Filler wire feeding is an effective strategy for optimizing weld morphology in laser welding. However, this approach significantly increases process complexity, where even a minor offset of the wire tip may induce welding defects. Using an integrated experimental and numerical approach, this study reveals the formation mechanisms of defects induced by wire offset in the longitudinal (Delta x) and transverse (Delta y) directions. The results indicate that the transverse wire offset has a more severe effect on weld morphology than the longitudinal wire offset. A transverse wire offset (Delta y = 0.5 mm) leads to asymmetric energy density and fluid flow, causing insufficient refilling of the keyhole and the formation of undercut defects on the wire offset side. When a longitudinal wire offset is introduced, two typical mass transfer modes are identified: the stable liquid bridge transfer mode and the unstable droplet transfer mode. With a positive offset (Delta x = 3 mm), underfill occurs at the initial stage due to the delay of wire feeding. Conversely, a negative longitudinal wire offset (Delta x =-2 mm) promotes a droplet transfer mode, where the periodic droplets disrupt the stability of the molten pool and result in humping defects. This study establishes a stable process window for wire offsets and elucidates that welding defects are governed by the coupling of asymmetric energy density distribution and molten pool dynamics, providing a scientific basis for optimizing the wire feeding process in laser welding.

Nickel aluminum bronze (NAB) alloy fabricated by directed energy deposition-arc (DED-arc) holds significant potential for marine applications. However, the influence of deposition path on its microstructure and mechanical anisotropy remains inadequately explored. In this study, cold metal transfer (CMT)-based DED-arc was used to fabricate NAB multi-layer multi-bead (MLMB) blocks with two deposition paths: inter-layer rotation of 180 degrees (SP-180) and 90 degrees (SP-90). To analyze the relationship between thermal cycles, microstructure heterogeneity, and anisotropy, macroscopic observation, microstructural characterization, and mechanical testing were conducted. The results reveal that DED-arc fabricated NAB develops three regions due to the MLMB thermal cycle: the internal region of the deposit layer (IRDL), the primary reheated zone (PRZ), and the secondary reheated zone (SRZ). Notably, the SRZ, exposed to dual thermal cycles, exhibits extensive kappa-phase aggregation and coarsening, which reduces local ductility and acts as a mechanical weak point by causing easy crack initiation and propagation. The deposition path directly controls the spatial distribution of the SRZ: SP-180 forms parallel SRZ bands along the Y-direction, while SP-90 creates a grid-like SRZ network in the XY plane. As a result of these distributions, SP-180 offers the highest tensile properties in the Y-direction and lowest in the Z-direction, and SP-90 eliminates in-plane (X/Y) tensile anisotropy but retains Z-direction weakness. However, both paths present limited strength anisotropy but significant ductility anisotropy. Overall, these findings provide a theoretical basis and process reference for selecting deposition paths and regulating anisotropy in DED-arc fabricated NAB.

In dissimilar welding, interfacial metallurgical bonding typically involves the formation of brittle intermetallic compounds (IMCs). Effective bonding without interfacial IMCs was reported only in a few combinations with high mutual solubility, such as Ag/Au, or in limited specific cases involving Al/steel welding, where interfacial amorphous phases formed. This study reveals a new metallurgical bonding mechanism in friction stir lap welding between immiscible AZ31 Mg alloy and DC01 steel, using high-resolution transmission electron microscopy. Rather than IMCs, AZ31 and DC01 were bonded via a nanometer-thick interfacial layer of Fe(Al) solid solution formed by Al atoms diffusing across the interface from AZ31. This mechanism was found highly effective, as evidenced by the lap shear strength of AZ31/DC01 joint, reaching 101 MPa, which is 78 % of the shear strength of AZ31 base material and 89 % higher than that of pure Mg/DC01 joint. Fracture predominantly occurred in AZ31 stir zone rather than right along interface.

