Cu-15Ni-8Sn合金的调幅相结构

利用透射电镜研究了Cu-15Ni-8Sn合金调幅相的显微结构和相变动力学.发现合金在完全淬火状态下,调幅分解迅速,调幅分解之后发生有序化.有序相具有DO22结构,由粗化的调幅组织转变为有序相的三种变体.分析有序化出现在调幅分解之后的原因是有序化需要的溶质原子浓度高于溶质原子的平均浓度,需要借助于调幅分解的成分起伏来达到.并推测有序相的形貌为针状.     

Strengthening in the Cu-9Ni-1.2Sn alloy

Data are presented describing quantitatively the structure development in the Cu-9.7 at% Ni-1.2 at% Sn alloy during ageing at 673 K. On the basis of these results the contributions to the strength of the alloy from different structure types are evaluated. These are discussed with respect to their additivity.     

Cu-9Ni-6Sn合金概述

综述了Cu-9Ni-6Sn合金的组织特征与强化机理,着重叙述了添加Mn对合金性能的改进,并介绍了合金的应用情况.     

机械合金化Cu-9Ni-6Sn合金的时效

本文对机械合金化法制备的 Cu-9Ni-6Sn合金的时效过程研究后发现 ,时效时发生调幅分解的临界温度为 4 0 0 -4 50℃。时效前施加一定冷形变量能够加速合金时效强化过程的进程 ,而且还提高了时效后硬度值。     

Three-dimensional reconstruction of anomalous eutectic in laser remelted Ni-30 wt.% Sn alloy

Abstract

Laser remelting has been performed on Ni-30 wt.% Sn hypoeutectic alloy. An anomalous eutectic formed at the bottom of the molten pool when the sample was remelted thoroughly. 3D morphologies of the α-Ni and Ni₃Sn phases in the anomalous eutectic region were obtained and investigated using serial sectioning reconstruction technology. It is found that the Ni₃Sn phase has a continuous interconnected network structure and the α-Ni phase is distributed as separate particles in the anomalous eutectic, which is consistent with the electron backscatter diffraction pattern examinations. The α-Ni particles in the anomalous eutectic are supersaturated with Sn element as compared with the equilibrium phase diagram. Meanwhile, small wavy lamella eutectics coexist with anomalous eutectics. The Trivedi–Magnin–Kurz model was used to estimate undercooling with lamellar spacing. The results suggest that the critical undercooling found in undercooling solidification is not a sufficient condition for anomalous eutectic formation. Besides, α-Ni particles in the anomalous eutectic do not exhibit a completely random misorientation and some neighboring α-Ni particles have the same orientation. It is shown that both the coupled and decoupled growth of the eutectic two phases can generate the α-Ni + Ni₃Sn anomalous eutectic structure.     

Three-dimensional reconstruction of anomalous eutectic in laser remelted Ni-30 wt.% Sn alloy

Laser remelting has been performed on Ni-30 wt.% Sn hypoeutectic alloy. An anomalous eutectic formed at the bottom of the molten pool when the sample was remelted thoroughly. 3D morphologies of the α-Ni and Ni₃Sn phases in the anomalous eutectic region were obtained and investigated using serial sectioning reconstruction technology. It is found that the Ni₃Sn phase has a continuous interconnected network structure and the α-Ni phase is distributed as separate particles in the anomalous eutectic, which is consistent with the electron backscatter diffraction pattern examinations. The α-Ni particles in the anomalous eutectic are supersaturated with Sn element as compared with the equilibrium phase diagram. Meanwhile, small wavy lamella eutectics coexist with anomalous eutectics. The Trivedi–Magnin–Kurz model was used to estimate undercooling with lamellar spacing. The results suggest that the critical undercooling found in undercooling solidification is not a sufficient condition for anomalous eutectic formation. Besides, α-Ni particles in the anomalous eutectic do not exhibit a completely random misorientation and some neighboring α-Ni particles have the same orientation. It is shown that both the coupled and decoupled growth of the eutectic two phases can generate the α-Ni + Ni₃Sn anomalous eutectic structure.     

