Papers by Keyword: Titanium

Abstract: Hydroxyapatite (HAp) derived from bovine bone waste is extensively explored for biomedical applications due to its close chemical resemblance to natural bone. However, its intrinsic brittleness and thermal instability remain critical limitations. In this study, HAp–titanium (5–20 wt.%) composites were synthesized using the self-propagating high temperature synthesis (SHS) method within the range of 750–950°C. X-ray diffraction (XRD) analysis confirmed the in-situ formation of CaTiO₃ at 850°C, which significantly improved densification and microstructural consolidation. At higher temperature (950°C), partial decomposition of HAp to tricalcium phosphate (TCP) was observed, consistent with phase evolution trends reported in the literature. Scanning electron microscopy (SEM) revealed distinct grain morphology transitions across the processing window, supporting the identified phase transformations. The results demonstrate a clear correlation between phase evolution and microstructural development: CaTiO₃ formation enhances densification, while TCP contributes to favorable bioresorbability. These findings highlight the tunability of SHS-derived HAp–Ti composites and their promising potential as bone substitute materials with adjustable bioactivity.

Abstract: Isothermal forging is a common method for manufacturing titanium alloys, but it involves complex processes and equipment. The oxidation of titanium leads to the formation of an alpha-case, which in turn promotes increased crack formation. To prevent this, inert gas is typically required. However, by encapsulating the titanium billet (Ti-6Al-4V) in a steel casing made of AISI 316L, a quasi-isothermal process can be achieved without the need for inert gas. This method maintains protection against oxidation while simultaneously reducing cooling. The sealing of the capsules is crucial to ensure that the titanium is effectively enclosed and protected from the surrounding gases. In this study, various encapsulation methods are compared, including rotary friction welding, diffusion bonding, and press-fitting a lid with an interference fit. The investigation involves differing contact conditions between the titanium and steel sleeve, as well as steel wall thicknesses of 2 mm and 4 mm. These factors showed no impact on the material flow or microstructure of the formed components. Encapsulation can prevent the formation of an alpha-case. Intermetallics form between the titanium and the steel capsule, depending on the contact conditions. The use of graphite as a separating agent prevents the formation of them.

Abstract: Bipolar plates are key components of fuel cell systems, as they significantly determine efficiency, power density, and service life. In aerospace applications, their importance is further emphasized due to the dual requirement of corrosion resistance and strict weight reduction. Titanium Grade 1 combines low density and excellent corrosion resistance. However, its industrial application is limited by restricted formability. The aim of this paper is a systematic investigation of the forming behavior of Titanium Grade 1 foil material in order to define forming limits and derive manufacturing-oriented design recommendations for bipolar plates in aviation. Procedure. Sixteen distinct geometry features were developed to represent characteristic forming conditions. In addition to cross-section variations, the flow field angle was systematically altered to assess its influence on local stress and strain distribution. Furthermore, the key process parameters forming speed, forming force, and lubricant amount were varied to evaluate their impact on the forming quality. The assessment focused on form filling and material thinning. For this purpose, metallographic cross-sections were prepared, and optical 3D measurements were conducted using a Keyence system to precisely capture local wall thickness variations. Key findings Process parameters: The forming behavior of Titanium Grade 1 is strongly influenced by the applied forming force and lubrication. Form filling becomes sufficient only above 350 MPa (3.000 kN), while the lubricant amount is decisive for achievable forming depths due to the hydrostatic oil cushion effect. In contrast, forming speed shows no significant influence. Anisotropy remains a critical factor, particularly in 0° rolling direction, where premature thinning leads to fracture. Geometry parameters: Small radii are highly critical, while feature depth leads to expectedly higher thinning. Steeper flank angles improve form filling but at the cost of increased thinning. Pitch shows limited influence, although it may become relevant at very small values. Channel design is challenging, as sharp flow field angles consistently result in severe thinning and pose difficulties in tool manufacturing.

Abstract: Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Abstract: Titanium is a Critical Raw Material for the European aerospace sector, yet its manufacturing is characterized by high buy-to-fly ratios and significant waste in form of chips. Solid-state recycling (SSR) presents a low-energy alternative to remelting for chip revalorisation. However, its viability is strictly limited by their oxidation. This study investigates the influence of milling parameters (cutting speed and radial depth of cut), and coolants (emulsion, LCO2 and dry), on cutting forces and chip quality (morphology and oxidation) to define a process window for generating low oxidation chips, enabling further SSR routes. By correlating cutting forces with chip analysis, the results reveal that emulsion cooling yields the chips with the least oxidation, despite potential oil contamination of the feedstock with oils. While LCO2 effectively reduces oxidation at lower material removal rates, high thermal loads overwhelm its cooling capacity, resulting in oxidation comparable to dry cutting. These findings establish the machining parameters necessary to produce high-quality, recyclable feedstock, bridging the gap between subtractive manufacturing and circular material flows.

