Browsing by Author "An, Ke"

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A study of lattice elasticity from low entropy metals to medium and high entropy alloys
(2015-05-01)
Huang, E-Wen
;
Yu, Dunji
;
Yeh, Jien-Wei
;
Lee, Chi
;
An, Ke
An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system and a face-centered-cubic stainless steel described as a medium-entropy system, are measured by in situ neutron-diffraction experiments subjected to continuous tension at room and several elevated temperatures, respectively. With spallation neutron, the evolution of multiple diffraction peaks is collected simultaneously for lattice-elasticity study. Temperature variation of elastic stiffness of a single face-centered-cubic-phase Ni and a single face-centered-cubic-phase Fe are compared as low-entropy metals. The CoCrFeMnNi high-entropy alloy shows distinct lattice anisotropy. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Element Effects on High-Entropy Alloy Vacancy and Heterogeneous Lattice Distortion Subjected to Quasi-equilibrium Heating
(2019-10-15)
Huang, E-Wen
;
Chou, Hung-Sheng
;
Tu, K. N.
;
Hung, Wei-Song
;
Tu-Ngoc Lam
We applied Simmons-Balluffi methods, positron measurements, and neutron diffraction to estimate the vacancy of CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs) using Cu as a benchmark. The corresponding formation enthalpies and associated entropies of the HEAs and Cu were calculated. The vacancy-dependent effective free volumes in both CoCrFeNi and CoCrFeMnNi alloys are greater than those in Cu, implying the easier formation of vacancies by lattice structure relaxation of HEAs at elevated temperatures. Spatially resolved synchrotron X-ray measurements revealed different characteristics of CoCrFeNi and CoCrFeMnNi HEAs subjected to quasi-equilibrium conditions at high temperatures. Element-dependent behavior revealed by X-ray fluorescence (XRF) mapping indicates the effect of Mn on the Cantor Alloy.
Hardening steels by the generation of transient phase using additive manufacturing
(2019-06-01)
Huang, E-Wen
;
Lee, Soo Yeol
;
Jain, Jayant
;
Tong, Yang
;
An, Ke
In the present work, the tensile properties of 15-5 PH steel fabricated by selective laser melting (SLM) were examined with respect to the transient austenite phase. Compared with the 8%-transient-phase sample, the 18%-transient-phase one shows higher ultimate tensile strength and relatively low yield strength, as well as hardening behavior. We conducted in-situ neutron-diffraction study to examine the microstructure evolution for mechanistic understanding. After applying the external load, most non-equilibrium, retained austenite in the 8% transient-phase sample transforms before the yield strength, whereas in the 18%-transient-phase sample only 50% of the austenite transforms. Accompanying with the phase transformation, a decrease in the dislocation density and the dislocation strain energy-assisted phase transformation of the ferrite phase are found in the 8%-transient-phase sample even before yielding, which, however, is not the case in the 18%-transient-phase sample. The study demonstrates the SLM enables tuning the amount of transient-phase ratio and coherency between phases to realize a mechanical property control for additive manufactured steel.
On plastic anisotropy and deformation history-driven anelasticity of an extruded magnesium alloy
(2020-02-01)
Wang, Huai
;
Lee, Soo Yeol
;
Wang, Huamiao
;
Woo, Wanchuck
;
Huang, E-Wen
The plastic anisotropy and unloading anelasticity of an extruded Mg-9 wt.%Al alloy (with two annealed textures) were investigated using in-situ neutron diffraction measurement and crystal plasticity modelling. The distinctive yielding and hardening behaviors during compressive and tensile loading-unloading cycles were interpreted by the alternative operations of different slip/twinning modes. We reveal that the micromechanical responses of differently-oriented grains strongly depend on their neighboring conditions and operative deformation mechanisms. Based on the modelling results, unloading anelasticity is hypothesized to be controlled by the plastic contribution of the hard deformation mode and its impeding effects on easier deformation modes. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Phase Stress Partition in Gray Cast Iron UsingIn SituNeutron Diffraction Measurements
(1970-01-01)
Tu-Ngoc Lam
;
Wu, Szu-Chien
;
Chae, Hobyung
;
Chen, Shi-Wei
;
Jain, Jayant
Gray cast iron comprises alpha-Fe, Fe3C and graphite with their different anisotropies in terms of structure and mechanical behavior. We perform two different deformation paths as tension-compression and compression-tension on bulk gray iron to capture the stress partitioning. Usingin situneutron diffraction, the composite-like deformation behaviors of alpha-Fe and Fe3C are revealed simultaneously. Within the elastic deformation stage, both deformation paths do not cause load transfer. However, when the applied compressive stress exceeds 300 MPa, there is a clear load sharing in both paths. From microscopic examinations, the debonding between matrix and graphite is clarified.