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It is generally accepted that the addition of Fe deteriorates the creep behavior of titanium alloys at elevated temperature. However, the effect of Fe at ambient temperature is not well documented. In this paper, the creep performance of an α/β titanium alloy with different Fe contents (0.05 and 0.20 wt%) was systematically studied at temperatures from the ambient to 500 °C. Creep resistance of samples with 0.20 wt% Fe was found to decrease at temperatures above 300 °C, but to increase at ambient temperature and 200 °C. The resulting stress exponent was in the range of 4.7–14.4, corresponding with dislocation creep. The fitted creep activation energy fell into two categories, i.e., 1) comparable with the self-diffusion activation energy of α-Ti at elevated temperature, and 2) remarkably higher than the former at 200–400 °C. The underlying mechanisms controlling creep processes at different temperatures were discussed. [ABSTRACT FROM AUTHOR]

Titanium alloys with the Widmanstatten microstructure usually exhibit high resistance to crack propagation and high fracture toughness. However, this has rarely been connected to mechanical twins. In this study, deformation twinning, which is popular in the fatigue crack tip plastic zone of α/β titanium alloys with the Widmanstatten microstructure, was systematically investigated with the electron backscatter diffraction technique. With the propagation of the fatigue crack, large-scale twins were generated due to the periodic loading and the crystallographic feature of the Widmanstatten microstructure, and they ultimately consumed the major volume of the parent α colony. Twin development with various ranks of Schmid factors (SF) was characterized, while ordinary deformation twins with relatively high rank SF grew most, extraordinary twins with very low rank SF were also activated, although restricted by the ordinary twins. The occurrence of extraordinary twins (including primary and secondary twins) was mainly attributed to the non-uniform local stress distribution induced by the plastic deformation compatibility between the neighboring units. Lastly, the influence of deformation twinning on the mechanical properties concerning crack propagation in hexagonal α-Ti alloys was discussed. [ABSTRACT FROM AUTHOR]

The phenomenon of room temperature creep in titanium alloys has drawn great attention for decades. With the increasing application of titanium alloys to the manned submersible pressure hull, the traditional calculation and analysis based on strength and stability cannot meet the requirement of structure design and safety evaluation for the spherical pressure hull completely. In this paper, a series of compressive creep tests were performed to reveal the change rule and distribution characteristics for creep behavior of the spherical pressure hull model. Results show that there is no measurable creep strain for pressure hull under maximum operating pressure and steady-state creep appeared in high stress areas of the pressure hull under 1.25 times maximum operating pressure, with the characteristics of internal creep strain and strain rate being greater than the external counterparts. The stress threshold value of the pressure hull model for steady-state creep is 853.7 MPa (equivalent to 0.88 R p0.2), and a creep constitutive equation is proposed based on improved Norton power law model. The results of this paper can provide support for the safety assessment and optimization design of manned submersibles for long-term service. • Experimental tests explore the compressive creep characteristic of pressure hull. • No measurable creep strain occurs for pressure hull under maximum operating pressure. • Steady-state creep appears under 1.25 times maximum operating pressure. • Stress threshold value is 853.7 MPa for pressure hull model under steady-state creep. • A creep constitutive equation is proposed based on improved Norton power law model. [ABSTRACT FROM AUTHOR]