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In order to explore the forming mechanism of direct energy deposition of magnesium-lithium alloy wire with high lithium content, this study introduces a novel approach utilizing Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM) to successfully fabricate thin-walled structures of LA103Z Mg–Li alloy. A comprehensive comparison was conducted to evaluate the microstructure and mechanical properties of different regions on CMT-WAAM samples, in addition to cast and rolled samples. The microstructure of CMT-WAAM samples is mainly composed of β-Li phase and fine needle shaped α-Mg phase, exhibiting a notable divergence from the microstructure observed in cast and rolled samples. It is noteworthy that the mechanical properties along the deposition direction exhibited significant variability in CMT-WAAM samples, but no significant anisotropy is discerned in the mechanical properties along the deposition and scanning directions. The discrepancies in mechanical properties across different regions are predominantly attributed to variations in grain size, and the size and proportion of the α-Mg phase and secondary phases, which are related to the low heat input and high cooling rate of the CMT-WAAM process. The mean tensile strength of CMT-WAAM samples is 159.5 MPa, marking a respective increase of 30.7% and 13.9% compared to cast and rolled samples. These findings underscore the outstanding strength of CMT-WAAM samples compared to conventionally formed samples. This study provides novel insights into additive manufacturing of dual-phase Mg–Li alloys for large-scale complex structures.

Wire arc additive manufacturing (WAAM) of Mg–Al-RE alloy is an essential technology for producing high-quality large-scale components with high manufacturing flexibility. In this study, WAAM was utilized to fabricate a thin-wall component made of Mg-8.2Al-0.6Y-0.4Ce (AE81) alloy. The microstructure and tensile properties of the fabricated component were investigated. The results showed that the as-built AE81 alloy exhibits superior isotropic tensile strengths and a homogeneous equiaxed α-Mg grains structure. Additionally, the alloy demonstrated a minimal growth in grain size after high-temperature solid solution treatment due to the presence of thermally stable Al11/rare earth (RE)3 phases at grain boundaries. Further ageing treatment induces the formation of high-density of β-Mg17Al12 precipitates within the α-Mg grains, resulting in a considerable precipitation strengthening effect. Consequently, the heat-treated AE81 alloy demonstrated significantly enhanced tensile strength of 280 MPa and acceptable ductility of 4.6%. The results also revealed that the formation of equiaxed grains during WAAM contributed to the isotropic mechanical properties. These findings can facilitate advancements in AM processes and the development of high-performance Mg alloys.

Wire and arc additive manufacturing (WAAM) technique has introduced a novel approach for producing complex Ti–6Al–4V parts with metric dimensions. However, the produced part leads to the development of a strong texture and anisotropic mechanical properties due to the formation of large columnar β grains. To resolve this issue, the plastic deformation of each deposited track through hammer peening was developed as a means to refine these large β grains. In this study, we have investigated an innovative approach to further enhance the efficiency of β grain refinement by minimizing the arc heat input associated with previous deposited layer, which is achieved by employing a C-type filler wire. Our findings reveal a notable enhancement in grain refinement efficiency through the utilization of a C-type filler wire with peening process, as compared to available conventional commercial round shape filler wire. Specifically, the employment of the C-type filler wire results in a reduced melt pool penetration depth of WAAM Ti–6Al–4V (3.3 mm), compared to the commercially available round shape (R-Type) filler wire (4.48 mm). Within the plastically deformed region by peening, fine and randomly oriented β grains are observed, extending to a depth of deformation reaching 844 ± 32.65 μm. Peening WAAM Ti–6Al–4V with the C-type filler wire leads to the development of isotropic mechanical properties in both horizontal and vertical directions, offering high strength due to the presence of small equiaxed β grains and thin α laths (0.56 ± 0.18 μm), in contrast to the use of conventional commercial round shape filler wire.

Mg-Gd-Y-Zn-Zr alloy is an important lightweight material in the aerospace field. Wire arc additive manufacturing (WAAM) provides a new route to fabricate large Mg alloy components. Here, a Mg-8Gd-4Y–1Zn-0.5Zr (wt.%) alloy was fabricated using WAAM based on the cold metal transfer (CMT) process. Subsequently, a short-time solid solution + aging treatment was designed to tailor the microstructure. In the as-fabricated condition, the microstructure mainly consisted of fine α-Mg, network (Mg,Zn)3(Gd,Y) eutectic phase, and lamellar γ′ basal precipitate. After 500 °C-1 h short-time solid solution, the eutectic phase rapidly dissolved, the long-period stacking ordered (LPSO) phase formed, and the fine grain was maintained. Due to the good deformation capacity of the fine grains and the kinking deformation capacity of the LPSO phase, the ductility was significantly improved from 5.2 ± 0.4% to 15.5 ± 1.1%. After further 200 °C-64 h artificial aging, dense β′ prismatic precipitates formed. Thanks to the synergistic strengthening of the fine grains and β′ prismatic precipitates, a yield strength of 242 ± 4 MPa was achieved. However, the kinking deformation of the LPSO phase was inhibited, resulting in a drastic decrease of ductility to 6.1 ± 0.5%. Overall, the combination of strength and ductility of the CMT-based WAAM-processed Mg-Gd-Y-Zn-Zr alloy under an optimized heat treatment regime can be superior to those of the cast Mg-Gd-Y-Zn-Zr alloys with similar contents of Gd and Y elements. This work can guide further performance optimization for WAAM-processed Mg-Gd-Y-Zn-Zr alloys.

Layered stainless steel samples were manufactured using Plasma Wire Arc Additive Manufacturing by depositing alternating layers of two dissimilar stainless steels onto an AISI 316L substrate. The selected materials were the M430 ferritic and M316L austenitic stainless steels. Comprehensive microstructural characterization in different areas, including interfaces between the two different materials, was achieved through optical microscopy and electron backscatter diffraction. Results revealed good weldability among the two-layered steels and on the substrate. Also, a gradient duplex structure was observed mainly at the layer interfaces, suggesting a nuanced blending of properties in the deposited zone. To establish a direct correlation with mechanical properties in the observed structures, macro and micro-hardness tests were conducted along the cross-section. These tests evidenced the presence of a harder phase along the interface compared to the individual materials. The microstructural analysis corroborated the presence of mixing between phases in conjunction with some areas of delta ferrite.

Wire-arc additive manufacturing (WAAM) technology offers an effective approach to fabricating complex metallic components. However, the existing WAAM process is limited in producing a metallic component with high mechanical strength. In this study, the ultrasonic strengthening grinding process (USGP) was proposed to enhance the mechanical properties of WAAM-processed 06Cr19Ni9 steel. A multiphase abrasive, comprising zirconia ceramic balls, brown corundum powder, and strengthening liquid, was propelled by an ultrasonic vibration and randomly impacted on the surface of the WAAM-processed sample. Subsequently, a uniaxial tensile test was conducted to evaluate its mechanical properties. The evolutions of microhardness, microstructure, and phase transformation were comprehensively analyzed. The results revealed that UGSP treatment promotes the generation of dendritic grains and dislocations, facilitates phase transitions, and augments stacking fault and twin band sizes. These cumulative effects enhanced the tensile properties of 06Cr19Ni9 steel. The resulted yield strength and tensile strength achieves a value of ∼970 MPa and ∼1032 MPa, respectively, which increased by ∼43.73% and ∼95.96% compared to the untreated sample. The finding suggested that the proposed method has great application prospects in improving mechanical properties of WAAM-processed components and has the advantages of high efficiency, low cost, and small equipment size.

