Atomic scale investigation of Cr precipitation in copper

Abstract

The early stage of the chromium precipitation in copper was analyzed at the atomic scale by Atom Probe Tomography (APT). Quantitative data about the precipitate size, 3D shape, density, composition and volume fraction were obtained in a Cu-1Cr-0.1Zr (wt.%) commercial alloy aged at 713K. Surprisingly, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction with the equilibrium Cu-Cr phase diagram. APT data also show that some impurities (Fe) may segregate along Cu/Cr interfaces. The concomitant evolution of the precipitate shape and composition as a function of the aging time is discussed. A special emphasis is given on the competition between interfacial and elastic energy and on the role of Fe segregation.

Grain refinement in a Cu–Cr–Zr alloy during multidirectional forging

“…It was assumed [12][13][14]19] that the high electrical conductivity is due to the very low solubility of Cr and Zr in Cu, whereas the excellent strength is attributed to dispersion hardening by the nanoscale precipitates. There is no doubt that the strength/conductivity properties of the Cu-Cr-Zr alloys result from precipitation behavior during aging at 723-773 K. The following precipitation sequence for coherent Cr-rich phase particles was revealed in a dilute Cu-Cr alloy [18,23]: (i) Cr-rich fcc spherical precipitates, which can be considered as Guinier-Preston zones; (ii) coherent round/elliptical shaped bcc precipitates of B2-type structure having a Nishiyama-Wassermann orientation relationship with copper matrix and a size of 10 nm or less; (iii) plate/round shaped bcc precipitates having a Kurdjumov-Sachs orientation relationship with copper and a size of $ 10 nm or higher. In ternary Cu-Cr-Zr alloys, the nanoscale particles of the Heusler phase CrCu 2 Zr belonging to the space group of Fm3m and having a Fe 3 Al lattice and equiaxed shape precipitate instead of the Cr-rich bcc phase [13].…”

“…These particles do not dissolve during solution treatment if the CrþZr content exceeds the equilibrium solubility of Cr and Zr [19]. Thus, the finely dispersed coherent particles of bcc Cr or the Heusler phase precipitated due to the decomposition of supersaturated solid solution are the main contributors to the strengthening [18][19][20][21][22]. Concurrently, Cr and Zr deplete the copper matrix and hence provide high electric conductivity.…”

“…The distribution of secondary phase particles in the Cu-Cr-Zr alloys has been considered in several works [2,12,13,[18][19][20][21][22]. It was assumed [12][13][14]19] that the high electrical conductivity is due to the very low solubility of Cr and Zr in Cu, whereas the excellent strength is attributed to dispersion hardening by the nanoscale precipitates.…”

Microstructure of phases in a Cu–Zr alloy

“…Thus, they are attractive candidates for railway contact wire [1,2], electrodes for spot welding [3,4], and heat exchangers [5]. The excellent strength (compared with pure copper) is attributed to the formation of the fine and uniform distribution Cu x Zr precipitation, whereas the high conductivity is due to the extremely low solubility of Zr in Cu matrix at room temperature [6].…”

Моделирование Распада Бинарных Сплавов На Основе Метода Функционала Плотности Свободной Энергии

“…Использование данного уравнения для описания про-цесса нуклеации также является весьма эффективным (см., например, [11,12]), поскольку позволяет рассмат-ривать кластеры, имеющие переменный состав и ха-рактеризующиеся протяженной областью сопряжения фаз и переменным поверхностным натяжением. При этом линейный размер кластеров зачастую оказывается сравнимым с размером области сопряжения фаз и может составлять несколько нанометров [11][12][13][14][15]. С помощью метода функционала плотности свободной энергии без каких-либо дополнительных приближений могут быть рассмотрены такие процессы как диффузионное взаи-модействие между кластерами и коагуляция (слияние) кластеров в процессе их роста с учетом неоднородности распределения состава сплава по объему системы.…”