Imperial College London

DrJunJiang

Faculty of EngineeringDepartment of Mechanical Engineering

Senior Lecturer
 
 
 
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Contact

 

jun.jiang

 
 
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Location

 

524City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

78 results found

Wang C, Cai W, Sun C, Li X, Qian L, Jiang Jet al., 2022, Strain rate effects on mechanical behavior and microstructure evolution with the sequential strains of TWIP steel, Materials Science and Engineering: A, Pages: 142673-142673, ISSN: 0921-5093

Journal article

Liu Y, Wang Y, Xu X, Hopper C, Dong H, Wang X, Zhu H, Jiang Jet al., 2021, The study of hot deformation on laser cladding remanufactured 316L stainless steel, Materials and Design, Vol: 212, Pages: 1-13, ISSN: 0264-1275

Laser cladding deposition (LCD) is widely used to remanufacture/repair workpieces because of its high design freedom to rebuild areas of damage. However, the process often introduces a columnar grain structure in the cladding layer, resulting in a large variation of microstructure and hardness across the cladding layer, welding interface, and base metal. Under fatigue and tensile loading, fractures can initiate in the lower hardness cladding layer. This study explores the feasibility of a new hybrid remanufacturing method integrating the LCD with a subsequent hot deformation process to refine grain structures, reduce hardness variations, and enhance mechanical properties. The effects of deformation temperatures and imposed plastic strains were studied by examining the microstructural and stress–strain behaviour of laser cladded 316L stainless steel. After LCD, compressive deformation was imposed at temperatures of 900 and 1100 °C, with engineering strain levels of 0.1 and 0.5. A high-quality metallurgical joint was achieved, with the optimal ultimate tensile strength and yield strength under process conditions of an engineering strain level of 0.5 imposed at 900 °C (35% improvement compared to the directly laser cladding remanufacturing process). Dynamic recrystallization process was observed by the electron back scatter diffraction technique to reveal the underlying mechanism.

Journal article

Hu Y X J, Jiang J, Lei M, Song M, Nikbin Ket al., 2021, Predicting Virtual Creep Crack Growth in a Simulated Titanium Aluminide Alloy Microstructure Containing Voids, Precipitates, and Grain/Grain Boundary Distortions, Engineering Fracture Mechanics, Pages: 108171-108171, ISSN: 0013-7944

Journal article

Luan Q, Wang J, Huang Y, Balint D, Jiang Jet al., 2021, How would the deformation bands affect recrystallization in pure aluminium?, Materials and Design, Vol: 209, ISSN: 0264-1275

Deformation bands (DBs), formed after plastic deformation, are known to have an impact on the recrystallization (RX) process. The exact mechanisms of how DBs influence grain nucleation and grain growth remain unclear. In this paper, deformed single and multicrystal pure aluminium samples are annealed to explore the likely effects of DBs on the grain nucleation and the subsequent grain growth. Regarding the prediction of the recrystallized (RXed) texture, it is noticeable that the orientations of nucleated grains nearby DB are originated from the orientation in DB. Regarding the nucleated positions, it is demonstrated that potential nucleation sites are more likely located in DBs in comparison with the initial grain boundary. Regarding the rate of RX, the number of nucleated grains is also predicted to have a strong positive correlation with the area fraction of DBs, which would consequently affect the kinetics of the grain growth in the deformed microstructure. All the above observations imply that the RX process is strongly controlled by the ensemble characteristics of DBs rather than the initial grain boundaries.

Journal article

Xi J, Hu Y, Xing H, Han Y, Zhang H, Jiang J, Nikbin Ket al., 2021, The Low-Cycle Fatigue Behavior, Failure Mechanism and Prediction of SLM Ti-6Al-4V Alloy with Different Heat Treatment Methods., Materials (Basel), Vol: 14, ISSN: 1996-1944

