Papers by Keyword: Ti-6Al-4V

Abstract: Ti-6Al-4V, renowned for its high strength and corrosion resistance, is a preferred material in aerospace and marine applications for lightweight structures due to its durability in challenging environments. Typically, GTAW welding is used for it’s fabrication. The residual tensile stresses produced after welding are known to worsen the corrosion and mechanical properties of welds. However, these properties can be improved by introducing near surface residual compressive stress by shot peening. When compared to the traditional shot peening treatment, the surface roughness that results from multiple shot peening with varying ball sizes and intensities can be significantly reduced. In the present work, Ti-6Al-4V plates were welded using conventional GTAW technique. Six different combinations of multiple shot peening treatments were applied to the welded specimens. Surface morphology and surface roughness were analysed. Surface residual stresses measurement were performed using by X-ray stress analyzer. Domain size and microstrain were measured using X-ray diffraction technique. Micro-hardness measurements were made along the weld thickness. Corrosion studies were carried out using potentiodynamic polarization test in 3.5% NaCl solution. The SP4 parameter comes out to have the best combination among all the multiple shot peened samples. It results in lowered surface roughness, higher compressive residual stress, better grain refinement, increased surface hardness, and enhanced corrosion resistance.

Abstract: In the present study, (TiO2/HAP) and TiO2 coatings were fabricated with electrophoreticdeposition on substrate for titanium alloy. This study aims to increase improve this alloyantibacterial properties by coating the surface with a bio ceramic (TiO2 and TiO2/HAP)nano-powders. Coating on Ti-6Al-4V with an electrophoretic deposition(EPD) technique,ideal conditions of 20V and a deposition time of (4 min). The surface properties of coatedsubstrates, such as, micro-hardness, surface roughness and wettability antibacterial test wereevaluated and compared to that of the uncoated substrate. The results showed that theelectrophoretic deposition is a favorable technique to make a bio coating on Ti-6Al-4Vsubstrate with excellent properties and structure for applications biomedical.The average micro-hardness of the TiO2/HAP coated sample is 1024 HV compared withthat of uncoated substrates is 80 HV. The average thickness of TiO2/HAP coating isdetermined to be (18µm) on the substrate surface at factor deposition time (4 min). The resultsof previous research indicate that the high wettability and surface roughness at the micronscale were for the synergistic effect of reduction on cell adhesion and growth.

Abstract: Micro EDM is unconventional metal removing technique that is effective in machining hard-to-cut conductive materials. It has a big potential in modifying surfaces of metallic bone implants for better biocompatibility by providing proper surface topography to ease cell adhesion. However, it is still important to study machining performance. This paper investigates material removal rate (MRR) and surface roughness (SR) of micro WEDM on Ti-6Al-4V alloy. Three level Taguchi’s design was implemented to observe the effect of capacitance and gap voltage. Moreover, analysis of variance (ANOVA) and grey relation analysis (GRA) allowed to investigate contribution of each parameter and find their best combination for multiple output optimization. Results showed that highest MRR of 1.72*10^-2 mm³/s can be achieved at 10 nF and 90 V values, while smallest SR of 0.309 µm can be achieved at 1nF and 90 V. In addition, the contribution and significance of capacitance on MRR and SR was considerably higher than the effect of gap voltage. Lastly, the optimal parameters for multiple output performance were calculated at 10 nF and 90 V values.

Abstract: Ti-6Al-4V alloy is not easy to machine complicated shapes due to its low thermal conductivity, so high-temperature forming techniques such as ring-rolling are being applied. When this high-temperature forming technology is applied, the microstructure is greatly changed by process variables, and the mechanical properties of the forming product are also different accordingly. In particular, in the case of the Widmanst tten structure, α lamellar spacing and colony size have a great influence on mechanical properties. Therefore, in this study, the most suitable process conditions were selected by performing a high-temperature compression test to apply the ring-rolling process to the Ti-6Al-4V alloy used as an aerospace material. After that, the microstructure of the forming product was observed, the effects of α lamellar spacing and colony size on the mechanical properties were confirmed, and the correlation between mechanical properties and microstructure was evaluated based on this.

Abstract: The forming limit diagram (FLD) is a widely used tool to assess the formability of a metal sheet [1]. The current study aims to investigate the influence of strain rate, material anisotropy and hardening on the FLD of Ti-6Al-4V predicted by the well-known Marciniak-Kuczynski (M-K) method. The tensile data of quasi-static (8 10^-5 s^-1), intermediate (0.5 s^-1) and dynamic experiments (approximately 1000 s^-1) on Ti-6Al-4V sheet are available at three different orientations, with respect to the rolling direction: 0°, 45° and 90°. Different hardening models are taken into account. Also, von Mises and Hill yield criterion are considered. The results show that the influence of the hardening law on FLD is significant. In particular, the most conservative limit strains are predicted by the Voce law because of its saturation characteristic. The yield criterion is found to only affect the right part of the FLD. Regarding the strain rate influence, the left part of the FLD is mainly dominated by the amount of uniform elongation, while the right part is strongly dependent on the yield function used. Therefore, for this region the effects of strain rate and yield function are difficult to distinguish. Finally, the effect of material anisotropy on the FLD is significant. Under quasi-static conditions, the Lankford coefficient seems to be the driving factor in uniaxial and equibiaxial deformation. However, in plane strain conditions the effect of the strain hardening exponent is dominant.

