A high speed tandem TIG welding process was adopted to manufacture titanium welded tubes. A coupled electrode, arc and weld pool numerical model was also developed to investigate the temperature distribution, arc plasma and molten metal flows, and energy propagation of this welding process. Under the driving of the electromagnetic force, arc plasmas under the leading and trailing electrodes flowed towards each other. The Marangoni stress was much higher than the arc shear stress, and was the main driving force for the backward molten metal flow on the top weld pool surface. The calculated arc efficiency of this welding process was 79.8%. The high speed tandem TIG welding process can improve the manufacturing efficiency and quality of titanium welded tubes. © 2023 The Nonferrous Metals Society of China

To suppress the amount of brittle Ti-Fe intermetallics in Ti-6Al-4V/304L joints, this study adopts the variable polarity cold metal transfer arc-brazing method using ERCuSi-A wires. The effects of the thermal distribution strategy on the welding process, penetration ratio, microstructure, and tensile strength are investigated by varying the electrode positive/electrode negative (EP/EN) ratio. With the ratio decreasing, more energy is conducted to the wire, thereby decreasing the high-temperature holding time. When the ratio decreases from 8:1 to 1:8, the thickness of the Ti-6Al-4V/seam transition zone containing a Ti-Cu interlayer and Ti5Si3 intermetallic layer decreases from 118 to 81 mu m. Along with the decrease in the interlayer thickness, the joint tensile strength initially increases from 216.28 to 261.69 MPa and then decreases to 211.29 MPa. A high EP/EN ratio results in a thick Ti-6Al-4V/seam transition zone that includes a Ti5Si3 layer. A low EP/EN ratio results in a thin Ti-6Al-4V/seam transition zone that includes Ti5Si3 distributed in the grain boundary. Both conditions reduce the tensile strength of the joints. The highest tensile strength is obtained when the ratio is 8:8, under which a thin transition zone and concentrated Ti5Si3 intermetallic layer can be generated. (C) 2020 The Authors. Published by Elsevier Ltd.

A novel high speed tandem TIG welding process was introduced to join pure titanium thin plates with high efficiency and high quality. In order to reveal coupled mechanisms of arc, weld pool and microstructure in this novel welding process, coupled electrode, arc and weld pool numerical models were developed for both the single TIG welding and high speed tandem TIG welding processes, to study the arc and weld pool behaviors in a similar line energy input condition. In the high speed tandem TIG welding, the arc interaction causes expansions of arcs, and decreases of current densities; therefore, the maximum arc temperature, arc velocity, and energy fluxes on the top weld pool surface decrease to the values similar to these in the single TIG welding. Owing to a "Pull-Push" flow pattern caused by the Marangoni force and arc shear stress on the top weld pool surface between two arcs, the fluid flow and energy propagation of the weld pool become much stronger. The existence time of high temperature is shorter, and the stirring effect of the weld pool is stronger, so finer weld microstructures can be obtained in the high speed tandem TIG welding. (C) 2020 Elsevier Ltd. All rights reserved.

The laser welding of commercial grades of pure titanium plate TA2 with 0.5 mm was taken, and the back area of the molten pool was photographed by high-speed camera. Also, the reasons of back spatters were studied. Spatters on the back side of the plate have three main types: continuous spatters, periodic spatters and no spatters. All continuous back spatters are accompanied by the appearance of keyhole, and the keyhole can be observed at the moment when periodic spatters appear. The downward shear stress applied by the downward jet of metal vapor from the keyhole is an important reason for backside spatter. Increased laser power or welding speed will increase shear force, eventually contributing to more spatters. When the defocused distance is increased to 30 mm, the keyhole is completely obscured on the back side, so there is no spatter at this time.

In this paper, the microstructure optimization and mechanical property of joints are studied when the Cu, CuSi3, and CuNi10 wires are used to Cold Metal Transfer arc-braze TC4 to 304L. Based on the microstructure analysis and thermodynamic calculation, the existing state of Ti and Fe atoms are transferred from high brittleness Ti-Fe to less brittle Ti-Fe-Si intermetallics when the welding wire is changed from Cu to CuSi3 due to the lower Gibbs free energy of Ti-Fe-Si intermetallics. Furthermore, the (Fe, Ni) solution and Ti-Ni intermetallics with the lowest hardness are formed when CuNi10 wire is used. Thus, three Ti-Fe suppression mechanisms are concluded: suppressed by forming intermetallics and diffusion inhibition, suppressed by forming intermetallics, and suppressed by forming intermetallics and solution. Based on the microstructure optimization, the max hardness of intermetallics layer decreases from 769 to 654 Hv and the max tensile strength increases from 186.4 to 319.4 MPa. However, all cracks of the joints with different wires will initiate from the bottom of the seam and propagate in the TC4/seam transition zone due to the high Schmid factor. Besides, the crack propagation rate of more than 200 m/s can be in-situ measured by high-speed camera with 200000 fps. © 2020 Elsevier B.V.

