19 results on '"Huang, Aijun"'
Search Results
2. Influence of Nonmetallic Interstitials on the Phase Transformation between FCC and HCP Titanium: A Density Functional Theory Study.
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Yang, Mengmeng, Hu, Jianan, Cao, Shuo, Feng, Guang, Yang, Yi, Liu, Renci, Li, Shujun, Zhao, Fu, Feng, Aihan, Hu, Qingmiao, Huang, Aijun, and Wang, Hao
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FACE centered cubic structure ,DENSITY functional theory ,PHASE transitions ,TITANIUM ,BAND gaps ,MATERIAL plasticity ,TITANIUM alloys - Abstract
In addition to the common stable and metastable phases in titanium alloys, the face-centered cubic phase was recently observed under various conditions; however, its formation remains largely unclarified. In this work, the effect of nonmetallic interstitial atoms O, N, C and B on the formation of the face-centered cubic phase of titanium was investigated with the density functional theory. The results indicate that the occupancy of O, N, C and B on the octahedral interstitial sites reduces the energy gap between the hexagonal-close-packed (HCP) and face-centered cubic (FCC) phases, thus assisting the formation of FCC-Ti under elevated temperature or plastic deformation. Such a gap further decreases with the increase in the interstitial content, which is consistent with the experimental observation of FCC-Ti under high interstitial content. The relative stability of the interstitial-containing HCP-Ti and FCC-Ti was studied against the physical and chemical origins, e.g., the lattice distortion and the electronic bonding. Interstitial O, N, C and B also reduce the stacking fault energy, thus further benefiting the formation of FCC-Ti. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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3. Influence of Oxygen and Zirconium Contents on The Mechanical Properties of Ti-23Nb-0.7Ta-Zr-O Alloys.
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Si, Kunlun, Wang, Xu, Yin, Zhaolong, Yang, Yi, Wu, Songquan, Li, Geping, Zhang, Kai, Wang, Hao, and Huang, Aijun
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ZIRCONIUM ,SOLUTION strengthening ,ALLOY testing ,TENSILE strength ,TITANIUM alloys - Abstract
Ti-23Nb-0.7Ta-(0, 2)Zr-(1.2, 4, 6, 10)O alloys were prepared using a non-consumable arc-melting method. The tensile property of Ti-23Nb-0.7Ta-2Zr-1.2O alloys was tested at temperatures from −196 °C to 750 °C. The influence of O and Zr contents on thermal forgeability, room-temperature hardness and tensile property at 750 °C was investigated. For Ti-23Nb-0.7Ta-2Zr-1.2O alloy, the tensile strength decreased, and the ductility increased with the temperature increase. O and Zr had a negative effect on the thermal forgeability. Room-temperature hardness and tensile strength increased with an increase in O and Zr contents due to interstitial, solid solution strengthening and second-phase strengthening. All of the alloys exhibited high ductility at 750 °C with the total elongation above 34% and reductions in area above 80%. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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4. Effect of Heat Treatment on Microstructure and Tensile Properties of Ti-6Al-4V Alloy Produced by Coaxial Electron Beam Wire Feeding Additive Manufacturing.
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Hu, Jianan, Zhang, Jiahua, Wei, Ya, Chen, Hao, Yang, Yi, Wu, Songquan, Kovalchuk, Dmytro, Liang, Enquan, Zhang, Xi, Wang, Hao, and Huang, Aijun
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TITANIUM powder ,EFFECT of heat treatment on microstructure ,FEED additives ,TITANIUM alloys ,ELECTRON beams ,ALLOYS - Abstract
A novel coaxial electron beam wire feeding additive manufacturing technology (CAEBWAM) was proposed in our previous work to refine the microstructure and improve the mechanical properties of titanium alloys. In the present work, different post-heat treatments were performed to understand the microstructure evolution and the resultant mechanical properties of CAEBWAMed Ti-6Al-4V alloy. The as-built sample was dominated by equiaxed prior β microstructure, with the first several deposited layers containing columnar prior β grain morphology. The as-built alloy showed a mixed microstructure composed of large α′ martensite and fine α + β lamella. As the annealing temperature was increased, α′ martensite decomposed into α + β phase, while the width of the α lamellae increased, causeing an increase in the ductility and a decrease in the strength. [ABSTRACT FROM AUTHOR]
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- 2021
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5. Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys.