Micro-yielding in a precipitation hardening Cu 1.81 wt % Be 0.28 wt % Co alloy

The microstrain characteristics of a polycrystalline Cu 1.81 wt % Be 0.28 wt % Co precipitation hardening alloy have been determined for various precipitate conditions. The friction stress derived from measurements of closed hysteresis loops was found to remain constant ( 3 MN m^–2) for all the conditions investigated. In contrast, the microscopic yield stress (MYS) remained constant (18 to 24 MN m^–2) for most ageing conditions, but increased significantly (to 48 to 64 MN m^–2) for conditions associated with a high G.P. zone or precipitate density.     

Microstructural and mechanical stability of Cu-6 wt. % Ag alloy

The microstructural and mechanical stability of Cu-6 wt. % Ag alloy obtained by cold rolling combined with intermediate heat treatments have been investigated. The stress-strain responses and fracture behavior of Cu-6 wt. % Ag alloy were examined and correlated with the microstructural change caused by thermo-mechanical treatments. The deformation bands stabilized by silver precipitates were observed in heavily rolled Cu-6 wt. % Ag alloy. The highly deformed microstructure stabilized by silver filament was observed to be unstable at temperatures above 200 °C. The strength of Cu-6wt.%Ag alloys were found to decrease remarkably if they were heat-treated above 300°C. The fracture surfaces of Cu-Ag two phase alloys showed typical ductile type fracture. The electrical conductivity did not change appreciably up to the aging temperature of 200°C and increased rapidly at temperatures above 300°C. The increase of the conductivity and the decrease of the strength can be associated with the microstructural coarsening of heavily deformed linear band structure. The difference of the UTS and the conductivity between the rolling direction and the direction perpendicular to the rolling direction (on the rolling plane) were found to be relatively small.     

Investigation of the annealing kinetics of quenched-in vacancies in the Al-0.1 wt % Mn alloy

Isochronal and isothermal annealing characteristics of Al-0.1 wt % Mn alloy quenched from the temperature range 400 to 600 C are investigated by electrical resistivity measurements. The two recovery stages in the alloy are similar to those found in pure aluminium excepting that the temperatures at which these stages occur in the alloy are higher than those in the pure metal. The isothermal annealing of vacancies in pure aluminium and the alloy quenched from 445 C obey first order kinetics. By comparing the rate constants for annealing of vacancies in pure aluminium and the alloy, the manganese-vacancy binding energy is calculated to be 0.12 eV. Deviation from the first order kinetics is observed in the alloy when the quenching temperature is 500 C. The annealing of vacancies in this case is analysed by computer simulation on the basis of a model where the migration of both divacancies and single vacancies to sinks are considered. This analysis also indicates that the manganese-vacancy binding energy is of the order of 0.1 eV. It is concluded that the value of binding energy obtained by the kinetic method is more reliable than that obtained by the equilibrium method.     

Crystal growth of the primary silicon in an Al-16 wt % Si alloy

Studies on the crystallographic growth habit of primary silicon crystals in an Al-16 wt% Si alloy were carried out by X-ray micro focus Laue analysis and ECP (electron channelling pattern) analysis. The plate-like primary silicon crystals grow by the same mechanism as that for germanium dendrites, i.e. the TPRE (twin plane re-entrant edges) mechanism. The spherical primary silicon crystal in sodium treated melts is composed of several pyramidal grains with tops at the centre of the sphere. Many of these grains have a twin relation to each other. The sodium enriched regions are found at the boundaries of these pyramidal silicon grains. The external surfaces of the spherical primary crystals exhibit regular crystal facets. The surface facets are most frequently parallel to {111} plane but there are also some facets parallel to other less densely packed planes such as {100}, {211} and so on.     

