Precipitation Process in a Cu-Ni-Be Alloy

Abstract

Abstract. The precipitation process in an aged Cu-1.9wt%Ni-0.3wt%Be alloy has been examined by high-resolution transmission electron microscopy. The precipitation sequence found is: GunierPreston (G.P.) zones → γ'' → γ' → stable γ. The disk-shaped G.P. zones and the disk-shaped γ'', γ' and γ precipitated phases are composed of monolayers of Be atoms on {100} α of the Cu matrix and alternative Be and Ni matrix layers parallel to {100} α . The γ'' phases consisting of two to eight Be-layers has a body-centered tetragonal (bct) lattice with a=b=0.24 nm and c=0.28 nm. The γ' or γ phase is bct with a=b=0.24 nm and c=0.26 nm or a=b=0.26 nm and c=0.27 nm. The γ'', γ' or γ phase aligns with the matrix according to the Bain orientation relationship. The growth kinetics of disk-shaped γ precipitates on aging at 500 o C has been also investigated. The {001} α habit planes of the γ precipitates migrate by a ledge mechanism. The average thickness of the γ disks increases with aging time t as t

Tensile-stress-induced growth of ellipsoidal ω-precipitates in a Ti–20wt%Mo alloy

“…The thickening of plate-shaped precipitates and grain-boundary allotriomorphs in several alloy systems, for example, the thickening of Cr-rich precipitates with a lath morphology in a Ni-Cr alloy [18] and plate-shaped γ-precipitates in a Cu−Ni−Be alloy [19], have been reported to occur with parabolic growth kinetics [10]. In contrast, in the case of interface-controlled growth of a precipitate, the interface velocity v I may be written as [16]: (4) where d is the interface width, ν is the vibrational attempt frequency, ∆G m is the difference in free energies per mol between the β-and ω-phases, ∆G d is the activation energy for interface transport, and R and T have their usual meanings.…”

Precipitation Characteristics of the Metastable γ″ Phase in a Cu-Ni-Be Alloy

“…By space migration, the solute atoms first moved to the α-Cu matrix’s <100> soft elastic direction and forms a single disc shape G.P. zones structure [ 11 , 13 , 19 ], which kept a completely coherent relationship with α-Cu and produced an elastic coherency strain field, with the strength of the alloy increasing rapidly with it. The conductivity increases rate was smaller than the hardness growth rate.…”

“…Ni atoms occupied the position of the body heart, the Be atoms were in the eight vertices, and unit cell structure was, as shown in Figure 7 f, a metastable γ″, γ′ phase with a BCT structure, with a lattice constant: a = b < c. In the Figure 6 a HRTEM diagram, the measurement location d (010) p = 0.259 nm, d (001) p = 0.368 nm, and the inter-planar distance of the γ″ phase (001) crystal plane’s two layers of Be atoms and the α-Cu matrix’s inter-planar distance were consistent. However, in the corresponding FFT reciprocal lattice diagram, (002) p and (002) α diffraction point locations were not coincident, which means that d (001) p < 0.368 nm, and the actual measured value was between 0.27 nm to 0.32 nm, Ken’ichi et al [ 21 ] measured the lattice constant of the γ″ phase of the Cu-Ni-Be alloy to be a = b = 0.253 nm, c = 0.29 nm and Watanabe et al [ 13 ] measured the lattice constant of the γ″ phase of the Cu-Ni-Be alloy to be a = b = 0.24 nm, c = 0.28 nm. Two layers of the structure of the γ″ phase were imaged by TEM, showing that its diffraction intensity was weak and vulnerable to interference by the α-Cu matrix’s diffraction wave, as shown in Figure 5 d. The 1/2 {220} α position did not show obvious γ″ phase diffraction spots, while these appeared in the Figure 6 b FFT reciprocal lattice.…”

“…zones, the metastable γ″ phase transforms to the γ′ phase and to the γ phase. This process is controlled by the Ni atom’s diffusion in the Cu matrix [ 13 ]. Research shows that the γ phase’s thickening rate is directly proportional to t 1/2 .…”

“…With the extension of heat preservation time, it forms disc shape structure by alternation and overlaying between the Be layer and the Ni layer. Watanabe et al [ 13 ] define the γ″ phase as a disc shape structure with two to eight layers of Be atoms. The γ′ phase has 10 to 20 layers of Be atoms, and the γ phase’s atomic layer is more than 24 layers.…”