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Oxygen is known to have a significant impact on the strength of Ti alloys, whereas it can also reduce the ductility substantially. Thus, the usage of oxygen to strengthen Ti is restricted in the industry. In this study, we rekindled the research of oxygen behavior in Ti with the purpose of developing Ti alloys with high strength and suitable ductility by using no expensive and poisonous element. To this end, experiments of producing high performance commercially pure Ti using only oxygen solid solution were carried out. The oxygen element was introduced into the Ti by two different powder metallurgy methods. The microstructural examination and mechanical test were performed for the samples, which indicated a strong hardening effect of oxygen in spite of the processing routes. Most importantly, the results suggested that a high elongation to failure of over 20% can still be obtained in the samples having yield stress over 800 MPa, up to an oxygen content of 0.8 wt%, which is far beyond the previously recognized limit. [ABSTRACT FROM PUBLISHER]

Oxygen solid solution has been long known as a double-edge sword to Ti alloys, where, on the one hand, it has a strong strengthening effect while, on the other hand, it also embrittles the alloys. In the present work, in-situ observations using SEM and EBSD were carried out under tension to explore the mechanism that controls those effects. The results suggest that, by increasing oxygen content, the 〈 a + c 〉 type slip becomes more favorable than the 〈 a 〉 type, other than suppressing deformation twinning. As a result, the crack nucleation sites transit from grain boundaries (especially at triple junctions) into grain interior with a planar shape, which finally leads to easy cleavage. Comprehensive analysis and discussion suggest that the transition of fracture mode is due to the presence of oxygen solutes that modify the local stress state of geometrically necessary dislocation (GND) pile-ups, which then interfere with the condition for { 11 2 ¯ 2 ¯ } twin nucleation and turn to the activation of { 11 2 ¯ 2 } 〈 a + c 〉 slips. [ABSTRACT FROM AUTHOR]

Given that commercial purity titanium (CP-Ti) doped with a high oxygen concentration has recently been reported with high mechanical performance, the present work investigated the failure behavior and its mechanisms of the material under uniaxial impact loading. Besides the strong hardening effect of oxygen, it was found that increasing oxygen content led to increased propensity for adiabatic shear failure in CP-Ti. The texture or grain orientation was also found to have profound influence on the formation of adiabatic shear band (ASB). Microstructural examinations on the postmortem high oxygen CP-Ti suggested that uniform and equi-axed nano-grains were produced within the ASB. The orientations of these nano-grains were analyzed using the precession electron diffraction (PED) technique. It provides direct evidence of phase transformation occurring in ASB. Then we demonstrate that the nano-grains in ASB formed from parent grains by phase transformation, indicating that the α→β→α phase transformation process takes part in ASB evolution and is an underlying mechanism of grain refinement. As such, this result is a supplement for traditional well-accepted dynamic recrystallization mechanism of ASB evolution. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion prepared Ti–O alloys exhibits good strength-ductility balance, while it's believed to be brittle. In this study, the mechanisms responsible for their high ductility are investigated. It was revealed that their α′-Ti grains, which originate from super-rapid cooling, possess distinctive deformation mode, and contributed to high ductility. [ABSTRACT FROM AUTHOR]

Several recent studies reported high ductility in the Ti–O alloy, which is believed to be brittle, but the mechanism explaining the ductility has not yet been clarified. This study focused on the relationship between grain size and ductility to elucidate the mechanism for the high ductility in the Ti–O alloy and found that the ductility decreased with an increasing grain size. Although the extrudate of a Ti-0.77 wt%O sintered alloy exhibited good ductility (>5%) up to a grain size of 49.8 μm, the alloy failed in the elastic area when the grain size exceeded 98.4 μm. Cracks with a size similar to the grain size were observed at the grain boundaries in the fracture area of these ductile fine-grain Ti–O alloys. In situ observations of the deformation behavior of the fine-grain Ti–O alloy revealed that crack propagation was suppressed due to the reduced stress intensity caused by crack refinement. In contrast, in the large-grain Ti–O alloy, the high stress intensity around the first crack caused immediate crack propagation and brittleness. [ABSTRACT FROM AUTHOR]

