Quantitative characterization of the microstructure of heat-treated Zr-Excel by neutron line profile analysis

Abstract

Neutron diffraction line profile analysis (DLPA) and transmission electron microscopy were used to characterize the components of the bimodal microstructure of Zr‐Excel (Zr–3.5Sn–0.8Mo–0.8Nb), a nuclear structural material. The dual microstructure, consisting of equiaxed primary grains and martensitic domains both having hexagonal close‐packed (h.c.p.) α crystal structure, forms when the as‐received Zr‐Excel alloy is heat treated at a high temperature and subsequently quenched, i.e. is solution treated. Because both microstructure components have the same crystal structure the reflections from the two components overlap significantly. The article presents how the multi‐phase analysis capability of modern DLPA methods can be used to model the measured neutron diffraction patterns as the sum of two sub‐patterns corresponding to the components of such a bimodal microstructure, which can be found in many hexagonal alloys relevant for industrial applications. The results show that the large equiaxed primary h.c.p. α grains have a highly correlated low‐density dislocation structure and large sub‐grains (∼300 nm), while the large martensitic domains have a randomly arranged very high density dislocation structure and sub‐grains the size of ∼30 nm. The significantly different defect structures of the primary and martensitic phases manifest as large differences in the hardness and ductility of the individual components. As a result of this duality of the mechanical properties, solution‐treated Zr‐Excel materials can be considered as analogous to metal matrix composites where a softer ductile matrix contains a harder brittle reinforcing phase.

Microstructure of nuclear structural materials, Zr and V-5Cr-5Ti, determined by X-ray line profile analysis

“…The theoretical models of dislocation and crystallite size implemented in the CMWP are described briefly as follows. According to the Krivoglaz-Wilkens theory the mean square strain 〈𝜀 g,𝐿 2 〉 in dislocated crystals is (Wilkens, 1970a;Krivoglaz, 1996):…”

“…Both the initial and the martensitic grains in the solution treated Zr-Excel alloy are the hexagonal closepacked crystallographic structures. For studying the influence of the microstructure on the mechanical behavior of the heat-treated Zr-Excel alloy,Ahmmed et al (2016) carried out neutron diffraction measurements to achieve dislocation densities and subgrain sizes corresponding to different components of such a bimodal microstructure.…”

Textúrált anyagok vonalprofil analízise

“…A neutrondiffraktométerek szögfelbontása általában lényegesen kisebb, mint a röntgendiffraktométereké. Az utóbbi évtizedekben azonban a spallációs neutronforrások megjelenésével jelentősen javult a neutrondiffraktométerek szögfelbontása, ami alkalmassá teszi őket a vonalprofil analízis számára is [Woo et al, 2010;Ahmmed et al, 2016] [Gurao et al, 2014] vagy extrudált Zirlcaloy-2 és Zircaloy-4 esetében [Tenckhoff & Rittenhouse, 1970], de ugyanezt a típusú textúrát találták hidegen hengerelt cirkónium esetén is [Wang & Huang, 2003]. Látni fogjuk, hogy az általunk vizsgált Zircaloy-2 mintadarab textúrája is ehhez nagyon hasonló, tipikus mintázatot mutat.…”