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Materials Characterization
Elsevier
Materials Characterization

Elsevier

1044-5803

Materials Characterization/Journal Materials CharacterizationSCIISTPAHCIEI
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    Influence of preparation technology on the microstructure and properties of Ag/SnO2Bi2O3CuO composite materials

    Wu, QiongXu, GuofuZhao, ChengweiHuang, Runzhang...
    14页
    查看更多>>摘要：Ag/SnO2 electrical contact material is currently recognized as the most promising environmentally friendly alternative material, but it has the problems of difficult processing and poor wettability between Ag matrix and SnO2 particles. Ag/SnO2Bi2O3CuO composite materials are prepared by reaction synthesis and powder metallurgy technology and the influence of different technology on the microstructure and properties are analyzed and discussed in this paper. The results indicate that the main phases in the Ag/SnO2Bi2O3CuO composite materials prepared by two kinds of technology are Ag, SnO2 and Bi2Sn2O7. The second phase oxide particles in Ag/ SnO2Bi2O3CuO composite materials prepared by two kinds of technology mainly have six kinds of distribution position. The physical and mechanical properties of Ag/SnO2Bi2O3CuO composite materials prepared by reaction synthesis technology are better than those by powder metallurgy technology. In addition, the microstructure of Ag/SnO2Bi2O3CuO composite materials prepared by the reaction synthesis technology is more uniform and the distribution of the second phase oxide particles is more dispersive than that by powder metallurgy technology. The difference of microstructure of Ag/SnO2Bi2O3CuO prepared by two kinds of technology mainly occurs in the raw materials and the process of sintering and reaction.
      原文链接:
    • NSTL
    • Elsevier

    Correlation of ferrite-phase reconfiguration and mechanical properties in thermally aged duplex stainless steel

    Liu, XuebingZhang, Xinfang
    12页
    查看更多>>摘要：The thermal aging behavior and subsequent recovery treatment of duplex stainless steel are investigated by mechanical properties testing and microstructure characterization. After thermal aging at 475 degrees C for 500 h, the ferrite phase undergoes severe spinodal decomposition and precipitation, which results in a significant increase in yield strength, and a substantial reduction in ductility. Combining the nano-indentation, geometric phase analysis, and tensile testing, it can be confirmed that spinodal decomposition is the main contributor to the hardening of the ferrite phase. The hardening of the ferrite phase is induced by the semi-coherent interface between alpha '-phase and alpha-phase and higher shear modulus of Cr-enriched domains. The increased yield stress calculated by the simplified equation is in good agreement with the experimental value. When the aged samples were treated by high-temperature annealing and pulsed electric field, the hardening is significantly eliminated, and the ductility is correspondingly restored. Further, the essence of the difference in required temperature to restore deteriorated performance is the change of system free energy caused by temperature and pulsed electric field.
      原文链接:
    • NSTL
    • Elsevier

    Characterization of age hardening mechanism of low-temperature aged low-carbon steel by transmission electron microscopy

    Kawahara, YasuhitoMaeda, TakuyaKinoshita, KeisukeTakahashi, Jun...
    10页
    查看更多>>摘要：Low-temperature aging treatment at 323 K results in the dramatical increase in hardness in low-carbon ferritic steels quenched from 983 K, possibly caused by carbon clusters and/or fine epsilon-carbides. In this study, transmission electron microscopy (TEM) analysis was carried out to characterize the change of the microstructure during the low-temperature aging treatment. Until the early stage of the peak hardness, the carbon clusters were formed homogeneously with zig-zag structures. At the latter stage of the peak hardness, it was found that the epsilon-carbides were partially precipitated within the carbon clusters, which suggested that the carbon clusters might have acted as the precursors of epsilon-carbides. In-situ tensile TEM observations showed that dislocation motions were free-glide type, and carbon clusters and fine-carbides interacted with dislocations via cutting-type. Dislocation interaction force was also evaluated, which suggested that the lattice misfit played as important role of the interaction mechanism.
      原文链接:
    • NSTL
    • Elsevier

    Investigations of interfacial reaction and toughening mechanisms of Ta fiber-reinforced TiAl-matrix composites

    Zhou, MiHu, RuiLi, JinguangYang, Chenyu...
    10页
    查看更多>>摘要：Continuous fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. Ta fiber with outstanding plasticity and toughness is regarded as a promising reinforcement. In this work, a 10 vol% Ta fiber-reinforced TiAl composite was prepared by combining slurry casting and vacuum hot pressing under condition of 1150 degrees C/ 35 MPa/ 2 h. Microstructure of interfacial reaction zone of the composite was investigated; meanwhile, thermodynamic calculation and theoretical analysis were conducted to explain the formation mechanisms of the reaction products. Three types of reaction products sigma-Ta2Al, B2 and alpha(2) phases were formed between Ta fiber and TiAl matrix. sigma phase was adjacent to Ta fiber with a fine grain structure, which was formed due to the lowest formation free energy. The aggregation of beta stabilizers in Ti-rich region resulted in the formation of B2 phase that was close to sigma phase. alpha(2) phase relied on B2 phase to nucleate and grow based on the Burgers relationship and their structure symmetry. Three-point bending tests show the fracture toughness (K-IC) of the Ta-f/TiAl composite was 58% higher than that of pure TiAl matrix. The main toughening mechanism of the Ta-f/TiAl composite was plastic deformation of the Ta fiber, meanwhile the interfacial debonding also had a contribution to toughening the TiAl alloy. The interfacial debonding location was mainly at the Ta/L-I-sigma interface due to the existence of thermal residual stress.
      原文链接:
    • NSTL
    • Elsevier

