Papers by Keyword: Titanium

Abstract: Friction stir diffusion bonding (FSDB) has been applied to lap dissimilar foils joints of aluminum alloy on top of commercial purity (CP) titanium. FSDB of the foils was successfully performed through stirring only the upper aluminum foil by the air spindle with an extremely-high rotation speed of 105,000 rpm. By using smooth surface of the tool tip, FSDB with micro indentation less than or equal 10μm could be carried out to improve the surface condition of the joint and the indentation depth required for joining was reduced. The material flow of the upper aluminum alloy foil in the FSDB was investigated by deposited platinum-palladium as the tracer material on the surface of the lower titanium foil. Then it was confirmed that the vestiges of vigorous stirring appeared in the region given at a distance from tool center while little vestiges was found in the other region. These regions seemed to be bounded by a radius of about 0.6 mm from the tool center. Moreover, the bonding strength distribution as a function of the distance from the tool center was likely correspondent to the stirring state.

Abstract: The subsurface fatigue crack generation processes in near α type titanium alloy were divided into four steps: (1) development of a saturated dislocation structure by cyclical micro-plastic strain accumulation, (2) generation of localized slip and/or microcracking to relax the stress concentration in the vicinity of a boundary, (3) microcrack growth and transition to main crack, and (4) crack propagation. The experimentals on transgranular facets formation in Ti-Fe-O alloy were reviewed and a subsurface fatigue crack generation model was discussed. The β platelets which were aligned between the recrystallized α grain and the recovered α grain were responsible for the microcrack generation to form (0001) tansgranular facet in the recrystallized α grains. A combination of the shear stress and tensile stress normal to the basal plane may give a trigger of the (0001) microcracking in the recrystallized α grain. The localized shear stress following slip off on the basal plane was activated at the microcrack tip in the recrystallizedαgrain, and the microcrack grew into the recrystallized α grain to form (0001) transgranular facet.

Abstract: The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.

Abstract: Additive manufacturing of titanium components offers several advantages compared to conventional production technologies such as higher material utilization efficiency and increased geometric possibilities. In comparison to laser powder bed processes, arc-based additive manufacturing processes have the additional advantage of an almost unlimited assembly space, higher deposition rates and an improved utilisation factor of raw materials. Disadvantages of wire-based methods are the restricted availability of different types of wire consumables, the fact that the wire feed rate is directly coupled to the heat input and the lack of possibility to create multi-material structures in-situ.Within this work, the 3D Plasma Metal Deposition (3DPMD) method, based on a plasma powder deposition process is introduced. 3DPMD has some special advantages compared to the established plasma powder process and other additive processes. For example, up to four powders, which can differ in terms of material and powder fraction, can be mixed within one layer. This allows a targeted adaption of local properties (microstructure, mechanical properties, wear resistance, porosity, etc.) to the targeted load type and level. The tailored introduction of reinforcement particles, e.g. tungsten or titanium carbides, into the component is a simple example.The study aims to demonstrate the suitability of the 3DPMD for the production of titanium components in layer-by-layer design. Various demonstrators are prepared and analysed. The microstructures, the porosity and the hardness values of the different structures are analysed.In summary, 3DPMD offers the possibility to produce titanium structures with and without reinforcement particles. Using automated routines, it is possible to generate metallic structures directly from the CAD drawings using welding robots. Microstructures and properties are directly related to the process and, therefore, structure-process-property relationships are discussed within this work.

Abstract: Hot-dip galvanized steel surfaces are cleaned, pre-treated with titanium-containing solution and then painted for use. Removal of the alumina layer from galvanized steel surfaces during the cleaning process is essential before effective paint application. Bad adhesion results if the alumina layer is not completely removed, and an insufficient concentration and uneven distribution of titanium oxide is formed across the galvanized surface during pre-treatment. The alkaline cleaner concentration must be optimized to ensure effective removal of the alumina layer. Hot-dip galvanized steel samples were cleaned using typical line conditions and cleaning solutions with varying free alkalinities. The alumina layer was then measured on each sample by glow-discharge optical emission spectroscopy. Thereafter, the samples were treated with titanium-containing pre-treatment solution. The titanium oxide concentration was measured by inductively coupled plasma optical emission spectroscopy. It was found that a free alkalinity of at least 3.2 mEq/L is required to fully remove the alumina layer. The alumina-free samples also gave a titanium oxide layer after pre-treatment within the target concentration of 4–8 mg/cm². A free alkalinity of 3.5 ml was thereafter implemented commercially: analysis of samples from two galvanizing lines showed no presence of alumina, a uniform titanium oxide distribution across the widths of the line samples and acceptable titanium concentrations.