TiAl-based alloys are considered promising high-temperature structural materials for aerospace and automotive engine applications due to their excellent mechanical properties. However, their inherent room-temperature brittleness and severe cracking susceptibility during additive manufacturing pose significant challenges. To address these issues, a novel TiAl-based composite was successfully fabricated via twin wire-directed energy deposition-arc by in-situ generating the Ti5Si3 phase through the co-feeding of commercially pure Ti (ERTi-2) and Al-Si (ER4043) wires. The microstructure evolution, mechanical properties, and underlying mechanisms were systematically investigated. Results show that the introduction of Si promotes the in-situ formation of Ti5Si3 with three distinct morphologies: elongated strips through the lamellae, interdendritic eutectic whiskers, and nano-scale precipitates within gamma lamellae or at alpha 2/gamma interfaces, forming an alternating layer-band-like microstructure along the building direction. Additionally, Si addition also reduces alpha 2phase content, refines lamellar colonies, causes lattice distortion, and facilitates stacking fault and gamma phase recrystallization, effectively suppressing cracks formation prevalent in the binary Ti45Al alloy. Compared with binary Ti45Al alloy, the Ti45Al2.3Si composite exhibits a 31.7% increase in ultimate tensile strength (from 303.2 MPa to 399.2 MPa) at 25 degrees C with comparable elongation, and a 116.8% increase (from 240.3 MPa to 521.1 MPa) at 750 degrees C accompanied by a 99.2% increase in elongation (from 2.46% to 4.9%). The strengthening is attributed to the synergism of grain refinement, solid-solution strengthening, second-phase strengthening and twinning-induced strengthening. This work provides a new strategy for the low-cost preparation of crack-free, low-density TiAl matrix composites with excellent comprehensive properties via additive manufacturing.

As a critical milestone of twin-wire directed energy deposition-arc (TW-DED-arc) technology, we present the first report on the excellent fatigue crack growth (FCG) performance of a Ti-48Al-2Cr-2Nb (TiAl-4822) alloy with a refined fully-lamellar microstructure. FCG tests conducted on standard compact tension specimens from two orthogonal directions under cyclic loading at 650 degrees C (R = 0.1) demonstrated a high fatigue threshold (similar to 8.0 MPam(1/2)) and low crack propagation rates compared to conventionally manufactured counterparts. The isotropic microstructure rendered crack resistance insensitive to deposition direction. In-situ tensile analysis under electron back scattered diffraction revealed that the enhanced performance originates from refined lamellar spacing, which promoted super-dislocation (SD) activity. Tortuous crack paths formed by mortise-tenon interlocks in inter-lamellar crack and zigzag trans-lamellar cracking, which effectively deflected cracks and dissipate energy. Furthermore, high volume fraction of gamma-phase (89.4%) with low stacking fault energy facilitated dislocation dissociation and deformation twinning (DT). These mechanisms collectively enhanced stress relaxation through twin interactions and SD immobilization, significantly improving crack resistance. This study not only reports a previously undocumented property profile but also underscores the technological potential of TW-DED-arc for manufacturing high-performance titanium aluminide components.

After years of research, laser powder bed fusion (LPBF) has developed as a high accuracy additive manufacturing (AM) method, thus has been considerably applied in aircraft component manufacturing. However, since LPBF has to be conducted in a high leveled inert gas atmosphere, the part size is significantly limited by the size of sealed box. Although meter-scaled LPBF equipment is reported to be available, it still challenges in fabricating efficiently of meter-scale dimensioned parts. In the present work, laser welding is used to assemble LPBF Ti-6Al-4V alloy 2.5 mm thickness thin sheets. Regarding the features of LPBF Ti-6Al-4V alloy, especially the grain microstructure and the inevitable pore defects, the influence of laser power is investigated systematically. The aim is to achieve high quality joint stronger than the LPBF base metal. Obtained results indicated that the improvement of laser power expands the weld width, and promotes the transformation of acicular α' martensite to α' lamellae, but increases the porosity. Tensile tests showed that the ultimate tensile strength of the laser welding joint achieves 1084.7 MPa when the laser power is 1750 W, in which case the specimen fractured in LPBF base metal rather than the weld zone or the heat-affected zone. The significance of the present work is twofold: On one hand, it provides an innovative way for LPBF to break through the bottleneck of limited manufacturing part size; and on the other hand, it clarifies how the laser power influences the welding joints in both microstructure and mechanical properties.

