Weijie Lu

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (87)190.76 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Titanium matrix composites were prepared by investment casting in a consumable arc skull casting furnace. With the addition of B4C, the average primary β grains are refined, and the morphology of α phase tends to be more equiaxed. The free energy for nucleation consisting of the bulk free energy, orientation-independent interfacial energy, and elastic strain energy is calculated to investigate the role of nucleation sites in determining the shape of critical nucleus. In the current study, the TiB whiskers were found to be arranged in the grain boundary and provide heterogeneous nucleation sites for α precipitates, and the interfacial energy is about 14 % more than that in Ti-64, while its elastic strain energy is reduced to about three quarters of the latter one.
    Journal of Materials Science 09/2015; 50(17). DOI:10.1007/s10853-015-9120-z · 2.31 Impact Factor
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    ABSTRACT: (TiB + TiC)/TC4 composites reinforced with different amounts of TiB whiskers and TiC particles are produced by common casting and hot forging technology. Then the fracture toughness of (TiB + TiC)/TC4 composites is analyzed by experiment and modeling. The experimental results indicate that not only reinforcement volume fraction but also the mole ratio between TiB whiskers and TiC particles can influence the fracture toughness of (TiB + TiC)/TC4 composites. Microstructure observations are carried out to examine the behavior of TiB whiskers and TiC particles in the fracture process. An analytical expression for predicting the fracture toughness of (TiB + TiC)/TC4 composites is built up. In particular, the coupling influences of TiB whiskers and TiC particles on the elastic modulus, yield strength, and fracture strain of TMCs are revealed in the modeling process. The results indicate that when TiB and TiC particles are coexisting in the TMCs, the fracture toughness of (TiB + TiC)/TC4 composites increases with the increase of the TiB whiskers aspect ratio, TiC particles volume fraction and size; however, with the increase of TiB whiskers volume fraction, the fracture toughness decreases. The breakage of TiB whiskers is the main reason for the fracture of TMCs. The acting mechanism of TiC particles on the fracture of TMCs transfers from blocking crack propagation and interfacial debonding to breakage with the increase of size, which can decrease the fracture toughness of (TiB + TiC)/TC4 composites. Considering the broken fraction of TiB whiskers, the fracture toughness of (TiB + TiC)/TC4 composites can be reasonably predicted.
    Metallurgical and Materials Transactions A 08/2015; 46(8). DOI:10.1007/s11661-015-2973-6 · 1.73 Impact Factor
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    ABSTRACT: In this study, equal channel angular pressing (ECAP) of (TiB + TiC)/Ti6Al4V titanium matrix composite was successfully carried out at 800 °C, the effect of pass number on the microstructure and mechanical properties was investigated. After each pass of ECAP, the evolution of the microstructure and mechanical properties of (TiB + TiC)/Ti6Al4V composite during thermal-mechanical processing was studied, the Vickers micro-hardness measurements and tensile testing were performed at room temperature. The results showed that the size of the reinforcements and grains were both fully refined to a smaller scale, a number of more homogeneous TiB short fibers and TiC particles have been attained after four ECAP passes. The tensile strength increased with increasing ECAP numbers and saturated after four ECAP passes to a yield strength of 1200 MPa, and microhardness was also significantly improved by means of this processing technology, the ductility of titanium matrix composite after the four ECAP passes was slightly greater than the first ECAP pass.
    Materials and Design 06/2015; 75. DOI:10.1016/j.matdes.2015.03.018 · 3.17 Impact Factor
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    ABSTRACT: In this paper, the morphologic evolution of α-phases and their influence on mechanical properties during the hot working process of the Ti-6Al-4V alloy has been quantitatively investigated. Samples with a variety of different features of α-phase were obtained by hot working. A quantitative analysis of SEM/OM images is carried out to determine the features of α-phase before and after deformation, including the length, thickness, aspect ratio and volume fraction of α-phase. It was found that the α-phase platelet thickness increases with the increasing of forging height reduction on subsequent solution and aging treatment, larger height reduction would reduce the aspect ratio and length of α-phase and further makes the α-phase closest to equiaxed morphology. Moreover, the influence of the α-phase features on the mechanical properties was systematically investigated. The results indicate that the mechanical properties are strongly determined by the features of the α-phase, especially the thickness and volume fraction of the α-phase. This work will optimize the mechanical property by means of microstructural control and deepen the understanding of influence of α-phase features on the mechanical properties.
