Browsing by Author "Lu, Yao"

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    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, Zhengyi
    A 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.
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    Compressive properties and fracture behaviours of Ti/Al interpenetrating phase composites with additive-manufactured triply periodic minimal surface porous structures
    (Springer, 2024-12-31) Li, Zhou; Mo, Haotian; Tian, Jiahao; Li, Junhao; Xia, Shiqi; Jia, Xianshi; Zhou, Libo; Lu, Yao
    The triply periodic minimal surfaces (TPMS) structure is regarded as a highly promising artificial design, but the performance of composites constructed using this structure remains unexplored. Two porosity levels of Ti/Al interpenetrating phase composites (IPCs) were fabricated by infiltrating ZL102-Al melt into additive-manufactured TC4-Ti scaffolds with the TPMS porous in this study. The combination of the two-phase alloys exhibits structural integrity at the interfacial region, as evidenced by microscopic surfaces observed in uncompressed IPCs. Quasi-static compression tests were performed to demonstrate that the Young’s modulus, yield stress and maximum compressive stress of IPCs exhibit significant enhancement when compared to the individual TPMS scaffolds, due to the supporting and strengthening effect of the filling phase. In the compression process of IPCs, defects emerge initially at the interface between the ZL102 phase and TC4 phase, triggering the fracture and slip of the ZL102 phase, eventually propagating to involve fracture in the TC4 phase. The deformation behaviours obtained from numerical simulation were combined to support these experimental phenomena. The results show that the corresponding stress concentration region is the central region of the spiral surface, the maximum stress concentration region of the ZL102 phase is the same as that of the TC4 phase, and the ZL102 phase effectively shares part of the loading. The Ti/Al IPCs achieve equivalent load-bearing capacity through a simplified interpenetration process and the utilisation of lighter materials.
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    Design of nonlinear gradient sheet-based TPMS-lattice using artificial neural networks
    (Elsevier, 2024-11-01) Li, Zhou; Li, Junhao; Tian, Jiahao; Xia, Shiqi; Li, Kai; Su, Guanqiao; Lu, Yao; Ren, Mengyuan; Jiang, Zhengyi
    Gradient triply periodic minimal surface (TPMS) structures are renowned for lightweight design and enhanced performance, but their complex and nonlinear configurations pose challenges in achieving targeted design goals. A new design methodology for the nonlinear gradient structure was proposed in this study, with the aim of achieving efficient and accurate modeling of complex and gradient sheet-based TPMS structures under specific performance objectives. This method utilized automated finite element (FE) simulations to obtain structure topology element densities under various boundary conditions. An artificial neural network (ANN) was then employed to efficiently predict the correspondence between these boundary conditions and topology element densities. A mapping was established between topology element densities and TPMS structural parameters, and the gradient structure was accurately constructed by using the voxel modeling technique. Taking a typical cantilever beam TPMS structure as an example of nonlinear gradient design, the results indicate that the error between the ANN-predicted and FE-simulated structure topology element densities is only 2.73 %, with prediction time being only 0.15 % of the simulation time. The thin regions of the gradient structure align with those geometrically removed in regular topology optimization scheme, achieving up to 65.45 % weight reduction, a 28.72 % improvement over the regular scheme, along with uniform structural stress transition and maximum stress reduction. TC4 alloy nonlinear gradient TPMS structures, printed by metal selective laser melting (SLM) technique, confirm the practical application value of this design method.
