TA10 and Q345 were joined by explosive welding (EXW), electron beam welding with a transition joint prepared by explosive welding (EBXW) and electron beam welding (EBW) with V/Cu interlayers. The comparison of the corrosion resistance of the three different joints was performed by immersion test, potentiodynamic polarization test and electrochemical impedance spectroscopy test. The microstructures of the interfaces between titanium and steel of the three joints were significantly different. There were intermetallic compound layers composed of FeTi and Fe2Ti along with the explosive interfaces for EXW and EBXW joints, while the microstructures of the EBW joint were composed of Q345/Cuss/(Fe,V)ss/(Ti,V)ss + Cuss/(Ti,V)ss + Ti3Cu4/TA10. The results of all the corrosion tests showed that the corrosion resistance of the EBW joint was the worst among the three joints, and the corrosion resistance of the EXW joint was similar to the EBXW joint. The corrosion attack was mainly occurred on the steel side, while the titanium was protected on account of the galvanic corrosion between titanium and steel. The corrosion products were mainly composed of α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4, Fe8(O, OH)16Cl13 and Fe(OH)3.
Niobium alloy and nickel-based superalloy exhibit high strength and remarkable corrosion resistance, joining them to fabricate composite structures could help to realize their potential. Nevertheless, research attention devoted to the joining of niobium alloy with nickel-based superalloy remains scarce. This study investigates direct diffusion bonding of these two materials. The microstructure of the joint is characterized in detail, with the typical joint microstructure being identified as GH4099 / (Ni, Cr)ss + Ni3Nb + Cr2Nb / Ni3Nb / Ni6Nb7 / Nb alloy. With holding time fixed at 60min and diffusion pressure maintained at 15MPa, the effects of diffusion bonding temperature on the microstructure and mechanical properties of joints are examined within the range of 900-1150 ℃. An increase in bonding temperature results in the formation of different intermetallic compounds within the joint. The primary cause of joint fracture is the presence of Cr2Nb and Ni6Nb7. The tensile strength of the joint initially increases and then decreases with increasing temperature, reaching a maximum value of 204MPa. This work expands the range of methods for joining niobium alloys to nickel-based superalloys, enabling bonding without the introduction of additional elements.
Wire Arc Additive Manufacturing (WAAM) is widely recognized for its high deposition efficiency and material utilization; however, its forming accuracy and process controllability remain limited due to the strong coupling of heat and mass transfer. To decouple molten droplet behavior from the arc environment, a pulsed gas-pressure-driven physical simulation platform was developed for controlled droplet generation and mechanism investigation. Experiments were conducted over a temperature range of 700 °C to 1200 °C, with a nozzle diameter of 0.6mm, pulsed gas pressure of 26 to 42 kPa, and gas opening time of 30 to 70 ms. The results demonstrate that, under single-parameter regulation, critical thresholds at approximately 900 °C, 36 kPa, and 50 ms induce a transition from the multiple pulses per droplet mode to the one pulse per droplet mode, resulting in discontinuous variations in droplet size. To overcome this limitation, a multimodal coordinated control strategy combining pulsed gas pressure and gas opening time was proposed and experimentally validated. By enabling continuous tuning of effective energy input, gap-free and continuous regulation of droplet size was achieved, eliminating size discontinuities and expanding the stable control range. The proposed system provides an arc-decoupled and highly controllable platform for investigating molten droplet dynamics. The demonstrated coordinated control strategy offers a practical pathway for improving droplet transfer stability and dimensional accuracy in WAAM, and supports the development of intelligent droplet control in metal additive manufacturing.
High-strength pipeline steels are widely employed for long-distance energy transportation due to their superior strength, toughness, and weldability. However, maintaining the structural integrity of girth welds under complex mechanical loading and harsh environmental conditions remains a major concern. This review synthesizes current understanding of mechanical degradation mechanisms in high-strength pipeline girth welds, with emphasis on the interplay among metallurgy, welding processes, and service performance. Particular focus is placed on two key mechanisms, including weld strength mismatching and heat-affected zone (HAZ) softening, which govern strain localization and premature failure. The role of geometric factors (e.g., pipe diameter, wall thickness, and weld misalignment) and service conditions in influencing degradation are also critically assessed. The analysis highlights that conventional welding practices and existing standards do not adequately account for actual strength mismatch, HAZ softening, or their combined effects on strain distribution. Consequently, current qualification approaches may be insufficient to ensure long-term reliability. Key limitations in existing studies are identified, and future directions are proposed, including the need for improved strain-based design methodologies, advanced multiscale modeling, and localized property evaluation to optimize welding performance.
Argon tungsten arc welding of TiAl base alloy using Ti-30Nb (at.%) filler metals was conducted. The results indicated that sound TiAl welded joints were achieved with preheating temperature of 498℃. Microstructure and properties of the welded TiAl joints were investigated. A transitional reaction zone, primarily consisting of γ-TiAl and α2-Ti3Al, was observed at the interface between the weld zone and the TiAl base alloy. Due to the intense reaction between the TiAl base metal and the Ti-Nb filler metal, amounts of acicular intermetallic compounds were formed within the central region of the weld zone, consisting of α2-Ti3Al and B2 phases. The tensile fracture of the joints exhibited brittle cleavage pattern. The average tensile strength of the welded joints at room-temperature reached 372.6MPa, about 73.1% of the base metal (BM), with joint fracture occurred in the weld zone. Owing to the solid-solution strengthening effect of Nb, the joint tensile strength retained 326.6MPa at 700 °C, and 300MPa at 750 °C.
