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The microstructure and cellular transition characteristics of an intermetallic Ti-42Al-3Nb-1Mo-0.1B (at.%) alloy were investigated. The as-cast microstructure of the alloy is mainly composed of (α2+γ) lamellar structure and (β+γ) mixture structure, which distributes along the boundaries of the lamellar colonies. In order to study the phase transformation of lamellar structure at aging temperature, a two-step heat treatment was carried out. After the first step of annealing treatment at 1,260 °C, the microstructure with relatively finer lamellar space and (γ+β/B2) mixture structure is obtained. Aging treatment, as the second heat treatment step, has significant influence on the microstructure, attributing to a cellular reaction of α2+γ→ γ+β. With the increase of aging temperature, the (α2+γ) lamellar structure continues to dissolve, whereas the contents of both the equiaxed γ and β/B2 grains continuously increase. Besides, the orientation of lamellae α2, equiaxed γ and equiaxed β/B2 in the cellular transition region follows a specific relationship of {0–11}ββ//{0001}α2α2//{1–11}γγ.

High Nb-TiAl (Ti-44Al-8Nb-0.2W-0.2B-0.5Y, at.%) ingot was fabricated by vacuum arc remelting (VAR). The as-cast ingot was hot-isostatic pressed (HIP) and homogenizing annealing processed. The influence of heat treatment temperature and thermomechanical processing on the microstructure and tensile property of the alloy was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and tensile tests. It was found that the high Nb-TiAl alloy after HIP and annealing was mainly composed of coarse α2/γ lamellae, β/B2 phase and γ phase and the solidification path of this alloy was: L→L+β→β→α+β→α→α+β+γ→α2+β+γ. The water quenching results showed that the alloy was in α single phase region at 1,340 °C. After heating at 1,340 °C for 30 min followed by furnace cooling, the alloy showed a full lamellar microstructure and its ultimate tensile strength was about 538 MPa, with an elongation of 0.3% at room temperature. Free-crack forged pancakes with fine-grained fully lamellar structure (FFLS) were obtained with an initial deformation temperature of 1,340 °C and the ultimate tensile strength of forged alloy was about 820 MPa, with an elongation of 0.9% at room temperature, which was much higher than that of alloy after HIP and annealing because of microstructural refinement.

Data-driven methods, which can explore the relationship among battery external parameters and battery states automatically without establishing complicated battery model, have been intensively applied to estimate state of charge (SOC), state of health (SOH) and remaining useful life (RUL) etc. Nevertheless, relatively few researches have been done on the selection of data-driven model parameters and the determination of model with the optimal comprehensive performance. To address these questions, this paper presents a multi-objective decision method for data-driven based estimation of battery states. This method adopts the combination of the analytic hierarchy process and the entropy weight method together with integrating subjective and objective weights. The mean absolute error and root squared mean error of training-set, validation-set and test-set are used as accuracy indexes, and modeling time is seen as computation burden index. These seven indexes are applied as objective criteria for the multi-objective evaluation method, successfully evaluating the comprehensive performance of estimation model. Moreover, with three cases for RUL estimation, the specific application process of selecting the model with the optimal comprehensive performance by the proposed method is presented in detail.

Isothermal compression tests of as-cast 5vol.% (TiBw + TiCp)/Ti composites were conducted in the deformation temperature ranging from 900 to 1100 °C and strain rate ranging from 0.001 to 1.0 s−1. The thermal deformation behavior and microstructure evolution mechanism of the material are studied to optimize the process parameters. Meanwhile, the flow stress-strain curves were measured. The activation energy decreases with increasing of compression temperature, which is related to the increase of β phase content with the increase of temperature. The constitutive equation was established to characterize the deformation behavior of 5vol.% (TiBw + TiCp)/Ti composites in hot compression. The softening mechanism is mainly dynamic recovery (DRV) and dynamic recrystallization (DRX) in different phase region. Transmission electron microscope (TEM) observation was used to study the effects of reinforcements on microstructural evolution. The results indicate that the reinforcement can prominently promote globularization of α lath in the α + β phase region. In the upper α + β phase region, the reinforcement promotes the formation of some subgrains in the matrix.

