高强β钛合金热变形过程中组织演变及热加工图研究进展

高强度β钛合金广泛应用于航空领域的大型承重部件。目前,大型零件一般采用模锻成型。不同的初始显微组织和变形工艺参数会显著影响流动行为。为了实现显微组织的精确控制,研究人员进行了大量的研究工作去分析热压缩过程中的组织演变和变形机制。本文重点综述高强度β钛合金在热变形过程中的组织演变,包括单相区的动态再结晶和动态回复,以及两相区中α相的动态演变。此外,总结热加工图中的最佳热加工区域、不稳定区域以及功率耗散效率与变形机制之间的关系。最后,强调利用热加工图优化工艺参数存在的问题和发展方向。

Hot deformation behavior and globularization mechanism of Ti-6Al-4V-0.1B alloy with lamellar microstructure

Hot deformation behavior and globularization mechanism of Ti6A14V0.1B alloy with lamellar micro structure were quantitatively studied through isothermal compression tests with the temperature range of 850950 ℃and strain rate range of 0.011.00 s1. The results show that the peak flow stress and steady stress are sensitive to the strain rate and temperature. The value of deformation activation energy is 890.49 kJmo11 in （a＋β） region. Dynamic recrystallization is the major deformation mecha nism. Flow softening is dominated by dynamic recrystallization at 850950 ℃. TiB particles promote the recrystallization of laths. Globularization processes consist of four steps： for mation of subgrain after dynamic recovery in a plates; subgrain boundary migration caused by interracial instability; interfacial migration promoting phase wedge into a phase; disintegrating of a laths by diffusion processes; and grain boundary sliding. Globularization mechanisms during hot deformation processes of the Ti6A14V0.1B alloy with lamellar structure are continuous dynamic recrystallization.

Dynamic stress–strain properties of Ti–Al–V titanium alloys with various element contents

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI,Ti–5Al–3V ELI,commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared.These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary a phase.Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s-1.The results show that Ti–6Al–4V alloy with equiaxed primary a(ap)volume fraction of 45 vol%or 67 vol%exhibits good dynamic properties with high dynamic strength and absorbed energy,as well as an acceptable dynamic plasticity.However,all the Ti53ELI specimens and Ti64ELI specimens with ap of 65 vol%were not fractured at a strain rate of4,000 s-1.It appears that the undamaged specimens still have load-bearing capability.Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al,V,Fe,and O increase,while dynamic strain is not sensitive to the composition in the appropriate range.The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.

Microstructure and mechanical properties of a new high-strength and high-toughness titanium alloy

In order to develop a new titanium alloy with a good combination of strength-ductility-toughness,a nearbeta titanium alloy was designed based on the already widely used Ti-1023 alloy.To avoid beta fleck occurring in the microstructure,the new Ti-Al-Fe-V(Cr,Zr) alloy has been made through decreasing the content of Fe,based on molybdenum equivalency and Bo-Md molecular orbital method(a method for new alloy designing based on the molecular orbital calculating).After primary design computation,Ti-Al-Fe-V(Cr,Zr) alloy was optimized as Ti-3Al-4.5Cr-1Fe-4V-1Zr finally.The microstructure and tensile properties of this alloy subjected to several commonly used heat treatments were investigated.The results show that the tensile strength of the alloy after solution treated below the β-transus temperature comes between 850 and 1100 MPa,with elongation in the range of 12.5 %-17.0 %.In solution-treated and solution-aged samples,a low-temperature aging at 500 ℃ results in the precipitation of finer α phase.With the increase in aging temperature,the secondary α phase becomes coarser and decreases in amount.Thus,it will lead to the increase in tensile ductility,but reduction in strength.Eventually,after modulated aging treatment,the alloy can obtain highstrength level with acceptable ductility.The tensile strength of the alloy can achieve 1273 MPa,with an elongation of 11.0 %.At the same time,the fracture toughness(K_(IC)) of the alloy achieves 83.8 MPa·m^(1/2).It is obvious that the newly designed alloy has achieved a good blend of strength-ductility-toughness.

