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A Q345 steel butt-welded joint was manufactured using laser–arc hybrid welding (LAHW) technology, and its microstructure, microhardness, and residual stress (RS) distribution were measured. Using ABAQUS software, a sequentially coupled thermo-metallurgical-mechanical finite element method was employed to model the welding RS distribution in the LAHW joint made of Q345 steel. The effects of solid-state phase transformation (SSPT) and transverse restraint on the welding RS distribution were explored. The results show that a large number of martensite phase transformations occurred in the fusion zone and heat-affected zone of the LAHW joint. Furthermore, the SSPT had a significant effect on the magnitude and distribution of RS in the LAHW joint made of Q345 steel, which must be taken into account in numerical simulations. Transverse restraints markedly increased the transverse RS on the upper surface, with a comparatively minor impact on the longitudinal RS distribution. After the transverse restraint was released, both the longitudinal and transverse RS distributions in the LAHW joint reverted to a level akin to that of the welded joint under free conditions.

Carbon/Carbon (C/C) composites exhibit excellent mechanical properties at high temperatures, making them widely used in aerospace, such as the leading edges of spaceplane wings and the nose cones of hypersonic aircraft. However, damage caused by rain erosion to C/C composites affects their mechanical properties and poses significant challenges during operational service periods. A jet impingement test platform was employed to conduct single and multiple water-jet erosion tests on three-dimensional orthogonal C/C composite materials and to investigate the residual mechanical properties of the specimens after jet impact. The damage was characterized using optical microscopy, scanning electron microscopy, and X-ray computed tomography. The results showed that the damage types of the C/C composite materials under water-jet impingement included fiber bundle fracturing, delamination, and debonding. The extent of erosion damage was positively correlated with the jet velocity and diameter. The changes in the multi-jet damage indicated a cumulative expansion process, and z-directional fiber bundles exhibited superior resistance to jet impact damage propagation. The results of the three-point bending tests showed that the greater the initial impact damage, the lower the residual mechanical properties of the materials, and the residual strength of the specimen suddenly decreased when damage occurred at the back of the specimen.

A selective laser-melted Al–Mn–Sc alloy with 99.9% relative density has been obtained in this work through systematic process optimization. The as-fabricated specimen had the lowest hardness and strength, but the highest ductility. The aging response has shown that 300 °C/5 h is the peak aged condition, and it had the highest hardness, yield strength, ultimate tensile strength, and elongation at fracture. Such a high strength was attributed to the uniformly distributed nano-sized secondary Al3Sc precipitates. A further increase in aging temperature to 400 °C resulted in an over-aged condition, which contained a reduced volume fraction of secondary Al3Sc precipitates and resulted in a reduced strength.

In order to fabricate homogeneous large-scale Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy bulk with fine and equiaxial β grain, we performed a series of multi-axial α + β field forging with 62 forging cycles on the large-scale Ti-5553 billet by using 12.5 MN high-speed hydraulic press. The β-annealed microstructure was the starting microstructure of the billet. After the 6th forging cycle, β grain deformed dramatically, and the grain-boundary network developed within the irregular β grain. As the forging cycle increased to 44, the volume fraction of the fine and equiaxial β grain that is less than 20 μm, which is caused by dynamic recrystallization, increased gradually. However, the incomplete dynamic recrystallization region within the original β grain could not be eliminated. As the forging cycle further increased, the volume fraction of the fine and equiaxial β grain did not increase. In contrast, the abnormal grain growth of the β phase occurred during 50th~62nd forging cycle. Here, we attribute the formation of the incomplete dynamic recrystallization region and the abnormal grain growth of the β phase to the high deformation rate of the α + β forging. The refining behavior of β grain and the abnormal coursing β grain, which is found during the multi-cycle multi-axial forging of large-scale Ti-5553 alloy billet, are seldom reported in the isothermal compression of small-scale Ti-5553 alloy specimen. The findings of the paper are instructive for improving the sub-transus forging strategy that is used to fabricate the large-scale homogeneity Ti-5553 alloy billet with fine and equiaxial β grain.