Wire arc additive manufacturing (WAAM) stands as an efficient and cost-effective method for producing large-scale engineering components while minimizing waste. This study explores the influence of WAAM process parameters on nickel aluminum bronze (NAB) parts, focusing on the wire feed rate (WFR) as a key factor governing heat input and its effects on bead geometry, microstructure, and mechanical properties. The investigation involved depositing a single bead from NAB alloy while varying the WFS within the 2–7 m/min range, resulting in heat inputs ranging from 20.600 to 57.960 kJ/m. The results revealed that increasing heat input up to 34.944 kJ/m led to an augmentation in the bead dimensions and increased hardness due to κ-precipitates formation within the α-Cu matrix. However, with further increments in heat input to 49.088 kJ/m and 57.960 kJ/m, the bead dimensions and hardness exhibited a decline as the uniformity of intermetallic κ distribution lessened. Through optimization of WAAM process parameters, a defect-free single-wall NAB was successfully manufactured with enhanced properties. The tensile strength along the horizontal direction for the single-wall NAB alloy was found to be superior to that of the vertical direction, irrespective of the specimen's extraction regions. Additionally, the bottom specimen exhibited slightly higher tensile strength than the center and upper specimens due to being the initial layers of the wall deposited on the substrate plate, undergoing a faster cooling rate. These findings underscore the potential of WAAM as a robust method for the fabrication of larger NAB components with precision and efficiency.

Here, wire-arc additive manufacturing (WAAM) is employed to fabricate Al–Ce–Mg heat-resistant aluminum alloy, considering its capability to manufacture large complex structures more efficiently. Large-sized faceted Al11Ce3 intermetallic compounds are formed in the as-cast alloy with a hypereutectic microstructure. The microstructure is transformed to a eutectic microstructure by non-equilibrium solidification of WAAM, consisting lamellar α-Al/A111Ce3 eutectics. The WAAM alloy shows enhanced mechanical strength and ductility at 200 °C, compared with the as-cast alloy. The significant improvements of ultimate tensile strength and elongation for the WAAM alloy are correlated with its higher strain hardening rate, along with the transition from cleavage fracture to dimple fracture. The cracking of All1Ce3 particles occurs preferentially during the elastic deformation stage, as revealed by in-situ testing, and the strain hardening capability of the as-cast alloy is reduced. Pore defects, 0.15 % in volume fraction, are produced via WAAM processing, and the plastic deformation promotes the pore growth and mergence, increases the pore volume fraction, and decreases the pore sphericity. Our results demonstrate that WAAM is strongly attractive for the fabrication of Al–Ce–Mg alloys, due to the enhanced high-temperature strength-ductility synergy.

Magnesium (Mg) alloys are the lightest structural metallic material, but it is hard to be applied to various industrial fields due to the crystallographic nature that is composed with hexagonal closed packed (HCP). Wire arc additive manufacturing (WAAM) could be a key to fabricating Mg parts with large sizes and complex designs. It has numerous advantages such as high material efficiency, short-delivery time by faster manufacturing speed, easy to modify, etc. Yet, most of the research mentioned the grain coarsening and degradation in mechanical properties when fabricating WAAM products using Mg alloy wires. To solve the problems, a solution was suggested with supposition that the lessen the deposit metal size a little by changing to the finer wire diameter can reduce the actual heat input and heat accumulation during the WAAM process. In this research, the WAAM of AZ31B has been conducted using a wire diameter of 1.0 mm rather using the 1.2 mm that is used in common. It was found that the finer (about 90 %) and equiaxed microstructure was composing the WAAM product made of wire diameter of 1.0 mm, and it results in about two times higher mechanical strength.

In this study the nickel-aluminide intermetallic cladded on AISI 1010 steed using dual wire arc process. The nickel-aluminide is fabricated in situ through an arc provided by a gas tungsten arc welding process and changing aluminum wire feeding rate. The research findings reveal that at a constant Ni wire feeding rate of 450 mm/min, by decreasing the Al wire feeding rate lower than 800 mm/min, the instability of the melt pool prevents the formation of a uniform deposit on the substrate. Although deposition has been done at an Al wire feeding rate higher than 1600 mm/min, transverse cracks have formed in the clad layer. Increasing the aluminum wire feeding rate from 1000 to 1400 mm/min decreases the dendritic arm size from 9.2 ± 0.1 to 4.1 ± 0.3 μm. Although unreacted nickel is visible in the microstructure at the Al wire feeding rate of 1000 mm/min, at a high feeding rate (1400 mm/min), most of the microstructure contains AlNi and Ni3Al intermetallic compounds. With the rise in Al wire feeding rate from 1000 to 1400 mm/min, both yield strength and ultimate tensile strength increase from 521.45 ± 14.16 to 620.89 ± 16.08 MPa and from 762.11 ± 19.89 to 855.65 ± 21.54 MPa, respectively. Intriguingly, the clad layer's tensile toughness decreases from 26.51 ± 2.43 to 18.32 ± 2.56 MJ m−3. By increasing the wire feeding rate from 1000 to 1400 mm/min, the wear rate at room temperature, 500 °C, and 800 °C increases by 61.2, 45.7, and 44.3%, respectively.

Cold Metal Transfer-Based Wire Arc Directed Energy Deposition (CMT-WA-DED) presents a promising avenue for the rapid fabrication of components crucial to automotive, shipbuilding, and aerospace industries. However, the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing applications. In this study, a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 alloy. Our findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy, primarily due to poor surface finish, tensile residual stress, porosity, and coarse grain microstructure inherent in the WA-DED process. Low Plasticity Burnishing (LPB) treatment is applied to mitigate these issues, which induce significant plastic deformation on the surface. This treatment resulted in a remarkable improvement of fatigue life by 42%, accompanied by a reduction in surface roughness, grain refinement and enhancement of compressive residual stress levels. Furthermore, during cyclic deformation, WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED + LPB specimens. A higher fraction of Low Angle Grain Boundaries (LAGBs) in WA-DED specimens contributed to multiple crack initiation sites and convoluted crack paths, ultimately leading to premature failure. In contrast, wrought and WA-DED + LPB specimens displayed a higher percentage of High Angle Grain Boundaries (HAGBs), which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths, thereby extending fatigue life. These findings underscore the effectiveness of LPB as a post-processing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy components. Our study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface defects, enabling their widespread use in load-bearing applications.

