Variations with oxygen concentration of titanium lattice parameters are obtained by means of ab initio calculations, considering the impact of oxygen ordering. The quasiharmonic approximation is used to take into account the thermal expansion at finite temperature. Results show that lattice parameters depend mainly on oxygen concentration and, to a lesser extent, on the ordering state. Knowing these theoretical variations, one can get insights into the composition of ordered compounds existing in Ti-O binary alloys from their lattice mismatch measured experimentally by x-ray diffraction. The approach is used in a binary alloy containing 6000 ppm in weight of oxygen. It is concluded that the ordered compounds, which are observed after a recrystallization heat treatment, do not have the expected Ti6O stoichiometry but have a composition close to the nominal concentration. Oxygen ordering proceeds, therefore, before oxygen partitioning in titanium.

This study delved into exploring microstructural states in a Ti–7Ag alloy to achieve targeted functional and structural properties. Specifically, the focus was on attaining a homogeneously precipitated state and a solid solution, known for their potential to combine functional traits like corrosion resistance and antibacterial activity with structural properties such as mechanical strength. However, obtaining these optimized microstructures presents challenges due to kinetic considerations. A key finding of this study was the crucial role of a pre-deformation stage, prior to heat treatment, to create an even distribution of fine Ti2Ag precipitates. Moreover, we demonstrated that starting from this precipitated state, a controlled dissolution step could yield a single-phase solid solution with similar grain size. Therefore, a tailored set of thermomechanical treatments was developed to achieve both microstructures, and these metallurgical states were fully characterized combining SEM (BSE imaging and EDS analysis), TEM, and XRD. Associated mechanical properties were also assessed by tensile testing. In addition, the process was proven to be robust enough to overcome potential industrial problems, such as slow cooling rates when water-quenching large ingots. Considering the limited existing documentation on microstructural features in Ti–Ag alloys, this work on this model alloy significantly advanced our current understanding of the broader Ti–Ag alloy system by providing new data and showcasing a tailored approach involving thermomechanical treatments.

Oxygen content has always been limited in commercial titanium and titanium alloys due to its propensity to induce a severe ductility loss. Yet, its effect on the macroscopical behavior has never been clearly understood and is still rather unclear considering the wide variability in the literature results. Here, we investigate the tensile properties of alpha-titanium with oxygen contents ranging from 0.15 to 0.80 weight percent (wt%). While the strain-hardening ability of oxygen is maintained, no ductility drop is observed up to 0.60 wt% of oxygen, thus allowing exceptional combinations of mechanical properties with an ultimate tensile strength (UTS) of 800 MPa and 29% of elongation at fracture for the Ti-0.6O alloy. Both high strength and ductility of these alloys result from the dislocations/precipitate's interactions. It is proposed that these interactions induce an important cross-slip ac-tivity responsible for a dislocation multiplication and a high work-hardening rate. With the addition of Zr, alloys exhibit an even more promising combination of mechanical properties, achieving 1,075 MPa of UTS and 28% of elongation at fracture for the Ti-4.5Zr-0.8O alloy. The mechanical properties of TiO and TiZrO alloys brought out in this study surpass those of Ti-6Al-4V alloy and open significant prospects for developing a new generation of oxygen-tolerant titanium alloys.

Plasticity of hexagonal titanium–aluminum alloys depends on the solute concentration and the order state of Al atoms. Development of short-range order (SRO) modifies Al strengthening and impacts the competition between prismatic and basal slip modes. Using ab initio calculations, we study the interaction of a screw dislocation with isolated Al atoms and Al pairs in an hcp Ti existing in short-range ordered Ti–Al alloys. Calculated activation energies reveal pronounced hardening caused by Al addition for both slip systems, which become competitive. This hardening is enhanced for Al pairs, resulting in a reduced plastic anisotropy of Ti–Al alloys with SRO.

The influence of short-time heat treatments on Ti-4.5Zr alloys (wt%) with respectively low (2000 ppm) and high (6000 ppm) oxygen contents is investigated with the aim of optimizing their strength/ductility trade-off. Starting from a cold-rolled state (85% of total thickness reduction), a high level of ductility is restored in both systems thanks to the recovery process while the resistance drop is limited, thus proving the effectiveness of the approach. This work highlights the potential of reaching a recovered microstructure to obtain optimized mechanical properties in Ti-Zr system.

Small addition of oxygen is currently used to improve the mechanical properties of titanium. It has been thought, until now, that oxygen fully dissolves in the titanium matrix, thus leading to a solid solution. However, we show here, with transmission electronic microscopy and X-ray diffraction, that oxygen can also form ordered precipitates with a Ti6O-type structure, even for a concentration as low as 0.15 wt% O. The ordered precipitates found in a series of pure binary Ti–O alloys are also visible in commercially pure titanium, including grades 2 and 4, two compositions widely used for technological applications.

The objective of this study was to develop a thermo-mechanical strategy to create a radial elasticity gradient in a β metastable Ti-Nb-Zr alloy, and to characterize it in terms of microstructural and mechanical properties. A first investigation was conducted on thin samples of Ti-20Nb-6Zr (at.%) submitted to various thermo-mechanical treatments. Microstructure-properties relationships and elastic variability of this alloy were determined performing uniaxial tensile tests, X-ray diffraction and scanning and transmission electron microscopies. Based on these preliminary results, mechanical deformation was identified as a potential way to lower the elastic modulus of the alloy. In order to create elastically graded pieces, shot-peening was therefore carried out on thicker samples to engender surface deformation. In this second part of the work, local mechanical properties were evaluated by instrumented micro-indentation. Experimental observations demonstrated that shot-peening enabled to locally induce martensitic transformation on surface, and a decrease in indentation elastic modulus from 85 to 65 GPa over 400 μm was highlighted. Surface deformation proved to be an efficient way of creating an elasticity gradient in β metastable titanium alloys. This combination of material and process could be suitable to produce dental implants with mechanically enhanced biocompatibility.

Recent works have shown that the elastic mismatch observed at the bone / implant interface could be responsible for stress shielding issues causing bone resorption phenomena and potentially implant failures. In the present study, new advanced thermomechanical approaches leading to titanium alloys with graded elastic properties are proposed. The underlying philosophy and the whole methodology is detailed here, from the selection of candidates with large elastic variability to the creation of gradients, involving the identification of microstructure-properties relationships and the use of appropriate thermo-mechanical treatments. Applied on Ti-Nb-Zr alloys, these original routes enabled to get the following graded properties: elastic modulus from 85 to 65GPa over 400μm for TNZ alloy by surface deformation, and from 130 to 75GPa over 100μm for Ti-13-13 by preferential dissolution. These promising results thus validated the previously designed material-strategy-process combinations.

A new titanium alloy family was developed aiming at creating a fully biocompatible alternative to titanium alloys currently on the dental implants market. Despite their hexagonal closepacked (HCP) single-phase structure, these Ti-Zr-O materials display an extremely interesting combination of properties. Zirconium is shown to be involved through a double contribution: on the one hand, a moderate but noticeable solid solution strengthening effect and on the other hand, a strong grain refinement. Therefore, the combination of both effects results in a beneficial strengthening of Ti-Zr-O alloys. However, the main remarkable aspect remains the outstanding hardening generated by extra high oxygen addition, occurring without any drop of ductility. The evolution of the dislocation network according to the oxygen content has been investigated to understand the underlying mechanisms in these Ti-Zr-O alloys, allowing to overcome the classical strength/ductility trade-off in commercial titanium alloys. Finally, the different perspectives of these findings in the field of biomedical and more generally in the field of titanium alloys are discussed.