Papers by Claudemiro Bolfarini
Engenharia no Século XXI – Volume 9, 2019
The Equal Channel Angular Extrusion in Grade 2 and 4 commercially pure titanium raises the yield ... more The Equal Channel Angular Extrusion in Grade 2 and 4 commercially pure titanium raises the yield strength, ultimate tensile strength, elongation, fatigue limit, besides to attend the requirements of torque and angle of rupture for implants.
Metallurgical and Materials Transactions A, 2021
Metals, 2021
A metastable beta TMZF alloy was tested by isothermal compression under different conditions of d... more A metastable beta TMZF alloy was tested by isothermal compression under different conditions of deformation temperature (923 to 1173 K), strain rate (0.172, 1.72, and 17.2 s−1), and a constant strain of 0.8. Stress–strain curves, constitutive constants calculations, and microstructural analysis were performed to understand the alloy’s hot working behavior in regards to the softening and hardening mechanisms operating during deformation. The primary softening mechanism was dynamic recovery, promoting dynamic recrystallization delay during deformation at higher temperatures and low strain rates. Mechanical twinning was an essential deformation mechanism of this alloy, being observed on a nanometric scale. Spinodal decomposition evidence was found to occur during hot deformation. Different models of phenomenological constitutive equations were tested to verify the effectiveness of flow stress prediction. The stress exponent n, derived from the strain-compensated Arrhenius-type constitu...
Soldagem & Inspeção, 2020
Resumo: O presente trabalho teve como objetivo a determinação dos parâmetros ótimos do processo d... more Resumo: O presente trabalho teve como objetivo a determinação dos parâmetros ótimos do processo de manufatura aditiva de Fusão Seletiva a Laser (FSL) para o aço 316L visando a obtenção de peças com alta densidade, utilizando equipamento fabricado no Brasil. Foi realizada também uma completa caracterização estrutural tanto da matéria prima utilizada (pó comercial) quanto das peças mais densas obtidas. As propriedades mecânicas das peças produzidas por FSL também foram avaliadas e comparadas com peça fabricada de forma convencional. Foi observado que a densidade das peças aumenta com o aumento da densidade volumétrica de energia fornecida pelo laser até atingir um patamar de máxima densidade. Um modelo polinomial foi proposto correlacionando a densidade volumétrica de energia utilizada com a densidade final da peça. As peças produzidas por FSL mostraram uma elevada densificação (densidade relativa superior a 99,49%) com uma reduzida porosidade homogeneamente dispersa no material. Uma ...
Materials Research, 2019
The effect of a surface treatment by Nd:YAG laser irradiation on the fatigue behavior of Ti-6Al-4... more The effect of a surface treatment by Nd:YAG laser irradiation on the fatigue behavior of Ti-6Al-4V ELI was studied. Axial fatigue tests were performed to obtain S-N curves in polished and laser treated conditions. Roughness measurements and scanning electron microscopy were used to characterize the features of the modified surface. A reduction in the fatigue strength of around 35% was obtained after the laser treatment of the material surface. Although the surface roughness was in the micrometer scale, a notch effect was suggested to be the reason for the deleterious influence of the laser on the fatigue strength. The reduction in the fatigue strength obligatory demands redesign of implants for laser modified surfaces of Ti-6Al-4V alloy.
Journal of Alloys and Compounds, 2017
The behaviour of the martensitic phase transformation of a Cu-Al-Ni-Mn shape memory alloy was stu... more The behaviour of the martensitic phase transformation of a Cu-Al-Ni-Mn shape memory alloy was studied for as-atomized and heat-treated powders. X-ray diffraction, microscopy techniques and thermodynamic calculations were used to understand the different transformation behaviour observed during differential scanning calorimetry (DSC) analysis. Two overlapped transformation peaks were observed in the DSC curves for the as-atomized powder. After annealing, the peaks progressively became only single peak when the annealing temperature and time were increased. No difference in phase formation and microstructure was observed by X-ray diffraction and scanning electron microscopy when compared as-atomized and annealed powders, although transmission electron microscopy analyses showed that the as-cast powders had more dislocations trapped in the microstructure than the annealed samples. Considering the experimental results and thermodynamic considerations, it was concluded that the smooth double peak effect in the as-atomized powders occurred due to a different state of internal stresses and elastic energy accumulation during forward transformation. The absence of this effect after heat treatment shows that the internal stresses and defects were annihilated after annealing, changing the elastic energy accumulation and the transformation behaviour. Understanding the martensitic transformation on Cu
Materials & Design, 2016
A new Fe 57 Cr 9 Nb 13 B 21 amorphous/ nanocrystalline coating was designed and obtained by HVOF ... more A new Fe 57 Cr 9 Nb 13 B 21 amorphous/ nanocrystalline coating was designed and obtained by HVOF thermal spray. • The microstructure of the HVOF coating was investigated in details to identify the crystalline phases. • Orientation image mapping was performed by TEM coupled with an ASTAR system to index the nanocrystalline phases. • The coating exhibits high microhardness and good wear resistance due to the composite structure of amorphous and nanocrystalline phases.
