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Materials Characterization
Elsevier
Materials Characterization

Elsevier

1044-5803

Materials Characterization/Journal Materials CharacterizationSCIISTPAHCIEI
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    (111674)Signifcant effects of grain size on mechanical response characteristics and deformation mechanisms of metastable austenitic stainless steel

    Guosheng SunMiaomiao ZhaoLinxiu Du
    13页
    查看更多>>摘要：Grain size of a 304 austenitic stainless steel was tuned via deformation-induced martensite transformation and austenite reversion annealing, and the signifcant effects of grain size on mechanical properties, strain hardening behavior, deformation mechanisms were studied. The results showed that grain refnement strengthening signifcantly increased the yield strength from 235 MPa (~20 μm) to 1030 MPa (~200 nm), meanwhile, the interaction of Lüders deformation and deformation-induced martensite transformation realized the stable propagation of Lüders bands, leading to a considerable total elongation (above 30%). It was inferred that martensitic transformation was enhanced with a decrease in grain size. The underlying reasons were attributed to the formation of carbide precipitation (M23C6) and the change of martensite nucleation sites depending on grain size. In coarse grains, α'-martensite formed at shear bands with or without the aid of ε-martensite, whereas α'-martensite mainly nucleated at grain boundaries and deformation twins in ultrafne austenite grains. Besides TRIP effect and dislocation glide, TWIP effect also became one of the dominate deformation mechanism with the decrease in austenite grain size.
      原文链接:
    • NSTL
    • Elsevier

    (111605)Simple optimization for strength and conductivity of Cu-Ni-Si alloy with discontinuous precipitation

    Jee Hyuk AhnSeung Zeon HanEun-Ae Choi
    6页
    查看更多>>摘要：A Cu alloy with discontinuous precipitation (DP) presents a mechanically lower strength, but a higher conductivity compared to an alloy with continuous precipitation (CP). We controlled the partial distribution of DP in the Cu matrix of Cu-4Ni-1Si alloy by changing aging time. Successive cold-working of the alloy showed that by controlling the CP and DP fractions, considerably wide ranges of strength and electrical conductivity, from 500 to 1170 MPa, and from 23 to 50% IACS, respectively, could be achieved. After cold-working, the DP region in the alloy was heavily deformed in comparison with the CP region, showing a drastic increase in strength, with only a small decrease in conductivity.
      原文链接:
    • NSTL
    • Elsevier

    (111692)Effect of heat input on microstructure and mechanical properties of TIG-welded semisolid cast AXE622 Mg alloy

    A. Habibi EftekharS. Mohsen SadrossadatM. Reihanian
    13页
    查看更多>>摘要：The present study investigats the effect of heat input on the microstructure and mechanical properties of the TIG-welded semisolid AXE622 alloy. Three heat inputs, 18 kJ/mm, 21 kJ/mm, and 24 kJ/mm are used, and the corresponding joints referred to as HI18, HI21, and HI24 joints. Results showed that the average grain size in the heat-affected zone (HAZ) (~38 μm, 50 μm, and 67 μm) was more considerable than that in the fusion zone (FZ) (~15 μm, 17 μm, and 18 μm) for the HI18, HI21, HI24 joint, respectively. The volume fraction of the second phases in FZ was signifcantly higher concerning the HAZ. The eutectic Mg17Al12 phase formed a network structure in FZ of the HI18 joint and fragmented in the HI21 joint, while less fragmentation was observed in the HI24 joint. The volume fraction, the average length, and the width of secondary phases decreased in the HAZ with increasing the heat input. The HI21 joints exhibited the largest tensile strength (~147 MPa) and elongation (~3%) and ruptured in the BM. With increasing the heat input, the hardness decreased in the HAZ and FZ. Besides, the hardness in FZ (~70 HV, 63 HV, and 58 HV) was more signifcant than that in the HAZ (~ 50 HV, 47 HV, 43 HV) for the HI18, HI21, and HI24 joint, respectively. The benefcial effect of semisolid processing was degraded due to the signifcant heat input imposed in the HAZ of the HI24 joint.
      原文链接:
    • NSTL
    • Elsevier

    (111668)Microsegregation of a new Ni-Co-based superalloy prepared by electron beam smelting layered solidifcation technology and its homogenization behavior

