@article{li_wang_zhang_li_fang_ma_2023, title={Strengthening mechanisms of a heterostructured pure aluminum with extraordinary mechanical properties}, volume={202}, ISSN={["1873-4189"]}, DOI={10.1016/j.matchar.2023.113049}, abstractNote={To achieve superior mechanical properties in metallic materials, one promising way is to make them into heterogeneous structures (HS). In this work, a novel HS including grain size and dislocation density is developed in commercial pure aluminum through cold-rolling and subsequent partial annealing processes. Tensile tests show that the HS specimen, annealed at 150 °C for 2 min with ∼31.1% recrystallized grains, have a high yield strength of ∼121 MPa and a good uniform elongation of ∼8.5%. The yield strength increases by 10% and the ductility increases by 7 times compared with the as-rolled specimen, respectively. Detailed microstructure characterizations confirm that a significant strain gradient was generated near the interface between the hard zone and soft zone, in which the slip and plugging of geometrically necessary dislocations act as an important role in the abnormal hardening and strengthening phenomena of the HS specimen. To quantify the specific contribution of each strengthening mechanism, we compare the experimental measurements with the theoretical calculations and confirm that the multiple deformation modes are activated by the deformation stress. The hetero-deformation-induced hardening and strengthening effects are responsible for the superior mechanical properties of the heterostructured pure aluminum.}, journal={MATERIALS CHARACTERIZATION}, author={Li, Junye and Wang, Guanghui and Zhang, Maofei and Li, Jiahao and Fang, Xiaotian and Ma, Xinkai}, year={2023}, month={Aug} }
 @article{wang_huang_ma_zhao_guo_fang_zhu_wei_2023, title={The optimum grain size for strength-ductility combination in metals}, volume={164}, ISSN={["1879-2154"]}, DOI={10.1016/j.ijplas.2023.103574}, abstractNote={A strength-ductility trade-off usually occurs when grains are refined to increase strength. A question arises on if there exists a grain size for the best strength-ductility combination, i.e., with the highest possible strain energy density limit and strength simultaneously. This issue is crucial for guiding the design of strong and tough structural materials. Here we reveal an optimum grain size (doptimum) on the order of a few micrometers, at which the strain energy density limit, estimated as the product of strength and uniform elongation, reaches a maximum while maintaining reasonably high yield strength. The doptimum is found to exist in a series of single-phase FCC, BCC and HCP materials, indicating it as a universal phenomenon. Theoretical models on the grain size-dependence of uniform elongation and ultimate strength are developed by considering dislocation accumulation in grain boundary affected region (Gbar) and grain interior based on the classical Kocks-Mecking-Estrin model. Combined with the Hall-Petch relationship, the models accurately predict the doptimum. Importantly, the models disclose this doptimum to be close to twice of the characteristic width of Gbar (lGbar), suggesting that it is exactly at or near the critical grain size with the strongest intragranular strain gradient effects.}, journal={INTERNATIONAL JOURNAL OF PLASTICITY}, author={Wang, Yanfei and Huang, Chongxiang and Ma, Xiaolong and Zhao, Jianfeng and Guo, Fengjiao and Fang, Xiaotian and Zhu, Yuntian and Wei, Yueguang}, year={2023}, month={May} }
 @article{yang_chen_ma_zhong_zhao_xiao_fang_2021, title={Improvement of strength and ductility in a gradient structured Ni fabricated by severe torsion deformation}, volume={826}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2021.141980}, abstractNote={The tensile deformation behavior and microstructure evolution of gradient structured (GS) Ni processed by severe torsion deformation (STD) were systematically investigated. The results show that the gradient shear strain from STD introduces gradient distributions of grain size, microhardness, frequency of low angle grain boundaries, Σ3 twins and geometrically necessary dislocations (GND) density along the radial direction. With the increasing torsional angle of STD, the yield strength and ultimate tensile strength increase correspondingly while the uniform elongation first decreases and then increases. When the torsional angle increases to a maximum torsional revolution of 16, this specific GS Ni undergoes a maximum shear strain and lead to a promoted strength-ductility synergy, showing yield strength of 592 MPa, ultimate tensile strength of 1019 MPa and uniform elongation of 8.58%, as well as the highest work hardening rate. The simultaneous improvement of mechanical property is due to the strong partitioning between the fine grain region and central coarse grain region, which induces a significant work-hardening at the early plastic deformation stage. Therefore, a high shear strain and delicate control of its gradient in STD can lead to a unique gradient structure in metals, which is a good strategy to improve the mechanical properties of rod products.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Yang, Liang and Chen, Zhuo and Ma, Xinkai and Zhong, Dongling and Zhao, Xiaojun and Xiao, Lei and Fang, Xiaotian}, year={2021}, month={Oct} }
