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The influence of partial substitution of Hf for Zr on the microstructure and thermal stability of near‐α high‐temperature titanium alloys is systematically investigated. The results show that the addition of Hf promotes the refinement of precipitated phases of the silicides and α2 phase and the (Ti,Zr,Hf)6(Si,Sn)3 S2‐type silicides were formed in alloys after aging treatment. During thermal exposure, both silicides and α2 phase in alloy with 2.5 wt% Hf exhibited excellent anti‐coarsening ability, which may be attributed to the slow diffusion of Hf in Ti that significantly inhibited the growth rate of the precipitated phase. The loss of plasticity of near‐α titanium alloys after thermal exposure is mainly due to the precipitation and coarsening of silicides and α2 phase, therefore, the Hf‐containing titanium alloy has more excellent thermal stability, i.e., the plasticity loss rate is decreased from 34.8% (the alloy without Hf) to 7.4% (the alloy with 2.5 wt% Hf). [ABSTRACT FROM AUTHOR]

A triple-microstructure with the precipitation of silicide along the α/β phase boundaries and α 2 phase in the Ti-5.8Al-3Sn-5Zr-0.5Mo-1.0Nb-1.0Ta-0.4Si-0.2Er alloy was prepared for improving thermal stability and creep resistance. The alloys were forged at 1050 °C and 1000 °C followed by solution treatment at 1000 °C for 1 h and subsequent ageing at 700 °C for 5 h. The effects of α morphology and precipitation characteristics on the thermal stability and creep performance of high-temperature titanium alloy were investigated. A triple-microstructure with the participation of silicide along the α/β phase boundary and α 2 phase was a promising structure with improved thermal stability and creep resistance. The plasticity loss rate was 25.0% after thermal exposure at 650 °C for 100 h due to the participation and coarsening of α 2 and silicide. Meanwhile, the plastic creep strain was 0.111% during the creep deformation at 650 °C for 100 h with an applied stress of 100 MPa, which was attributed to the inhibition of silicide and α 2 phase for boundary migration and dislocation slipping. Furthermore, the mutual precipitation of coarsening silicide and α 2 phase inside α matrix was a significant reason for the dramatic decrease in the thermal ability, which also worsened the inhibition for dislocation climbing of silicon element during the creep deformation. [ABSTRACT FROM AUTHOR]

Dislocation boundary response and characteristic micro-structure were investigated in commercial pure titanium during the penetration impact and dynamic compression. The initial dislocation boundary induced by cold rolling can strengthen the adiabatic shearing sensitivity of commercial pure titanium during the penetration impact, which is consistent with the mechanical response and micro-structure during the dynamic compression. The compression with a loading direction vertical to the initial geometrically necessary boundaries (GNBs) results in the decrease in the spacing between GNBs, while the compression with a loading direction parallel to the initial GNBs attributes to the generation of new dislocation boundary crossed with the initial one. Then, a model of distribution and morphology of dislocation boundary around crater is proposed. [ABSTRACT FROM AUTHOR]

Isothermal compression testing of Ti–5.8Al–3Sn–5Zr–0.5Mo–1.0Nb–1.0Ta–0.4Si–0.2Er titanium alloy is performed on a Gleeble-3500 thermal simulator, and the corresponding microstructures are analyzed to clarify the softening mechanism and participates evolution. A constitutive equation compensated by strain has been established to describe the hot deformation behavior of the alloy. The deformation activation energies are calculated to be 369760.93–699310.86 J/mol in α + β two-phase region and 268030.03–325800.41 J/mol in β single-phase region. At a temperature of 880 °C, the main softening mechanism is the continuous dynamic recrystallization of lamellar α colony, controlled by the mechanical rotation of the sub-grain followed by dislocation climbing and annihilation by diffusion. Meanwhile, the dominant softening mechanism is the discontinuous dynamic recrystallization of β phase during the deformation at temperatures of 920 °C–1080 °C. Silicide containing Er with an average diameter of 20 nm is formed during the water quenching. [ABSTRACT FROM AUTHOR]