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    Enhanced performance of micro deep drawing through the application of TiO2 nanolubricant and graphene lubricants on SUS 301 stainless steel foil
    (MDPI, 2023-10-23) Pan, Di; Zhang, Guangqing; Jia, Fanghui; Lu, Yao; Wang, Jun; Li, Zhou; Li, Lianjie; Yang, Ming; Jiang, Zhengyi
    first_pagesettingsOrder Article Reprints Open AccessArticle Enhanced Performance of Micro Deep Drawing through the Application of TiO2 Nanolubricant and Graphene Lubricants on SUS 301 Stainless Steel Foil by Di Pan 1ORCID,Guangqing Zhang 1,Fanghui Jia 1,Yao Lu 2,Jun Wang 2,Zhou Li 3,Lianjie Li 4,Ming Yang 5ORCID andZhengyi Jiang 1,* 1 School of Mechanical, Materials, Mechatronic and Biomedical Engineering, Wollongong, NSW 2522, Australia 2 Welding Engineering and Laser Processing Centre, Cranfield University, Bedfordshire MK43 0AL, UK 3 College of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China 4 School of Intelligent Manufacturing and Control Engineering, Shanghai Polytechnic University, Shanghai 201209, China 5 Graduate School of System Design, Tokyo Metropolitan University, Hino, Tokyo 191-0055, Japan * Author to whom correspondence should be addressed. Processes 2023, 11(10), 3042; https://doi.org/10.3390/pr11103042 Received: 2 September 2023 / Revised: 17 October 2023 / Accepted: 20 October 2023 / Published: 23 October 2023 (This article belongs to the Special Issue Processing, Manufacturing and Properties of Metal and Alloys) Downloadkeyboard_arrow_down Browse Figures Versions Notes Abstract In recent years, the quest for effective lubrication in micro deep drawing (MDD) has seen promising advancements. In this study, the influence of TiO2 nanolubricants and graphene lubricants on the performance of 301 stainless steel foil in MDD is examined. The MDD undergoes an extensive evaluation of various lubrication conditions, including dry, TiO2 nanolubricant, graphene lubricant at concentrations of 2.5 mg/mL, 5.0 mg/mL, and 10.0 mg/mL, as well as combined applications of TiO2 and graphene lubricants. Utilising a 5.0 mg/mL graphene lubricant together with TiO2 nanolubricants led to a significant reduction in drawing force, highlighting the synergistic efficacy of this combined lubricant. A pronounced enhancement in the consistency of the produced microcups was also attained. These results emphasise the promise of TiO2 nanolubricant and graphene lubricants in optimising the MDD process.
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    Ex situ analysis of high-strength quenched and micro-alloyed steel during austenitising bending process: numerical simulation and experimental investigation
    (Springer, 2022-05-11) Lu, Yao; Xie, Haibo; Wang, Jun; Jia, Fanghui; Lin, Fei; Zhou, Cunlong; Xu, Jianzhong; Han, Jingtao; Jiang, Zhengyi
    This paper compares the microstructure and mechanical evolution in a high-strength quenched and micro-alloyed steel during the austenitising bending process. Simulation results indicated a new finding that the stress neutral layer (SNL) tends to move to the tension zone during straining. The hardness gradient detected from the centre to compression/tension zones was resulted from comprehensive factors: First of all, the location of SNL revealed a prominent impact on strength. Second, the dislocation accumulation would be responsible for the hardness gradient on the surfaces. In addition, the overall strength decrease during straining was mainly ascribed to integrated effects of dynamic recovery (DRV) and dynamic recrystallisation (DRX). Apart from that, overall smaller martensite packet size and coarser prior austenite grains resulted in the increased hardness value at a lower bending degree. Also, the high consistency between experimental and simulation results is instructive for the practical forming process of railway spring fasteners.
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    Exploring the use of graphene lubricant and TiO2 nanolubricants in micro deep drawing of stainless steel SUS301
    (Springer, 2024-01-25) Pan, Di; Zhang, Guangqing; Jia, Fanghui; Wu, Hui; Lu, Yao; Zhang, Tao; Li, Lianjie; Lin, Fei; Yang, Ming; Jiang, Zhengyi
    This study investigates the effects of different lubrication conditions on drawing force and microcup formation during micro deep drawing (MDD). Results show that graphene lubricant, in combination with TiO2 nanolubricants, has the potential to reduce friction during MDD. The peak drawing force was reduced by 15.39% when both lubricants were used together, while the use of TiO2 nanolubricant and 10.0 mg/ml graphene lubricant reduced it by 6.03% and 14.52%, respectively. The study also reveals that lubricants reduce wrinkling during the formation of microcups by minimising energy consumption during the primary formation. However, the combination of TiO2 nanolubricant and graphene lubricant can cause inhomogeneous formation on the upper part of the blank, leading to more apparent wrinkling. Overall, the study highlights the potential of TiO2 nanolubricant and graphene lubricant in reducing friction and improving microcup formation during MDD.
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    Forming rate dependence of novel austenitising bending process for a high-strength quenched micro-alloyed steel: experiments and simulation
    (MDPI, 2025-02-06) Lu, Yao; Wang, Jun; Li, Zhou; Lin, Fei; Pan, Di; Jia, Fanghui; Han, Jingtao; Jiang, Zhengyi
    This austenitising bending investigation was carried out in a vacuum environment with the forming rates of 1, 10, and 100 mm/min under a certain bending temperature of 900 °C by a thermomechanical simulator. The enhanced strength at the accelerated forming rate and on the compression/tension zones throughout the thickness of the bent plates was discussed in detail in terms of dislocation pile-up, smaller prior austenite grain size, dynamic recrystallisation, smaller martensite packet, and stress-neutral layer. Since the simulation results were validated to match the experimental trend, this investigation could be applied as a valuable reference to simulate the practical manufacturing process of railway fasteners.