High-temperature deformation behaviors of Ti-2Al-9.2Mo-2Fe alloy with boron

Hot deformation behaviors of Ti-2Al-9.2Mo-2Fe alloy with boron were investigated in a hot compression test at temperatures ranging from 850 to 1000℃and strain rates ranging from 0.01 to 10.00 s^(-1).With strain rate decreasing and deformation temperature increasing,dynamic recrystallization(DRX)was promoted in both alloys.The nucleation mechanism of DRX involved grain boundary bulging and subgrain rotation.In case of deformation at low temperatures and high strain rates,the boronfree alloy only showed dynamic recovery(DRV)phenomenon.However,due to the particle-stimulated nucleation mechanism of recrystallization by TiB particles,the boron-containing alloy shows DRX at that condition.These DRX grain nuclei are formed by lattice rotation and subgrain growth from deformation zone in the initial grains,which are close to those of TiB particle.Moreover,the flow stress of the boron-containing alloy is lower than that of the boron-free alloy due to the grain refinement during hot deformation process.

Quasi-static and dynamic plastic deformation behavior in titanium with vanadium addition

Compressive properties,microstructure features and deformation modes were investigated in binary Ti-(2,4,8)wt%V alloys during quasi-static(1×10^(-3)s^(-1))and dynamic(3×10^(3)s^(-1))compressions.The compressive behavior shows a strong dependence on the loading strain rate and vanadium content contained in pure Ti,such that the flow stress increases with the increase in strain rate and vanadium content ranging from 2 wt%to 8 wt%.The microstructure features are clearly different from each other for alloys with different vanadium contents or under quasi-static and dynamic loading conditions.An examination of deformation microstructures by optical microscopy and electron backscattered diffraction indicates that twinning behavior occurs during quasi-static and dynamic compressions and the twinning density increases with strain rate increasing but decreases with vanadium addition.The existence of{1012},{1121}and{1122}type twinning was further identified.With the help of the calculated Schmid factor map,the values of critical resolved shear stress of twinning types mentioned above have been obtained and verified to be rarely affected by the loading strain rate but sensitive to the vanadium content.In vanadium-rich alloys(Ti-8V),twins are rarely observed but dislocation slip mechanism is active by transmission electron microscopy investigations.With vanadium content increasing,both the critical resolved shear stress of twinning types and the content ofβphase with abundant slip systems increase,reflecting a suppression of twinning but an active dislocation slip mechanism.

Novel twinned Al3Sc dendrites in as-casted Al-Sc alloy

Al-Sc alloys with high Sc contents are served as sputtering targets for making high-performance piezoelectric devices.The micro structure of these alloys would affect the sputtering process and the final quality of the functional devices.In this study,the microstructure in as-c as ted Al-20%Sc(in atomic ratio)alloys is characterized and the feathery Al3Sc grains with twin relationships are reported for the first time.The crystallographic features of twined structures and growth directions are quantitatively analyzed by electron backscatter diffraction(EBSD)technique.

Phase precipitation behavior and tensile property of a Ti-Al-Sn-Zr-Mo-Nb-W-Si titanium alloy

The characteristic of precipitation behavior of a2 phase and silicide, and the tensile properties at room temperature and 650℃after heat treatments in anovel TiAl-Sn-Zr-Mo-Nb-W-Si titanium alloy（BTi-6431 S） were investigated by microstructure analysis and mechanics performance testing. The results show that no second phase precipitates after solution treatment(980 ℃/2 h, air cooling（AC）). However, when the solution-treated specimens are aged at 600 ℃（600 ℃/2 h,AC）,α;phase precipitates in the primary α phase, and the size of α;phase increases with the aging temperature increasing to 750 ℃. Meanwhile, 50-100-nm S2-type silicide particles precipitate along lamellar phase boundaries of transformed β phase after aging at 750 ℃. BTi-6431 S alloy shows the best650 ℃ ultimate tensile strength（UTS） and yield strength（YS） when treated in solution treatment. However, aging treatment results in a decline in 650 ℃ ultimate tensile strength. This may be attributed to the loss of solution strengthening due to the depletion of Al, Si and Zr of the matrix caused by the precipitation of Ti;Al and（TiZr）;Si;.Silicide is a brittle phase; therefore, its precipitation causes a sharp decrease in the room-temperature ductility of BTi-6431 S alloy.