It has been challenging to achieve good strength-ductility synergy in titanium metal matrix composites (Ti-MMCs). Herein we report a new Ti-MMC produced by multi-directional forging (MDF) undertaken in near β phase region. The developed composite exhibits a microstructure featuring dynamically recrystallized (DRX) ultrafine α-Ti matrix with uniformly dispersed micrometer sized TiB whiskers and submicrometer sized Y2O3 particles. This unique microstructure renders the composite an exceptionally high strength and good ductility at room temperature. The strengthening mechanism of the dually reinforced Ti composite is discussed.

To further improve the mechanical properties of the as-cast 7.5 vol.% TiBw/Ti&ndash, 6Al&ndash, 2.5Sn&ndash, 4Zr&ndash, 0.7Mo&ndash, 0.3Si composite, multi-directional forging (MDF) and subsequent heat treatments were carried out to adjust TiB whiskers (TiBw) and matrix characteristics. The effect of various microstructures on the tensile properties and fracture toughness of the composites was analyzed in this paper. After MDF, the TiBw are broken into short rods with a low aspect ratio and display a random distribution. Moreover, distinct microstructures were obtained after thermomechanical processing and different heat treatments. Both room-temperature and high-temperature tensile strength and ductility are improved after thermomechanical processing. By increasing the solution-treatment temperature, the microstructures transform from equiaxed to fully lamellar. A simultaneous improvement of the room-temperature and high-temperature properties is associated with the microstructural changes. In addition, the fracture toughness exhibits an increasing trend as the volume fraction of equiaxial &alpha, phases decreases. The lamellar microstructure demonstrates excellent fracture toughness due to deflection of the crack propagation path.

The medium-sized Longgen Pb-Zn deposit deposit (proven Pb + Zn resources of 0.13 Mt, 3.21% Pb and 2.43% Zn) is located in the western Nyainqentanglha belt in southern Tibet. The orebodies occurring as stratiform, lenticular and vein types are hosted in the skarn or marble along the contacts between the limestones and the granite porphyries. Alteration zonations are observed from granite porphyry to limestone, the proximal garnet is reddish-brown and becomes more pale brown and green with distance. The values of grossular gradually increase, while the andradite end members gradually decrease with distance (And(92.5−99.5)Gro(0.5−7.5)Pra(0.0−0.1) to And(9.0−36.5)Gro(63.4−90.9)Pra(0.1−0.5)). Similarly, the values of diopside (Di9.2–30.4Hd65.9–89.9 Jo0.6−3.7 to Di65.2–77.6Hd21–33.2Jo1.3−1.7) gradually increased close to the limestone. Retrograde metasomatic minerals overprint the prograde skarn and are dominantly composed of epidote, actinolite, ilvaite, and chlorite. The ore minerals consist mainly of galena and sphalerite, followed by magnetite, pyrite, pyrrhotite, chalcopyrite, molybdenite and bornite. At least five stages have been recognized, and from stage I to stage V, the δ18Ofluids values are 7.7% to 8.3%, −6.0% to −4.4%, −8.8% to −6.4%, −8.7% to −3.3%, and −13.2%, respectively. The δD values from stages I to V are −141.1% to −129.4%, −136.5% to −124.2%, −129.5% to −106.4%, −126.6% to −101.4%, and −106.8%, respectively. The δD and δ18Ofluids indicate that the ore-forming fluids gradually evolved from magmatic to meteoric in origin. The main types of fluid inclusions for the Longgen deposit are liquid-rich inclusions. Laser Raman analysis indicates that the fluid inclusions within the studied minerals are dominated by H2O, although some contain CO2 gas. Given the fluid inclusion data, the ore-forming fluids of stages I and II were most likely high-temperature (460–480 and 340–360 °C) and low-moderate salinity (7.9–15.0 and 2.4–12.6 wt% NaCl eq.) fluids, which were formed in a magmatic–hydrothermal system in stage I and as a mixture of magmatic and meteoric waters in stage II. In the subsequent stages (III and IV), the fluids changed to moderate temperature (230–270 and 160–200 °C) and low-moderate salinity (0.2–14.8 and 0.9–10.6 wt% NaCl eq.) mixed fluids of magmatic and meteoric waters. In the last stage V, the fluids changed to low-temperature (130–160 °C) and low-salinity (0.2–5.6 wt% NaCl eq.) meteoric water. The δ13C values in calcite lie within a narrow range of −6.1% to −4.4%, similar to that for the magmatic source, which indicates that the carbon was sourced from the granite porphyry. Sulfur (δ34S = 0.4–5%, estimated δ34Sfluids = 2.77%) and lead isotopic compositions of sulfides (206Pb/204Pb = 18.549–18.776, 207Pb/204Pb = 15.685–15.839 and 208Pb/204Pb = 38.94–39.592, similar to the whole-rock values for the granite porphyry) indicate that the ore-forming materials were derived mainly from the granite porphyry, which originated from the Nyainqentanglha Group. Consequently, taking the data together suggests that the Longgen Pb–Zn deposit is a typical skarn deposit related to Palaeocene magmatic-hydrothermal systems, and that fluid cooling caused by fluid mixing is the most crucial mechanism for Pb-Zn deposition.