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Liu, Yang, Lim, Samuel C.V., Ding, Chen, Huang, Aijun, and Weyland, Matthew
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FRACTURE toughness ,TITANIUM alloys ,HEAT treatment ,GRAIN size ,CRYSTAL grain boundaries ,TAGUCHI methods ,HYPEREUTECTIC alloys - Abstract
• The relative importance of β grain size and STA process parameters were analyzed using an orthogonal array method. • The relationship between specific microstructural features with strength, ductility and fracture toughness were established. • The contradictory β grain size effect on fracture toughness was explained. • A table was proposed to quasi-quantitatively unravel the competitive effect of microstructural features. The competitive effect of microstructural features including primary α (α p), secondary α (α s), grain boundary α (α GB) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes. The relative effect of β grain size and STA (solution treatment and ageing) processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method. These results were further explained via correlating microstructure with the fracture toughness and tensile properties. It was found that large numbers of fine α s precipitates and continuous α GB played greater roles than other features, resulting in a high strength and very low ductility (<2%) of STA process samples. The β grain size had a negative correlation with fracture toughness. In the samples prepared by BASCA (β anneal slow cooling and ageing) process, improved ductility and fracture toughness were obtained due to a lower density of α s precipitates, a basket-weave structure and zigzag morphology of α GB. For this heat treatment, an increase in prior β grain size had an observable positive effect on fracture toughness. The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained. It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties. This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties. A novel table was proposed to quasi-quantitatively unravel these competitive effects. [ABSTRACT FROM AUTHOR]
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- 2022
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6. {332}<113> Twinning transfer behavior and its effect on the twin shape in a beta-type Ti-23.1Nb-2.0Zr-1.0O alloy.
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Yang, Yi, Zhang, Bohua, Meng, Zhichao, Qu, Lei, Wang, Hao, Cao, Sheng, Hu, Jianan, Chen, Hao, Wu, Songquan, Ping, Dehai, Li, Geping, Zhang, Lai-Chang, Yang, Rui, and Huang, Aijun
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MOLECULAR dynamics ,FRACTURE mechanics ,STRESS concentration ,TWIN boundaries - Abstract
• Twinning transfer (TT) behavior depends on crystallographic alignment factor (m') of two twinning systems and misorientation angle (MA) of grain pairs. • The twin shape is dependent on the occurrence of TT. Twins always present a ruler shape when TT can occur and present a lenticular shape when TT is not able to occur. • A possible mechanism for the relationship between the twin shape and TT behavior is proposed based on the assumption of limited average concentrated stress in front of twin tips in different grain pairs. 1) For the grain pair with a low MA and a high m', such concentrated stress could be released effectively by inducing the outgoing twining in the neighboring grain, forming a ruler-shaped paired twins. 2) For the grain pair with a high MA and a small m', such concentrated stress could be reduced effectively by enlarging the distance between micro-twin tip and grain boundary along the [113] direction, forming a lenticular-shaped twin. The interaction between twins and grain boundaries (GB) has an important influence on the deformation and fracture behavior of materials. In the present work, {332}<113> twinning transfer (TT) behavior and its effect on the twin shape in a deformed β-type Ti-23.1Nb-2.0Zr-1.0O Ti alloy were investigated experimentally and with molecular dynamics simulation. The crystallographic alignment factor of the two twinning systems in the neighboring grains and the misorientation angle of the grain pairs were found to influence the occurrence of TT. This further determines the twin shape: twins present a ruler shape when TT occurs but are in a lenticular shape otherwise. Such different twin shapes are attributed to the local stress states related to TT occurring or not. Both ruler-shaped paired twinning and lenticular twinning would provide effective mechanisms to release or reduce the stress concentration in front of the twin tips in different grain pairs. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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7. Effect of strain rate and temperature on the deformation behavior in a Ti-23.1Nb-2.0Zr-1.0O titanium alloy.
