日本金属学会誌
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
早期公開論文
早期公開論文の5件中1~5を表示しています
  • 万谷 義和, 竹元 嘉利
    原稿種別: 論文
    論文ID: JC202407
    発行日: 2024年
    [早期公開] 公開日: 2024/07/19
    ジャーナル フリー 早期公開

    The metastable-phase characteristics of Ti–Nb alloys can be exploited to improve their functional properties such as damping. In this study, we investigated the structural changes in the metastable quenched martensite structure of Ti–Nb alloys subjected to heating and tensile strain. We examined the differential scanning calorimetry (DSC) heating curves in the reduction state, X-ray diffraction (XRD) profiles under loading/unloading, and material properties such as Young’s modulus and internal friction upon heating. In the DSC heating curve of the 10%-cold-rolled Ti15Nb specimen, an exothermic peak was observed, and for Ti18Nb and Ti20Nb, the exothermic peak exhibited broadening. We speculate that the underlying reason is the biphasic formation resulting from specimen deformation. From the XRD measurements, we found that the lattice tended to shrink upon stress application and recover upon unloading. Significant changes in Young's modulus and internal friction were observed in the α′′ structures of Ti18Nb and Ti20Nb during initial heating up to 373 K. We posit that the material properties changed owing to structural changes, such as lattice-constant changes, biphasic formation, and crystal orientation changes, resulting from heating or plastic deformation.

  • 御手洗 容子, 井上 恭史, 黒田 知暉, 松永 紗英, 戸田 佳明, 松永 哲也, 伊藤 勉, 小笹 良輔, 石本 卓也, 中野 貴由
    原稿種別: 論文
    論文ID: JA202406
    発行日: 2024年
    [早期公開] 公開日: 2024/06/14
    ジャーナル フリー 早期公開

    Powder bed fusion using a laser beam (PBF-LB) was performed for Ti-6Al-4Nb-4Zr (mass%) developed by our group to improve the oxidation resistance at temperatures greater than 600℃ by adding Nb and Zr to near-α alloys. Microstructure evolution of the PBF-LB samples by heat treatment was investigated, especially for heat treatment duration in the α + β phase, cooling rate, and heat treatment in the β phase. The equiaxed α phase formed during heat treatment along the melting-pool boundaries. The high volume fraction of the α phase and high Nb contents in the β phase was obtained by slow cooling (furnace cooling) compared with fast cooling (air cooling). The α/β lamellar structure formed in the melting pool boundaries with 100 µm in size and no equiaxed α phase formed along the boundaries by heat treatment in the β phase regime. Creep life at 600℃ and 137 MPa was similar for the air-cooled and furnace-cooled samples, but the slightly slower deformation was obtained in the furnace-cooled sample. Creep life of the sample heat treated in the β phase region drastically increased due to the absence of the equiaxed α phase. Dominant deformation mechanism of creep was grain boundary sliding. The small equiaxed α phase accelerated grain boundary sliding.

     

    Mater. Trans. 64 (2023) 1175-1182に掲載.AbstractおよびFigs. 5-9のキャプションを修正.

    Creep tests were performed at 600℃ and 137 MPa for the PBF-LB, and the creep curves were plotted together with the forged samples performed in the previous study. The creep life strongly depends on melting pool size or grain size [16]; that is, the shortest creep life was obtained in the forged sample with bi-modal (10 µm), then it increased as grain size increased as B-HT (100 µm), D-HT (300 µm). The longest one was obtained in the forged sample with a lamellar structure (550 µm). Creep behavior in primary and steady-state regimes of samples heat treated at 970℃ followed by air cooling or furnace cooling were similar in that of B-HIP due to similar microstructure. The creep strain was smaller in the furnace-cooled sample with a large volume fraction of the α phase and high Nb contents in β phase, but the effect of the lamellar spacing was small. Heat treatment at 1100℃ in β phase effectively improved creep life. Fullsize Image
     
  • 真中 智世, 堤 祐介, 高田 雄京, 陳 鵬, 蘆田 茉希, 土井 康太郎, 片山 英樹, 塙 隆夫
    原稿種別: 論文
    論文ID: JC202404
    発行日: 2024年
    [早期公開] 公開日: 2024/07/12
    ジャーナル フリー 早期公開

