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As a high-performance lightweight structural material with superior strength, Ti55531 titanium alloy has been widely adopted in critical load-bearing components such as landing gears and airframe frames in the aerospace sector to achieve significant weight reduction. However, when the tensile strength of Ti55531 exceeds 1250 MPa, the fracture toughness typically falls below 50 MPa·m1/2. In this study, we addressed this challenge by precisely controlling the cooling rate during β annealing heat treatment. Through careful regulation of the cooling rate from the high-temperature β phase region to the aging temperature region, the Widmanstätten structure was successfully introduced into the Ti55531 titanium alloy. The experimental results demonstrate that this microstructure achieves a high tensile strength of 1252 MPa at a cooling rate of 2.5 °C/min, while simultaneously improving the elongation and fracture toughness to 9% and 84 MPa·m1/2, respectively. Microstructural analysis reveals that the basket-weave structure plays a crucial role in maintaining high strength. Meanwhile, the Widmanstätten structure effectively increases the energy required for crack extension by resisting crack propagation and altering the crack propagation path, thus significantly enhancing fracture toughness. These findings offer a promising pathway for overcoming the traditional trade-off between strength and toughness in high-performance titanium alloys.

Mechanical property anisotropy is one of the issues that are limiting the industrial adoption of additive manufacturing (AM) Ti-6Al-4V components. To improve the deposits’ microstructure, the effect of high-pressure interpass rolling was evaluated, and a flat and a profiled roller were compared. The microstructure was changed from large columnar prior β grains that traversed the component to equiaxed grains that were between 56 and 139  μ m in size. The repetitive variation in Widmanstätten α lamellae size was retained; however, with rolling, the overall size was reduced. A “fundamental study” was used to gain insight into the microstructural changes that occurred due to the combination of deformation and deposition. High-pressure interpass rolling can overcome many of the shortcomings of AM, potentially aiding industrial implementation of the process.

In this paper, we prepared titanium alloy through near-net forming green manufacturing, and then we quantitatively deformed the alloy and finally analyzed the deformation and fracture mechanism of the alloy. The result indicates that the deformation mechanism of those containing α + β lamellar structures is different from that of traditional structures. Especially, the lamellar structure can absorb the deformation energy of the alloy, thus improving the comprehensive properties of the alloy, of which the α phase mainly contributes to the plasticity of the alloy, while the β phase mainly contributes to the strength of the alloy. The two-phase combination will improve the mechanical properties of the alloy, which is completely different from the traditional strengthening mechanism of the basket structure and Widmanstatten structure.

Ti65 titanium alloy samples were fabricated by laser deposition manufacturing (LDM) technology, and defects, microstructures and mechanical properties of the LDMed Ti65 samples were investigated. Results showed that there were pores and lack of fusion defects in the sample deposited with low-power laser, and an obvious crack appeared at the bottom of the sample. While in the sample deposited with high-power laser, the pores were much smaller and no other detected defects. After annealing, the defects of these samples did not change markedly. Widmanstatten microstructure was exhibited and no strengthening phases were precipitated in the low-power laser-deposited sample. Lamellar microstructure was exhibited, and Ti 3 Sn strengthening phases and tungsten-rich phases were presented in the high-power laser-deposited sample. After annealing, both of them changed to basketweave microstructures, but α lamellas of the high-power laser-deposited sample were coarsened more notably. The average strength and plasticity of the high-power laser-deposited sample were higher than those of the low-power laser-deposited sample by 6 MPa and 1.4%, respectively. After annealing, strength and plasticity of these samples were improved, and the average strength and plasticity of the high-power samples were still higher than those of the low-power samples by 22 MPa and 3.9%, respectively. The microhardnesses of the as-deposited and annealed samples deposited with high-power laser were greater than those of the corresponding samples deposited with low-power laser.

The α variant selection and microstructure evolution in a new metastable β titanium alloy TB17 were studied in depth by DTA, microhardness, XRD, SEM, and EBSD characterization methods. Under the rapid cooling rate conditions (150 °C/min–400 °C/min), only a very small amount of granular αWM (α Widmanstatten precipitates within the grains) precipitated within the grains. The secondary α phase precipitated in the alloy changed from granular to fine needle-like at moderate cooling rates (15 °C/min–20 °C/min). When continuing to slow down the cooling rates (10 °C/min and 1 °C/min), the αGB (α precipitates along the β grain boundaries), αWGB (α Widmanstatten precipitates that developed from β grain boundaries or αGB) and αWM grew rapidly. Moreover, the continuous cooling transformation (CCT) diagram illustrated the effect of cooling rate on the β/α phase transition. EBSD analysis revealed that the variants selection of α near the original β grain boundary is mainly divided into three categories. (i) The double-BOR (Burgers orientation relationship) αWGB colonies within neighboring β grains grow in different directions but have the same crystallographic orientation. (ii) The double-BOR αWGB colonies within neighboring β grains have different growth directions and different crystallographic orientations. (iii) The double-BOR αWGB colonies within the same grain have the same growth direction, but different crystallographic directions. And these double-BOR αWGB colonies correspond to two variants of the given 0001α//110β.