Selective laser melting (SLM) is a promising additive manufacturing (AM) process for high-strength or high-manufacturing-cost metals such as Ti-6Al-4V widely applied in aeronautical industry components with high material waste or complex geometry. However, one of the main challenges of AM parts is the variability in fatigue properties. In this study, standard cyclic fatigue and monotonic tensile testing specimens were fabricated by SLM and subsequently heat treated using the standard heat treatment (HT) or hot isostatic pressing (HIP) methods. All the specimens were post-treated to relieve the residual stress and subsequently machined to the same surface finishing. These specimens were tested in the low-cycle fatigue (LCF) regime. The effects of post-process methods on the failure mechanisms were observed using scanning electron microscopy (SEM) and optical microscopy (OM) characterization methods. While the tensile test results showed that specimens with different post-process treatment methods have similar tensile strength, the LCF test revealed that no significant difference exists between HT and HIP specimens. Based on the results, critical factors influencing the LCF properties are discussed. Furthermore, a microstructure-based multistage fatigue model was employed to predict the LCF life. The results show good agreement with the experiment.

Journal article

Guo X, Sun C, Wang C, Jiang J, Fu MWet al., 2021, Study of dislocation-twin boundary interaction mechanisms in plastic deformation of TWIP steel by discrete dislocation dynamics and dislocation density-based modeling, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 145, ISSN: 0749-6419

Journal article

Wang Y, Liu Y, Lan B, Jiang Jet al., 2021, A study of solid-state bonding-by-hot-deforming mechanism in Inconel 718, Journal of Materials Processing Technology, Vol: 295, ISSN: 0924-0136

Solid-state bonding shows irreplaceable advantages in joining similar and dissimilar materials with poor weldability compared with fusion welding methods. To widen its applications in manufacturing safety-critical structural parts, a sound bonding quality must be achieved under less strict conditions. In this work, the metallurgical bonding is formed by hot compressing two Inconel 718 parts to different strain levels at the temperature of 1150 °C, strain rate of 0.1s−1 under a low vacuum. Full tensile strength and ductility comparable to the parent materials have been achieved for the first time by 0.5 engineering strain. The severe plastic deformation at hot temperature rapidly bonds the two parts by effectively closing the interface micro-voids, breaking up the oxide film, and in the meantime, accelerating the grain boundary(GB) migration through the dynamic recrystallization(DRx). Based on these observations, a theoretical model is proposed to describe the bonding process under hot deforming condition and the achieved relative interface bond quality, in which the cohesion between oxide-oxide and oxide-metal is assumed, and impairing effect of remaining dispersed oxides is minimized with the attempt of introducing a strain-amplifying factor. The insights and model provide the basis for further understanding of the solid-state bonding-by-hot-deforming under practical conditions and explore its wider application with ideal joint integrity.

Journal article

Lan B, Wang Y, Liu Y, Hooper P, Hopper C, Zhang G, Zhang X, Jiang Jet al., 2021, The influence of microstructural anisotropy on the hot deformation of wire arc additive manufactured (WAAM) Inconel 718, Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing, Vol: 823, Pages: 1-14, ISSN: 0921-5093

Hybrid additive manufacturing, incorporating additive manufacturing (AM) and other thermo-mechanical processes, has been developed to improve AM mechanical properties by modifying the as-deposited microstructure and eliminating defects. Additive manufactured parts present strong anisotropic properties, as shown by the anisotropic columnar grain morphology and texture. Samples of AM Inconel 718 were tested at high temperature and under uniaxial compression over a range of conditions. The evolution of microstructural anisotropy and the viscoplastic behaviour under these hot deformation processes was studied. The microstructure and texture evolution were characterised with optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the initial anisotropic microstructure had a negligible effect on flow stress and slip system activation during the hot deformation. The shape of original grains did, however, play a predominant role in determining the final microstructure. When the compression direction was perpendicular to the longitudinal of columnar grains, a more uniform microstructure was obtained under high-flow-stress conditions. This preferred compression direction provides guidance for hot deformation in hybrid additive manufacturing practice. Furthermore, for the nickel alloy studied, controlling the deformation direction to achieve a fine grain structure at a lower temperature (950 °C, lower than δ-solvus) brings practical benefits in the form of possible further δ grain refinement and less demanding thermal conditions during subsequent deformation processes.