Magnetic intensities from 0 to 18.0 mT and CuNi10 wire were employed in Cold Metal Transfer (CMT) joining of Ti6Al4V to 304 L stainless steel. The axial external magnetic field (EMF) could improve the wetting behavior and modify the microstructure of arc-brazed joints. A rotated bell-shaped arc was formed owing to the Lorentz force acting during the welding process, resulting in short arc length, wide arc width, and low temperature of the melting pool. The liquid metal in the melting pool exhibited an incomplete circular motion on the surface owing to the pulsed plasma shear stress and Lorentz force caused by the radial current and axial magnetic field. With increasing magnetic intensity, the inner layer containing beta +pi +phi (NiTi + NiTi2 + CuTi) and pi+psi+phi) (NiTi2+ CuTi2+CuTi) and outer layer containing gamma +Delta ((Cu, Ni) + TiNiCu) became thinner and more uniform because of the intense flow and short reaction time at high temperature. The microstructure on the 304 L side of the joints changed from columnar dendrites to coarsened grains. With increasing magnetic intensity, the tensile strength of the joints increased from 270.7 to 387.8 MPa. All the samples fractured at the Ti6Al4V/seam interfacial layer of the joints.

In this paper, multi-pass hot compression experiments of pure titanium TA1 was investigated with Gleeble-3500 thermal simulation test machine at an initial temperature of 880°C. The purpose is to investigate the effects of hot compression on the deformation of a electron beam cold hearth melting (EBCHM) single casting TA1 slab. The microstructure of the sample was analyized by metallograph and electron backscatter diffraction (EBSD), and the dynamic recovery was found to be the main recovery mechanism. The recrystallization nucleation mechanism were mainly bulging at grain boundary and merging of sub-grain. © Published under licence by IOP Publishing Ltd.

Wire feed speeds of 3.5, 4.5, and 5.5 m/min and offset positions of 1 and 2 were employed for this study with an ERCuSi-A weld wire. The microstructures of the joints, which include a Cu/Ti interface layer consisting of Ti2Cu, TiCu, and AlCu2Ti, a Cu-matrix seam consisting of Cu and petal-shaped Fe-Si-Ti intermetallics, and a Cu/Fe interface layer consisting of alpha-Fe and Cu, were studied. The formation enthalpy calculated from the Miedema model can explained the microstructure evolution mechanism. The interface thickness and ultimate tensile strength were found to increase with wire feed speed. The highest tensile strength of the joint was 294 MPa, fracturing at the Cu/Ti interface. Offsetting the welding torch to the TC4 side increased the amount and size of the Fe-Si-Ti intermetallics, degrading the tensile strength. Four fracture modes were proposed to differentiate the crack propagations in the joints, which were determined by the interfacial bonding strength and the Fe-Si-Ti intermetallics in the weld seam.

Dissimilar titanium alloy TC4/304 L stainless steel joints suffer from the brittle and inevitable FeTi and Fe2Ti intermetallic compounds. Cold metal transfer (CMT) arc-brazing method was used to join titanium alloy TC4 to 304 L stainless steel by using Cu, CuNi10, and CuNi30 wires. The effects of Ni addition on the microstructure and mechanical property were studied. With the addition of Ni, Fe-Ti intermetallic compounds was removed. TC4/seam interfaces containing TiNiCu, Ti2Cu, TiCu, TiCu4, and TiNi formed instead of those with Fe2Ti, FeTi, Ti2Cu, TiCu, TiCu2Al, and τ4 (Ti37Cu63-xFex). (Fe, Ni) dendritic grains and (Cu) solution formed instead of amount of Fe-Ti intermetallics in the seam and on the 304 L/seam interfaces. The reason is different intermetallic formation enthalpies and solution enthalpies calculated from Miedema model. Due to the thinner and less brittle TC4/seam interface layer, the highest tensile strength was 334 MPa when the CuNi10 wire was used. Excessive Ni content resulted in a reduction of strength due to the formation of an excessively thick and uneven TC4/seam interface. All joints fractured at the TC4/seam interface. © 2019

The anisotropy of wire-arc additively deposited nickel-aluminum bronze alloy is studied by microstructure observation and room temperature mechanical property testing. The applied heat treatments have effectively modified the as-fabricated {0 1 1} , {1 1 1}texture into {1 1 1}. According to the microstructures, the single tempering has resulted in lowest anisotropy while heat treatment with prior homogenization and quenching process induces even intensified annealing textures. However, as shown by the tensile tests, the quenching process is necessary for favorable mechanical properties in the wire-arc additive manufacturing fabricated nickel-aluminum bronze component; therefore, a balance between homogenization annealing and κ-phase precipitation is indicated. Meanwhile, the function of κ-phase precipitates on grain rotation and growth during post-production heat treatment is explained in detail. © 2019, Springer-Verlag London Ltd., part of Springer Nature.