Research progress on hot deformation behavior of high-strength β titanium alloy: flow behavior and constitutive model

High-strength β titanium alloys represented by near β titanium alloy and metastable β titanium alloy are preferred materials for large-scale load-carrying structures.In order to achieve the precise regulation of microstructure in the deformation process, massive efforts have been made to study the flow behavior and microstructure evolution of βtitanium alloy in the hot deformation process. This paper reviews the flow behavior of high-strength titanium alloy,including the effects of initial microstructure, deformation process parameters, work hardening, and dynamic softening on flow stress. Furthermore, the effects of deformation process parameters on the apparent activation energy for deformation and strain rate sensitivity coefficient are analyzed. The discontinuous yield phenomenon is discussed,and the constitutive models of flow stress are summarized.Furthermore, some microstructural evolution models are reviewed. Finally, the development direction and difficulties of the flow behavior and constitutive model are pointed out.

Microstructure and tensile properties of Ti-62421S alloy plate with different annealing treatments

Ti-62421S （Ti-6A1-2Sn-4Zr-2Nb-lMo-0.2Si） is a novel short-time using high-temperature titanium alloy. The effects of annealing on microstructure and tensile properties of Ti-62421S alloy plate were studied through optical microscopy （OM）, electron probe microanalysis （EPMA）, transmission electron microscopy （TEM）, and tensile tests. The results show that, with annealing tem- perature increasing, the volume fraction of primary α（αp）- phase decreases while that of transformed β（βt）-structure and secondary α （αs）-phase increases. The room-temperature strength and plasticity are insensitive to annealing temperature. However, with annealing temperature increasing, the tensile strength decreases at 550℃, while increases at 600 and 650℃ instead. It is suggested that, at 550℃, the strengthening mechanism is mainly boundary strengthening and the biggest contributor is ap-phase by providing αp/β-boundary area. Above 600 ℃, the strengthening mechanism is grain strengthening, where αs-phase strengthens the β-phase.

High-temperature deformation behavior of a beta Ti-3.0Al-3.5Cr-2.0Fe-0.1B alloy

The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. The strain rate ranging from 0.01 to 10.00 s^-1 and the deformation temperature ranging from 800 to 950 ℃ were considered.The flow stress and the apparent activation energy for deformation, along with the constitutive equation, were used to analyze the behavior of the Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy. The processing map was established. The effect of strain rate on the microstructure at 850 ℃ was evaluated.The flow stress-strain curves indicated that the peak flow stresses increased along with an increase in the strain rate and decreased as the deformation temperature increased.Based on the true stress-true strain curves, the constitutive equation was established and followed as the ε= 6.58×10-（10）[sinh（0.0113σ）]-（3.44）exp（-245481.3/RT）. The processing map exhibited the ＂unsafe＂ region at the strain rate of10 s^-1 and the temperature of 850 ℃,and the rest region was ＂safe＂. The deformation microstructure demonstrated that both dynamic recovery（DRV） and dynamic recrystallization（DRX） existed during deformation. At the lower strain rate of 0.01 s^-1, the main deformation mechanism was the DRV, and the DRX was the dominant deformation mechanism at the higher strain rate of 1.00 s^-1.

Dynamic response and plastic deformation behavior of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V alloys under high-strain rate

Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope（OM） was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band（ASB） is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.

α_(2) phase precipitation behavior and tensile properties at room temperature and 650℃ in an(α+β) titanium alloy

The microstructure,room temperature and 650℃ tensile properties of an(α+β) titanium alloy were investigated after aging over a temperature range of 600-750℃ following solution treatment.The results exhibit that both aging temperature and aging time influence the precipitation behavior of α_(2) phase,and the size ofα_(2) phase affects the tensile properties.The growth speed ofα_(2) phase gets quicker with the aging temperature increasing under the same aging time.For a given aging temperature,the size of α_(2) phase gets larger when prolonging the aging time.There are significant improvements in yield and ultimate tensile strength at room temperature and 650 ℃ after aging at 600℃ for 2 h,but these values decrease with the size of α_(2) phase increasing.It is found that α_(2) phase,less than 7 nm,does not impair the roomtemperature ductility.However,when the size of α_(2) phase grows up from 7 to 15 nm,ductility decreases drastically.During 650 ℃ tensile process,with the particle size increasing from 3 to 15 nm,the interaction between moving dislocations and coherent particles changes from cutting mechanism to bypass mechanism.