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

Abstract

The precipitation sequence of a Cu-Ni-Be alloy is: α-Cu supersaturated solid solution → Guinier-Preston (G.P.) zones → metastable γ″ → γ′ → stable γ (NiBe) phase. The micro-hardness and electrical conductivity during the aging process were measured. The precipitation characteristics and the distribution of the γ″ phase, under peak aging conditions, were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area diffraction pattern (SADP), and high-resolution transmission electron microscopy (HRTEM). The results show that the orientation relationship of the γ″ phase/α-Cu matrix is: (001)p//(001)α; [100]p//[110]α (p: Precipitates, α: α-Cu supersaturated solid solution), which is in accordance with the Bain relationship in a FCC/BCC (face centered cubic/body centered cubic) structure, with the unique habit plane being {001}α. While the zone axis is parallel to [001]α, three forms of γ″ phases are distributed on the projection surface at the same time. The (001) reciprocal-lattice positions of γ″ phase in SADP are diffusely scattered, which is consistent with the variation of the d(001) value of the γ″ phase. The intra-range variation is related to the distortion of the (001) plane of the γ″ phase, due to interfacial dislocations and distortion strain fields. The lattice of the γ″ phase in the HRTEM images was measured as a = b = 0.259 ± 0.002 nm and c = 0.27–0.32 nm. With the increase of thermal exposure time, the stable γ phase has a NiBe phase structure (Standard Card Number: PDF#03-1098, a = b = c = 0.261 nm), and the long diffuse scattering spots will transform into single bright spots. The edge dislocation, generated by interfacial mismatch, promotes the formation of an optimal structure of the precipitated phase, which is the priority of growth in the direction of [110]p.

Influence of Oxidation Processing Temperature on the Structure, Mechanical and Tribological Properties of Titanium Using Carbon Sheets

“…The amount of oxygen on the surface of the sample is large, which plays a leading role in the reaction with titanium. At this time, Ti + O 2 = TiO 2 (6) reaction is likely to occur, and TiO 2 is formed on the outermost surface. This is also the reason why a large amount of TiO 2 was detected at higher temperature.…”

“…In the widespread applications of the materials, the surface of titanium shows relatively poor mechanical properties, and the improvement of the surface layer is strongly demanded for longer service-life of the various apparatus. To solve this problem, a series of industrial techniques have been developed [2], including deposition and diffusion [3][4][5][6]. The main purpose of surface treatment is to improve the abrasive resistance of titanium, extend its service-life, and reduce the waste of resources.…”

Effects of Cold Rolling and Aging Treatment on the Properties of Cu-Be Alloy

“…Cu-Be alloy has been used very widely for springs, diaphragms, bearings and non-sparking tools because it has excellent mechanical properties, high electrical conductivity, and high corrosion resistance. Aging after quenching from solution treatment remarkably hardens the alloy [1][2][3][4]. The precipitation sequence in this alloy has been extensively studied and can be summarized as follows [5][6][7][8]: α supersaturated solid-solution→G.P zones →γ΄΄→γ΄→γ (Cu-Be).…”