The microstructure and micro-orientation evolution of a novel high-temperature titanium alloy were characterized during a two-step deformation process. In the first step, the specimens were deformed at temperatures of 800, 850, 900 and 950 °C, and subsequently deformed in the same β-phase region of 1050 °C. The specimens pre-strained at 800 °C and 950 °C were fully recrystallized during the β-phase deformation process. By contrast, the specimens pre-strained at 850 and 900 °C were not fully recrystallized during the β-phase deformation process. This indicates that the extent of dynamic recrystallization did not increased monotonically with the pre-strain temperature. The extent of dynamic recrystallization was related to the stored energy accumulated in the α and β-phase during the pre-strain deformation. The change in stored energy was based on the difference in microstructure morphology produced by different pre-deformation temperatures,and stored energy was quantitatively estimated based on the local misorientation distribution. Meanwhile, the generation of dynamically recrystallized grains was beneficial to decreasing the generation possibility of the macro-zone. This decrease was attributed to the refinement of β-grains and randomly distributed orientation, which was also related to the decrease in the typically distributed "two parallel wings" orientation between the α and β phase induced by uncrystallized deformation. Additionally, the two-step deformation process with the pre-strain at the (α + β) middle regime was an effective strategy to promote the dynamic recrystallization and decrease the generation probability of the macro-zone. • A deformation process to promote the dynamic recrystallization of parent β phase. • The extent of recrystallization was not linearly related to pre-strain temperature. • The pre-strain was a strategy to decrease the generation possibility of macro-zone. [ABSTRACT FROM AUTHOR]

Abstract: TC21 titanium alloy was hot compressed isothermally at temperatures ranging from 880°C to 950°C and strain rates ranging from 0.01 to 10s−1. Microstructures were investigated by electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM), and processing maps were developed at different strains. It is found that strain rate is a key factor for the formation of hot deformation microstructure. The stress–strain curves were exhibited flow softening behavior at high strain rate above 1s−1, while equiaxed grains were found at lower strain rates. There is no large instability zone besides two peak-areas of 880–900°C, 1–10s−1 and 925–950°C, 10−0.5 to 10s−1. [ABSTRACT FROM AUTHOR]

A series of ternary Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) biomedical titanium alloy was designed to develop potential biomedical materials. The effect of the Fe content on microstructure, mechanical properties, Young's modulus, and electrochemical behavior was studied in depth. The developed Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) alloys are mainly composed of α and β phases. The results indicated that the grain size of the β phase in Ti–6Zr-xFe alloys decreased with the increase of Fe element. The increase of Fe content also caused the decrease of α phase fraction, increase of β phase fraction and formation of ω phase. Besides, the increase of Fe content improved the microhardness (264, 300, 328, and 348 HV) and ultimate tensile strengths (748, 829, 917, and 994 MPa) of Ti–6Zr-xFe alloys due to the contribution of solid-solution strengthening effect for higher Fe contents, the refined strength of the β phase and the dispersion strength of ω phase. Young's modulus of Ti–6Zr-xFe alloys was 90, 93, 93, and 94 GPa, which was lower than that of Ti–6Al–4V alloy. Moreover, the Ti–6Zr-xFe alloy with the addition of 4 and 5 wt % Fe displayed excellent corrosion resistance. These results show that Ti–6Zr-xFe alloys are potential biomedical materials. • A series of novel Ti–6Zr-xFe biomedical titanium alloys was designed. • β grain size is refined with increasing Fe content. • Microhardness, tensile strength, and Young's modulus increase with increasing Fe. • Ti–6Zr-xFe alloys display excellent corrosion resistance at 4 and 5 wt % Fe. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) process belongs to a layer-by-layer additive manufacturing technology, which has different temperature gradients, cooling rates, and reheating treatment in different regions due to the variation of the thermal histories for different layers during SLM process. This work aims to study the microstructural homogeneity evolution of β phases, such as size, morphology, distribution, crystallographic orientation, and phase composition in different regions of the SLM Ti-6Zr-5Fe near β titanium alloy. The results indicate that the microstructure in different regions of SLM Ti-6Zr-5Fe alloy sample is quite different. The β phase in the bottom area had the smallest size about 7.25 μm, the β phase in the side-top area had the largest size about 20.56 μm. The β phase in the side-middle and middle part had a lower aspect ratio of 1.52 and 1.59, the β phase in the side-bottom and top part had a larger aspect ratio of 1.93 and 1.92. Most of the β phase in the side-bottom and top part had the 〈001〉 crystal orientation towards build direction and laser moving direction, the texture type in other regions was random. The α phase in the top of the SLM Ti-6Zr-5Fe sample had a smaller size than that in the middle and bottom of the sample. Meanwhile, the microhardness in the top of SLM Ti-6Zr-5Fe sample was higher than that in the middle and bottom of the sample. The temperature gradients, cooling rates, and reheating treatment play different leading roles in different regions of the SLM Ti-6Zr-5Fe alloy sample. • β phase size, morphology, crystallographic orientation are not entirely the same. • α phase size in middle and bottom is larger than that in the top. • Microhardness in the top is higher than that in the middle and bottom. • Temperature gradients, cooling rates, reheating treatment play different roles. [ABSTRACT FROM AUTHOR]

