| 초록 |
In situ neutron diffraction enables us to understand the thermal, mechanical properties in terms of the macroscopic (bulk) and mesoscopic (lattice) scales simultaneously. Two kinds of in situ neutron diffraction experiments in high-entrophy alloys (HEAs) were reviewed in this presentation. Firstly, the coefficient of thermal expansion (CTE) was examined in an Al0.5CoCrFeNiCu HEA. A rod type specimen was prepared with the dimension of 3-mm in diameter and 25-mm in parallel length and the volume expansion was measured as a function of temperature from ambient to 750 °C. The lattice spacing changes were obtained from the bcc (110) and (211) peaks and those were converted to the thermal linear expansion (%) and the CTE. The results show that the CTE was about 12.3 x 10-6 °C-1 (up to 600oC) and it is similar to the sum of the CTE of each atoms multiplied by the atomic percentage. Secondly, an equiatomic, face-centered-cubic, CoCrFeMnNi alloy was tensile tested at 800 K and 1,000 K under a pseudo creep condition. The nominal strain rate was 6.7 x 10-6 s-1. The evolutions of lattice strains, peak widths, and intensities of several hkl reflections suggest that the dominant deformation mode is the dislocation glide at 800 K and diffusion-controlled dislocation creep at 1,000 K. TEM analysis results will support. |
