Browsing by Author "Diao, Chenglei"
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Item Open Access Additive manufacturing of a functionally graded high entropy alloy using a hybrid powder-bed wire-based direct energy deposition approach(Elsevier, 2023-01-23) Lu, Yao; Wang, Jun; Williams, Stewart; Zhu, Lisong; Ding, Jialuo; Diao, Chenglei; Jiang, ZhengyiA functionally graded AlxCoCrFeNi high entropy alloy with a variation in Al concentration along the building direction was in-situ produced using a hybrid powder-bed wire-based direct energy deposition process. A continuous transition from a single FCC structure to a major BCC+minor FCC dual-phase structure was achieved, benefiting from the remelting and reheating process during the deposition. In the FCC→BCC transition zone, the dendritic core region is identified as an FCC matrix decorated by AlNi-rich ordered B2 precipitates. The interdendritic area shows B2 precipitating in the FeCr-rich disordered A2 matrix. Additionally, the interface between the two regions shows that the A2 phase and ordered Cr3Fe intermetallic phase precipitate at the B2 phase. The mechanical properties show a tendency for higher strength and hardening rate but lower plasticity corresponding to the areas with higher Al content. Through quantitative estimation of different strengthening mechanisms, the contribution from precipitation strengthening became increasingly apparent as Al content increased. Other strengthening modes, including solid solution and dislocations, also contribute to the total strength. This investigation realises a novel additive manufacturing method combining powder bed and wire feeding, which can produce a more convenient and cost-effective gradient material with a complex composition.Item Open Access Element partitioning and electron backscatter diffraction analysis from feeding wire to as-deposited microstructure of wire and arc additive manufacturing with super duplex stainless steel(Elsevier, 2019-12-24) Zhang, Xiaoyong; Wang, Kehong; Zhou, Qi; Kong, Jian; Peng, Yong; Ding, Jialuo; Diao, Chenglei; Yang, Dongqing; Huang, Yong; Zhang, Tao; Williams, Stewart W.The redistribution of alloying elements and the crystallographic characterizations in wire and arc additive manufactured (WAAM) super duplex stainless steel (SDSS) was investigated from the wire to the final as-deposited structure. The results showed that elemental partitioning between austenite and ferrite was suppressed in the last layer and the solidified droplet. The high Ni content but low Cr and N contents in the initial state of the intragranular austenite (IGA) confirmed the predominance of the chromium nitrides acted as the nucleation sites. Gathering of nitrogen was found more distinct in the coarsening IGA, Widmanstätten austenite (WA) than the grain boundary austenite (GBA). The columnar epitaxial ferrite presented a strong <001> texture in the deposition direction, while the <001> and <101> orientations was found in the austenite. Random orientations of the intragranular secondary austenite was revealed. The Rotated Cube texture of the austenite grains were consumed by the “recrystallization” textures (Brass, Rotated Brass, Cu, R, E, and F) caused by the austenite reformation. The low-angle interphase boundaries between austenite and ferrite were predominated in the as-deposited wall, and, at which, the K–S orientation took the crucial part. A Taylor factor analysis revealed that through fabrication via additive process, the austenite became oriented “harder” and contributed most to good mechanical properties. The textured microstructure contributed about a 2.6% higher engineering strain in the Z direction and a 27.8 MPa higher yield strength in the X direction.Item Open Access Fatigue strengthening of damaged steel members using wire arc additive manufacturing(Elsevier, 2023-03-17) Ghafoori, E.; Dahaghin, H.; Diao, Chenglei; Pichler, N.; Li, L.; Mohri, M.; Ding, Jialuo; Ganguly, Supriyo; Williams, StewartIn this study, a directed energy deposition (DED) process called wire arc additive manufacturing (WAAM) is employed for the fatigue strengthening of damaged steel members. Three steel specimens with central cracks were tested under a high-cycle fatigue loading (HCF) regime: (1) the reference specimen; (2) the WAAM-repaired specimen with an as-deposited profile, and (3) the WAAM-repaired specimen machined to reduce stress concentration factors (SCF). The corresponding finite element (FE) simulation of the WAAM process was calibrated using static experimental results, which revealed the main mechanism. The process was found to introduce compressive residual stresses at the crack tip owing to the thermal contraction of the repair. The FE results also revealed that stress concentration exists at the root of the as-deposited WAAM; this stress concentration can be mitigated by machining the WAAM to a pyramid-like shape. The fractography analysis indicated that the cracks were initiated at the WAAM-steel interface, and microscopic observations revealed that the microcracks were arrested by the porosities in the melted interface. The results of this pioneering study suggest that WAAM repair is a promising technique for combating fatigue damage in steel structures.Item Open Access Hybrid wire - arc additive manufacture and effect of rolling process on microstructure and tensile properties of Inconel 718(Elsevier, 2021-09-08) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Diao, Chenglei; Zhang, Xiaoyong; Williams, StewartWire - arc additive manufacture (WAAM) is suitable for Inconel 718 components due to its high deposition efficiency. However, large columnar dendrites decrease the mechanical properties and can cause severe mechanical anisotropy. Cold rolling and warm rolling through flame heating have been investigated to analyze their effects on microstructure and tensile properties compared to as-deposited WAAM material. Standard solution and double aging (SA), as well as homogenization followed by solution and aging (HSA) heat treatments were compared. The results show that the large columnar dendrites change to finer equiaxed grains 16.4 μm and 26.2 μm in size for warm and cold rolled alloy, respectively. This increases to 22.5 μm and 30.1 μm after HSA treatment. The microhardness and strength of rolled material increase significantly and the warm rolled material after HSA treatment exceeds that of the wrought alloy. While the as-deposited and cold rolled samples both show significant anisotropy, isotropic tensile properties are obtained for warm rolled plus HSA heat treated samples. Finer equiaxed grains with more dispersive distributions of γ' and γ" strengthening precipitation contribute to the superior mechanical properties for warm rolled material. For both the cold and warm rolled material, there was an elongation decrease due to precipitated particles, which also led to a trans-granular ductile fracture mode. The strengthening mechanism of the hybrid rolling process was analyzed and found to be related to work hardening, grain boundary strengthening, precipitated strengthening phases and the δ phase.Item Open Access Investigation of 300M ultra-high-strength steel deposited by wire-based gas metal arc additive manufacturing(Springer, 2023-11-01) Wang, Jun; Diao, Chenglei; Taylor, Mark; Wang, Chong; Pickering, Ed; Ding, Jialuo; Pimentel, Misael; Williams, Stewart300 M ultra-high-strength steel (UHSS) is widely used to produce landing gear components for aircraft. The conventional manufacturing route for these components involves extensive machining and significant material wastage. Here, the application of wire-based gas metal arc additive manufacturing to produce 300 M UHSS parts was investigated. In particular, the influence of torch shielding atmosphere on the process stability and material performance of 300 M UHSS was investigated. The shielding gases used for comparison are pure Ar, Ar with 2.5% CO2, Ar with 8% CO2, Ar with 20% CO2, and Ar with 2% CO2 and 38% He. It was found that the arc length decreased, the transfer mode changed from spray to droplet mode, and spattering became more severe as the CO2 proportion increased. Additionally, replacing Ar with He led to a broader arc core, and a slightly shorter arc length and maintained a spray transfer, which decreased spatter. The wall surface roughness followed the trend in spatter, becoming worse with the increasing CO2 proportion, and better with He addition. Adding CO2 and He in pure Ar significantly increased the bead and wall width. The microstructure and mechanical properties exhibited a strong location dependence in the as-built state, with fresh martensite and higher strength in the top region, and tempered martensite and better ductility in the reheated bulk. Generally, torch shielding gas composition appeared to have no significant effect on the microstructure evolution. This study provides a reference for the subsequent application of gas metal arc additive manufacturing to aircraft landing gear mass production to achieve a high deposition rate and process stability simultaneously.Item Open Access Manufacture of large-scale space exploration components using wire + arc additive manufacturing(ICAS - International Council of the Aeronautics Sciences, 2022-11-28) Diao, Chenglei; Eimer, Eloise ; Mancini, Simone; Krishnaswamy, Surya; Schwarz, Florian; Pagone, Emanuele; Ding, Jialuo; Williams, Stewart; Pinter, Zsolt; Martina, FilomenoCranfield University, Thales Alenia Space and WAAM3D together, combining their expertise knowledge and technologies on Wire + arc additive manufacture (WAAM), created a route for manufacturing large-scale space exploration Components using WAAM which could be used in future large scale-space exploration component manufacturing. In this project, several different sections of the development of WAAM technology are applied to manufacture a large-scale space exploration component including FEA simulation, inter-layer machining and cold work, intelligent toolpath planning and sustainability calculations. WAAM proved to be a very promising technique in future large-scale component manufacturing.Item Open Access Metal 3D-printing for repair of steel structures(Ernst & Sohn (Wiley), 2023-09-12) Ghafoori, Elyas; Dahaghin, Hamid; Diao, Chenglei; Pichler, Niels; Li, Lingzhen; Ding, Jialuo; Ganguly, Supriyo; Williams, StewartThis work employs an innovative technique, wire arc additive manufacturing (WAAM) which is a type of directed energy deposition, for fatigue strengthening of cracked steel components. Different steel plates with a central crack were tested under high-cycle fatigue loading regime, including a reference plate, a plate repaired by WAAM with as-deposited profile, and a plate repaired by WAAM and subsequently machined to reduce stress concentration factors. Corresponding finite element simulation was conducted to provide a better understanding on the mechanism of WAAM-repair. The