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Yang, Yi, Xu, Di, Cao, Sheng, Wu, Songquan, Zhu, Zhengwang, Wang, Hao, Li, Lei, Xin, Shewei, Qu, Lei, and Huang, Aijun
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TITANIUM alloys ,STRAIN rate ,DEFORMATIONS (Mechanics) ,STRESS concentration ,TRANSMISSION electron microscopy ,LOW temperatures ,CRYSTAL grain boundaries - Abstract
• Compression behavior of a Ti-23.1Nb-2.0Zr-1.0O (at.%) alloy has been explode in a temperature range of 100−200 °C and a strain rate range of 0.1-1000 s
−1 . • Multiple deformation modes, including dislocation slip, {332}〈113〉 twinning, {112}〈111〉 twinning, stress-induced α" martensitic (SIMα") and stress-induced ω phase (SIω) transformations were observed at high strain rates and low deformation temperatures. • Both twinning and SIω transformations prefer to be activated at low deformation temperatures and high strain rates. The compression behavior of a Ti-23.1Nb-2.0Zr-1.0O (at.%) alloy was investigated at strain rates from 0.1 s−1 to 1000 s−1 and temperatures from 100 °C to 200 °C on a Gleeble 3800 system and Split Hopkinson Pressure Bar (SHPB) compressive tester. Optical microscopy, electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution during the deformation. Numerous deformation phenomena, including dislocation slip, twinning of both {332}〈113〉 and {112}〈111〉 modes, stress-induced α" martensite (SIMα") and stress-induced ω (SIω) transformations, were observed. The preferred activation of twinning and SIω transformations was observed in the sample compressed at lower temperatures and/or higher strain rates. The underlying mechanism is that twinning and stress induced phase transformations are attribute to higher stress concentrations at β grain boundaries and additional energy supplied by a higher strain rate, as well as high stacking fault energy because of higher temperature. [ABSTRACT FROM AUTHOR]- Published
- 2021
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8. Microstructure and Texture Evolution in Double-Cone Samples of Ti-6Al-4V Alloy with Colony Preform Microstructure.
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Yang, Kun, Lim, Chao, Zhang, Kai, Sun, Jifeng, Yang, Xiaoguang, Huang, Aijun, Wu, Xinhua, and Davies, Christopher
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MATERIALS compression testing ,MICROSTRUCTURE ,TITANIUM alloys ,STRAIN rate ,HEAT treatment ,FINITE element method - Abstract
Heat-treated Ti-6Al-4V forged bar with colony microstructure was machined into double-cone-shaped samples for a series of isothermal uniaxial compression test at 1223 K (950 °C) with varying constant crosshead speeds of 12.5, 1.25, and 0.125 mms to a height reduction of 70 pct. Another set of samples deformed under the same conditions were heat treated at 1173 K (900 °C) for an hour followed by water quench. Finite element modeling was used to provide the strains, strain rates, and temperature profiles of the hot compression samples, and the microstructure and texture evolution was examined at four positions on each sample, representative of different strain ranges. Lamellae fragmentation and kinking are the dominant microstructural features at lower strain range up to a maximum of 2.0, whereas globularization dominates at strains above 2.0 for the as-deformed samples. The globularization fraction generally increases with strain, or by post-deformation heat treatment, but fluctuates at lower strain. The grain size of the globular α is almost constant with strain and maximizes for samples with the lowest crosshead speed due to the longer deformation time. The globular α grain also coarsens because of post-deformation heat treatment, with its size increasing with strain level. With respect to texture evolution, a basal transverse ring and another component 30 deg from ND is determined for samples deformed at 12.5 mms, which is consistent with the temperature increase to close to β-transus from simulation results. The texture type remains unchanged with its intensity increased and spreads with increasing strain. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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9. Effects of Post Heat Treatments on Microstructures and Mechanical Properties of Selective Laser Melted Ti6Al4V Alloy.
