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Bulk ultra-fine grain (UFG) structure materials have attracted considerable interest during the last two decades due to their promising physical and mechanical properties without the complications of contamination or porosity [1-3]. One of the most common methods to produce such materials is the equal-channel angular pressing (ECAP) technique [1]. The ECAP is a cold/warm-working process, which imposes extremely large strains repeatedly on bulk materials in order to attain grain refinement and significant hardening through in an extremely fine-grained structure formed by simple shear processes [1]. Bulk UFG materials free of porosity produced by ECAP provide new opportunities to study their properties for comparison with conventional coarse grain (CG) materials. In the course of ECAP, the grain structure is refined to nanoscopic and sub-microcrystalline scale, together with dislocation hardening; this can result in the spectacular enhancement of material strength, while retaining adequate ductility. Up to now, much work has been done on mechanical properties, fatigue behaviors and microstructures evolution of UFG materials prepared by ECAP [4~20]. The experimental data covers copper, aluminium, magnesium, titanium, nickel and steel. For UFG copper, the primary effort has been on pure copper. There are few reports on copper alloys, especially on precipitation-hardened copper-based alloys. The addition of precipitation-hardening alloying elements influences the physical properties, mechanical behavior and microstructure of many alloys. Gubicz et al. [21] studied the effect of Mg on the microstructure and mechanical properties of aluminum. The tensile properties and microstructural evolution were strongly influenced by the interaction between the Mg solute atoms and the dislocations in an Al-Mg alloy. In the present investigation, we studied the microstructure of an UFG Cu-Cr alloy prepared by ECAP. The main purpose of this work was to observe the effect of trace Cr on the microstructure and to seek an optimal method of preparing such materials. There are several reasons for the choice of a Cu-Cr alloy in the present work: firstly, compared with aluminum and an Al-Mg alloy, copper has a lower stacking fault energy (SFE), and Cu-Cr alloys are precipitation strengthened; therefore, the strengthening mechanism may be different from results reported for other materials [21]. Second, coarse grained Cu-Cr alloy, as an ordinary copper-based alloy, had been widely studied previously, thereby providing a reference database. Third, a Cu-Cr alloy can be readily produced and processed by ECAP. |
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wangjianna
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5楼2009-09-24 20:44:23
wangjianna
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xucz(金币+3,VIP+0):thank you 9-25 09:08
xucz(金币+5,VIP+0):谢谢，最后一段的句式很好！ 9-25 09:32
xucz(金币+3,VIP+0):thank you 9-25 09:08
xucz(金币+5,VIP+0):谢谢，最后一段的句式很好！ 9-25 09:32
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第一句 due to their promising physical and mechanical properties and with no complications of contamination or porosity,Bulk ultra-fine grain (UFG) structure materials have attracted considerable interest during the last two decades 第五行。。。through in ...没看懂 第六行：能说一种材料提供了供人们学习的机会吗？Bulk UFG materials， which are free of porosity and produced by ECAP, provide new opportunities to study their properties in comparison with conventional coarse grain (CG) materials. 第三段：an UFG Cu-Cr alloy prepared by ECAP was studied the microstructure in this work, the purpose is to ......such materials. Cu-Cr alloy was chosen here for the following reasons: copper has a lower stacking fault energy (SFE)compared to aluminum, Cu-Cr alloys are precipitation strengthenedcompared to Al-Mg alloy; therefore, the strengthening mechanism may be different from that of other materials; ...... |
2楼2009-09-24 15:02:23
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4楼2009-09-24 15:13:07
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6楼2009-09-24 20:45:20
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