In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44Al alloy have been studied in this work. The as-cast microstructure morphology changes from ( γ +α 2 ) lamellar colony and β / β 0 + γ mixture structure to β / β 0 phase matrix widmannstatten structure, when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and α phase, the angles between the lamellar orientation and the block β / β 0 phase are roughly at 0°, 45° and 90°. Comparing with heat treatment microstructure, the hot compression microstructure contains less β / β 0 phase, however, the β / β 0 phase containing 2Mo alloy and 3Mo alloy hot compressed at 1275 °C has the inverse tendency. In addition, (α 2 + γ ) colony is decomposed by the discontinuous transformation.

The microstructure evolution and tensile properties of Ti-48Al-2Cr-2Nb-0.25Ni alloy fabricated by the induction skull melting (ISM) process were investigated. Results showed that the influence of trace Ni addition on the cast microstructure was slight, while the γ phase fraction increased relatively. After tensile tests at elevated temperature, nanoscale τ3 particles precipitated within the lamellar colony in the gauge area. The τ3 phase exhibited the specific orientation relationship with the α2 and γ phases: ( 22 4 2 ) τ 3 // ( 40 4 1 ) α 2 // ( 113 ) γ and [ 1 1 00 ] τ 3 //[11 2 0] α 2 //[ 1 10]γ . At elevated temperature, the UTS and ef were enhanced evidently by Ni addition than that of Ti-48Al-2Cr-2Nb alloy. Dislocations were pinned by the nanoscale τ3 precipitates during tensile deformation at elevated temperature. The nanoscale τ3 precipitates and increased γ phase fraction induced by Ni alloying could account for the notable tensile properties in the present work. The precipitation behavior and the main strengthening mechanism were analyzed and discussed in detail.

The strain rate sensitivity evolution of Ti-22Al-25Nb (at%) alloy was studied using strain rate jump testing technique. The strain rate jump tests were conducted over a wide range of strain rates (2.5 × 10−4–1.6 × 10−2 s−1) at temperatures of 930 °C and 970 °C. The increase in strain rate has a hardening effect on the alloy, leading to an increase in the flow stress. Deformation at higher strain rates always has shorter hardening stage and higher softening rates. The strain rate sensitivity index, m, monotonically decreases with increasing the strain rate, but the decreasing rate gradually slows down. The alloy shows relatively high m-values and the strain rate variation has stronger effect on m-values at higher deformation temperatures. The m-value presents uncertain changes with increasing the strain during high temperature deformation. At 970 °C, m-values almost keep constant with increasing strain due to the microstructure stability, while the grain refinement during deformation at 930 °C leads to an increase in m-values with increasing the strain.

Accurate estimation for state-of-energy (SOE), defined as the ratio of residual available energy to maximum available energy, is an important task in battery management system. Nevertheless, the reduction in maximum available energy caused by battery degradation may lower SOE estimation accuracy, which is almost ignored in existing SOE estimation algorithms. To ensure precise SOE prediction over battery's whole lifetime, a joint estimation method for maximum available energy and SOE is proposed in this paper. Firstly, the parameters of the first-order RC battery model are online identified by forgetting factor recursive least square, where rough SOE is inferred directly from identified open-circuit-voltage (OCV). Considering OCV change at adjacent sampling time, a third-order extended Kalman filter is established to correct OCV and estimate maximum available energy with identified parameters and rough SOE. Finally, the predicted maximum available energy is further transmitted into adaptive extended Kalman filter to estimate SOE. The feasibility, prediction accuracy and robustness ability are verified with Federal Urban Driving Schedule tests under the temperature range of 0 °C–50 °C. Validation results indicate that the proposed joint estimation method can still provide accurate maximum available energy and SOE prediction results even though there exist various forms of interferences.