Diagram of TiO decomposition and strengthening mechanism of HOC-Ti. [Display omitted] • An in-situ study revealed a complete decomposition of TiO particles in α-Ti matrix at elevated temperatures. • An intermediate product of low-valence titanium oxide (Ti 2 O) adjoining the TiO phase was observed in the process of TiO decomposition. • High strength commercially pure titanium was produced by precision control of oxygen content without expense of ductility. Oxygen has been known as an effective strengthening element in titanium (Ti) and its alloys. However, an over-dose of oxygen can also lead to embrittlement of Ti alloys. To precisely control and push the limit of oxygen in Ti and its alloys, we studied the decomposition process of Ti oxides in pure α-Ti matrix using an in-situ high-temperature scanning electron microscope. The experimental results revealed that TiO particles decomposed in α-Ti at elevated temperatures and the oxygen atoms gradually diffused into the matrix, following the Fick's second law. Then, the samples with different oxygen contents were produced using the aforementioned strategy, for which the oxygen content, microstructure, and mechanical properties were measured. The results revealed that the oxygen content can be precisely controlled, which can achieve an ultra-high tensile strength of close to 1100 MPa, at no expense of elongation-to-failure, with incorporating 0.87 wt% oxygen. An analysis showed that the strength contribution from oxygen follows the Labusch law. These findings offer a novel approach to design high-performance Ti alloys with non-toxic and cheap elements. [ABSTRACT FROM AUTHOR]

Oxygen solid solutions are well known to impose a strong hardening effect on Ti and its alloys, but induce the undesirable embrittlement behavior. In order to improve the ductility of Ti materials with high oxygen content, Ti(O), herein, a heteromicrostructure consisting of two phases with different oxygen contents was synthesized by redistributing the oxygen solutes through heat treatment over the dual (α + β) phase temperature range, followed by water quenching. The heteromicrostructure formation and plastic deformation mechanisms were investigated by erectron backscattered diffraction (EBSD) analysis of the quenched Ti(O) material under tensile deformation coupled with SEM. It was found that the elongation at break of the sintered Ti-0.94 mass% O alloy remarkably recovered from 6% to 19% owing to the above-mentioned heat treatment and water quenching process. The quenched Ti(O) material consisted of equiaxed grains with high oxygen content, fine α' phase grains, and misorientation regions in the equiaxed grains with low oxygen content. The high and low oxygen content phases were derived from the α and β phases, respectively. The β phase was responsible for plastic deformation, which improved the tensile elongation of the Ti(O) material. [ABSTRACT FROM AUTHOR]

In order to improve the strength of commercially pure Ti (CP-Ti) for oral implants, the high oxygen content Ti (HOC-Ti) was prepared via powder metallurgy. Its composition and mechanical properties were then characterized. After surface treatment by sandblasting and acid etching (SLA), the surface morphology, wettability and roughness of the HOC-Ti and CP-Ti sample were examined. In an in vitro test that followed an evaluation of the protein adsorption capacity of HOC-Ti, the mouse preosteoblast cells were inoculated onto the specimens to evaluate their biocompatibility, in comparison with those of CP-Ti. The oxygen concentration of the HOC-Ti increased to 0.62 wt%, which is higher than the 0.26 wt% of the CP-Ti, while their compositions and microstructures were very similar. The tensile and compressive yield strength of the HOC-Ti (800 MPa) was improved significantly in comparison to that of the CP-Ti (530 MPa). After surface treatment, a unique structure of micropores with a diameter of 380 nm was observed on the entire surface of the HOC-Ti that facilitates cell adhesion and proliferation. The wettability of the HOC-Ti was obviously superior (p < 0.05). The in vitro study showed that the MC3T3-E1 cells inoculated on the surface of HOC-Ti exhibited a homogeneous microstructure, and the viability was higher than that of the control group on days 4 and 7 (p < 0.05). In addition, the number and differentiation activity of cells that adhered to the surface of the HOC-Ti increased significantly on day 7 (p < 0.05). The experimental results showed that, in view of its mechanical properties and biocompatibility, HOC-Ti is superior to CP-Ti and is promising for oral implant applications. Unlabelled Image • The high oxygen concentration titanium(HOC-Ti) was produced by powder metallurgy(PM). • The surface characteristics and biocompatibility of HOC-Ti were evaluated after SLA. • The oxygen content of HOC-Ti was 0.62 wt% higher than that of CP-Ti, while their structures were similar. • The yield strength of HOC-Ti was increased to 800 MPa, and the elongation-to-failure remained over 20%. • HOC-Ti exhibits excellent biocompatibility in vitro and is promising for oral implant applications. [ABSTRACT FROM AUTHOR]