Welding of thick Ti-6Al-4V plates often produces coarse columnar grains and a wide heat-affected zone (HAZ), degrading joint strength and reliability. Recently, a tailored narrow-gap oscillating laser-TIG hybrid welding (NG-OL-TIG) technique has shown promise for high-performance thick Ti-6Al-4V welds. In this study, 100 Hz and 10 kHz pulsed currents were incorporated into NG-OL-TIG welding for 25 mm-thick Ti-6Al-4V plates to optimize microstructure and mechanical properties. Compared with direct-current (DC) welding, pulsed current improved microstructural uniformity and mechanical performance. At a high-frequency pulsed (HFP) current of 10 kHz, the HAZ width decreased by 26 % and the primary beta-grain width by nearly 50 %. In the fusion zone (FZ), the HFP current promoted a columnar-to-equiaxed transition (CET) by intensifying thermal fluctuations, characterized by a temperature gradient of similar to 370 K/mm, a cooling rate of similar to 300 K/s, and a solidification rate of similar to 2.6 mm/s. alpha'-martensite were refined by about 60 %, maintaining tensile ductility with only 3.7 % hardness increase. The -40 degrees C impact toughness at the fusion line (FL) reached 30 +/- 2 J, exceeding that of the base metal (BM). This study proves HFP's role in achieving high-quality thick Ti-6Al-4V welds during the NG-OL-TIG process.

The interconnection joints in space solar cells represent the weakest link in the cell array structure, and their operational reliability is vital for the longevity of the solar cell array. This study investigates the interconnected structures of space GaAs solar cells by analyzing the failure behavior and mechanisms of the joints under conditions of thermal shock and atomic oxygen (AO) irradiation. First-principles simulations reveal that the oxidation mechanism of Ag in an AO environment is temperature-dependent. Microstructural and X-ray diffraction analyses confirm that the oxidation products include AgO and Ag2O. Thermal shock testing has demonstrated significant degradation in both microstructure and mechanical properties. As the number of thermal shock cycles increases, cracks initiate at the edges of the interface and propagate toward the center of the joint. After 2000 cycles, cracks form along the Ag/Au interface, a result of stress concentrations stemming from mismatches in thermal expansion coefficients. Under the combined effects of AO and thermal cycling, AO oxidizes the Ag foils into Ag2O/AgO films. Additionally, the cyclic thermal stresses induced by thermal shock cause warping at the edges of the joints and lead to interfacial cracking, thereby reducing the effective contact area. Concurrently, thermal stress accelerates the peeling of the oxide film, exacerbating AO corrosion and further thinning the Ag layer, which makes it more prone to local deformation and stress concentration. These interconnected effects lead to cracks preferentially initiating at the joint edges and propagating along the interface, ultimately compromising the reliability of the interconnected structure.