 @article{fang_he_zheng_ma_kaoumi_li_zhu_2020, title={Effect of heterostructure and hetero-deformation induced hardening on the strength and ductility of brass}, volume={186}, ISSN={["1873-2453"]}, url={https://doi.org/10.1016/j.actamat.2020.01.037}, DOI={10.1016/j.actamat.2020.01.037}, abstractNote={Heterostructured materials have been reported to possess superior combinations of strength and ductility, which is attributed to hetero-deformation induced (HDI) strengthening and work hardening. However, the influence of heterostructural parameters on the evolution of HDI stress and mechanical behavior during tensile deformation is not well understood. In this paper, heterostructured brass (Cu–30%Zn) was fabricated by cold rolling and partial annealing, to produce heterostructures with different heterostructural parameters, including domain volume fraction, domain thickness/spacing and domain misorientation. It was found that HDI hardening was dominant when the tensile strain was less than ∼4.5%, while conventional dislocation hardening became more effective at higher strain levels. Quick accumulation of geometrically necessary dislocations was found in the domain boundary regions, leading to high HDI stress. Higher domain misorientation was found more effective in developing HDI hardening. These findings elucidate the effect of heterostructure on strength and ductility, which can help with the design of heterostructured materials for superior mechanical properties.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Fang, X. T. and He, G. Z. and Zheng, C. and Ma, X. L. and Kaoumi, D. and Li, Y. S. and Zhu, Y. T.}, year={2020}, month={Mar}, pages={644–655} }
 @article{wang_huang_fang_hoeppel_goeken_zhu_2020, title={Hetero-deformation induced (HDI) hardening does not increase linearly with strain gradient}, volume={174}, ISSN={["1359-6462"]}, DOI={10.1016/j.scriptamat.2019.08.022}, abstractNote={Hetero-deformation induced (HDI) hardening has been attributed to geometrically necessary dislocations (GNDs) that are needed to accommodate strain gradient near the interfaces of heterostructured domains. Here we report that HDI hardening does not increase linearly with increasing strain gradient in the interface-affected zone. This is because some GND pileups may be absorbed by the interface and consequently does not contribute to HDI hardening with increasing strain gradient. Higher mechanical incompatibility across interface produces higher strain gradient. The strain gradient-dependent strengthening effect of heterostructured interface mainly originates from the development of HDI stress.}, journal={SCRIPTA MATERIALIA}, author={Wang, Y. F. and Huang, C. X. and Fang, X. T. and Hoeppel, H. W. and Goeken, M. and Zhu, Y. T.}, year={2020}, month={Jan}, pages={19–23} }
 @article{wang_huang_li_fang_wang_he_guo_zhu_2020, title={Shear band stability and uniform elongation of gradient structured material: Role of lateral constraint}, volume={37}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2020.100686}, abstractNote={Here we report a shear bands-dominated deformation principle for the gradient material composed of two nanostructured gradient layers (NGLs) and a coarse-grained (CG) interior. Multiple shear bands form in the NGL to accommodate the applied strain. The magnitude of uniform elongation depends on shear band stability, and shear band stability is determined by the intensity of constraint between NGL and CG interior. Specifically, the stronger the constraint, the denser and more stable the shear bands dispersed in the NGL, thereby leading to larger uniform elongation. This finding sheds insight into the theoretical basis of harnessing dispersed stable shear bands in heterostructures by optimizing microstructure architecture.}, journal={EXTREME MECHANICS LETTERS}, author={Wang, Yanfei and Huang, Chongxiang and Li, Zhongkai and Fang, Xiaotian and Wang, Mingsai and He, Qiong and Guo, Fengjiao and Zhu, Yuntian}, year={2020}, month={May} }
 @article{li_fang_wang_jiang_wang_liu_wu_zhu_koch_2020, title={Tuning heterostructures with powder metallurgy for high synergistic strengthening and hetero-deformation induced hardening}, volume={777}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2020.139074}, abstractNote={Heterogeneous-lamella-structured Fe-Cu composites were fabricated using powder metallurgy, displaying an inverse “banana” curve between the strength and ductility. The density of domain interfaces and the strength difference between hard and soft domains can be tuned independently, providing a promising way to further study the hetero-deformation induced strengthening mechanisms of heterogeneous-lamella-structures.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Li, Z. K. and Fang, X. T. and Wang, Y. F. and Jiang, P. and Wang, J. J. and Liu, C. M. and Wu, X. L. and Zhu, Y. T. and Koch, C. C.}, year={2020}, month={Mar} }