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Liu, Jianwen, Liu, Jie, Li, Yixin, Zhang, Ruifeng, Zeng, Zhuoran, Zhu, Yuman, Zhang, Kai, and Huang, Aijun
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SELECTIVE laser melting ,EFFECT of heat treatment on microstructure ,MECHANICAL heat treatment ,HEAT treatment of metals ,SCANNING electron microscopes ,CRYSTAL grain boundaries ,TITANIUM alloys ,HEAT treatment - Abstract
The unique thermal history of selective laser melting (SLM) can lead to high residual stress and a non-equilibrium state in as-fabricated titanium alloy components and hinders their extensive use. Post heat treatment, as a classical and effective way, could transform non-equilibrium α' martensite and achieves desirable mechanical performance in SLMed Ti alloys. In this study, we aimed to establish the correlation between the microstructure and mechanical performances of SLMed Ti6Al4V (Ti-64) by using different heat treatment processes. The columnar prior β grain morphology and grain boundary α phase (GB-α) after different heat treatment processes were characterized, with their influences on the tensile property anisotropy fully investigated. Scanning electron microscope (SEM) observation of the fracture surface and its cross-sectional analysis found that the tensile properties, especially the ductility, were affected by the GB-α along the β grain boundary. Furthermore, the discontinuous ratio of GB-α was firstly proposed to quantitatively predict the anisotropic ductility in SLMed Ti-64. This study provides a step forward for achieving the mechanical property manipulation of SLMed Ti-64 parts. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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10. Formation mechanism of ultrafine α+β structure in Ti-6Al-4V alloy during β→αm→α+β continuous phase transformation.
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Hu, Jianan, Jiang, Yuan, Yang, Yi, Xing, Hui, Han, Fuzhou, Zhou, Gang, Zhang, Kai, Xin, Shewei, Zhang, Siyuan, Huang, Jian, Wang, Hao, Li, Geping, Zhang, Lai-Chang, and Huang, Aijun
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PHASE transitions , *ALLOYS , *TITANIUM alloys , *COOLING - Abstract
Although massive transformation has been increasingly observed in titanium alloys, the decomposition mechanism of the massive transformation product (α m) is still unclear. Here, the β→α m →α+β continuous phase transformation in Ti-6Al-4V alloy during cooling was studied. We found that massive transformation occurs at a moderate cooling rate below 291.5 °C/s, forming irregular featureless α m. The thermodynamically unstable α m is supersaturated with β stabilizers, and it tends to decompose into ultrafine α+β structure during the continuous cooling at ever-lower cooling rates and temperatures. In the initial stage of α m decomposition, misfit dislocations appear as a predecessor and split α m into strips. Accompanied by the elemental redistribution, misfit dislocations are accommodated and replaced by β phase. Both the formation and decomposition of α m follow the typical Burgers orientation relationship. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2024
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11. Microstructure refinement induced by elastic compressive stress in Ti-6Al-4V alloy.
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Zhang, Yinan, Jiang, Yuan, Si, Kunlun, Xin, Shewei, Zhang, Siyuan, Hou, Fengqi, Zhang, Kai, Hai, Jiawei, Xiao, Lehao, Yang, Yi, Wang, Hao, Huang, Aijun, and Zhang, Lai-Chang
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TITANIUM alloys , *MICROSTRUCTURE , *ALLOYS , *GIBBS' free energy , *PHASE transitions - Abstract
The β→α transformation is a crucial and fundamental phase transformation in titanium and its alloys. This work investigated the effect of elastic compressive stress (ECS) on the microstructure and mechanical property during cooling from β phase region to α + β phase region in Ti-6Al-4V alloy. Results indicated that ECS in this process results in significant refinement and increased aspect ratios of α lamellae (α L) and α colonies (α C). These changes are attributed to the enhanced phase transformation driving force to promote nucleation of α lamellae. The ECS-cooling induced alloy exhibits higher hardness than the stress-free counterpart, mainly resulting from the refined microstructure. This work provides a potential method to tailor the microstructure and improve the mechanical properties of Ti alloys. [Display omitted] • The phenomena of α L refinement are for the first time identified under elastic stress, and the formation mechanism of such phenomena was elucidated. • The elastic compressive stress influences Gibbs free energy are the main reasons for the refinement and variant selection of α lamellae and α colony in Ti-6Al-4V alloys. [ABSTRACT FROM AUTHOR]
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- 2024
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12. Investigation of fatigue behavior of laser powder bed fusion Ti-6Al-4V: Roles of heat treatment and microstructure.