existing central crack in the reference plate propagated and led to a rupture after 0.94 million cycles, while those in the two WAAM-repaired plates did not propagate, due to the increased net cross-section and the compressive stresses induced by the depositing process. However, in the second plate, a new crack initiated at the root of WAAM profile as a result of local stress concentration, and the fatigue life reached 2.2 million cycles (2.3 times as the reference plate). The third plate, on the other hand, survived more than 9 million fatigue cycles with no visible degradation, thanks to its smooth machined profile. The findings of this work indicate that WAAM repair shows great potential as a technique to address fatigue-related damages in steel structures.Item Open Access Numerical analysis of heat transfer and fluid flow in multilayer deposition of PAW-based wire and arc additive manufacturing(Elsevier, 2018-04-05) Bai, Xingwang; Colegrove, Paul A.; Ding, Jialuo; Zhou, Xiangman; Diao, Chenglei; Bridgeman, Philippe; Hönnige, Jan Roman; Zhang, Haiou; Williams, Stewart W.A three-dimensional numerical model has been developed to investigate the fluid flow and heat transfer behaviors in multilayer deposition of plasma arc welding (PAW) based wire and arc additive manufacture (WAAM). The volume of fluid (VOF) and porosity enthalpy methods are employed to track the molten pool free surface and solidification front, respectively. A modified double ellipsoidal heat source model is utilized to ensure constant arc heat input in calculation in the case that molten pool surface dynamically changes. Transient simulations were conducted for the 1st, 2nd and 21st layer depositions. The shape and size of deposited bead and weld pool were predicted and compared with experimental results. The results show that for each layer of deposition the Marangoni force plays the most important role in affecting fluid flow, conduction is the dominant method of heat dissipation compared to convection and radiation to the air. As the layer number increases, the length and width of molten pool and the width of deposited bead increase, whilst the layer height decreases. However these dimensions remain constant when the deposited part is sufficiently high. In high layer deposition, where side support is absent, the depth of the molten pool at the rear part is almost flat in the Y direction. The profile of the deposited bead is mainly determined by static pressure caused by gravity and surface tension pressure, therefore the bead profile is nearly circular. The simulated profiles and size dimensions of deposited bead and molten pool were validated with experimental weld appearance, cross-sectional images and process camera images. The simulated results are in good agreement with experimental results.Item Open Access Optimising two-stage vacuum heat treatment for a high-strength micro-alloyed steel in railway spring clip application: impact on microstructure and mechanical performance(MDPI, 2023-07-10) Lu, Yao; Wang, Jun; Pan, Di; Han, Jian; Zhu, Lisong; Diao, Chenglei; Han, Jingtao; Jiang, ZhengyiThe heat treatment process is a vital step for manufacturing high-speed railway spring fasteners. In this study, orthogonal experiments were carried out to obtain reliable optimised heat treatment parameters through a streamlined number of experiments. Results revealed that a better comprehensive mechanical performance could be obtained under the following combination of heat treatment parameters: quenching temperature of 850 °C, holding time of 35 min, medium of 12% polyalkylene glycol (PAG) aqueous solution, tempering temperature of 460 °C, and holding time of 60 min. As one of the most important testing criteria, fatigue performance would be improved with increasing strength. Additionally, a high ratio of martensite to ferrite is proven to improve the fatigue limit more significantly. After this heat treatment process, the metallographic microstructure and mechanical properties satisfy the technical requirements for the high-speed railway practical operation. These findings provide a valuable reference for the practical forming process of spring fasteners.Item Open Access Oxide accumulation effects on wire + arc layer-by-layer additive manufacture process(Elsevier, 2017-10-20) Xu, Xiangfang; Ding, Jialuo; Ganguly, Supriyo; Diao, Chenglei; Williams, Stewart W.A maraging steel wall structure was built layer-by-layer to study oxide accumulation mechanisms and the influence of oxides on the subsequent deposition. An online arc welding camera was also applied to investigate the wetting and spreading behaviour of the deposition on different surface conditions. Two maraging steel walls were deposited under torch shielding only and torch plus tent shielding conditions respectively to study the effect of oxides on the mechanical properties. Upon deposition a mixture of Fe, Al and Ti oxides formed, floated to the weld pool surface and accumulated layer by layer, deteriorating the surface condition such that it was rough and porous, which adversely affected the stability of arc and the wetting and spreading process of the weld pool in subsequent layers. The accumulation of oxides added to the uncertainty of the layer dimension and worsened the surface finish to reduce the structural integrity. Despite that the majority of the oxides floated to the weld pool surface, oxides (up to a few hundred nanometers in diameter) were found to be dispersed in the