Latest ArticlesIn the aerospace field, welding serves as the primary joining process for TA3 alloy components,and the microstructure and mechanical properties of its welded joints have a significant impact on the service safety of welded components. This study compares the tensile properties of the base metal and welded specimens and studies the deformation morphology before and after tension using scanning electron microscopy combined with electron backscatter diffraction. The results show that the microstructure of TA3 alloy is equiaxed α grains before welding, and massive, acicular and serrated α grains appear after welding. The yield strength (378 MPa) and tensile strength (458 MPa) of welded specimens are higher than that of base material specimens, but the elongation is lower. The reason is that after the base meterial sample is welded, the welding temperature has the effect of aging treatment on the sample. There exists aging hardening, and the grain size inside the weld area becomes smaller, which will increase the tensile strength. Because the microhardness of the weld zone is obviously higher than that of the base metal zone, the fracture of the welded joint is located in the base meterial zone. The deformation mechanism of the weld zone is stress-induced deformation twin (2)[3] and (12)[13], with a Schmid factor of 0.038, exhibiting high shear stress and strong coordination of grain deformation. Deformation twins (2)[3] also appear in the base material region, but the Schmid factor is 0.078, indicating a relatively high degree of stress concentration.
Carbon fiber reinforced thermoplastic composites(CFRTP) have superior comprehensive mechanical property,as well as rapid prototyping,weldability and recyclability.The application of CFRTP are gradually increasing in aerospace,vehicle manufacturing and other fields.Ultrasonic welding is recognized as one of the most suitable methods for CFRTP.With the increase of the application of CFRTP in aerospace main load-bearing structures,the discrete solder joints in the form of traditional ultrasonic spot welding are difficult to meet the requirement of the strength of them.Accordingly,foreign scholars have proposed ultrasonic continuous welding technology to realize the seam welding connection of CFRTP structures,which has not been reported in domestic literature.In this paper,the research results of CFRTP ultrasonic continuous welding are reviewed from four aspects:CFRTP ultrasonic continuous welding equipment,joint design,process characteristics and quality inspection.The scientific problems and technical bottlenecks to be solved in CFRTP ultrasonic continuous welding are discussed,so as to provide a reference for the development of CFRTP ultrasonic continuous welding technology of our country.
The β titanium alloy Ti-1300 is fabricated utilizing laser engineered net shaping (LENS) technology. This study systematically examine the microstructural evolution of the alloy along the deposition direction during the LENS process, and elucidate the intrinsic relationship between its mechanical properties and microstructure. The results indicate that the thermal cycling of each deposited layer in the LENS process has a profound impact on the microstructural evolution. Initially, columnar crystals are formed with a thickness of (15.6±1.2) mm, comprising approximately 20% of the total deposited thickness. Subsequently, these grains transform into equiaxed grains. Within the as-deposited grains, the microstructure undergo a transition from a basket-weave structure to a lamellar structure, and the discontinuous grain boundary α phase changes to a continuous grain boundary α phase along the deposition direction. Notably, the basket-weave microstructure imparts exceptional strength to the alloy. However, the continuous grain boundary α phase tends to promote intergranular fracture, resulting in reduced ductility.
The thinning is a trend in the development of high-end electrical steel. Although its iron loss can be further reduced, the larger cold rolling reduction and the surface effect can influence the microstructure and texture of the final product, thereby affecting the magnetic properties. The two-stage cold rolling method can optimize the texture and increase the proportion of {100} and Goss textures. The influence of processing parameters on the microstructure, texture, and magnetic properties of a 0.10 mm thick ultra-thin non-oriented electrical steel is investigated by the two-stage cold rolling method, with a focus on the role of surface effects during prolonged holding. The results show that cube and Goss textures coexist in the final sheets produced by the two-stage cold rolling method. Furthermore, when the combined reduction from the two stages falls within the range of approximately 75% to 81%, the resulting texture and magnetic properties are superior to those of samples with reduction combinations of 90%/50% and 50%/90%. Within the temperature range of 840-920 ℃, the influence of time on grain growth is greater than that of temperature, and grain growth is affected by the surface effect in all cases. During isothermal annealing at 920 ℃, the 0.1 mm thick sample exhibits a more significant surface effect compared to the 0.27 mm thick sample, meaning grain growth is significantly hindered; the average grain size after the annealing for 60 min could not exceed the sheet thickness of 100 μm. In contrast, the average grain size of the 0.27 mm thick sheet grows to 175 μm.
