Fabrication of Ni, Si and Mg Supersaturated Solid Solutions in Al by Mechanical Alloying

Nanocrystalline Ag-28Cu supersaturated solid solution is prepared by mechanical alloying (MA) using a planetary ball mill. The mechanical alloyed powders are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and differential scanning calorimeter (DSC). XRD patterns show that the main peak of Ag-28Cu supersaturated solid solution exists at about 2θ=39° when the milling time is 30h. HRTEM images show that the grain sizes of as-prepared solid solutions have distributions from 10nm to 15nm. The interplanar spacing of (111) plane for fcc Ag-28Cu supersaturated solid solution is about 2.24Å. DSC measurement result indicates that the melting temperature of Ag-28Cu supersaturated solid solution is 783.8°C. The Ag(Cu) supersaturated solid solutions are in metastable state and they will be transformed into Ag-rich phase and Cu-rich phase simultaneously by annealing at 215°C- 415°C.

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Mathematical Modeling of Solid-State Diffusion during Mechanical Alloying

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.249.105 ◽

2006 ◽

Vol 249 ◽

pp. 105-110 ◽

Cited By ~ 8

Author(s):

Boris B. Khina ◽

Boleslaw Formanek

Keyword(s):

Plastic Deformation ◽

Solid State ◽

Mechanical Alloying ◽

Solid Solutions ◽

Point Defects ◽

Physical Mechanism ◽

Solid State Diffusion ◽

State Diffusion ◽

Wide Range ◽

Supersaturated Solid Solutions

It is known experimentally that solid-state interdiffusion is substantially enhanced during plastic deformation. This is especially noticeable in Mechanical Alloying (MA) which is used for producing a wide range of metastable materials (supersaturated solid solutions, amorphous phases, nanostructures) with unique properties. However, a physical mechanism of enhanced diffusion during MA is not clearly understood yet, and a comprehensive model of this complex phenomenon has not been developed so far. Moreover, the role of the diffusion process in MA is hotly debated in literature. In this work a new, self-consistent mathematical model of solid-state interdiffusion in a binary substitutional system A-B during periodic plastic deformation is developed. The model includes basic physical factors that affect diffusion, such as generation of non-equilibrium point defects by gliding screw dislocations during deformation and their relaxation in periods between impacts. The cross-link terms are considered, and interaction of point defects with edge dislocations and incoherent phase boundary A/B is taken into account. Computer simulation is performed using realistic data (e.g., quasi-equilibrium self-diffusion coefficients known in literature) and the process parameters typical of MA in a vibratory mill. A repeated “deformation-rest” cycle is considered. The results of modeling reveal the physical mechanism of the enhancement of solid-state diffusion by periodic plastic deformation during MA and demonstrate that within the frame of this approach supersaturated solid solutions can form within a reasonably short processing time.

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Microstructure and Homogeneity of Nanocrystalline Co–Cu Supersaturated Solid Solutions Prepared by Mechanical Alloying

Journal of Materials Research ◽

10.1557/jmr.1997.0134 ◽

1997 ◽

Vol 12 (4) ◽

pp. 936-946 ◽

Cited By ~ 22

Author(s):

J. Y. Huang ◽

Y. D. Yu ◽

Y. K. Wu ◽

D. X. Li ◽

H. Q. Ye

Keyword(s):

Electron Microscopy ◽

Mechanical Alloying ◽

Solid Solutions ◽

High Resolution Electron Microscopy ◽

Face Centered Cubic ◽

Transmission Electron ◽

Resolution Electron ◽

Supersaturated Solid Solutions ◽

Face Centered ◽

Fcc Phase

Mechanical alloying (MA) has been performed in the CoxCu(100-x) (x = 10, 25, 50, 60, 75, and 90) system. High resolution electron microscopy (HREM) and field emission gun transmission electron microscopy (FEG TEM) were used to characterize the microstructure and homogeneity of the nanocrystalline Co25Cu75 solid solution. After 20 h of MA, all the mixtures show an entirely face-centered cubic (fcc) phase. HREM shows that the ultrafine-grained (UFG) materials prepared by MA contain a high density of defects. Two kinds of typical defects in UFG Co25Cu75 are deformation twins and dislocations. The dislocations are mostly 60° type, and in many cases they dissociate into 30° and 90° partials. The grain boundaries are ordered in structure, curved, and slightly strained, which is similar to that observed in NC–Pd. Nanoscale energy dispersive x-ray spectroscopy (EDXS) shows that the Co concentration in both the interior of grains and the GB's is close to the global composition, which proves that supersaturated solid solutions are indeed formed. In the meantime EDXS revealed that the mixing of Co and Cu in the solid solutions is homogeneous at nanometer scale. MA in the Co–Cu system is suggested to be a diffusion-controlled process, and stress-stimulated diffusion is proposed to be the reason for the formation of supersaturated solid solutions in this immiscible system.

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