Claudemiro Bolfarini

Amorphous phase formation in spray deposited AlYNiCo and AlYNiCoZr alloys

Al 85 Y 8 Ni 5 Co 2 and Al 84 Y 3 Ni 8 Co 4 Zr 1 (at%) alloy billets were prepared by spray forming. Two ratios of volumetric gas flow rate to mass of metal flow rate (G/M) were used for the Al 85 Y 8 Ni 5 Co 2 alloy (G/M 5 6.4 m 3 /kg and 10.0m 3 /kg) and one G/M (8.7 m 3 /kg) was used for the Al 84 Y 3 Ni 8 Co 4 Zr 1 alloy. The superheat temperature was 1170K and the diameter of the nozzle bore of the atomizer used was 4.4 mm. The molten metal was sprayed at a rate of 3.1 kg/min and nitrogen gas was used for atomization. The resulting billets weighed about 7.0kg and 2.1kg for the Al 85 Y 8 Ni 5 Co 2 and Al 84 Y 3 Ni 8 Co 4 Zr 1 alloys, respectively. The overspray powder was collected in a cyclone separator and accounted for about 19% and 30% of the starting charge for the Al 85 Y 8 Ni 5 Co 2 and the Al 84 Y 3 Ni 8 Co 4 Zr 1 alloy, respectively. The billets and the powder were analyzed by X-ray diffraction using Cu K a radiation (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) system, electron probe microanalysis (EPMA) and transmission electron micros

Amorphous phase formation during spray forming of Al84Y3Ni8Co4Zr1 alloy

Abstract In this investigation the Al84Y3Ni8Co4Zr1 alloy has been processed by spray forming to investigate the potential of achieving substantial fractions of the amorphous phase in the billet. The alloy was prepared by spray metal forming using the ratio of volumetric gas flow rate to mass of metal flow rate of 8.7 m 3 / kg . The resulting billet, weighting 2.1 kg, as well as the powders produced by the particles that had not hit the growing billet (overspray), were characterized by using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powders had particles with spherical morphology in the size range of few microns to 100 μm with the median particle diameters about 20±1 μ m. The resulting billet contained only crystalline phases nevertheless the powder was composed of about 40% volume fraction of amorphous phase. This result indicates that the heating of the billet, by the heat release during solidification of the liquid and semi-solid particles was at temperature and for time enough for crystallization.

Growth of aluminum-free porous oxide layers on titanium and its alloys Ti-6Al-4V and Ti-6Al-7Nb by micro-arc oxidation

The growth of oxides on the surfaces of pure Ti and two of its ternary alloys, Ti-6Al-4V and Ti-6Al-7Nb, by micro-arc oxidation (MAO) in a pH 5 phosphate buffer was investigated. The primary aim was to form thick, porous, and aluminum-free oxide layers, because these characteristics favor bonding between bone and metal when the latter is implanted in the human body. On Ti, Ti-6Al-4 V, and Ti-6Al-7Nb, the oxides exhibited breakdown potentials of about 200 V, 130 V, and 140 V, respectively, indicating that the oxide formed on the pure metal is the most stable. The use of the MAO procedure led to the formation of highly porous oxides, with a uniform distribution of pores; the pores varied in size, depending on the anodizing applied voltage and time. Irrespective of the material being anodized, Raman analyses allowed us to determine that the oxide films consisted mainly of the anatase phase of TiO2, and XPS results indicated that this oxide is free of Al and any other alloying element.

Amorphous phase formation in Fe-6.0wt%Si alloy by mechanical alloying

Mechanical alloying, MA, is a high-energy ball milling technique, in which elemental blends are milled to achieve alloying at atomic level. This communication describes the results of an investigation on the phase transformation of a mixture of Fe and Si powders with 6wt%Si during MA processing. Besides the verification of the effect of milling time on the structure and on the compositional homogeneity, this study was undertaken in order to confirm, by using TEM technique, the possibility of amorphous phase formation for Si content lower than 17.7wt%.

Osteoblasts behavior on chemically treated commercially pure titanium surfaces

Surface modifications of commercially pure titanium (Cp-Ti), a material widely used to produce dental implants, can induce specific responses on osteoblastic cells after implantation. This work aims to investigate the influence of chemically modified surfaces of Cp-Ti by acid etching or acid etching plus alkaline treatment on the gene expression of human osteoblastic (Hob) cells. Roughness and contact angle measurements were carried out to evaluate the surface properties of the samples. The surface morphology was investigated with scanning electron microscopy. Chemical composition was analyzed by energy dispersive X-ray spectroscopy (EDS). The expression levels of some bone-related genes (ALPL, COL1A1, COL3A1, SPP1, RUNX2, and SPARC) were analyzed using real time Reverse Transcription-Polymerase Chain Reaction (real time RT-PCR). The results showed that all the chemical modifications studied in this work influenced the surface morphology, wettability, roughness and induced an osteoconductive behavior. The samples that were acid etched and alkaline treated showed a more pronounced effect.