The mechanical properties of polymer matrix composites often decrease due to hygrothermal environment. The hygrothermal aging tests and the compression tests are carried out before and after aging on the T700/BP9916 composites plate with open-hole, and the open-hole compression(OHC) strength is obtained. The residual stress distribution in the specimen after hygrothermal aging is simulated by ABAQUS software. Based on the hygrothermal expansion behavior and linear relationship between mechanical properties and the moisture absorption, OHC tests before and after hygrothermal aging are simulated. The results show that the moisture absorption of the T700/BP9916 composites have typical Fick diffusion behavior, and the maximum load of the OHC after hygrothermal aging decreases by approximately 5.2%. The internal stress caused by hygrothermal aging is very small and have no impact on the strength. The relative mass increment-time curve of moisture absorption obtained from the FEM simulation is in good agreement with the experimental. The relative error of maximum load of OHC test between the simulated and the experimental value is only 0.88% with non-hygrothermal aging, and the relative error is 6.21% during the hygrothermal environment. The increase in error is due to the fact that only the linear relationship between hygrothermal effect and the linear decline of material properties is considered in the simulation calculation.
Interlayer crack is a significant obstacle to the wide-scale implementation of light-cured additive manufacturing in industrial applications. The formation mechanism of crack defects during the forming and debinding stages of the process is investigated and their effects on the properties of light-cured ZrO2 ceramics are analyzed. Furthermore, the study compares and analyzes the influence of exposure time and debinding rate on the distribution of cracks in ZrO2 ceramics. The research analyzes and compares the influence of exposure time and debinding rate on the distribution of cracks in ZrO2 ceramics. The results indicate that it is easier to obtain defect-free ceramic green bodies when the slice thickness matches the exposure layer thickness. Moreover, the study observes that the green body exhibits the least number of surface cracks when the debinding rate is set at 0.1 ℃/min. Consequently, the research achieves the successful production of ceramic parts with a density of 99% and a flexural strength of 450 MPa.These findings establish a solid scientific foundation and provide valuable technical guidance for the manufacturing and application of defect-free ZrO2 ceramics using light-cured additive manufacturing.
To address the evolving demands for the clean and efficient utilization of coal, efforts have been devoted to the research and development of C700R-1 nickel-based alloy rotor forgings for advanced ultra-supercritical steam turbine rotors. Concurrently, tests are conducted on the conventional mechanical properties and creep rupture properties of the trial-manufactured rotor forgings. The results show that the use of the closed upsetting+extrusion method enables the high-homogeneity forging of Φ850 mm forgings. The as-forged grain size of the developed large-section forgings ranges from grade 4 to grade 7, and the grain size after heat treatment is approximately grade 3. Due to the rapid cooling rate of the edge parts after solid solution, a large number of uniform and fine γ' phases precipitate in the subsequent aging process. Therefore, the tensile properties of edge position are slightly better than those of the heart and 1/2R position. The variation of tensile properties in different directions of edge position is small. The room temperature tensile strength can reach 950 MPa, the yield strength can reach 600 MPa, and the V-notch absorbed energy at room temperature is beyond 70 J at different positions after heat treatment. The tensile strength can reach 750 MPa, yield strength can reach 500 MPa at 700 ℃. The plasticity is higher than 25% at room temperature and 700 ℃. The creep life exceeds 7000 h in the condition of 700 ℃/300 MPa. Through the deformation mode of closed upsetting+extrusion and reasonable heat treatment process, the homogenization manufacturing of nickel base alloy forgings with a section grade of Φ850 mm, which provides key data for the subsequent manufacturing of full-size nickel base alloy rotor forgings.
