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ISSN 1005-0302
CN 21-1315/TG
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      20 April 2018, Volume 34 Issue 4 Previous Issue    Next Issue
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    Orginal Article
    Characterization of lattice defects in metallic materials by positron annihilation spectroscopy: A review
    J. Mater. Sci. Technol., 2018, 34 (4): 577-598.  DOI: 10.1016/j.jmst.2017.11.050
    Abstract   HTML   PDF

    Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron annihilation spectroscopy is a non-destructive technique which enables characterization of open volume lattice defects in solids on the atomic scale. Positron lifetime and Doppler broadening of annihilation photo-peak are the most common observables related to positron annihilation process. Positron lifetime spectroscopy enables to identify defects in solids and to determine their concentrations while coincidence measurement of Doppler broadening provides information about local chemical environment of defects. This article provides a review of the state-of-art of defect characterization in bulk metallic materials by positron annihilation spectroscopy. Advanced analysis of positron annihilation data and recent developments of positron annihilation methodology are described and discussed on examples of defect studies of metallic materials. Future development in the field is proposed as well.

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    Influence of Al2O3 particle pinning on thermal stability of nanocrystalline Fe
    G.B. Shan, Y.Z. Chen, M.M. Gong, H. Dong, B. Li, F. Liu
    J. Mater. Sci. Technol., 2018, 34 (4): 599-604.  DOI: 10.1016/j.jmst.2017.11.035
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    Second-phase particle pinning has been well known as a mechanism impeding grain boundary (GB) migration, and thus, is documented as an efficient approach for stabilizing nanocrystalline (NC) materials at elevated temperatures. The pinning force exerted by interaction between small dispersed particles and GBs strongly depends on size and volume fraction of the particles. Since metallic oxides, e.g. Al2O3, exhibit great structural stability and high resistance against coarsening at high temperatures, they are expected as effective stabilizers for NC materials. In this work, NC composites consisting of NC Fe and Al2O3 nanoparticles with different amounts and sizes were prepared by high energy ball milling and annealed at various temperatures (Tann) for different time periods (tann). Microstructures of the ball milled and annealed samples were examined by X-ray diffraction and transmission electron microscopy. The results show that the addition of Al2O3 nanoparticles not only enhances the thermal stability of NC Fe grains but also reduces their coarsening rate at elevated temperatures, and reducing the particle size and/or increasing its amount enhance the stabilizing effect of the Al2O3 particles on the NC Fe grains.

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    Glass formation adjacent to the intermetallic compounds in Cu-Zr binary system
    Yinxiao Wang, Jiahao Yao, Yi Li
    J. Mater. Sci. Technol., 2018, 34 (4): 605-612.  DOI: 10.1016/j.jmst.2017.09.008
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    On the contrary to the common belief that glass formation is unfeasible near terminal intermetallic compound due to fast crystallization kinetics, here we present our findings that bulk metallic glasses are readily formed near intermetallic compounds, far away from the traditional region of glass forming near eutectics. While the intermetallic compounds themselves are not possible glass formers, bulk metallic glasses can be quenched compositionally neighboring the intermetallic compounds as close as 0.5 at.%. Taking binary Cu-Zr as a model system, the phenomenon of two optimum glass forming compositions sandwiching the corresponding intermetallic compounds (Cu51Zr14, Cu10Zr7, CuZr, CuZr2 and Cu8Zr3) is observed consistently. This new scenario of “intermetallic glass” is verified by the thermodynamic principle that the alloy liquids neighboring the intermetallic compounds possess lower Gibbs free energy than that of the compounds themselves. Furthermore, the sluggish crystallization behavior of these liquids provides an additional kinetic explanation.

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    Modelling thermodynamics of nanocrystalline binary interstitial alloys
    Guibin Shan, Yuzeng Chen, Mingming Gong, Hao Dong, Feng Liu
    J. Mater. Sci. Technol., 2018, 34 (4): 613-619.  DOI: 10.1016/j.jmst.2017.09.003
    Abstract   HTML   PDF

    Grain boundary (GB) segregation in nanocrystalline alloys can cause reduction of GB energy, which leads to thermodynamic stabilization of nanostructures. This effect has been modelled intensively. However, the previous modelling works were limited to substitutional alloy systems. In this work, thermodynamics of nanocrystalline binary interstitial alloy systems was modelled based on a two-sublattice model proposed by Hillert [M. Hillert, et al. Acta Chem. Scand., 24 (1970) 3618] and an atomic configuration for nanocrystalline systems proposed by Trelewicz and Schuh [J.R. Trelewicz, et al. Physical Review B, 79 (2009) 094112]. The modelling calculations agree with the reported experimental data, indicating that the current thermodynamic model is capable of accounting for the alloying effect in the nanocrystalline binary interstitial alloys.

