Papers by Keyword: Ti6Al4V Alloy

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Authors: Adriana Bigi, E. Boanini, Barbara Bracci, A. Facchini, Silvia Panzavolta, F. Segatti, L. Sturba
Abstract: We employed a slightly supersaturated solution (Ca/P) with an ionic composition simpler than that of simulated body fluid (SBF) to obtain a fast biomimetic coating on Ti6Al4V substrates. The results of thin film X-ray diffraction, FTIR, SEM, TEM-ED investigations indicate that hydroxyapatite (HA) nanocrystals are laid down in a few hours on the susbstrates. The amount of deposition increases with the immersion time. Furthermore, the thin layer of HA deposited after 3 h soaking in Ca/P solution acts as a catalyst for the further deposition of apatite from SBF.
Authors: A. Colin, Christophe Desrayaud, Marie Mineur, Frank Montheillet
Abstract: The aim of this work is to study the flow instabilities occurring during hot forging of titanium alloy blades. In this view, the viscoplastic deformation behaviour of Ti-6Al-4V alloy is investigated by means of torsion tests under isothermal hot working conditions at temperatures ranging from 800 to 1020 °C and strain rates of 0.01, 0.1 and 1s−1. The thermomechanical processing is performed up to a true strain of 10. The flow stress data are analysed in terms of strain rate and temperature sensitivities. A constitutive equation that relates not only the dependence of the flow stress on strain, strain rate and temperature, but also for the fraction of each phase α and β is proposed. Two mechanical models are compared : the uniform strain rate model (Taylor) and the uniform plastic energy model (IsoW). The usual strain rate sensitivity and activation energy values of Ti-6Al-4V alloy are obtained by fitting the experimental data. Furthermore, specific values of strain rate sensitivities and activation energies are calculated for the α and β phases providing thus a constitutive law based on the physics of the α / β phase diagram. The flow stress is then related to strain by an empirical equation taking into account the flow softening observed after a true strain of 0.5 and the steady state flow reached after a true strain of 4. Comparison of the calculated and measured flow stresses shows that the constitutive equation predicts the experimental results with a reasonable accuracy. The above constitutive equation is then used for simulating forging processes by the finite element method. The calculations exhibit the localisation of deformation produced by shearing effects in the form of the classical X shape.
Authors: Gang Wang, Jun Chen, X.Y. Ruan
Abstract: The complex superplastic forming (SPF) technology applying gas pressure and compressive axial load is an advanced forming method for bellows made of titanium alloy, which forming process consists of the three main forming phases namely bulging, clamping and calibrating phase. The influence of forming gas pressure in various phases on the forming process are analyzed and models of forming gas pressure for bellows made of titanium alloy are derived according to the thin shell theory and plasticity deformation theory. Using model values, taking a two-convolution DN250 bellows made of Ti-6Al-4V titanium alloy as an example, a series of superplastic forming tests are performed to evaluate the influence of the variation of forming gas pressure on the forming process. According to the experimental results models are corrected to make the forming gas pressures prediction more accurate.
Authors: L. Qian, J. Mei, Xin Hua Wu
Authors: Rajiv S. Mishra, Shaun McFadden, Amiya K. Mukherjee
Authors: Vitali F. Nesterenko, Sastry S. Indrakanti, Singh N. Brar, YaBei Gu
Authors: Kenneth T. Stanton, Jean François Vanhumbeeck
Abstract: Fluorapatite-mullite glass-ceramics have been shown to be bioactive in the cerammed state and the present study examines how they may be deposited on biomedical-grade titanium alloy substrates for orthopaedic applications. A simple deposition route was used for initial application of the material in the glassy state and it was then cerammed in-situ. This cheap and non-line-of-sight route produces well adherent coatings by virtue of a reaction between the coating and substrate during the ceramming step. Several characterization techniques including DSC and XRD have been used to determine the crystallization behaviour of the glass-ceramic ex-situ and electron microscopical techniques have been used to characterize glass-ceramic microstructures and the nature of the coating-substrate interfacial region.
Authors: J. Kim, Y.C. Choi, Hyoung Seop Kim, Sun Ig Hong
Abstract: Biomimetic apatite deposition behaviors on Zr-1Nb and Ti-6Al-4V plate with various surface conditions were examined. Both alloys were polished with abrasive papers to have different roughness and some of them were treated in NaOH before deposition of apatites in the simulated body fluid. After, 10 days immersion in a SBF, NaOH treated Zr-1Nb and Ti-6Al-4V were completely coated with apatite. The deposition rate of apatite was higher on NaOH-treated Ti-6Al- 4V than on NaOH-treated Zr-1Nb initially, but the deposition rate on Zr-1Nb accelerated after 2 days and the total weight gain due to the deposition on Zr-1Nb approached to that of Ti-6Al-4V. NaOH treatment was found to enhance the deposition rate of apatite on Ti-6Al-4V significantly. On the other hand, the deposition rate of Zr-1Nb was not influenced by NaOH treatment. Without NaOH treatment, the polished Zr-1Nb with abrasive paper was found to induce more apatite nucleation than the polished Zr-6Al-4V. The presence of apatite was confirmed by XRD analysis. SEM observation revealed a conglomerated granular structure with elongate plates.
Authors: Young Gun Ko, Yong Nam Kwon, Jung Hwan Lee, Dong Hyuk Shin, Chong Soo Lee
Abstract: Cavitation behavior during superplastic flow of ultra-fine grained (UFG) Ti-6Al-4V alloy was established with the variation of grain size and misorientation. After imposing an effective strainup to 8 via equal-channel angular pressing (ECAP) at 873 K, alpha-phase grains were markedly refined from 11 μm to ≈ 0.3 μm, and misorientation angle was increased. Uniaxial-tension tests were conducted for initial coarse grained (CG) and two UFG alloys (ε = 4 and 8) at temperature of 973 K and strain rate of 10-4 s-1. Quantitative measurements of cavitation evidenced that both the average size and the area fraction of cavities significantly decreased with decreasing grain size and/or increasing misorientation. It was also found that, when compared to CG alloy, cavitation as well as diffused necking was less prevalent in UFG alloys, which was presumably due to the higher value of strain-rate sensitivity. Based on the several theoretical models describing the cavity growth behavior, the cavity growth mechanism in UFG alloys was suggested.
Authors: Zhong Hua Li, Qing Wang, Dong Li Sun, Li Ping Zhang
Abstract: The effects of hydrogen on the microstructure and hot deformation behavior of Ti-6Al-4V alloy were studied, and the differences of microstructure and high temperature compressive behavior between the specimens hydrogenised various time at 700 oC and with the same hydrogen contents were analyzed. The results showed that the addition of hydrogen decreases the deformation resistance of Ti-6Al-4V alloy at high temperature. The flow stresses of specimens with the same hydrogen content declined as the prolongation of hydrogenating time. The microstructure observation indicated that stick-type microstructure was obtained in Ti-6Al-4V alloy annealed at 700 oC for 2 hours. Hydrogenation at 700 oC for 2 hours resulted in fine α plate in β transformed microstructure. When the hydrogenation time was prolonged to 6 hours, the volume fraction of newly-formed α plates increased and the prior α plates became coarser.
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