Silicon carbide and 2024 aluminum alloy powders with average particle sizes of 14 μm and 15 μm are selected as the reinforcement phase and matrix alloy, respectively. SiCp/2024Al composites with volume fractions of 35%, 45%, and 55% are fabricated by hot isostatic pressing. The influence of aging treatment on the mechanical properties of the composites is investigated. The results show that aging treatment significantly enhances the hardness of the composites. Increasing the aging temperature and the volume fraction of SiC both shorten the peak aging time of the composites. When the aging temperature is increased from 160 ℃ to 190 ℃, the peak aging time of the composite with a 35% volume fraction is reduced from 9.5 h to 2 h. At 190 ℃, the peak aging time of all three volume fraction composites is shortened to 2 h. The precipitation strengthening of the matrix alloy during the heat treatment process results in higher flexural strength in the aged composites compared to the as-sintered composites with the same volume fraction. The higher the matrix alloy content, the more significant the strengthening effect. Among them, the peak-aged composite with a 35% volume fraction exhibits the highest flexural strength, reaching 901 MPa at 170 ℃. With the increase of volume fraction, the matrix alloy content decreases, reducing the ability of the material to alleviate local stress concentration through plastic deformation. Moreover, defects in the composites gradually increase. Therefore, both the as-sintered and heat-treated composites with a 55% volume fraction exhibit lower flexural strength. However, the micro-yield strength of the aged composites is higher than that of the as-sintered composites. The aged composite with a 45% volume fraction generally has the highest micro-yield strength, fluctuating in the range of 361-380 MPa, while the aged composite with a 55% volume fraction has the lowest micro-yield strength. The micro-yield strength of the composite with a 35% volume fraction initially increases and then decreases with increasing temperature, reaching its highest value (368 MPa) at 180 ℃, slightly higher than that of the composite with a 45% volume fraction under the same conditions.
With the improvement in aeroengine performance,critical components (such as centrifugal impellers) operate under high-temperature,high-stress,and complex load conditions. Geometric discontinuities (such as ventilation holes and fillet radii) have become weak points for fatigue failure. This study focused on TA19 material,preparing smooth and U-shaped notch specimens for low-cycle fatigue tests under high-temperature conditions. Fatigue life data have fitted using the Weibull distribution,and an improved iterative fatigue life model is proposed to address the limitations of traditional models in regions with stress concentration. The model incorporates the stress concentration factor (Kt) and first-order reliability theory for correction. The results indicate that due to stress concentration effects,U-shaped notch specimens exhibit more concentrated fatigue life distributions,whereas smooth specimens show greater variability. The Kolmogorov-Smirnov test verifies that the data conforms to the Weibull distribution characteristics. The revised model significantly improves the prediction accuracy,with most of the predicted data falling within±1.5 times the scatter band. Additionally,P-S-N curves for different failure probabilities are constructed,providing a valuable reference for the reliable fatigue life prediction of complex structures.
The Fe-Ga alloy, a novel magnetostrictive material, distinguishes itself with a low driving magnetic field and remarkable magnetostrictive performance. As an alloy, it has garnered significant attention from researchers in solid-state physics and materials science due to its cost-effectiveness, superior mechanical properties, and high stability. These advantages make it particularly appealing for applications in micro-displacement devices, vibrators, and sensor technologies. The magnetostrictive characteristics of Fe-Ga alloys are influenced by various factors, including material texture orientation, magnetic domain distribution, alloying element additions, and, most importantly, the alloy’s phase structure. This paper provides an in-depth exploration of the phase structure of Fe-Ga alloy and comprehensively summarizes the impacts of various preparation methods on enhancing the preferred grain orientation 〈100〉. It further examines the effects of specific external magnetic fields and prestresses on altering the distribution of magnetic domains, as well as the influence of incorporating rare earth elements on improving magnetostrictive performance. Additionally, the article introduces recent research advancements regarding the influence of heat treatment on phase structure transformation and nanoprecipitate phase precipitation on the magnetostrictive properties of Fe-Ga alloys,contributing to advancing the understanding, promotion, and application of Fe-Ga alloy in the field of structure-function integrated precision device manufacturing.