Papers by Author: Daniel Rodrigues

Abstract: The use of pressed and sintered aluminum, obtained by the powder metallurgy route, to produce large quantities of near-net-shaped components is increasing rapidly in the automobile industry. The production of lightweight pieces of Al by powder metallurgy has attracted increasing attention due to its unique properties. Sintering helps develop mechanical strength and other properties in commercial alloys obtained by powder metallurgy. Sintering of Al can be achieved only upon formation of a liquid phase capable of destroying the extremely stable oxide layer on the surface of the Al particles. The aim of this investigation was to analyze the effect of compaction pressure on sintering of atomized ASTM 2124 type alloy. Powder characterization was carried out using scanning electron microscopy (SEM). The specimens were axially compacted at pressures of 500, 600 and 700 MPa. Differential scanning calorimetry (DSC) was carried out to determine the sintering temperature of the alloy powder. The specimens were sintered at 570° C. Characterization of the sintered material consisted of density measurements and optical as well as SEM examinations. Nevertheless, even the low recycling cost of Al , what increases its useful time and stabilizes its value, the large amount of energy required to obtain it reduce its application.

Abstract: This study reports the results of investigations carried out to determine the Curie temperature (Tc) of various homogenized praseodymium-based alloys represented by the formula: Pr14Fe79.9-xCo16B6Nbx (where x = 0, 0.01, 0.05, 0.1, 0.15, 0.50). The influence of niobium content on the microstructure of these alloys has investigated. The Curie temperature decreased about 3 °C for x = 0.5 at. %. It has been observed a remarkable grain refinement on the microstructure of the Pr14Fe79.8Co16B6Nb0.1 alloy when compared to the niobium-free alloy (x = 0 at. %).

Abstract: Ni-Fe based soft-magnetic alloys, processed via Metal Injection Molding (MIM), were investigated regarding the influence of processing route on final magnetic properties and compared to fully dense cast materials. The process variations included high and low temperature debinding, different sintering routes and the application of hot isostatic pressing (HIP). The different densities resulting from the process variations were related to maximum magnetic permeability. Results have shown that density, in the range between 7,5g/cm³ and 8,0g/cm³, does not have significant influence on the maximum permeability, allowing cost-effective process routes. It was also verified that fullydense cast alloys still exhibits superior properties, with lower coercive fields and higher permeability, but results achieved after HIP process overcame even the values of these commercial grade alloys.

Abstract: The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.

Abstract: In plain iron powder or powder mixtures sintering process, it is very important to control the dimensional change. In the sintering associated events, such as lubricant removal, atomic motion and phase transformation could change dimensions over a wide range. Dilatometric analysis has shown that most contributions in the dimensional change in the sintering of iron powder mixtures were due to the combination of several effects occurring in all stages of the processing, including the heating and cooling stages. The present paper has the objective of studying the dimensional behavior and to determine the transformation temperature of a composite powder mixture of a plain iron powder with various additions of high-alloyed steel, carbon, nickel and lubricant powders, during sintering by dilatometric analysis.

Abstract: Osseointegrable surgical implants are usually made on titanium or titanium alloys. The osseointegration process is improved by surface conditioning of these implants, increasing surface area with no loosing of bio-compatibility, i.e., without contamination by non bio-compatible materials. The surface conditioning of these implants might be accomplished in different ways: blasting, chemical etching, deposition, etc. Two alternatives considering titanium powders are discussed in this work: blasting and plasma spraying deposition. Results are presented in terms of topography of osseointegrable surgical implants through scanning electron microscopy techniques.

Abstract: This paper reports the results of investigations carried out to determine the Curie temperature (Tc) of some annealed praseodymium-based alloys represented by the formula Pr14Fe79.9-xCoxB6Nb0.1. The Curie temperature of these permanent magnet alloys increase linearly with the cobalt content at about (10.2±0.3) oC/at%. Pr14Fe80B6 and Pr14Fe79.9B6Nb0.1 magnetic alloys with a Tc of 290oC have been used as a standard reference. Magnets were prepared from the alloys using the hydrogenation, disproportionation, desorption and recombination (HDDR) process.

Abstract: Austenitic stainless steel filters are mostly used when there is an aggressive environment condition, especially when good corrosion and mechanical resistance at relatively high temperature are required. These filters are usually obtained from non-spherical, mostly atomized powders by cold pressing and sintering. In order to achieve an adequate performance concerning permeability, powders with a narrow range of particle size should be used. However, besides particle size distribution, apparent density of the selected powder, which can be adjusted by the particle size, shape and distribution, affects the performance of the final product. Particle size distribution, particle shape and particle surface roughness control apparent density. This work presents some results on the evaluation of such effect.

Abstract: MnZn ferrites are conventionally produced by the ceramic method that involves the solid state reaction of metallic oxides or carbonates at high temperatures. The particles obtained by this method are rather large and non-uniform in size. In order to overcome the difficulties arising out of the ceramic process, the coprecipitation method has been used as an alternative route to produce chemically homogeneous powders with fine particle size. In this work MnZn ferrites powders were produced by the coprecipitation method. The calcination conditions, such as temperature (900oC to 1100oC) and atmosphere (air and nitrogen), were investigated. X ray diffractometry, scanning electron microscopy, thermomagnetic analysis and vibration sample magnetometry were used to characterize the obtained samples. The results indicated that when the samples were calcined in nitrogen atmosphere, the ferrite formation occurred at low calcination temperatures and presented better magnetic properties than those calcined in air.

Abstract: In this study, the addition of calcium phosphate powders to an alginate matrix was evaluated as a strategy to modulate enzyme release-kinetics from alginate microspheres and, simultaneously, to improve cell adhesion to the polymer. Pre-adsorption of the enzyme to the ceramic powders resulted in a more adequate release pattern. The ratio of ceramic-to-polymer had a pronounced effect on osteoblast adhesion to microspheres. Cells were only able to spread on microspheres with the highest percentage of ceramic (0.4 w/w using a 1.5% w/v alginate solution).