    Microstructure and properties of multilayer WC-40Co coating on Ti-6Al-4V by electron beam cladding

    Wang, WenqinZhang, ShiqiXiao, ShengSato, Yutaka S....
    12页
    查看更多>>摘要：Single, double, and triple-layer WC-40Co coatings were prepared by electron beam (EB) cladding to improve the wear resistance of Ti-6Al-4V. The microstructure, micmhardness, wear resistance, and corrosion resistance of the coatings were investigated. The results demonstrated that the three types of coatings consisted of beta (Ti, W), TiCo, (Ti, W) C1-X, (W, Ti)C1-X, and a small amount of Ti2Co. The core/shell structure of (W, Ti)C1-X/(Ti, W) C1-X was observed by TEM, and the phase interfaces were studied. The hardness and wear resistance of triple-layer coating was the highest, and its wear resistance was improved by 11.5 times that of the substrate. The wear mechanisms of the substrate, single- and double-layer coating was oxidative and abrasive wear, while the triple-layer coating exhibited abrasive wear. The corrosion resistance of the single- and double-layer coatings was better than that of the substrate; however, the triple-layer coating surface was significantly damaged owing to the cracks.
      原文链接:
    • NSTL
    • Elsevier

    A study on the creep behavior of alloy 709 using in-situ scanning electron microscopy

    Bowen, PaulRabiei, AfsanehLall, Amrita
    22页
    查看更多>>摘要：In this research, an experimental evaluation of creep properties of Alloy 709 in the temperature range of 750-850 degrees C was undertaken. Alloy 709 is a novel austenitic stainless steel with 20% Cr and 25% Ni by wt% that was developed for application in structural components of nuclear power plants. Creep rupture tests were conducted in an in-situ heating-loading and Scanning Electron Microscope (SEM) unit equipped with Electron Backscatter Diffraction (EB SD) detector and Energy Dispersive Spectroscopy (EDS). "Real-time" creep damage mechanisms of Alloy 709 at various stresses and temperatures using a flat, un-notched sample with continuously reducing cross-section is studied so that the failure and maximum creep damage occurred at the center of the sample where the in-situ SEM imaging could be focused. Accelerated creep tests at temperatures and stresses above service conditions were performed by employing multiple blocks of constant loads where the loads were increased once the sample attained constant creep rate, indicating a secondary creep regime. This technique ensures multiple data points can be obtained from the same test, saves the time required for an otherwise long-term creep test and usage of SEM. Coincident Site Lattice (CSL) boundary maps were collected as control maps before testing, and the grain boundaries were observed during the creep test to understand the effect of grain boundary character on the creep damage mechanism. Void growth, grain boundary separation, and sliding were found to be the main creep mechanisms whose rate is dependent on stress and temperature. Failure mechanisms studied on the fracture surface using SEM fractography were correlated to the sample surface observations to create complementary information to better understand the underline creep mechanism of Alloy 709.
      原文链接:
    • NSTL
    • Elsevier

    Effect of Cerium and Aluminium on the phase stability and properties of polycrystalline Cu-Al-Be shape memory alloys

    Narasimha, Guniputi BalaMurigendrappa, S. M.
    9页
    查看更多>>摘要：This study presents the outcomes of an investigation of the effect of wt% of cerium and Aluminium on the phases, crystal structure, microstructure, morphology, phase transformation temperatures, shape recovery ratio and mechanical properties of the polycrystalline Cu-Al-Be shape memory alloys (SMAs). SMAs exhibit martensite phase at room temperature up to 0.49 wt% of Be and >= 0.52 wt% of Be transforms to austenite phase. An increase in cerium by 0, 0.05, 0.1, 0.15 and 0.2 wt% decreases the grain size by 0, 70.87%, 82.73%, 83.8% and 94.6%, respectively. An increase in cerium increases the transformation temperatures owing to the Al-rich secondary precipitates, and the shape recovery ratio reduces. Alloying cerium of 0.1 wt% exhibits a maximum tensile strength of 474 +/- 23 MPa with the ductility of 24.11 +/- 1.42%.