This paper investigates the influence of loading directions on mechanical performance, damage behavior and failure mechanisms of a mill-annealed Ti-6Al-4V (TC4) alloy thick plate at the strain rate of 2000/s. The plate possesses {11-20} texture and consists of globular α grain, fine equiaxial α grain, α laminate that is parallel to the normal direction (ND) of the plate and grain-boundary β laminate. The yield strength and the flow stress of the plate are not affected by the loading directions, while the fracture strain in ND is 38.2% and 32.2% higher than that in the rolling direction (RD) and the traverse direction (TD). As it is loaded in the RD and TD, the deformation mechanism of the alloy is dislocation slip. However, the deformation mechanisms in ND are dislocation slip and {10-12} twinning. The activation of {10-12} twinning could delay the formation of the adiabatic shearing band (ASB). Multiple adiabatic shearing bands (ASBs) form as the compression direction is in the RD and TD. In contrast, as the compression direction is in ND, only one ASB could be observed. The dramatic adiabatic shear could not result in the dynamic recrystallization of the mill-annealed TC4 alloy but could lead to the formation of nano-sized α laminate. The compressive fracture mechanism of the alloy plate is the crack propagation in the main ASB, which is not affected by the loading directions. Here we attribute the superior dynamic failure strain in the ND of the plate to the {10-12} twinning induced by {11-20}α texture, cooperative deformation ability of the α laminate and higher shear strain within the ASB. The findings of our work are instructive for reducing foreign object damage to mill-annealed TC4 alloy fan blades.

Selective laser melting (SLM) can be used to manufacture complex parts, however, it is difficult to make large parts due to the size limitation of the SLM equipment. In application, smaller selective laser-melted (SLMed) Ti-6Al-4V (TC4) parts can be brazed or welded to form larger components. In the brazing, AgCuTi is often used to braze TC4. However, the wettability of AgCuTi on the SLMed TC4 should be evaluated before joining the SLMed TC4 parts. As a result, wetting and spreading tests and brazing experiments should be undertaken to successfully join the SLMed TC4 parts. In this study, a LINKAM TS 1500 high-temperature hot stage was used to test the brazability of the AgCuTi on the surface of SLMed TC4. Different temperatures and dwell times were used: (i) 850 °C 900 °C and 950 °C, holding for 120 s, were used to study the temperature effects; (ii) 20 s, 120 s and 200 s were used at 850 °C to study the dwell time effects. The R~t model was used to describe the wetting and spreading process. The results of this study can provide basic data for the joining of SLMed TC4 in industry.

The wetting kinetics of nickel-based filler metal (BNi2) over selective laser-melted Ti-6Al-4V (SLMed TC4) titanium alloy in a protective argon atmosphere is experimentally investigated using a real-time in situ hot stage equipped with an optical microscope. The spreading processes at different temperatures are similar, and the overall wetting/spreading process can be roughly divided into three stages: (i) an initial stage, (ii) a rapid spreading stage, and (iii) an asymptotic stage. Moreover, the wetting kinetics of the BNi2/SLMed TC4 system can be expressed by empirical power exponential function Rn~t with n = ~1. In the process of spreading, Ti-based solid solution (Ti(ss)) and intermetallic compound (Ti2Ni and TiB2) were formed at the interface within the reaction domain, and the phase transition of α’ martensitic to α-Ti and β-Ti also took place. The influence of elevated temperature on the spreading and wetting kinetics of the BNi2/SLMed TC4 system was studied, and the results show that the increase of temperature has a slightly promoting effect on the spreading, but a limited impact on the value of n. In addition, the spreading and wetting kinetics of BNi2/SLMed TC4 system are similar to those of BNi2 on conventional forged TC4 substrate.

The mechanical characterization of textile composites is a challenging task, due to their nonuniform deformation and complicated failure phenomena. This article introduces a three-dimensional mesoscale finite element model to investigate the progressive damage behavior of a notched single-layer triaxially-braided composite subjected to axial tension. The damage initiation and propagation in fiber bundles are simulated using three-dimensional failure criteria and damage evolution law. A traction–separation law has been applied to predict the interfacial damage of fiber bundles. The proposed model is correlated and validated by the experimentally measured full field strain distributions and effective strength of the notched specimen. The progressive damage behavior of the fiber bundles is studied by examining the damage and stress contours at different loading stages. Parametric numerical studies are conducted to explore the role of modeling parameters and geometric characteristics on the internal damage behavior and global measured properties of the notched specimen. Moreover, the correlations of damage behavior, global stress–strain response, and the efficiency of the notched specimen are discussed in detail. The results of this paper deliver a throughout understanding of the damage behavior of braided composites and can help the specimen design of textile composites.