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    Revisiting intrinsic brittleness and deformation behavior of B2 NiAl intermetallic compound: A first-principles study
    studyHui Xing, Anping Dong, Jian Huang, Jiao Zhang, Baode Sun
    J. Mater. Sci. Technol., 2018, 34 (4): 620-626.  DOI: 10.1016/j.jmst.2017.11.038
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    For NiAl intermetallic compound with B2 structure, there is still no calculation combining models of single and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittleness and toughness have not been used to analyze its deformation behavior. Thus, first-principles calculation was applied to comprehensively study the elastic properties, ideal strength, generalized stacking fault energy and surface energy of B2-NiAl intermetallic compound. The results suggest that calculations based on the current basic set give more accurate lattice parameters and elastic moduli. The Pugh criterion and Cauchy pressure cannot be used to interpret the intrinsic brittleness of NiAl. In comparison, the ductility parameter based on the strain energy under elastic instability and ZCT and Rice criteria based on generalized stacking fault energy and surface energy successfully identify the intrinsic brittleness of the NiAl intermetallic compound. The reason why [111] slip always occurs in the deformation along [100] direction was clarified by examining the critical value for brittle-ductile transition. The results of density of state indicate shear deformation has less impact on structural stability, and the change of charge density difference implies that <001> shear induces more intensive redistribution of charge density, which is well correlated to the brittleness and deformation behavior of NiAl intermetallic compound.

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    Simulations of deformation and damage processes of SiCp/Al composites during tension
    J.F. Zhang, X.X. Zhang, Q.Z. Wang, B.L. Xiao, Z.Y. Ma
    J. Mater. Sci. Technol., 2018, 34 (4): 627-634.  DOI: 10.1016/j.jmst.2017.09.005
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    The deformation, damage and failure behaviors of 17 vol.% SiCp/2009Al composite were studied by microscopic finite element (FE) models based on a representative volume element (RVE) and a unit cell. The RVE having a 3D realistic microstructure was constructed via computational modeling technique, in which an interface phase with an average thickness of 50 nm was generated for assessing the effects of interfacial properties. Modeling results showed that the RVE based FE model was more accurate than the unit cell based one. Based on the RVE, the predicted stress-strain curve and the fracture morphology agreed well with the experimental results. Furthermore, lower interface strength resulted in lower flow stress and ductile damage of interface phase, thereby leading to decreased elongation. It was revealed that the stress concentration factor of SiC was ~2.0: the average stress in SiC particles reached ~1200 MPa, while that of the composite reached ~600 MPa.

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    Enhanced oxidation resistance of Mo-12Si-8.5B alloys with ZrB2 addition at 1300°C
    Juan Wang, Bin Li, Shuai Ren, Rui Li, Tao Wang, Guojun Zhang
    J. Mater. Sci. Technol., 2018, 34 (4): 635-642.  DOI: 10.1016/j.jmst.2017.09.010
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    Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB2 alloys were fabricated using mechanical alloying, followed by hot-pressing. Both alloys exhibited uniform microstructure, with the Mo3Si and Mo5SiB2 phases distributing dispersedly in the α-Mo matrix. Mo-12Si-8.5B-1.0wt%ZrB2 showed a finer-grained microstructure than Mo-12Si-8.5B alloy owing to the addition of ZrB2. The results of isothermal oxidation tests at 1300 °C in air revealed that Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB2 alloys initially suffered a transient stage with high mass loss due to the volatilization of MoO3, and then achieved a steady stage owing to the formation of a protective borosilicate scale on the alloy surface. Especially, the transient stage of Mo-12Si-8.5B-1.0wt%ZrB2 alloy was shortened to be less than 300 s, and the mass loss of this stage was reduced by at least 88% compared with that of Mo-12Si-8.5B alloy, indicating a significant improvement in the oxidation resistance. The addition of ZrB2 not only resulted in a continuous borosilicate scale quickly covering the entire base alloy during the transient stage, but also improved the protectiveness of the borosilicate scale of the steady stage by bringing out a large number of ZrO2/ZrSiO4 particles embedded discontinuously in the borosilicate scale, which effectively restricted the inward diffusion of oxygen by acting as diffusion barriers and decreased the thickness of inner oxide layers in particular.