    International Journal of Modern Physics B 04/2015; 29(10n11):1540012. DOI:10.1142/S0217979215400123 · 0.94 Impact Factor
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    ABSTRACT: The flow behavior of forged commercial purity (CP) titanium powder compact was studied by developing a processing map. CP titanium powder was sintered to 94% relative density, then hot compressed in a Gleeble thermal-mechanical simulator at strain rates ranging from 0.001 to 10 s−1 and deformation temperatures ranging from 600 to 800 °C. The hot forging process improved the densification to 98-99.9% and reduced the grain size from 93 to 10 µm by the occurrence of dynamic recrystallization. The fully dynamic recrystallization region is in the range of deformation temperature of 750-800 °C and strain rate of 0.001-0.01 s−1, with a power dissipation efficiency higher than 40%, determined by constructing a processing map and analyzing the volume fraction of dynamic recrystallization. This research provides a guide for powder compact forging of power metallurgy titanium by providing the hot compression parameters, which can lead to an improved microstructure and densification.
    Journal of Materials Research 04/2015; 30(08):1-9. DOI:10.1557/jmr.2015.84 · 1.82 Impact Factor
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    ABSTRACT: Titanium matrix composites(TMCs) are prepared by investment casting in a vacuum consumable kish furnace. The effects of B4C additions on the microstructures and tensile properties of TMCs are investigated. With the addition of B4C, the microstructure of TMCs is refined and the strength is improved. The yield strength of TMCs is evaluated by a comprehensive model that combines the strengthening effects of TiB whiskers/TiC particles, grain refinement and solution strengthening of the matrix, which is consistent with the experimental results in the current study. It is found that the yield strength enhancement of TMCs is mainly due to grain refinement and solution strengthening. During tensile deformation, the dislocation piles up at the interface between TiB whisker and matrix, which allows the TiB whiskers to bear extra load and therefore enhances the strength of TMCs. The plastic deformation is localized due to the action of TiB whiskers and this results in the brittle fracture of TMCs.
    Materials Science and Engineering A 03/2015; 628:366-373. DOI:10.1016/j.msea.2015.01.067 · 2.41 Impact Factor
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    ABSTRACT: (TiB + La2O3)/Ti composites were in situ synthesized and deformed with different deformation degrees. The influence of TiB whisker orientation and grain refinement on the creep properties of titanium matrix composites (TMCs) are discussed. The creep test reveals that the steady state creep rate of TMCs first decreases and then increases with the increase of deformation degree, which can be attributed to competing effects: TiB whisker rotating to the rolling direction, α plate grain boundary hindering and pinning dislocations can all decrease the creep rate, however, dislocation movement on the α plate grain boundary and dislocation emitting from the α plate grain boundary can both increase the creep rate.
    Materials and Design 11/2014; 63:50–55. DOI:10.1016/j.matdes.2014.05.063 · 3.17 Impact Factor
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    ABSTRACT: This study presented a novel fabrication process for TiNi thin films by vacuum diffusion technology using reactive Ni/Ti/Ni multilayer thin films. The sandwiched thin films were prepared by chemical nickel plating. Ni/Ti/Ni multilayer films were heat treated for various diffusion times and temperatures and the influences of the temperature and diffusion time on the interdiffusion behavior of the Ti-Ni system were researched in detail. The results showed that a homogeneous TiNi thin film was obtained at 1173 K with a diffusion time of 4 h. Moreover, the formation sequence of the intermetallics in the Ti-Ni diffusion system was investigated by thermodynamic analysis and experiment. It was found that three compounds - TiNi3, Ti2Ni, and TiNi - formed in the diffusion process at the Ti/Ni interfaces. More importantly, the nucleation of TiNi3 and Ti2Ni was prior to that of TiNi because of the lower reaction Gibbs free energy and increasing interface energy of TiNi3 and Ti2Ni.
    Journal of Materials Research 10/2014; 29(22). DOI:10.1557/jmr.2014.264 · 1.82 Impact Factor
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    ABSTRACT: Rolling contact fatigue (RCF) behaviors of titanium matrix composites (TiB + TiC)/Ti–6Al–4V are investigated, including the microstructural variables, the stress distribution and the RCF life. The effect of reinforcements on RCF is observed in detail. The microstructural information, especially pertaining to the reinforcements, is obtained through scanning electron microscope. The influence of reinforcements on stress distribution is studied via analyses of subsurface stress distributions based on an approximate numerical method, in which the reinforcement distributions are taken into account. The results reveal that the existence of reinforcements causes RCF life reduction due to the stress concentration in and around the reinforcements.
