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Ceramic coatings containing two-dimensional materials (2D materials) provide effective protection for light alloys during wear, significantly improving their anti-friction performance. MoS2 has proven highly effective in enhancing the anti-friction performance of ceramic coatings, particularly when synthesized via plasma electrolytic oxidation (PEO). However, dislocation pinning due to the incoherent interfaces in MoS2/TiO2 coatings tends to cause localized stress concentrations and brittle fracture, requiring effectively improve nanomechanical properties by optimizing interface design. To address these issues, this study used ultrasonic-assisted PEO to disperse graphene oxide (GO), which provided more possibility for in-situ synthesis MoS2, ultimately resulting in MoS2 with modified interlayer spacing. The change in interlayer spacing induced dislocation evolution at incoherent interface, leading to dual interface formation. At MoS2 (0.534 nm)/TiO2 interface: dislocation dipoles evolve to create considerable distortion, facilitating releasing shear stresses and inhibiting crack propagations. This process is followed by dislocation annihilation, keeping to stable interfacial bonding. Additionally, the others form strong dislocation pinning to obstruct dislocation slip and enhancing deformation resistance at MoS2 (0.227 nm)/TiO2 interface. The combined effects of dual interfacial enhancements resulted in a 90.0 % reduction in friction coefficients of the MoS2/GO/TiO2 coating compared to the traditional ceramic coating. This facile technique provides a new strategy to fabricate self-lubricating ceramic coatings on light alloys, while the introduction of ultrasound during PEO offers valuable guidance for applying ultrasound in the synthesis of 2D materials.

Recently, there has been a growing anticipation for developing titanium alloys with low cost and excellent properties. Working towards this goal, a hierarchical phase structure comprising micron-scale α phase and micron-scale and nano-scale α′ phases in Ti-Al-V-Fe-Mo alloys was obtained via vacuum melting, forging, and solution treatment. The high-density hierarchical α′ martensite in Ti-Al-V-Fe-Mo alloys exhibits the high grain boundary density and the weak segregation of Fe and Mo. It promotes the formation of passivation films with low defect density and high film resistance on the alloy surface and the homogenous distribution of solutes within the matrix. This homogeneity significantly diminishes the tendency for pitting corrosion and enhances the overall corrosion resistance of the alloys. In addition, the analysed results of the valence electron theory model show the high electron density difference at α(0001)//β(110) is the primary reason for pitting in the interface of α/β. And the low strongest-bond energy of the α phase leads to its preferential corroded. The calculated results provide theoretical support for the experimental phenomena.

A prominent strengthened Y2O3 stabilized t-ZrO2 (YSTZ)/MgO nanocomposite coating is achieved by the plasma electrolytic oxidation (PEO) process and in-situ synthesized YSTZ reinforced phase with a quantitative control approach. The idea of activating double slip systemic semi-coherent interface dislocations in YSTZ/MgO nanocomposite coating to realize crack self-healing is proposed. High dislocation densities are associated with {101} YSTZ slip and {111} MgO slip system to coordinate interfacial deformation to stop crack initiation and propagation. This crack propagation path can absorb more fracture energy, providing more opportunities for crack deflection and bridge, which closes crack and realizes crack self-healing.

Ti-5321 alloy formed by laser cladding has good mechanical properties. By subsequent heat treatment of the alloy, not only can rich microstructures be obtained, but its strength, toughness, or damage tolerance performance can also be improved. Four typical microstructures, including basket-weave structure, large layer structure, ultrafine needle-like structure, and rod-like structure were constructed through different heat treatments. Basket-weave structure is composed of slender lamellar α, which has the best plasticity and toughness. Due to the large orientation difference between adjacent lamellar α and the susceptibility to multiple slip during crack propagation, this will greatly increase the crack propagation resistance and the curvature of the crack propagation path, which is beneficial for improving the damage tolerance performance of the alloy. Large layer structure is composed of large layer α and ultrafine needle-like α, with the highest strength. The orientation difference between adjacent large layer α is extremely small and prone to {10–11} pyramidal slip. The crack propagation resistance is reduced, which in turn damages the damage tolerance performance of the alloy. Ultrafine needle-like structure is entirely composed of ultrafine needle-like α, with high strength and extremely low plasticity and toughness. The orientation difference between adjacent needle-like α is single, making it prone to pyramidal slip and first-order pyramidal slip. The strength of rod-like structure matches well with its plasticity and toughness. There are multiple slip systems in rod-like structure and there is significant difference in orientation between adjacent α. Large orientation differences will have certain hindering effect on crack deflection.

