Weijie Lu

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (75)88.54 Total impact

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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. · 2.91 Impact Factor
  • 10/2014; 29(22).
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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. · 1.98 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. · 1.94 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.
    Materials science & engineering. C, Materials for biological applications. 12/2013; 33(8):4551-4561.
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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. · 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; · 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.
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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; · 1.96 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. · 2.14 Impact Factor
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    ABSTRACT: Titanium matrix composites reinforced by TiB whiskers and La2O3 particles are synthesized in a consumable vacuum arc remelting furnace by an in situ technique based on the reaction between Ti, LaB6 and oxygen in the raw material. The titanium matrix composites are hot rolled with degrees of deformation of 60%, 80%, 90% and 95%. The effects of the hot rolling degree of deformation on the mechanical properties of the composites are investigated by experiment and modeling. In particular, the variation in the inclination of the TiB whiskers during rolling is quantified in the model. The results show that, with increasing degree of deformation, the mechanical properties of composites are improved. Modeling of the mechanical properties reveals that grain refinement and TiB whisker rotation during rolling contribute to the improvement in the yield strength of the titanium matrix composites. Electron backscatter diffraction and transmission electron microscopy observations are used to study the texture of the composites. It is found that the orientation relationships between Ti matrix and TiB whiskers are [1 1 −2 0]Ti || [0 1 0]TiB, (0 0 0 1)Ti || (0 0 1)TiB and (1 −1 0 0)Ti || (1 0 0)TiB. TiB whiskers rotate in the rolling direction (RD) with increasing degree of deformation, which results in a higher intensity [1 1 −2 0]Ti || RD fiber due to the special orientation relationship between TiB and the Ti matrix.
    Acta Materialia. 04/2012; 60(s 6–7):2656–2667.
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    ABSTRACT: Ti–xNb–3Zr–2Ta alloys (x = 33, 31, 29, 27, 25) (wt.%) were fabricated by vacuum non-consumable arc melting and hot forging. The hot-forging specimens were solid solution treated at 1053 K for 1.8 ks followed by water quenching (WQ) and air cooling (AC) respectively. The microstructure of hot-forging specimens with different deformation rate and solid solution treated at different temperatures was investigated. The result showed that a large amount of α" martensite appeared in the WQ group while only a little amount of α" phase could be found in the AC group. Moreover, for the WQ group, less niobium resulted in more diffraction peaks of α" phase in XRD profiles. This result suggested that the stability of β phase decreased with the decrease of Nb content. The microhardness of Ti–xNb–3Zr–2Ta (wt.%) alloys was improved significantly with the decreasing Nb content in both WQ group and AC group. Increasing deformation ratio could effectively refine β grains for Ti–25N–3Zr–2Ta (wt.%). Both acicular martensite and lath martensite were found in the transmission electron microscope observation of Ti–25Nb–3Zr–2Ta (wt.%) alloy. Martensitic internal twins were identified as well.
    Materials Science and Engineering: C. 03/2012; 32(2):126–132.
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    ABSTRACT: The microstructure and phase constitutions of TixNb3Zr2Ta alloys (x=35, 31, 27, 23) (wt%) were studied. With a lower niobium content the grain size of β phase in TixNb3Zr2Ta alloys increased significantly, and the TixNb3Zr2Ta system was more likely to form α″ phase and even α phase. Tensile tests showed that UTS of TixNb3Zr2Ta alloys improved as the Nb content was decreased. Cyclic loading-unloading tensile tests were carried on TixNb3Zr2Ta alloys. Ti23Nb3Zr2Ta and Ti27Nb3Zr2Ta alloys featured the best superelasticity among the alloys studied. The pseudoelastic strain ratio of Ti35Nb3Zr2Ta alloy decreased a lot as the cycle number increased. Ti31Nb3Zr2Ta alloy showed only minimum superelasticity. This is because Ti23Nb3Zr2Ta and Ti27Nb3Zr2Ta alloys had higher yield strength than Ti31Nb3Zr2Ta did, which allowed martensite phase to be induced. On the contrary, Ti31Nb3Zr2Ta alloy exhibited better shape memory property than Ti27Nb3Zr2Ta, Ti23Nb3Zr2Ta and Ti35Nb3Zr2Ta titanium alloys. β phase, α phase and α″ phase were found in Ti23Nb3Zr2Ta alloy by TEM observation. The dislocation density of α phase was much lower than that of β phase due to their crystal structure difference. This may explained why Ti23Nb3Zr2Ta with α phase possessed higher tensile strength. The incomplete shape recovery of Ti23Nb3Zr2Ta alloy after unloading resulted from two sources. Plastic deformation occurred in β phase, α phase and even α″ phase under dislocation slip mechanism, and incomplete decomposition of α″ martensitic phase resulted in unrecovered strain as well.
    Journal of the mechanical behavior of biomedical materials. 02/2012; 12:151-9.
