Conrado Ramos Moreira Afonso

Influence of phase transformations on dynamical elastic modulus and anelasticity of beta Ti-Nb-Fe alloys for biomedical applications

Recent studies in materials for biomedical applications have focused on β-titanium alloys that are highly biocompatible, free of toxic elements and with an elastic modulus close to that of human bone (10-40 GPa). Beta Ti-xNb-3Fe (x=10, 15, 20 and 25 wt%) alloys were obtained by rapid solidification and characterized by anelastic relaxation measurements at temperatures between 140 K and 770 K, using a free-decay elastometer, as well as analysis by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The observed stabilization of the β-phase with rising Nb content was linked to the strength of the relaxation peak around 570 K. The phase transformations detected in the anelastic relaxation spectra agreed with those observed in the DSC curves. However, the results from anelastic relaxation spectra provide more detailed information about the kinetics of phase transformations. At temperatures between 140 K and 300 K, there was an indication of a reversible transformation in the alloys studied. The elastic modulus measurements showed a hardening of the material, between 400 K and 620 K, related to the ω-phase precipitation. However, the starting temperature of ω-phase precipitation was clearly influenced by the Nb content, showing a shift to high temperature with increasing percentage of Nb. At temperatures above 620 K, a fall was observed in the dynamical elastic modulus, accompanied by a relaxation peak centered at 660 K, which was attributed to the growing α-phase arising from the ω-phase, which acts as a nucleation sites or from the decomposition of the metastable β-phase. XRD patterns confirmed the formation of β, α and ω phases after mechanical relaxation measurements. A predominant β phase with dendritic morphology was observed, which became more stable with 25 wt% Nb. The lowest elastic modulus was of 65 GPa obtained in the Ti-25Nb-3Fe alloy, representing a good low value for a β-Ti alloy with a relatively low addition of β stabilizing elements (Nb and Fe).

Aspectos metalúrgicos de revestimentos dissimilares com a superliga à base de níquel inconel 625

To extend the life and reliability of pipes and equipment in oil & gas production and processing settings is a continuous demand. These aspects are essentially dependent on corrosion resistant alloys used. In this context, the weld overlay with Ni-based superalloys is a great interesting alternative, since improve the corrosion resistance without increase the cost of manufacture when compared to massive equipment. Thus, the objective of this study was to evaluate the metallurgical aspects of Inconel 625 weld overlays deposited by GTAW cold wire feed process. The welds were performed using a robotic workbench, an electronic power supply and a data acquisition system. The microstructural characterization was carried out using scanning electron microscopy (SEM), transmission electron microscopy (MET), electron dispersive spectroscopy (EDS) and X-ray diffraction. The results shown that the microstructure of overlays was formed by a gamma matrix and secondary phases rich in Nb. These precipitates were identified as Nb-rich Laves phase and a complex TiN/NbC.

Ti-Nb thin films deposited by magnetron sputtering on stainless steel

Thin films of Ti-Nb alloys were deposited on AISI 316L stainless steel substrate by magnetron sputtering, and the structure, composition, morphology, and microstructure of the films were analyzed by means of x-ray diffraction (XRD), (scanning) transmission electron microscopy (TEM) coupled with energy-dispersive x-ray spectroscopy, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). Thin films of four compositions were produced: Ti85Nb15 (Ti-26 wt. % Nb), Ti80Nb20 (Ti-33 wt. % Nb), Ti70Nb30 (Ti-45 wt. % Nb), and Ti60Nb40 (Ti-56 wt. % Nb). Structural characterization by XRD indicated that only the β phase was present in the thin films and that the increase in the Nb content modified the alloy film texture. These changes in the film texture, also detected by TEM analysis, were attributed to different growth modes related to the Nb content in the alloy films. The mean grain sizes measured by AFM increased with the Nb amount (from 197 to 222 nm). XPS analysis showed a predominance of ox...