Reduced activation ferritic/martensitic (RAFM) steel with high strength and neutron radiation damage resistance is deemed one of the promising structural materials for fusion blankets. In this study, RAFM steel tube was prepared through wire arc additive manufacturing, and the evolution of phase composition, microstructural features and mechanical properties during the as-built and heat treatment processes were investigated. The results show that the as-built state is predominantly composed of α-Fe, and the microstructure's morphology from bottom to top consists of alternating columnar grain regions, equiaxed coarse grain regions, and fine grain regions. Normalizing and tempering treatment eliminates the heterogeneous microstructure, resulting in the presence of M23C6 carbides enriched with Cr and W, as well as MX phases enriched with Ta and V. Partitioning heat treatment results in the formation of ultrafine martensitic, quenched martensite and bainitic microstructures. The mechanical properties of wire arc additively manufactured RAFM steel are influenced by variations in microstructure. The coarse-grained region formed in the as-built state represent weak links. Normalizing and tempering treatment reduces the strength while improving ductility. Partitioning heat-treated RAFM steel exhibited a high strength of 1.1 GPa and an elongation of approximately 10.9%. This study provides a method of combining additive manufacturing with heat treatment to enhance the strength and ductility of RAFM steel simultaneously.

Graded materials are promising alloys due to their improved strength and ductility. In this study, a functionally graded Alx-Co-Cr-Fe-Ni high entropy alloy with a variation of Al concentration along the building direction was produced in-situ by dual wire arc additive manufacturing for the first time, and the microstructure and mechanical properties of the deposited alloy were investigated. The results showed that the FCC + BCC dual-phase gradually transformed to a single BCC phase with increasing Al content, the precipitation temperature of the ordered B2 phase became high, and the precipitation temperature range of the disordered BCC phase became wider, which promoted the formation of the disordered BCC phase. With the change in phase ratio, the hardness gradually increased from 342 HV to 397 HV, and the bottom deposited alloy had an optimal combination with a compressive strength of 827.4 MPa and elongation of 42.3%. Compared to the bottom region, the top region shows much higher sliding wear resistance. The high-density dislocations and grain refinement result in better toughness and strength in the bottom region, while the segregation of Cr elements at the grain boundaries changes the properties of the grain boundaries and makes them more brittle in the top region. This investigation realizes a novel method to fabricate GHEAs, which can produce a more convenient and cost-effective gradient material with a complex composition.

Gas tungsten arc welding (GTAW) based wire arc additive manufacturing (WAAM) process is first used to fabricate a thin wall of LA103Z magnesium-lithium alloy. Results indicate that the grain size of the LA103Z thin-walled bottom region significantly differs from that of the middle and top regions. The main phases present in the LA103Z thin wall include α-Mg and β-Li phases, along with some particulate second phases (LiAl, Li2MgAl). Moreover, the thermal action of the subsequent sedimentary layer promotes the transformation of β-Li→α-Mg+β-Li and Li2MgAl →LiAl phase. The mechanical properties of the LA103Z thin wall are affected by a combination of factors such as grain size, the proportion of the α-Mg phase, and morphology. The tensile strength of the LA103Z thin-walled samples in the bottom, middle, and top regions is measured at 195.1 MPa, 181.8 MPa, and 201.4 MPa, respectively, with corresponding elongation percentages of 3.4%, 7.3%, and 12.4%. In the building direction, the tensile strength is recorded as 177.7 MPa, with an elongation percentage of 7%. The study reveals that WAAM-GTAW has the potential to make magnesium-lithium alloys more widely available.

Multi-wire arc additive manufacturing (MWAAM) enabled customized production with high deposition efficiency and low cost as compared to the common wire arc additive manufacturing (WAAM) technology. In this paper, two titanium alloy components were prepared using the MWAAM technique, and the microstructures, mechanical properties, and wear behaviors of Ti–6Al–4V (TC4) alloy and Ti-6.5A1-3.5Mo-1.5Zr-0.3Si (TC11) alloy were investigated. The results showed that the microstructure distribution of TC11 alloy prepared by MWAAM was more intensive and the length and width of the lamellar α-Ti phase were significantly reduced compared with that of TC4 alloy. The polar densities corresponding to the texture in the two selected regions of the TC4 alloy and the TC11 alloy were 17.30 and 17.69, respectively. The proportion of the HAGBs of the TC4 sample and the TC11 sample were 99.07 % and 99.43 %, respectively. The average microhardness on the X–Y plane of TC4 and TC11 alloys were 316.17 HV and 366.14 HV, respectively, while the average microhardness on the Y-Z plane were 318.18 HV and 358.10 HV, respectively. The average compression yield strengths of TC4 and TC11 alloys were 836.61 MPa and 1088.33 MPa, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.479 and 0.455 under 20 N, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.472 and 0.432 under 60 N, respectively. The average yield strength, average ultimate strength, proportion of HAGBs, and microhardness of TC11 alloy were all higher than that of TC4 alloy. These results indicated that TC11 alloy had advantages over TC4 alloy in terms of mechanical properties and microstructure, with higher strength and deformation resistance. The properties of titanium alloy samples prepared by MWAAM were not lower than those of titanium alloy samples prepared by single wire WAAM, while MWAAM significantly better than single wire WAAM in deposition efficiency. The results obtained in this paper can help to prepare titanium alloy components with excellent mechanical properties more efficiently in MWAAM process.

This study investigated the correlation between the MnS·xMnO·yAl2O3·zSiO2·TiN complex inclusions and localized corrosion initiation of the wire arc additively manufactured (WAAMed) super duplex stainless steel (SDSS) part. The results showed that partial dissolution of crystalline MnS within the complex inclusions generated an acidic aggressive environment to led the dissolution of amorphous oxides part, thereby triggering the process of localized corrosion. Additionally, micro-crevices between the inclusions and metallic matrix exacerbated localized corrosion. Finally, the catalytic-occluded cells accelerated propagation of pits. Hence, formation of high density of inclusions resulted in the poor localized corrosion resistance and repassivation ability of the as-built WAAMed SDSS.

In this study, gas tungsten arc welding (GTAW) based dual wire additive manufacturing (D-WAAM) is adopted to fabricate the functionally graded material (FGM) from stainless steel (SS) 304 to Fe–40Al, using SS 304 and aluminum alloy (AA) 1070 wires. The Al/Fe atomic ratio varies from 0 to 40 % by varying the ratio of the wire feed speeds of the SS and AA wires. The chemical composition, phases, microstructure, and mechanical properties of the FGM are investigated. The results showed that with the increase of Al content, microstructures evolve as follows: γ-Fe → γ-Fe + α-Fe → α-Fe → Fe3Al → FeAl. Cracks occur in FeAl region, caused by the high stress and the low plasticity. Dislocation walls prevent the large grains from slipping, leading to the loss of plasticity. The microhardness of SS 304 to Fe–40Al FGM ranges from 188HV0.5 to 558HV0.5. As Al content increases, the ultimate compressive strength decreases from 1820 MPa to 1061 MPa. The results on microstructure and mechanical properties provide guidance for the preparation of steel - aluminum alloy FGMs.