Journal article

Xiong Y, Luan Q, Zheng K, Wang W, Jiang Jet al., 2021, Understanding the Strain Path Effect on the Deformed Microstructure of Single Crystal Pure Aluminum, METALS, Vol: 11

Journal article

Guo L, Yuan J, Pei J, Zhao Y, Zhang K, Jiang Jet al., 2021, Study of the microstructure, bonding evolution and mechanical properties of continuously extruded magnesium AZ31 sheet, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 819, ISSN: 0921-5093

Journal article

Jing Y, Ren XY, Shang Y, Xiong H, Jiang Jet al., 2021, Develop a novel high-strength vacuum brazing technique for γ-TiAl intermetallic, International Journal of Lightweight Materials and Manufacture, Vol: 4, Pages: 237-245

Limited strength and ductile joints for bonding γ-TiAl intermetallics are one of the main concerns on γ-TiAl applications in the aerospace industry. In this study, a new ductile brazing filler with TiZrCuNi system was developed by an established model for calculating the electrons distribution of the unit cell for the filler. Three kinds of fillers with fixed amount of Cu and Ni as 25 wt.%, but different Zr level (25, 18, 10 wt.%) were designed. It was found that the filler diffusion was affected by the filler composition, which was insufficient with high Zr content up to 37.5 wt.%. And the defects such as the voids and the cracks were observed with medium Zr level as 25 wt.% and brazing temperature as 1000 °C. The sound joints by Zr as 18 wt.% and 10 wt.% filler at 950 °C and 980 °C respectively were achieved with tensile strength as 520 MPa–570 MPa at room temperature. This tensile strength was remained as 495 MPa in average at 600 °C. The strong joints were attributed to the fine, randomly oriented Ti3Al grains and evenly distributed elements at the interfaces.

Journal article

Zheng J-H, Pruncu C, Zhang K, Zheng K, Jiang Jet al., 2021, Quantifying geometrically necessary dislocation density during hot deformation in AA6082 Al alloy, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 814, ISSN: 0921-5093

Journal article

Pruncu CI, Jiang J, 2021, Modeling and Optimization in Manufacturing Toward Greener Production by Integrating Computer Simulation, Publisher: John Wiley & Sons, ISBN: 9783527346943

The book elaborates on the foundations and applications of computational modeling and optimization processes, as well as recent developments in the field.

Book

Zhang K, Zheng J-H, Hopper C, Sun C, Jiang Jet al., 2021, Enhanced plasticity at cryogenic temperature in a magnesium alloy, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 811, ISSN: 0921-5093

Journal article

Hopper C, Pruncu CI, Hooper PA, Tan Z, Yang S-T, Liu Y, Jiang Jet al., 2021, The effects of hot forging on the preform additive manufactured 316 stainless steel parts, Micron, Vol: 143, Pages: 103026-103026, ISSN: 0968-4328

Additive Manufacture (AM) offers great potential for creating metallic parts for high end products used in critical application i.e. aerospace and biomedical engineering. General acceptance of AM within these fields has been held back by a lack of confidence in the consistency of the mechanical properties of AMed parts associated by the occurrence of porosity, large columnar grains and texture. In this research, to counters this problem we have combined hot forging and subsequent heat treatment. Although, perhaps not best suited to components featuring fine detail, this technique should be well suited to the manufacture of forged components such as fan blades. Here, AM is able to create a near net-shape blank which is then hot forged to size, eliminating intermediate production stages and generating good mechanical properties in the final component. The material used in the current study is AM 316 L Stainless Steel. By altering the printing parameters of the AM machine, two batches of samples were built, each displaying a different porosity content. This allowed the influence of initial build quality to be illustrated. By comparing the two sample batches, it was possible to gain an insight into the possibilities of controlling porosity and material microstructure. The success of the proposed hot forging and heat treatment technique was validated by mechanical testing (i.e. tensile and hardness experiments) and microstructure evolution characterization (i.e. optical microscopy observation and electron backscatter diffraction (EBSD) techniques). The results revealed that the post processing strategy reduced material porosity and enabled the creation of a more robust microstructure, resulting in improved mechanical properties of the AM material.