Journal of Electroanalytical Chemistry, 2015
A new direct approach for model identification is proposed. It allows a more accurate survey of t... more A new direct approach for model identification is proposed. It allows a more accurate survey of the different relaxation processes yielding distinct time constants in electrochemical impedance spectroscopy. With the help of self-organized TiO 2 nanotubes layers grown in pure Ti substrates, it is shown that the conventional impedance data representation methods are susceptible to miss some information that is made accessible by the frequency survey of a eff , the effective CPE exponent parameter. In the specific case of the present work, the alternative representation proposed here shows that the electrochemical behavior of the TiO 2 layers exposed to Ringer physiological solution is characterized by up to three time constants related to a simple double-layered structure composed by a dense barrier and the porous nanotubes one, instead of the ubiquitous two time constants mentioned in the literature for the same systems.
Surface and Coatings Technology, 2014
Fe-based bulk metallic glass alloy Fe-based bulk metallic glass coatings Amorphous coatings Coati... more Fe-based bulk metallic glass alloy Fe-based bulk metallic glass coatings Amorphous coatings Coatings of a Fe 43.2 Co 28.8 B 19.2 Nb 4 Si 4.8 alloy on AISI 1020 steel substrates were produced by laser cladding. By properly selecting the processing parameters adherent tracks with negligible dilution could be obtained. For the processing conditions used the clad material presents a graded structure consisting of 5 layers with different microstructures, resulting from the prevalent material solidification path. Solidification starts by epitaxial growth of Fe-Co δ-ferrite on the δ-ferrite resulting from heating of the substrate near the fusion line into the δ-ferrite stability temperature range. This first stage of solidification leads to the formation of consecutive layers consisting predominantly of δ-ferrite and formed by plane front, cellular and columnar dendritic solidification. The solidification of Fe-Co δ-ferrite leads to the segregation of B and Nb first frontally, to the bulk of the liquid, then to the interdendritic regions, resulting in the precipitation of a boride containing eutectic. Initially, the eutectic precipitates in the interdendritic regions, resulting in a layer of material comprised of δ-ferrite dendrites and interdendritic eutectic, then in a layer of material where the eutectic is the bulk alloy constituent. Eventually, a layer of amorphous material with homogeneously dispersed dendrites of Fe-Co δ-ferrite forms in most of the coating thickness. These embedded dendrites form by equiaxed solidification within the supercooled liquid at the trailing edge of the melt pool, from δ-ferrite dendrite fragments and boride particles carried from the growing columnar layer into the liquid bulk by Marangoni convection, driven by the temperature gradients existing within the melt pool. They play a critical role in defining the excellent properties of the coating material: a very high hardness of 1040 ± 16 HV0.5 associated to a reasonable ductility, allowing the formation of crack-free coatings, in contrast with the bulk alloy prepared by spray forming, either in the as-prepared condition or after laser melting.