In this study, the tensile properties and impact properties of TA2 welded pipes at different temperatures were tested and the microstructural differences between the base metal and the weld were analyzed. The results showed that the yield strength of the welds of both welding processes was higher than that of the base metal and the elongation was more stable. Welds affected by magnetic fields had more stable shrinkage and higher impact toughness. The difference in mechanical properties of the three samples came from the difference in structure. The base metal had a fine equiaxed structure, the ordinary K-TIG welding seam had a thicker Widmanstatten structure, and the magnetic field K-TIG welding seam had a finer Widmanstatten structure.

A petrochemical company’s pipeline ruptured in the flowmeter bypass of the main steam pipeline during a steam blowdown before commissioning, resulting in material failure and inoperability. The cause of the pipe rupture needed to be detected experimentally. To study the failure in the steam pipeline of a flowmeter of bypass rupture, visual inspection, mechanical properties testing, chemical composition analysis, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Mechanical property. The experiments confirmed the reason for the bypass rupture of the 15CrMoG steam pipeline: improper heat treatment transforms the material’s structure, and the pearlite spheroidization (PC) leads to the deterioration of the material’s mechanical properties. The main manifestations are as follows: the grains in the superheated zone of the welding exhibit a coarse morphology, and a distinctive superheated Widmanstatten structure is formed due to rapid cooling, resulting in a significant reduction in material plasticity and impact toughness. High-temperature oxidation occurs, accompanied by localized enrichment of Cr-element in certain areas, while other regions experience Cr depletion, resulting in the deterioration of material properties.

This study aims to compare the microstructure of 17–4 PH stainless steel (SS) manufactured via laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED) in non-heat treated (NHT) and heat treated conditions. In addition, the room-temperature tensile behavior of heat-treated L-PBF and LP-DED 17–4 PH SS has been investigated and compared with that of the wrought counterpart with the same heat treatment conditions. The results show that the L-PBF specimens have a finer microstructure (ferrite + lath martensite) than the LP-DED ones (massive ferrite + Widmanstätten ferrite) in NHT condition. Electron backscatter diffraction analysis shows that the L-PBF and LP-DED specimens have twin-based substructure lath martensite after heat treatment. Despite the lower tensile strength of the LP-DED specimens compared with the L-PBF ones, the ductility of peak-aged LP-DED specimens was reduced due to the presence of the δ-ferrite phase having a significant plastic deformation incompatibility with the martensite.

The mechanisms of microstructure transformation and mechanical anisotropy of laser-MIG hybrid additive manufacturing TC11 titanium alloy after solution aging treatment are investigated. In this paper, different solution temperatures and cooling modes are applied to tailor the microstructure and improve high-temperature properties and anisotropy. The result shows the microstructure of the samples in the as-deposited state is dominated by a widmanstatten structure composed of lamellar α clusters. Following solution aging treatment, a large area of basket-weave structure is obtained in the samples. A major influence of spheroidization of lamellar α clusters and dynamic recrystallization on mechanical anisotropy is revealed. The heat-treated samples exhibit more superior combined strength, elongation, impact toughness. The hardness difference between the layers and mechanical anisotropy decreases. During high-temperature tensile tests, the tensile strength increases with rising solution temperature; while, the elongation shows the opposite trend. The tensile fracture exhibits abundant uniform equiaxed dimples, and the fracture mode changes from intergranular fracture to transgranular fracture. Solution treatment at 990 °C for 2 h followed by air cooling is considered to be the optimal heat treatment process. Consequently, it results in a high tensile strength of 811 MPa and an excellent impact toughness of 50 J, representing improvements of 16.08% and 71.08%.

As an important technology in additive manufacturing (AM), laser directed energy deposition (LDED) has gained increasing applications due to its high deposition rate, great volume density of formed parts, and simple system of manufacturing apparatus. Nowadays, an increasing number of aerospace components made of Ti6Al4V are being processed using LDED techniques to enhance material utilization and augment the freeform fabrication capability. However, as a crucial factor in determining the mechanical properties, predicting and controlling the microstructure morphologies of the AM processed Ti6Al4V components are still challenging. In this article, an integrated process-microstructure numerical model for phase transformation kinetics and α lath width evolution kinetics during the LDED process of Ti6Al4V components is proposed and validated. Firstly, the heat transfer model of the LDED process and its spatial multiscale considerations are introduced. Then, an integrated microstructural evolution model including the formation and dissolution of grain boundary α , Widmanstätten colony/basketweave α , martensite α ’ and β phases, and the coarsening kinetics of Widmanstätten colony/basketweave α lath is proposed, validated, and compared with the previous models through numerous experimental data. Finally, the thermal model is verified and then coupled with the integrated microstructural evolution model to investigate the microstructural evolution during the LDED process of a Ti6Al4V block. The simulated volumetric phase fractions and α lath width distribution closely match experimental observed phenomenon, including layer band distribution, interlayer microstructure characteristics, and martensite features on the sample cross-section. Therefore, the proposed integrated process-microstructure numerical model could be useful for engineers to understand and control the part-scale or interlayer-scale process-microstructure relationships in LDED-processed Ti6Al4V parts.