Abstract: The addition of titanium is a well-known microalloying concept for hot rolled structural steels. Concerning advanced high strength steels for the automotive sector, the use of Ti microalloying (usually with Nb-V) has been an active research area. However, Ti addition has not been explored in depth. For the current contribution, a laboratory hot rolled 0.2C-2.4Mn-1.5Si steel with and without Ti addition was studied. Mechanical testing of the hot strip revealed a very high UTS (1GPa) for the Ti added steel, whilst for the unalloyed chemistry the UTS was some 300 MPa lower. Observation of the hot rolled microstructures via optical microscopy showed a significantly higher hardenability for the Ti added steel. Moreover, X-ray diffraction analysis indicated a significant amount of retained austenite in the Ti added strip, which transformed completely to martensite after the tensile test. Further analysis via TEM and chemical extraction indicated that Ti was present both as Ti (C,N) precipitates and in solution. Finally, in light of these observations, the possible mechanisms leading to the enhanced hardenability observed for the Ti added hot rolled strip steel were discussed.

Abstract: This study presents a novel method for mechanically interlocking dissimilar alloys of pure titanium with steel through using the principles of friction stir forming (FSF) technique. In present study, titanium plate is placed on top of a steel sheet containing a screwed hole. FSF is conducted on top of the titanium alloy, which produces sufficient heat to plasticize the alloy. This results in a flow of titanium into the screw hole in the steel, due to the plastic deformation, thereby mechanically interlocking titanium with the steel. The mechanical properties of the developed interlock are investigated through tensile and hardness tests and microstructural observation.

Abstract: Titanium nitride (TiN) film on titanium film (Ti) was formed by magnetron sputtering method. Pure titanium substrates with TiN/Ti multi-layered films deposited using DC sputter-deposition machine in Ar gas atmosphere, in order to improve not only the blood compatibility of pure titanium but also the adhesion between the deposited TiN coating and the pure titanium substrate. The effects of the thickness of a pure titanium interlayer on adhesion of the TiN coating to the pure titanium substrate were investigated. And the effects of the TiN coating obtained in this study on blood compatibility were also investigated. The obtained multi-layered films looked yellow gold and appeared to be uniform and adhesive without any peel-offs. Based on the results of the platelet test, the ratio of the number of adhered platelets for the TiN/Ti film to that for the pure titanium substrate was estimated to be 0.54. Thus it was found that the platelet adhesion of the obtained TiN/Ti film was much smaller than the pure titanium, concluding that the TiN coating improved the blood compatibility.

Abstract: We aimed to investigate the effects of alumina blasting and alkaline treatment on the immobilization of gelatin-fluvastatin complexes on titanium disks. Blasted titanium disks were submicron-sized porous while the alkaline treated disks were submicron-and nanoporous. XPS analysis revealed homogeneous coverage of titanium disks with a gelatin layer on top of an intermediate polydopamine treatment. The highest amount of fluvastatin immobilization was observed on top of alkaline treated titanium as compared to the blasted disk. A combination of alkaline pre-treatment followed by polydopamine-assisted immobilization of gelatin facilitated optimal loading of fluvastatin onto titanium dental implants.

Abstract: 60CaO-30P₂O₅-(10 ̶ x)Nb₂O₅-xTiO₂ (x = 0 ~ 10, mol%) glasses were prepared in order to obtain biomaterials with high chemical durability and therapeutic ions releasability. Dissolution test of these glasses using Tris buffer solution showed the controlled release of niobate ions from Nb₂O₅-containing glasses and the formation of calcium titanate in some of them. These behavior might induce positive effects for bone regeneration.