Flexible solar cells, featured by lightweight and bendable properties, have emerged as the ideal material for next-generation spacecraft power systems. Solar cells are joined via interconnectors to form solar cell arrays, where joining quality determines system reliability and lifespan. However, conventional parallel gap resistance welding, a standard method for rigid solar cells, often leads to weak joints and cell damage when applied to flexible solar cells. Both the joining quality and cell damage are essentially governed by the thermo-mechanical synergistic action. However, the underlying mechanisms by which this action impacts interfacial joining and cell damage remain poorly understood. Without a sound theoretical basis, process development is severely restricted. This study first systematically elucidated the joining and cell damage mechanisms in parallel gap resistance welding of flexible solar cell-interconnector. Results indicated that the parallel gap resistance welding relied on instantaneous solid-state interdiffusion, requiring a peak temperature of similar to 700 degrees C to achieve atomic bonding and minimize interfacial defects (micro-voids and micro-gaps). Nevertheless, the high temperature induced softening and compressive deformation of the polyimide substrate in the weld zone, causing stress concentration and cracking in the semiconductor. Additionally, the thermal effect accelerated the GaAsIn-Au interdiffusion, forming Au-In liquid at the weld center; this liquid migrated outward and solidified, resulting in semiconductor-substrate debonding. Based on these findings, a parallel gap resistance soldering method was proposed. A single-micron Au-Ge alloy layer was plated on the interconnector as a solder layer to lower the required joining temperature and suppress the formation of brittle intermetallic compounds that degrade long-term reliability in space environments. Meanwhile, localized pulsed heating generated by the parallel gap resistance welder was utilized to achieve reliable interfacial joining with minimized thermo-mechanical impact. The joining mechanism was transformed from solid-state interdiffusion to liquid-solid interdiffusion coupled with epitaxial growth. This approach not only eliminated interfacial defects but also reduced the critical joining temperature to similar to 395 degrees C, effectively avoiding cell damage including cracking and debonding. Compared to parallel gap resistance welding, parallel gap resistance soldering achieved an similar to 11-fold increase in joint peel peak load and expanded the welding window by 200%. This work provides an innovative strategy for achieving intermetallic-free, defect-free and damage-free interconnection of flexible solar cells, and promotes the advancement of micro-joining technology for components sensitive to thermo-mechanical action and requiring long-term service in extreme environments.

Achieving controlled ferrite–austenite balance remains challenging in duplex stainless steel (DSS) fabricated by directed energy deposition via arc (DED-arc). Commercial wires ER2209 (8.6 wt% nickel (Ni)) yields > 65 % austenite, while ER2205 (5.2 wt% Ni) yields < 44 %, indicating optimal Ni levels lie between 5.2–8.6 wt%. However, DSS wires within this range have not yet been commercialized, leading to high trial-and-error costs. This study introduces a dual-wire DED-arc (DW-DED-arc) method, blending ER2205 and ER2209 wires for precise Ni control. The effects of heat input and Ni content are systematically investigated. When Ni content is 6.9 wt%, reducing heat input from 657 J/mm to 355 J/mm decrease austenite content from 81.2 % to 62.8 %, increasing tensile strength but reducing elongation. At constant 600 J/mm, lowering Ni content from 6.9 wt% to 5.2 wt% reduces austenite content from 78.0 % to 53.7 %, similarly increasing strength and decreasing elongation. Crucially, at 600 J/mm, DSS with 5.2 wt% Ni (53.7 % austenite) and 6.1 wt% Ni (61.3 % austenite) achieved near-balanced phases while exhibiting optimal tensile properties. The DW-DED-arc method effectively controls DSS microstructure and provides an innovative approach for developing new material compositions from existing wires, offering valuable insights for DED-arc fabricated DSS.

TiAl alloys are pivotal for aero-engine applications due to exceptional high-temperature properties, yet their inherent brittleness challenges traditional manufacturing. Additive manufacturing (AM) techniques, including electron beam melting (EBM), laser-based methods (LAM), and directed energy deposition-arc (DED-arc), offer innovative pathways to overcome these limitations. This review systematically analyses defects (cracking and Al loss) formation mechanisms of AM-fabricated TiAl alloys. EBM, with high preheating, effectively suppresses cracking but exacerbates Al loss under vacuum, while LAM minimizes Al evaporation yet suffers from thermal stress-induced cracks. DED-arc balances cost-efficiency and density but faces compositional inhomogeneity. Subsequently, we discuss microstructural characteristics, evolution mechanisms, and property features and failure mechanisms, including tensile strength, fracture toughness, creep, fatigue, oxidation, and wear resistance. Regulation strategies, such as process optimization, alloying and heat treatment, are also analysed systematically to address defects and enhance performance. Additionally, the current research status of AM-fabricated TiAlbased bimetallic structures is scrutinized, revealing challenges in interface bonding and properties enhancement. Finally, we outline future research directions, emphasizing the need for standardized AM processes, advanced alloying designs, and multi-energy field coupling techniques to achieve large-scale, crack-free TiAl components with superior mechanical properties. This review serves as a valuable reference for advancing high-quality AM of TiAl alloys.