Wire-arc additive manufacturing (WAAM) was used in aeronautical engineering due to its low equipment cost and ability to create complex shapes. However, the fatigue behavior of WAAM titanium alloy, specifically for low cycle fatigue (LCF), was poorly studied. This paper investigated the microstructure and mechanical behavior of WAAM TC17 in both vertical and horizontal orientations. Fully reversed LCF tests were conducted on specimens with varying strain amplitudes from ±0.4 % to ±1.2 %. The results found that the ultimate tensile and yield strength were similar for both vertical and horizontal samples, but the elongation in the horizontal orientation was approximately 60 % lower than that in the vertical orientation. Considering the cyclic loading behavior, both vertical and horizontal samples exhibited cyclic softening characteristics at high strain amplitudes (0.8%–1.2 %). Additionally, the cyclic softening rate (CSR) of horizontal samples exhibited a higher than that of vertical samples at high strain amplitude. The LCF cracks of WAAM TC17 were initiated from the surface and internal defects of the samples. The LCF performance of the horizontal samples was found to decrease than that of vertical samples. Specifically, the fatigue performance of the horizontal samples is lower by 36.7 % compared to the vertical samples when the number of cycles is 103.

This work studied the effect of solution heat treatment on the microstructure and properties of the Al–Cu alloy fabricated by wire arc additive manufacturing (WAAM), and focused on the influence of porosity and second phase evolution on the tensile properties and fatigue resistance of the alloy. The results show that with solution heat treatment at 530 °C for 1h, Al–Cu alloy fabricated by WAAM with low porosity (2.4 %) and high peak hardness (148.2 HV) can be obtained. Higher solution temperatures significantly increased the porosity, and extending the solution time caused the problems of increased porosity, micropore growth, microcracks as well as cavity. Influence of porosity on fatigue resistance is more significant than that on tensile properties. The results of tensile tests suggest that the effect of porosity on the strength of T6-treated alloy is limited and much smaller than that of the precipitation strengthening induced by precipitates, while the results of the fatigue crack propagation tests imply that porosity plays the dominant role in the fatigue crack propagation behaviors of the T6-treated alloy.

WAAM and LDM are two typical DED technologies. WAAM-LDM additive manufacturing technology can achieve the purpose of producing large and complex Ti–6Al–4V components, improving processing efficiency and precision. However, there is a lack of in-depth research on the microstructure evolution mechanism and the fracture behavior of WAAM-LDM samples. Therefore, horizontal and vertical WAAM samples were invoked as the substrate for LDM processes in this study, and the mechanical properties and tensile fracture behavior under different load directions were evaluated. The results show that the samples fabricated by WAAM-LDM manufacturing consist of four zones: WAAM zone, heat affected zone (HAZ), remelting zone (RZ) and LDM zone. WAAM zone mainly composed of coarse colony structure, HAZ and RZ are dominated by α colonies and fine basketweave structure, respectively, and LDM zone consists of acicular α phases and fine basketweave structure. The thickness of α laths shows a trend of ‘WAAM > HAZ > LDM > RZ’. The strengths are greatly improved at the interfaces due to the good metallurgical bonding and finer microstructure. All the fractures locate at WAAM zone during tensile test and propagate along the basketweave structure. These strengths of WAAM-LDM samples under the action of horizontal loading are higher than that of WAAM samples, and all the elongations of WAAM-LDM samples are higher than 10 %.

Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time (IDT) in the wire and arc additive manufacturing (WAAM) process of Mg alloy. The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 °C at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 µm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 °C, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 µm, while the arc zone owned coarse grains with the size of 24.5 µm. The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.

Wire arc additive manufacturing (WAAM) of Mg-RE (rare-earth)-Zn alloys is important for meeting the requirements of lightweight large-scale components with high manufacturing flexibility. The Mg-8.1Gd-2.6Y-0.7Zn-0.5Zr (GWZ831K, wt.%) alloys were fabricated through the use of WAAM technology, and the microstructure evolution along the building direction and corresponding mechanical properties were then studied. The as-built sample in this paper was composed of finely equiaxed ɑ-Mg grains, eutectic (Mg, Zn)3(Gd, Y) phase, cubic phase, and γʹ precipitates. Furthermore, due to the in-suit heat treatments that were induced by the multiple thermal cycles, more γʹ precipitates were observed in the middle region. The microstructures at different heights were characterized by alternatively distributed fine equiaxed grains (melt pool boundaries, MPB) and coarse equiaxed grains (melt pools, MP). The mechanical properties of the as-built component were found to exhibit yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of 159 ± 1.0 MPa, 237 ± 4.0 MPa, and 6.7 ± 0.4 % in the building direction (BD) and 163 ± 5.1 MPa, 242 ± 8.7 MPa, and 7.0 ± 0.7 % in the traveling direction (TD). This demonstrates that the WAAM-processed GWZ831K alloy has good isotropy.

Wire arc additive manufacturing (WAAM) offers significant advantages in rapid manufacturing of complex integral parts. In this study, Mg-Gd-Y-Zn-Zr alloy deposited walls were fabricated by cold metal transfer (CMT) based WAAM. The interface bonding relationship between the additive zone and the substrate was studied, as well as the effect of the microstructure of the additive zone on the mechanical properties. The precipitated phase Mg24Y5 mainly distributed at the grain boundary was found in the additive zone of deposited walls, nano-scale contact interface and diffusion bonding interface were formed between β-Mg24Y5 and α-Mg (OR: [001]β-Mg24Y5//[10 1‾ 0]α-Mg), and a portion of the 18 R-LPSO phase to 14H-LPSO phase transition occurred in the substrate zone. In each layer of deposited metal, the bottom zone had a higher cooling rate than the top zone, which led to the supersaturation of rare earth elements. The precipitated phases between different deposition layers showed a decreasing trend from the bottom zone to the top zone due to the complex multiple thermal cycles in the additive manufacturing process. Compared with the cast Mg-Gd-Y-Zn-Zr alloy, the mechanical properties (UTS, YS and EL) of the Mg-Gd-Y-Zn-Zr alloy fabricated by WAAM were significantly increased. The ultimate tensile strength of the deposited walls along the travel direction was 227.27 MPa, and the elongation was 8.08 %.

The present study is focused on investigating the feasibility of additive manufacturing of single crystal nickel components using MIG processed wire arc additive manufacturing (WAAM) technique. The feasibility was validated by depositing the material first on 99.999 % pure polycrystalline nickel substrate and then onto a 99.995 % pure single crystal nickel specimen oriented in direction. Optical microscopy and EBSD results prove the possibility for regions of single crystal to be deposited. The process yielded distinct regions of single crystal. Columnar and equiaxed grains occurred in a region with the highest local thermal gradient and slowest solidification rate. EBSD analysis confirmed that the single crystal region revealed in optical microscopy was in one orientation and the etchant was effective in highlighting individual grain boundaries.