The tension-compression asymmetry including the yielding and strain hardening asymmetry of a commercially pure titanium (CP-Ti) at room temperature was studied using uniaxial tensile and compressive tests. The deformation twinning modes responsible for the tension-compression asymmetry were analyzed using the electron back scattered diffraction technology. The CP-Ti exhibits a strong tension-compression asymmetry in yielding and strain hardening. The prismatic 〈a〉 slip is the most easiest to activate either for tension or compression. The deformation twinning mode can be characterized by the secondary { 10 1 ¯ 2 } twin variants in primary { 11 2 ¯ 2 } twins for tension and the secondary { 11 2 ¯ 2 } twin variants in primary { 10 1 ¯ 2 } twins for compression. The secondary twin variants are the dominated twinning modes whether for tension or compression, determining the final yielding behavior of the titanium. The stress required to activate the secondary extension twins in tension is larger than that to activate the secondary contraction twins in compression, leading to the tension-compression asymmetry in yielding. The strain hardening enhancement of the CP-Ti is a result of the combination of the Hall-Petch hardening by grain refinement and texture hardening by lattice re-orientation both resulting from the deformation twinning. The stronger effect of these two hardening mechanisms on compression than on tension leads to the tension-compression asymmetry in strain hardening.

New type beta-gamma TiAl alloy of nominal composition of Ti-44Al-4Nb-4V-0.3Mo-Y (at%) was fabricated by induction skull melting, which was designed based on the study of the microstructural effects of Mo, Cr, V, and Nb on TiAl alloy. The microstructure, oxidation resistance, hot workability, and tensile properties were studied by SEM in BSE mode, XRD, Gleeble 3800, as well as Instron 5500 R, respectively. The oxidation resistance of this new designed Mo containing beta-gamma TiAl alloy was better than that of only Nb and V containing beta-gamma TiAl alloy. With a better hot workability at temperature under 1200 °C, Ti-44Al-4Nb-4V-0.3Mo-Y alloy was successfully hot forged at 1150 °C with a traditional hydraulic machine without thermal insulation measure. Though containing abound order β 0 phase, the new fabricated beta-gamma TiAl alloy still has a high elongation at 850 °C, because of less α 2 +γ lamellar colonies containing. Benefits of partly replacing Mo with V was avoiding omega phase precipitation, and not damaging the hot workability.

In this paper, as cast 2.5 vol% (TiBw+TiCp)/Ti composites were subjected to direct rolling down to 45%, 65% and 85% reduction in thickness in the (α+β) phase region. The microstructure evolution and tensile properties of the composites during direct rolling were investigated. The results show that increasing of the rolling deformation contributes to the refinement of primary α phase (αp) and the improvement of the distribution uniformity of TiBw and TiCp. Furthermore, both the tensile strength and elongation are significantly enhanced with increasing of the rolling deformation. As the rolling reduction reaches 85%, the 2.5 vol% (TiBw+TiCp)/Ti composites exhibit an excellent balance of strength and elongation to failure both at RT and 600 °C, which is mainly attributed to the microstructure refinement and the load-sharing effect of TiBw and TiCp. Fracture analysis shows that the fracture TiBw and TiCp followed by the ductile failure of the matrix is the failure mechanism of the composites both at RT and 600 °C.

Microstructural evolution of the as-forged Ti-44Al-8Nb-0.2W-0.2B-Y alloy during high temperature tensile tests between 650 and 950 °C, at strain rates of 1×10−4 s−1, 2×10−4 s−1 and 5×10−4 s−1, is investigated in this study. Tensile properties of the alloy are extremely sensitive to the test temperature and strain rate. At a strain rate of 5×10−4 s−1, ductile-brittle transition temperature (DBTT) of this alloy is between 750 and 800 °C. At lower temperatures, the principal deformation mechanism involves breaking down of remnant lamellar structure and deformation of twins. Above 900 °C, dynamic recrystallization (DRX) occurs and the extent of DRX improves with an increase in temperature and strain as well as a decrease in strain rate. Under specific test conditions, the ω phase forms by the solid-state phase transformation: α2→γ+ω. The inhomogeneous microstructure remarkably influences the mechanical properties of the hot-forged pancake.