Materials Science and Engineering: A, 2007
Aluminum additions to brittle Fe-6.5 wt.% Si alloys made possible the mechanical processing of th... more Aluminum additions to brittle Fe-6.5 wt.% Si alloys made possible the mechanical processing of these alloys at lower temperatures and thus being determinant in the development of the texture. The aim of this work was to analyse the evolution of the crystallographic texture of a spray-formed (SF) Fe-6.5 wt.% Si-1.0 wt.% Al during rolling operation for thin sheets production. The SF deposit was warm-rolled and then air cooled to obtain partial recrystallisation. The initial texture (0 1 1) [01 1] [1 0 0] (// to normal direction-ND) of the deposit was changed to approximately (0 1 3) [11 0] [1 1 0] (8 • from ND) after the last reduction step. The maxima intensities of texture was found at 700 • C (89% of reduction) showing the influence of rolling temperature; after warm-rolling the entire texture changes to a partial ND fibre running from {0 0 1} to {1 1 0}, with negligible Goss intensities. The transition away from an ND fibre texture in the lattermost case (99.5% reduction) was in turn associated with the near-absence of shear bands.
Journal of Non-Crystalline Solids, 2010
An investigation was made into the thermal stability and mechanical behavior under nanoindentatio... more An investigation was made into the thermal stability and mechanical behavior under nanoindentation of a new glassy alloy with composition Ni 50 Nb 28 Zr 22 , produced in the form of melt-spun ribbons and copper mold-cast wedges. The alloy composition was designed based on the lambda criterion combined with the electronegativity difference among the elements. X-ray diffraction and scanning electron microscopy confirmed that the ribbons and wedges (up to 200 μm in thickness) are amorphous. The thermal properties of these samples were evaluated by differential scanning calorimetry (DSC). Nanoindentation revealed that the hardness of this alloy, around 10 GPa, is among the highest reported for metallic glasses. Remarkably, the cast wedge exhibits greater hardness and higher elastic modulus than the ribbon. This correlates with the larger amount of frozen-in free volume in the ribbons than in the cast wedges, as evidenced by DSC. In addition, finite element simulations of nanoindentation curves were performed. The Mohr-Coulomb yield criterion allows for better adjustment of the experimental data than the pressure-independent Tresca yield criterion. The simulations also reveal that the cohesive stress in the ribbons is lower than in the wedges, which explains the difference in hardness and Young's modulus between the two samples.
Journal of Non-Crystalline Solids, 2010
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Journal of Non-Crystalline Solids, 2008
In the present work, the glass forming ability (GFA) and its compositional dependence on Al-NiCe ... more In the present work, the glass forming ability (GFA) and its compositional dependence on Al-NiCe system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al 85 Ni 15ÀX Ce X (X = 4,5,6,7,10), Al 90 Ni 5 Ce 5 , Al 89 Ni 2.4 Ce 8.6 , Al 80 Ni 15.6 Ce 4.4 and Al 78 Ni 18.5 Ce 3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al-NiCe system alloys were enhanced by increasing the solute content and specifically the Ce content.
Journal of Non-Crystalline Solids, 2001
The corrosion resistance of Fe–M–B–Cu alloys in which M is a transition metal of two first series... more The corrosion resistance of Fe–M–B–Cu alloys in which M is a transition metal of two first series, particularly concerning the effect of composition and also concerning the affect of corrosion on magnetic properties have not been evaluated. In this paper, the effect of composition and partial crystallization on corrosion resistance of Fe80Nb3.5Zr3.5B12Cu1, Fe80Nb3.5Mo3.5B12Cu1, Fe80Zr3.5Mo3.5B12Cu1 and Fe80Mo7B12Cu1 amorphous alloys and its
Journal of Alloys and Compounds, 2013
Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit hi... more Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250°C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75 lm, and also after the extrusion at 375°C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys.
Journal of Alloys and Compounds, 2011
The thermal crystallization of Al-based metallic glasses can be described in association with the... more The thermal crystallization of Al-based metallic glasses can be described in association with the topological instability criterion. In the present work, we report on the crystallization behavior and glass forming ability of Al-rich, Al-Ni-Sm alloys, designed with compositions corresponding to the same topological instability condition of ≈ 0.1. Amorphous melt-spun alloys were prepared with the following compositions, varying the ratio of Ni and Sm elements: Al 87.5 Ni 4 Sm 8.5 , Al 83.5 Ni 10 Sm 6.5 , Al 80.5 Ni 14.5 Sm 5 and Al 76.5 Ni 20.5 Sm 3. The glass forming ability of each alloy composition was evaluated based on the thermal parameters obtained from DSC runs and on X-ray diffraction patterns. Better glass forming ability was observed in compositions whose Sm content was increased and Ni content reduced. Thermal crystallization of the alloys with low Sm content showed only one crystallization peak and no glass transition event. In alloys with higher rare-earth content, a glass transition event was clearly detected before the crystallization event. The results are interpreted considering the different types and proportions of Sm-Al and Ni-Al clusters that can be formed in the alloys along the ≈ 0.1 line. They also emphasize the relevance of these different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallization.