The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %.

Broadening the understanding of the anisotropic behavior of super duplex stainless steel (SDSS) fabricated by wire arc additive manufacturing (WAAM) can provide valuable insights for designing and optimizing WAAM components. The purpose of this study is to investigate the anisotropic behavior between mechanical properties, corrosion resistance, microstructure and crystallographic features of wire arc additive manufactured (WAAMed) SDSS thin-wall component, by means of optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), hardness testing, tensile testing and electrochemical corrosion testing. Meanwhile, a control sample set prepared from commercial hot-rolled SAF 2507 SDSS was also investigated for comparison. The results show that the mechanical properties and corrosion behaviors of WAAMed SDSS are anisotropic, which are attributed to the nonequilibrium phase ratio and anisotropic crystal features in the as-built WAAMed SDSS affected by the repeated thermal cycles inherent to WAAM process.

TC4 titanium alloy wire arc additive manufacturing (WAAM) is easy to produce coarse columnar β grain structure which affects mechanical properties. So in this paper, an innovative process of interpass milling assisted TC4 titanium alloy gas tungsten arc welding (GTAW) WAAM is proposed. The controlling interpass milling depth is used to improve the microstructure and mechanical properties of TC4 titanium alloy parts during the GTAW-WAAM. The results showed that the coarse columnar β grains and fine α phase were observed in the non-interpass milling part. When the interpass milling assistance GTAW-WAAM was employed, the coarse columnar β grains transformed into short columnar and equiaxed grains. With the increased of interpass milling depth, the average size of α phase was gradually refined to 13.5 μm below. The highest average microhardness in the top, middle and bottom areas obtained by using the interpass milling depth of 300 μm were 369 HV0.2, 371 HV0.2 and 371 HV0.2 respectively, which was increased by 32 HV0.2, 28 HV0.2 and 26 HV0.2 compared with non-interpass milling respectively. The horizontal and vertical ultimate tensile strength first increases and then decreases with the increase of interpass milling depth, reaching its maximum at a milling depth of 300 μm. The highest tensile strength of the horizontal and vertical directions obtained by using the interpass milling depth of 300 μm were 1022 MPa and 1042 MPa. The level of the ultimate tensile strength is related to the combined proportion of total average β grain size and total average

Heterogeneous microstructure designs have attracted a great deal of attention, not only because they have the potential to achieve an ideal combination of two conflicting properties, but also because the processes involved in their fabrication are cost-effective and can be scaled up for industrial production. The process parameters in the preparation process have an important effect on the microstructure and properties of alloy members prepared by wire arc additive manufacturing (WAAM) technology. It was expected that the spatial heterogeneous microstructure with large microstructural heterogeneities in metals can be formed through changing the process parameters. In this work, homogeneous NiTi thin-walled component and heterogeneous NiTi thin-walled component were fabricated using WAAM technology by adjusting the heat input. The effects of deposition height and heat input on the microstructure, mechanical properties and wear properties of WAAM NiTi alloys were investigated. The results show that grains were gradually refined with the increase of deposition height in the homogeneous WAAM NiTi component. The ultimate tensile strength of homogeneous WAAM NiTi component increased from 606.87 MPa to 654.45 MPa and the elongation increased from 12.72% to 15.38%, as the increase of deposition height. Moreover, the homogeneous WAAM NiTi component exhibited excellent wear resistance, the coefficient of friction decreased from 0.760 to 0.715 with the increase of deposition height. Meanwhile, the grains in the heterogeneous WAAM NiTi component shows the finest grains in the central region. The ultimate tensile strength of the lower region, middle region and upper region of heterogeneous WAAM NiTi components were 556.12 MPa, 599.53 MPa and 739.79 MPa, and the elongations were 12.98%, 16.69%, 21.74%, respectively. The coefficient of friction for the lower region, middle region and upper region of heterogeneous WAAM NiTi components were 0.713, 0.720 and 0.710, respectively. The microhardness and cyclic compression properties of the homogeneous components with higher heat input were better than those of the heterogeneous components for the same deposition height. The tensile yield strength, elongation and wear resistance of the heterogeneous components were superior compared to the homogeneous components. These results can be used to optimize the WAAM process parameters to prepare NiTi components with excellent mechanical properties.

The evolution of grain structure, precipitates and mechanical properties of the ZL205A alloy prepared by wire arc additive manufacturing were investigated. The results show that the as-deposited alloy consists of equiaxed and columnar grains in the bottom region. As the deposition height increases, the alloy mainly consists of equiaxed grains. The evolution of columnar to equiaxed grains is explained by the solidification theory. The needle-like θ′-Al2Cu precipitates in Cu-rich regions surrounding the α-Al+θ-Al2Cu eutectics. As the part deposited first is subjected to multiple cycles of heating by the subsequently deposited layers, the volume fraction and average size of θ′ precipitates gradually decrease with the increase of deposition heights. The microhardness of the as-deposited alloy fluctuates in the range of 74.6–84.5 HV. The mechanical properties of the horizontal specimens at different heights are affected by the combination of grain structure, precipitates and pores, and that of the specimens in the middle region are optimal. The mechanical properties of the horizontal and vertical specimens show isotropic. Attributed to the grain boundary strengthening and precipitation strengthening, the yield strength (132.9 MPa) and elongation (15.9%) of the as-deposited alloy are approximately 31.3% and 211.8% higher than that of the as-cast alloy, respectively.

Wire arc additive manufacturing (WAAM) is a suitable method for fabricating large high-strength components made of the Al–Zn–Mg–Cu alloy. However, the solidification behavior of this alloy is complex due to its composition. The inhomogeneous solidification microstructure results in numerous defects during the deposition process, hindering the application of the deposited Al–Zn–Mg–Cu alloy. This study aims to analyze the microstructure evolution under different process parameters and reveal the relationship between the solidification behavior of the molten pool, pore defects, and grain morphology. Thin-walled components based on Al–Zn–Mg–Cu alloy were fabricated using WAAM under different parameters. The results showed that increasing deposition current initially decreased and subsequently increased pore defects, while the proportion of twinned dendrites exhibited the opposite trend. A lower deposition speed reduced pore defects by promoting gas escape, whereas a higher deposition speed led to the precipitation of Al3Zr, grain refinement, and the suppression of twin dendrite growth. A faster wire feeding speed had a better suppression effect on defects, while a slower wire feeding speed inhibited the growth of twinned dendrites, promoting the directional growth of regular dendrites.