additively manufactured structure and might be one of the strengthening sources resulting in a 11% increase in UTS and a 19% decrease in elongation compared to the structure built in the torch plus tent shielding condition.Item Open Access A passive imaging system for geometry measurement for the plasma arc welding process(Institute of Electrical and Electronics Engineers, 2017-03-22) Font comas, Tomas; Diao, Chenglei; Ding, Jialuo; Williams, Stewart W.; Zhao, YifanAutomatic and flexible geometry measurement of the weld pool surface can help better understand the complex welding processes and even provide feedback to better control this process. Most of existing imaging systems use an additional source of illumination to remove the light interference coming from the welding arc but it is usually costly. This paper introduces a novel low-cost optical-sensor-based monitoring system working under passive mode to monitor the wire + arc additive manufacture (WAAM) process, particularly for plasma arc welding. Initially, configurations and parameters of camera are investigated to achieve good visualisation of weld pool. A novel camera calibration methodology using the nozzle of a CNC machine is then proposed for this imaging system allowing estimation of the camera position with respect to the inspecting surface and its orientation in an easy-to-use approach. The verification tests show that the average error of the calibration is less than 1 pixel. As a case study, an image analysis routine is proposed to measure the width of the bead during the welding process. The results show that the proposed system is effective to measure the dimension of weld pool.Item Open Access A simplified modelling approach for thermal behaviour analysis in hybrid plasma arc-laser additive manufacturing(Elsevier, 2022-06-25) Wang, Chong; Sun, Yongle; Chen, Guangyu; Chen, Xin; Ding, Jialuo; Suder, Wojciech; Diao, Chenglei; Williams, StewartHybrid plasma transferred arc (PTA)-laser additive manufacturing (AM) has the potential to build large-scale metal components with high deposition rate and near-net shape. However, the process is complex with many parameters adjustable for process control, which determine the thermal behaviour and thus the final structure and properties of the deposited components. In this study, a three-dimensional steady-state finite element model with two independent circular surface heat sources was developed, validated, and used to analyse the thermal behaviour in hybrid PTA-laser AM of Ti-6Al-4V. Artificial conductivity in three orthogonal directions was applied in the melt pool to compensate for the melt pool convection effect. The predicted melt pool geometry, heat-affected zone and thermal cycles had good agreement with the corresponding experimental data. This model has advantages over the widely used volumetric heat source model, since it is more representative of the energy sources used, giving accurate thermal prediction for a wide range of process parameters. As the heat source parameters in this model are directly linked to the actual arc/laser size, it enables to capture heat source size effect on the hybrid process. In addition, it is easier to calibrate compared to the model with volumetric heat sources due to the fewer empirical parameters involved. It was found that in the investigated ranges of all the parameters, the melt pool geometry is more sensitive to laser power and travel speed compared to arc-laser separation distance and laser beam size. The full-field distributions of the cooling rate and temperature gradient in the hybrid process were obtained and the roles that different process parameters played on them were also studied, which provided useful thermal information for metallurgical analysis.Item Open Access Study on strengthening mechanism of Ti/Cu electron beam welding(Elsevier, 2017-02-20) Guo, Shun; Zhou, Qi; Peng, Yong; Xu, Xiangfang; Diao, Chenglei; Kong, Jian; Luo, TianYuan; Wang, Kehong; Zhu, JunWelding-brazing method is widely used for dissimilar metals welding. However, it is becoming increasingly difficult to further improve the connection strength by controlling the formation of the transition layer. In this study, an innovative welding method referred to as adjacent welding was addressed, which greatly improved the tensile strength of Ti/Cu dissimilar joint. The strength of new joint could reach up to 89% that of copper base metal, compared to the use of a traditional welding-brazing method which strength coefficient is within the limit of 70%. In order to determine the strengthening mechanism of adjacent welding, optical microscopy, SEM, EDS and XRD were applied for the analysis of microstructure and phase structure. Furthermore, tensile strength was also tested. The results show that due to the process of remelting and reverse solidification of intermetallic compounds (IMCs) layer, a less complex and thinner IMCs layer was formed and TiCu (553 HV) with high embrittlement existing in the front of titanium substrate was changed into Ti2Cu (442 HV). Performances of joints were optimized by these changes. An interpretation module was presented for the mechanism.Item Open Access Video for Fig. 4b(Cranfield University, 2022-06-17 09:57) Wang, Chong; Sun, Yongle; Chen, Guangyu; Chen, Xin; Ding, Jialuo; Suder, Wojciech; Diao, Chenglei; Williams, StewartThis is a supplementary video for Fig 4b, showing the hybrid PTA-laser melting process with a laser leading configuration.