Low-Temperature Aging Mechanisms in U-6wt% Nb

Hsiung, L L

Lawrence Livermore National Laboratory

关键词: Aging;    Alloys;    X-Ray Diffraction;    Superlattices;    Phase Stability;   

DOI  :  10.2172/15011604
RP-ID  :  UCRL-TR-208589
RP-ID  :  W-7405-ENG-48
RP-ID  :  15011604

美国|英语

来源: UNT Digital Library

【 摘 要 】

Phase stability and aging mechanisms in a water-quenched (WQ) U-6wt% Nb (U-14at% Nb) alloy artificially aged at 200 C and naturally aged at ambient temperature for 15 years have been investigated and studied using Vickers-hardness measurement, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM) techniques. Age hardening/softening phenomenon is recorded from the artificially aged samples based upon the microhardness measurement. The age hardening can be readily rationalized by the occurrence of fine-scaled Nb segregation, or spinodal decomposition, within the {alpha}'' domains, which results in the formation of a modulated structure containing nano-scaled Nb-rich and Nb-lean domains. Prolonged aging leads to age softening of the alloy by coarsening of the modulated structure. Chemical ordering, or disorder-order phase transformation, is found within the naturally aged alloy according to TEM observations of antiphase domain boundaries (APBs) and superlattice diffraction patterns. A possible superlattice structure for the ordered {alpha}'' phase observed in the naturally aged sample and underlying low-temperature aging mechanisms are proposed.