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Liu, Jianwen, Zhang, Kai, Liu, Jie, Wang, Hao, Yang, Yi, Yan, Liangming, Tian, Xinni, Zhu, Yuman, and Huang, Aijun
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HEAT treatment , *ALLOY fatigue , *FATIGUE cracks , *FATIGUE life , *MICROSTRUCTURE , *TITANIUM alloys , *HIGH cycle fatigue , *METAL fatigue - Abstract
• The influence of the GB-α on the fatigue behavior of LPBF Ti–64 was investigated. • HCF property is improved due to low aspect ratio α lath and discontinuous GB-α. • Discontinuous GB-α could improve the crack propagation resistance. • α lath with a low aspect ratio inhibits the crack initiation at the interface. High cycle fatigue (HCF) performance of additive manufactured (AM) titanium products is of great significance for its structural and functional applications. However, tying fatigue performance to the complex microstructures in AM titanium alloys is challenging. The work here carried out a thorough investigation into the influence of microstructures (particularly the grain boundary α-phase (GB-α) with varied morphologies) on the fatigue performance of laser powder bed fusion (LPBF) Ti–6Al–4V (Ti-64). Results showed that the improvement in the high-cycle fatigue life of LPBF Ti-64 could be achieved by the formation of low aspect ratio α lath and discontinuous GB-α via optimized post-fabrication heat treatment. Discontinuous GB-α could fully accommodate the deformation, improving the fatigue crack propagation resistance. Moreover, α lath with a low aspect ratio could lead to less strain accumulation on the interface between adjacent α lath, and thereby inhibit the crack initiation at these interfaces. This study enhances the understanding of how LPBF-induced complex microstructures influence fatigue behavior, and provides a pathway for the improvement of fatigue performance of additive manufactured titanium alloy. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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13. Rapid hardening response of ultra-hard Ti-6Al-2Sn-4Zr-6Mo alloy produced by laser powder bed fusion.
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Peng, Huizhi, Wu, Shun, Kan, Wen Hao, Lim, Samuel Chao Voon, Zhu, Yuman, and Huang, Aijun
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POWDERS , *LASERS , *RESIDUAL stresses , *TITANIUM alloys , *MARTENSITIC transformations - Abstract
Post heat treatment is essential for additively manufactured alloys to eliminate residual stress and in some cases further improve mechanical performance. This study systematically investigated the hardening response of a Ti-6Al-2Sn-4Zr-6Mo alloy processed by laser powder bed fusion (LPBF) to a one-step heat treatment. The results revealed significant hardening at both 500 °C and 650 °C. Most notably, an ultra-high peak-hardness of 563VHN was achieved within 5 mins of heat treatment at 650 °C due to a unique martensite-decomposed α+β microstructure consisting of alternating long β laths that are ∼5 nm thick and α laths that are ∼35 nm thick, and within the α laths are also short β laths that are ∼2 nm thick with an ∼11 nm inter-spacing. The influence of both types of β laths on the α lath thickness was established and related to the ultra-high hardness observed, which provides new insight for the design of new metastable LPBF-processed Ti alloys. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2023
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14. Fatigue behaviour of L-DED processed Ti-6Al-4V with microstructures refined by trace boron addition.