Effects of Cooling Rate and Sn Addition on the Microstructure of Ti-Nb-Sn Alloys

Ti-based alloys present unique properties and hence, are employed in several industrial segments. Among Ti alloys, β type alloys form one of the most versatile classes of materials in relation to processing, microstructure and mechanical properties. It is well known that heat treatment of Ti alloys plays an important role in determining their microstructure and mechanical behavior. The aim of this work is to analyze microstructure and phases formed during cooling of β Ti-Nb-Sn alloy through different cooling rates. Initially, samples of Ti-Nb-Sn system were prepared through arc melting furnace. After, they were subjected to continuous cooling experiments to evaluate conditions for obtaining metastable phases. Microstructure analysis, differential scanning calorimetry and X-ray diffraction were performed in order to evaluate phase transformations. Depending on the cooling rate and composition, α” martensite, ω phase and β phase were obtained. Elastic modulus has been found to decrease as the amount of Sn was increased.

Characterization of Glass Forming Alloy Fe43.2Co28.8B19.2Si4.8Nb4 Processed by Spray Forming and Wedge Mold Casting Techniques

Bulk glassy alloys based on the Fe-Co-B-Si-Nb system have already achieved high levels of mechanical strength. The present work investigated the microstructural evolution of Fe43.2Co28.8B19.2Si4.8Nb4 alloy during the spray forming and wedge mold casting processes, with emphasis on the formation of amorphous phase. The microstructure was evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The region outer the spray deposit showed the formation of an amorphous structure with a thickness of ~2.5 mm, while that of the wedge-shaped sample exhibited a thickness of up to ~1.5 mm, suggesting that both processes show a promising potential for the production of bulk glass alloys.

Nanocrystalline material in toroidal cores for current transformer: analytical study and computational simulations

Based on electrical and magnetic properties, such as saturation magnetization, initial permeability, and coercivity, in this work are presented some considerations about the possibilities of applications of nanocrystalline alloys in toroidal cores for current transformers. It is discussed how the magnetic characteristics of the core material affect the performance of the current transformer. From the magnetic characterization and the computational simulations, using the finite element method (FEM), it has been verified that, at the typical CT operation value of flux density, the nanocrystalline alloys properties reinforce the hypothesis that the use of these materials in measurement CT cores can reduce the ratio and phase errors and can also improve its accuracy class.

Effects of Omega Phase on Elastic Modulus of Ti-Nb Alloys as a Function of Composition and Cooling Rate

Titanium alloys comprise a versatile class of biomedical materials. Among them, β- titanium alloy is one of the most promising metallic materials for biomaterial applications thanks to their high mechanical strength, good corrosion resistance and excellent biocompatibility. This study purported to analyze the phase stability in Ti-Nb alloys, evaluating the influence of the Nb content on the microstructure obtained under different heat treatment conditions. To this end, Ti-Nb alloys containing 5 to 35% (wt.%) of Nb were prepared and evaluated. The samples were arc melted and characterized using optical microscopy, transmission electron microscopy and X-ray diffraction. Young’s modulus was evaluated primarily by acoustic techniques.