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    ABSTRACT: PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.
    Physica B Condensed Matter 01/2012; · 1.28 Impact Factor
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    ABSTRACT: Trace reinforcements can significantly refine microstructure and improve mechanical performance of composite. In this work, the in situ synthesized Ti–5Al–5Mo–5V–1Fe–1Cr titanium matrix composite containing trace TiB and TiC is fabricated. The microstructural characteristics and tensile properties of the heat-treated materials are investigated, with particular emphasis on researching the spheroidization of α phase and the effects of trace reinforcements. It is revealed that it presents the division of α grain during spheroidization process. The separated α phase, near equiaxed α phase and short-rod α phase tend to be spheroidized during the processing of diffusion. The trace reinforcements can accelerate the spheroidization of α by accelerating the extent of diffusion and then the microstructural homogeneity is promoted. The composite manifests excellent comprehensive mechanical properties due to the microstructural improvement and the effect of the trace reinforcements.
    Materials Science and Engineering A 12/2011; · 2.41 Impact Factor
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    ABSTRACT: The recrystallization behavior of surface deformation layer of (TiB+TiC)/Ti–6Al–4V and Ti–6Al–4V were both investigated during isothermal annealing using X-ray diffraction line profile analysis. The surface deformation layer was introduced by shot peening treatment. The results revealed that with increasing the time of isothermal annealing, the microstructure variations at shot peened layer were obvious. Based on the results of line profile analysis, the recrystallization activation energies were calculated by computer regression analysis, and it showed that the recrystallization activation energy of (TiB+TiC)/Ti–6Al–4V was larger than that of Ti–6Al–4V, which was ascribed to the effect of reinforcements hindering the movements of dislocations, grain and subgrain boundaries in the process of recrystallization. The hindrance effect of reinforcements as sink sources of dislocations gliding resulted that the decrease rate of dislocation density of the composite was slower than that of the matrix. In addition, the relaxation activation energies were obtained according to the analysis of microstrain relaxation, and after isothermal annealing, the depth distribution of domain sizes from the top surface was investigated and discussed in detail. According to above analysis, the results showed that the thermostability of the composite was higher than that of the matrix because of the effect of reinforcements.
    Materials Science and Engineering A 12/2011; · 2.41 Impact Factor
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    ABSTRACT: Thermal stability of in situ synthesized (TiB+La2O3)/Ti composite is investigated. The phase analysis is identified by X-ray diffraction. Microstructure of the melted and forged titanium matrix composites (TMCs) after heat treatment is characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The room temperature tensile properties after an additional thermal exposure at 873K, 923K or 973K for 100h are tested. After the thermal exposure, the strength of specimen increases and ductility decreases. This is attributed to precipitation of ordered α2 phase (Ti3Al) and S1 (silicide) in the titanium matrix composites after the thermal exposure.
    Materials Science and Engineering A 06/2011; 528(15):4883-4887. · 2.41 Impact Factor
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    ABSTRACT: The microstructures of in situ synthesized (TiB + La2O3)/Ti composite after β and TRIPLEX heat treatment are investigated. The room temperature tensile properties of the titanium matrix composites (TMCs) are tested, and thermal stability is carried out at 600, 650 and 700 °C for 100 h, respectively. The results show that the microstructure of specimen after β heat treatment is widmanstätten, while it is similar to basketweave after TRIPLEX heat treatment. Room tensile properties of specimen after TRIPLEX heat treatment are better than those of β heat treatment. After thermal exposure, the strength of specimens treated by β and TRIPLEX heat treatment increases, while the ductility decreases sharply, this is attributed to the precipitation of Ti3Al and silicides. The thermal stability of specimen after TRIPLEX heat treatment is better than that after β heat treatment.
    Journal of Alloys and Compounds. 01/2011; 509(1):52–56.
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    ABSTRACT: The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (
    Materials & Design - MATER DESIGN. 01/2011; 32(5):2934-2939.
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    ABSTRACT: The surface layer characteristics of shot peened (TiB+TiC)/Ti–6Al–4V composite are investigated using X-ray diffraction line profile analysis. The structural breadth, domain sizes, microstrain and dislocation densities of the matrices and composite are obtained. The results show that the domain sizes are refined after shot peening, and the dislocation densities are increased sharply in the near surface layer, which result from the high kinetic energy of shot balls in the process of shot peening. Comparing with the calculated results of the matrices and composite, it can be found that the microstructure variations of matrices are more severe than composite's, which is ascribed to the effect of reinforcements' resistance to the surface layers' deformation. Besides, the distributions of residual stresses and microhardness with different shot peening intensities and reinforcement volume fractions have been discussed, and the effects of reinforcements and shot peening intensities have been indicated. According to above detailed discussions, the results reveal that shot peening is an essential process of improving the surface properties of titanium matrix composite.
    Surface & Coatings Technology - SURF COAT TECH. 01/2011; 206(2):511-516.