sinterização e facilitar a densificação do TiB2. Os resultados apontam a sinterização por plasma pulsado como uma técnica eficiente na densificação de compósito cerâmico TiB2 - AlN. Elevado grau de densificação foi alcançado mesmo utilizando tempos de sinterização relativamente curto.

ABSTRACT Titanium diboride (TiB2) is a ceramic material that highlight because of its high mechanical resistance, chemical stability and hardness in high temperatures. However, characteristics as low sinterability and fracture toughness restrict its usage on termomechanical applications. Non-conventional sintering techniques as SPS and sintering aid as AlN and Si3N4 can reduce sintering temperature and increase fracture toughness of TiB2. The objective of this work is to evaluate the efficiency of spark plasma sintering (SPS) technique on the manufacturing of titanium diboride. Aluminum nitride (AlN) was used as additive to reduce sintering temperature and time and enhance tib2 densification. The results indicate that spark plasma sintering is an efficient technique in the densification of TiB2 - AlN ceramic composite. High degree of densification was achieved even using relatively short sintering time.

No presente estudo foi introduzido zinco na mistura reativa composta por Ni-Mn e grafite. O objetivo da impregnação da mistura com zinco foi tentar controlar o processo de nucleação e crescimento dos cristais de diamante. Os resultados obtidos mostraram que a adição de zinco promove um significativo aumento na produtividade dos cristais, em torno de 40%, permitindo ainda a obtenção de cristais com alta friabilidade.

In the present work zinc was introduced in the reactive mixture composed by Ni-Mn and graphite. The main objective of the zinc impregnation was to control the diamond nucleation process and crystal growth of particles. The results indicated that the zinc addition promotes a significant diamond yield by synthesis cycle, around 40%. Additionally, the diamond powder obtained has a high friability.

The work reported on here involved the development of several samples of "diamond-SiC" composite produced under sintering pressures of up to 9.0 GPa at temperatures of up to 1973 7K. The average size of the diamond micropowder crystals used was 40/28 µm. The sintering process was carried out in a 2500-ton hydraulic press equipped with an anvil-type high-pressure device having a toroidal work surface and a central concavity diameter of 20 mm. The microhardness and wear resistance of the samples were found to be dependent on the sintering pressure. The experimental results indicated that the maximum microhardness and minimum wear resistance coefficients of each compact were attained when the pressure applied during sintering exceeded 6.5 GPa. Based on the established values of pressure, this study served to identify the types of devices applicable for the manufacture of composite material inserts for a variety of rock drilling applications.