    International Journal of Fatigue 09/2014; 66:127–137. DOI:10.1016/j.ijfatigue.2014.03.019 · 1.69 Impact Factor
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    ABSTRACT: Different additions of B4C were introduced into TC4 to alter the microstructure and mechanical properties. The morphologies of reinforcements are related to the solidification paths. The refinement of lamellar spacing lambda is based on the precipitation pattern of beta-phases. Microhardness, compression elastic modulus (E-c), and elastic modulus of the matrix (Em) appear non-linear relationships with B4C additions. Due to the refinement of lamellar spacing with Hall-Petch-type relationships, and the solution strengthening of C on the alpha + beta matrix, the effect of reinforcements on the mechanical properties will be more efficient when the additions of B4C are no more than 0.19 wt%. When the additions of B4C are more than 0.19 wt%, the efficiency will decrease.
    Acta Metallurgica Sinica (English Letters) 04/2014; 27(2):205-210. DOI:10.1007/s40195-014-0035-5 · 0.43 Impact Factor
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    ABSTRACT: After shot peening (SP), the variations of microstructures and hardness of (TiB + TiC)/Ti–6Al–4V were investigated. The microstructures of the surface and cross-section were studied, and the results revealed that the convex and concave features appeared on the surface after SP. Based on the microstructures of cross-section, the micrograph showed the random inclination of reinforcements in the surface layer, which illuminated that the reinforcements were yielded to the random deformation of matrix during SP. The variations of hardness before and after SP were investigated via the nano-indentation method. The results indicated that the variations of hardness were caused by the different extent of deformation under surface. All results were discussed in detail.
    Surface and Coatings Technology 04/2014; 244:69–77. DOI:10.1016/j.surfcoat.2014.01.053 · 2.20 Impact Factor
  • MATERIALS TRANSACTIONS 01/2014; 55(1):141-146. DOI:10.2320/matertrans.M2013187 · 0.61 Impact Factor
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    ABSTRACT: In this paper, an equal channel angular pressing method is employed to refine grains and enhance mechanical properties of a new β Ti-35Nb-3Zr-2Ta biomedical alloy. After the 4th pass, the ultrafine equiaxed grains of approximately 300nm and 600nm are obtained at pressing temperatures of 500 and 600°C respectively. The SEM images of billets pressed at 500°C reveal the evolution of shear bands and finally at the 4th pass intersectant networks of shear bands, involving initial band propagation and new band broadening, are formed with the purpose of accommodating large plastic strain. Furthermore, a unique herringbone microstructure of twinned martensitic variants is observed in TEM images. The results of microhardness measurements and uniaxial tensile tests show a significant improvement in microhardness and tensile strength from 534MPa to 765MPa, while keeping a good level of ductility (~16%) and low elastic modulus (~59GPa). The maximum superelastic strain of 1.4% and maximum recovered strain of 2.7% are obtained in the billets pressed at 500°C via the 4th pass, which exhibits an excellent superelastic behavior. Meanwhile, the effects of different accumulative deformations and pressing temperatures on superelasticity of the ECAP-processed alloys are investigated.
    12/2013; 33(8):4551-4561. DOI:10.1016/j.msec.2013.07.010
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    ABSTRACT: β type titanium alloys have attracted much attention in the biomedical field because they consist of non-cytotoxic elements, show high corrosion resistance, and are biologically compatible. In this study, a novel β type titanium alloy (Ti35Nb3Zr2Ta) with a Young's modulus of 48 GPa was fabricated and the alloy's corrosion resistance and in vitro response were determined. The results indicate that the novel alloy exhibits comparable corrosion resistance when compared with Ti6Al4V, but in vitro experiments show that osteoblasts attach, spread, proliferate, and differentiate better on Ti35Nb2Ta3Zr than on Ti6Al4V. The high corrosion resistance and satisfactory biocompatibility make the novel Ti35Nb3Zr2Ta alloy a promising biomaterial for surgical implants.
    Biomedical Materials 09/2013; 8(5):055004. DOI:10.1088/1748-6041/8/5/055004 · 2.92 Impact Factor
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    ABSTRACT: The surface properties of (TiB + TiC)/Ti-6Al-4V before and after shot peening (SP), have been investigated. The results indicate that the increased reinforcements and SP intensities enhance the surface roughness after SP. Both compressive residual stresses (CRS) and hardness increase with the increase of SP intensity, which is mainly due to the plastic deformation and high dislocation density in the near surface layer. Moreover, the reinforcement particles can act as the block sources during dislocation movements. After an appropriate SP treatment, the increased CRS and hardness are beneficial to industrial applications.