Morphological characteristic of the conventional and melt-spun Al-10Ni-5.6Cu (in wt.%) alloy

The Al-10Ni-5.6Cu alloy was prepared by conventional casting and further processed melt-spinning technique. The resulting conventional cast and melt-spun ribbons were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy together with energy dispersive spectroscopy, differential scanning calorimetry and microhardness techniques. The X-ray diffraction analysis indicated that ingot samples were α-Al, intermetallic Al₃Ni and Al₂Cu phases. The optical microscopy and scanning electron microscopy results show that the microstructures of rapidly solidified ribbons are clearly different from their ingot alloy. Al-10Ni-5.6Cu ribbons reveal a very fine cellular structure with intermetallic Al₃Ni particles. Moreover, at high solidification rates the melt-spun ribbons have a polygonal structure dispersed in a supersaturated aluminum matrix. The differential scanning calorimetry measurements revealed that exothermic reaction was between 290 °C and 440 °C which are more pronounced in the ternary Al-10Ni-5.6Cu alloy.     

Effect of Zn addition,strain rate and deformation temperature on the tensile properties of Sn–3.3 wt.% Ag solder alloy

Stress–strain characteristics of the binary Sn–3.3 wt.% Ag and the tertiary Sn–3.3 wt.% Ag–1 wt.% Zn solder alloys were investigated at various strain rates (SR, ε^·) from 2.6 × 10^− 4 to 1.0 × 10^− 2 s^− 1 and deformation temperatures from 300 to 373 K. Addition of 1 wt.% Zn to the binary alloy increased the yield stress σ_y and the ultimate tensile stress σ_UTS while a decrease of ductility (total elongation ε_T) was observed. Increasing the strain rate (ε^·) increased both σ_y and σ_UTS according to the power law σ = C ε^·m. A normal decrease of ε_T with strain rate was observed according to an empirical equation of the form ε_T = A exp (− λε^·); A and λ are constants. Increasing the deformation temperature decreased both σ_y and σ_UTS in both alloys, and decreased the total elongation ε_T in the Zn-free binary alloy, whereas ε_T was increased in the Zn-containing alloy. The activation energy was determined as 41 and 20 kJ mol^− 1 for these alloys, respectively. The results obtained were interpreted in terms of the variation of the internal microstructure in both alloys. The internal microstructural variations in the present study were evaluated by optical microscopy, electron microscopy and X-ray diffraction. The results show the importance of Zn addition in enhancing the mechanical strength of the Sn–3.3 wt.% Ag base alloy.     

Effect of grain size upon flow and fracture in a precipitation-strengthened Ti-8 wt % Al-0.25 wt % Si alloy

The interaction of grain size and precipitation strengthening has been studied in a Ti-8 wt % Al-0.25 wt %Si alloy. Grain sizes varying from 9 to 90m were produced by warm-working and annealing the alloy in the single--phase field. A uniform distribution of the coherent ₂ particles in the matrix was produced by ageing the alloy in the two-phase ( + ₂) field. The yield strength Hall-Petch slopes of the alloys with and without the ₂ precipitates were found to be nearly equal, indicating that the precipitation and grain-boundary strengthening are linearly additive. While specimens containing no precipitates exhibited a high ductility for all grain sizes, the ductility of the specimens with the ₂ particles decreased drastically with increasing grain size. TEM examination of the specimens containing the precipitates revealed a highly planar, localized slip and SEM examination of the fracture surfaces of these specimens revealed a transition in fracture behaviour from highly dimpled to mixed cleavage and intergranular with increasing grain size.     

On the formation of a microduplex structure in a Cu-15 wt% Ni-37.5 wt% Zn alloy

Interaction of recrystallization and precipitation during annealing of a cold-worked supersaturated solid solution can lead to the formation of an ultrafine grain size, two-phase microstructure, termed microduplex. In Cu-15 wt % Ni-37.5 wt % Zn this process requires prior cold-work of more than 60% RA. Cell walls and subgrain boundaries introduced by the deformation act as preferred nucleation sites for second phase particles. A high density of small particles is formed before recrystallization can start. Recrystallization then becomes controlled by the coarsening of the particles. A microstructure with grains and particles of less than 1 μm diameter results.