Based on classical nucleation and growth theory, the phase evolution of martensite α′ phase of additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V-0.7Nb alloy under different annealing temperatures (600–960 °C) was systematically investigated. The results show that: Owing to insufficient diffusion of alloy elements during laser deposition, numerous β-stabilizing elements are retained in α′ phase and the microstructure is made up of 95.4% α′ phase and 4.6% β phase. According to TEM, EBSD, SEM/EDX results, the α′ phase can be divided into α′ phase containing more β-stabilizing elements (α′β), α′ phase containing more Al (α′Al). Under annealing condition, martensite decomposition tends to occur at the α′/α' interfaces and the matrix of α′β phase. In the matrix of α′β phase, fine adjacent α′ phase precipitates at β phase because a lot of β-stabilizing elements are consumed by precipitated β phase, thus improving the precipitation of adjacent α′ phase. The decomposition of α′ phase is controlled by diffusion of alloy elements. As the temperature increases, the diffusion of alloy elements and degree of α′ martensitic decomposition become more sufficient. When the Al content in the α′ phase reaches that in equilibrium α phase, the lattice parameters of α′ phase increase from a = 2.97 Å, c = 4.72 Å to a = 3.04 Å, c = 4.77 Å and meanwhile the α′ martensitic decomposition is finished.

Microstructure induced duplex Hall-Petch effect and its strengthening/toughening mechanisms in SiC@TC4 composites prepared by spark plasma sintering were systematically investigated in the current study. The microstructure characterization demonstrated that SiC additions significantly tailored the microstructure of SiC@TC4 composites. The SiC additions distinctly refined the grain size of SiC@TC4 composites. Increasing SiC addition also changed the microstructure of SiC@TC4 composites from the Widmanstätten type to the duplex type. Large SiC addition almost inhibited the formation of continuous αGB phase in SiC@TC4 composites. The growth of α phase was promoted due to the energy storage effect inside the TC4 alloy powders during the sintering process. SiC addition distinctly improved the tensile strength while seriously deteriorating the plasticity of SiC@TC4 composites compared to that of TC4 alloy. However, SiC@TC4 composites with various SiC additions exhibited the similar plasticity. SiC additions also resulted in different tribological properties of SiC@TC4 composites. The TC4-0.1SiC exhibited the worse tribological properties than that of TC4 alloy due to the softened matrix and low SiC addition. TC4-0.3SiC and TC4-0.5SiC composites exhibited the more excellent tribological properties due to the more SiC addition. A duplex Hall-Petch model was proposed to evaluate the multiple strengthening and toughening mechanisms in the SiC@TC4 composites.

Pure Ti and binary Ti–6Al alloy have been employed as the investigated targets of our research. The strengthening effects of Al element on strength and impact toughness in titanium alloy were systematically investigated. The experimental results indicated that the addition of Al element significantly improved the tensile strength while deteriorating the plasticity and impact toughness. Analysis of deformation mechanisms indicated that addition of Al element strongly inhibited the dislocation movement and deformation twinning in titanium alloy. The theoretical results demonstrated that the dissolution of Al atoms reset the atomic bond configurations and electronic structures of the α-Ti lattice. Therefore, the lattice resistance to dislocation nucleation and dislocation gliding was significantly improved which led to the strong strengthening effect of Al element in α-Ti. The lattice resistance to the shearing atomic motion of deformation twinning was also improved due to the dissolution of Al atoms. Moreover, the strengthening of Al element was revealed at the electronic level by employing the empirical electron theory (EET) of solids and molecules. The strengthening effects of Al element in titanium was also quantitatively evaluated according to the valence electron structure (VES) parameters. A prediction model for the tensile strength of α-type Ti-xAl alloys was proposed based on the quantitative strengthening of Al element. The high accuracy of the prediction model for strength of Ti-xAl alloy was verified by the average error (3.58%) between the computational strength and experimental results.