Journal article

Zhang K, Shao Z, Daniel CS, Turski M, Pruncu C, Lang L, Robson J, Jiang Jet al., 2021, A comparative study of plastic deformation mechanisms in room-temperature and cryogenically deformed magnesium alloy AZ31, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 807, ISSN: 0921-5093

Journal article

Wang CH, Sun CY, Qian LY, Cai W, Jiang J, Xiao Yet al., 2021, Dynamic mechanical behaviour induced by adiabatic temperature rise of Fe-Mn-Al-C steel, MATERIALS SCIENCE AND TECHNOLOGY, Vol: 37, Pages: 280-291, ISSN: 0267-0836

Journal article

Zhou X, Shao Z, Zhang C, Sun F, Zhou W, Hua L, Jiang J, Wang Let al., 2020, The study of central cracking mechanism and criterion in cross wedge rolling, International Journal of Machine Tools and Manufacture, Vol: 159, ISSN: 0890-6955

Cross wedge rolling (CWR) is an innovative metal forming process to manufacture axisymmetric stepped shafts used in the transport industry. Central cracking, also called the Mannesmann Effect, consistently occurs in the central region of the CWR workpiece. This results in reduced product quality and increased costs due to rejected and failed parts. However, the understanding of central cracking mechanism and criterion is limited due to the complex stress states in CWR and the experimental limitations. A large number of CWR tests and different die geometries are required in the identification of the potential mechanistic factors such as the axial tensile stress, secondary tensile stress, shear stress and cyclic loading. Also, there is as yet no efficient method of determining the material constants associated with the central cracking fracture criteria. These problems are addressed in the present study. A physical model was built to reproduce the industrial CWR process. A newly designed model material (plasticine/flour composite) was used to mimic the material flows and internal fracture behaviours found in commercial CWR workpieces. This allowed a variety of die shapes to be rapidly and cost-effectively 3D printed, thereby enabling specific stress states to be achieved within the workpiece. Via experimental observations and the corresponding finite element modelling under different die geometries, the maximum shear stress was identified as the dominant factor for central cracking. The fracture criterion involving the maximum shear stress was quantitatively verified to be accurate and robust in predicting central cracking moments and locations. A novel approach using simplified die geometries to determine the associated material constants was proposed and validated. The high accuracy and cost/time efficiency of this new approach will be a significant benefit to fundamental research and also in industrial applications.

Journal article

Sun F, Pruncu CI, Penchev P, Jiang J, Dimov S, Blackman BRKet al., 2020, Influence of surface micropatterns on the mode I fracture toughness of adhesively bonded joints, International Journal of Adhesion and Adhesives, Vol: 103, Pages: 1-11, ISSN: 0143-7496

Surface patterning has been used to enhance the fracture toughness of adhesive joints. In this study, the effect of the variable bondline thickness introduced by the patterns and the effect of pattern geometry on the fracture behaviour of adhesive joints were analysed. Surface patterns including longitudinal grooves, transverse grooves, dimples and grids were fabricated by means of laser texturing. The patterned surfaces were bonded using a tough structural adhesive and the mode I fracture toughness was measured using the J-integral method. The toughness of the patterned joints was compared with the results from bonding with control surfaces and with grit blasted in combination with chromic acid etched (GB-CAE) surfaces. It was shown that both longitudinal and transverse grooves led to the highest value of toughness. Grids patterns yielded a toughness close to the GB-CAE treatment, both of which were higher than the dimple patterns. It was also shown that the variable bondline thickness due to the existence of surface patterns, which influences the size of the plastic zone, reduced rather than increased the fracture toughness.

Journal article

Jiang Y, Offer GJ, Jiang J, Marinescu M, Wang Het al., 2020, Voltage hysteresis model for silicon electrodes for lithium ion batteries, including multi-step phase transformations, crystallization and amorphization, Journal of the Electrochemical Society, Vol: 167, Pages: 1-9, ISSN: 0013-4651

Silicon has been an attractive alternative to graphite as an anode material in lithium-ion batteries (LIBs). The development of better silicon electrodes and the optimization of their operating conditions for longer cycle life require a quantitative understanding of the lithiation/delithiation mechanisms of silicon and how they are linked to the electrode behaviors. Herein we present a zero-dimensional mechanistic model of silicon anodes in LIBs. The model, for the first time, quantitatively accounts for the multi-step phase transformations, crystallization and amorphization of different lithium-silicon phases during cycling while being able to capture the electrode behaviors under different lithiation depths. Based on the model, a linkage between the underlying reaction processes and electrochemical performance is established. In particular, the two sloping voltage plateaus at low lithiation depth are correlated with two electrochemical phase transformations and the emergence of the single broad plateau at high lithiation depth is correlated with the amorphization of c-Li15Si4. The model is then used to study the effects of crystallization rate and surface energy barriers, which clarifies the role of surface energy and particle size in determining the performance behaviors of silicon. The model is a necessary tool for future design and development of high-energy-density, longer-life silicon-based LIBs.

