Vania Trombini

Spark plasma sintering (SPS) de nanocompósitos de Al2O3-ZrO2

A recent alternative to sintering nanometric ceramics is Spark Plasma Sintering - SPS. This process permits the sintering at lower temperatures and short times producing materials with density near the theoretical density with small grain sizes. In this work alumina powder with well dispersed 5%vol addition of nanometric zirconia inclusions were obtained and sintered using SPS method by heating to temperatures ranging from 1250 to 1400 oC and different holding times were applied to determine the best condition for obtaining dense material with minimal grain growth. The samples were characterized by apparent density measurement, high-resolution SEM, and microhardness. The results show microstructural evolution for different sintering temperatures and holding times and the effect of inclusions on the alumina matrix grain growth, which is related to the results of densification under SPS conditions. Using the SPS method it was possible to obtain samples with full density at 1300 oC and holding time of 2 min with homogeneous microstructure, and microhardness near 22 GPa.

Obtained of Diamond Nanometric Powders Using High Energy Milling for the Production of Alumina-Diamond Nanocomposites

The addition of nanometric particles of a second phase into ceramics matrix is one of the most recent alternatives in the development of materials with high mechanical properties and wear resistance. These nanostructured materials can be defined as systems that have at least one microstructural characteristic of nanometric dimensions (less 100nm). In this work aluminadiamond nanocomposites were produced using diamond nanometric powders obtained by high energy milling. Diamond powder was produced in the SPEX shaker/mill during 6h, with a ball-tomass ratio of 4:1. The crystallite size was 30nm. After the elimination of the Fe deriving of the contamination during the milling, and desaglomeration, this nanometric powder was added in the alumina matrix in the ratio of 5wt%. The powder densification was performed by hot pressing sintering. The obtained nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness, and they have promising characteristics regarding abrasion and wear resistance.

Densification of Reactive Milled Al2O3-TiC Composite Powders

The synthesis of Al 2 O 3 - TiC composite powder can be achieved by reactive milling of powder mixtures of TiO 2 , Al and C. In this case the reactive milling occurs through a sudden highly exothermic self-sustaining reaction started after a certain milling time. Due to the high temperatures reached during the reaction, the products are formed as strong agglomerates. For the synthesis of the Al 2 O 3 + TiC, probably due the high melting point of the reaction products, particularly of the TiC, these agglomerates are formed by crystallites in the nanometric range. In the present work, Al 2 O 3 - TiC composite was synthesized by reactive milling in a shaker/mill apparatus, followed by a deagglomeration processing. The products of reactive milling were mixed with a commercial ultra-fine alumina powder to produce alumina matrix composites with 5 wt% of TiC. The powder densification was performed by hot pressing and by pressureless sintering between 1400 and 1600 °C. We report on the microstructure characterization of the dense TiC+Al 2 O 3 composites by SEM and TEM. It was observed that TiC is dispersed in the alumina matrix microstructure as both agglomerated inclusions and also dispersed nanometric inclusions. Vickers Hardness measurements of the sintered composites indicated values of about 13.0GPa.

Sintering Study of Al2O3/NbC/Wc Micro-Nanocomposite

Ceramic materials based on alumina are considered excellent for produce cutting tools used to machining hard metals. However, low mechanical strength and toughness presented by these materials limit their application. Traditionally particles, such as TiC, TiN and ZrO2, are added to the alumina matrix to improve their mechanical properties, increasing the range of applications. Recent studies have shown that the addition of particles of different sizes in alumina matrix can promote simultaneous increase in mechanical strength and tenacity. In this work sintering behavior of Al2O3 micro-nanocomposite containing nanometric particles of NbC and micrometric particles of WC, was studied by dilatometry using heating rate of 20°C/min up to 1800°C. The addition of carbides in alumina matrix is prejudicial to sintering causing an increase in temperature of shrinkage.

Otimização dos processos de moagem e secagem do pó de alumina/TiC obtido por moagem reativa

Agglomerates in ceramic powders often cause heterogeneities and defects in the final ceramic product, due to differential densification of the agglomerates during the sintering stage. Hence, control of the processing steps is important to form ceramic bodies without agglomerates and with a homogeneous microstructure. In this study, the processing conditions to reduce aggregate formation during high-energy milling and control of the powder drying step were evaluated to attain a microstructure consisting of small grains and a homogeneous distribution of TiC inclusions in the matrix.

Utilization of NbC Nanoparticles Obtained by Reactive Milling in Production of Alumina Niobium Carbide Nanocomposites

The increased interest in nanostructured materials is due to improvements in the mechanical properties presented for these materials. Significant increases in properties such as hardness, wear resistance and in some cases, strength and toughness of nanostructured ceramics have been reported, compared to conventional ceramics. High-energy milling can lead to selfsustaining reactions in a variety of systems. In this study, reactive high-energy milling was used to synthesis niobium carbide (NbC) nanoparticles. The reaction products were de-agglomerated and mixed with commercial ultra-fine alumina powder to produce alumina matrix nanocomposites with 5vol% of nanometric NbC. Alumina/NbC nanocomposite produced using powder obtained by reactive present good microstructural characteristic, high densities, good hardness and higher toughness. What makes this material an interesting alternative for production of ceramic cutting tools.

Production and Characterization of Alumina-Diamond Composites and Nanocomposites

One of the most recent alternatives in the development of materials with high mechanical properties and wear resistance is the addition of nanometric and/or micrometric particles of a secondary phase into ceramic matrices. Nanostructured materials can be defined as systems that have at least one microstructural characteristic of nanometric dimensions (less than 100nm). In this work, alumina-diamond nanocomposites were produced using nanometric diamond powder obtained by high energy milling in a SPEX mixer mill for 6h. The crystallite size was 30nm. After deagglomeration, the diamond powder was added to the alumina matrix in a ratio of 5wt%. The samples were isostatically pressed and high-vacuum sintered. The resulting nanocomposites and composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and by microhardness, diametral compression and wear resistance tests. The results confirmed the promising wear characteristics of the alumina-diamond nanocomposite.

Nanocompósitos de Al2O3-SiC sinterizados por "spark plasma sintering" (SPS)

(Alumina-silicon carbide) nanocomposite has been extensivelly studied due to its promising results regarding its mechanical properties. The processing of this material usually involves high cost, once the use of hot pressing is necessary for obtaining dense materials. A more recent alternative for sintering nanocrystalline ceramics is the Spark Plasma Sintering - SPS. In this work alumina powders with 5%vol SiC inclusions were sintered using the SPS method at temperatures varying from 1500 to 1600 °C, using different holding times. The effect of temperature and hold time on density and microstructure was investigated. The best results in microestucture and microhardness measurements were shown at 1500 °C and time of landing of 7 min.