Walter José Botta Filho

Mechanical and Reactive Milling of a TiCrV BCC Solid Solution

Nowadays, many efforts have been concentrated in research and development of hydrogen absorbing materials due to a possible application as electrode for rechargeable batteries, on board hydrogen storage systems, getters, catalysts, etc. Novel technologies for materials processing have been used to generate new alloys with metastable structures, such as amorphous and/or nanocrystalline alloys. In this context, mechanical milling or mechanical alloying is a very attractive way to produce this alloys, specially when carried out under hydrogen atmosphere (reactive milling). In this work, we have studied the structural evolution of a TiCrV bcc solid solution during mechanical and reactive milling. The process parameters analyzed were: milling atmosphere (argon and hydrogen), milling time and gas pressure into the vials (in the case of reactive milling). Structural evolution was investigated by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). Hydrogen contents of the reactive milled alloys were determined using a Leco analyzer. Differential scanning calorimetry (DSC) was used to determine the hydrogen desorption temperature and the stability of the alloys.

Microstructure and wear resistance of spray-formed supermartensitic stainless steel

Since the early 90’s the oil industry has been encouraging the development of corrosion and wear resistant alloys for onshore and offshore pipeline applications. In this context supermartensitic stainless steel was introduced to replace the more expensive duplex stainless steel for tubing applications. Despite the outstanding corrosion resistance of stainless steels, their wear resistance is of concern. Some authors reported obtaining material processed by spray forming, such as ferritic stainless steel, superduplex stainless steel modified with boron, and iron-based amorphous alloys, which presented high wear resistance while maintaining the corrosion performance

Hydrogen Activation Behavior of Commercial Magnesium Processed by Different Severe Plastic Deformation Routes

Severe plastic deformation (SPD) techniques are being considered as low cost processing routes for Mg alloys, aiming hydrogen storage applications. The main objective is to develop air-resistant materials, with lower specific surface area in comparison with ball-milled powders, but with still attractive H-sorption kinetics associated to the microstructural refinement. In this study, the effects of different SPD processing routes (high-pressure torsion, extensive cold rolling and cold forging) in the hydrogen activation behavior of Mg was evaluated. The results show that both microstructural and textural aspects should be controlled during SPD processing to obtain Mg alloys with good H-sorption properties and enhanced activation kinetics.

Magnesium-Nickel alloy for hydrogen storage produced by melt spinning followed by cold rolling

Severe plastic deformation routes (SPD) have been shown to be attractive for short time preparation of magnesium alloys for hydrogen storage, generating refined microstructures and interesting hydrogen storage properties when compared to the same materials processed by high-energy ball milling (HEBM), but with the benefit of higher air resistance. In this study, we present results of a new processing route for Mg alloys for hydrogen storage: rapid solidification followed by cold work. A Mg

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.

Nanostructured Al89Fe10Zr1 Alloy Obtained by Mechanical Alloying

In this work we have used mechanical alloying to produce nanocrystalline Al89Fe10Zr1 alloy powder. The effect of the milling time and the thermal stability of the product powder were evaluated by differential scanning calorimetry and X-ray diffraction. Scanning electron microscopy and transmission electron microscopy were also used for the microstructural characterisation of the powder. The mechanically alloyed powder was composed by a nanocrystalline supersaturated solid solution of α-Al, with average nanocrystals size of 15 nm. The following phases were formed during heating: Al6Fe, Al13Fe4 and Al3Zr besides an unknown metastable phase. In the fully annealed alloy the phases observed were α-Al, Al13Fe4 and Al3Zr.

Anelastic Relaxation Measurements in Nb-46wt%Ti Alloys with Interstitial Solutes in Solid Solution

Anelastic relaxation measurements were performed in a Nb-46wt%Ti alloy, in the temperature range of 300 to 700 K, using a torsion pendulum operating at an oscillating frequency near 2.0 Hz. The samples were measured in different conditions: cold worked, annealed in ultra-high vacuum and doped with several quantities of nitrogen. The relaxation spectra obtained were resolved into their component peaks, corresponding to the different kinds of interaction of the interstitial solutes with the metallic matrix. The relaxation parameters of each process were calculated using Debye’s elementary peaks.

Rapidly Solidified Al-Si-Mg Alloy

Rapid solidification processes, RSP, are powerful tools to induce microstructural modifications, which may improve mechanical properties of metallic alloys. In this paper the influence of rapid solidification on the formation of the undesirable brittle intermetallic compounds promoted by Mg, Si and Fe in Al-9Si-0.7Mg (A359-type) alloy have been investigated by using of water-cooled wedge-copper mould for the rapid solidification process. The microstructures have been evaluated by using a combination of X-ray diffraction (XRD), optical (OM), scanning (SEM) and transmission electron microscopy (TEM), and by Vickers microhardness. By increasing the cooling rate the secondary dendritic arm spacing decreased and the formation of Mg2Si and Al8Si6Mg3Fe phases were suppressed. At the same time an increase in the hardness was observed. These microstructural and mechanical properties changes associated with the rapid solidification process might be attributed to the increased solid solution content of the alloying elements in the Al matrix. Introduction Aluminum-silicon alloys are widely used for automobile parts production due to their excellent castability and high strength-to-weight ratio. Magnesium is often added to increase the strength and hardenabilty of the Al-Si cast parts [1]. Iron and manganese are also present in these alloys, either introduced by the scrap or deliberately added to provide material special properties. On the other hand, due to the low solid solubility of Fe, Si and Mg in Al, during conventional casting precipitation of Al5FeSi, Al8Si6Mg3Fe, Mg2Si and other intermetallic phases with complex structures is observed. Rapid solidification processes, RSP, are powerful tools to induce microstructural modifications; besides the formation of homogeneous and refined microstructures [2], they can also increase the solid solubility limit of some elements in the matrix [3, 4] and therefore suppress the formation of some precipitates or to modify their morphology. The objective of the present study is to analyze the influence of rapid solidification process on the microstructure of an Al-9Si-0.7Mg (A359 type) alloy, focusing on the possibility of minimizing the formation of intermetallic compounds. Experimental Procedure Ingots of commercial Al-9Si-0.7Mg (A359-type) alloy, whose chemical composition is shown in Table 1, have been melted and cast into a water-cooled wedge-section copper mould, with a wedge angle of 5 o , 10 mm wide and 50 mm high. The melt, pouring systems and the mould were installed in a single melt-spinning device chamber. Processing was under argon atmosphere and the molten alloy at a temperature of 830°C was ejected with an overpressure of 200 mbar into of the copper mould. The samples naturally aged for more than a week have been characterized by using a combination of optical microscopy (OM), scanning (SEM) and transmission electron microscopy (TEM, Philips CM120), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and by Vickers microhardness measurements. Samples for TEM were thinned by ion milling using a dual guns system operating at 5kV with 800 μA per gun. The secondary dendrite arm spacing, DAS, was Journal of Metastable and Nanocrystalline Materials Online: 2004-07-07 ISSN: 2297-6620, Vols. 20-21, pp 594-598 doi:10.4028/www.scientific.net/JMNM.20-21.594

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.