    Cu-AI-BeShape memory alloysCeriumGrain refinementCu9Al4MECHANICAL-PROPERTIESRAPID SOLIDIFICATIONGRAIN-REFINEMENTMICROSTRUCTUREMARTENSITENISTABILIZATIONCEBEHAVIOR

      原文链接:
    • NSTL
    • Elsevier

    Atomic scale understanding of Kurdyumov-Sachs path during BCC to FCC phase transformation in iron-gallium alloy

    Yang, TianziGou, JunmingLiu, XiaolianZhang, Yiqun...
    7页
    查看更多>>摘要：The Kurdyumov and Sachs (K-S) orientation relationship between body-centered-cubic (bcc) and face-centeredcubic (fcc) phases has been observed in numerous systems undergone displacive component-involved phase transformations. However, the atomic level evidence for its theoretical path containing two steps of lattice shear is still rare. In this work, we provided an atomic-scale understanding of the K-S path by capturing the early-stage phase transformation from bcc to fcc via a coupled diffusional-displacive mechanism in an aged Fe 72 Ga 28 alloy. Nano-embryonic product phases are directly observed, formed firstly by one lattice shear of (21 (1) over bar)-bcc planes along [(1) over bar1 (1) over bar] -bcc direction and further lattice shear of the (011)-bcc planes along [(11) over bar2]-fcc direction. The thermally-activated atomic diffusions are involved in the formation of equilibrium fcc phase. These results may not only help to understand the diverse phase transformations in Fe-Ga alloys, but also add atomistic insights towards the solid-state transformation mechanism between bcc and fcc phases.
      原文链接:
    • NSTL
    • Elsevier

    Ultrathin-gauge high silicon non-oriented electrical steel with high permeability and low core loss fabricated by optimized two-stage cold rolling method

    Li, Zhi-hongXie, Song-kangWang, Guo-dongLiu, Hai-tao...
    17页
    查看更多>>摘要：In the present work, the evolution of microstructure and texture and the resultant magnetic properties with different rolling reductions and intermediate annealing temperatures during two-stage cold rolling process were systematically studied. The one-stage cold rolling was also employed for comparison. It was found that finally annealed sheet fabricated by one-stage rolling exhibited pronounced alpha*-fiber ({h,1,1} 1/h,1,2 ) and gamma-fiber ((111)//ND) textures. By contrast, the two-stage rolling significantly weakened the unfavorable gamma-fiber texture and enhanced the lambda-fiber ((100)//ND), Goss ({110} (001)) and near-Brass ({110} (112)) textures in final sheets. Meanwhile, the introduction of intermediate annealing reduced the grain boundary density and deformation stored energy in secondly cold-rolled microstructure. The nucleation rate of recrystallization was hence decreased, thereby increasing the final grain size. Increasing intermediate annealing temperature in two-stage rolling process further optimized the recrystallization texture and increased the final grain size. It is noted that the gamma-fiber texture in final sheets was gradually decreased with the decrease of second rolling reduction, while the lambda-fiber texture and grain size were both increased firstly and then decreased. Eventually, an optimized combination of magnetic properties (B50 = 1.709 T, P15/50 = 1.828 W/kg, P10/400 = 11.92 W/kg) was obtained via a higher intermediate annealing temperature (950 degrees C) and an appropriate second rolling reduction (75%). Furthermore, the deformation and recrystallization behaviors of specifically oriented grains (i.e., lambda-, Goss and near-Brass grains) were discussed in detail.
      原文链接:
    • NSTL
    • Elsevier

    Detailed characterizations of microstructure evolution, corrosion behavior and mechanical properties of refill friction stir spot welded 2219 aluminum alloy

    Zou, YangfanLi, WenyaXu, YaxinYang, Xiawei...
    15页
    查看更多>>摘要：2.0 mm thick 2219-O (upper plate) and 8.0 mm thick 2219-C10S (lower plate) were successfully fabricated using refill friction stir spot welding (RFSSW), and the microstructure evolution, corrosion behavior and mechanical properties of the joints were investigated. The results indicated that the stir zone (SZ) is characterized by refined and equiaxed grains due to dynamic recrystallization, whose grain size gradually increases, and the texture intensity decreases with the increase of the distance from the upper plate top surface. Tangled dislocations and dislocation cells are observed in the SZ, while rod-like precipitates with 20 nm-100 nm length are found in the base material (BM) of the lower plate. Also, numerous Al2Cu particles are observed in the upper plate BM, while only a few particles are aggregated in the lower plate BM. However, Al2Cu particles are fragmented and uniformly distributed in the SZ. The hardness of the upper plate and the lower plate is approximate 50 HV and 160 HV, respectively. The hardness increases gradually from top to bottom of the cross-section. The self-corrosion potential and corrosion current density of the SZ are -0.45 V and 5.62 x 10(-5) A/cm(2), respectively. In comparison, those of the BM of the upper plate are -0.49 V and 3.16 x 10(-3) A/cm(2), and those of the lower plate BM are -0.68 V and 7.94 x 10(-3) A/cm(2). The electrochemical experiment indicated that the SZ presents excellent corrosion resistance, followed by upper plate BM and then lower plate BM. The corroded area has mainly occurred at the lower plate BM when the joint cross-section is immersed in the EXCO solution for one hour. However, upper and lower plate BMs are eroded seriously when the immersion time increases to two hours. Nevertheless, no obvious corrosion can be observed in the SZ. The mechanical analysis indicated that the tensile load decreases from 7.25 to 4.10 kN, and the tear load decreases from 3.20 to 1.78 kN after being immersed in the 3.5% NaCl solution for 48 h.
      原文链接:
    • NSTL
    • Elsevier