    Hongyang CuiYi TanRusheng Bai
    10页
    查看更多>>摘要：The electron beam smelting layered solidifcation technology (EBS-LST) is put forward to fabricate a new Ni-Co-based superalloy with less segregation. The microstructures and homogenization behavior of the prepared ingot were studied. The experimental results show that the cross-sectional microstructure of the EBS-LST alloy consists of four typical areas, namely melted zone (MZ), partially fusion zone (PFZ), heat affected zone (HAZ), and bottom layer (BL). During the EBS-LST solidifcation process, the cooling rate is calculated to be 22.3 k/s according to the well-established model associated with secondary dendrite arm spacing. It can be inferred that the EBS-LST will reduce the solidifcation time, and thus eliminating the macrosegregation, and weaken the microsegregation of the ingot effectively. The effect of homogenization treatment on the microsegregation and microstructure evolution of the alloy is also studied. The residual segregation index equation during homoge-nization is constructed for the diffusion behavior of the strongly segregated elements of Ti and W. The diffusion coeffcients DW and DTi are calculated as 3.9 × 10~(-15) m~2-s~(-1) and 5.4 × 10~(-15) m~2-s~(-1), respectively.
      原文链接:
    • NSTL
    • Elsevier

    (111699)The microstructure evolution and irradiation hardening in 15Cr-ODS steel irradiated by helium ions

    S.Z. DiaoQ. ZhaoS.L. Wang
    9页
    查看更多>>摘要：Oxide dispersion strengthened (ODS) steels with excellent irradiation swelling resistance and high temperature creep resistance are regarded as one of the priority candidate materials for the frst wall/blanket materials in fusion reactors. Microstructure evolution and irradiation hardening in 15Cr-ODS steel irradiated by helium ions at R.T. and 400 ℃ respectively have been studied by transmission electron microscopy and nanoindentation technique. Three main oxides were identifed, including high-density dispersed Y-Ti-O nanoclusters, tens of nanometers Y_2TiO_5 and a few hundred nanometers Y2Ti2O7 particles with the largest size but the least density. Helium bubbles were homogeneously distributed in the matrix in both irradiated specimens and the aggregation state of bubbles near GBs was related to the nature of GB. The average size of bubbles increased and the density decreased in the steel irradiated at elevated temperature. A defect-depleted zone was observed near a GB with a Y_2TiO_5 precipitate imbedded and a large helium bubble was present at the interface of the Y_2TiO_5 particle/GB. It suggests that the GBs combined with Y_2TiO_5 can enhance the aggregation of helium bubbles since GBs can act as defect sinks as well as diffusion channels and Y_2TiO_5 has a high ability of trapping helium atoms. Signifcant irradiation hardening was obtained at both irradiation temperatures. The relationship between microstructure and the irradiation hardening was discussed.
      原文链接:
    • NSTL
    • Elsevier

    (111655)Effect of the magnitude of sub-boundary angles on the abnormal grain growth rate of Goss grains in Fe-3%Si steel

    Tae-Young KimTae-Wook NaHyung-Seok Shim
    8页
    查看更多>>摘要：In spites of extensive studies, the selective abnormal grain growth (AGG) of Goss grains in Fe-3%Si steel remains still unclear. Here, the effect of the magnitude of sub-boundary angles on AGG behavior was investigated both by computer simulations and experiments. In 3-dimensional Monte Carlo simulations of grain growth based on the realistic grain boundary energy distribution data, the grains of Goss orientation, which are given the sub-boundaries, grew abnormally and smaller sub-boundary energies resulted in larger Goss grains. Additionally, a Fe-3%Si steel, after primary recrystallization, was heated to 1050 ℃ to induce AGG. Measurements of sub-boundary angles for three different sizes of abnormally growing Goss grains by synchrotron X-ray micro-diffraction after the initial stage of secondary recrystallization showed that the misorientation of the sub-boundary angles was 0.41° for the small Goss grain of 734 μm. Moreover, the average misorientation of sub-boundary angles was 0.33° for the medium Goss grain of 1050 μm and 0.25° for the large Goss grain of 2978 μm. In contrast, the average misorientation angles of the sub-boundaries after the fnal stage of secondary recrystallization were only 0.05°. The results indicate that the sub-boundary angle is a determining parameter for the size of abnormally growing grains.
      原文链接:
    • NSTL
    • Elsevier

    (111645)Unearthing principal strengthening factors tuning the additive manufactured 15-5 PH stainless steel

    Hobyung ChaeMao Yuan LuoE-Wen Huang
    9页
    查看更多>>摘要：Additive manufactured (AM) materials exhibit enhanced performance, while post-processing is essential to reinforce its properties. Controlling the tunable factors and the underlying strengthening mechanisms during the post-processing are a key to answering the calls from the industry and end users. We identifed the principal strengthening factors that contribute to AM stainless steel under heat-treatment and weighed their importance. The as-built sample exhibited a unique microstructure with a heterogeneous grain size distribution, a small amount of retained austenite, high dislocation density, and dispersed oxide particles. The strengthening primarily by dislocation forest and additionally by heterogeneous grain size contributed to the as-built sample. Although aging slightly decreased dislocation strengthening, superior aging enhancement was achieved by Cu-precipitates. The solid-solutionizing not only increased the effective grain size but also reduced the dislocation density by eliminating the heterogeneous microstructure, which deteriorated the precipitation hardenability. Our fndings shed light on the performance optimization of AM metals.
      原文链接:
    • NSTL
    • Elsevier