The hot deformation behavior and microstructure evolution of a 7.5 vol.% TiBw/near &alpha, Ti composite with fine matrix microstructure were investigated under the deformation conditions in a temperature range of 800&ndash, 950 &deg, C and strain rate range of 0.001&ndash, 1 s&minus, 1 using plane strain compression tests. The flow stress curves show different characteristics according to the various deformation conditions. At a higher strain rate (1 s&minus, 1), the flow stress of the composite continuously increases until a peak value is reached. The activation energy is 410.40 kJ/mol, much lower than the activation energy of as-sintered or as-forged composites. The decreased activation energy is ascribed to the breaking of the TiBw reinforcement during the multi-directional forging and the resultant fine matrix microstructure. Refined reinforcement and refined matrix microstructure significantly improve the hot deformation ability of the composite. The deformation conditions determine the morphology and fraction of &alpha, and &beta, phases. At 800&ndash, 900 &deg, C and 0.01 s&minus, 1 the matrix &alpha, grains are much refined due to the continuous dynamic recrystallization (CDRX). The processing map is constructed based on the hot deformation behavior and microstructure evolution. The optimal hot processing window is determined to be 800&ndash, C/0.001&ndash, 0.01 s&minus, 1, which lead to CDRX of primary &alpha, grains or dynamic recovery (DRV) and dynamic recrystallization (DRX) of &beta, phase.

In this study, 2.5 vol% TiBw /Ti composites were subjected to isothermal multi-directional forging (IMDF) at 1020 °C with various strain rates, aimed to investigate the spheroidization behavior of TiBw /Ti composites with initial widmanstatten microstructure. It is found that strain rate has a significant effect on the spheroidization of microstructure. Dynamic recovery (DRV) of α phase occurs at high strain rate while dynamic recrystallization (DRX) dominates microstructure spheroidization with the decreasing of strain rate. It is worth noting that α lamella and α colony exhibit different spheroidization behavior, which leads to the heterogeneity of microstructure. Moreover, the relationship between crystallographic orientation and imposed strain play an important role in the spheroidization process. The schmid factor calculated by EBSD was used to identify and predict heterogeneous deformation phenomena of α colony. The spheroidization process can be promoted by TiB whiskers due to the introduction of large deformation in the matrix.

In the paper, 2.5 vol% (TiB + TiC)/Ti composite has been fabricated by in situ casting route. 1-D forging and subsequent multistep rolling in (α + β) phase field are conducted on the as-cast composite and, accordingly, the matrix microstructure is significantly refined, and the distribution uniformity of reinforcements is greatly improved. The tensile properties of the composites with different processing states are tested at room temperature (RT), 600 and 700 °C. The results indicate that thermomechanical processing (TMP) can drastically improve strength and elongation of the as-cast composite both at RT and 600 °C. As tensile temperature increases to 700 °C, the UTSs of the composites gradually reduce while the elongations of the composites are enhanced remarkably after TMP. The degradation in UTS can be related to the matrix softening and interfacial debonding at 700 °C.

The microstructure evolution of as-rolled Ti-45Al-9Nb-0.3Y alloy as well as the nanohardness of β/B2 matrix was investigated by means of scanning electron microscopy (SEM) in backscattered electron mode (BSE) mode, transmission electron microscopy (TEM) and nanoindentation. This high Nb containing TiAl based alloy was rolled with 50%, 60%, 65% reduction, respectively. Omega phase precipitated in B2 phase with an orientation relationship of {110} β //{11 0} ω and 1> β // ω . Moreover, with the increase of deformation reduction, rod-like structure which was formed in γ grain transformed from (α 2 +γ) lamellae structure into α 2 phase only. Additionally, nanoinentation experiment revealed that the precipitation hardening of ω phase increased the hardness of β/B2 phase.

