Materials Science Forum Vols. 727-728

Abstract: Compacts made of sintered diamond powder (DP) are not only extensively used but also essential cutting inserts for operations such as machining metal components or drilling rocks for petroleum extraction. The high pressure and high temperature (HPHT) sintering can be achieved either by an initial mixture of DP with a metallic binder or by first processing the DP at HPHT, which creates a sintered skeleton, followed by the molten metallic binder infiltration. This work investigates the infiltration of Cu, Co and Ni, as binders, into sintered diamond powders with different particles size. It was found that migration of the liquid phase through the sintered diamond skeleton complies with the Darci Law. The penetration coefficient varied from 0.89 x 10^-7 to 6.41 x 10^-7 μm² indicating that the migration is affected by several factors.

Abstract: Particle reinforced metal matrix composites have received considerable interest over many years and continue still under constant development to gain wider industrial applications. New technique of production of carbetos of refractory metals (WC, NbC, TaC, Ta_xNb_y) has been developed, synthesizing nanostructured carbides that show improvement of diverse properties of the materials to the gotten ones for the conventional processes. The properties of sintered composites are determined not only by the nature and quality of the raw materials employed but also by microstructure and porosity resulting from the processing techniques e sintering method. In this study, additions of 20 wt% NbC nanoparticles or micro-particles in the ferrite matrix were performed with the aim of improving the mechanical and use properties. Ancorsteel Fe 1000B powder from Hoengans Corp. was used together with the graphite, and a small amount of Fe₃P, to induce liquid phase sintering. NbC nanoparticles or micro-particles were inserted into the Fe 1000B matrix by wet grinding (acetone) in a mill of planetary type of high energy. The angular velocity of the mill was kept constant at 300 rpm with milling time of 10 hours. The composites powders milled were annealed at 900 ° C for 1 hour under flowing hydrogen e argon, and a priori were pressed into cylindrical pellets under 600 MPa and sintered the plasma. Finally, the sintered pellets were evaluated through the testing: SEM, microhardness and density. It was noticeable the behavior of the composites Fe 1000B - NbC was affected by the content of nanoparticles of NbC added as well as by processing parameters, particularly plasma sintering.

Abstract: This work presents the structural characterization of Ti-10Si-5B and Ti-20Si-10B (at-%) alloys produced by high-pressure assisted sintering. Sintering was performed in air at 1100 and 1200 °C for 60 s using pressure levels of 5 GPa. Structural evaluation of sintered samples was conducted by means of scanning electron microscopy and energy dispersive spectrometry. Samples were successfully consolidated after sintering, which presented theoretical density values higher than 99%. The microstructures of the sintered Ti-10Si-5B and Ti-20Si-10B alloys revealed the presence of the Ti_SS, TiB, TiB₂, Ti₅Si₃, Ti₅Si₄, TiSi, and TiSi₂.phases. A small amount of Ti₆Si₂B was formed after high-pressure assisted sintering of the Ti-20Si-10B alloy (5GPa, 1100°C for 60 s) indicating that equilibrium structures were not achieved during short sintering times. No oxygen and carbon contamination was detected in structures of Ti-Si-B alloys after high-pressure sintering at 1100 and 1200 °C without controlled atmosphere.

Abstract: Powder of Fe₇₂Nb₄Si₁₀B₁₄ (%at) glassy alloy was obtained by gas atomization in order to investigate the possibilities of amorphous phase formation due to the high cooling rates (10³ 10⁵ K/s) involved in this process. The ratio between the gas volumetric and the metal mass flow rates used was 1.0, and nitrogen (N₂) was used as the atomization gas. The powder, sieved in different granulometric size ranges, was characterized through: X-ray diffratometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Fe₇₂Nb₄Si₁₀B₁₄ (%at) bulk metallic glass (BMG) showed completely or partially glassy structure depending on the size range. The obtaining of powders with glassy structure that could be applied as shot penning powder particles and thermal spray feeding powder for metallic coatings or would make possible the production of bulk glassy materials by warm consolidation of such powders or even a millimeters thick deposit obtained by spray forming with glassy or metastable microstructure that would be very interesting considering applications as soft ferromagnetic parts.