Gas Atomization of Nanocrystalline Fe63Nb10Al4Si3B20 Alloy

Powder of Fe63Nb10Al4Si3B20 (%at) alloy was processed by gas atomization to investigate the formation of novel microstructures due to the high cooling rates involved in this process. The ratio between the gas volumetric flow rate and the metal mass flow rate used was 0.23, and nitrogen was used as the atomization gas. The powder, with a median particle diameter about 120μm, was sieved in the granulometric size ranges of 5-20, 20-30, 30-45, 45-75, 75-106, 106-150, 150-180, >180μm, and then were characterized by X-ray diffratometry (XRD), differential scanning calorimetry (DSC), scanning and transmission electron microscopy (SEM and TEM, respectively) both equipped with energy dispersive spectroscopy (EDS). Powder in the range of 5-45μm contain α-Fe nanocrystals embedded in an amorphous matrix. In the size range of 45-150μm, the powder contains, besides α-Fe nanocrystals embedded in an amorphous matrix, particles of FeB and Fe23B6 intermetallic phases. For the size range > 150μm, the powder showed particles with Fe-α nanocrystals embedded in an amorphous matrix and partially crystalline particles with Fe-α, FeNbB and FeB phases. The volume fraction of the amorphous phase decreased with the increase of the granulometric size range. The nanocrystallization of the powder in the smaller size ranges opens the possibility for the production of a bulk nanocrystalline deposit produced by spray forming and its application as a soft ferromagnet. Introduction Spray forming via gas atomization i nvolves the conversion of a liquid metal stream into variously sized droplets, which are then propelled away from the region of atomization [1] by the fast flowing, atomizing gas. The droplet trajectories are interrupted by a substrate which collects and solidifies the droplets into a coherent, near fully dense deposit [2-5]. By continuous movement of the substrate relative to the atomizer as deposition proceeds, large deposits can be produced in a variety of geometries including deposits, tubes and strips [2]. In spray forming process, the powder that is not incorporated in the deposit and is collected at the bottom of the atomization chamber is called overspray. Usually, the amount of this overspray powder is in the range of 10-30% in weight of the starting charge [2]. The challenge is to obtain a significant fraction of amorphous phase in the powder to be hot consolidated into bulk volumes [3,4]. The great interest in amorphous and nanocrystalline ferromagnetic alloys is the fact that they show excellent soft magnetic properties [6-10]. In particular, in the partially crystallized state, the structures are known as “nanocrystalline” and consist of an amorphous matrix containing α-Fe nanocrystals, which can exhibit high effective permeability and low coercive force, plus a high saturation magnetic flux density [10]. These properties make these alloys promising candidates for several practical applications such as cores of power transformers [6], data communication interface components, electro-magnetic interference prevention components, magnetic heads, sensors, magnetic shielding and reactors [7]. The challenge in the Journal of Metastable and Nanocrystalline Materials Online: 2004-07-07 ISSN: 2297-6620, Vols. 20-21, pp 175-182 doi:10.4028/www.scientific.net/JMNM.20-21.175

Microstructure of Spray Formed Fe83Nb4ZrTiB9Cu2 Alloy

In this study the Fe 83 Nb 4 Zr 1 Ti 1 B 9 Cu 2 (%at) alloy was processed by spray forming with the aim of investigate the formation of novel microstructures by the high cooling rate involved in this process. The ratio between the gas mass flow rate (kg/min) and the metal mass flow rate (kg/min) used was 0.25, and nitrogen was used as the atomization gas. The resulting billet, weighting about 0.8 kg, as well as the overspray powders, with a median particle diameter about 150μm, were characterized by using X-ray difflatometry, differential scanning calorimetry and scanning and transmission electron microscopy. The microstructure observed in both overspray powder and deposit was fully crystalline formed by α-Fe, fcc-Cu and the intermetallic Fe 2 Zr phases. SEM together with the EDS analysis of these phases is presented. The Fe 83 Nb 4 Zr 1 Ti 1 B 9 Cu 2 (%at) alloy presented a very fine microstructure of the α-Fe grains which decreases as the granulometric size ranges of the overspray powder diminishes due to the increasing in the cooling rate. The deposit showed irregular porosity due to the high fraction of solid particles that hit the substrate during deposition stage.

Microstructural Evolution of HSLA ISO 3183 X80M (API 5L X80) Friction Stir Welded Joints

Evaluation was made of friction stir welded joints, identifying conditions that resulted in satisfactory welded joints free from defects and with microstructural characteristics that provided good mechanical properties. Microstructural characterization and cooling curve analysis of the joints with lower and higher heat inputs evidenced deformation below and above the non-recrystallization temperature (Tnr) and dynamic recrystallization during microstructural evolution. Microscopy analyses showed acicular ferrite, bainitic ferrite, and coalesced bainite microstructures in the stir zone of the cold weld (lower heat input), while the stir zone of the hot weld (higher heat input) contained bainitic ferrite, acicular ferrite, coalesced bainite, martensite, and dispersed carbides. Granular bainite and dispersed carbides were observed in all the heat affected zones. Analysis of the microstructural transformations, together with the thermal history of the joints, showed that the variable that had the greatest influence on the morphology of the bainite (granular bainite/bainitic ferrite) was the deformation temperature.