Gilbert Silva

Phase Transformations during the Preparation of Ti6Si2B by High-Energy Ball Milling

Recently, it was identified the existence of a new intermetallic phase in the Ti-Si-B ternary system with atomic composition near Ti6Si2B. In the present work, we report on the phase transformations during the preparation of Ti-22.2Si-11.1B and (TiH2)-22.2Si-11.1B (at.-%) powders in a planetary Fritsch P-5 ball mill from high-purity elemental powders. To understand the phase transformations, powder Ti-22.2Si-11.1B and (TiH2)-22.2Si-11.1B samples milled for 90 h were vacuum heated at various temperatures. The starting materials and milled powders were characterized by means of X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopes, and differential scanning calorimetry (DSC). Results indicate that the Ti peaks widen and weaken with the increasing milling time and the silicon was practically dissolved into Ti and TiH2 lattices during milling and formed solid solutions in pre-alloyed Ti-22.2Si-11.1B and (TiH2)-22.2Si-11.1B powders, respectively. The use of titanium hydride instead of titanium as starting material allowed accelerating the mechanical alloying process, i.e., the Ti6Si2B phase was formed during heating at lower temperatures than in case of titanium as starting material. As previously observed, the decomposition reaction of the titanium hydride occurred near 550C. Powder (TiH2)-22.2Si-11.1B sample milled for 90 h presented very fine particle size lower than 20 nm. The ternary Ti6Si2B phase was formed in powder Ti-22.2Si-11.1B samples after heat treatment. Traces of Ti and Ti5Si3 were also detected.

Pathophysiological, cardiovascular and neuroendocrine changes in hypertensive patients during the hemodialysis session

The pathophysiological mechanisms of arterial hypertension during hemodialysis (HD) in patients with end-stage renal disease (ESRD) are still poorly understood. The aim of this study is to investigate physiological, cardiovascular and neuroendocrine changes in patients with ESRD and its correlation with changes in blood pressure (BP) during the HD session. The present study included 21 patients with ESRD undergoing chronic HD treatment. Group A (study) consisted of patients who had BP increase and group B (control) consisted of those who had BP reduction during HD session. Echocardiograms were performed during the HD session to evaluate cardiac output (CO) and systemic vascular resistance (SVR). Before and after the HD session, blood samples were collected to measure brain natriuretic peptide (BNP), catecholamines, endothelin-1 (ET-1), nitric oxide (NO), electrolytes, hematocrit, albumin and nitrogen substances. The mean age of the studied patients was 43±4.9 years, and 54.6% were males. SVR significantly increased in group A (P<0.001). There were no differences in the values of BNP, NO, adrenalin, dopamin and noradrenalin, before and after dialysis, between the two groups. The mean value of ET-1, post HD, was 25.9 pg ml−1 in group A and 13.3 pg ml−1 in group B (P=<0.001). Patients with ESRD showed different hemodynamic patterns during the HD session, with significant BP increase in group A, caused by an increase in SVR possibly due to endothelial dysfunction, evidenced by an increase in serum ET-1 levels.

Effect of the Reinforcement Volume Fraction on Mechanical Alloying of AA2124 – SiC Composite

Mixtures of AA2124 aluminum alloy powder and SiC particles at volume fractions of 10 vol.% and 20 vol.% were milled in a high energy planetary ball mill under an argon atmosphere, for times of 2.5h to 60 h, aiming to produce Al alloy-SiC nanocomposites. Optical microscopy (MO) and scanning electron microscopy (SEM) were used to evaluate the morphological and microstructural evolution of the powder composite, occurred during mechanical alloying. The crystallite size was determined using the Williamson-Hall method to analyze the X-ray peak broadening. It was observed that increasing the volume fraction of SiC, the mechanical alloying stages were accelerated: a finer composite powder was obtained at a shorter milling time as well as the morphology of the particles became more equiaxed. The XRD analysis showed the reduction of crystallite size of the aluminum alloy matrix with increasing milling time and that this effect is more pronounced with high volume fraction of SiC. The results show that the increase in the volume fraction of reinforcement particles increases the work hardening and fracture occurrence in the aluminum alloy powder during the milling, affecting the structural evolution of the composite.