Hot deformation behavior of high Nb containing TiAl based alloy with a nominal composition of Ti–44Al–8Nb–0.2W–0.2B–0.1Y at 1225 °C and 1275 °C is investigated. The deformation mechanism of α phase is dynamic recovery at 1275 °C, whereas γ phase is mainly dynamic recrystallized. It is revealed that α phase is softer and easier to be deformed when the alloy is deformed at 1275 °C. The reasons of the different deformation behavior between 1225 °C and 1275 °C, as well as the different deformation behavior between α phase and γ phase are analyzed. A multistep deformation process at gradually lowered temperature is proposed to eliminate the adverse influence of remnant lamellar structure on mechanical properties. Keywords: Titanium aluminum, Microstructure, Deformation mechanism

The relationship between the compositional zonation of garnet in skarn deposits and the evolution of physicochemical conditions of ore-forming fluids is not clear and needs further investigation. This study presents the characteristics of trace elements of garnet from the Longgen skarn Pb-Zn deposit, Tibet with an aim to reveal the evolution trend of the physical and chemical conditions (fO2 and pH) of ore-forming fluids and to explore the fingerprint of garnet trace elements in different types of skarn deposits. Based on robust alteration halo, mineral assemblages and petrographic observation, the garnets of the Longgen skarn Pb-Zn deposit are divided into two types: (1) distal exoskarn garnet near limestone with ore-bearing and fine oscillatory zoning (Adr39.9-75.0; Grt1, Adr represents andradite) and (2) proximal exoskarn garnet (core: Adr32.9-70.7; rim: Adr83.3-99.5) with Pb-Zn-rich mineral and coarse oscillatory zoning (Grt2). According to the total rare earth element (ΣREE) content in the garnet compositional zone, Grt1 is further divided into three component zones: Grt1-1 (heavy rare earth element (HREE)-enriched chondrite-normalized REE distribution patterns and positive Eu-anomaly (δEu > 1, δEu = 2*(Eusample/Euchondrite)/(Smsample/Smchondrite + Gdsample/Gdchondrite)), Grt1-2 (HREE-enriched REE patterns with negative Eu-anomaly (δEu 1). Similarly, five component zones were identified in Grt2: Grt2-1 (REE-rich REE patterns with δEu 1), and Grt2-5 (LREE-enriched REE patterns with δEu The fractionation of LREE with HREE and the behavior of Eu indicate that the physical–chemical conditions during the formation of Grt1-1-Grt1-2 and Grt2-1-Grt2-3 were near neutral (pH = 6–7), and changed to mildly acidic in Grt1-3 and Grt2-4-Grt2-5 (pH

The crack initiation mechanism and fatigue behaviour of thermomechanically processed PM Ti–6Al–4V was systematically studied as a function of microstructural modifications and the associated crystallographic texture. Uniaxial fatigue tests, fractographic analysis and thorough EBSD analysis were performed on an extruded blended elemental PM Ti–6Al–4V alloy to reveal the relationship between crystallographic texture and fatigue properties. We demonstrate that the fatigue crack initiation mechanism is related to the microstructural features of the alloy (colonies in the lamellar microstructure, colony-like primary α plates in the acicular microstructure, and strongly textured primary α grains in the bimodal microstructure) and not to porosity. Through in-depth crystallographic analysis, we demonstrate that the highest fatigue strength achieved with the bimodal microstructure is due to the sharp [10 1 ‾ 0]//extrusion direction crystal texture of the primary α grains which require higher applied stresses in order to induce deformation along basal systems as well as crack opening along basal planes. The crystallographic texture of the alloy thermomechanically processed in the β field is not favourable for fatigue and the resulting lamellar microstructure has the lowest fatigue strength as grains are easily deformed along basal systems. The grain refinement typical of the solution and aged acicular microstructure increases the fatigue resistance with respect to the lamellar microstructure as fatigue strength increases with the reduction of the slip length.

The mechanical properties and strain-rate strengthening mechanism of single-phase TiZrHfNbTaMox (x = 0.25, 0.5, and 0.75) refractory high entropy alloys (RHEAs) upon dynamic loading are investigated. Dynamic compression with varying strain rates of 2100–6000 s−1 at room temperature are performed by the split-Hopkinson pressure bar (SHPB), and the dynamic yielding strength is about 1.3 times of the quasi-static one. Positive strain-rate sensitivity (SRS) on the yielding strength is available, and the work-hardening is weakened but the yielding strength is improved with increasing strain rates due to the adiabatic heating upon dynamic loadings and the dislocation movement resistance, respectively. Considering the adiabatic temperature rise converted by plastic deformation work at high strain rates, the flow behavior is characterized by employing the modified Johnson-Cook model. A semi-empirical Zerilli-Armstrong constitutive model is proposed to predict yielding strengths at various strain rate.