Achieving high filling efficiency, low distortion, and defect-free welding of thick Ti-6Al-4V plates remains a major challenge in deep-sea manufacturing. In this work, the narrow gap oscillation laser–TIG (NG-OL-TIG) welding was developed and applied to 25 mm Ti-6Al-4V butt joints and further validated on a 50-mm thickness.This innovative technique combines the deep penetration and precision of laser welding with the thermal stability and filler compatibility of TIG, enhanced by laser beam oscillation that improves sidewall fusion and suppresses porosity. Firstly, optimized parameters achieved a welding speed of 0.2 m/min, over twice the speed of a traditional TIG welding for a thick Ti-6Al-4V. Secondly, a double-sided welding effectively reduced distortion. Thirdly, a metallographic analysis of the 25-mm joint showed continuous columnar grains and α′ martensite but no cracks or lack-of-fusion, with the joint’s strength exceeding the base metal. Finally, the same process was applied to a 50-mm-thick plate, achieving a defect-free welding without post-weld heat treatment, demonstrating both process scalability and technical superiority. This method provides a practical and reliable solution for the fabrication of critical thick titanium alloy structures.

Directed energy deposition-arc (DED-arc) has received significant attention as a promising metal additive manufacturing technology for fabricating medium and large-sized components. It is well known that the deposition path and process parameters must be configured before printing. The deposition path is obtained by slicing the 3D model and performing path planning based on shape parameters, while the process parameters determine whether the material can be deposited according to the desired geometry. Therefore, matching appropriate process parameters to the shape parameters is essential to ensure forming accuracy. This study proposes a method for creating a DED-arc process database to achieve parameter matching. First, a point cloud processing algorithm automatically extracts the geometry of single beads. Then, Random Forest classification and regression models are trained to determine the process parameter working envelope and predict bead geometry, respectively. Furthermore, a multi-layer single-bead overlapping model and a multi-bead overlapping model were developed to calculate the shape parameters of thin-walled and solid components based on an elliptic function representation of bead geometry. The resulting database enables parameter matching for thinwalled and solid components, ensuring the selected process parameters remain within the working envelope. An automated system was also developed to construct the DED-arc process database efficiently by conducting singlebead deposition experiments. Using this system, a CMT-based DED-arc process database for nickel-aluminumbronze alloys was successfully established, and the system's applicability to steel and aluminum alloys was verified.

Twin-wire directed energy deposition-arc (TW-DED-arc) has demonstrated feasibility in fabricating TiAl alloys. Unfortunately, it is hard to simultaneously guarantee the effective product utilization, and suppress the anisotropy. To break the trade-offs, a novel depositing strategy of an interpass remelting (IR) process, a representative of low-carbon-friendly and easy-to-operate processing route, is designed to fabricate Ti-48Al-2Cr-2Nb (TiAl-4822) alloy without chemical adjustment. The results indicated that the IR process promoted high-fraction equiaxed grains of similar to 90 %, much higher than that fabricated by constant process (CP). The IR process significantly increased the microstructural and mechanical isotropy of TW-DED-arc fabricated TiAl-4822 alloy. For microstructural isotropy, the IR process facilitated the growth of equiaxed grains with appropriate size, twin thickness refinement, and micro-segregation improvement. The IR process also strengthened the alpha(2)/gamma phase interface and gamma/gamma twinning boundaries. For mechanical isotropy, the IR process generated superior tensile properties along different directions of TW-DED-arc fabricated TiAl-4822 alloy wall compared to CP process and other fabricating techniques. Meanwhile, the exceptional strength retention of about 97 % at 650 degrees C was maintained. This work provides a new perspective to optimize microstructure and mechanical properties of TiAl-4822 alloys, facilitating further development of TW-DED-arc and its application in aerospace industry.