Syntheses of the Ni3Ti, NiTi, and NiTi2 Compounds by Mechanical Alloying

The aim of this work is to prepare the Ni3Ti, NiTi, and NiTi2 compounds by mechanical alloying from elemental Ni-25at.%Ti, Ni-50at.%Ti, and Ni-66.6at.%Ti powder mixtures. The milling process was carried out in a planetary ball mill under argon atmosphere using a rotary speed of 200rpm, stainless steel balls (10 and 19 mm diameters) and vials (225mL), and a ball-to-powder weight ratio of 10:1. Following, the milled powders were heat treated at 900oC for 1h in order to attain the equilibrium microstructures. The milled powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis via EDS. Similar ball milling behavior of Ni-Ti powders was noted in this work, e.g., a pronounced cold-welding between ductile powders occurred during the initial milling times. The Ni3Ti, NiTi, and NiTi2 compounds were synthesized after milling for 30h. Atomic disordering of the NiTi and NiTi2 compounds was achieved, and amorphous structures were then formed in Ni-50Ti e Ni-66.6Ti powders milled for 60h and 210h, respectively. Homogeneous matrixes constituted by the Ni3Ti, NiTi, and NiTi2 phases were formed in Ni-Ti powders after heat treatments at 900oC for 1h. Iron contamination lower than 2 at-% was measured by EDS analysis in heat-treated Ni-Ti alloys.

Sinterização da liga WC/10Co por altas pressões

Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders, compacting, and liquid phase sintering. A new method to process hardmetal parts are described here. Parts of WC/10%wt Co were processed by using high pressure and high temperature sintering. It was used the pressure of 5GPa, temperatures of 1200, 1300, and 1400oC, and times of 1and 2 minutes of sintering. The best results was density =95,5%, hardness HV45 =10GPa and fracture toughness of KIc =11MPa.m½.

Structural Evaluation of Mechanically Alloyed Ti-Nb Powders

This work discusses on the structural evaluation of mechanically alloyed Ti-Nb powders. The Nb amount was varied between 20 and 50 wt-%. The milling process was carried out in a planetary Fritsch P-5 ball mill under Ar atmosphere. The structural evaluation was conducted by scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry. During ball milling it was noted an excessive agglomeration of ductile Ti-Nb powders on the balls and vial surfaces, and the final amount of remaining powders was then drastically reduced into the vials. This fact was more pronounced with the increased Nb amount in starting powders. Typical lamella structures were formed during ball milling, which were refined for the longest milling times, and fine and homogeneous structures were formed in Ti-Nb (Nb=20-50wt-%) powders. XRD results indicated that the full width at half maximum values of Ti peaks were continuously increased while that the crystallite sizes were reduced for longer milling times due to the severe plastic deformation provided during ball milling of Ti-Nb powders. However, the EDS analysis revealed the presence of Nb-rich regions in Ti-Nb powders after ball milling. The critical ball milling behavior of ductile Ti- Nb powders contributed for reducing the yield powder and increasing the structural heterogeneity.

Effect of Milling Parameters on the TiB and TiB2 Formation in Ti-50at%B and Ti-66at%B Powders

This work discusses on the effect of milling parameters on the TiB and TiB2 formation in Ti-50at%B and Ti-66at%B powders, respectively. Both powder mixtures were processed in a planetary ball Fritsch P-5 ball mill under Ar atmosphere, varying the milling parameters: rotary speed (150 and 200 rpm), size of balls (10 and 19mm diameter) and ball-to-powder weight ratio (2:1 and 10:1). In order to obtain the equilibrium structures the milled powders were heated at 1200oC for 1h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal analysis (DSC). XRD results indicated that extended Ti(B) solid solutions were formed during ball milling of Ti-50at%B and Ti-66at%B powders. After milling for 170h it was noted the TiB and TiB2 formation in Ti-50B and Ti-66B powders processed under higher-energy condition. DSC analysis revealed that the TiB2 formation was completed during heating of mechanically alloyed Ti-66at%B powders only. After heating at 1200oC for 1h, a large amount of TiB and TiB2 was found in Ti-B powders milled under higher energy condition.