Abstract: This study presents the investigation of friction coefficient effect on stress-strain distribution of ceramic coated aeroengine specific material substrate using explicit finite element method. Half-cylinder-on-flat contact configuration subjected to normal and tangential loading is examined. Elastic ceramic coated elastic-plastic Ti-6Al-4V and Super CMV substrates are assigned to study the influence of different friction coefficient on contact pressure, von Mises stress, tangential stress and equivalent plastic strain distribution. The outcome of present research is quite revealing that stress-strain distribution response is remarkable for sliding step which experiencing significant traction compared to normal loading step. Higher possibilities of coated substrate equivalent plastic strain (plastic deformation) are registered under higher friction coefficient cases due to substantial resistance to overcome relative to tangential motion of contacting bodies.

Abstract: For obtaining a unique microstructure in Ti-6Al-4V, hydrogen is utilized as a temporary alloying element; therefore, the mechanism of hydrogen diffusion in α and β phases should be understood. In this study, the electrochemical hydrogenation was applied to the half-length of thin titanium rods, and the diffusion annealing heat treatment was implemented at different temperatures. The hydrogen diffusion coefficient of α phase (D_α) and the hydrogen diffusion coefficient of β phase (D_β) was determined by employing Abaqus software and C^# program for three different homogeneous microstructures. The obtained results showed that D_β increases, and D_α decreases when the hydrogen concentration in β phase increases. Furthermore, it was observed that each microstructure has a specific temperature in which the maximum hydrogen amount is absorbed. The hydrogen uptake depends more on the volume fraction of β phase than the volume fraction of α phase, which is considered an obstacle to hydrogen diffusion in this alloy.

Abstract: Industrial pure titanium (TA2) and Ti-6Al-4V (TC4) have been widely available for chemical equipment. However, the corrosion resistance changes during their post-fire performance. In this research, the electrochemical properties of industrial pure titanium and Ti-6Al-4V after heat treatment and different cooling methods were analyzed by AC impedance technique and dynamic polarization method. The results support two conclusions. Firstly, when the temperature is approximate to the phase transition point, for pure titanium and its alloys, water-cooling can obtain better corrosion resistance than air-cooling. With regard to pure titanium, its best corrosion resistance can be obtained at 800°C under water-cooling. For Ti-6Al-4V, its best corrosion resistance can be obtained when the temperature reached 910 °C under water cooling condition. Secondly, the corrosion current density under acid corrosion condition has risen compared with neutral corrosion condition. These results can provide some experimental data and theoretical basis for post-fire anticorrosion performance of titanium materials, and also support the safety, risk evaluation of titanium equipment.

Abstract: The electron beam melting-printed Ti6Al4V shows a great potential application for orthopedic implants and aerospace in recent years. A systematic study on the microstructure of additive manufactured Ti6Al4V by electron beam melting both parallel to and perpendicular to the building directions (Z axis) is presented in the present investigation. The results showed that the microstructure of the alloy was α lamina with HCP structure and β bar with BCC structure. The original β phase grew as columnar crystal along the direction of construction, showing an equiaxial shape in the cross section, numerous small α lamellae block the original β phase, and presenting a cluster distribution on the original β grain boundary, and a basket-like distribution in the original β grain. This may be due to the rapid cooling of the small pool after melting, the repeated heating of the subsequent constructed layer on the formed layer, and the subsequent limited vacuum cooling, resulting in the formation of the micro morphology, which leads to the original β grain boundaries broken, and the formation of a distinctive basket or widmanstatten structure [1, 2]. In addition, XRD results indicated that there was α′ martensite, part of which has been decomposes into α phases and β phases, SEM and TEM experiments also proved this. Of note is that random distribution dislocation was observed in TEM. Using EBSD results, and it may be understand that the sample build direction was parallel to [0001] crystal orientation and build plane parallel to (1210) and (1100) crystal facets.

Abstract: The present work is focused on one Additive Manufacturing (AM) process – Laser powder Metal Deposition (LMD-p) – and on one metallic alloy – Ti-6Al-4V. State of the art on LMD-p on Ti-6Al-4V alloy shows that three kinds of process parameters influence mechanical properties of building parts: raw materials (powder and substrate), machine parameters (Laser Power (P), Powder Flow (F) and Building Speed (V)), and building strategies (part orientation, waiting time between layers, etc.). Thus, this paper relates to first manufacturing investigations on small sized specimens (bead, wall and block) with the aim of providing a better knowledge about the first steps of manufacturing. Particularly, this paper is dedicated to the study of machine parameters (P, F and V). First, the influence of each machine parameter on 28 beads is studied separately. The geometrical aspect (high, width, dilution) of each bead is microscopically measured. Similarly, combinations of parameters (P/F, Energy Density and Powder Density) are introduced to increase parameters degree of freedom. First results show that P, V and F have a major influence on the beads’ geometry. In addition, a window process map is plotted and allows determining functional areas of machine parameters. From this map, walls (vertical superposition of one bead) are manufactured and microscopically observed. Functional sets of parameters from walls are selected and blocks can be built.