Journal article

Zinong T, Bing Z, Jun J, Zhiqiang L, Jianguo Let al., 2020, A study on the hot roll bonding of aluminum alloys, Procedia Manufacturing, Vol: 50, Pages: 56-62, ISSN: 2351-9789

Joining of aluminum alloys through plastic deformation and short-time diffusion bonding has significant applications in a wide range of engineering sectors. It is also important in the elimination of voids and defects in casting ingots through hot rolling processes. An aluminum alloy, AA1060, was selected for the roll-bonding experimental research at vacuum conditions. Parameters including grain size and orientation, dislocation distribution, oxide film breakage, interface welding ratio were studied and analyzed at different hot rolling conditions. Analytical techniques were also developed to analyze the deformation, stress and strain states of the material at hot rolling conditions. The results show that under the condition of 580℃ and 60% deformation, the welding interfaces disappears, and the alloy matrix structure is not overburned.

Journal article

Zhang K, Shao Z, Jiang J, 2020, Effects of twin-twin interactions and deformation bands on the nucleation of recrystallization in AZ31 magnesium alloy, Materials & Design, Vol: 194, ISSN: 0264-1275

Investigating recrystallization is essential to optimize the microstructure including texture weakening and grain refinement in the rolling of magnesium alloys, thus to improve the mechanical properties of magnesium sheets for industrial applications. This research has gained an in-depth understanding of the effects of deformation bands and twin-twin interactions on recrystallization, which will potentially lead to improved manufacturing processes and mechanical properties of magnesium alloys. To study their individual effects, the recrystallization mechanisms of the room-temperature (RT)-rolled and liquid-nitrogen-temperature (LNT)-rolled samples during the annealing process were analysed with the quasi-in-situ electron backscatter diffraction method, respectively. It is found that recrystallization mainly occurred in deformation bands in the RT-rolled sample, which enhanced the initially formed texture, due to oriented and inhomogeneous grain growth. However, it is of great interest to see that the recrystallized sites were mainly located around the (101 ̅2)-(011 ̅2) twin-twin interactions with high kernel average misorientation (KAM) values in the LNT-rolled samples, resulting in rather weaker texture, finer grain size and more homogeneous microstructure, because of the randomized orientations of recrystallized grains and uniform grain growth, while almost no recrystallization was observed around the single tension twin variant.

Journal article

Pruncu CI, Hopper C, Hooper PA, Tan Z, Zhu H, Lin J, Jiang Jet al., 2020, Study of the effects of hot forging on the additively manufactured stainless steel preforms, Journal of Manufacturing Processes, Vol: 57, Pages: 668-676, ISSN: 1526-6125

The production of wrought stainless steel components in power generators can involve a combination of many manufacturing processes. These are expensive in tooling costs and number of operations, as in the Hot Forging (HF) of stainless steel turbine blades. Additive Manufacturing (AM) techniques provide a valuable opportunity to produce near-net-shaped preforms, thus avoiding the material wastage and high tooling costs associated with the intermediate stages of HF processes. This study focuses on the proposed hybrid AM and HF method, in which AM is used to produce near-net–shape preforms which are subsequently formed into net-shaped parts by HF. The HF process is used to significantly reduce the material defects introduced by, and intrinsic to, AM processes. To understand the mechanical and microstructure changes during various AM and HF conditions, single-phase 316 L stainless steel was used as the test material. Samples were produced by AM using a laser powder-bed fusion AM machine. Two different AM build directions were used to produce samples, so, as to allow evaluation of the anisotropic properties induced by AM. These samples subsequently underwent a HF process, in which various processing conditions of plastic strain and forging temperature were applied, to study the general effects of thermal plasticity on the AM microstructure. Tensile testing, optical microscopy (OM), scanning electron microscope (SEM) together with electron backscatter diffraction (EBSD) techniques were used to characterise the evolution of mechanical properties, porosity and grain size. The HF technique was found to remove defects from the AM material, resulting in enhanced mechanical strength, ductility, and isotropy. The technique therefore offers a potential alternative to conventional forging while retaining the required level of material performance.