    Applied Surface Science 09/2013; 280:981-988. DOI:10.1016/j.apsusc.2013.05.135 · 2.54 Impact Factor
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    ABSTRACT: A strategy of nanodispersion toughening is utilized to improve the ductility in micron particulate-reinforced aluminum composites, which involves increasing the strain hardening rate by introducing Al2O3 nanodispersoids into the ultrafine-grained (UFG) matrix using flake powder metallurgy. The as-fabricated B4C/UFG Al(Al2O3) exhibits simultaneous enhancement in tensile plasticity (8.9%) and strength (364 MPa) compared with its counterpart without the nanodispersoids. Thus, nanodispersion toughening promises an easy but effective pathway to optimize the strength and ductility of particulate-reinforced UFG metallic composites.
    Scripta Materialia 04/2013; 68(8):555–558. DOI:10.1016/j.scriptamat.2012.11.024 · 2.97 Impact Factor
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    ABSTRACT: Titanium (Ti) alloys of the β-type are highly attractive metallic materials for biomedical applications due to their low elastic modulus, high corrosion resistance and notable biocompatibility. A new β-type Ti35Nb2Ta3Zr alloy with a low Young's modulus of approximately 48 GPa was previously fabricated. In the present study, the biocompatibility of this alloy was evaluated. In an in vitro assay, the Ti35Nb2Ta3Zr alloy did not markedly affect the adhesion of MG63 osteoblast cells, but it increased their proliferation, alkaline phosphatase (ALP) activity, calcium deposition and mRNA expression of osteogenic genes (i.e., ALP, osteocalcin, osteopontin). In an in vivo study, no marked histological differences were observed between the new bone formed on the surface of Ti35Nb2Ta3Zr and that formed on the surface of control Ti6Al4V rods placed in the medullary canal of rabbit femurs. Additionally, no significant differences were observed in the failure load of Ti35Nb2Ta3Zr and Ti6Al4V in pull-out tests. In conclusion, the Ti35Nb2Ta3Zr alloy with a lower elastic modulus closer to that of human bone has significant bone tissue compatibility equal to that of Ti6Al4V, which has been widely used in orthopedic applications.
    International Journal of Molecular Medicine 01/2013; 31(3). DOI:10.3892/ijmm.2013.1249 · 1.88 Impact Factor
  • MATERIALS TRANSACTIONS 01/2013; 54(12):2245-2251. DOI:10.2320/matertrans.M2013250 · 0.61 Impact Factor
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    ABSTRACT: Ti–5Al–5Mo–5V–1Fe–1Cr Ti alloy and Ti–5Al–5Mo–5V–1Fe–1Cr Ti matrix composites containing different weight fractions of trace TiB and TiC are fabricated via in situ synthesis method. The as-cast ingots are subjected to thermo-mechanical processing and heat treatment. The Widmannstatten structure is obtained after the heat treatment. The microstructure length scales of the materials are identified. The identification indicates that 0.4 wt.% TiB and 0.1 wt.% TiC can reduce the average size of the β grains by more than 50%. Whereas the extent of the microstructure refinement gradually decreases while increasing the weight fraction of the trace reinforcements. The influences of weight fraction and morphology of the trace TiB and TiC on microstructure refinement are researched in this work. Moreover, the tensile properties of the heat-treated materials are examined. It is revealed that Hall–Petch mechanism plays an identically important role in improving the mechanical properties of the composites comparing with the load bearing and dispersion strengthening of the trace reinforcements.
    Composites Part B Engineering 12/2012; 43(8):3334–3337. DOI:10.1016/j.compositesb.2012.01.075 · 2.98 Impact Factor
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    ABSTRACT: Shot peening is well known as an effective and important surface treatment method to improve the surface properties of metallic components. In this work, both the experiments and numerical modelling of the residual stress distribution introduced by shot peening in deformed surface layer of Ti–6Al–4V have been investigated. The program of ABAQUS/Explicit has been used in 2-dimensional and 3-dimensional models for the dynamic analysis of impacting. After shot peening, the residual stresses distribution along the depth variation from top surface have been measured by X-ray method. The distribution of residual stress by simulation is according with the result of experiment, and the compressive residual stresses have formed in the surface layer and the maximum appear on the subsurface layer. The results indicate that the max compressive residual stresses range from −870 to −1000 MPa. After shot peening, the microstructure of peened surface from the section plane has been observed and the indentations on the surface are obvious. All results have been discussed in detail.
    Materials and Design 10/2012; 41:314-318. DOI:10.1016/j.matdes.2012.05.024 · 3.17 Impact Factor