超精細結晶使用商用純銅材料利用滾筒堆積 探討微結構演化、機械性質、應變硬化行為 指導老師: 戴子堯 老師 報告者: 洪瑩儒 Date ﹕2015/12/29

Outline 1.Introdiction 2.Materials and experimental procedure 3.Results and discussions Microstructural evolutions Microhardness Tensile test data Strain hardening behavior 4.Conclusions

Introdiction The most employed conventional method to strengthen materials adding alloying elements. this method increases the cost of the final product and decreases the corrosion resistance of materials. the ARB method is suitable to fabricate UFG sheets or plates for industrial application because of high productivity rate, continuous production, and simplicity of required facilitie Among them copper, due to its great demandin electronic industries for relatively high-strength and high conductivity,fabricated by theARB technique study is presented on investigation of the effect of ARB process on Microstructure evolutions, mechanical properties, and strain hardening behavior of commercial pure copper

Materials and experimental procedure The commercial pure copper (99.96 wt%) sheets were annealed at 480 °C for 7200 s in an inert environment before ARB process Microstructures were characterized using optical microscopy (OM) and TEM (Philips-EM208S) operating at 100 kV. Grain size measurements were also conducted using AFM images of ARB-processed samples Hardness measurements were performed using a Vickers microhardness tester (維氏硬度) under a load of 100 g and time of 20 s. The average of ten measurements for each sample was considered. The specimens of the tensile test were prepared by an electrod scharge machining method . The gauge length,the width and the thickness

Results and discussions annealed pure copper Microstructural evolutions three cycles ARB four cycles ARB average grain size around 26 μm average grain size is about 280 nm average grain size about 200 nm

Results and discussions Microstructural evolutions 1 ARB cycle 2 ARB cycle 3 ARB cycle 4ARB cycle measured grain size values by AFM images and TEM micrographs are very close low angle boundaries to high angle grain boundaries by dislocation accumulation migration of new high anglegrain boundaries and formation of well-defined UFG structure

Results and discussions Microhardness Annealed sample:68HV 132HV 130HV 119HV 112HV One ARB cycles:112HV Two ARB cycles:119HV 68HV Three ARB cycles:130HV Four ARB cycles:132HV Significant increase in microhardness after the first cycle seems to be related to high rate of strain hardening which is due to high dislocation density

Results and discussions Tensile test data 最大抗拉強度 70 203 360 396 降伏強度 The high strength and low elongation in tensile tests are the typical behavior of ARB-processed UFG materials the number of cycles increased,(YS) and (UTS) improved by nearly the same trend The reduction of ductility in ARBed samples is essentially because of to strain hardening that inhibits the mobility of dislocations.

Results and discussions Strain hardening behavior  

Conclusions A significant reduction in grain size of ARB-processed samples is observed and mean grain size reached to 200 nm after four cycles of ARB. The microhardness investigation shows a rapid increase in hardness after the first ARB cycle, however, the growth rate in hardness drops at higher ARB cycles, and finally reaches the saturation state, which is due to the steady-state density of dislocations The yiled and tensile strength of four cycles were higher that of the initial sample strain hardening ability in the ARB-processed materials are controlled by two major origins: dislocation density and grain size

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