This study proposes an effective repair technology using arc additive manufacturing for pressurized water reactors (PWRs) in nuclear power plants (NPP) aimed at avoiding complete replacements and post-weld-heat treatments (PWHTs) of component parts while ensuring safety and reliability. Effective repair technology is defined as economic and process efficiency, because of maintenance costs and radiation exposure, and it is critical in related industries. The technology is designed to relieve the hardness and martensite fraction of the welding heat affected zone (HAZ) of low alloy steels (SA508) in PWRs penetration/nozzles by heat source generated in the WAAM process, thus ensuring structural integrity. In the first layer of wire arc additive manufacturing processes, 89.6% of the martensite phase was formed in the HAZ of SA508, which was significantly reduced to 45.7% due to repetitive thermal behaviors at the third layer. The resulting process dramatically reduced hardness from 450Hv in the initial layer additive manufacturing to 320Hv in 3 layers without additional heat treatments. Moreover, the study quantitatively investigated the martensite starting temperature (Ms) and bainite starting temperature (Bs) and analyzed the microstructure and mechanical behavior of the developed process using thermodynamic calculation (CALPHAD), finite element method (FEM) simulation, and microstructure quantitative analysis by electron backs-catter diffraction (EBSD). The proposed technologies and their quantitative analysis results can be a substantial alternative to the repair technology for penetration/nozzles in nuclear primary water cooling reactor applications, complying with ASME Sec.IX Qw-462.12 and ISO 15614-1.

Magnesium (Mg) alloys have a low density among the structural metals, but it is hard to be plastically deformed due to their crystallographic nature. Wire arc additive manufacturing (WAAM) could be one of the alternative processes to fabricate the Mg products for various industrial applications. Nonetheless, it is used in limited industrial fields due to challenging issues such as low commercial availability of wire, high oxygen affinity, explosive and flammable hazard, and typical defects of WAAM like distortion and side collapse, grain coarsening, etc. In this research, it was tried to find out the better way to fabricate the WAAM of AZ31 alloy. An additional Ar gas side shielding was given during the WAAM process, and compared with the conventional shielding method. It was observed that the global shielding affects the microstructural evolution of the WAAM product, and influences the mechanical property in a positive way.

The dynamic tensile mechanical properties of 18Ni350 maraging steel (M350) fabricated by wire arc additive manufacturing (WAAM) was investigated by the split Hopkinson tensile bar (SHTB) and microstructural analysis. The results show that the yield stress (YS) of M350 samples, both in as-built and heat-treated state, increases firstly and then decreases with increasing strain rate. The YS of the as-built sample reaches the maximum value of 2195 MPa at 1230s−1, and that increases to 3395 MPa after heat treatment, due to the precipitation of intermetallic. Compared with the sample in the horizonal direction, the sample in the vertical direction exhibits a higher dynamic strength, due to the preferred growth of columnar crystal along the vertical direction during WAAM process. Under dynamic load, the retained austenite transformed into martensite and the oxide inclusions are cracked, resulting in a heterogeneous fracture morphology. Based on those results the hardening model and the anisotropic model of the strain rate sensitive material fabricated by WAAM were established. The results can provide a guidance for the reliability evaluation of maraging steel fabricated by WAAM under dynamic load conditions.

In this paper a novel method was proposed for monitoring the defects of surface oxidation in copper alloy wire arc additive manufacturing (WAAM) which using voltage sensor. Due to the good fluidity of liquid copper alloy, the dimension of copper alloy WAAM process is difficult to control especially in the height direction. This will lead to error accumulation with the layers increasing during WAAM period. The phenomenon of error accumulation will cause continuous changes in the distance between the welding wire and substrate, result in inappropriate gas protection which will lead to surface oxidation defects happen. To monitoring this defect，time-frequency analysis method was used to compare the voltage signals between normal and anomaly WAAM process. The result show that the voltage signal of abnormal weld bead appears fluctuations in its peak value, and the voltage waveform of the normal WAAM process is relatively smooth. Furthermore, continuous wavelet transform (CWT) method is used to convert one-dimensional time-series voltage signals into two-dimensional time-frequency images, which is combined with deep learning method to establish an online monitoring model to monitor the surface oxidation defects in the process of copper alloy WAAM. The accuracy of the proposed model can reach 95.83%, and t-SNE(t-distributed stochastic neighbor embedding) algorithm is used to visualize the performance of the model. The result indicates that the voltage signal characteristics of normal and abnormal WAAM processes were significantly distinguished.

This paper is focused on improving material formability in hybrid wire-arc additive manufacturing comprising metal forming stages to produce small-to-medium batches of customized parts. The methodology involves fabricating wire arc additive manufactured AISI 316L stainless steel parts subjected to mechanical and thermal processing (MTP), followed by microhardness measurements, tensile testing with digital image correlation, as well as microstructure and microscopic observations. Results show that mechanical processing by pre-straining followed by thermal processing by annealing can reduce material hardness and strength, increase ductility, and eliminate anisotropy by recrystallizing the as-built dendritic-based columnar grain microstructure into an equiaxed grain microstructure.

A novel cold metal transfer and pulse (CMT-P) hybrid arc technology was introduced for additive manufacturing of high-strength aluminum alloy 2024 (AA2024). The effects of process parameters, namely the wire-feed speed, travel speed, and CMT/P ratio (ratio of number of CMT stages to pulse stages in a cycle), on the porosity and surface roughness of AA2024 CMT-P additive manufacturing were systematically investigated using the response surface methodology and an improved non-dominated sorting genetic algorithm (NSGA). The results showed that the wire-feed speed had the greatest effect on the porosity and surface roughness. The porosity initially decreased and then increased with an increase in the wire-feed speed. However, the surface roughness decreased with an increase in the wire-feed speed. Moreover, the porosity was reduced with a decrease in the travel speed. With an increasing travel speed, the surface roughness initially decreased and then increased. Furthermore, for both porosity and surface roughness, the best results were obtained at a CMT/P ratio of 1/4. Thus, high porosity and surface roughness in the additive-manufactured parts were caused by high values of wire-feed speed, travel speed, and CMT/P ratio. In addition, using the optimized process parameters, additive parts with low porosity and low surface roughness could be produced.

In this paper, arc oscillation is applied in the fabrication of 2319 aluminum alloy samples by cold metal transition wire arc additive manufacturing process (CMT-WAAM). The porosity, microstructure and mechanical properties of 2319 aluminum alloy under different arc oscillation patterns were discussed. The results showed that the stirring of arc oscillation can influence the molten pool shape and improve the fluidity, change the thermal distribution and the growth direction of columnar crystal. Arc oscillation has a obvious effect on reducing the grain size and proportion of pores. After using the spiral arc oscillation pattern and asymmetrical trapezoid arc oscillation pattern, the volume fraction of pores reduced from 2.64% to 1.09% and 1.22%, and the size of pores was mainly smaller than 40 μm, respectively. The tensile strength in vertical direction and plasticity were improved with arc oscillation, but its effect on the horizontal tensile strength was not noticeable. After solid solution-aging treatment, the tensile strength of the sample with spiral arc oscillation pattern increased to 277 MPa, with a cross-section reduction of 3.6%.