Journal of Alloys and Compounds, 2009
The different types of thermal crystallisation behaviours observed during continuous heating of A... more The different types of thermal crystallisation behaviours observed during continuous heating of Al-based metallic glasses have been successfully associated with the topological instability criterion, which is simply calculated from the alloy composition and metallic radii of the alloying elements and aluminium. In the present work, we report on new results evidencing the correlation between the values of and the crystallisation behaviours in Al-based alloys of the Al-NiCe system and we compare the glass-forming abilities of alloys designed with compositions corresponding to the same topological instability condition. The results are discussed in terms of compositional and topological aspects emphasizing the relevance of the different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallisation.
In the present work, we report on the corrosion properties of the Fe 60 Cr 8 Nb 8 B 24 (at.%) all... more In the present work, we report on the corrosion properties of the Fe 60 Cr 8 Nb 8 B 24 (at.%) alloy produced using pure and commercial materials in the following conditions: amorphous ribbons, partially crystallized ribbons and coatings produced by spray deposition and powder flame spraying process, in this case LVOF (low velocity oxygen fuel). The amorphous ribbons showed excellent corrosion resistance with formation of a stable passive film that ensured a very large passivation plateau. The (LVOF) coatings presented high fraction of amorphous phase with a layered structure, high porosity (16.2%) and low oxidation level (~0.1%). The spray formed coatings presented crystalline structure with low porosity (1.9%) and low oxidation level (~0.1%). The coatings showed higher corrosion current densities (up to two orders of magnitude) compared to the amorphous ribbons of the same composition for all pH. This deterioration in the corrosion properties were found to be impaired by the presence of crystalline phases.
Materials Research, 2017
Nanotechnology is seeing as having potential to raise benefits to several research and applicatio... more Nanotechnology is seeing as having potential to raise benefits to several research and application areas. Recently materials with nanostructured surfaces of nanopores, nanotubes and nanowires have become an important investigation field, since their chemical and physical properties may be substantially different from those of the corresponding substrate. In face of the necessity of assuring that such modifications are not deleterious to the mechanical behavior, the purpose of this work was to evaluate the fatigue performance of CP-Ti grade 2 with the surface modified by the formation of nanotubes on their different crystalline structures. The nanotubes layers were produced by anodic oxidation using a potential of 20V during 1h and a solution of glycerol, H 2 O and NaF, and analyzed by scanning electron microscopy. In order to obtain the anatase and rutile structures, annealing treatments were respectively performed at 450°C and 650°C. The axial fatigue tests were conducted in physiological solution at 37°C following the stepwise load increase approach. When compared to the material without surface modification (polished surface), the results showed that the anatase phase did not affect the fatigue response, maintaining the fracture stress in 500 MPa, whereas the rutile phase caused a decrease to 450 MPa.
Materials Letters, 2016
Abstract Highly ordered arrays of TiO 2 nanotubes are being considered as very promising to impro... more Abstract Highly ordered arrays of TiO 2 nanotubes are being considered as very promising to improve the osseointegration of titanium based implants to living tissues. However, this improvement must be accompanied by no drawback in the mechanical properties, which is the case of several surface modification techniques available for biomaterials. Therefore, this work investigated for the first time the effect of the surface modification by TiO 2 nanotubes formation on the fatigue response of Ti-6Al-4V biomedical alloy. Highly organized nanotubes with an average diameter and length respectively of 90 and 600 nm were successfully produced by electrochemical anodization. Based on the standardized staircase method, fatigue tests of the treated specimens were conducted in physiological media at 37 °C, and compared to the untreated polished specimens. The mean and standard deviation values of the fatigue limit calculated through the Dixon-Mood equations were equal for both surface conditions. This result suggests that the employed condition of anodization was satisfactory on growing a nanotubes coating that was not deleterious to the fatigue performance of the alloy, what is a relevant achievement that assures the possibility of having high osseointegration and at the same time keeping the mechanical properties.
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Papers by Claudemiro Bolfarini