1. 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

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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.

9. Results and discussions Strain hardening behavior

10. 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

11. Thanks for your attention !!
STUST
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