Thickness of the intermetallic compounds(IMC) layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints. However, the thickness of IMC layer can be only obtained by metallurgical microscopy, which is destructive and has to break down the weld. Therefore, it is crucial to find a reliable approach that can non-destructively predict the thickness of IMC layer in practical application. In the current study, Mg alloy and Al alloy were friction stir butt welded(FSW) under different tool rotation speeds(TRS) to obtain different thicknesses of IMC layers. As the TRS increased from 400 rpm to 1000 rpm, thickness of the IMC layer increased from 0.4 μm to 1.3 μm, the peak welding temperatures increased from 259℃ to 402℃, and the Z-axis downforces decreased from10.5 kN to 3.2 k N during welding process. Higher TRS would generally induce higher welding heat input, which promotes the growth of the IMC layer and the softening of base materials. The IMC layer formed through solid-state diffusion and transformation instead of eutectic reaction according to the welding temperature history and interfacial microstructure, and its evolution process was clearly observed by plan view. In order to incorporate the effect of dramatic change of welding temperature which is the characteristic feature of FSW, Psd Voigt function was used to fit the welding temperature histories. A new prediction formula was then established to predict thicknesses of IMC layers with considering sharp welding temperature change. Predicted thicknesses gave good agreement with measured thicknesses obtained experimentally under different welding parameters, which confirmed the accuracy and reliability of the new prediction formula. Based on this prediction formula, the time period of temperature higher than 200℃ during welding was found critical for the thickening of interfacial IMC layers.

High-frequency pulsed (HFP) gas tungsten arc welding (GTAW) has shown excellent performance in welding of aluminum alloys in recent years, which makes itself a promisingly potential technique for part manufacturing in aviation industry. However, existing researches generally focuses on the effect of a single parameter while lacks multivariable researches. Considering of the fact that gap and misalignment are inevitable in real part clamping, adaptive intelligent welding is usually used during automatic manufacturing, which means under the control of filler wire amount per length of a weld, other parameters including current, welding speed and wire feed speed during one single weld are changing according to the specific clamping situation. Therefore, the influence of specific energy input led by different welding parameters within one adaptive welding program on microstructure and mechanical property of the weld needs to be clarified. This study investigates the effect of welding heat input (ranging from 1048.3J/mm to 825.6J/mm within one adaptive welding program control) on the formation quality of 3.25mm thick 6061 aluminum alloy joints fabricated by HFP-GTAW with 4043 filler wire. According to the obtained results, non-monotonic relationship between heat input and porosity, with an optimal minimum of 4.92% achieved at an intermediate heat input of 856.8J/mm. The 21.2% decrease of energy input during welding process would reduce the average grain size in the weld center and adjacent to fusion line by 18.6% and 19.4%, respectively. The ratios between fluctuation range to minimum value in average yield and the relative ranges of yield strength and ultimate tensile strength across the tested heat inputs were 14.7% and 12.7%, respectively. The findings provide a general overview on how the microstructure and mechanical properties would fluctuate in an adaptively controlled HFP-GTAW fabricated aluminum alloy weld.

