Browsing by Author "Zhang, Tao"
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Item Open Access Comparative analysis of cold and warm rolling on tensile properties and microstructure of additive manufactured Inconel 718(Springer, 2022-01-14) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, Xin; Zhang, XiaoyongDespite the high efficiency and low cost of wire + arc additive manufacture (WAAM), the epitaxial grown columnar dendrites of WAAM deposited Inconel 718 cause inferior properties and severe anisotropy compared to the wrought components. Fundamental studies on the influence of one-pass cold and warm rolling on hardness and microstructure were investigated. Then the interpass cold and warm rolling on tensile properties were also analyzed. The results show that the one-pass rolling increases the hardness and displays a heterogeneous hardness distribution compared to the as-deposited material, and the warm rolling exhibits a larger and deeper strain compared to cold rolling. The columnar dendrites gradually change to cell dendrites under the rolling process and then change to equiaxed grains with the subsequent new layer deposition. The average grain size is 16.8 μm and 23.5 μm for the warm and cold rolling, respectively. The strongly textured columnar dendrites with preferred < 001 > orientation transform to equiaxed grains with random orientation after rolling process. The grain refinement contributes to the dispersive distributed strengthening phases and the increase in its fraction with heat treatment. The as-deposited samples show superior tensile properties compared to the cast material but inferior compared to the wrought components, while the warm-rolled samples show superior tensile properties to wrought material. Isotropic tensile properties are obtained in warm rolling compared to cold rolling. The rolling process and heat treatment both decrease the elongation and lead to a transgranular ductile fracture mode. Finally, the rolling-induced strengthening mechanism was discussed.Item Open Access Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures(Elsevier, 2021-07-03) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, XinInferior mechanical properties and severe anisotropy behavior of wire + arc additive manufactured (WAAM) Inconel 718 due to the large epitaxial grown columnar dendrites restrict the industrial application of WAAM deposition. Cold rolling was integrated into the WAAM deposition process and the effect of rolling force on microstructure, precipitatation distribution and tensile properties at ambient and elevated temperatures were investigated. The results show that the hardness of cold-rolled samples is much larger than that of the as-deposited and it increases with the increase in the rolling force. The columnar dendrites of the as-deposited sample changed to finer equiaxed grains of 26.5 and 14.7 μm after cold rolling with the force of 50 kN and 75 kN, respectively. Meanwhile, more uniformly distributed grains and less δ phase appear for 75 kN rolled sample. The stress-strain curves are smooth for the tensile tests at ambient temperature, while there are serrations at elevated temperature due to the dynamic strain aging behavior. The as-deposited sample shows inferior tensile properties to the wrought material at ambient and elevated temperatures. The cold-rolled samples both exceed the wrought material at ambient temperature; however, they show higher strength but lower elongation compared to the wrought material. The 75 kN cold rolled sample shows much higher strength and similar elongation to the wrought material for the test at elevated temperature. The grain morphology and recrystallization, as well as the strengthening mechanism of hybrid deposition and cold rolling process were discussed.Item Open Access An efficient constrained weighted least squares method with bias reduction for TDOA-based localization(IEEE, 2021-02-05) Zhang, Liang; Zhang, Tao; Shin, Hyo-SangThis paper addresses the source location problem by using time-difference-of-arrival (TDOA) measurements. The two-stage weighted least squares (TWLS) algorithm has been widely used in the TDOA location. However, the estimation accuracy of the source location is poor and the bias is significant when the measurement noise is large. Owing to the nonlinear nature of the system model, we reformulate the localization problem as a constrained weighted least squares problem and derive the theoretical bias of the source location estimate from the maximum-likelihood (ML) estimation. To reduce the location bias and improve location accuracy, a novel bias-reduced method is developed based on an iterative constrained weighted least squares algorithm. The new method imposes a set of linear equality constraints instead of the quadratic constraints to suppress the bias. Numerical simulations demonstrate the significant performance improvement of the proposed method over the traditional methods. The bias is reduced significantly and the Cramér–Rao lower bound accuracy can also be achievedItem Open Access Efficient underwater acoustical localization method based on time difference and bearing measurements(IEEE, 2020-12-16) Zhang, Liang; Zhang, Tao; Shin, Hyo-Sang; Xu, XiangThis article addresses the underwater acoustical localization problem by using the time-difference-of-arrival (TDOA) and bearing-angle-of-arrival (BAOA) measurements. For the underwater acoustic equipment, such as the ultrashort baseline system (USBL), whose bearing measurements are different from the traditional angle-of-arrival (AOA) model, a closed-form solution for the hybrid TDOA/BAOA-based source localization problem is developed. However, the solution suffers from the measurement noise and cannot achieve the Cramer–Rao lower bound (CRLB) performance in the case of large measurement noise. Thus, an iterative constrained weighted least-squares method is presented to further minimize the error in the case of large noise. The CRLB for hybrid TDOA/BAOA source localization is analyzed, and the solution is proved to achieve the CRLB performance. Numerical simulations and field tests demonstrate that the proposed method outperforms the traditional methods in terms of estimation bias and accuracy. It can achieve the CRLB performance better.