The directed energy deposition (DED) processes, such as laser metal deposition or Wire Arc Additive Manufacturing (WAAM), are gradually becoming the preferred method for fabrication of large-scale components using metal additive manufacturing (AM) technology. In this work, the possibility of fatigue life enhancement in WAAM built low carbon steel components, by means of rolling and laser shock peening surface treatment techniques, was investigated. A series of fatigue crack propagation tests were performed on surface treated ER70S-6 and ER100S-1 WAAM built specimens, and the results were analysed and compared with the untreated materials tested under the same loading conditions. The obtained results were interpreted in terms of the sensitivity of the cracking behaviour to the specimen orientation and extraction location. Furthermore, the residual stress profiles were measured, before and after applying the surface treatment techniques, and the effects of locked-in residual stresses on the fatigue performance of WAAM built components were discussed. Finally, a detailed texture analysis was performed on the surface treated and untreated regions of both WAAM built materials considered in this work. The obtained results from this study provide an insight into the advantages and disadvantages of various surface treatment techniques for fatigue life enhancement of WAAM built components with the view to extend the application of this advanced manufacturing technology to a wider range of industrial applications.

In this work, a new current waveform, the AC/DC mix current waveform was employed to improve the microstructure and mechanical properties of 307Si stainless steel component during the TIG based wire arc additive manufacturing (TIG-WAAM). The results showed that the morphology of γ-austenite is changed from the columnar dendrites (with DC mode) to the equiaxed dendrites (with AC/DC mix mode). The grain size was refined due to the reduction of the temperature gradient in the AC/DC mix mode. The degree of refinement grain is increased with the increase of AC ratio. The tensile strength of the 70%DC+30%AC-sample in the traveling and building directions are respectively increased by about 60 MPa and 41 MPa compared with that of the 100%DC-sample. The grain refinement is the mainly reason of the improvement of mechanical properties of the TIG-WAAM component with the AC/DC mix mode.

In recent years, there has been a heightened focus on multiplex porosity due to its significant adverse impact on the mechanical properties of aluminum alloy components produced through wire arc additive manufacturing (WAAM). This study investigates the impacts of the process parameters and dimension parameters on the relative densities of WAAM 2219 aluminum alloy components by conducting experiments and investigates the changes in high relative density process windows with different dimension parameters. The findings reveal a hierarchy in the influence of various parameters on the relative density of the 2219 aluminum alloy: travel speed (TS), wire feed speed (WFS), the number of printed layers (L), interlayer cooling time (ICT), and theoretical length of weld (TLW). A series of data for analysis was produced through a designed experiment procedure, and on the basis of this, by integrating the data augmentation method with the eXtreme Gradient Boosting (XGBoost) algorithm, the relationship among the process parameters, dimension parameters, and relative density was modeled. Furthermore, through leveraging the established model, we analyzed the changes in the optimized process window corresponding to a high relative density with the L. The optimal windows of WFS and TS change when the L reaches a certain value. In contrast, the optimal window of ICT remains consistent despite an increase in the L. Finally, the relative density and mechanical properties of the formed 20-layer specimens within the model-derived window were verified. The relative density of the specimens within the window reached 98.77%, the ultimate tensile strength (UTS) reached 279.96 MPa, and the yield strength (YS) reached 132.77 MPa. This work offers valuable insights for exploring the process window and selecting process parameters through a more economical and faster approach in WAAM aluminum components.

Additive Manufacturing is a manufacturing process that consists of obtaining a three-dimensional object from the deposition of material layer by layer, unlike conventional subtractive manufacturing methods. Wire Arc Additive Manufacturing stands out for its high productivity among the Additive Manufacturing technologies for manufacturing metal parts. On the other hand, the excessive heat input promotes increased residual stress levels and the occurrence of defects, such as pores, voids, a lack of fusion, and delamination. These defects result in abnormalities during the process, such as disturbances in electrical responses. Therefore, process monitoring and the detection of defects and failures in manufactured items are of fundamental importance to ensure product quality and certify the high productivity characteristic of this process. Thus, this work aimed to characterize the effects of different contaminations on the electric arc behavior of the Wire Arc Additive Manufacturing process and the occurrence of microscopic defects in thin walls manufactured by this process. To investigate the presence of defects in the metal preforms, experimental conditions were used to promote the appearance of defects, such as the insertion of contaminants. To accomplish the electric arc behavior analysis, voltage and current temporal data were represented through histograms and cyclograms, and the arc stability was assessed based on the Vilarinho index for a short circuit. Effectively, the introduction of contaminants caused electric arc disturbances that led to the appearance of manufacturing defects, such as inclusions and porosities, observed through metallographic characterization. The results confirm that the introduction of contaminations could be identified early in the Wire Arc Additive Manufacturing process through electric arc data analysis.

A single-bead multilayer martensitic stainless steel thin wall was fabricated using the wire arc additive manufacturing (WAAM) process. After the WAAM process, the tempering heat treatment was carried out to homogenize the microstructure distribution in the wire arc additive manufactured (WAAMed) part. To optimize the tempering temperature, the as-WAAMed samples were subjected to varying tempering temperatures of 300, 500, 600, and 700 °C for 2 h. The heterogeneous structure within the as-WAAMed part was hardly eliminated by the low tempering temperatures of 300 and 500 °C. On the other hand, the inhomogeneous hardness profiles were significantly homogenized by the tempering temperature of 600 and 700 °C. Tempering at 600 °C removed the heterogeneous structure, resulting in the effective homogenization of the significantly heterogeneous hardness profile and microstructure distribution in the as-WAAMed part. Tempering at 700 °C led to the lower hardness than that at 600 °C.The anisotropic tensile properties of the as-WAAMed part were also eliminated after tempering at 600 °C. The significant differences in the toughness of the different layers of the as-WAAMed part were effectively reduced by proper tempering. The slight decrease in toughness of the post-process heat-treated sample from the bottom to the top of the thin wall was mainly caused by the increase in the martensitic block size inherited from the prior austenite grain structure. This study suggests that tempering at 600 °C for 2 h is an effective post-process heat treatment to homogenize the microstructure and mechanical properties of as-WAAMed 2Cr13 martensitic stainless steel.

Ultrasonic impact treatment (UIT) is considered to solve the defects of wire arc additive manufacturing (WAAM) components such as coarse grain size, large residual stress, and poor mechanical properties. In this paper, the effects of UIT on the microstructure and mechanical properties of 2219 aluminum alloy WAAM components were systematically studied. The effect of UIT on grain size and porosity was investigated by metallographic experiments. Electron backscattering diffraction (EBSD) was used to analyze the effect of UIT on grain orientation and texture. The chemical composition and phase composition were characterized by energy dispersive spectrum (EDS) and transmission electron microscopy (TEM). The effect of UIT on mechanical properties was analyzed by tensile test. Therefore, the influence and strengthening mechanism of UIT on WAAM components are analyzed.The results show that UIT can refine the grain size and reduce porosity. In addition, UIT can increase the dislocation density, improve the surface residual stress, and distribute the precipitated phase evenly in the matrix, thus effectively improving the mechanical properties of the WAAM components. This study provides a basis for improving the quality of WAAM components, and has reference value for the application of WAAM and UIT technology, as well as the regulation of the microstructure and properties of 2219 aluminum alloy.