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    In situ investigation on densification mechanism of Ti-20Al-19Nb (at.%) alloy by TiH2-assisted pressureless sintering
    (Elsevier, 2023-06-20) Cai, Qi; Yu, Qilin; Li, Xinyao; Lu, Yao; Li, Yanmo; Cui, Ganggang
    Dense Ti-20Al-19Nb (at.%) alloys can be cost-effectively fabricated by TiH2-assisted pressureless sintering; nevertheless, the densification mechanism remains controversial without understanding the entire sintering process. By in situ observing the surface morphology of the Ti/Al/Nb and Ti/TiH2/Al/Nb compacts upon heating, the densification mechanism of the Ti-20Al-19Nb alloys was elucidated in this study. In addition to the reported reason that the dehydrogenation of TiH2 provided reactive Ti, the densification of Ti-20Al-19Nb alloy was found to be strongly associated with the phase transformations upon sintering. The TiH2 participated in the reverse eutectoid transformation, α-Ti + δ-TiH2 → β-Ti, inducing the α/β and TiH2/β grain boundaries for the rapid diffusion of Al. The reaction of Ti(s) + Al(s) → TiAl3(s) was then accelerated, and the majority of the Al phase was consumed in the solid state, which significantly reduced the pores from the transient liquid Al. The activation energy of the Ti-Al reaction decreased with the addition of TiH2, and the growth mode of the TiAl3 phase was changed. By removing the large pores at 700 °C, the Ti-Al intermetallic phases were well connected, forming the continuous interdiffusion route for Ti, Al, and Nb. The diffusion of Nb, as well as the phase transformation of α2 → B2, was then promoted, and the ripening time for the B2 phase was increased. As a result, the density and mechanical properties were improved. The initial results of this study provided a foundation for the cost-effective fabrication of high-strength Ti-Al alloys containing refractory elements.
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    Inverse design of cellular structures with the geometry of triply periodic minimal surfaces using generative artificial intelligence algorithms
    (Elsevier, 2024-12-15) Li, Zhou; Li, Junhao; Tian, Jiahao; Xia, Shiqi; Li, Kai; Li, Maojun; Lu, Yao; Ren, Mengyuan; Jiang, Zhengyi
    Triply periodic minimal surfaces (TPMS) exhibit excellent mechanical and energy absorption properties due to their structural advantages. However, existing porous TPMS structural design methods are constrained to a forward process from structural parameters to mechanical properties. This study proposed an inverse design method that combines bidirectional generative adversarial networks (BiGAN) and mechanical performance targets, resulting in a combined TPMS structure of Primitive and IWP types with superior buffering and energy absorption capabilities. The results show that under a single load value target condition of the designed structure, the minimum deviation index (R2) between the load value corresponding to the displacement point and the target load value is only 0.987, and the maximum mean absolute percentage error (MAPE) is only 5.92 %. When considering the elastic modulus target, the approach successfully conducts two sets of combined structural designs meeting the requirements of both high and low elastic moduli. When targeting the specified load-displacement curve conditions, specifically when combining high elastic modulus with ascending plasticity, the designed structures exhibit an error of only 2.2 % compared to the target property. Moreover, the quasi-static uniaxial compression experiments conducted on additively manufactured designed structures confirm that the experimental curves match the target curves in terms of deformation trends and load value ranges. The success of this inverse design approach for cellular TPMS structures has the potential to expedite new structural material development processes.
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    A novel Ti/Al interpenetrating phase composite with enhanced mechanical properties
    (Elsevier, 2023-12-09) Li, Zhou; Mo, Haotian; Tian, Jiahao; Li, Jiahao; Hu, Xiao; Xia, Shiqi; Lu, Yao; Jiang, Zhengyi
    Lightweight, energy-absorbing materials with excellent mechanical properties are highly desired in practical engineering applications. A novel Ti-Al interpenetrating phase composite (Ti/Al IPC) was successfully fabricated by filling an Al alloy (ZL102) in the pores of an additively manufactured triply periodic minimal surface (TPMS) structure composed of Ti alloy (TC4). This IPC demonstrates a remarkable combination of attributes, including a high yield stress of 305 MPa, a Young's modulus of 64 GPa, and an ultimate tensile strength of 420 MPa. These mechanical properties are 1.5 to 2.9 times stronger than those of a single TC4 TPMS structure of the same size. The enhanced performance can be attributed to the synergistic strengthening and toughening effect resulting from the internal interpenetration of the ZL102 phase within the structure.