Application of mathematical simulation and the factorial design method to the optimization of the atomization stage in the spray forming of a Cu–6% Zn alloy

Abstract Process parameters optimization for the spray forming of a Cu–6% Zn alloy was developed by a combination of mathematical simulation and the factorial design method (FDM). The finite difference method was used for the mathematical simulation of the atomization stage and two levels FDM was applied considering the initial gas velocity, the axial distance between the atomizer and the substrate, the superheating of the melt and the melt flow rate. The validation of the optimized process parameters was done by processing the Cu–Zn alloy, a high-density deposit, as high as 98.5% of the theoretical density with a very homogeneous microstructure being produced.

Gene expression of human osteoblasts cells on chemically treated surfaces of Ti-6Al-4V-ELI.

Surface modifications of titanium alloys are useful methods to enhance the biological stability of intraosseous implants and to promote a well succeeded osseointegration in the early stages of implantation. This work aims to investigate the influence of chemically modified surfaces of Ti-6Al-4V-ELI (extra-low interstitial) on the gene expression of human osteoblastic (HOb) cells. The surface treatments by acid etching or acid etching plus alkaline treatment were carried out to modify the topography, effective area, contact angle and chemical composition of the samples. The surface morphology was investigated using: scanning electron microscopy (SEM) and confocal laser-scanning microscope (CLSM). Roughness measurements and effective surface area were obtained using the CLSM. Surface composition was analysed by energy dispersive X-ray spectroscopy (EDX) and by X-Ray Diffraction (XRD). The expression levels of some bone related genes (ALPL, COL1A1, COL3A1, SPP1, RUNX2, and SPARC) were analysed using real-time Reverse Transcription Polymerase Chain Reaction (real-time RT-PCR). The results showed that all the chemical modifications studied in this work influenced the surface morphology, wettability, roughness, effective area and gene expression of human osteoblasts. Acid phosphoric combined to alkaline treatment presented a more accelerated gene expression after 7days while the only phosphoric etching or chloride etching combined to alkaline treatment presented more effective responses after 15days.

Numerical evaluation of reduction of stress shielding in laser coated hip prostheses

The increasing use of titanium alloys as biomaterials can be attributed, among other factors, to their low Young modulus compared to other alloys with similar mechanical strength. However, Ti-6Al-4V alloy, the alloy most widely used in implants, has a stiffness of about 110 GPa, which is much higher than the typical stiffness of 20 GPa of human bone. In the specific case of hip arthroplasty, this difference in stiffness reduces the load imposed on the femur through the stress shielding phenomenon, which, in the medium term, usually results in the loss of bone density. One way to reduce this phenomenon is by using TiNbTaZr (TNTZ) alloys, which have a stiffness of about 47 GPa. This work uses numerical simulation to evaluate the effectiveness of TNTZ laser coated on a Ti-6Al-4V hip prosthesis in reducing stress shielding. The results show that this may improve the performance of the prosthesis, extending its service life.

Microstructure and Magnetic Properties of Fe-6.5wt%Si Alloy Obtained by Spray Forming Process

Deposits of the Fe-6.5wt%Si alloy produced by spray forming were annealed at temperatures between 900 and 1300oC, during 1h in vacuum and quenched in oil at temperatures between 300 and 700oC, separately. Magnetic properties, singular microstructure and random crystallographic texture were measured. After annealing at 1250°C for 1h under vacuum, the average grain size is of 500 μm, the grain orientation is random and the magnetic properties were: power loss of 1.30 W/kg, maximum permeability of 15400 and coercive force of 40 A/m, at B=1 T, f=60 Hz by using 0.60 mm thick rings for all studied samples. Higher annealing temperatures cause no decreasing of these properties. After quenched at 700°C, an improvement the magnetic properties where detected due to antiphase domain B2 growth. The magnetic properties were: power loss of 1.59 W/kg, maximum permeability of 12300 and coercive force of 76 A/m, at B=1 T, f=60 Hz.

Chemistry and tensile properties of a recycled AA7050 via spray forming and ECAP/E

The aim of this work is to evaluate the conjugation of advanced processing techniques, such as spray forming, extrusion and ECAP as a processing route for reuse of machining chips generated during aircrafts manufacturing parts from AA7050-T7451 raw material plates supplied according to AMS 4050H1. In this way, the sprayforming process was used for remelting, and billet production, followed by extrusion and ECAP. At the end of the process, an artificial aging according to AMS 2772E 2 was conducted. An assessment of chemical composition, microstructure, and mechanical properties evolution throughout the process were performed. The results have showed that this proposed route may be used as a potential technological route for secondary aluminum source. For extrusion route for overaged condition, 144 MPa yield strength and 14% of elongation was attained. Beside this, at this stage of work, was verified that the hot extrusion process is more effective for reduction of porosity and microstructure development than ECAP, but on the other hand this one has reduced porosity dispersion significantly for the extrusion parameters adopted. The adopted homogenization schedule, followed by artificial aging after has resulted in excessive grain growth.