As aerospace technology advances, the urgent need for cost-effective, scalable space energy solutions has become apparent in constellation satellites. Silicon (Si) solar cells, known for their low cost and satisfying photoelectric conversion efficiency, present a promising low-cost alternative for space energy supplement. This study utilized parallel gap resistance welding (PGRW) to attach silver (Ag) foil made interconnectors to sintered Ag electrodes of Si solar cells, aiming to achieve an optimal solid phase diffusion bonding in the joining interface by carefully controlling the input energy. Compared to the traditional soldering process, the present PGRW technique on one hand possesses outstanding working efficiency, and on the other hand is solder-free which allows the manufactured solar cell panel to serve in more severe temperature changing environment. According to the obtained material characterization and tensile shear test results, the joint achieves an average 45° tensile-shear force of 1.0 N/point when PGRW input energy density is set at 55.70 J/mm2. The post-welded solar cells also demonstrate exceptional photovoltaic performance, which indicates the fact that the PGRW process has caused no damage to the Si solar cell substrate. During the PGRW process, the sintered Ag layer softens, and the porosity at the electrode joints reduces with increased energy input. The interface between the Ag foil and sintered Ag electrode of the Si solar cell shows a connection by solid-phase element diffusion rather than melting. This finding suggests that PGRW is a promising method for welding sintered Ag paste electrodes, providing critical data support for future space power generation using Si solar cells.

Although tailoring the Al-Si coating thickness is effective in the suppression of S-ferrite in the laser welding of AlSi coated press-hardened steel (PHS), the underlying mechanistic pathway from the coating thickness to the microstructure remains unclear. This study elucidates this pathway by unveiling the interdependencies among the molten pool dynamics, Al migration, and phase transformation through a combined experiment-simulation approach. The results reveal that a thinner Al-Si coating (15 mu m) enhances laser absorption efficiency to 54.06 %, inducing more vigorous fluid flow that homogenizes Al distribution and forms a fine-grained martensitic fusion zone (FZ). In contrast, the thicker coating (30 mu m) decreases the laser absorption efficiency (49.55 %), and the Al element is trapped around the upper fusion line and in the lower region of the FZ, stabilizing the formation of S-ferrite. Numerical simulation demonstrates that the thinner coating shortened the residence time of L -* S and promoted S -* y transformation, ensuring complete austenitization. Consequently, the thinner coating significantly improves the tensile properties of the weld joints, achieving a 19.9 % increase in ultimate tensile strength (from 1296.78 MPa to 1554.39 MPa) and a 190.4 % improvement in elongation (from 1.56 % to 4.53 %) compared to the thicker coating. This work provides mechanistic evidence for industrial adoption of thin Al-Si coatings as a cost-effective alternative in the laser welding of PHS.

Recently, additive manufacturing of titanium aluminide has attracted widespread attention. Since titanium aluminide is an ideal structure material for high-temperature, corresponding mechanical properties are of great significance. In present work, tensile properties from 25 degrees C to 1050 degrees C and fatigue properties at 650 degrees C were examined for the first time on twin-wire directed energy deposition-arc (TW-DED-arc) manufactured Ti-48Al2Cr-2Nb (TiAl-4822) alloy. Importantly, fracture characteristics and deformation mechanisms were systematically investigated. Similar with extensively investigated titanium aluminide, TW-DED-arc manufactured TiAl4822 alloy generally tends to decrease strength while increase elongation versus temperature during tensile process. Meanwhile, anomalous increase of strength is detected at 750 degrees C, and brittle-to-ductile transition temperature (BDTT) is around 850 degrees C. At 25 degrees C and 550 degrees C, gamma/alpha 2 lamellar interface and lamellar colony boundary as well as special microstructures are weak positions and susceptible to microcracking, and mechanical twining dominates deformation mode. By comparison, in temperature range of 650 degrees C-950 degrees C, gamma/alpha 2 interface and colony boundary are weaker, while deformation mechanism shifts to mechanical twinning and dislocation slip. Moreover, dynamic recrystallization (DRX) starts at 850 degrees C and further affects tensile behaviors, especially at 1050 degrees C. The fatigue limit (107 cycles) at 650 degrees C is approximately 335 MPa, ratio of which to tensile strength is calculated to be 0.71, indicating good fatigue resistance of as-manufactured TiAl-4822 alloy. Irrespective of stress level, crack prefer to initiate and propagate at gamma/alpha 2 interface and colony boundary. Both mechanical twining and dislocation slip are activated during fatigue process, but their morphologies vary with stress level. In sum, these findings provide a valuable reference for mechanical properties of additively manufactured titanium aluminide.