Search NASA⌕ Search

Engineering topics

Ko, J. Y. P.

Publications and source records attributed to Ko, J. Y. P..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A comparison study of local lattice distortion in Ni 80 Pd 20 binary alloy and FeCoNiCrPd high-entropy alloy

In this paper, the effect of alloying Pd on the local lattice distortion (LLD) in the Ni and FeCoNiCr host matrixes is quantified by integrating local structure characterization and theoretical calculations. The local structure measurements reveal that the mean LLD in the FeCoNiCrPd high-entropy alloy (HEA) is twice as high as the Ni 80 Pd 20 binary alloy though the FeCoNiCr base alloy has a negligible mean LLD. Density functional theory calculations unveil that the unexpected high mean LLD in FeCoNiCrPd is related to the high fluctuation of LLD in the FeCoNiCr matrix. Finally, these observations suggest a synergetic effect of chemical complexity on HEAs' mean LLD.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Local lattice distortion in NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys investigated by synchrotron X-ray diffraction

Severe lattice distortion is presumptively considered as a core effect of high-entropy alloys, but quantitative measurements are still missing. Here, we demonstrate that the lattice distortion in high-entropy alloys can be quantitatively analyzed based on pair distribution function obtained from synchrotron X-ray diffraction. By applying this method to equiatomic NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys, we found that the local lattice distortion in the NiCoCr (0.23%) and FeCoNiCrMn (0.24%) alloys are comparable while negligible in the FeCoNiCr alloy (0.04%). Furthermore, the origin of local lattice distortion in the NiCoCr and FeCoNiCrMn concentrated alloys was discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Local Structure and Short-Range Order in a NiCoCr Solid Solution Alloy

Multi-element solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the unique local structural characteristics. We measured the local structure of a NiCoCr solid solution alloy with X-ray/neutron total scattering and extended X-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis (PDF) did not exhibit distinct structural distortion. But, EXAFS analysis suggested that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) plays a role in the distinct low values of electrical and thermal conductivities in Ni-based solid solution alloys when Cr is incorporated. Both the long-range and local structures of the NiCoCr alloy upon Ni ion irradiation were studied and an irradiation-induced enhancement of SRO was found.

36 MATERIALS SCIENCE↗