Abstract: In this work, microstructural changes in coatings deposited by hypersonic thermal spraying technique (HVOF) were subjected to adhesive wear tests. Materials subjected to wear lose efficiency, increase costs and direct or indirect way can stop large production systems. The mechanisms involved in this type of wear can be minimized by the microstructural changes that in many cases reduces or stops the loss of material. To perform this assessment coatings compounds of Cr₃C₂25 (80 Ni-20 Cr) e Al₂O₃.TiO₂ (87-13) investigated had similar hardness values (1000 HV) and chemical characteristics. Were subjected to the ASTM G99 using commercial hard metal pin 2 mm, load 50N force and tangential velocity of 0.5 m/s. Worn surfaces and debris were analyzed by optical microscopy, scanning electron microscope and mass loss. The results show high resistance sprayed coatings worn surfaces and debris were fragile nature with little loss of material during the tests.

Abstract: Titanium nitride (TiN) is a hard material, often used as coating to improve the wear properties of titanium alloys in machining, implant and aerospace applications. Electron Beam Physical Vapor Deposition (EB-PVD) is a technique which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum, producing a thin film in a substrate. In this work, results of TiN films depositions on Ti-13Nb-13Zr substrates by EB-PVD are studied. Titanium targets were obtained by a purified ingot and the substrates produced by powder metallurgy. Sintered samples of Ti-13Nb-13Zr and TiN layers were characterized by X-ray diffraction, scanning electron microscopy, Vickers microhardness and wear tests. The TiN films presented high hardness values, continuity and large thickness. The coatings improved the tribological properties of the substrate due to high adhesion and low wear rate.

Abstract: The purpose of this paper is to study metal separation from a sample composed of a mixture of the main types of spent household batteries, using a hydrometallurgical route, evaluating the parameters effect of the liquidliquid extraction, with Cyanex 272, and stripping. The preparation of solution consisted of: grinding the waste of mixed batteries, reduction and volatile metals elimination using electric furnace and acid leaching. With the best results obtained after liquidliquid extraction and stripping it was possible to get 4 solutions of metal sulfates that they could be used in posterior metals recovery by electroplating, they are: 1) to copper recovery: Cu 203.7 g L^-1 + Co 20.8 g L^-1 + Mn 2,626.6 g L^-1; 2) to cobalt recovery: Co 364.0 g L^-1; to manganese recovery: Mn 49,929.0 g L^-1 and 4) to nickel recovery: Ni 1,241.9 g L^-1.

Abstract: Cerium oxide has a high potential to be apply in removing pollutants combustion powders, organic materials from waste water and in the technology of fuel cells. Nickel oxide is an attractive material due to its excellent chemical stability, and their optical, electrical and magnetic proprieties. In this work, CeO₂-NiO systems on molar ratios of 1:1, 1:2 and 1:3 citric metal-acid were synthesized by using Pechinis method. The change in compositions and calcined temperature were studied by different techniques such as: XDR and SEM. It was also done a microstructural study by Rietvelds method, whose routine was designed to run in the Fullprof Suite program, and analyzed by pseudo-Voigt function. It has noticed that the molar ratio between metal-citric acid in the system CeO₂-NiO 1:1, 1:2 and 1:3 has a strong influence on microstructural proprieties, crystallite size and cell micro-deformations and can be used to control these proprieties.

Abstract: Some materials have been applied in many surrounding conditions as sensors, electronic devices and other applications. Inexpensive and reliable temperature and flow measurement are important in many applications including, for example, environmental monitoring and control, indoor air conditioning, weather forecasting, automotive and aerospace systems. Special ceramics are an example of such materials. Neodymium-Barium-Copper is a special ceramic that has high electrical conductivity and airflow sensor characteristics. This property is influenced by high energy milling of the powder, when it is not sintered. To evaluate the influence of this type of milling it was carried out an analysis of particle size as a function of milling time. SEM images and granulometric analysis showed significant reduction of particle size with the increase of milling time. For longer times of milling the mixture of precursor powders is favored, resulting in better homogeneity of the ceramic. This is reflected in the properties of airflow sensor.

Abstract: The barium and strontium titanate (BST) ceramics have been used with great success as excellent dielectrics in the construction of high voltage (HV) commercial ceramic capacitors with reduced dimensions because of their high dielectric constant. However, the main point of this paper is to investigate other type of ceramic known as PZT (Lead Zirconate Titanate) normally used as piezoelectric sensors in industrial applications. The idea herein is to use the PZT ceramics as HV dielectrics for applications in high-energy storage systems by de-poling their piezoelectric properties in order to avoid dielectric damage and losses at high frequencies. For this, de-poled PZT-4 ceramic samples (30 mm × 2 mm) were submitted to HV tests, in which their dielectric breakdown strength and dielectric constant variation with the applied voltage were assessed. These results obtained confirmed the use of PZT in applications that require reasonable dielectric constant stability (< 15 %) with voltage and HV dielectric breakdown (40 kV/cm) for compact high-energy storage devices.