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    Microstructures and tensile properties of laser cladded AerMet100 steel coating on 300 M steel
    Jian Liu, Jia Li, Xu Cheng, Huaming Wang
    J. Mater. Sci. Technol., 2018, 34 (4): 643-652.  DOI: 10.1016/j.jmst.2017.11.037
    Abstract   HTML   PDF

    A layer of AerMet100 steel was coated on the surface of forged 300 M steel using laser cladding technique. The chemical compositions, microstructures, hardness and tensile properties of this AerMet100/300 M material were systematically investigated. Results show that the composition of the AerMet100 clad layer is macroscopically homogeneous, and a compositional transition zone with width of 150 μm is observed between the clad layer and heat affected zone. Microstructures in transition zone transform from the fine needle-like bainite in 300 M steel to the lath tempered martensite in AerMet100 clad layer. Microstructures in heat affected zone also gradually change from the thick plate bainite and blocky retained austenite (unstable heat affected zone) to fine needle-like bainite and film-like austenite (stable heat affected zone) due to different thermal cycle processes. Thick plate bainite together with blocky retained austenite in unstable heat affected zone reduce the strength and ductility of AerMet100/300 M material. However, the tensile specimens, consisting of clad layer and stable heat affected zone, show slightly inferior mechanical properties to 300 M steel. Ductile fracture exists in AerMet100 clad layer while quasi-cleavage fracture occurs in the stable heat affected zone.

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    Microstructure evolution and mechanical properties of linear friction welded S31042 heat-resistant steel
    Yanmo Li, Yongchang Liu, Chenxi Liu, Chong Li, Zongqing Ma, Yuan Huang, Zumin Wang, Wenya Li
    J. Mater. Sci. Technol., 2018, 34 (4): 653-659.  DOI: 10.1016/j.jmst.2017.11.031
    Abstract   HTML   PDF

    S31042 heat-resistant steel was joined by linear friction welding (LFW) in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint. With increasing the distance from the weld zone to the parent metal, the austenitic grain size gradually increases from?~1 μm to ~150 μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength (about 731 MPa) of the welded joint is comparable to that of the S31042 in the solution-treated state.

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    Effect of cold deformation on corrosion fatigue behavior of nickel-free high nitrogen austenitic stainless steel for coronary stent application
    Jun Li, Yixun Yang, Yibin Ren, Jiahui Dong, Ke Yang
    J. Mater. Sci. Technol., 2018, 34 (4): 660-665.  DOI: 10.1016/j.jmst.2017.10.002
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    Due to the excellent mechanical properties, good corrosion resistance, high biocompatibility and nickel-free character, the high nitrogen nickel-free austenitic stainless steel (HNASS) becomes an ideally alternative material for coronary stents. Stent implantation works in harsh blood environment after a balloon dilatation, i.e., the material is used in a corrosive environment with a permanent deformation. The present study attempts to investigate effects of pre-straining on high-cycle fatigue behavior and corrosion fatigue behavior of HNASS in Hank’s solution and the relevant mechanism for coronary stents application. It is found that higher pre-straining on HNASS results in higher strength and maintains almost same corrosion resistance. Fatigue limit of 0% HNASS is 550 MPa, while corrosion fatigue limit is 475 MPa. And improvement in fatigue limit of 20% and 35% pre-strained HNASS is in comparison with the 0% HNASS, while corrosion would undermine the fatigue behavior of HNASS. In a suitable range, the pre-straining had a beneficial effect on corrosion fatigue strength of HNASS, such as nearly 300 MPa improved with 20% cold deformation. This result provides a good reference for predicting the life of HNASS stent and as well its design.

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    Distinct dendritic α phase emerging on the surface of primary α phase in a compressed near-α titanium alloy
    Z. Liu, Z.B. Zhao, J.R. Liu, Q.J. Wang, R. Yanga
    J. Mater. Sci. Technol., 2018, 34 (4): 666-669.  DOI: 10.1016/j.jmst.2017.10.011
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    The characteristic of the surface morphology of primary α phase was studied in a deformed near-α titanium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α + β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epitaxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.

