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Aiming at the problem of deterioration of the properties of beta titanium alloy welded joints due to many porosity defects and coarse grains, multi-vibrator ultrasonic-assisted laser welding (M—ULW) technology was used to improve the structure and properties of beta titanium alloy welded joints. The microstructure evolution, tensile strength, elongation, and fracture behavior of the weld joint were studied through scanning electron microscopy, electron back-scatter diffraction, and a universal testing machine. The results show that ultrasonic vibration has no effect on the phase composition of titanium alloy welds during ultrasonic-assisted laser welding. However, it caused all grains in the weld to be transformed into equiaxed grains, and the higher the amplitude, the finer and more uniformly distributed were the equiaxed grains. When the ultrasonic amplitude reached 20 μm, the fine equiaxed crystals were uniformly distributed throughout the weld, and the average grain size of the weld was 56.15 um, which is only one-third of that of the unultrasonicated laser welded joint. Ultrasonic refinement makes the joint grain size decrease, weakens the beta titanium alloy {200} direction weaving, increases the dislocation density within the weld; and increases the tensile strength of the welded joint. The tensile strength of the welded joints exceeded that of the base material by 907 MPa, and the elongation was significantly increased by a factor of 1.8 compared with that of the un-ultrasonicated laser welded joints, resulting in a shift of the fracture location from the center of the weld to the heat-affected zone.

This paper uses the SPH method to study snow disasters, including the snow flow model of a vertical water diffusion equation and heat balance equation. The advantage of the SPH method is that it can capture particles’ positions, which can be used to track the initial position distribution of hazardous particles. At the same time, a particle modeling method based on pixel value is proposed, which has certain advantages in dealing with the boundary modeling of different materials. In addition, snow disaster prevention and the control of classic embankment and cutting procedures were carried out. The final treatment results showed that the number of snow particles on the subgrade surface was reduced by about 90%. The validity and feasibility of the snow disaster simulation software based on the SPH method are verified by comparison with the experimental results.

The method of improving the microstructure and thus the properties of alloys by adjusting their composition has been widely used in the study of high entropy alloys (HEAs). However, most studies have focused on improving the properties of HEAs with face-centered cubic (FCC) or body-centered cubic (BCC) structures by adjusting the contents of elements such as Ni, Al, Ti, Cr, Mn and Mo. The doping of B, Mg and Zr also has a certain effect on the mechanical properties of HEAs. In this paper, the phase structure, microstructure, and mechanical properties of Ni45.5Co22Fe22Al5Ti5 HEA doped with B, Mg, and Zr were investigated. The results demonstrated that the three-phase structures of FCC matrix, L12 precipitate, and BCC phase were present in all the as-cast HEAs of Ni45.5Co22Fe22Al5Ti5×0.5 (X = B, Mg, and Zr). The microstructures of the as-cast alloys showed typical dendritic and inter-dendritic architecture. The maximum hardness was found in the alloy doped with B element, with a value of 433 HV. During the compressive test at room temperature, neither the Mg0.5 HEA nor the Zr0.5 HEA cracked until the load limit, but the B0.5 HEA cracked at a compressive strain of about 12%. B0.5 HEA had the highest compressive yield strength of the three alloys, followed by Zr0.5 HEA, while Mg0.5 HEA had the lowest, with values of 1030 MPa, 754 MPa, and 628 MPa, respectively. The work is expected to provide a boost for the research on the optimization of the properties of new HEAs reinforced by precipitation of L12 phase by providing a simple solution-microalloying method.

In this study, the cold rolling microstructure and static recrystallization mechanism of the high strength titanium alloy Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe were systematically investigated. Results show that the cold rolling microstructure is mainly composed of the elongated deformed β grains containing micro-shear bands. After annealing at 815 °C for 2 min, the fine SRXed grains are observed, mainly concentrated in the micro-shear band, the grain boundary and the interior of the deformed grain. The sub-grain structure obtained by static recovery inside the deformed grain produces continuous SRX during the annealing treatment. Meanwhile, geometric and discontinued SRXed grains are also observed in the large deformed β grain and at the trigeminal grain boundaries, respectively. Many ultra-fine grains appear inside the micro-shear band, exhibiting a phenomenon of the micro-shear band assisting SRX. With the increase in the annealing holding time, the elongated β grains are significantly refined and the degree of recrystallization is continuously improved. In addition, the recrystallization behavior also results in a significant change in the fiber texture. With the extension of the annealing holding time, the rolling texture type evolves gradually, with the {111} γ-fiber texture to weak α-fiber, γ-fiber, and Goss-fiber.

To further improve the mechanical properties of the as-cast 7.5 vol.% TiBw/Ti–6Al–2.5Sn–4Zr–0.7Mo–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 α phases decreases. The lamellar microstructure demonstrates excellent fracture toughness due to deflection of the crack propagation path.

The hot deformation behavior and microstructure evolution of a 7.5 vol.% TiBw/near α-Ti composite with fine matrix microstructure were investigated under the deformation conditions in a temperature range of 800−950 °C and strain rate range of 0.001−1 s−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−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 α and β phases. At 800−900 °C and 0.01 s−1 the matrix α 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 800−950 °C/0.001−0.01 s−1, which lead to CDRX of primary α grains or dynamic recovery (DRV) and dynamic recrystallization (DRX) of β phase.

In this study, the effect factors on the formation of lamellar structure for Ti-45Al-5.4V-3.6Nb-Y alloy and Ti-44Al-4Nb-4V-0.3Mo-Y alloy is discussed in detail. During heat treatment in different procedures, temperature was the common factor influencing the formation of lamellar structures of Ti-45Al-5.4V-3.6Nb-Y and Ti-44Al-4Nb-4V-0.3Mo-Y alloys. In the range of 1230 °C and 1300 °C, the volume fraction of lamellar structure in Ti-45Al-5.4V-3.6Nb-Y alloy was proportional to the annealing temperature. However, between 1210 °C and 1260 °C, the volume fraction of lamellar structure in Ti-44Al-4Nb-4V-0.3Mo-Y alloy deceased when temperature was located in the α + γ + β triple phase field and then increased when temperature was in the α + β binary phase field. Besides the influence of temperature, the lamellar structure formation of Ti-44Al-4Nb-4V-0.3Mo-Y alloy was also affected by the β-phase stabilizing element.

In this study, a Ti composite reinforced with 5 vol. % (TiBw + TiCp) was fabricated by an in situ casting route. Open die forging in (α + β) 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.