The effect of deformation temperature on microstructure evolution and mechanical properties of a near α titanium alloy during isothermal multiple die forging (IMDF) is systematically investigated. Present study describes the grain refinement mechanism at different deformation temperature by electron back-scatter diffraction (EBSD) characterization. The results indicated that the grain refinement as a result of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). With the decrease of deformation temperature, the mechanism of DRX converts from DDRX to CDRX. The formation of new grains by CDRX mechanism is mainly attributed to the progressive rotation of sub-grains. Moreover, the fresh grains resulted from DDRX process form along the serrated grain boundaries by bulging. It indicates that the superior tensile strengths of the IMDFed titanium alloy at room temperature (RT) and 650 °C are attributed to grain boundary strengthening and dislocation strengthening. However, grain boundary strengthening no longer works above 650 °C, leading to rapid decreases in tensile strengths.

In this paper, microstructure evolution, deformation texture and nanoindentation properties of an intermetallic Ti-43Al-9V-0.2Y (at. %) alloy have been investigated after hot rolled in α+β+γ (R#1) and β (R#2) phase field regions. The primary components of sample R#1 are (β+γ) mixture and (α2+γ) lamellar structure. With the temperature increases to 1250 °C, the microstructure of R#2 shows a new characteristic of martensitic α2 and acicular γ phase. And γ phase has different precipitation mechanisms by hot rolling at 1200 °C and 1250 °C. In R#1, γ phase is obtained through three provenances, which are the precipitating from β to form (β+γ) mixture, the precipitating from α phase to form (α2+γ) lamellar structure, and the remnant γ phase during cooling from α+β+γ phase field. However, for R#2, γ phase always nucleates and grows within β matrix. Meanwhile, microstructure evolution of R#2 is discussed. In addition, the increase in rolling temperature also results in a significant change of the fiber texture. Comparing with γ phase, β phase has the stronger texture, which is due to the formation of γ grain along the K-S orientation relationship in β phase. In R#1 state, β phase exhibits a typical {121} texture, while γ phase shows {031} and {112} texture. Aiming at R#2, β phase displays {010} cube texture, and γ phase has {-215} and Goss {110} texture. The hardness (H) and reduced elastic modulus (Er) are investigated by nanoindentation. The (β+γ) mixture structure in R#2 has the highest H (12.63 GPa), whereas the Er is related to the microstructure composition.

In this study, a Ti composite reinforced with 5 vol. % (TiBw + TiCp) was fabricated by an in situ casting route. Open die forging in (&alpha, + &beta, ) phase region was conducted on the composite casting. The microstructures of the as-forged composite pancake are inhomogeneous in terms of matrix microstructure and distribution of reinforcements. The matrix grains are gradually refined from the periphery to centre of the pancake. The reinforcements TiBw and TiCp tend to be uniformly distributed in the centre region. It is suggested that the microstructure difference can be mainly ascribed to the temperature variation from the periphery to the centre. The tensile testing results show that the centre region of the composite pancake exhibits higher strength than the peripheral region. The mechanical behaviour of the composite pancake with the temperature is discussed.

This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s−1. The flow stress decreases with a decreased strain rate and an increased temperature. A constitutive equation was established for this alloy and the dependence of activation energy on temperature and strain rate is discussed. We further proposed a processing map using the dynamic materials model. On the processing map various domains of flow stability and flow instability can be identified. The deformation mechanisms associated with flow stability regions are mainly dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow instability is manifested in the form of the band of flow localizations. The optimum processing conditions are suggested such that the temperature range is from 780 to 880 °C and the strain rate ranges from 0.001 to 0.01 s−1.

The microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si fiber were investigated. When the rotation speed increased from 2000 to 2600 r/min, the appearance of the wire was uniform with no Rayleigh-wave default. The structure was mainly composed of fine α2 (α) phase dendritic crystal and a second phase between dendrite arms and grain boundaries. The precipitated second phases were confirmed to be Ti5Si3 from the eutectic reaction L→Ti5Si3 + α and TiB. As the lower content of Si and higher cooling rate, a divorced eutectic microstructure was obtained. Segregation of Ti, Nb, B, Si, and Al occurred during rapid solidification.