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    On the composition gradient of steel/Invar functionally graded material manufactured by wire-based direct energy deposition
    (Elsevier, 2024-09-25) Wang, Jun; Biswal, Romali; Chen, Guangyu; Pardal, Goncalo Rodrigues; Lu, Yao; Ding, Jialuo; Williams, Stewart
    This study utilized double-wire plasma arc direct energy deposition to produce functionally graded materials (FGMs) with two transition designs, abrupt (AT) and gradual (GT), from Er90s steel to Invar. The study systematically compared the transition in chemical composition, microstructure, phase evolution, thermal stress, and mechanical performance. Both FGM types exhibited a band structure in the Er90s section and coarse columnar grains in the Invar section, with the AT deposit showing a 1 mm thick, defect-free interface and the GT deposit having an 18 mm thick transition region with distinct boundaries. It revealed diverse microstructures across the transition zones, including fine ferrite, martensite with minor retained austenite (RA), coarse columnar austenite with martensite dendrites, and single FCC austenite. The GT sample uniquely featured a microstructure of martensite laths inside prior austenite decorated by RA semicontinuous network, with a crack detected due to dilatational stresses from martensite transformation. Hardness was similar in both FGM types, with higher values at the interfaces, especially in the GT FGM. The GT FGM demonstrated higher strength but lower ductility compared to the AT FGM, with failure occurring in the Invar portion for both. Thermal stress modelling indicated smoother stress transitions in the GT sample but no significant performance differences between Er90s and Invar. This study showcases the effectiveness of double-wire plasma arc DED in producing steel/Invar FGMs with varying composition gradients. It also underscores the importance of selecting the right mixing ratio for Er90s/Invar FGM deposits to avoid cracking and deterioration of properties in the gradient area.
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    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, Zhengyi
    The 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.
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    Physical simulation and numerical simulation of flash butt welding for innovative dual phase steel DP590: a comparative study
    (MDPI, 2023-05-03) Song, Jingwen; Zhu, Lisong; Wang, Jun; Lu, Yao; Ma, Cheng; Han, Jian; Jiang, Zhengyi
    In this study, the microstructure and performance of newly designed dual-phase steel (DP590) after joining by flash butt welding (FBW) for vehicle wheel rims was analysed and compared by two simulations, i.e., physical simulation and numerical simulation, due to the high acceptance of these two methodologies. Physical simulation is regarded as a thermal–mechanical solution conducted by the Gleeble 3500 simulator and which can distribute the heat-affected zone (HAZ) of the obtained weld joint into four typical HAZs. These are coarse-grained HAZ, fine-grained HAZ, inter-critical HAZ and sub-critical HAZ. A combination of ferrite and tempered martensite leads to the softening behaviour at the sub-critical HAZ of DP590, which is verified to be the weakest area, and influences the final performance due to ~9% reduction of hardness and tensile strength. The numerical simulation, relying on finite element method (FEM) analysis, can distinguish the temperature distribution, which helps us to understand the relationship between the temperature distribution and real microstructure/performance. Based on this study, the combination of physical and numerical simulations can be used to optimise the flash butt welding parameters (flash and butt processes) from the points of temperature distribution (varied areas), microstructure and performance, which are guidelines for the investigation of flash butt welding for innovative materials.
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    Strain hardening and strengthening mechanism of laser melting deposition (LMD) additively manufactured FeCoCrNiAl0.5 high-entropy alloy
    (Elsevier, 2022-10-05) Zhu, Lisong; Geng, Keping; Wang, Jun; Sun, Da; Shan, Mengdie; Lu, Yao; Zhang, Xuesong; Cai, Yangchuan; Han, Jian; Jiang, Zhengyi
    In order to develop the high-entropy alloy (HEA) with low cost and excellent mechanical properties for structural applications, the FeCoCrNiAl0.5 HEA has been fabricated by laser melting deposition, one of the advanced additive manufacturing methods. Strain hardening behaviour has been analysed and discussed using the combination of characterisation techniques. The LMD-ed FeCoCrNiAl0.5 had a true yield strength and strain of ∼463 MPa and 2.94%. Also, the true tensile strength of the LMD-ed FeCoCrNiAl0.5 reached 876 MPa, together with the ductility of 24.97% (engineering strain). The LMD-ed FeCoCrNiAl0.5 HEA exhibited a dual-phase structure of 93% face-centred cubic (FCC) phase and 6.9% ordered B2 phase. The phase boundary between the disordered FCC and ordered B2 phases played a key role in the barrier, which can block the movement of dislocations because of the lattice distortion, very large angle, and mismatch of the lattice. Dislocation pile-up and tangle caused the dislocation density near the phase boundaries to be higher than that in other areas, meanwhile, they further prevented the movement of dislocation under stress as they generated back stress, therefore LMD-ed FeCoCrNiAl0.5 HEA had a good strain hardening behaviour with a strain hardening exponent of 0.92. This study provided an innovative insight into the development of HEAs with ordered phase by laser additive manufacturing for structural applications.