Browsing by Author "Yu, Dunji"

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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.
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.
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.