 @article{ma_li_sun_hou_fang_zhu_koch_2019, title={Achieving Gradient Martensite Structure and Enhanced Mechanical Properties in a Metastable beta Titanium Alloy}, volume={50A}, ISSN={["1543-1940"]}, DOI={10.1007/s11661-019-05157-5}, number={5}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, author={Ma, Xinkai and Li, Fuguo and Sun, Zhankun and Hou, Junhua and Fang, Xiaotian and Zhu, Yuntian and Koch, Carl C.}, year={2019}, month={May}, pages={2126–2138} }
 @article{ma_li_fang_li_sun_hou_cao_2019, title={Effect of strain reversal on the stress-induced martensitic transformation and tensile properties of a metastable beta titanium alloy}, volume={784}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2019.01.010}, abstractNote={In this study, the effect of strain reversal on the evolution of microstructure and mechanical properties was investigated. Metastable β titanium alloy samples with single β phase were twisted up to 360° with different strain paths: monotonic torsion (MT) and cyclic forward-reverse torsion (CFRT). The results revealed CFRT with strain reversal accumulated lower dislocation density and less martensitic transformation in comparison with MT under the same accumulative strain. The stress-induced martensitic transformation (SIMT) was retarded by strain reversal and this suppression of martensitic transformation is more pronounced with the decreasing amplitude of strain reversal. It was further observed that CFRT samples with a gradient α″ martensite have a higher mechanical property both in strength and ductility than MT samples, which are due to interactions between α″ martensite and dislocation slip, especially the kinks of α″ martensite.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Ma, Xinkai and Li, Fuguo and Fang, Xiaotian and Li, Zhongkai and Sun, Zhankun and Hou, Junhua and Cao, Jun}, year={2019}, month={May}, pages={111–116} }
 @article{fang_he_ruiz_zheng_wang_li_zhu_2019, title={Influence of annealing parameters on the mechanical properties of heterogeneous lamella structured 5083 aluminum alloy}, volume={9}, ISSN={["2410-3535"]}, DOI={10.22226/2410-3535-2019-4-556-560}, abstractNote={1Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA 2Department of Microsystems — IMS, Faculty of Technology, Natural Sciences and Maritime Sciences, University of South-Eastern Norway, Postboks 235, 3603, Kongsberg, Norway 3Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695, USA 4School of Aeronautics and Astronautics, Sichuan University, Chengdu, 610065, China 5Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang, 110819, China 6Nano and Heterogeneous Structural Materials Center, Nanjing University of Science and Technology, Nanjing, 210094, China}, number={4}, journal={LETTERS ON MATERIALS}, author={Fang, X. T. and He, G. Z. and Ruiz, M. and Zheng, C. and Wang, Y. F. and Li, Z. K. and Zhu, Y. T.}, year={2019}, month={Dec}, pages={556–560} }
 @article{ma_li_sun_hou_li_fang_2019, title={Strain rate dependence of the indentation size effect in Ti-10V-2Fe-3Al alloy}, volume={35}, ISSN={["1743-2847"]}, DOI={10.1080/02670836.2019.1612596}, abstractNote={ The influence of strain rates on the indentation size effect (ISE) was explored experimentally. A strong ISE phenomenon on the hardness of Ti–10V–2Fe–3Al (Ti-1023) alloy was found when the peak-load was less than 3500 mN, regardless of the variation of loading rates. However, as indenter strain rates increased, the degree of ISE reduced considerably, which was related to the decrease of the internal indentation length scale ranging from 23.08 to 6.80 µm. Furthermore, a positive strain rate sensitivity of the hardness in the whole peak-load range was found in Ti-1023 alloy, which showed a linear function of indenter load. The underlying mechanism was well explained by the variation of geometrically necessary dislocation and statistically stored dislocations in Ti-1023 alloy. }, number={9}, journal={MATERIALS SCIENCE AND TECHNOLOGY}, author={Ma, Xinkai and Li, Fuguo and Sun, Zhankun and Hou, Junhua and Li, Jinghui and Fang, Xiaotian}, year={2019}, month={Jun}, pages={1107–1113} }
 @article{fang_ma_zhang_zhu_2016, title={Nucleation of deformation twins in nanocrystalline fcc alloys}, volume={96}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2016.1240379}, abstractNote={Abstract An earlier dislocation model for predicting the grain size effect on deformation twinning in nanocrystalline (nc) face-centred-cubic (fcc) metals has been found valid for pure metals but problematic for alloys. The problem arises from the assumption that the stacking-fault energy (γSF) is twice the coherent twin-boundary energy (γfcc), which is approximately correct for pure fcc metals, but not for alloys. Here we developed a modified dislocation model to explain the deformation twinning nucleation in fcc alloy systems, where γSF ≠ 2γtwin. This model can explain the differences in the formations of deformation twins in pure metals and alloys, which is significant in low stacking-fault energy alloys. We also describe the procedure to calculate the optimum grain size for twinning in alloy systems and present a method to estimate γtwin.}, number={36}, journal={PHILOSOPHICAL MAGAZINE}, author={Fang, Xiaotian and Ma, Xiaolong and Zhang, Liwen and Zhu, Yuntian}, year={2016}, pages={3790–3802} }