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Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 他4名*
Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)Face-centered cubic (FCC) equi-atomic multi-principal element alloys (MPEAs) exhibit excellent mechanical properties from cryogenic to room temperatures. At room temperature, deformation is dominated by dislocation slip, while at cryogenic temperatures (CTs), reduced stacking fault energy enhances strain hardening with twinning. This study uses in-situ neutron diffraction to analyze the temperature-dependent deformation behavior of Al
(CoNiV)
, a dual-phase (FCC/BCC) medium-entropy alloy (MEA). At liquid nitrogen temperature (LNT), deformation twinning in the FCC matrix leads to additional strain hardening through the dynamic Hall-Petch effect, giving the appearance of improved strengthening at LNT. In contrast, BCC precipitates show dislocation slip at both 77 K and 298 K, with temperature-dependent lattice friction stress playing a significant role in strengthening. The study enhances understanding of deformation behaviors and provides insights for future alloy design.
Naeem, M.*; Rehman, A. U.*; Romero Resendiz, L.*; Salamci, E.*; Aydin, H.*; Ansari, P.*; Harjo, S.; Gong, W.; Wang, X.-L.*; 他3名*
Communications Materials (Internet), 6, p.65_1 - 65_13, 2025/04
The need for lightweight materials with mechanical integrity at ultralow temperatures drives the development of advanced alloys for cryogenic use. Additive manufacturing via laser powder bed fusion (LPBF) offers a scalable way to create alloys with tailored properties. Here, we show that LPBF-processed Al10SiMg exhibits a high ultimate tensile strength (395 MPa) and uniform elongation (25%) at 15 K. These enhancements stem from grain refinement, increased geometrically necessary dislocations, and stress partitioning between the Al matrix and the stiffer Si phase, aiding strain accommodation. 
neutron diffraction reveals that the Si phase, with its higher yield strength, bears most of the load, while the Al matrix undergoes continuous strain hardening, extending deformation capacity. These results highlight Al10SiMg's promise for cryogenic applications such as hydrogen storage, aerospace, and quantum computing hardware.
Naeem, M.*; Ma, Y.*; Tian, J.*; Kong, H.*; Romero-Resendiz, L.*; Fan, Z.*; Jiang, F.*; Gong, W.; Harjo, S.; Wu, Z.*; et al.
Materials Science & Engineering A, 924, p.147819_1 - 147819_10, 2025/02
被引用回数：1 パーセンタイル：0.00(Nanoscience & Nanotechnology)Face-centered cubic (fcc) medium-/high-entropy alloys (M/HEAs) typically enhance strength and ductility at cryogenic temperatures via stacking faults, twinning, or martensitic transformation. However, in-situ neutron diffraction on VCoNi MEA at 15 K reveals that strain hardening is driven solely by rapid dislocation accumulation, without these mechanisms. This results in increased yield strength, strain hardening, and fracture strain. The behavior, explained by the Orowan equation, challenges conventional views on cryogenic strengthening in fcc M/HEAs and highlights the role of dislocation-mediated plasticity at low temperatures.
neutron diffractionNaeem, M.*; Ma, Y.*; Knowles, A. J.*; Gong, W.; Harjo, S.; Wang, X.-L.*; Romero Resendiz, L.*; 他6名*
Materials Science & Engineering A, 916, p.147374_1 - 147374_8, 2024/11
被引用回数：3 パーセンタイル：57.76(Nanoscience & Nanotechnology)Heterostructured materials (HSMs) improve the strength-ductility trade-off of alloys, but their cryogenic performance under real-time deformation is unclear. We studied heterostructured CrCoNi medium-entropy alloy via neutron diffraction at 77 K and 293 K. A significant mechanical mismatch between fine and coarse grains led to an exceptional yield strength of 918 MPa at 293 K, increasing to 1244 MPa at 77 K with a uniform elongation of 34%. This strength-ductility synergy at 77 K is attributed to high dislocation pile-up density, increased planar faults, and martensitic transformation. Compared to homogeneous alloys, HSMs show promise for enhancing cryogenic mechanical performance in medium-/high-entropy alloys.
Kim, Y. S.*; Chae, H.*; Lee, D.-Y.*; Han, J. H.*; Hong, S.-K.*; Na, Y. S.*; Harjo, S.; 川崎 卓郎; Woo, W.*; Lee, S.-Y.*
Materials Science & Engineering A, 899, p.146453_1 - 146453_7, 2024/05
被引用回数：4 パーセンタイル：79.11(Nanoscience & Nanotechnology)This work focused on the mechanical properties and serration-involved deformation behavior of advanced alloys at 15 K. Evolution of stacking faults and 
-martensite improved the mechanical performance of CoCrNi alloys, and significant strain-induced martensite transformation of DED-SS316L led to superior strength and strain hardening. A magnitude in stress drop was governed by dislocation density, phase type, and lattice defects, irrespective of processing method. FCC {200} notably was influenced recovery behavior after stress drop, and the contribution of strain energy density by serration on tensile toughness was the greatest for HR-CoCrNi.
Mao, W.*; 伊東 達矢; Gong, W.; 川崎 卓郎; Harjo, S.; Gao, S.*; 辻 伸泰*
no journal, ,
結晶粒径を超微細化したSUS304(UFG-304)鋼の低温引張変形その場中性子回折実験を行い、結晶粒径を超微細化することによって低温での変形挙動がどのように変化するのか、またどのようなメカニズムで発現するのかを調べた。UFG-304鋼の降伏強度は、変形温度が低くなるに伴い増大し、77Kでは約1.4GPaに達した。しかし、降伏後の応力減少量は室温に比べて大きくなった。リューダス変形は低温においても発生したが、そのひずみ量は変形温度が低くなるに伴い小さくなった。低温ではリューダス変形後の均一変形も見られ、大きな加工硬化が伴い、ネッキングまでに大きな伸びをもたらした。均一変形中の加工硬化率は、温度の低下に伴い増大した。この挙動については、その場中性子回折データを用いてメカニズムを説明する。
Harjo, S.
no journal, ,
Applications in aerospace, linear motors, and other fields have created a need for superior structural materials at cryogenic temperatures. In response, it has become necessary not only to develop structural materials with excellent mechanical properties at cryogenic temperatures, but also to investigate the cryogenic deformation mechanism of such materials. We have developed a cryogenic horizontal deformation tester and an in-situ measurement method during cryogenic deformation on the neutron diffractometer TAKUMI installed at the high intensity pulsed neutron facility, J-PARC. We have also already obtained several excellent results from the in situ measurements during cryogenic deformation, which will be presented in this presentation.
Harjo, S.; 川崎 卓郎; Gong, W.
no journal, ,
The demand for superior structural materials at cryogenic temperatures has surged due to applications in aerospace, linear motors, and various other fields. Consequently, there is an urgent need not only to engineer materials with exceptional mechanical properties under cryogenic conditions but also to delve into the mechanisms of cryogenic deformation. However, the scarcity of equipment for conducting cryogenic deformation tests poses a challenge. In response to this challenge, we have devised a cryogenic horizontal deformation machine and an in-situ measurement technique for cryogenic deformation using TAKUMI, a neutron diffractometer at the high-intensity pulsed neutron facility, J-PARC. Through in situ measurements during cryogenic deformation, we have already attained several promising results, which will be detailed in this presentation.
