Papers by Keyword: Ti-6Al-4V

Abstract: Using a sol-gel method and impregnation technology to produce nanoenamel coating on polished Ti-6Al-4V alloy. The morphology, structure and phase composition of nanoenamel coatings modified on mild steel were identified with X-ray diffraction (XRD), scanning electro microscopy (SEM) and tested by some electrochemical methods, such as open circuit potential and potentiodynamic polarization testing [1]. All of these method can select the samples which perform the best corrosion resisitance.

Abstract: A high biocompatibility apatite coated titanium (Ti) could be achieved by biomimetic method. The method is beneficial in surface modification by lowering the processing cost and flexibility. However, the bond between apatite and titanium implant is weak. The structure and composition of apatite formed is different from the apatite in bone. The aim of this research was to investigate the effects of heat and alkali treatment on the physical and chemical properties of Ti6Al4V surfaces and to observe the formation of apatite in Dulbecco’s Phosphate Buffered Saline with CaCl2 and MgCl2 (DPBS) solution on the treated Ti6Al4V for medical implants. Ti discs were surface modified by alkali etching using 5M NaOH at temperature 60°C for 24 hours. A stable mechanical structure of sodium titanate layer formed on alkali-treated is consolidating by heat treated at 500°C and 600 °C. Treated samples were then incubated at 37°C into DPBS solution for 3 days. The morphology structure, phase changes and chemical composition were characterized by using Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Powder Diffraction (XRD). The results shows that apatite coating in globular shape, a group of flakes was found on the samples’ surfaces that had been pre-treated with 5M NaOH at temperature 60°C without thermal treatment and thermal treated at 500°C.

Abstract: Ti-6Al-4V alloy is one of the most important engineering alloys, combining attractive properties with inherent workability. The aim of this study is to investigate the effect of strain rate on the compressive mechanical properties of Ti6Al4V alloy manufactured by a selective laser melting process. The mechanical tests were performed by means of a compression split Hopkinson pressure bar apparatus under high strain rate ranging from 1400 s^-1 to 4500 s^-1. The true stress-strain curves obtained from static and dynamic compressive tests show strain rate sensitivity from quasi-static (peak strength 1300MPa) to high strain rate (peak 1500 MPa). Within the high strain rate range tested, the strain rate sensitivity is not remarkable. The fractographic analysis shows a relatively smooth and smeared fractured surface along with a dimple like structure. The observation of elongated dimples confirms the operation of a dynamic shear failure mechanism for the additively manufactured Ti-6Al-4V parts.

Abstract: This paper details experimental results when turning Ti-6Al-4V using water-miscible vegetable oil-based cutting fluid. The effects of coolant concentration and working conditions on tool flank wear and tool life were evaluated. L27 fractional factorial Taguchi array was employed. Tool wear (VB_B) ranged between 28.8 and 110 µm. The study concluded that a combination of VOs based cutting fluid concentration (10%), low cutting speed (58 m/min), feed rate (0.1mm/rev) and depth of cut (0.75mm) is necessary to minimise VB_B. Additionally, it is noted that tool wear was significantly affected by cutting speeds. ANOVA results showed that the cutting fluid concentration is statistically insignificant on tool flank wear. A notable increase in tool life (T_L) was recorded when a lower cutting speed was used.

Abstract: In this paper, we investigated changes in active slip systems of α-phase of Ti-6Al-4V alloy under a cyclic plastic loading using a crystal plasticity finite element method. In the analyses, a bicrystal model was employed, and the crystallographic orientations were set so as that prismatic <a> or basal slip system was the primary slip system in each grain. The results showed that there was a mechanism where the basal slip systems could reach the stage of activation under the cyclic plastic loading even though the condition was that the prismatic <a> slips initially operate. The reason for the activity changes was due to the changes in the incompatibility between the grains by the work hardening, and the effect of the incompatibility on activities of slip systems appeared even in the perpendicular arrangements of the grains to the loading direction.

