Browsing by Author "Lai, Bo-Hong"

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Comparing Cyclic Tension-Compression Effects on CoCrFeMnNi High-Entropy Alloy and Ni-Based Superalloy
(2019-08-01)
Lam, Tu-Ngoc
;
Chou, You-Shiun
;
Chang, Yao-Jen
;
Sui, Tsung-Ruei
;
Yeh, An-Chou
An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings.
Element Effects of Mn and Ge on the Tuning of Mechanical Properties of High-Entropy Alloys
(1970-01-01)
Tu-Ngoc Lam
;
Tsai, Che-Wei
;
Chen, Bo-Kai
;
Lai, Bo-Hong
;
Liu, Hung-Chih
Substitution of Ge for Mn increases the elastic moduli of different {h k l} orientations of the CoCrFeMnNi-based high-entropy alloy. Our findings indicate that tuning minor element compositions may result in improved strength-ductility combination. The underlying deformation mechanisms of CoCrFeNiGe(0.3)were examined byin situneutron diffraction and analysis of the associated diffraction profiles during tensile deformation. The strain-hardening response of CoCrFeNiGe(0.3)exhibited a dominant mechanism of mechanical twinning at moderate and large strains at room temperature. The evolution of the bulk work hardening rate was consistent with the convolutional multiple whole profile fitting results, which exhibited a continuous increase in twin formation probability. The microstructural development was also investigated by transmission electron microscopy, which revealed the formation of huge amounts of deformation twins in CoCrFeNiGe(0.3)at room temperature.