Ana Lúcia Diegues Skury

A Novel Method for Obtaining Polycrystalline Diamond Cutters

The present work comprises a study about the possibility of obtaining polycrystalline diamond cutters through a novel method of sintering both layers at the same time. This possibility was tested through the sintering of a diamond layer over a hard metal (WC+15wt%Co) support under conditions of 5.0 and 6.5 GPa of pressure and 1400 to 1600º C of temperature. The sintering conditions were imposed in two ways: directly, or with pre-sintering. The samples were tested by measuring microhardness, wear resistance, densification, and SEM. The results of the tests have shown the possibility of obtaining good quality inserts by sintering both layers of compacted powder.

Effect of Nanodiamond Addition on the Mechanical Properties of Polycrystalline Metallic and Polymeric Composites

One way to develop a new composite material or to improve its performance is to reinforce the matrix with a stronger dispersive phase. In principal, nanodiamonds can be used as reinforcement of composites owing to high surface energy, which allows an effective structure interaction with most utilized matrices. In this work, polycrystalline metallic–based composites and polymeric-based composites were investigated for the effect caused by addition of nanodiamonds. These composites were obtained at high compression pressures and combine with temperatures for certain short processing times. It was found that even small additions of nanodiamonds increase the wear resistance of the investigated composites.

Metal Matrix Composites from Powder Mixtures of Copper, Tungsten, Aluminum and Nanodiamonds

Composites are versatile materials owing to their extensive possibilities of improving mechanical properties by distinct matrix reinforcements. In particular, it has been shown that diamonds are very effective reinforcement for metal matrix composites (MMC). In this work, the properties and microstructure of plain Al matrix composites reinforced with up to 50 wt.% of nanodiamonds as well as Cu, W, Al MMCs reinforced with 1% nanodiamonds were investigated. Composites were fabricated by processing metallic powders of Cu, W and Al as well as nanodiamond particles at sintering conditions of 2 GPa of pressure and 700°C for times up to 5 minutes. As compared to the other nanodiamond reinforced MMCs, the investigated composite presented improved microhardness and reduced wear in abrasive tests.

Boron Nitride Ceramic Composite Obtained by High Pressure and High Temperature Sintering

In the present work, by selecting Si3N4, TiB2 and Al2O3 as binding agents as well as La3O2 as an additive, sintered wBN composites were studied. By modifying the number of sintering cycles, the composites processed at 4.5GPa and 1800°C showed improved mechanical properties. The degree of transformation of the wBN, as well as the chemical reactions during the sintering process were discussed. This new composite material was found to present polycrystalline structure that provides superior cutting properties. Moreover, owing to superior properties, the wBN composite sharpens itself during cutting.

Some properties of diamonds synthesized in the new Mg–Ni–C system

Diamonds obtained in the Mg–C system were found to exhibit semi-conducting properties and cubic morphology. In these cases, strict synthesis processing parameters are required (8.0–8.5 GPa and 1800–2100 °C). The present work aims to study the mechanical and electrical properties of diamonds in the new Mg–Ni–C system. The new system has the advantage of allowing the reduction of synthesis parameters. The Mg–Ni alloy was initially produced by the preparation (4.0 GPa/1300 °C) of a Mg and Ni powders mixture. Diamond synthesis was conducted (5.5–7.7 GPa and 1250–1700 °C) with compositions varying between 15 at% Mg+85 at% Ni, and 85 at% Mg+15 at% Ni. Semi-conducting diamond was obtained with granulometry ranging from 40 to 250 μm. Some crystals displayed a cubic morphology. The best results were obtained for pressures ranging from 6.5 to 7.7 GPa, and temperatures ranging from 1550 °C to 1700 °C.

Propriedades mecânicas e termomecânicas de compósitos com partículas de diamante dispersas em matriz epoxídica modificada na razão resina/endurecedor

The mechanical properties of composites with dispersed diamond particles in epoxy matrix cured with different proportions of hardener to monomer ratio, characterized by the resin/hardener ratio (phr) were studied. An investigation on the thermo-mechanical behavior of these composites was also carried out by dynamical mechanical analysis (DMA). In the present work a complete evaluation of the mechanical properties was carried in a wide interval of phr associated with possible technological applications. Composites with up to 30 wt. % of diamond particles dispersed in type DGEBA/TETA epoxy matrix were fabricated with phr ratios varying from 7 to 21. For all investigated conditions, the composite strength decreased with the amount of incorporated diamond. Matrices with phr above the stoichiometric 13 were associated with composites with better mechanical performance. The DMA results showed that the storage modulus increases with the amount of diamond particles incorporated in the composite. The values obtained for the delta tangent, allowed an evaluation of possible mechanisms that contribute to the thermal mechanical performance of these composites.

Harder and Denser AlN-TiB2 Ceramic Composites Processed by Spark Plasma Sintering

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.

Mechanical Properties and Abrasive Behavior of Diamond Incorporated Epoxy Composites

The thermal and mechanical properties assessed respectively by dynamic mechanical analysis and flexural bend tests as well as the abrasive behavior obtained by wear tests of diamond particles incorporated epoxy matrix composites were investigated. Diamond particles with sizes in the range of 45 to 115 µm, synthesized at high pressure and temperature, were mixed in amounts of 20 and 40 wt% with dyglycidyl of the bisphenol A, DGEBA, epoxy resin cured with stoichiometric ratio of tetraetylenepentamine, TEPA, hardener. These composites were dynamic mechanical, DMA analyzed and three points bend tested. The behavior of the composites as abrasive tool for industrial polishing of ornamental rocks was evaluated by wear tests. The results showed an improved performance of the DGEBA/TEPA composites with incorporation of diamond particles.

Hard Metal Matrix Composites Reinforced with Cubic Boron Nitride

Cubic boron nitride (cBN) composites with hardmetal such as metal turning and rocks drilling, WC-Co, matrix are alternative substitutes for similar diamond composites in high speed machining operations and rocks and drilling. Although it possesses related technical properties close to diamond, cBN has the inconvenience of reacting with hardmetals. This deteriorates the composite properties. A possible solution to this negative effect is to apply high pressures during the sintering operation. In this work, powder mixtures of cBN with a hardmetal (WC15%Co) were subjected to pressures up to 7.0GPa and temperatures up to 1400°C for 40 seconds. The results showed significantly higher values of hardness and compressive strength as well as an improved wear resistance.

Sintering of Cubic Boron Nitride Using Titanium Based Binders

As a superhard material, next to diamond, the cubic boron nitride (cBN) is of great interest owing to its efficiency in machining ferrous alloys. In nature, only the hexagonal, hBN, exists. In practice, high pressure and high temperature (HPHT) synthesis has to be used to produce small cBN crystals. For larger size machining inserts, the powder-like cBN crystals need to be sintered at specific HPHT conditions using a metallic binder. The present work investigates the sintering of cBN inserts using a Ti-based binder at 7 GPa of pressure and 1800°C. The results disclosed relatively high hardness for the inserts and revealed their effectiveness in machining high strength steels.