This work reveals the relaxation phenomenon induced by the localized atomic segregation during harmonic vibrations, which engenders substantial fluctuations in the dynamic modulus. The relaxation peak occurs when the dynamic modulus undergoes a sudden increase upon temperature reduction to −20 °C. This occurrence is caused by interstitial carbon atoms undergoing segregation and dragging dislocations to accumulate near grain boundaries. It leads to an increase in elastic strain energy, resulting in local stress concentrations and cracks initiation in heat affected zone (HAZ) and weld zone (WZ). The elevated value of the dynamic modulus within the HAZ facilitates a substantial internal accumulation of elastic strain energy. Consequently, this accumulation allows cracks to propagate rapidly along grain boundaries within the HAZ. Secondary cracks form in dispersed localized stress concentration zones in the WZ, which can inhibit crack propagation during harmonic vibration. This work will provide detailed insights and theoretical studies on the harmonic vibrational behavior of heterogeneous metals at low temperatures.

In this work, the trade-off between transformation toughening of ZrO2/TiO2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO2 (dt-ZrO2). A negative correlation between dt-ZrO2 and phase transition temperature (Ms) was also established based on strain energy and chemical free energy in ZrO2/TiO2 ceramic coatings. Interestingly, t-ZrO2 grains lost toughening effects when the dt-ZrO2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the dt-ZrO2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (011) t-ZrO2 and (110) TiO2 was enhanced and t-ZrO2 was completely stabilized when dt-ZrO2 reaches critical size. This work elucidates the effect of size effect on Ms and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature.

Strain hardening remains challenging for maintaining the plasticity of metals, especially those of high strength. The hetero-deformation induced (HDI) stress can effectively alleviate the problem, specifically with a large mechanical response mismatch. Accordingly, the strain localization and hardening in dual-phase steel consisting of ductile ferrite (F) and almost undeformed bainite (B) were investigated by calculating HDI stress (σh) based on the tensile load-unload-reload (LUR) hysteresis loop and modified equation. Of particular note is that strain localization first appears in the ferrite, and then transfers to the F/B interface during tensile LUR. The generated σh by the accumulation of geometrically necessary dislocations (GNDs) inhibits the mobile dislocation, thereby reducing the strain difference, which promotes the transfer of strain localization. The transformation of strain localization changes the hardening behavior from ferrite hardening to F/B interfacial hardening. The results state clearly that the σh enhances strain hardening while induced strain localization maintains tensile plasticity. Eventually, with the increase σh, the failure of dual-phase steel tends to transition from initial ductile fracture to brittle fracture.

Magnesium (Mg) alloys are popular among structural materials due to their high specific strength and good machinability. However, poor corrosion resistance limits its application in harsh environments, which requires ceramic coating to overcome the shortage of corrosion sensitivity. In this work, ZrO2/MgO ceramic coating was in situ synthesized by plasma electrolytic oxide (PEO) technology, coatings with different pore structures were fabricated by adjusting the pH of the electrolyte, and X-ray computed tomography (XCT) is used to quantitatively investigate the pore structure in ceramic coating. As the pH of the electrolyte increases from 3 to 12, the Zr(OH)4 colloidal particles from electropositive to electronegative charges. Electropositive Zr(OH)4 moves to the anode by diffusion, while electronegative Zr(OH)4 participates in the growth of the coating by electromigration. Due to the electromigration mode at pH = 12, the ZrO2 deposited around the pores caused a change in the pore structure from interconnected to isolated, which resulted in a reduction of the overall porosity to 8.06%. Isolated pores effectively prevent the penetration of corrosive media, resulting in the corrosion current density (icorr) being nearly 46 times lower than the coating with pH = 3. This study presents a novel strategy of adjusting pore structure to enhance the corrosion resistance of ZrO2 ceramic coating, which may have implications for various applications.