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Zhang, Kai, Liu, Ying, Tian, Xinni, Yang, Yi, Zhu, Yuman, Bermingham, Michael, and Huang, Aijun
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ALLOY fatigue , *FATIGUE life , *FATIGUE cracks , *MICROSTRUCTURE , *HIGH cycle fatigue , *TITANIUM alloys - Abstract
• A mixed equiaxed + columnar prior-β grain microstructure was achieved by 0.05 wt% boron addition. • High-cycle fatigue property was improved significantly in Ti-64-0.05B. • Fatigue crack propagation resistance was reduced due to the prior-β grain size reduction and the TiB particle precipitation. Boron is a powerful grain solute that promotes substantial microstructural refinement in titanium alloys produced by additive manufacturing. However, the fatigue performance of boron refined additive manufactured titanium alloys remained unknown. In this study, a thorough investigation into the high-cycle fatigue life and crack propagation rates of laser direct energy deposited Ti-6Al-4V with a trace boron addition was carried out. The high-cycle fatigue life was significantly improved, as the refined microstructure increased the crack initiation resistance. However, the crack propagation resistance estimated from spectrum loading was reduced, due to the refined prior-β grains and TiB particles. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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- View/download PDF
15. The mechanisms behind the tribological behavior of titanium alloys processed by laser powder bed fusion sliding against steel.
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Kan, Wen Hao, Peng, Huizhi, Lim, Samuel, Zhu, Yuman, Zhang, Kun, and Huang, Aijun
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TITANIUM alloys , *TITANIUM powder , *HEAT treatment , *MECHANICAL wear , *ADHESIVE wear , *FRETTING corrosion - Abstract
The sliding behavior of two titanium alloys processed by laser powder bed fusion, with and without heat treatment, was investigated alongside two as-received conventionally-processed versions of these alloys. These samples presented a wide range of microstructures often encountered in Ti alloys. Oxidative, abrasive and adhesive wear always occurred when sliding against steel. However, wear rates were similar regardless of the friction and hardness if material removal mainly occurred through abrasion and/or adhesion. Martensitic phases decomposed during sliding while nano-crystalline grains enhanced oxidative wear which reduced friction. With a stable nanocrystalline microstructure that confers ultrahigh hardness, wear rate and friction can be substantially reduced by promoting oxidative over abrasive or adhesive wear. • Dry sliding of two conventionally- and LPBF-processed Ti alloys was investigated. • A nano-crystalline microstructure enhances oxide formation which reduces friction. • α′ or α″ is unstable in the presence of frictional heat and oxygen diffusion. • A stable ultrahard nanocrystalline microstructure can reduce both wear and friction. • This microstructure promotes oxidative wear and minimizes adhesion/abrasion. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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16. Discovering the role of the defect morphology and microstructure on the deformation behavior of additive manufactured Ti–6Al–4V.
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Liu, Jie, Zhang, Kai, Liu, Jianwen, Zhang, Ruifeng, Zeng, Zhuoran, Zhu, Yuman, and Huang, Aijun
- Subjects
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MICROSTRUCTURE , *TITANIUM alloys , *DEFORMATIONS (Mechanics) , *TENSILE tests , *MARKET penetration - Abstract
The defects remain a significant issue for additive manufactured titanium alloys, which hinders their further market penetration. In this work, we proposed a new understanding of the inhomogeneous microstructure formation affected by defects with detailed EBSD characterization, and how the defects and inhomogeneous microstructures determined the strain accumulation behavior by in-situ SEM tensile testing. Smaller prior β grains and coarser α laths were identified around the defects. In-situ tensile behavior investigations revealed that irregularly-shaped and elongated defects with high stress intensity factor ( Δ K I) could induce severe strain accumulation, showing that the defect morphology was the primary factor that could determine the strain accumulation behavior. In the meantime, the inhomogeneous microstructures around the defects could further contribute to the strain accumulation, with the coarser α laths more favorable for deformation and stronger microtexture for easier slip transmission. In addition, microcracks were found initiated from a spherical pore with small loading, and arrested due to the negligible strain accumulation. Further characterization showed that oxidation, which was found more probable in spherical pores, was the cause of this microcrack initiation. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2022
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17. Effects of the morphology of grain boundary α-phase on the anisotropic deformation behaviors of additive manufactured Ti–6Al–4V.
