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Investigation on Aluminium Based Composites Reinforced by Ultrafined Amorphous Particles

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Tutor: DuXingZuo
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Course: Materials Science
Keywords: aluminum base composite,mechanical alloying,step-wise increased milling rate,amo
CLC: TB33
Type: Master's thesis
Year:  2012
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Abstract:
In this paper, Ni-Nb base non-equilibrium nanometeric particles were prepared by Mechanical Alloying (MA), which were added to the Al matrix as the second strengthening particles with the powder volume fractions of 0%, 2.5%, 5%, 10% and 20%. After that, the Al matrix composite materials were formed by vacuum hot pressing sintering. By using optical microscope, scanning electron microscope¡¢X-ray diffraction¡¢hardness¡¢compressive tests, the forming process of amorphous particles and mechanical properties of the resultant materials were investigated.First of all, by using the pure powders of Ni and Nb, the resultant powders with the composition of Ni60Nb40 were synthesized by mechanical alloying of gradually increasing the speed of milling. Use the X-ray diffraction phase technique to analyze the final milling products. The results show that by taking the way of wet grinding and gradually increasing the speed of milling could promote the formation of amorphous nanoscale particles. The formation of this amorphous alloy stmes from grain refinement in which the surface area of particles increases during the process of milling, enhancing a variety of defects and stress effects.By using optical microscope to observe the Al matrix including strengthening particles respectively showed that the second strengthening phase and the matrix displayed a good combination, in which no porosity between them could be observed. And the second strengthening phase was uniformly dispersed in the matrix. The mechanical properties of these five speciemens at room temperature were evaluated by hardness and compression. It is found that with the content of second phase increase, the hardness and strenghth of the composites increased gradually, while plasticity decreased gradually. Amorphous particles have better strengthening effect capability than the saturated particle. High-strength amorphous particles make the dislocations cutting through the particles with smaller breaking angle, so they can strongly hinder the movement of dislocations, and thus produce more significant strengthening effect. All these results have shown that low-content powder of second particles and good dispersion of nano-scale amorphous particles reinforced aluminum matrix composites have good mechanical properties, high specific strength, and thus is a promising application of high-strength structural materials.
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