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a //ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial //ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.

In contemporary logistics, the deployment of fixed-wing unmanned aerial vehicles (UAVs) as a transportation platform is experiencing rapid advancements, garnering substantial application within numerous logistic operations with pronounced efficacies. There are notable impediments to the utilization of commercial logistic-oriented fixed-wing UAVs, including elevated procurement and maintenance costs, extensive maintenance intervals, and unsuitability for small-volume, low-altitude transport tasks. These factors collectively exacerbate the risk associated with enterprise procurement and elevate the cost–benefit ratio. This study introduces the design and fabrication of a cost-efficient UAV for logistic delivery purposes, constructed primarily from cost-effective wood materials. This UAV is engineered to ferry payloads of up to 1000 g across a predefined aerial route at an altitude of 40 m. Upon reaching the designated location, the UAV is programmed to initiate the identification of the drop zone, thereafter descending to facilitate the release of the cargo. To mitigate the impact force during the landing phase, the payload was encapsulated within a sponge-damping layer, thereby preserving the integrity of the transported items. The empirical findings from outdoor delivery trials underscore the UAV’s ability to precisely execute payload drops at the targeted locations, confirming its potential to fulfill the logistical requirements for the transportation and delivery of small-volume items in a cost-effective, low-altitude framework. This investigation contributes to the burgeoning discourse on leveraging ultra-low-cost UAVs in logistics, offering a feasible solution to the challenges of cost and efficiency in UAV-operated delivery systems.

In this paper, micro harmonic vibration was applied to the typical titanium alloys to clarify their damping performance at cryogenic temperatures. The effects of vibration modulus at different frequencies were elaborately analyzed, and the crack propagation mechanism was discussed. The increase of internal dislocations improves the damping performance and eventually leads to interface cracking, which is positively correlated with frequency. More importantly, dislocations of β phase aggregated at the interface, leading to interface cracks and transgranular fractures by stress concentration. Whereas, dislocations in the α phase are first activated and then glide toward the boundary to cause cracking, resulting in intergranular fracture. During harmonic vibration at 0∼−60 °C with 200 Hz, the crack propagation of α phase always has a hysteresis behavior compared with that of β phase. When ΔK = 0.137 MPa m1/2 (−60 °C, 200 Hz), the second crack tip of β phase is deflected in different directions, leading to higher harmonic vibration energy is consumption. As a result, the crack growth rate slows down and the damping performance reaches its peak. This contribution is expected to provide experimental data and theoretical support for the vibration damping behavior of typical titanium alloys at cryogenic temperature.

The occurrence of recrystallization will cause catastrophic damage to the structure of metallic single crystal, which can be avoided by choosing crystal orientation reasonably. In this work, the effect of crystal orientation on the recrystallization behavior of single crystal is investigated using multi-scale characterization method. The electron backscattered diffraction analysis shows that in mesoscopic scale, the recrystallization behavior of Mo–3Nb single crystal exhibits a strong orientation dependence, which the new recrystallization grains are produced in the -oriented single crystal, while the single crystal structure is still retained in other orientations. At the micro scale, the elongated dislocation cells with certain misorientations appear in the -oriented single crystal, while only the dislocation walls and parallel dislocation cells distribute on the single crystal with the and orientations, respectively. The length of dislocation lines in deformed single crystal with orientation is calculated using molecular dynamics to be 3491.22 Å, which is much longer than that of the orientation (1133.27 Å) and the orientation (2862.68 Å), suggesting a higher crystal distortion and easier recrystallization in the orientation. In addition to the coalescence mechanism of discontinuous sub-grains, the shear band also plays an important role in promoting recrystallization nucleation. This work provides reference value for the secondary processing of molybdenum single crystal, so as to obtain more excellent products and expand its potential application.