In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i) Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii) The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii) The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv) Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time.

The effect of target phosphorus (P) content on the precipitates, microstructure, texture, magnetic properties, and mechanical properties of low-carbon (C) and low-silicon (Si) non-oriented electrical steel (NOES) was investigated and the influence mechanism was clarified. The results indicate that the precipitates in the steels are mainly aluminum (Al)-manganese (Mn)-Si-bearing complex nitrides ((Al,Si,Mn)xNy) and P-bearing complex nitrides ((Al,Si,Mn)xNy-P). Increasing target phosphorus content in the steels decreases (Al,Si,Mn)xNy, and increases (Al,Si,Mn)xNy-P. The number density of the precipitates is the lowest, and the average size of the precipitates and grain size of the finished steel is the largest in the samples with target P content at the 0.14% level (0.14%P-targeted). The average grain size and microstructure homogeneity of the steels are influenced by the addition of phosphorus. The content of the {111} component decreases, and the favorable texture increases after phosphorus is added to the steel. The magnetic induction of the steel is improved. Grain refinement and microstructure inhomogeneity lead to an iron loss increase after target phosphorus content increases in the steel. The best magnetic induction B50 is 1.765 T in the 0.14%P-targeted samples. The tensile strength and yield strength are improved owing to solid solution strengthening and the grain refinement effect of phosphorus added to the steels.

In this study, niobium was added into grain-oriented silicon steels, four Nb-bearing hot-rolled bands with Nb content range from 0–0.025 wt% were prepared and a detailed study of the micro characterization (microstructure, texture and precipitates) of hot-rolled bands was carried out by various analysis methods, such as EBSD and TEM. The results indicate that the precipitates in Nb-free steel are MnS and AlN; however, in the Nb-bearing steel they are MnS, AlN and Nb(C, N). The precipitates are finer and more dispersed in Nb-bearing steel, and a stronger pining force was obtained, which contributes to the finer microstructure and less recrystallization fractions of the hot-rolled bands. A larger volume fraction and stronger intensity of Goss texture is presented in steel with 0.025 wt% Nb due to the effective inhibiting effect. However, it has little effect on the changes of microstructure and texture when the Nb content is more than 0.009 wt%.

The alkaline components in red mud represent one of the crucial factors restricting its application, especially for the construction and building industry. The phase state of alkaline components has a significant influence on the dealkalization of red mud. In this work, an environmentally friendly acid leaching strategy is proposed by controlling the phase transformation of red mud during active roasting pretreatment. With a moderate roasting temperature, the alkaline component is prevented from converting into insoluble phases. After acid leaching with a low concentration of 0.1 M, a high dealkalization rate of 92.8% is obtained. Besides, the leachate is neutral (pH = 7) and the valuable metals in red mud are well preserved, manifesting a high selectivity and efficiency of diluted acid leaching. The calcination experiment further confirms the practicability of the strategy in the construction field, where the cementitious minerals can be formed in large quantities. Compared with the traditional acid leaching routes, the diluted acid leaching strategy in this work is acid saving with low valuable element consumption. Meanwhile, the secondary pollution issue can be alleviated. Hence, the findings in this work provide a feasible approach for the separation and recovery of alkali and resource utilization of red mud.

The effects of Nb content on precipitation, microstructure, texture and magnetic properties of primary recrystallized grain-oriented silicon steel were investigated by various methods. The results show that the precipitates in primary recrystallized sheets are mainly MnS, Nb(C,N), composite precipitates of MnS and AlN, and composite precipitates of Nb(C,N) and AlN. Adding niobium could refine the primary recrystallized microstructure. The steel with 0.009 wt% Nb possesses the finest and the most dispersed precipitates, which contributes to the finest primary recrystallized microstructure due to the strong pinning force. Adding niobium is beneficial to obtain large volume fraction favorable texture for grain-oriented silicon steel, and the effect of Nb addition is not obvious when the content is higher than 0.009 wt%. After final annealing, the steel with 0.009 wt% Nb shows the best magnetic properties, B800 = 1.872 T, P1.7/50 = 1.25 W/kg.