Journal article

McGilvery C, Jiang J, Rounthwaite N, Williams R, Giuliani F, Britton Tet al., 2020, Characterisation of carbonaceous deposits on diesel injector nozzles, Fuel: the science and technology of fuel and energy, Vol: 274, Pages: 1-9, ISSN: 0016-2361

Diesel injector nozzles are highly engineered components designed to optimise delivery of fuel into the combustion chamber of modern engines. These components contain narrow channels to enhance spray formation and penetration, hence mixing and combustion. Over time, these injectors can become clogged due to fouling by carbonaceous deposits which may affect the long-term performance of a diesel engine. In this paper we explore the chemical composition and structure of deposits formed within the nozzle at the nanometre scale using electron microscopy. We focus on comparing deposits generated using a chassis dynamometer-based test with Zn fouled fuel with a DW10B dirty up test. We have developed and applied a method to precisely section the deposits for ‘top view’ scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis of the morphology and relative accumulation of deposits formed during chassis dynamometer and engine based dirty-up tests. We extend this analysis to finer length scales through lift-out of ~70 nm thick electron transparent cross section foils, including both the metal substrate and deposit, using focussed ion beam (FIB) machining. These foils are analysed using scanning transmission electron microscopy (STEM) and STEM-EDS. These thin foils reveal thin-film growth and chemical stratification of Zn, C, O and other elements in the organic deposit layers developed during growth on the steel substrate during industry standard fouling tests.

Journal article

Zhang K, Zheng J-H, Huang Y, Pruncu C, Jiang Jet al., 2020, Evolution of twinning and shear bands in magnesium alloys during rolling at room and cryogenic temperature, Materials and Design, Vol: 193, Pages: 1-11, ISSN: 0264-1275

Twinning and shear bands are two main deformation structures in magnesium alloys at low temperatures, however, the relationship between these two deformation structures is still under debate. To clarify their relationship and behaviours at low temperatures, rolling tests to various thickness reductions at room temperature (RT) and liquid nitrogen temperature (LNT) were conducted for AZ31 magnesium alloys. The evolutions of shear bands and twinning, and their interactions with geometrically necessary dislocation (GND), were observed during the RT- and LNT-rolling process. Abundant shear bands, evolving from {101 ̅1}-{101 ̅2} double twins (DTWs), were observed in the RT-rolled samples, while a high quantity of twins, including {101 ̅2} tension twins (TTWs), twin-twin interactions and twinning sequence, were observed in the LNT-rolled samples. More importantly, a rarely observed twinning sequence behaviour, namely primary TTW-TTW interactions→ secondary TTW-TTW interactions, creating a 45° <202 ̅1 ̅> misorientation peak, was studied. Abundant GNDs accumulated around these twin-twin interactions, twinning sequence, DTWs and shear bands, while the GND density was low around TTWs. This research delivers a systematic investigation into the deformation structures in Mg alloys during the rolling process from RT to cryogenic temperature and provides insights into the newly discovered twinning sequence and twin-twin interactions.

Journal article

Yasmeen T, Zhao B, Zheng J-H, Tian F, Lin J, Jiang Jet al., 2020, The study of flow behavior and governing mechanisms of a titanium alloy during superplastic forming, Materials Science and Engineering: A, Vol: 788, Pages: 1-19, ISSN: 0921-5093

TA15 (Ti–6Al–2Zr–1Mo–1V) is a near-α titanium alloy and has wide applications in the aerospace industry because of its high strength to mass ratio, good weldability, and superior creep resistance at high temperatures up to 550 °C, compared to other titanium alloys. This study investigates the flow behavior and microstructural evolution as functions of temperatures and strain rates during deformations under the superplastic conditions at 880 °C/0.01s−1, 900 °C/0.01s−1, 880 °C/0.001s−1, and 920 °C/0.0005s−1. Results showed that this alloy exhibit excellent superplastic behavior for all selected temperatures and strain rates. The maximum tensile elongation of 1450% is achieved at 880 °C with a strain rate of 0.001s−1. Flow softening is observed under deformation conditions of 880 °C/0.01s−1 and 900 °C/0.01s−1, while strain hardening is observed at deformation conditions of 880 °C/0.001s−1 and 920 °C/0.0005s−1. These complex flow behaviors are rationalized by characterizing the underlying microstructures on the interrupted tensile samples using electron backscatter diffraction (EBSD) and backscattered electrons (BSE). The geometrically necessary dislocations (GNDs) density, which is caused by lattice rotation and misorientations and plays a vital role in the plastic constitutive behaviors, was for the first time, systematically revealed. Together with other key microstructures, i.e. grain sizes, texture, phase fractions, the results show that the dominant deformation mode changes at initial, intermediate, and final stages of the deformation. The probable deformation mechanisms, such as grain boundary sliding (GBS) under different deformation conditions, are discussed in terms of grain morphology, GNDs, and texture evolution. Also, it is observed that the β-phase transformation is accelerated during deformation and contributes to the enhancemen