Ceramic coatings are in general a kind of brittle material because they are predominantly made up of ionic crystals that avoid dislocation motion caused by lattice distortion. In this regard, a remarkable toughened ZrO2/MgO nanocomposite coating is obtained by the plasma electrolytic oxidation (PEO) process and in-situ synthesized ZrO2 with quantitative control approach. It is revealed that the toughening behavior of the ZrO2/MgO coating is related to the coordination and diversion of lattice distortion at the metallic oxide interface, which induces distinct dislocation motion at the interface. The semicoherent interface between m-ZrO2 and MgO is verified to act as a buffer to realize toughening of the nanocomposite coating through dislocation slipping induced by lattice coordinated distortion. Simultaneously, significant interfacial lattice distortion transfer and dislocation pinning are discovered at the semicoherent interface between t-ZrO2 and MgO, which are beneficial to toughness enhancement of the nanocomposite coating. The results indicate that the toughening effect occurs along with dislocation slipping and pinning caused by lattice distortion of the ZrO2/MgO semicoherent interface, which enables the toughness of novel nanocomposite coating to reach 2.7 times of the traditional PEO coating.

This study examined the effects of different carbon nanomaterials on the mechanical and tribological properties of titanium matrix composites. Carbon nanotubes (CNTs), graphene nanoplates (GNPs) and graphene oxide nanoplates (GOs) reinforced Ti–6Al–2Sn–2Zr–3Mo–1Cr–2Nb–Si (TC21) titanium matrix composites were prepared by spark plasma sintering. In the three carbon nanomaterials, CNTs react with the TC21 matrix to form TiC, while GNPs and GOs react with the TC21 matrix to form a TiC coated GNPs/GOs sandwich structure, and the formation of TiC phase promotes the interfacial bonding of the composite. GOs/TC21 composites exhibit better strength and wear resistance than the other two composites. GOs/TC21 composite exhibits excellent mechanical properties, i.e., yield strength of 1043 MPa, the ultimate tensile strength of 1183 MPa and an elongation about of 8%. The wear loss of GOs/TC21 composite decreased by 24.2% compared to that of the TC21 alloy. The superior mechanical and tribological performances of GOs/TC21 composites are attributed to the TC21 matrix strengthening brought by the TiC particles/TiC coated GNPs/GOs sandwich structure and the lubricating properties of the residual GOs, which demonstrates that GOs is an ideal filler for TC21 alloy.

The influence of morphology of the Ti2Cu phase on biological corrosion and antibacterial properties of Ti-Cu alloy was investigated by micro-galvanic corrosion. Elongated “micro-galvanic cells” were formed between lamellar Ti2Cu phase (L-Ti2Cu) and α-Ti matrix due to the different Volta potentials. The corrosion rate (Vcorr) of L-Ti2Cu was twice that of granular Ti2Cu phase (G-Ti2Cu) because lamellar Ti2Cu phase had more galvanic interface. The release of Cu2+ ions in L-Ti2Cu was 55 % higher than G-Ti2Cu, reaching 99.5 % of the antibacterial rate in L-Ti2Cu and providing a great potential in clinical application for dental implants.

This paper reviews the dislocation slip behavior of α phase in α, near α and α + β titanium alloys dominated by α-Ti deformation under quasi-static loading. The relation of slip activity, slip transfer, slip blocking, twinning and crack initiation is discussed, mainly combined with in situ tensile technology. The slip behavior in Ti-alloys is analyzed in detail from the aspects of critical resolved shear stress (CRSS), grain orientation distribution and geometric compatibility factor m′. In addition, slip blocking is an important factor of the formation of twins and micro-cracks. The interaction of slip behavior and interfaces is clarified systematically. Finally, the insufficiency of current research, future research directions and key difficulties of study are also discussed.