In this paper, semi‐solid Al–7Si–0.4Mg–x erbium(Er) (x = 0, 0.1, 0.3, 0.5, 0.8 wt%) alloys are fabricated via electromagnetic stirring method. The effects of Er on the microstructures and mechanical properties of semi‐solid Al–7Si–0.4Mg alloys are investigated. Results show that the eutectic π‐phase is modified to fine sized Er‐poor π‐phase and primary α‐Al is refined in semi‐solid Al–7Si–0.4Mg alloys with the addition of Er. Meanwhile, the plate‐like shape eutectic Si is transformed into fibrous eutectic Si with addition of Er, which has an excellent modification effect on the eutectic Si. Nucleation rate of the Er‐poor π‐phase is increased with a higher super cooling rate, which causes the refinement of primary α‐Al and the modification of eutectic Si phase. With the addition of 0.3 wt% Er, semi‐solid Al–7Si–0.4Mg alloys obtain the best tensile properties. The ultimate tensile strength and elongation values are 228 MPa and 10.4%, which is increased by 7% and 50% than Er‐free alloy, respectively. With the addition of Er into semi‐solid Al–7Si–0.4Mg alloys, the Chinese script π‐Fe phase is modified to fine size and globule Er‐poor π‐phase. The addition of 0.3% Er to semi‐solid Al–7Si–0.4Mg alloy improves the tensile strength about 7%, especially elongation (50%), which is attributed to the combined action of eutectic Si modification, primary α‐Al grain refinement, and π‐phase modification. [ABSTRACT FROM AUTHOR]

A novel microstructure i.e., lamellar bimodal microstructure (LBM) was prepared in high temperature titanium alloy. The morphology of primary α phase and secondary α phase were tailored by hot rolling and cyclic phase transformation, respectively. The LBM possess the excellent tensile yield strength and elongation to failure of 995.5 MPa and 16.7 % at room temperature and 569.5 MPa and 31.6 % at 650 °C, respectively. The refined primary α platelet and secondary α colony were the main strengthening mechanisms of LBM at room temperature. Meanwhile, the formation of geometrically necessary dislocations provide an assistant work hardening effect. In addition, unique lamellar bimodal structure and α colony refinement enhance the hindering effect of secondary α phase on primary α phase deformation at 650 °C. This strategy may provide a new route to design novel high-temperature titanium microstructure with excellent tensile properties at room and high temperature. [ABSTRACT FROM AUTHOR]