Journal article

Ren X, Ren H, Shang Y, Xiong H, Zhang K, Zheng J, Liu D, Lin J, Jiang Jet al., 2020, Microstructure evolution and mechanical properties of Ti2AlNb/TiAl brazed joint using newly-developed Ti-Ni-Nb-Zr filler alloy, PROGRESS IN NATURAL SCIENCE-MATERIALS INTERNATIONAL, Vol: 30, Pages: 410-416, ISSN: 1002-0071

Journal article

Bhaduri D, Penchev P, Dimov S, Essa K, Carter LN, Pruncu CI, Jiang J, Pullini Det al., 2020, On the surface integrity of additive manufactured and post-processed AlSi10Mg parts, 5th CIRP CSI 2020, Publisher: Elsevier BV, Pages: 339-344, ISSN: 2212-8271

The research centres on the evaluation of surface integrity of AlSi10Mg parts produced via laser-based powder bed fusion (LPBF) process, followed by vibratory surface finishing. The alloy is chosen for its applications in lightweight components used in electronic packaging, automotive and aerospace sectors. Initial experiments involve optimisation of key LPBF process parameters by analysing the surface roughness and density data of the built parts. A Taguchi L18 orthogonal array is used for the optmisation trials with variations in the laser power (P), beam scanning speed (v), hatch spacing (H) and island size (I). Latter experimental phase deals with microhardness and microstructure assessment of heat treated LPBF specimens that are produced using the optimised LPBF parameters, i.e. P: 250 W, v: 1500 mm/s, H: 75 µm and I: 2 mm. Microhardnesses of the annealed samples reduce by ~12% with respect to the as-built parts and the values remain almost unchanged from the annealed state following solution treatment and ageing. The fish-scale like melt-pools observed on the unheat treated samples begin to fade off in the annealed specimens and completely disappear after solution treatment and ageing, with silicon particles dispersed all over the aluminium matrix. The final experimental phase involves vibratory surface finishing of the as-built LPBF parts using a vibrating ceramic media mixed with different acid and amine based liquid compounds for 1-6 hours, followed by vibrating in a maize based media for another 1-6 hours. The process aids in reducing the parts’ roughness, Sa by ~35-70%, however the effect is more prominent when using the ceramic media.

Conference paper

Zhou X, Shao Z, Pruncu CI, Hua L, Balint D, Lin J, Jiang Jet al., 2020, A study on central crack formation in cross wedge rolling, Journal of Materials Processing Technology, Vol: 279, ISSN: 0924-0136

Cross wedge rolling (CWR) is an innovative roll forming process, used widely in the transportation industry. It has high production efficiency, consistent quality and efficient material usage. However, the continual occurrence of crack formation in the centre of the workpiece is a critical problem excluding the CWR technique from more safety-critical applications, in particular, aerospace components. The mechanisms of central fracture formation are still unclear because of a combination of complicated stress and strain states at various stages of CWR. Thus, the aim of this study is to understand the stress/strain distribution and evolution during the CWR process and identify the key variables which determine central crack formation. A comprehensive investigation was then conducted to simulate 27 experimental cases. The stress and strain distributions in the workpiece were evaluated by finite element analysis. Various damage models from literature were applied and compared. A new fracture criterion was proposed, which was able to successfully determine the central crack formation in all 27 experimental cases. This criterion can be applied in CWR tool and process design, and the enhanced understanding may enable the adoption of CWR by the aerospace industry.

Journal article

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