Short-time processing route has been designed to manufacture cost-affordable and high-quality powder metallurgy (PM) metastable β titanium alloy, containing rapid powder consolidation (modified thermomechanical pressing), one-step thermomechanical processing (simple open die uniaxial hot forging by industrial press) and fast heat treatment (one-step annealing at various temperatures for only one hour). Based on comprehensive microstructure characterizations and mechanical property examinations, underlying microstructural evolution mechanism and microstructure-property relationship of the produced alloys were uncovered and elucidated thoroughly. Homogeneous macrostructure and fine-grain microstructure without undissolved particles and large pores are obtained for the alloy after thermomechanical powder consolidation as a result of the concurrent effect of external deformation and high-temperature diffusion. One-step open-die forging is verified to produce full-dense and sound PM alloy pancake with large-scale and high strength. Attributed to the harmonious concurrence of hierarchical α precipitation and heterogeneous grain structure, synergistic strength-ductility combinations are achieved for the alloy after specific processing and heat treatment with the tensile strength and strain at failure values of 1386.5 MPa/7.3% and 1252.3 MPa/9.0%, respectively. These strength-ductility combinations are comparable and/or even better than other metastable β titanium alloys prepared by some PM and ingot metallurgy approaches with relatively high cost and time consumption.

The impact toughness of a high-strength metastable β titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with two typical microstructures is studied by Charpy impact tests. The bimodal microstructure (BM) and the lamellar microstructure (LM) are obtained by the solution and aging treatments and the β annealing, slow cooling and aging treatments, respectively. In the impact crack initiation process, the deformation capacities of the primary α (αp) phase, secondary α (αs) phase and transformed β (βt) matrix in the BM are very different, and the stress gradient at the interface of the three causes the crack initiation. The lamellar α (αl) phase and βt in the LM satisfy the BOR relationship, and the effective slip transfer between α and β phases slows down the crack initiation. Meanwhile, the appearance of deformation twins in the LM improves the crack initiation energy. In the crack propagation process, the lack of coordinated deformation between the α and β phases in the BM leads to rapid crack propagation. In the LM, the deformation of αl and βt is relatively more coordinated, so the severe plastic deformation is only concentrated near the crack and at the interface. The secondary crack initiation and the crack propagation along the twin boundary reduce the stress concentration at the crack tip. The deformation twins and zigzag propagation path can improve the crack propagation energy. To summarize, the alloy with LM exhibits better impact toughness than the alloy with BM.

Gradient structure metals have good comprehensive properties of strength and toughness and are expected to improve the dynamic mechanical properties of materials. However, there are few studies on the dynamic mechanical properties of gradient structured materials, especially titanium alloys. Therefore, in this study, ultrasonic surface rolling is used to prepare a gradient structure layer on the surface of Ti-6Al-4V, and the quasi-static and dynamic compressive properties of coarse-grained Ti-6Al-4V (CG Ti64) and gradient-structured Ti-6Al-4V (GS Ti64) are investigated. The results show that a GS with a thickness of 293 µm is formed. The quasi-static compressive strength of GS Ti64 is higher than that of CG Ti64. Both CG Ti64 and GS Ti64 exhibit weak strain hardening effects and strain rate insensitivity during dynamic compression, and the compressive strength is not significantly improved. The lateral expansion of CG Ti64 is more obvious, while the lateral side of GS Ti64 is relatively straight, indicating that uniform deformation occurs in GS Ti64. The α phase in the GS produces dislocation cells and local deformation bands, and the lamellar structure is transformed into ultrafine crystals after dynamic compression. Both of them produce an adiabatic shear band under 2700 s−1, a large crack forms in CG Ti64, while GS Ti64 forms a small crack, indicating that GS Ti64 has better resistance to damage. The synergistic deformation of GS and CG promotes Ti-6Al-4V to obtain good dynamic mechanical properties.