    In orthopedics, occasionally, different types of metals are used in applications in which they are in contact with each other. However, few studies have electrochemically investigated the galvanic corrosion of orthopedic implants formed of different metals. In this study, galvanic corrosion of Ti–6Al–4V ELI alloy, Co–Cr–Mo alloy, and 316L type stainless steel, which are used in orthopedics, and a newly developed Zr–1Mo alloy as a low-magnetic susceptibility material was evaluated in saline. Coupling of the Ti–6Al–4V ELI and Co–Cr–Mo alloys did not exhibit localized corrosion and maintained highly stable passive films. Coupling of the 316L type stainless steel and Co–Cr–Mo alloy, temporary localized corrosion occurred. Similarly, coupling of the Zr–1Mo and Co–Cr–Mo alloys, temporary localized corrosion occurred. However, both of 316L type stainless steel and Zr–1Mo alloy were finally repassivated spontaneously with the immersion time. The degree of the localized corrosion of the Zr–1Mo alloy was smaller than that of 316L type stainless steel. No galvanic current was observed when the Ti–6Al–4V ELI and Co–Cr–Mo alloys were coupled. A slight galvanic current flowed when 316L type stainless steel or the Zr–1Mo alloy was coupled with the other alloys; however, the galvanic current with the Zr–1Mo alloy coupling recovered to zero after a certain period owing to repassivation. No metal ions were detected from the couplings with Zr–1Mo alloy.

  • 山﨑 重人, 松尾 啓史, 森川 龍哉, 田中 將己
    原稿種別: 論文
    論文ID: J202404
    発行日: 2024年
    [早期公開] 公開日: 2024/07/05
    ジャーナル フリー 早期公開

    Microscopic stress-strain curves were obtained by applying stress measurements using the HR-EBSD method and strain measurements using the DIC method to the same field of view in SEM in-situ tensile tests. From the analysis of these microscopic stress-strain curves, yield stress map and work hardening rate map were successfully produced. The relationship between these mechanical property value maps and the microstructure is investigated. The yield stress maps confirm the tendency of the local yield stress to show different values for different grains, but the Schmid factor alone cannot explain the magnitude of the yield stress. When adjacent grains with significantly different Schmid factors deformed cooperatively, the yield stress is found to increase as a result of stress partitioning. Localized regions of extreme work hardening rates were observed in the work hardening rate maps. These regions were located close to grain boundaries with low m′ values where slip transfer was difficult and an interruption of the slip bands was observed. In addition, the rate of increase of GND density with strain was large in these regions. From these results, it can be understood that the extreme work hardening rates are due to increased back stresses caused by the accumulation of dislocations on low m′ grain boundaries.

  • 國枝 真衣, 鈴木 飛鳥, 高田 尚記, 加藤 正樹, 小橋 眞
    原稿種別: 論文
    論文ID: JA202401
    発行日: 2024年
    [早期公開] 公開日: 2024/04/19
    ジャーナル フリー 早期公開

    The optimization of processing parameters is indispensable for the laser powder bed fusion (L-PBF) process. The deposited energy density (DED) is one of the process indexes for the L-PBF process and has a simplified formula of P·v−0.5, where P is the laser power, and v is the scan speed. This parameter describes the change in the relative density and the melt pool morphology with laser power and scan speed well, whereas it does not include the effect of other processing parameters, e.g., hatch spacing (S). In the present study, an attempt was made to incorporate the effect of S into DED. Al-12Si (mass%) alloy cube samples were fabricated by L-PBF under various P, v, and S, for evaluating the relative density and the melt pool morphology. The melt pool depth and width of L-PBF-manufactured Al-12Si alloy increased linearly with P·v−0.5 and did not exhibit a clear correlation with S. Based on the experimental observation, the effect of hatch spacing on DED was estimated to be S−0.5, and a new index of P·v−0.5·S−0.5 was proposed. This index described the change in the relative density of the L-PBF-manufactured Al-12Si alloy with laser conditions (P, v, and S) well when the thermal conduction mode melting was dominant. This study also indicated the limitation of the applicability of P·v−0.5·S−0.5 under the keyhole or transition mode melting.

     

    Mater. Trans. 64 (2023) 1099-1106に掲載

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