Abstract: Massively carbon supersaturated (MCSed) tool steel dies were prepared for dry, galling free forging, microtexturing and fine-blanking of titanium and titanium alloy eye-glass frame parts. Titanium temples were forged in dry and galling-free to investigate the role of MCS treatment to reduce surface roughing of temples. They were also micro-textured to discuss the superiority of MCS to product quality. Dry, galling-free fine-blanking was utilized to describe the life-time extension of MCSed tool steel dies. Various eye-glass frame parts were forged in dry to state the statistic evaluation on the galling-free manufacturing features. The intermediate chemical treatments as well as barreling and polishing steps were saved to reduce the amount of wastes from manufacturing factories of titanium and titanium alloy eye-glass frames toward zero emission.

Abstract: NiTi alloy has desired engineering properties with many applications, such as biomedical, aerospace, automotive, etc, where several researchers have investigated the development of ternary and quaternary alloying of NiTi to further enhance its performance for demanding technological applications. However, there are limited studies on the effects and synergy of Re and Mo on the nanomechanical properties of NiTi alloy, despite the highly recommended effect of Re on the mechanical properties of Ni-based superalloys. Therefore, this study bridged this gap by developing NiTi-Re-Mo alloy via the spark plasma sintering technique and investigating its nanomechanical properties in relation to NiTi, NiTi-Re, and NiTi-Mo alloys. It was noted that NiTi-Re-Mo has better nanomechanical responses than other developed NiTi-based alloys. For instance, the hardness and elastic modulus of NiTi-Mo-Re increased to about 28236.7 MPa and 483.4 GPa from 4460.7 MPa and 122.5 GPa for NiTi alloy, respectively. These significant increments were credited to the synergy effect of Re and Mo, the solution and hard phase precipitation strengthening of the NiTi system, which also contributed to the reduction of dislocations and improved mechanical locking of the NiTi system. This makes the alloy desirable for high mechanical strength applications.

Abstract: Optimizing the mechanical properties of aluminum to titanium welds is crucial to establish applications for dissimilar lightweight structures in the aerospace industry. In this context, solid-state welding technologies have proven effective in terms of short joining cycles, allowing the combination of cost-effective production and structural weight optimization. However, metallurgical effects between aluminum and titanium in the joint interface are still not completely understood due to differences in physical as well as chemical characteristics. In this study, aluminum alloy 6013 was welded to Ti6Al4V by refill Friction Stir Spot Wel ding, including systematic variations of Mg and Si alloying element content in the used AA6013 sheets. In total five different Al alloys were welded to the titanium to investigate the influence of Mg and Si during processing. Apart from the material selection, the weld strength is mainly influenced by the intermetallic compound thickness at the interface, which in turn primarily depends on the exposed temperature cycle. Consequently, major interest during this study was given on the temperature evolution, interfacial features and the global mechanical properties.

Abstract: This research work focuses on the atomic study of hexagonal titanium (Ti) in order to estimate the relative accuracy of DFT (Density Functional Theory) and Molecular Statics (MS) approaches to better understand the interactions between solute atoms and twins. Four twins (2 tensile twins and 2 compressive twins) were modeled and then doped with the following elements: hydrogen, oxygen, nitrogen, aluminum and vanadium (H, O, N, Al, V). The formation energies of the twins as well as the segregation energies of the solute atoms were calculated to better predict the concentration heterogeneities of these elements in the material and their possible influence on local mechanical properties.

Abstract: Laser powder bed fusion (LBPF) is currently the most mature metal additive manufacturing (AM) technology. While it does not have the same flexibility as directed energy deposition techniques to produce compositional gradients, LPBF can still be used to generate bimetallic parts by depositing one metal on a build plate made of another. Here, we print combinations of Ti-6Al-4V with Ta and characterize defects that occur at the interface. We use thermodynamic modeling to explain the formation of keyhole porosity and solidification cracks when Ta is built on a Ti baseplate, and the lack of defects when the materials are reversed. By understanding the mechanisms that lead to defect formation, the methodology demonstrated here can be applied to other material systems to efficiently design bimetallic LPBF processes.