    (111709)Microstructural evolution and mechanical property of Al-Mg-Mn alloys with various solidifcation cooling rates

    Minqiang GaoYu WangBowei Yang
    10页
    查看更多>>摘要：In the present work, the microstructural evolution and mechanical property of as-cast Al-6 Mg-0.8Mn alloys with respect to the solidifcation cooling rate was investigated. The results demonstrate that as the cooling rate increases from 0.5 K/s to 46.9 K/s, the average grain size decreases frstly and then increases slightly; the average secondary dendrite arm spacing, the average length of Al6Mn and Al3Mg2 phases decreases. A high cooling rate (21.3 K/s and 46.9 K/s) causes the increase in the solute segregation/shrinkage porosities, and a low cooling rate (0.5 K/s) leads to the formation of casting defects, thus deteriorating the mechanical properties of alloys. The alloy with the cooling rate of 5.4 K/s shows an optimum mechanical property i.e., the tensile strength, yield strength, and elongation are 298.7 MPa, 133.8 MPa, and 30.5%, respectively. The enhanced strength-ductility synergy is mainly attributed to the refned secondary dendrite arm spacing and reduced casting defects. This work provides a reference for the fabrication of as-cast Al-Mg-Mn alloys with excellent mechanical performance.
      原文链接:
    • NSTL
    • Elsevier

    (111700)Microstructure stability and high temperature wear behavior of an austenite aging steel coating by laser cladding

    Wei JiangYunlai Deng
    12页
    查看更多>>摘要：An austenite aging steel coating was prepared by laser cladding on H13 steel in order to overcome the poor thermal stability and high-temperature wear resistance of the latter. The microstructure, element and phase distribution of the austenite aging steel coating were investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and recrystallization were determined by quasi-in-situ EBSD. High temperature wear tests for the austenite aging steel coating and H13 steel were performed on a high temperature pin-on-disk friction and wear tester, and their wear resistance was comparatively evaluated. The austenite aging steel coating was dominated by γ-Fe as matrix phase, while micrometer-grade NiAl and nano-scale Ni3Ti existed as strengthening phases. These fne particles existing in the grain boundary of the coating could effectively improve the recrystallization resistance and thermal stability, which was confrmed by quasi-in-situ EBSD and thermal stability tests. Owing to such superior thermal stability, oxidative mild wear prevailed for the austenite aging steel coating in most of sliding conditions except for 600 ℃ and 150 N, where a mild-to-severe wear transition of oxidative wear occurred. In particular, the plastic extrusion wear of H13 steel at 600 ℃ and 150 N was impeded due to the existence of laser-cladded austenite aging steel coating.
      原文链接:
    • NSTL
    • Elsevier

    (111656)Effect of ferrite-austenite morphology and orientation relationship on bainite transformation in low-alloy TRIP steels

    Tongliang WangLihe QianWenlu Yu
    10页
    查看更多>>摘要：To reveal the effects of large amounts of ferrite on bainite transformation behavior, the morphological and orientation relationship between ferrite (a) and austenite (y) reversed from different initial microstructures during intercritical annealing, as well as their effects on subsequent bainite transformation, were investigated by scanning electron microscopy, electron-backscattered diffraction, and dilatometry analysis. The austenite and ferrite reversed from quenched martensite exhibited an alternately arranged lamellar structure. The austenite maintained a Kurdjumov-Sachs (K-S) orientation relationship with ferrite. In the subsequent austempering, bainitic transformation exhibited a strong variant selection phenomenon. Austenite reversed from cold-deformed martensite was dispersed around ferrite, and the orientation relationship between austenite and ferrite was irrational. During austempering, the bainite nucleation rate at K-S-oriented α/γ interfaces was much higher than that at irrational-oriented α/γ interfaces. First, the alternately arranged ferrite and austenite lamellae increased the total length of α/γ interfaces per unit area, i.e., α/γ interfacial density, for bainite nucleation. Second, the activation energy for bainite nucleation at the K-S-oriented α/γ interface was lower. The K-S-oriented α/γ interfaces facilitated bainite nucleation accompanied by strong variant selection, thereby accelerating the kinetics of bainite transformation.
      原文链接:
    • NSTL
    • Elsevier