In this work, wall-shaped NiTi components were fabricated by cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) with optimized depositing speed. The microstructure, mechanical properties, and wear performance of the as-fabricated specimens along the building direction, together with their correlations were investigated in-depth. Coarse columnar grains were refined gradually with the increase of wall height. An equiaxed microstructure was obtained in the upper region. The Ni4Ti3 precipitates were distributed in the matrix. The microhardness, critical stress, and elongation increase monotonously with the increase of wall height. Plastic deformation, together with wear-induced work hardening is the main form of wear, which is mainly hindered by the superelasticity of NiTi alloys. Good homogeneity of the microstructure, mechanical properties, and wear resistance is obtained due to the CMT process with optimized depositing speed, indicating that this technique provides great potential to make novel NiTi flexible structures.

The deposition bead geometry in the arc strike zone is often abnormal compared with that in the middle deposition zone. The accumulation of these errors in the deposition process results in defects in the overall geometry of the deposition bead. To prevent the accumulation of such errors, this study aimed to address the irregular deposition bead shape and deviation of the deposition bead geometry in the arc strike zone without changing the deposition path or introducing external devices. A support vector machine classifier, which is a typical application of machine-learning classification models, was used to obtain the deposition condition ranges for a uniform deposition bead shape. The deposition conditions of the arc strike and middle deposition zones that could reduce the deviation of the deposition bead geometry in the arc strike zone were obtained using support vector machine regression. These conditions were applied in the form of variable conditions in single-path deposition. Five-layer deposition was conducted to validate the regression model. As a result of the validation experiment, the average height and width errors in the arc strike zone were 0.36% and 1.28%, respectively, and the average height and width errors in the middle deposition zone were 0.64% and 1.26%, respectively. Therefore, the regression model can be used for accurate deposition, thereby reducing the post-processing cost.

To maximize the benefits of wire arc additive manufacturing (WAAM) processes, the effect of post-deposition heat treatment on the microstructure and mechanical properties of WAAM AZ80M magnesium (Mg) alloy was investigated. Three different heat treatment procedures (T4, T5 and T6) were performed. According to the results, after T4 heat treatment, the microsegregation of alloying elements was improved with the eutectic structure dissolved. Samples after T5 heat treatment inherited the net-like distribution of secondary phases similar to the as-deposited sample, where the eutectic structure covering the interdendritic regions and the β-phase precipitated around the eutectic structure. After T6 heat treatment, the tiny β-phases re-precipitated from the matrix and distributed in inner and outer of the grains. The hardness distribution of the samples went through T4 and T6 heat treatment was more uniform in comparison to that of T5 heat treated samples. The tensile test showed that the T6 heat treatment improved the strength and ductility, and the anisotropy between horizontal and vertical can be eliminated. Moreover, T4 treated samples exhibited highest ductility.

Although wire arc additive manufacturing (WAAM) of Ti alloys using gas metal arc yields a high deposition rate, cathode spots exhibit unstable behavior. In this study, the cold-metal-transfer process and an electrode-negative (EN) polarity were used in the WAAM process of the Ti–6Al–4V alloy. High-speed imaging was performed to investigate the mechanisms to stabilize cathode plasma jets, arc plasma, and molten metal transfer in the EN polarity. Arc plasma and cathode jets had the same direction, and sound cathode jets were shrouded by arc plasma in the EN mode. The metal transfer was also stabilized by balanced plasma formation under the EN mode, and inconsistent wire melting under the electrode-positive (EP) mode was mitigated. In the deposition test using the EN mode, distributed heating of the substrate and depressed molten pool were observed, which resulted in a 21.0% increase in the bead width and 27% decrease in the wetting angle compared with the EP mode. This study demonstrated that the instability of the gas metal arc WAAM process of Ti alloys can be overcome with the EN-mode cold metal arc process.

Additive manufacturing (AM) processes are playing a significant role in several industrial sectors such as construction and machine building industries, involving a wide variety of metallic materials. Among these, the AM of aluminium alloys has developed significantly over the last decade, mainly through Powder Bed Fusion (PBF) and Directed Energy Deposition (DED) processes. Despite the many advantages of AM technology, some large or complex products cannot be produced entirely without the use of conventional manufacturing and joining processes, generally for financial or operational reasons. In this way, the ability to join conventionally and additively manufactured components or parts represents a crucial step towards their future use and the consolidation of conventional and additive manufacturing technologies. Despite the growing interest in AM technologies, there is still a significant lack of information on the joining of conventionally and additively manufactured components. The present work proposes a first review of the literature evaluating the weldability of AM aluminium alloys. The focus is on the use of fusion and solid-state welding processes and analysing the achieved microstructural evolution and mechanical properties. A clear relationship is observed between the AM technology used to produce the part, and the physical principles of the joining process. In addition, the gaps in the literature are highlighted to enable focused future work.

In this paper, the droplet transfer behavior, geometric characteristics of weld bead and formability of CMT MIX + Synchropulse (CSP) wire + arc additively manufactured Inconel 718 alloy under high wire feeding speed are studied. The results show that a CSP cycle is composed of a CSP high-frequency pulse stage (CSP–HFP) and CSP-CMT stage, and the periods ratio is about 1.7:1. The high frequency and large average welding current of CSP-HFP increase the arc force, which further increases the droplet impact force on the molten pool. The molten pool is significantly deformed, resulting in the penetration depth of the CSP weld bead (1.8 mm) apparently higher than that of CMT (0.5 mm). The surface of the CMT-WAAM sample is more rough and irregular. The large penetration depth provides sufficient support for the molten pool, which promotes the overall stability of the molten pool. The increase of the droplet impact and arc forces enhance the convections in the molten pool, which finally suppresses the overflow phenomenon.

Mechanical parts manufactured using additive manufacturing (AM) processes are used in various fields, such as the aerospace, automobile, and machine tool fields. Recently, many researchers have been actively researching AM processes, owing to their advantages in fabricating complex-shaped components that are difficult to process using conventional processes such as rolling, forging, and casting. One of the AM processes, wire arc additive manufacturing (WAAM), is widely used for manufacturing and repair. Mechanical parts usually suffer from severe damage, such as wear and cracks, during operation. Therefore, research on the damaged parts is often required for repairs. This study was performed to investigate the repair of damaged parts using WAAM in machine tool remanufacturing. In general, these parts are often damaged owing to falls of the workpieces and the inexperience of workers; the cross slide is one of the parts damaged most often in a lathe. Accordingly, this study used the cross slide as an example. First, the damaged area was partially cut flat. Second, it was filled with a metal wire using WAAM. Third, post-processing was performed to adjust the surface quality and shape accuracy. Then, the microstructure, chemical composition, and mechanical property of the repaired part were analyzed. Finally, the repaired cross slide was used to replace damaged parts. In general, this method can be applied to various mechanical parts such as impellers, turbine blades, and machine tools.