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    Microstructure, mechanical and tribological properties of TiAl-based composites reinforced with high volume fraction of nearly network Ti2AlC particulates
    Jun Cheng, Shengyu Zhu, Yuan Yu, Jun Yang, Weimin Liu
    J. Mater. Sci. Technol., 2018, 34 (4): 670-678.  DOI: 10.1016/j.jmst.2017.09.007
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    TiAl-based composites reinforced with different high volume fractions of nearly network Ti2AlC phase have been successfully prepared by mechanical alloying and hot-pressing method. Their microstructure, mechanical and tribological properties have been investigated. Ti2AlC network becomes continuous but the network wall grows thicker with increasing the Ti2AlC content. The continuity and wall size of the network Ti2AlC phase exert a significant influence on the mechanical properties. The bending strength of the composites first increases and then decreases with the Ti2AlC content. The compressive strength of the composite decreases slightly compared to the TiAl alloy, but the hardness is enhanced. Due to the high hardness and load-carrying capacity of the network structure, these composites have the better wear resistance. And this enhancement is more notable at low applied loads and high Ti2AlC content. The mechanisms simulating the role of network Ti2AlC phase on the wear behavior and the wear process of TiAl/Ti2AlC composites at different applied loads have been proposed.

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    Flow behavior and processing map for hot deformation of ATI425 titanium alloy
    Qinggang Meng, Chunguang Bai, Dongsheng Xu
    J. Mater. Sci. Technol., 2018, 34 (4): 679-688.  DOI: 10.1016/j.jmst.2017.07.015
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    Flow behavior and processing map play important roles in the hot deformation process of titanium alloys. In this research, compression Gleeble tests have been carried out to investigate the stress-strain relationship at temperatures ranging from 700 to 1000 °C and strain rates ranging from 0.001 to 1 s-1 for ATI 425 titanium alloy. Arrhenius type constitutive equation was obtained to describe the compressive flow behavior with modification of additional deformation dead zone, friction model, temperature model and strain rate. The introduction of novel calculation method for α value in Arrhenius equation gives more accurate fitting than traditional one. Processing maps were drawn based on the distribution of dissipator co-content, and optimized deformation temperature and strain rate range obtained. It is proven to be accurate and effective through the experimental results. The microstructure analysis shows that more dynamic recrystallization can be achieved in the area with larger η value on the processing map.

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    Building metallurgical bonding interfaces in an immiscible Mo/Cu system by irradiation damage alloying (IDA)
    Jinlong Du, Yuan Huang, Chan Xiao, Yongchang Liu
    J. Mater. Sci. Technol., 2018, 34 (4): 689-694.  DOI: 10.1016/j.jmst.2017.10.009
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    For the immiscible Mo/Cu system with a positive heat of mixing (ΔHm > 0), building metallurgical bonding interfaces directly between immiscible Mo and Cu and preparing Mo/Cu laminar metal matrix composites (LMMCs) are very difficult. To solve the problem, a new alloying method for immiscible systems, which is named as irradiation damage alloying (IDA), is presented in this paper. The IDA primarily consists of three steps. Firstly, Mo is damaged by irradiation with multi-energy (186, 62 keV) Cu ion beams at a dose of 2 × 1017 ions/cm2. Secondly, Cu layers are superimposed on the surfaces of the irradiation-damaged Mo to obtain Mo/Cu laminated specimens. Thirdly, the irradiation damage induces the diffusion alloying between Mo and Cu when the laminated specimens are annealed at 950 °C in a protective atmosphere. Through IDA, Mo/Cu LMMCs are prepared in this paper. The tensile tests carried out for the Mo/Cu LMMCs specimens show that the Mo/Cu interfaces constructed via IDA have high normal and shear strengths. Additionally, the microstructure of the Mo/Cu interface is characterized by High Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX) attached in HRTEM. The microscopic characterization results show that the expectant diffusion between Mo and Cu occurs through the irradiation damage during the process of IDA. Thus a Mo/Cu metallurgical bonding interface successfully forms. Moreover, the microscopic test results show that the Mo/Cu metallurgical interface is mainly constituted of crystalline phases with twisted and tangled lattices, and amorphous phase is not observed. Finally, based on the positron annihilation spectroscopy (PAS) and HRTEM results, the diffusion mechanism of IDA is discussed and determined to be vacancy assisted diffusion.

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    High strength-ductility nano-structured high manganese steel produced by cryogenic asymmetry-rolling
    rollingBin Fu, Liming Fu, Shichang Liu, Huan Rong Wang, Wei Wang, Aidang Shan
    J. Mater. Sci. Technol., 2018, 34 (4): 695-699.  DOI: 10.1016/j.jmst.2017.09.017
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    A bulk nanostructured twinning-induced plasticity (TWIP) steel with high ductility and high strength was fabricated by cryogenic asymmetry-rolling (cryo-ASR) and subsequent recovery treatment. It was found that the cryo-ASRed TWIP steels exhibit simultaneous improvements in the ductility, strength and work hardening. Typical microstructures of the cryo-ASR TWIP steel were characterized by shear bands and intensive mechanical nano-sized twins induced by cryogenic deformation. These mechanical nano-scale twins remain thermally stable during the subsequent recovery treatment. It is believed that the ductility enhancement and high work-hardening ability for the cryo-ASR TWIP steels should be mainly attributed to the high-density pre-existing nano-scale twins.