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Liu, Jianwen, Zhang, Kai, Gao, Xiang, Wang, Hao, Wu, Songquan, Yang, Yi, Zhu, Yuman, and Huang, Aijun
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CRYSTAL grain boundaries , *GRAIN , *DEFORMATIONS (Mechanics) , *TITANIUM alloys , *TENSILE tests , *MICROSTRUCTURE - Abstract
[Display omitted] • With the transverse loading direction, the strain localization was found within the continuous grain boundary α-phase. • Discontinuous grain boundary α-phase could fully accommodate uniform deformation together with the matrix microstructure. • An effective approach that eliminates the anisotropy in additive manufactured Ti-6Al-4V was provided. Grain boundary α-phase (GB-α) in titanium alloys is the vulnerable site for failure, while the correlation between deformation behavior and local dislocation motion is still ambiguous. In this study, we made a detailed investigation into the deformation behavior of GB-α with different morphologies in a laser powder bed fusion (LPBF) fabricated Ti-6Al-4V (Ti-64) by using in-situ and interrupted tensile testing, and discussed the underlying mechanisms of dislocation motion. The deformation-induced dislocations were found severely accumulated within the continuous GB-α with the transverse loading direction, which corresponds to the strain localization, while uniformly distributed between the continuous GB-α and surrounding grains with the perpendicular tensile loading. In contrast, discontinuous GB-α could fully accommodate uniform deformation with the matrix microstructure under both loading directions. The new understanding of dislocation motions in GB-α provides a novel perspective to effectively eliminate the tensile property anisotropy with the columnar microstructure present in LPBF Ti-64. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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- View/download PDF
18. Grain boundary α-phase precipitation and coarsening: Comparing laser powder bed fusion with as-cast Ti-6Al-4V.
- Author
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Liu, Jianwen, Zhang, Kai, Yang, Yi, Wang, Hao, Zhu, Yuman, and Huang, Aijun
- Subjects
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CRYSTAL grain boundaries , *KIRKENDALL effect , *POWDERS , *LASERS , *ELECTRON backscattering , *TITANIUM alloys - Abstract
Grain boundary α-phase (GB-α) precipitation and coarsening behavior in Ti-6Al-4V (Ti-64) processed by laser powder bed fusion (LPBF) were investigated and compared with those in as-cast Ti-64. GB-α in LPBF processed Ti-64 tended to precipitate at the triple junctions (TJs) of the β-phase grain boundaries during the subsequent annealing process. Kinetic analysis on GB-α showed that the coarsening mechanisms varied in LPBF processed Ti-64 at different annealing temperatures (bulk diffusion at 750 °C and interface reaction at both 850 and 950 °C), while were consistent in as-cast Ti-64 (interface reaction at all the three temperatures). The inconsistent coarsening mechanisms were attributed to the GB-α curvature difference caused by the different α lamellae nucleation mechanisms. These findings could help rationalize the GB-α morphology evolution and benefit the further mechanical property manipulation in LPBF processed titanium alloys. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2022
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- View/download PDF
19. Experimental and crystal plasticity modelling study on the crack initiation in micro-texture regions of Ti-6Al-4V during high cycle fatigue tests.
- Author
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Liu, Wencheng, Huang, Jia, Liu, Jianwen, Wu, Xinhua, Zhang, Kai, and Huang, Aijun
- Subjects
- *
CRYSTAL models , *CRACK initiation (Fracture mechanics) , *FATIGUE testing machines , *HIGH cycle fatigue , *STRESS concentration , *FATIGUE cracks - Abstract
• Fatigue cracks were initiated at the interface between two micro-textured regions. • Crystal plasticity model was used for quantifying the micromechanical response. • Stress concentration and dislocation pile-up lead to the fatigue crack initiation. Micro-textured regions (MTRs) are the presence of large regions of α grains aggregates with strong local texture, which are detrimental to the fatigue performances in titanium alloys. This work proposes an EBSD map-image based crystal plasticity model to study the fatigue crack initiation in MTRs. Crystal plasticity simulations reveal that the crack initiation may be attributed to the significantly high plastic strain accumulated on prismatic a slip systems leading to significantly high dislocation pile-ups, and high stress concentrations on the cluster of hard grains leading to the stress redistribution and cleavage fracture of the specimen. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
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