Determination of Surface Roughness in Turning of Aluminum Bronze Alloy (UNS С 63020) Using Cutting Tools with Carbide Geometry Positive and Negative

In todays industry, production processes evolve every day, together with the development of new materials and geometries for tools and machines more accurate and efficient. These new technologies allow more flexible processes, such as replacement of the grinding process by turning of hardened materials. This change brings significant reductions in costs of tooling, setup time and machining.This work is a study of the conditions for turning aerospace alloy - Bronze Aluminum (UNS 63020)-hardened and tempered with a hardness of 35 HRC with carbide tools with positive and negative geometry.We analyzed the surface roughness of the specimen and as a criterion for end of life of the cutting tool was used to flank wear, crater wear, chip on the tool and/or the breach thereof.All the cutting parameters, when in their highest levels, do not contribute significantly to the reduction in tool life, while the surface roughness for the increase in the feed (f) and the cutting speed (vc) showed a greater influence on surface finish of the piece.

Syntheses of TiB and TiB2 by High-Energy Ball Milling

The present work reports on the syntheses of TiB and TiB2 by high-energy mechanical milling from high-purity elemental powders: Ti (99.9 wt.-%, spherical, -150 mesh) and B (99.5 wt.%, irregular, -40 mesh). Titanium hydride (99.7 wt.-%, chip) was also used in place of titanium to produce TiB. The high-energy milling was carried out in a planetary ball mill under high-purity argon atmosphere using a ball/powder weight ratio of 2:1, milling speed of 150 rpm, stainless steel vial (225 mL) and high-Cr hardened steel balls (10 mm of diameter). The powders were characterized by means of X-ray diffraction (XRD), scanning electron (SEM) and transmission (TEM) microscopes, and differential scanning calorimetry (DSC). TiB was successfully produced after heating of mechanically alloyed Ti-50at.%B and TiH2-50at.%B powders. The decomposition of the titanium hydride occurred during heating in the temperature range 500 to 600 o C. TiB2 was also formed after heating at 1100 and 1200 o C.

Production and Characterization of Ti-Nb Alloys, Using Powders Obtained by HDH Process Aiming the Development of Biomaterials

Titanium is a metal that has high melting point 1668 ° C, the boiling point of 3287° C, low density (4.54 g/cm3) and modulus of elasticity around 12.7 MPa x104. However, one of the most important properties is the biocompatibility, which makes this metal to be the most widely used in biomedical. Several alloys were developed using titanium such as the alloy Ti-6Al-4V, however Al and V show toxic characteristics to the organism. The alloy TiNb has been studied to replace the alloy Ti-6Al-4V, because it presents high biocompatibility, low modulus of elasticity, high corrosion resistance and low toxicity. The alloy TiNb can be obtained by conventional melting route or powder metallurgy, where the powders can be obtained by spray drying, chemical reactions and the process of hydrogenation and dehydrogenation (HDH).The hydrogenation is carried out by inserting hydrogen in the structure of Ti and Nb in vacuum at high temperatures, forming a phase extremely fragile called hydride of Ti and Nb, thus enabling the reduction of particle size by milling. Upon heating under vacuum, the hydrogen is extracted to yield the metals Ti and Nb since the hydrogen forms a reversible phase with metals. This work aims the production and characterization of the alloy TiNb where the powders are obtained through the HDH process, varying the concentration of Nb by weight from 10 to 50%.To analyze the morphology and pore size, formation and composition of phases, we used the techniques of microstructural characterization and mechanical by scanning electron microscopy, BET, X-ray diffraction and compression test. The results showed a heterogeneous distribution of Nb in the matrix Ti as well as a decrease in the modulus of elasticity with increase in percentage of Nb.