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    Energy paths of twin-related lattice reorientation in hexagonal metals via ab initio calculations
    Gang Zhou, Lihua Ye, Hao Wang, Dongsheng Xu, Changgong Meng, Rui Yang
    J. Mater. Sci. Technol., 2018, 34 (4): 700-707.  DOI: 10.1016/j.jmst.2017.09.009
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    Employing ab initio calculations, we systematically investigated the energy paths of [101ˉ2]twin-related lattice reorientation in hexagonal metals Be, Mg, Sc, Ti, Co, Y, Zr, Tc, Ru, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Re, and Os. Among the studied systems, lattice reorientation energy increases in the order of Mg, Gd, Tb, Dy, Zr, Tc, Ti, Ho, Y, Co, Er, Sc, Be, Tm, Lu, Hf, Re, Ru and Os. The reorientation process consists of shear and shuffle components. Concerning the significance of shuffle, these hexagonal metals fall into two groups. In the first group, which includes Mg, Co, Ru, Re and Os, regardless of the shear amount, subsequent shuffle is an energy-uphill process, while in the second group, which includes Ti, Tc, Be, Y, Gd, Tb, Dy, Ho, Zr, Er, Sc, Hf, Lu and Tm, shuffle becomes an energy-downhill process if shear component reaches an adequate level (at least 60%). These results qualitatively explain the present observation of lattice reorientation in hexagonal metals, and shed light upon a general understanding on the [101ˉ2] twinning behavior in the aim of improving materials properties.

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    New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength
    D. Li, Z.W. Zhu, A.M. Wang, H.M. Fu, H. Li, H.W. Zhang, H.F. Zhang
    J. Mater. Sci. Technol., 2018, 34 (4): 708-712.  DOI: 10.1016/j.jmst.2017.07.008
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    Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite (MGC) was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength (~1618 MPa), plasticity (~4.3%) and specific fracture strength (384 × 103 N m kg-1) in compression. The maintained yield strength results from the unique microstructure composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plasticity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass (MG) by such a lay-up method can be an effective way to improve mechanical properties of MG.

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    Microstructure and brazing mechanism of porous Si3N4/Invar joint brazed with Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler
    fillerJ. Zhang, J.Y. Liu, T.P. Wang
    J. Mater. Sci. Technol., 2018, 34 (4): 713-719.  DOI: 10.1016/j.jmst.2017.07.001
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    Porous Si3N4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe2Ti and Ni3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si3N4/TiN + Ti5Si3/Ag-Cu eutectic/Cu/Ag-Cu eutectic/Cu-rich layer + diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150 μm, the joint strength first increased and then decreased. In this research, the maximum shear strength (73 MPa) was obtained when being brazed at 1173 K with a 100 μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe2Ti and Ni3Ti intermetallics played the major role in the improvement of joint strength.

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    Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature
    Xiongfei Wang, Chendong Shao, Xia Liu, Fenggui Lu
    J. Mater. Sci. Technol., 2018, 34 (4): 720-731.  DOI: 10.1016/j.jmst.2017.06.015
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    This work focused on the low-cycle fatigue (LCF) behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding (NG-SAW) process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain (CSS) curve and Manson-Coffin (M-C) curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal (BM) at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone (OTZ) at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV-OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.

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    Variation of crystal orientation during epitaxial growth of dendrites by laser deposition
    Guowei Wang, Jingjing Liang, Yizhou Zhou, Libin Zhao, Tao Jin, Xiaofeng Sun
    J. Mater. Sci. Technol., 2018, 34 (4): 732-735.  DOI: 10.1016/j.jmst.2017.05.002
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    A nickel-based superalloy was deposited onto a single crystal substrate based on epitaxial laser metal forming (E-LMF). The microstructure development in two depositions has been researched. For the first time, the crystal orientation of dendrites varying beyond 20° was found when the dendrites deflected in deposition. In addition, a new grain boundary was found between different orientation dendrites in a grain, and the detected grain boundary angle was 23°. The result shows that flowing field in laser pool is responsible for this phenomenon.

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