Um roteiro para a produção de metal duro com maior resistência à corrosão

RESUMO: Com o objetivo de racionalizar o desenvolvimento de compósitos de metal duro com maior resistência à corrosão, realizou-se um estudo sistemático da influência de vários parâmetros que determinam o seu desempenho. Neste trabalho apresentam-se resultados da influência de parâmetros relacionados com a constituição do material (tipo de ligante e tamanho de grão de carboneto de tungsténio - WC) e de parâmetros do ambiente de serviço (pH e temperatura). O estudo socorreu-se principalmente de métodos electroquímicos e de análise da superfície.info:eu-repo/semantics/publishedVersio

Corrosion behaviour of WC hardmetals with nickel - based binders

Cobalt is the standard binder in tungsten carbide (WC) hardmetals due to its compatibility with the WC phase, resulting in composites with exceptional hardness and wear resistance. However, their corrosion resistance is not satisfactory in many applications, leading to the early deterioration and failure of tools and equipment. In this work, the corrosion of WC hardmetals with three alternative binders (FeCoNi, NiCrCoMo and NiCrMo) is compared with a benchmark WC-Co composite, using electrochemical techniques such as open circuit potential (OCP) monitoring, polarisation curves and electrochemical impedance spectroscopy (EIS), assisted by scanning electron microscopy (SEM).publishe

Abrasive wear resistance of WC-Co and WC-AISI 304 composites by ball-cratering method

In the present work, the effect of different binder materials on the tribological properties of cemented carbides was studied. Flat samples of conventional WC–Co, and newly developed WC–AISI 304 stainless steel (SS) composites with and without carbon addition were surface finished by grinding and polishing. Comparative experiments were performed using a ball-cratering tribometer. Worn surfaces were characterized by optical microscopy, surface scanning topography and scanning electron microscopy. It was found that the abrasive wear resistance of the developed WC–SS composites is higher than that of conventional WC–Co and decreases with the carbon addition, in a direct relation with the decreasing hardness. The mechanisms of wear degradation are discussed

Structure and dielectric characterization of a new A site deficient La5 3MgTaO6 perovskite

he crystal structure of new A site deficient La5 3MgTaO6 perovskite was investigated by neutron, X ray and electron diffraction. Neutron and X ray powder diffraction spectra were refined in the monoclinic I2 m space group, with the parameters of the unit cell a 5.6304 2 angstrom, b 5.6226 2 angstrom, c 7.9434 2 angstrom and beta 90.04 1 degrees. This structural model presumes a random distribution of the vacancies and takes into account both a rock salt type Mg2 Ta5 cation ordering and a a c 0 configuration of the octahedral tilting. Electron diffraction showed that the crystal structure is more complex at the local level due to a short range vacancy ordering. This observation in combination with the symmetry analysis leads to the conclusion that the C2 m symmetry with 2 root 2a p x 2 root 2a p x 2a p supercell is more adequate for the description of the crystal structure in the local level. Dielectric measurements performed in a wide frequency range were correlated with the crystal structure and compared with other ordered double perovskites. Far infrared spectroscopy was used to characterize the lattice contribution to the dielectric response at the microwave frequencies. The complex dielectric function was evaluated and extrapolated down to the gigahertz range. The effect of the vacancies on the intrinsic dielectric losses is discussed based on the spatial phonon correlation model. c 2006 Elsevier Inc. All rights reserve

Development of WC-NiCrMo hardmetals

The demand for improved components with a wide range of properties is a reality in today's hardmetal market. Furthermore, supply shortages of raw materials such as W and especially Co resulted in rapid price fluctuations. Combined with stricter environmental legislation and health protection, these facts prompt the demand for alternative or modified binders. Therefore, in this work, WC-NiCrMo composites were developed as a potential alternative to conventional WC-Co hardmetals. To evaluate this new hardmetal composite, prototypes of submicrometric WC with approximately 15 vol% of NiCrMo binder were produced by conventional powder metallurgy route. Thermodynamic assessment, wettability testing and constant heating rate dilatometry were performed to design an adequate sintering route. A detailed characterization of the mechanical properties (Young's modulus, Vickers hardness and fracture toughness), together with corrosion resistance assessment (OCP, polarization curves, EIS) and abrasive wear (ball-cratering) resistance evaluation were undertaken. Good wettability of molten NiCrMo binder on WC surface was observed, and highly dense compacts could be successfully attained by gas pressure sintering. The new WC-NiCrMo composite has lower hardness but higher corrosion resistance and better wear resistance than the conventional WC-Co hardmetals.publishe