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 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, ZhengyiThis 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.Item Open Access Geomagnetic gradient-assisted evolutionary algorithm for long-range underwater navigation(IEEE, 2020-10-30) Zhang, Jiayu; Zhang, Tao; Shin, Hyo-Sang; Wang, Jian; Zhang, ChenExtensive research results have shown that animals like pigeons and turtles can use geomagnetic information for long-distance migration and homing. This article studies the bionic navigation method inspired by magnetotaxis behavior without prior knowledge. The problem of bionic geomagnetic navigation is generalized as an autonomous search of navigation path under the excitation of geomagnetic environment. The geomagnetic gradient-assisted evolutionary algorithm for long-range underwater navigation is proposed. In order to optimize the navigation path, the heading angle predicted by the geomagnetic gradient is used to constrain the sample space in the evolutionary algorithm. Then, according to the principle of multiparameter simultaneous convergence, the evaluation function is improved to enhance the reliability and accuracy of the navigation path. Simulations of the algorithm before and after improvement are carried out based on the data retrieved from the enhanced magnetic model (EMM). The performance of the improved method is evaluated and verified in the case of the area with normal geomagnetic field (GF), geomagnetic anomaly area, and multiple destinations. The simulation results show that the search efficiency and the straightness of the navigation path are greatly improved. The reason is that the constraint of sample space reduces the randomness in the process of navigation path search, and the improved evaluation function can evaluate the quality of samples more accurately. The improved algorithm also has good performance in the geomagnetic anomaly area, which indicates the potential application in the future.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 In-situ structural identification of Zr3Al2 type metastable phase during crystallization of a Zr-based MG(Elsevier, 2016-08-21) Xing, Yan; Li, Yan; Wang, Xiangke; Yu, Xiangtian; Zhang, Tao; Georgarakis, KonstantinosA metastable phase was detected using higher energy synchrotron radiation when Zr-based metallic glass (MG) was annealed under vacuum in Linkam hot stage at 848 K. The formation and transformation processes of metastable phase were recorded by synchrotron radiation method. The metastable phase during crystallization was identified as Zr3Al2 structure type according to powder diffraction and TEM analysis. The structure of Zr3Al2 type MCP was experimentally evidenced by 3D diffraction patterns and mathematically described. The identification of Zr3Al2 MCP could be helpful for the understanding of cluster structure of MG.Item Open Access Study on location-related thermal cycles and microstructure variation of additively manufactured Inconel 718(Elsevier, 2022-04-04) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Chen, Xin; Zhang, XiaoyongThe complicated thermal history of wire + arc additive manufacturing (WAAM) will affect the microstructure variation and mechanical properties of the as-deposited material. Numerial models of Inconel 718 in WAAM deposition were established and the location-related thermal history and temperature distribution were analyzed. A hybrid method of WAAM and cold rolling was investigated and its effect on the microstructure distribution and texture was investigated compared to that in as-deposited condition. The results show that WAAM deposition features repeated thermal cycles, high heating rate and low cooling rate. The trough values of the thermal cycles first increases and then decreases, while the peak temperature always decreases with the proceeding of the deposition process. The as-deposited samples show columnar dendrites and its average dendrite arm spacing increases with the increased build height due to the location-related heat accumulation. The strongly textured columnar dendrites with preferred <001> orientation transform to equiaxed grains with random orientation in heat-affected zone after cold rolling process, and its average size decreases with the increased rolling force. The as-deposited samples show the strongest intensity of 7.609 for the {100} family of grains oriented along the transverse direction; while it decreases to 3.629 and 2.057 for the cold rolled conditions with the force of 50 kN and 75 kN, respectively. The relationship between thermal history and the microstructure distribution was discussed. The mechanism of hybrid WAAM and cold rolling method consisted of spatially and temporally heterogeneous work hardening and recrystallization.