Isothermal compression tests of Ti-5553 (Ti-5Al-5V-5Mo-3Cr) alloy, produced by a fast consolidation approach from blended elemental powder mixture, were performed on a Gleeble® 3800 thermal-physical simulator to investigate its hot deformation behaviour. The samples were compressed in a wide temperature range from 700 ºC to 1150 ºC and a moderate-high strain rate of 1 s-1, with the sample deformation degree of 30%, 50% and 70%, respectively. Flow instability occurred when the deformation temperature was less than 900 ºC. Dynamic recovery (DRV) accompanied by dynamic recrystallization (DRX) become the dominated mechanisms at the medium temperature range between 900 ºC and 1000 ºC, while almost only DRV features could be observed at high temperature (1050 ºC ~ 1150 ºC). Moreover, α phase globalization could be identified in the alloy deformed in (α+β) region. DRV, DRX, α globalization and the transformation of α to β phase were promoted with the increasing deformation degree.

The comparisons of mechanical properties and fracture behaviour between as-consolidated PM Ti-5553 alloy and as-cast IM Ti-5553 alloy were investigated through tensile, fracture toughness and impact toughness tests in this research. The slightly higher strength but much higher ductility and toughness can be identified in IM alloy specimens, which is also confirmed by the fracture behaviour of the specimens after mechanical tests. IM alloy specimens always exhibit the ductile dimple fracture mechanism in the different tests, while the fracture mechanism of PM alloy specimens indicates a high loading rate sensitivity, changing from the mixed ductile-brittle quasi-cleavage fracture into the brittle cleavage fracture mechanism accompanied by the remarkable decrease of impact toughness. The relatively low mechanical properties, especially the ductility and the brittle fracture behaviour of as-consolidated PM Ti-5553 alloy, are mainly explained by the differences in the initial microstructures between these two alloys.

To realize the systematic comparison of the hot workability and guide the further hot-processing of powder metallurgy (PM) and ingot metallurgy (IM) Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloys, the hot deformation behaviour and microstructural evolution of the two alloys were investigated at a wide temperature range of 700 °C–1100 °C and strain rate of 0.001 s−1-10 s−1. The activation energy maps and processing maps for both PM and IM alloys were constructed, as well as the specific deformation mechanisms were identified for each processing region. The results showed that PM alloy has lower deformation resistance, smaller activation energy and larger optimal processing windows than those of IM alloy. The dynamic α precipitation mechanisms in PM alloy were diffusional globularization and coarsening, rather than diffusionless shearing and fracturing in IM alloy. The extensive dynamic recrystallization (DRX) happened at 900 °C–1050 °C for PM alloy and at 1000 °C–1100 °C for IM alloy. The DRX process was dominated by discontinuous dynamic recrystallization (DDRX) for PM alloy while continuous dynamic recrystallization (CDRX) for IM alloy. Furthermore, PM alloy had smaller flow instability region than IM counterpart in the hot processing map. The schematic deformation mechanism maps were eventually developed for both PM and IM Ti-5553 alloys. Keywords: Ti-5553 alloy, Deformation mechanism differences, Powder metallurgy, Ingot metallurgy, Hot deformation behaviour, Microstructural evolution

Time series forecasting and analysis are widely used in many fields and application scenarios. Time series historical data reflects the change pattern and trend, which can serve the application and decision in each application scenario to a certain extent. In this paper, we select the time series prediction problem in the atmospheric environment scenario to start the application research. In terms of data support, we obtain the data of nearly 3500 vehicles in some cities in China fromRunwoda Research Institute, focusing on the major pollutant emission data of non-road mobile machinery and high emission vehicles in Beijing and Bozhou, Anhui Province to build the dataset and conduct the time series prediction analysis experiments on them. This paper proposes a P-gLSTNet model, and uses Autoregressive Integrated Moving Average model (ARIMA), long and short-term memory (LSTM), and Prophet to predict and compare the emissions in the future period. The experiments are validated on four public data sets and one self-collected data set, and the mean absolute error (MAE), root mean square error (RMSE), and mean absolute percentage error (MAPE) are selected as the evaluationmetrics. The experimental results show that the proposed P-gLSTNet fusion model predicts less error, outperforms the backbone method, and is more suitable for the prediction of time-series data in this scenario. [ABSTRACT FROM AUTHOR]