Abstract: Titanium alloys are widely used in many industrial applications such as in aeronautics due to their combination of good mechanical properties, excellent corrosion resistance and low density. The mechanical behaviour of titanium alloys is known to exhibit a peculiar dependence on both deformation temperature and strain rate. Titanium alloys show significant room temperature creep and they are very sensitive to dwell fatigue and sustained load cracking. This behaviour is related to the viscosity of plastic deformation in titanium alloys, which can be represented by a strain rate sensitivity (SRS) parameter. The present study aims to compare the tensile behavior of two different titanium alloys, Ti-6Al-4V and β21S, which exhibit dissimilar microstructures. Results of tensile tests, performed under constant strain rate and including strain rate changes, are reported in terms of flow stress, ductility and SRS over a wide range of temperatures.

Abstract: In past few decades, a lot of research has been done in the field of machining to improve the quality of machined surface. Out of these machining operations, drilling is widely used in the areas of marine and aerospace for assembly requirements. Titanium alloy Ti-6Al-4V, owing to its vast applications, is regarded as an important material for these industries. Ti-6Al-4V is categorized as difficult to machine material. Based on above stated facts, an experimental study was conducted on the dry drilling of Ti-6Al-4V. The objective of this study was to establish the correlations between drilling parameters such as feed rate and spindle speed, and quality of machined surface which is evaluated in terms of drill hole diameter deviation, exit burr height and surface roughness.

Abstract: This study observes the behaviors of selective laser melted (SLM) Ti-6Al-4V cylindrical samples when compressed along different directions. The effects of defect and microstructures upon compression behaviors are discussed. The disc-shape defects formed between the building layers does not affect the compression strength of SLM samples tested along different directions. The compression strength is up to 1330 MPa. The columnar structures formed along the building direction causes the plastic deformation to vary greatly with sample orientations. The samples compressed along the building Z direction sustain up to 24.4% deformation, while the samples compressed along the horizontal X and Y directions show a much lower fracture strain of 13.9%. The plastic deformation of columnar grains in crack propagation were observed greater than compressing with the columnar boundaries lying parallel to the compression surfaces. The disc-shape pores also tend to coalesce with each other in the X and Y samples causing a more brittle behaviors.

Abstract: Linear friction welding (LFW), an emerging automated technology, has potential for solid-state joining of dissimilar materials (bi-metals) to enable tailoring of the mechanical performance, whilst limiting the assembly weight for increased fuel efficiency. However, bi-metallic welds are quite difficult to manufacture, especially when the material combinations can lead to the formation of intermetallic (brittle) phases at the interface, such as the case with assembly of Ti base alloys with Ni base superalloys. The intermetallic phase, once formed, lowers the performance of the as-manufactured properties and its growth during elevated temperature service can lead to unreliable performance. In this project, it was demonstrated that linear friction welding can be applied to join Ti-6%Al-4%V (workhorse Ti alloy) to INCONEL^® 718 (workhorse Ni-base superalloy) with minimized interaction at the interface. Of particular merit is that no intermediate layer (between the Ti alloy and Ni-base superalloy) was needed for bonding. Characterization of the bi-metallic weld included macro-and microstructural examination of the flash and interface regions and evaluation of the hardness.

Abstract: With the purpose of fabricating equiaxed and bimodal Ti-6Al-4V alloy with different grain/primary α (α_p) sizes, thermomechanical processing and additional annealing were carried out on samples with martensite initial microstructure. Deformation at 700°C with a strain rate of 0.01s^-1 to a true strain of 0.8 could effectively break the martensite initial microstructure into ultrafine-grained (UFG) equiaxed microstructure (mean grain size of 0.51μm) with reasonable uniformity. Subsequent annealing at 930°C with different periods were conducted to change the equiaxed microstructure into bimodal microstructures. The holing time proved to be more critical than heating rate for determining the α_p size. An UFG bimodal Ti-6Al-4V with the average α_p size of 0.55μm was successfully obtained for the first time by annealing the UFG equiaxed Ti-6Al-4V at 930°C for 2 seconds. The mechanical properties of the equiaxed and bimodal Ti-6Al-4V with different grain/α_p sizes were evaluated by tensile tests at room temperature. The bimodal Ti-6Al-4V showed superior balance between strength and uniform elongation than that of the equiaxed Ti-6Al-4V. Moreover, the uniform elongation in the bimodal Ti-6Al-4V was nearly unaffected by reduction of the α_p size.